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Stability analysis of the projectile based on random center manifold reduction

Yong Huang, Chunyan Yang

Accepted Manuscript , doi: 10.1016/j.taml.2022.100385

[Abstract] (0) [PDF 955KB] (0)

Abstract:
The center manifold method has been widely used in the field of stochastic dynamics as a dimensionality reduction method. This paper studied the angular motion stability of a projectile system under random disturbances. The random bifurcation of the projectile is studied using the idea of the Routh-Hurwitz stability criterion, the center manifold reduction, and the polar coordinates transformation. Then, an approximate analytical presentation for the stationary probability density function is found from the related Fokker–Planck equation. From the results, the random dynamical system of projectile generates three different dynamical behaviors with the changes of the bifurcation parameter and the noise strength, which can be a reference for projectile design.

Constitutive modeling of particle reinforced rubber-like materials

Sankalp Gour, Deepak Kumar

Accepted Manuscript , doi: 10.1016/j.taml.2022.100383

[Abstract] (0) [PDF 1005KB] (0)

Abstract:
The present study is focused on the constitutive modeling for the mechanical behavior of rubber reinforced with filler particles. A filler-dependent energy density function is proposed with all the continuum mechanics-based necessities of an effective hyperelastic material model. The proposed invariant-based energy function comprises a single set of material parameters for a material subjected to several modes of loading conditions. The model solution agrees well with existing experimental results. Later, the effect of varying concentrations of filler particles in the rubber matrix is also studied.

A structure-preserving algorithm for time-scale non-shifted Hamiltonian systems

Xue Tian, Yi Zhang

Accepted Manuscript , doi: 10.1016/j.taml.2022.100368

[Abstract] (0) [PDF 2402KB] (0)

Abstract:
The variational calculus of time-scale non-shifted systems includes both the traditional continuous and traditional significant discrete variational calculus. Not only can the combination of Δ and ∇ derivatives be beneficial to obtaining higher convergence order in numerical analysis, but also it prompts the timescale numerical computational scheme to have good properties, for instance, structure-preserving. In this letter, a structure-preserving algorithm for time-scale non-shifted Hamiltonian systems is proposed. By using the time-scale discrete variational method and calculus theory, and taking a discrete time scale in the variational principle of non-shifted Hamiltonian systems, the corresponding discrete Hamiltonian principle can be obtained. Furthermore, the time-scale discrete Hamilton difference equations, Noether theorem, and the symplectic scheme of discrete Hamiltonian systems are obtained. Finally, taking the Kepler problem and damped oscillator for time-scale non-shifted Hamiltonian systems as examples, they show that the time-scale discrete variational method is a structure-preserving algorithm. The new algorithm not only provides a numerical method for solving time-scale non-shifted dynamic equations but can be calculated with variable step sizes to improve the computational speed.

Shapes of the fastest fish and optimal underwater and floating hulls

Igor Nesteruk

Accepted Manuscript , doi: 10.1016/j.taml.2022.100378

[Abstract] (0) [PDF 816KB] (0)

Abstract:
A streamlined shape of the best swimmers removes the boundary-layer separation and ensures a laminar flow pattern. The fastest fish have a very sharp convex nose (rostrum), the purpose of which remains unclear. The bodies of revolution similar to their shapes are analyzed in steady underwater and floating motion. The sources and sinks were located on the axis of symmetry and above the water surface to estimate the pressure on the body and the vertical velocities on the water surface. It was shown that the flow patterns on a special shaped body with concave nose has no stagnation points and ensure small values of the water surface elevation. These fact allow diminishing the maximum pressure on the surface and wave drag. Special shapes with the sharp concave nose and negative pressure gradients on their surface could be parts of the low drag underwater and floating hulls.

Influence of physical parameters on the collapse of a spherical bubble

Bo-Hua Sun

Accepted Manuscript , doi: 10.1016/j.taml.2022.100369

[Abstract] (0) [PDF 4010KB] (0)

Abstract:
This paper examines the influence of physical parameters on the collapse dynamics of a spherical bubble filled with diatomic gas (κ = 7/5). The problem is formulated by the Rayleigh-Plesset dynamical equation, whose numerical solutions are carried out by Maple. Our studies show that each physical parameter affects the bubble collapse dynamics in different degree, which reveals that bubble collapse dynamics must considers all the parameters including liquid viscosity, surface tension, etc, else the outcome cannot be trusted.

An iterative data-driven turbulence modeling framework based on Reynolds stress representation

Yuhui Yin, Zhi Shen, Yufei Zhang, Haixin Chen, Song Fu

Accepted Manuscript , doi: 10.1016/j.taml.2022.100381

[Abstract] (0) [PDF 2962KB] (0)

Abstract:
Data-driven turbulence modeling studies have reached such a stage that the basic framework is settled, but several essential issues remain that strongly affect the performance. Two problems are studied in the current research: (1) the processing of the Reynolds stress tensor and (2) the coupling method between the machine learning model and flow solver. For the Reynolds stress processing issue, we perform the theoretical derivation to extend the relevant tensor arguments of Reynolds stress. Then, the tensor representation theorem is employed to give the complete irreducible invariants and integrity basis. An adaptive regularization term is employed to enhance the representation performance. For the coupling issue, an iterative coupling framework with consistent convergence is proposed and then applied to a canonical separated flow. The results have high consistency with the direct numerical simulation true values, which proves the validity of the current approach.

Determination of the full-field stress and displacement using photoelasticity and sampling moiré method in a 3D-printed model

Zhangyu Ren, Qi Zhang, Yang Ju, Huimin Xie

Accepted Manuscript , doi: 10.1016/j.taml.2022.100380

[Abstract] (0) [PDF 1771KB] (0)

Abstract:
The quantitative characterization of the full-field stress and displacement is significant for analyzing the failure and instability of engineering materials. Various optical measurement techniques such as photoelasticity, moiré and digital image correlation methods have been developed to achieve this goal. However, these methods are difficult to incorporate to determine the stress and displacement fields simultaneously because the tested models must contain particles and grating for displacement measurement; however, these elements will disturb the light passing through the tested models using photoelasticity. In this study, by combining photoelasticity and the sampling moiré method, we developed a method to determine the stress and displacement fields simultaneously in a three-dimensional (3D)-printed photoelastic model with orthogonal grating. Then, the full-field stress was determined by analyzing 10 photoelastic patterns, and the displacement fields were calculated using the sampling moiré method. The results indicate that the developed method can simultaneously determine the stress and displacement fields.

Predicting solutions of the Lotka-Volterra equation using hybrid deep network

Zi-Fei Lin, Yan-Ming Liang, Jia-Li Zhao, Jiao-Rui Li

Accepted Manuscript , doi: 10.1016/j.taml.2022.100384

[Abstract] (0) [PDF 1404KB] (0)

Abstract:
Prediction of Lotka-Volterra equations has always been a complex problem due to their dynamic properties. In this paper, we present an algorithm for predicting the Lotka-Volterra equation and investigate the prediction for both the original system and the system driven by noise. This demonstrates that deep learning can be applied in dynamics of population. This is the first study that uses deep learning algorithms to predict Lotka-Volterra equations. Several numerical examples are presented to illustrate the performances of the proposed algorithm, including Predator nonlinear breeding and prey competition systems, one prey and two predator competition systems, and their respective systems. All the results suggest that the proposed algorithm is feasible and effective for predicting Lotka-Volterra equations. Furthermore, the influence of the optimizer on the algorithm is discussed in detail. These results indicate that the performance of the machine learning technique can be improved by constructing the neural networks appropriately.

Mechanical characteristics of composite honeycomb sandwich structures under oblique impact

Yuechen Duan, Zhen Cui, Xin Xie, Ying Tie, Ting Zou, Tingting Wang

Accepted Manuscript , doi: 10.1016/j.taml.2022.100379

[Abstract] (0) [PDF 1244KB] (0)

Abstract:
Carbon fiber reinforced polymer (CFRP) and CFRP-based composite honeycomb sandwich structures are particularly sensitive to impact. The mechanical characteristics of composite honeycomb sandwich structures under oblique impact are studied by numerical simulation and experiment. The oblique impact model is established, and the reliability of the model is verified by the oblique impact test. To further analyze the influence of structural parameters on energy absorption under oblique impact, the influence of impact angle, face sheet thickness, wall thickness, and height of the honeycomb is numerically studied. The results show that the impact angle has an important effect on energy distribution. The structural parameters also have an effect on the peak contact force, contact time, and energy absorption, and the effect is different from normal impact due to the presence of frictional dissipation energy. Compared with normal impact, the debonding of oblique impact will be reduced, but the buckling range of the honeycomb core will be expanded.

An analysis on a rigid-flexible coupling system of an oscillating mass and a rotating disk

JIAN LIU, KAI ZHANG, ZHANFANG LIU

Accepted Manuscript

[Abstract] (15) [PDF 0KB] (0)

Abstract:
A mass-rod-disk system consisting of an oscillating mass attached to a rigid rotating disk by an elastic rod is designed to study rigid-flexible coupling mechanism.Suppose the rod is lightweight and has enough stiffness,the theorems of linear momentum and angular momentum are applied to the mass-rod-disk system based on the kinematic description of the system.With respect to two deflections of the mass and one angular velocity of the system,a group of nonlinear differential equations are established where the tangential inertial force,centrifugal force,Coriolis force as well as the moments of additional inertial forces take important effects on the dynamic response.For the sake of description,these three types of inertial forces mentioned before are referred to as additional inertial forces in this paper.The horizontal deflections of the mass and the angular velocity of the disk rotating about a fixed-axis are numerically solved for the prescribed external torque.The oscillating trajectory of the mass is deeply influenced by the additional inertial forces,meanwhile the dynamic fluctuations of the angular velocity and rotary inertia of the system are strongly affected by the mass oscillation.

Motion of a sphere and the suspending low-Reynolds-number fluid confined in a cubic cavity

Gaofeng Chen, Xikai Jiang

Accepted Manuscript

[Abstract] (13) [PDF 0KB] (0)

Abstract:
Dynamics of a spherical particle and the suspending low-Reynolds-number fluid confined by a cubic cavity were studied numerically.We calculated the particle's hydrodynamic mobilities along x-,y-,and z directions at various locations in the cavity.The mobility is largest in the cavity center and decays as the particle becomes closer to no-slip walls.It was found that mobilities in the entire cubic cavity can be determined by a minimal set in a unit tetrahedron therein.Fluid vortices in the cavity induced by the particle motion were observed and analyzed.We also found that the particle can exhibit a drift motion perpendicular to the external force.Magnitude of the drift velocity normalized by the velocity along the direction of the external force depends on particle location and particle-to-cavity sizes ratio.This work forms the basis to understand more complex dynamics in microfluidic applications such as intracellular transport and encapsulation technologies.

Hydrothermal analysis of non-Newtonian fluid flow (blood) through the circular tube under prescribed non-uniform wall heat flux

Shahin Faghiri, Shahin Akbari, Mohammad Behshad Shafii, Kh. Hosseinzadeh

Accepted Manuscript

[Abstract] (19) [PDF 0KB] (0)

Abstract:
Non-Newtonian fluids are described by the nonlinear relationship between shear stress and rate of deformation at a specified temperature and pressure[1].The flows of non-Newtonian fluids play important role in many industrial applications and disciplinary fields such as biomedicine,polymer and food processing,thermal oil recovery,and discharge of industrial wastes[2-8].From a mechanical engineering viewpoint,the complicated rheological behavior of shear-thinning fluid like blood cannot be modeled by a very plain,one parameter,and linearized law of viscosity as presented by Newton[9-13].The properties of this type of fluid can only be characterized by higher-order constitutive equations,such as the power-law model[14-16],which considers thefluid's nonNewtonian featuresincluding shear thinning and yield stress characteristics[17-22].In the recent few decades,the investigation of fluid dynamics and heat transfer in the non-Newtonian fluid flow has been identified as one of the most important issues for researchers.In points of the fact,comprehension of the property of non-Newtonian fluid movement and the thermal-mechanical behavior of the fluid stream can result in a better understanding of scientific phenomena occurring in real life[23-28],which has triggered many investigators in different branches of engineering to concentrate on the non-Newtonian fluid flow simulation with different methodologies.

Independent component analysis of streamwise velocity fluctuations in turbulent channel flows

Ting Wu, Guowei He

Accepted Manuscript

[Abstract] (18) [PDF 0KB] (2)

Abstract:
Independent component analysis (ICA) is used to study the multiscale localised modes of streamwise velocity fluctuations in turbulent channel flows.ICA aims to decompose signals into independent modes,which may induce spatially localised objects.The height and size are defined to quantify the spatial position and extension of these ICA modes,respectively.In contrast to spatially extended proper orthogonal decomposition (POD) modes,ICA modes are typically localised in space,and the energy of some modes is distributed across the near-wall region.The sizes of ICA modes are multiscale and are approximately proportional to their heights.ICA modes can also help to reconstruct the statistics of turbulence,particularly the third-order moment of velocity fluctuations,which is related to the strongest Reynolds shear-stressproducing events.The results reported in this paper indicate that the ICA method may connect statistical descriptions and structural descriptions of turbulence.

Investigation of nanofluid flow in a vertical channel considering polynomial boundary conditions by Akbari-Ganji's method

M. Fallah Najafabadi, H. TalebiRostami, Kh. Hosseinzadeh, D. D. Ganji

Accepted Manuscript

[Abstract] (14) [PDF 0KB] (0)

Abstract:
In this research,a vertical channel containing a laminar and fully developed nanofluid flow is investigated.The channel surface's boundary conditions for temperature and volume fraction functions are considered qth-order polynomials.The equations related to this problem have been extracted and then solved by the AGM and validated through the Runge-Kutta numerical method and another similar study.In the study,the effect of parameters,including Grashof number,Brownian motion parameter,etc.,on the motion,velocity,temperature,and volume fraction of nanofluids have been analyzed.The results demonstrate that increasing the Gr number by 100% will increase the velocity profile function by 78% and decrease the temperature and fraction profiles by 20.87% and 120.75%.Moreover,rising the Brownian motion parameter in five different sizes (0.1,0.2,0.3,0.4,and 0.5) causes lesser velocity,about 24.3% at first and 4.35% at the last level,and a maximum 52.86% increase for temperature and a 24.32% rise for ψ occurs when N_b rises from 0.1 to 0.2.For all N_t values,at least 55.44%,18.69%,for F(η),and Ω(η),and 20.23% rise for ψ(η) function is observed.Furthermore,enlarging the N^r parameter from 0.25 to 0.1 leads F(η) to rise by 199.7%,fluid dimensionless temperature,and dimensional volume fraction to decrease by 18% and 92.3%.In the end,a greater value of q means a more powerful energy source,amplifying all velocity,temperature,and volume fraction functions.The main novelty of this research is the combined convection qth-order polynomials boundary condition applied to the channel walls.Moreover,The AMG semi-analytical method is used as a novel method to solve the governing equations.

A new dynamic subgrid-scale model using artificial neural network for compressible flow

Han Qi, Xinliang Li, Ning Luo, Changping Yu

Accepted Manuscript

[Abstract] (14) [PDF 0KB] (0)

Abstract:
The subgrid-scale (SGS) kinetic energy has been used to predict the SGS stress in compressible flow and it was resolved through the SGS kinetic energy transport equation in past studies.In this paper,a new subgrid-scale (SGS) eddy-viscosity model is proposed using artificial neural network to obtain the SGS kinetic energy precisely,instead of using the SGS kinetic energy equation.Using the infinite series expansion and reserving the first term of the expanded term,we obtain an approximated SGS kinetic energy,which has a high correlation with the real SGS kinetic energy.Then,the coefficient of the modelled SGS kinetic energy is resolved by the artificial neural network and the modelled SGS kinetic energy is more accurate through this method compared to the SGS kinetic energy obtained from the SGS kinetic energy equation.The coefficients of the SGS stress and SGS heat flux terms are determined by the dynamic procedure.The new model is tested in the compressible turbulent channel flow.From the a posterior tests,we know that the new model can precisely predict the mean velocity,the Reynolds stress,the mean temperature and turbulence intensities,etc.

Stirring by anisotropic squirming

Zhi Lina, Sirui Zhu, Lingyun Ding

Accepted Manuscript

[Abstract] (19) [PDF 0KB] (0)

Abstract:
We consider a fluid stirred by the locomotions of squirmers through it and generalize the stochastic hydrodynamic model proposed by Thiffeault et.al.[1,2]to the case in which the swimmers move in anisotropically random directions.A non-diagonal effective diffusivity tensor is derived with which the diffusive preference of a passive particle along any given direction can be computed to provide more details of the phenomena beyond scalar statistics.We further identify a fraction from the orthogonal decomposition of the drift-induced particle displacement to distinguish the underlying nonlinear mixing mechanism for different types of swimmers.Numerical simulations verify the analytical results with explicit examples of prescribed,anisotropic stirring motions.We also connect our formulation to several measures used in clinical medical research such as diffusion tensor imaging where anisotropic diffusion has a significant consequence.

Optimization for vibro-impact nonlinear energy sink under random excitation

Jiamin Qian, Lincong Chen

Accepted Manuscript

[Abstract] (14) [PDF 0KB] (0)

Abstract:
Excessive vibrations,such as those stimulated by strong wind and severe earthquake,tend to reduce the comfort of user,shorten structure lifespan,and in extreme cases lead to structural failure or even large number of casualties[1].The attachment of nonlinear energy sink (NES) induces targeted energy transfer (TET) in an irreversible manner,thus effectively attenuating undesirable vibration[2,3].Among various forms of NES,employing the nonsmooth nonlinear element in NES which is termed as vibro-impact NES (VI-NES)[4,5].The competence of VI-NES in reducing structural response has been confirmed numerically,theoretically and experimentally[6-8].However,due to the nonlinear properties of the VI-NES and external stimuli including strong winds or severe earthquakes are random in nature,obtaining a clear analytical solution of VI-NES damper system (VI-NES-DS) under random loads still poses a challenge.In addition,general and cost-effectively optimization procedures have not been available for the design of VI-NES.This work constructs an analytical optimization procedure of VI-NES-DS subjected to random excitation.By resorting to nonsmooth transformation and stochastic averaging method (SAM)[9,10],the approximate probability density function (PDF) of the VINES-DS can be determined in a closed form.On this base,a procedure to optimize the parameters of the system is established minimizing the displacement variance of the VI-NES-DS.Finally,numerical demonstrations are performed and related results are compared with pertinent data obtained by Monte Carlo simulations (MCS).

Performance improvement of the stochastic-resonance-based tri-stable energy harvester under random rotational vibration

Tingting Zhang, Yanfei Jin, Yanxia Zhang

Accepted Manuscript

[Abstract] (15) [PDF 0KB] (0)

Abstract:
The vibration energy harvesting has been widely concerned by many scholars as a possible solution for continuous power supply of low-power electronics[1-5].For instance,Liu et al.[1]proposed a new quasi-conservative stochastic averaging for nonlinear vibration energy harvesters (VEHs) driven by Gaussian colored noise.They[3]further investigated the stochastic dynamics of a bi-stable VEH under filtered Gaussian white noise by combining an improved coordinate transformation.In recent years,the development of wireless sensor nodes for rotational equipment has attracted an increasing attention on energy harvesting from rotational motion[6-10].For example,Hsu et al.[6]presented a comprehensive design of a passively self-tuning composite cantilever beam for energy harvesting under rotational motion to improve power output performance.Green et al.[8]established the model of rotational energy harvester in a probabilistic manner by exploiting experimental data combined with Bayesian approach.Unfortunately,the previous investigations of tri-stable energy harvesters (TEHs) under rotational vibrations tend to ignore the effect of random excitation on system dynamics,which will result in a mismatch with the actual situation.Furthermore,the neglect of the nonlinear harvesting circuit makes the harvested alternating current incapable of powering electronics.Therefore,motivated by the above reasons,the TEH interfaced with a standard rectifier circuit under random rotational environment is considered in this paper.

An alternative form of energy density demonstrating the severe strain-stiffening in thin spherical and cylindrical shells

Md. Moonim Lateefi, Deepak Kumar, Somnath Sarangi

Accepted Manuscript

[Abstract] (16) [PDF 0KB] (0)

Abstract:
In the current scenario,rubbers and rubber-like materials have attracted many researchers for modern soft engineering and medical field applications[1-3].Since the 1940s,enormous progress has been achieved in developing hyperelastic material modeling to characterize the stress-strain response at large deformations.The significant results have been obtained in incompressible hyperelastic material modeling and have also been experimentally confirmed[4,5].This remarkable success projected a considerable light on the physical behavior of rubber-like materials.However,the theory of elasticity for hyperelastic materials subjected to large deformations is highly nonlinear.Therefore,so many mathematical difficulties are still encountered at the current time.In general,rubber-like materials are assumed to be an incompressible isotropic hyperelastic materials.A preliminary step toward complete modeling is analyzing their elastic properties and nonlinear stress-strain characteristics[6,7].In line with that,the uniaxial and biaxial loading tests on such materials reveal a nonlinear stress-strain response with higher extensibility in the lowstress range and progressively lower extensibility at large strain.This phenomenon is well-known as "strain-hardening" or "strainstiffening".

Hydrothermal analysis of Hybrid nanofluid flow on a vertical plate by considering slip condition

M. R. Zangooee, Kh. Hosseinzadeh, D. D. Ganj

Accepted Manuscript

[Abstract] (16) [PDF 0KB] (0)

Abstract:
Hybrid nanofluids have attracted burgeoning attention owing to their outstanding capacity to improve heat transfer.The influence of velocity and temperature slip parameter and Nanoparticls'(NPs') volume fraction on a vertical plate in the existence of suction has been explored in this work.The investigation's controlling partial differentiation equations were transformed into a conventional differential equation mechanism using resemblance modifications.Equations were then solved employing the fifth-order Runge-Kutta method.The skin coefficient of friction,temperature,and temperature gradient all rise when the volume percentage of NPs increases from 0 to 2%.Furthermore,a rise in the temperature slip variable was linked to a drop in the Nusselt number (heat transfer).The Nusselt number increased 0.15% and 5.63% respectively when the velocity slip parameter enhanced from 0 to 5 and the NPs volume percentage were increased from 0 to 1.5%.Furthermore,an increase in the temperature slip from 0 to 3 inflated the x-direction skin friction coefficient 8.2%,while inflation in the velocity slip from 0 to 5 was associated with a decline in the x-direction skin friction coefficient 95%.

A machine learning based solver for pressure Poisson equations

Ruilin Chen, Xiaowei Jin, Hui Li

Accepted Manuscript

[Abstract] (15) [PDF 0KB] (0)

Abstract:
The Navier-Stokes equations are nonlinear partial differential equations (PDEs) describing viscous fluid flow,which are applicable to various scientific and engineering flow problems,such as river flow,air flow around wings,ocean currents,blood flow in the human cardiovascular system,etc.The solution of the NavierStokes equations is of great significance in the field of fluid mechanics.The convection term leads to the high nonlinearity of Navier-Stokes equations,and the solutions contain multi-scale flow structures.Nowadays,the numerical method is still a workhorse tool for solving complex flow phenomena.Thanks to the rapid growth of computer computing power and speed,the computational fluid dynamics (CFD) has made great progress[1-4].For incompressible Navier-Stokes equations,the main difficulty of numerical solution lies in the treatment of pressure,that is,how to deal with the coupling between velocity and pressure under incompressible constraints.To overcome this difficulty,Chorin[5]proposed the projection method (or fractional step method),which is widely used for its skillfully decoupling of the velocity and pressure fields.In the projection method,an incomplete form of momentum equations is first solved to obtain an intermediate velocity field,which is usually not divergence-free,then the velocity field is projected into the divergence-free field without changing the vorticity.This projection step is achieved by solving the pressure Poisson equation (PPE) and is usually more timeconsuming and computationally expensive than other steps in the overall solution process.

Elastoplastic constitutive modeling under the complex loading driven by GRU and small-amount data

Zefeng Yu, Chenghang Han, Hang Yang, Yu Wang, Shan Tang, Xu Guo

Accepted Manuscript

[Abstract] (16) [PDF 0KB] (0)

Abstract:
Engineering structures often are subjected to a variety of load types.Some parts of them may experience a complex deformation history,for example,plastic deformation under cyclic loading.The materials of such structures often include nonlinearity and path (history) dependence.Appropriate nonlinear constitutive models considering loading path (history) can assist in structural design,help monitor structural health and assess the redundancy life of the engineering structures.Many constitutive models have been proposed to describe the behavior of elastoplastic materials[1-4]based on an explicit-functions-based paradigm with basic elements such as the plastic flow,loading and unloading judgment etc..However,the formulation of function-based constitutive model along with the traditional approach is a challenging and time-consuming job.It requires complex mathematical derivation and intuition into the plastic deformation mechanisms of the materials.In recent years,with the development of the data-driven approach and the machine learning by the deep neural networks[5,6],building the constitutive models through the combination of data science and solid mechanics attracted the research attention of the researchers around the world.

Mathematical modeling of fractional derivatives for magnetohydrodynamic fluid flow between two parallel plates by the radial basis function method

Saman Hosseinzadeh, Seyed Mahdi Emadi, Seyed Mostafa Mousavi, Davood Domairry Ganji

Accepted Manuscript

[Abstract] (15) [PDF 0KB] (0)

Abstract:
Investigations into the magnetohydrodynamics of viscous fluids have become more important in recent years,owing to their practical significance and numerous applications in astro-physical and geo-physical phenomena.In this paper,the radial base function was utilized to answer fractional equation associated with fluid flow passing through two parallel flat plates with a magnetic field.The magnetohydrodynamics coupled stress fluid flows between two parallel plates,with the bottom plate being stationary and the top plate moving at a persistent velocity.We compared the radial basis function approach to the numerical method (fourth-order Range-Kutta) in order to verify its validity.The findings demonstrated that the discrepancy between these two techniques is quite negligible,indicating that this method is very reliable.The impact of the magnetic field parameter and Reynolds number on the velocity distribution perpendicular to the fluid flow direction is illustrated.Eventually,the velocity parameter is compared for diverse conditions α,Reynolds and position (y),the maximum of which occurs at α=0.4.Also,the maximum velocity values occur in α=0.4 and Re=1000 and the concavity of the graph is less for α=0.8.

Clamping force of a multilayered cylindrical clamper with internal friction

Bo-Hua Sun, Xiao-Lin Guo

Accepted Manuscript

[Abstract] (16) [PDF 0KB] (0)

Abstract:
Holding an object by clamping force is a fundamental process for functional structures in natural and manmade systems.Examples encompass different applications as shown in Fig.1,such as,medical clips,glass frame,hairband,headphone as well as robots[1-3]

Simulation and experimental analysis of melt pool evolution in laser engineered net shaping

Zhuangzhuang Mao, Wei Feng, Ce Hao, Zhanwei Liu

Accepted Manuscript

[Abstract] (14) [PDF 0KB] (0)

Abstract:
In this work,the evolution of melt pool under single-point and single-line printing in the Laser Engineered Net Shaping (LENS) process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.

Research on synchronous measurement technique of temperature and deformation fields using multispectral camera with bilateral telecentric lens

Wenxiong Shi, Yangyang Li, Ru Chen, Chenghao Zhang, Zhanwei Liu, Huimin Xie, Fei Liu

Accepted Manuscript

[Abstract] (121) [PDF 1224KB] (10)

Abstract:
The hot-section parts easily occur the creep-fatigued interaction under the condition of mechanical-thermal coupled load during the period of service, which may lead to the damage of the parts, and therefore, the measurement and characterization of thermal-deformed fields of the parts are important to understand its damage process. Aiming at relevant demand, the bilateral telecentric-multispectral imaging system was established, the research of synchronous measurement technique of the temperature and deformation fields was developed. On the one hand, the measurement technology for surface temperature of the object was developed using the two-color images captured by the multispectral camera with bilateral telecentric lens and combined with colorimetric method. On the other hand, the 2D-DIC measurement technique of the multispectral camera was developed by conducting digital image correlation analysis using the blue light images before and after deformation, which can measure the high temperature deformation field of the object (the blue light images were filtered by multispectral camera). Results showed that the bilateral telecentric lens is used to replace the ordinary optical lens for imaging, which can effectively eliminate the distortion of the multispectral imaging system. Since the temperature measurement process of this measurement system is little affected by the emissivity of the object, therefore, it has excellent robustness. The thermal expansion coefficients of the nickel alloys are evaluated at the temperature ranges of 700-1000 ℃, indicating this system can achieve the synchronous and precise measurement of the temperature and deformation fields of the object.

Importance of Induced Magnetic Field and Exponential Heat Source on Convective Flow of Casson Fluid in a Micro-channel via AGM

A. Hasibi, A. Gholami, Z. Asadi, D. D. Ganji1

Accepted Manuscript

[Abstract] (107) [PDF 1302KB] (4)

Abstract:
The study of the natural convective flow of a fluid in the presence of an induced magnetic field has always been of considerable importance due to its many applications in various areas of science, technology, and industry, such as the operation of magnetohydrodynamic generators. This study addresses an analysis of exponential heat source and induced magnetic field on the second-class convection of Casson fluid in a microchannel. The flow is in a vertical microchannel organized by two vertical plates. The answer to governing equations has been grabbed for temperature field, induced magnetic field, and velocity via Akbari-Ganji’s method (AGM). Nusselt number, skin friction coefficient, and current density are approximated. Graphs that describe the conclusion of influential physical variables on velocity, temperature, current density, induced magnetic field, and skin friction coefficient distributions are shown. Comparison of results with numerical method (Runge-Kutta-Fehlberg, RKF-45), homotopy perturbation method (HPM), and AGM confirms the accuracy of answers obtained with AGM.

On the Number of Fractured Segments of Spaghetti Breaking Dynamics

Yi Zhang, Xiang Li, Yuanfan Dai, and Bo-Hua Sun

Accepted Manuscript

[Abstract] (160) [PDF 5720KB] (4)

Abstract:
Why are pieces of spaghetti generally broken into three to ten segments instead of two as one thinks? How can one obtain the desired number of fracture segments? To answer those questions, the fracture dynamics of a strand of spaghetti is modelled by elastic rod and numerically investigated by using finite-element software ABAQUS. By data fitting, two relations are obtained: the number of fracture segments in terms of rod diameter-length ratio and fracture limit curvature with the rod diameter. Results reveal that when the length is constant, the larger the diameter and/or the smaller the diameter-length ratio D/L, the smaller the limit curvature; and the larger the diameter-length ratio D/L, the fewer the number of fractured segments. The relevant formulations can be used to obtain the desired number of broken segments of spaghetti by changing the diameter-to-length ratio.

Design of elliptical underwater acoustic cloak with truss-latticed pentamode materials

Yuanyuan Ge, Xiaoning. Liu, Gengkai Hu

Accepted Manuscript

[Abstract] (116) [PDF 1351KB] (15)

Abstract:
Pentamode acoustic cloak is promising for underwater sound control due to its solid nature and broadband efficiency, however its realization is only limited to simple cylindrical shape. In this work, we established a set of techniques for the microstructure design of elliptical pentamode acoustic cloak based on truss lattice model, including the inverse design of unit cell and algorithms for latticed cloak assembly. The designed cloak was numerically validated by the well wave concealing performance. The work proves that more general pentamode acoustic wave devices beyond simple cylindrical geometry are theoretically feasible, and sheds light on more practical design for waterborne sound manipulation.

Peng Zhang, Yanchong Duan, Qiang Zhong, Danxun Li, Shengfa Yang, Jiang Hu, Wenjie Li

Accepted Manuscript

[Abstract] (99) [PDF 957KB] (1)

Abstract:
Decelerating open-channel flow is a type of flow that gradually moves forward with decreasing velocity and increasing water depth. Although all flow parameters change along the streamwise direction, previous studies have revealed that these parameters' vertical distributions at different sections can be universally described with a single profile when being non dimensionalised by appropriate scales. This study focuses on the population trends of spanwise rotational motions at various sections along the main flow direction by particle imaging velocimetry (PIV) measurement. The wall-normal population distributions of density, radius, swirling strength, and convection velocity of the prograde and retrograde motions show similar trends in uniform open-channel flows. The dimensionless representation is invariant along the main flow direction. This study's results indicate the self-similar characteristic of population trends of spanwise rotational motions prevails in decelerating open-channel flow.

Optimal thermal design of anisotropic plates with arbitrary cutouts using genetic algorithm

Mohammad Jafari, Soheila Yari, Mohammad Jafari

Accepted Manuscript

[Abstract] (86) [PDF 1751KB] (1)

Abstract:
Anisotropic plates in different applications may have geometric defects such as openings and cracks. The presence of the opening disturbs the heat flow, which creates significant thermal stress around the opening. When the heat flux is high enough, these extreme stresses can lead to structural failure. This article aims to obtain the optimal parameters for achieving the minimum value of the normalized stress near the cutout’s boundary in perforated anisotropic plates utilizing the genetic algorithm. Optimization parameters include the curvature of opening’s corners, orientation angle of opening, fibers angle, heat flux angle, and opening’s elongation. The plate is under heat flux, and the opening’s border is thermally insulated. The stress distribution around the opening is calculated using Lekhnitskii’s complex variable method and complex potential functions. The genetic algorithm is then implemented to find the optimal values for design parameters. The results show that by selecting the optimal parameters related to the anisotropic material and the opening’s geometry, the stress intensity factor of the perforated anisotropic plates is remarkably reduced. Furthermore, this optimization algorithm can be extended to find the optimized parameters and achieve the optimal designs in anisotropic and isotropic perforated plates under thermal loadings.

Optimal Patching Locations and Orientations for Maximum Energy Harvesting Efficiency of Ultrathin Flexible Piezoelectric Devices Mounted on Heart Surface

Yangyang Zhang, Ji Wanga, Chaofeng Lü

Accepted Manuscript

[Abstract] (138) [PDF 161KB] (2)

Abstract:
Flexible piezoelectric energy harvesters (PEHs) have gained lots of attention in recent years, because of their potential biomechanical applications, such as powering implantable devices. Several in vivo animal experiments have demonstrated that the output power of a flexible PEH varies remarkably with patching orientations and locations, but the underlying mechanism remains unclear yet. Herein, an electromechanical model for a flexible PEH installed on a beating heart is proposed, and a concise relationship between the output power of the device and myocardium strain is established. The results demonstrate that the patching orientations have a significant impact on the output power of the PEH, and the optimal patching orientations for all patching locations are approximately 15-20 degree for PEHs mounted on the left ventricle. The simple theoretical method provided here would be universally effective for choosing the optimal patching locations and orientations of flexible PEHs installed on a nonhomogeneous deformed surface.

A nonlinear analysis of surface acoustic waves in isotropic elastic solids

Haoxiang Wu, Rongxing Wu, Tingfeng Ma, Zixiao Lu, Honglang Li, Ji Wang

Accepted Manuscript

[Abstract] (314) [PDF 176KB] (9)

Abstract:
With the fast evolution of wireless and networking communication technology, applications of surface acoustic wave (SAW), or Rayleigh wave, resonators are proliferating with fast shrinking sizes and increasing frequencies. It is inevitable that the smaller resonators will be under a strong electric field with induced large deformation, which has to be described in wave propagation equations with the consideration of nonlinearity. In this study, the formal nonlinear equations of motion are constructed by introducing the nonlinear constitutive relation and strain components in a standard procedure, and the equations are simplified by the extended Galerkin method through the elimination of harmonics. The wave velocity of the nonlinear SAW is obtained from approximated nonlinear equations with boundary conditions through a rigorous solution procedure. It is shown that if the amplitude is small enough, the nonlinear results are consistent with the linear results, demonstrating an alternative procedure for nonlinear analysis of SAW devices working in nonlinear state.

A modified discrete element method for concave granular materials based on energy-conserving contact model

Ting Qiao, Ji Li, Shunying Ji

Accepted Manuscript

[Abstract] (195) [PDF 926KB] (2)

Abstract:
The development of a general discrete element method for irregularly shaped particles is the core issue of the simulation of the dynamic behavior of granular materials. The general energy-conserving contact theory is used to establish a universal discrete element method suitable for particle contact of arbitrary shape. In this study, 3D modeling and scanning techniques are used to obtain a triangular mesh representation of the true particles containing typical concave particles. The contact volume-based energy-conserving model is used to realize the contact detection between irregularly shaped particles, and the contact force model is refined and modified to describe the contact under real conditions. The inelastic collision process between the particles and boundaries are simulated to verify the robustness of the modified contact force model and its applicability to the multi-point contact mode. In addition, the packing process and the flow process of a large number of irregular particles are simulated with the modified DEM to illustrate the applicability of the method of complex problems.

Thermal energy storage inside the chamber with a brick wall using the phase change process of paraffinic materials: A numerical simulation

M. Javidan, M. Asgari, M. Gholinia, M. Nozari, A. Asgari, D. D. Ganji

Accepted Manuscript

[Abstract] (193) [PDF 936KB] (0)

Abstract:
Phase change materials are one of the potential resources to replace fossil fuels in regards of supplying the energy of buildings. Basically, these materials absorb or release heat energy with the help of their latent heat. Phase change materials have low thermal conductivity and this makes it possible to use the physical properties of these materials in the tropical regions where the solar radiation is more direct and concentrated over a smaller area. In this theoretical work, an attempt has been made to study the melting process of these materials by applying constant heat flux and temperature. It was found that by increasing the thickness of phase change materials’ layers, due to the melting, more thermal energy is stored. Simultaneously it reduces the penetration of excessive heat into the chamber, so that by increasing the thickness of paraffin materials up to 20 mm, the rate of temperature reduction reaches more than 18%. It was also recognized that increasing the values of constant input heat flux increases buoyancy effects. Increasing the Stefan number from 0.1 to 0.3, increases the temperature by 6%.

Capturing the Baroclinic Effect in non-Boussinesq Gravity Currents

Shengqi Zhang, Zhenhua Xia

Accepted Manuscript

[Abstract] (275) [FullText HTML] (238) [PDF 2971KB] (3)

Abstract:
Direct numerical simulations of two-dimensional gravity currents with small and medium density variations are performed using different non-Boussinesq buoyancy approximations. Taking the full low-Mach-number approximation as the reference, the accuracy of several buoyancy terms are examined. It is found that all considered buoyancy terms performed well in the cases with small density variation. In the cases with medium density variation, the classical gravitational Boussinesq's buoyancy term showed the lack of accuracy, and a simple correction did not make any improvement. In contrast, the recently introduced second-order buoyancy term showed a significantly higher accuracy. The present results and our previous derivations indicate that simple algebraic buoyancy approximations extended from the Boussinesq's gravitational buoyancy are unlikely to achieve an accuracy beyond first order. Instead, it seems necessary to solve at least one extra Poisson equation for buoyancy terms to capture the higher-order baroclinic effect. An approximate analysis is also provided to show the leading term of the non-Boussinesq effect corresponding to gravity.

A universal bifurcation mechanism arising from progressive hydroelastic waves

Zhan Wang

Accepted Manuscript

[Abstract] (278) [FullText HTML] (250) [PDF 3365KB] (11)

Abstract:
A unidirectional, weakly dispersive nonlinear model is proposed to describe the supercritical bifurcation arising from hydroelastic waves in deep water. This model equation, including quadratic, cubic, and quartic nonlinearities, is an extension of the famous Whitham equation. The coefficients of the nonlinear terms are chosen to match with the key properties of the full Euler equations, precisely, the associated cubic nonlinear Schrödinger equation and the amplitude of the solitary wave at the bifurcation point. It is shown that the supercritical bifurcation, rich with Stokes, solitary, generalized solitary, and dark solitary waves in the vicinity of the phase speed minimum, is a universal bifurcation mechanism. The newly developed model can capture the essential features near the bifurcation point and easily be generalized to other nonlinear wave problems in hydrodynamics.

Multiscale mechanics of noncovalent interface in graphene oxide layered nanocomposites

ZeZhou He, YinBo Zhu, HengAn Wu

Accepted Manuscript

[Abstract] (291) [FullText HTML] (243) [PDF 3077KB] (10)

Abstract:
Noncovalent interfaces play a vital role in inelastic deformation and toughening mechanisms in layered nanocomposites due to their dynamical recoverability. When interfacial engineering is applied to design layered nanocomposites, shear-lag analysis is usually implemented to evaluate the capability of interfacial loading transfer. Here, we introduce a multiscale shear-lag model that correlates macroscale mechanical properties with the molecular mechanisms to quantify the effects of interfacial configuration in graphene oxide (GO) layered nanocomposites. By investigating the mechanical responses of commensurate and incommensurate interfaces, we identify that the commensurate interface exhibits a pronounced size effect due to the nucleation and propagation of interfacial defects, whereas the incommensurate interface displays uniform deformation. Our predictions are further validated through large-scale molecular dynamics simulations for GO layered nanocomposites. This work demonstrates how size effects and interfacial configurations can be exploited to fabricate layered nanocomposites with superior mechanical properties despite relying on weak noncovalent interfaces.

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Clustering solver for displacement-based numerical homogenization

Shaoqiang Tang, Xi Zhu

Theoretical and Applied Mechanics Letters 12 (2022) 100306. doi: 10.1016/j.taml.2021.100306

[Abstract] (30) [PDF 1905KB] (4)

Abstract:
Based on strain-clustering via k-means, we decompose computational domain into clusters of possibly disjoint cells. Assuming cells in each cluster take the same strain, we reconstruct displacement field. We further propose a new way to condensate the governing equations of displacement-based finite element method to reduce the complexity while maintain the accuracy. Numerical examples are presented to illustrate the efficiency of the clustering solver. Numerical convergence studies are performed for the examples. Avoiding complexities which is common in existing clustering analysis methods, the proposed clustering solver is easy to implement, particularly for numerical homogenization using commercial softwares.

Thermal energy storage inside the chamber with a brick wall using the phase change process of paraffinic materials: A numerical simulation

M. Javidan, M. Asgari, M. Gholinia, M. Nozari, A. Asgari, D. D. Ganji

Theoretical and Applied Mechanics Letters 12 (2022) 100329. doi: 10.1016/j.taml.2022.100329

[Abstract] (130) [PDF 2523KB] (0)

Abstract:
Phase change materials are one of the potential resources to replace fossil fuels in regards of supplying the energy of buildings. Basically, these materials absorb or release heat energy with the help of their latent heat. Phase change materials have low thermal conductivity and this makes it possible to use the physical properties of these materials in the tropical regions where the solar radiation is more direct and concentrated over a smaller area. In this theoretical work, an attempt has been made to study the melting process of these materials by applying constant heat flux and temperature. It was found that by increasing the thickness of phase change materials' layers, due to the melting, more thermal energy is stored. Simultaneously it reduces the penetration of excessive heat into the chamber, so that by increasing the thickness of paraffin materials up to 20 mm, the rate of temperature reduction reaches more than 18%. It was also recognized that increasing the values of constant input heat flux increases buoyancy effects. Increasing the Stefan number from 0.1 to 0.3, increases the temperature by 6%.

Numerical simulation of droplet coalescence based on the SPH method

Kaiwen Gu, Tieqiang Gang, Lijie Chen

Theoretical and Applied Mechanics Letters 12 (2022) 100333. doi: 10.1016/j.taml.2022.100333

[Abstract] (132) [PDF 4342KB] (6)

Abstract:
In this paper, the smoothed particle hydrodynamics (SPH) method is employed in modeling and numerical simulation of droplet coalescence. Considering the effect of tangential force on boundary material, besides normal force, tangential force is also introduced in the continuum surface force (CSF) model. The formation of droplet, the coalescence processes of two droplets and three droplets are simulated by the modified CSF model. The validity of the modified model is verified from the aspects of the morphological change of the droplet, the smoothness of free surface and the conservation of the centroid of the system. Compared with finite element method, the results of the modified CSF model show that tangential force plays a crucial role in the CSF model when dealing with model boundary with curves and sharp angles.

Similarity solutions of Prandtl mixing length modelled two dimensional turbulent boundary layer equations

Bo-Hua Sun

Theoretical and Applied Mechanics Letters 12 (2022) 100338. doi: 10.1016/j.taml.2022.100338

[Abstract] (16) [PDF 1012KB] (0)

Abstract:
The exact similarity solutions of two dimensional laminar boundary layer were obtained by Blasius in 1908, however, for two dimensional turbulent boundary layers, no Blasius type similarity solutions (special exact solutions) have ever been found. In the light of Blasius' pioneer works, we extend Blasius similarity transformation to the two dimensional turbulent boundary layers, and for a special case of flow modelled by Prandtl mixing-length, we successfully transform the two dimensional turbulent boundary layers partial differential equations into a single ordinary differential equation. The ordinary differential equation is numerically solved and some useful quantities are produced. For numerical calculations, a complete Maple code is provided.

Optimal patching locations and orientations for maximum energy harvesting efficiency of ultrathin flexible piezoelectric devices mounted on heart surface

Yangyang Zhang, Ji Wang, Chaofeng Lü

Theoretical and Applied Mechanics Letters 12 (2022) 100341. doi: 10.1016/j.taml.2022.100341

[Abstract] (13) [PDF 2072KB] (0)

Importance of induced magnetic field and exponential heat source on convective flow of Casson fluid in a micro-channel via AGM

A. Hasibi, A. Gholami, Z. Asadi, D. D. Ganji

Theoretical and Applied Mechanics Letters 12 (2022) 100342. doi: 10.1016/j.taml.2022.100342

[Abstract] (17) [PDF 2646KB] (0)

Abstract:
The study of the natural convective flow of a fluid in the presence of an induced magnetic field has always been of considerable importance due to its many applications in various areas of science, technology, and industry, such as the operation of magnetohydrodynamic generators. This study addresses an analysis of exponential heat source and induced magnetic field on the second-class convection of Casson fluid in a microchannel. The flow is in a vertical microchannel organized by two vertical plates. The answer to governing equations has been grabbed for temperature field, induced magnetic field, and velocity via Akbari-Ganji's method (AGM). Nusselt number, skin friction coefficient, and current density are approximated. Graphs that describe the conclusion of influential physical variables on velocity, temperature, current density, induced magnetic field, and skin friction coefficient distributions are shown. Comparison of results with numerical method (Runge-Kutta-Fehlberg, RKF-45), homotopy perturbation method, and AGM confirms the accuracy of answers obtained with AGM.

Optimal thermal design of anisotropic plates with arbitrary cutouts using genetic algorithm

Mohammad Jafari, Soheila Yari, Mohammad Jafari

Theoretical and Applied Mechanics Letters 12 (2022) 100343. doi: 10.1016/j.taml.2022.100343

[Abstract] (15) [PDF 3019KB] (0)

Abstract:
Anisotropic plates in different applications may have geometric defects such as openings and cracks. The presence of the opening disturbs the heat flow, which creates significant thermal stress around the opening. When the heat flux is high enough, these extreme stresses can lead to structural failure. This article aims to obtain the optimal parameters for achieving the minimum value of the normalized stress near the cutout's boundary in perforated anisotropic plates utilizing the genetic algorithm. Optimization parameters include the curvature of opening's corners, orientation angle of opening, fibers angle, heat flux angle, and opening's elongation. The plate is under heat flux, and the opening's border is thermally insulated. The stress distribution around the opening is calculated using Lekhnitskii's complex variable method and complex potential functions. The genetic algorithm is then implemented to find the optimal values for design parameters. The results show that by selecting the optimal parameters related to the anisotropic material and the opening's geometry, the stress intensity factor of the perforated anisotropic plates is remarkably reduced. Furthermore, this optimization algorithm can be extended to find the optimized parameters and achieve the optimal designs in anisotropic and isotropic perforated plates under thermal loadings.

Self-similarity of spanwise rotational motions' population trends in decelerating open-channel flow

Peng Zhang, Yanchong Duan, Qiang Zhong, Danxun Li, Shengfa Yang, Jiang Hu, Wenjie Li

Theoretical and Applied Mechanics Letters 12 (2022) 100344. doi: 10.1016/j.taml.2022.100344

[Abstract] (18) [PDF 2484KB] (0)

Abstract:
Decelerating open-channel flow is a type of flow that gradually moves forward with decreasing velocity and increasing water depth. Although all flow parameters change along the streamwise direction, previous studies have revealed that these parameters' vertical distributions at different sections can be universally described with a single profile when being nondimensionalised by appropriate scales. This study focuses on the population trends of spanwise rotational motions at various sections along the main flow direction by particle imaging velocimetry (PIV) measurement. The wall-normal population distributions of density, radius, swirling strength, and convection velocity of the prograde and retrograde motions show similar trends in uniform open-channel flows. The dimensionless representation is invariant along the main flow direction. This study's results indicate the self-similar characteristic of population trends of spanwise rotational motions prevails in decelerating open-channel flow.

Research on synchronous measurement technique of temperature and deformation fields using multispectral camera with bilateral telecentric lens

Wenxiong Shi, Yangyang Li, Ru Chen, Chenghao Zhang, Zhanwei Liu, Huimin Xie, Fei Liu

Theoretical and Applied Mechanics Letters 12 (2022) 100345. doi: 10.1016/j.taml.2022.100345

[Abstract] (21) [PDF 3237KB] (1)

Abstract:
The hot-section parts easily occur the creep-fatigued interaction under the condition of mechanicalthermal coupled load during the period of service, which may lead to the damage of the parts, and therefore, the measurement and characterization of thermal-deformed fields of the parts are important to understand its damage process. Aiming at relevant demand, the bilateral telecentric-multispectral imaging system was established, the research of synchronous measurement technique of the temperature and deformation fields was developed. On the one hand, the measurement technology for surface temperature of the object was developed using the two-color images captured by the multispectral camera with bilateral telecentric lens and combined with colorimetric method. On the other hand, the 2D-DIC measurement technique of the multispectral camera was developed by conducting digital image correlation analysis using the blue light images before and after deformation, which can measure the high temperature deformation field of the object (the blue light images were filtered by multispectral camera). Results showed that the bilateral telecentric lens is used to replace the ordinary optical lens for imaging, which can effectively eliminate the distortion of the multispectral imaging system. Since the temperature measurement process of this measurement system is little affected by the emissivity of the object, therefore, it has excellent robustness. The thermal expansion coefficients of the nickel alloys are evaluated at the temperature ranges of 700-1000 ℃, indicating this system can achieve the synchronous and precise measurement of the temperature and deformation fields of the object.

Useful zero friction simulations for assessing MBS codes Pascal's formula giving wheelsets frequency for zero wheel-rail friction

Jean Pierre Pascal

Theoretical and Applied Mechanics Letters 12 (2022) 100348. doi: 10.1016/j.taml.2022.100348

[Abstract] (14) [PDF 1994KB] (0)

Abstract:
Present study provides a simple analytical formula, the "Klingel-like formula" or "Pascal's Formula" that can be used as a reference to test some results of existing railway codes and specifically those using rigid contact. It develops properly the 3D Newton-Euler equations governing the 6 degrees of freedom (DoF) of unsuspended loaded wheelsets in case of zero wheel-rail friction and constant conicity. Thus, by solving numerically these equations, we got pendulum like harmonic oscillations of which the calculated angular frequency is used for assessing the accuracy of the proposed formula so that it can in turn be used as a fast practical target for testing multi-body system (MBS) railway codes. Due to the harmonic property of these pendulum-like oscillations, the square ω² of their angular frequency can be made in the form of a ratio K/M where K depends on the wheelset geometry and load and M on its inertia. Information on K and M are useful to understand wheelsets behavior. The analytical formula is derived from the first order writing of full trigonometric Newton-Euler equations by setting zero elastic wheel-rail penetration and by assuming small displacements. Full trigonometric equations are numerically solved to assess that the formula provides ω² inside a 1% accuracy for usual wheelsets dimensions. By decreasing the conicity down to 1×10^-4 rad, the relative formula accuracy is under 3×10^-5. In order to test the formula reliability for rigid contact formulations, the stiffness of elastic contacts can be increased up to practical rigidity (Hertz stiffness×1000).

Crack propagation simulation in brittle elastic materials by a phase field method

Xingxue Lu, Cheng Li, Ying Tie, Yuliang Hou, Chuanzeng Zhang

2019, 9(6): 339-352 doi: 10.1016/j.taml.2019.06.001

[Abstract](1432) [FullText HTML](833) [PDF 3845KB](94)

Mechanistic Machine Learning: Theory, Methods, and Applications

2020, 10(3): 141-142 doi: 10.1016/j.taml.2020.01.041

[Abstract](8708) [FullText HTML](736) [PDF 3081KB](85)

Investigation on Savonius turbine technology as harvesting instrument of non-fossil energy: Technical development and potential implementation

Aditya Rio Prabowo, Dandun Mahesa Prabowoputra

2020, 10(4): 262-269 doi: 10.1016/j.taml.2020.01.034

[Abstract](1188) [FullText HTML](571) [PDF 3192KB](84)

On the Weissenberg effect of turbulence