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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] (0) [PDF 1224KB] (0)
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] (0) [PDF 1302KB] (0)
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] (0) [PDF 5720KB] (0)
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] (0) [PDF 1351KB] (0)
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.
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
Accepted Manuscript
[Abstract] (0) [PDF 957KB] (0)
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] (0) [PDF 1751KB] (0)
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] (39) [PDF 161KB] (1)
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.
Numerical simulation of droplet coalescence based on the SPH method
Kaiwen Gu, Tieqiang Gang, Lijie Chen
Accepted Manuscript , doi: 10.1016/j.taml.2022.100333
[Abstract] (50) [PDF 1366KB] (4)
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.
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 , doi: 10.1016/j.taml.2022.100329
[Abstract] (45) [PDF 2459KB] (0)
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%.
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] (131