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Corrected proof , doi: 10.1016/j.taml.2020.01.050
[Abstract] (35) [FullText HTML] (4) [PDF 3118KB] (0)
Abstract:
In recent years, shear horizontal (SH) waves are being paid more and more attention to in structural health monitoring as it has only one displacement component. In this paper, a unidirectional SH wave transducer based on phase-controlled antiparallel thickness-shear (d15) piezoelectric strips (APS) is proposed. Here two pairs of identical APS were used each of which is a bidirectional SH wave transducer. By setting the interval between the two pairs of APS as 1/4 wavelength and the excitation delay between them as 1/4 period of the central operating frequency, unidirectional SH waves can be excited. Both finite element simulations and experiments were performed to validate the proposed design. Results show that SH0 waves were successfully excited only along one direction and those along the unwanted directions were suppressed very well. The proposed unidirectional SH wave transducer is very helpful to study the fundamentals and applications of SH waves.
Corrected proof , doi: 10.1016/j.taml.2020.01.045
[Abstract] (119) [FullText HTML] (75) [PDF 3136KB] (1)
Abstract:
The rock fragmentation involves the inter-block and the intra-block fracture. A simulation method for rock fragmentation is developed by coupling Voronoi diagram (VD) and discretized virtual internal bond (DVIB). The DVIB is a lattice model that consists of bonds. The VD is used to generate the potential block structure in the DVIB mesh. Each potential block may contain any number of bond cells. To characterize the inter-block fracture, a hyperelastic bond potential is employed for the bond cells that are cut by the VD edges. While to characterize the intra-block fracture, an elastobrittle bond potential is adopted for the bonds in a block. By this method, both the inter-block and intra-block fracture can be well simulated. The simulation results suggest that this method is a simple and efficient approach to rock fragmentation simulation with block smash.
Corrected proof , doi: 10.1016/j.taml.2020.01.046
[Abstract] (96) [FullText HTML] (76) [PDF 5934KB] (0)
Abstract:
This paper deals with a numerical study of weak shock-waves propagation and their attenuation in channel flow having different heights and exhibiting a hollow circular cavities with different depths and diffraction angles inside. The effect of initial diffraction angle and cavity depth on the shock mitigation is investigated. A better shock attenuation is achieved with diffraction angle \begin{document}$\theta_{w} = 90^\circ$\end{document} by a factor of approximately 17% in terms of shock-Mach number and 38% in terms of total energy. The obtained results show also, in addition to the initial diffraction angle and cavity depth, the importance of reducing the channel heights as well as the position of the reduced section in achieving an optimal shock-wave attenuation. The presence of a cavity inside the channel helps to attenuate faster the shock wave. The underlying physics relies on the shock diffraction phenomenon that generates large amount of vortical structures capable of dissipating part of the shock energy by inducing a pressure loss behind it. A subtle arrangement of channel position/height and a cavity location leads to an efficient pressure attenuation by approximately a factor of 57% for \begin{document}$M_s = 1.6$\end{document} and 16% for \begin{document}$M_s = 1.1$\end{document} .
Corrected proof , doi: 10.1016/j.taml.2020.01.049
[Abstract] (22) [FullText HTML] (7) [PDF 2754KB] (1)
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The aim of the present study is to design a new fifth order system of Emden-Fowler equations and related four types of the model. The standard second order form of the Emden-Fowler has been used to obtain the new model. The shape factor that appear more than one time discussed in detail for every case of the designed model. The singularity at η = 0 at one point or multiple points is also discussed at each type of the model. For validation and correctness of the new designed model, one example of each type based on system of fifth order Emden-Fowler equations are provided and numerical solutions of the designed equations of each type have been obtained by using variational iteration scheme. The comparison of the exact results and present numerical outcomes for solving one problem of each type is presented to check the accuracy of the designed model.
Accepted Manuscript , doi: 10.1016/j.taml.2020.01.030
[Abstract] (186) [FullText HTML] (124) [PDF 3192KB] (5)
Abstract:
The nonlinear thermoelastic responses of an elastic medium exposed to laser generated short-pulse heating are investigated in this article. The thermal wave propagation of generalized thermoelastic medium under the impact of thermal loading with energy dissipation is the focus of this research. To model the thermal boundary condition (in the form of thermal conduction), generalized Cattaneo model (GCM) is employed. In the reference configuration, a nonlinear coupled Lord-Shulman-type generalized thermoelasticity formulation using finite strain theory (FST) is developed and the temperature dependency of the thermal conductivity is considered to derive the equations. In order to solve the time-dependent and nonlinear equations, Newmark's numerical time integration technique and an updated finite element algorithm is applied and to ensure achieving accurate continuity of the results, the Hermitian elements are used instead of Lagrangian's. The numerical responses for different factors such as input heat flux and nonlinear terms are expressed graphically and their impacts on the system's reaction are discussed in detail. The results of the study are presented for Green–Lindsay model and the findings are compared with Lord-Shulman model especially with regards to heat wave propagation. It is shown that the nature of the laser's thermal shock and its geometry are particularly determinative in the final stage of deformation. The research also concluded that employing FST leads to achieving more accuracy in terms of elastic deformations; however, the thermally nonlinear analysis does not change the results markedly. For this reason, the nonlinear theory of deformation is required in laser related reviews, while it is reasonable to ignore the temperature changes compared to the reference temperature in deriving governing equations.
Accepted Manuscript , doi: 10.1016/j.taml.2020.01.042
[Abstract] (167) [FullText HTML] (111) [PDF 3173KB] (11)
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A new computational procedure for modelling the structural behavior of stiffened plates with symmetry boundary conditions is here presented. It uses two-dimensional finite elements as a way to decrease computational time without losing precision thanks to a relatively small number of elements applied for analyzing out-of-plane displacements (deflections) and stresses. Adding, the constructal design method was included in the procedure, together with the Exhaustive Search technique, with the scope to optimize the stress/strain status of stiffened plates by design changes. For the purpose, a reference plate without stiffeners was initially design and used as starting point. Part of the volume was reshaped into stiffeners: thickness was reduced maintaining unchanged weight, length and width. The main goal was to minimize strains and stresses by geometric changes. Results demonstrated that, thanks to this design procedure, it is always possible to find an adequate geometry transformation from reference plate into stiffeners, allowing significant improvements in mechanical behavior.
Accepted Manuscript , doi: 10.1016/j.taml.2020.01.040
[Abstract] (138) [FullText HTML] (100) [PDF 3172KB] (1)
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The emergence of new types of composite materials, the depletion of existing hydrocarbon deposits, and the increase in the speed of trains require the development of new research methods based on wave scattering. Therefore, it is necessary to determine the laws of wave scattering in inhomogeneous media. We propose a method that combines the advantages of a numerical simulation with an analytical study of the boundary value problem of elastic and acoustic wave equations. In this letter we present the results of the study using the proposed method: the formation of a response from a shear wave in an acoustic medium and the formation of shear waves when a vertically incident longitudinal wave is scattered by a vertical gas-filled fracture. We have obtained a number of analytical expressions characterising the scattering of these wave types.
Accepted Manuscript , doi: 10.1016/j.taml.2020.01.044
[Abstract] (94) [FullText HTML] (80) [PDF 2598KB] (1)
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Accelerated proximal gradient methods have recently been developed for solving quasi-static incremental problems of elastoplastic analysis with some different yield criteria. It has been demonstrated through numerical experiments that these methods can outperform conventional optimization-based approaches in computational plasticity. However, in literature these algorithms are described individually for specific yield criteria, and hence there exists no guide for application of the algorithms to other yield criteria. This short paper presents a general form of algorithm design, independent of specific forms of yield criteria, that unifies the existing proximal gradient methods. Clear interpretation is also given to each step of the presented general algorithm so that each update rule is linked to the underlying physical laws in terms of mechanical quantities.
Accepted Manuscript , doi: 10.1016/j.taml.2020.01.037
[Abstract] (222) [FullText HTML] (104) [PDF 2952KB] (1)
Abstract:
Ultrasound guided breast biopsy navigation system with a graphical user interface and a passive robotic needle holder is developed to increase the performance and reliability of the radiologist. Ultrasound calibration and tool tip calibration are required before using the system. A ladder phantom is developed to be used for ultrasound calibration in real time system with only one ultrasound image required. The passive robotic needle holder structure results in an identity matrix for the makes the rotation matrix; therefore, only translation and scaling are required in the system. This method can be applied to multiple ultrasound depths, which has a relationship at each depth and a relationship to the ultrasound image on the display. The results show high accuracy (<1 mm.) and rapid calibration (5-10 minutes) which is suitable for a real time system like a breast biopsy navigation system based on tests with a breast phantom.
Accepted Manuscript , doi: 10.1016/j.taml.2020.01.047
[Abstract] (114) [FullText HTML] (71) [PDF 2830KB] (4)
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In this paper, the models describing the charge transfer between two sand particles due to collisions are reviewed. By comparing the experimental results and the calculated results by the models carried on an individual particle due to a single collision, it indicates the Mosaic model is more reasonable to describe the collision charging mechanism. The Mosaic model cannot only describe the dependence of the collision charges on the relative collision speed and the particle size, but also reveal the relationship between the collision charges with the environmental temperature, the relative humidity and the material parameters, e.g., the absorption energy. Based on the Mosaic model, the model to describe the charges transfer due to multiple collisions is also developed, which can be used to calculate the charges carried by sand particles due to multiple collisions in the wind blown sand flux.
Corrected proof , doi: 10.1016/j.taml.2020.01.024
[Abstract] (248) [FullText HTML] (320) [PDF 3178KB] (12)
Abstract:
A physical mechanism by which nose bluntness suppresses second-mode instability is proposed. Considered are 7 degree half-angle straight cones with nose bluntness radii of 0.15 mm, 3.556 mm, 5 mm, 9.525 mm, 12.7 mm and 25.4 mm at tunnel conditions relevant to the AFOSR-Notre Dame Large Mach 6 Quiet Tunnel. It is shown that second-mode suppression is achieved via entropy layer modulation of the basic state density gradient. A weakening of the density gradient disrupts the acoustic resonance necessary to sustain second-mode growth. These results are consistent with the thermoacoustic interpretation which posits that second-mode instability can be modeled as thermoacoustic resonance of acoustic energy trapped within an acoustic impedance well. Furthermore, the generalized inflection point criterion of Lees and Lin is applied to develop a criterion for the existence of second-mode instability based on the strength of the basic state density gradient.
Corrected proof , doi: 10.1016/j.taml.2020.01.026
[Abstract] (216) [FullText HTML] (140) [PDF 2986KB] (2)
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The presence of solid particles or water droplets in continuous fluid flow can either induce turbulence attenuation or amplification. The modification of the state of the turbulence depends on the characteristics of the particles, such as volume fraction, mean diameter, mass density, or carrier phase flow properties. In this brief review, the main physical concepts related to the most important physical aspects of turbulence modulation are summarized. Different criteria used to distinguish the enhancement or the attenuation effects of the particles on the carrier phase flows are recalled. For the interest of large-scale industrial applications, several theoretical, experimental and empirical approaches are discussed, which provides an interesting framework for the study of the effect of particles on turbulence behavior modification.
Corrected proof , doi: 10.1016/j.taml.2020.01.013
[Abstract] (200) [FullText HTML] (127) [PDF 3402KB] (4)
Abstract:
Pressure drop and liquid hold-up are two very important fluid flow parameters in design and control of multiphase flow pipelines. Friction factors play an important role in the accurate calculation of pressure drop. Various empirical and semi-empirical closure relations exist in the literature to calculate the liquid-wall, gas-wall and interfacial friction in two-phase pipe flow. However most of them are empirical correlations found under special experimental conditions.In this paper by modification of a friction model available in the literature, an improved semi-empirical model is proposed. The proposed model is incorporated in the two-fluid correlations under equilibrium conditions and solved. Pressure gradient and velocity profiles are validated against experimental data.Using the improved model, the pressure gradient deviation from experiments diminishes by about 3%; the no-slip condition at the interface is satisfied and the velocity profile is predicted in better agreement with the experimental data.
Corrected proof , doi: 10.1016/j.taml.2020.01.034
[Abstract] (201) [FullText HTML] (121) [PDF 3189KB] (13)
Abstract:
Environmental risk due to excessive residual emission is rising. Greenhouse effect, ice melting in the Arctic, reduction of air quality are several concerns which need immediate development and change. Energy harvesting equipment is one of the key solutions. Environment potential, e.g. water resource can be collaborated with mechanical equipment to harvest clean energy. Savonius turbine has been proposed and studied for this purpose and can be placed on several energy resources, i.e. water and wind. Still, real-world implementation of this technology is lacking, especially in tropical archipelago countries which have abundant water resources. In this work, assessment of Savonius turbine technology as instrument to harvest clean energy is conducted. A series of development on the turbine performance and technical modification is considered as reference to implement the technology in water and open air environments. It is noted that rotor design, operation depth and nozzle attachment are several key influencing factors.