Showing papers in "Journal of Mechanics in 2014"
TL;DR: In this article, the analysis of the buckling and vibration of single-layered graphene sheets, resting on Pasternak's elastic foundations with various boundary conditions, is presented.
Abstract: In this article, the analyses of the natural frequency and buckling of orthotopic nanoplates, such as single-layered graphene sheets, resting on Pasternak's elastic foundations with various boundary conditions are presented. New functions for midplane displacements are suggested to satisfy the different boundary conditions. These functions are examined by comparing their results with the results obtained by using the functions suggested by Reddy (Reddy JN. Mechanics of Composite Materials and Structures: Theory and Analysis. Boca Raton, FL: CRC Press; 1997). Moreover, these functions are very simple comparing with Reddy's functions, leading to ease of calculations. The equations of motion of the nonlocal model are derived using the sinusoidal shear deformation plate theory (SPT) in conjunction with the nonlocal elasticity theory. The present SPT are compared with other plate theories. Explicit solution for buckling loads and vibration are obtained for single-layered graphene sheets with isotropic and orthotropic properties; and under biaxial loads. The formulation and the method of the solution are firstly validated by executing the comparison studies for the isotropic nanoplates with the results being in literature. Then, the influences of nonlocal parameter and the other parameters on the buckling and vibration frequencies are investigated.
37 citations
TL;DR: In this paper, the effects of variable viscosity and thermal conductivity on the natural convection heat transfer over a vertical plate embedded in a porous medium saturated by a nanofluid are investigated.
Abstract: The effects of variable viscosity and thermal conductivity on the natural convection heat transfer over a vertical plate embedded in a porous medium saturated by a nanofluid are investigated. In the nanofluid model, a gradient of nanoparticles concentration because of Brownian motion and thermophoresis forces is taken into account. The nanofluid viscosity and the thermal conductivity are assumed as a function of local nanoparticles volume fraction. The appropriate similarity variables are used to convert the governing partial differential equations into a set of highly coupled nonlinear ordinary differential equations, and then, they numerically solved using the Runge-Kutta-Fehlberg method. The practical range of non- dimensional parameters is discussed. The results show that the range of Lewis number as well as Brownian motion and thermophoresis parameters which were used in previous studies should be reconsidered. The effect of non-dimensional parameters on the boundary layer is examined. The results show that the reduced Nusselt number would increase with increase of viscosity parameter and would decrease with increase of thermal conductivity parameter.
37 citations
TL;DR: In this paper, the peristaltic flow of nanofluids under the effect of slip conditions was theoretically investigated and the exact solutions were successfully obtained and reported for the first time in the present work.
Abstract: The peristaltic flow of nanofluids under the effect of slip conditions was theoretically investigated. The mathematical model was governed by a system of linear and non-linear partial differential equations with prescribed boundary conditions. Then, the exact solutions were successfully obtained and reported for the first time in the present work. These exact solutions were then used for studying the effects of the slip, thermophoresis, Brownian motion parameters and many others on the pressure rise, velocity profiles, temperature distribution, nanoparticle concentration and pressure gradient. In addition, it is proved that the obtained exact solutions are reduced to the literature results in the special cases.In the general case, it was found that on comparing the current solutions with the approximate ones obtained using the homotopy perturbation method in literature, remarkable differences have been detected for behaviour of the pressure rise, velocity profiles, temperature distribution, nanoparticle concentration and finally the pressure gradient. An example of these differences is about effect of the Brownian motion parameter on the velocity profile; where it was shown in this paper that the small values of this parameter have not a significant effect on the velocity, while this situation was completely different in the published work. Many other significant differences have been also discussed. Therefore, these observed differences recommend the necessity of including the convergence issue when applying the homotopy perturbation method or any other series solution method to solve a physical model. In conclusion. The current results may be considered as a base for any future analysis and/or comparisons.
37 citations
TL;DR: In this article, the authors describe the time-dependent flow of an incompressible third grade fluid filling the porous half space over an infinite porous plate, induced due to the motion of the porous plate in its own plane with an arbitrary velocity V(t).
Abstract: This work describes the time-dependent flow of an incompressible third grade fluid filling the porous half space over an infinite porous plate. The flow is induced due to the motion of the porous plate in its own plane with an arbitrary velocity V(t). Translational type symmetries are employed to perform the travelling wave reduction into an ordinary differential equation of the governing nonlinear partial differ- ential equation which arises from the laws of mass and momentum. The reduced ordinary differential equation is solved exactly, for a particular case, as well as by using the homotopy analysis method (HAM). The better solution from the physical point of view is argued to be the HAM solution. The essentials features of the various emerging parameters of the flow problem are presented and discussed.
31 citations
TL;DR: In this article, a hybrid method combining the finite element method with series expansion is applied to solve scattering problems in a subregion enclosing the surface irregularity with a semi-circular auxiliary boundary.
Abstract: The responses to an incident plane SH wave on or near a surface irregularity which is embedded in an elastic half-plane are investigated. The surface irregularity represents a canyon, an alluvial valley or a hill. The wave function expansion method has been employed to solve surface irregularities, such as a semi-cylindrical canyon, a semi-cylindrical alluvial valley, or a semi-elliptical canyon and a semielliptical alluvial valley. These solutions to the scattering problem of SH wave can be used to test the accuracy of the other numerical methods. But solutions for surface irregularities with arbitrarily shapes cannot be found easily. A hybrid method combines the finite element method with series expansion is applied to solve scattering problems in this study. A subregion encloses the surface irregularity with a semi-circular auxiliary boundary can be meshed by the finite element method. By using the transfinite interpolation (TFI) produces excellent grid mesh on the subregion. The advantage of TFI is the flexibility to facilitate modeling of the subregion. On the other hand, the boundary data can be formulated by using a series representation with unknown coefficients. The Lamb’s solution which satisfies the traction free condition and the radiation condition at infinity is implemented to be the basis function. The unknown coefficients can be obtained by satisfying the continuity conditions of the semi-circular auxiliary boundary between the subregion and the half-plane. The hybrid method that combines TFI with series expansion is successfully herein to solve the scattering problem by a surface irregularity. Numerical results in this study for special cases agree well with those in the published literatures. In this study, the steps and skills of hybrid method are described systematically and completely to solve the surface irregularity.
22 citations
TL;DR: Three-wave mutual-checking method is developed, which is based on the conservation of the momentum of the whole system, which provides a checking mechanism, so some human error can be avoided when process the same experiment data.
Abstract: Two-wave methods and Three-wave method are conventional methods to process the SHPB experiment data. Due to the presence of transient waves in dynamic experiments, both the stress and strain fields within a specimen are seldom absolutely uniform. Different date processing methods lead to different results. In this paper, we have developed a program to compare the results getting from different methods. The difference of the strains corresponding to the ultimate stress can reach 20%. Which one is better? One material shouldn't have different constitutive. In order to solve the problem, we have developed Three-wave mutual-checking method, which is based on the conservation of the momentum of the whole system. This method provides a checking mechanism, so some human error can be avoided when process the same experiment data. By this method, different person can obtain the only credible stress-strain curve based on the same test data.
20 citations
TL;DR: In this paper, the nonlinear vibration of microbeams made of functionally graded (FG) materials is investigated under different boundary conditions, including length scale parameters, material gradient index and geometrical parameters.
Abstract: Based on the Timoshenko beam model, the nonlinear vibration of microbeams made of functionally graded (FG) materials is investigated under different boundary conditions. To consider small scale effects, the model is developed based on the most general form of strain gradient elasticity. The nonlinear governing equations and boundary conditions are derived via Hamilton's principle and then discretized using the generalized differential quadrature technique. A pseudo-Galerkin approach is used to reduce the set of discretized governing equations into a time-varying set of ordinary differential equations of Duffing-type. The harmonic balance method in conjunction with the Newton-Raphson method is also applied so as to solve the problem in time domain. The effects of boundary conditions, length scale parameters, material gradient index and geometrical parameters are studied. It is found that the importance of the small length scale is affected by the type of boundary conditions and vibration mode. Also, it is revealed that the classical theory tends to underestimate the vibration amplitude and linear frequency of FG microbeams.
17 citations
TL;DR: In this article, the buckling analysis for a ring-stiffened cylindrical shell consisted of functionally graded material (FGM) subjected to hydrostatic pressure and thermal loads was performed.
Abstract: This paper studies the buckling analysis for a ring-stiffened cylindrical shell consisted of functionally graded material (FGM) subjected to hydrostatic pressure and thermal loads. Material properties of the ring-stiffened FGM cylindrical shell are assumed to be temperature-dependent, and vary smoothly through the thickness direction of the structure according to a volume exponent. Based on the Donnell assumptions, buckling loads of the ring-stiffened FGM cylindrical shell are presented by utilizing the Galerkin method. Numerical results reveal that thermal loads, volume exponent and geometric parameters have significant effects on the buckling behavior of the ring-stiffened cylindrical shell.
15 citations
14 citations
TL;DR: In this paper, a mixed convection stagnation point flow of nanofluids over a stretching/shrinking surface is studied numerically in the presence of thermal radiation and viscous dissipation.
Abstract: In this paper, mixed convection stagnation point flow of nanofluids over a stretching/shrinking surface is studied numerically in the presence of thermal radiation and viscous dissipation. The governing boundary layer equations are transformed into a system of nonlinear ordinary differential equations, by using a similarity transformation, which are then solved numerically using a fifth-order Runge-Kutta-Fehlberg method with shooting technique. The effects of various physical parameters are analyzed and discussed. Computed results are presented in graphical and tabular forms. It is found that the Richardson number, thermal radiation and internal heat generation/absorption have interesting and significant effects on skin-friction and local Nusselt number for all the three types of nanofluids.
14 citations
TL;DR: In this article, the authors considered the MHD free convection and mass transfer boundary layer flow of an incompressible electrically conducting fluid past an accelerated infinite vertical flat plate embedded in porous medium with ramped wall temperature.
Abstract: The unsteady MHD free convection and mass transfer boundary layer flow of an incompressible electrically conducting fluid past an accelerated infinite vertical flat plate embedded in porous medium with ramped wall temperature is considered here. It is assumed that the plate accelerates in its own plane in the presence of thermal radiation incorporating first order chemical reaction. The governing equations are solved analytically using the Laplace transformation technique. The flow phenomenon has been characterized with the help of flow parameters such as permeability parameter, Hartmann number, phenomenon has been characterized with the help of flow parameters such as permeability parameter, Hartmann number, thermal radiation parameter etc. The influences of these parameters on the velocity, temperature field and concentration distribution have been studied and the results are presented graphically and discussed quantitatively. Also, the effects of the various parameters on the skin friction coefficient, the rate of heat and mass transfer at the surface are discussed.
TL;DR: In this paper, analytical simulations of the steel-laminated elastomeric bearing (SLEB) using a three-dimensional (3D) finite element model incorporating material, geometric nonlinearities, and a frictional contact algorithm in LS-DYNA code is conducted.
Abstract: In this paper, analytical simulations of the steel-laminated elastomeric bearing (SLEB) using a three- dimensional (3D) finite element model incorporating material, geometric nonlinearities, and a frictional contact algorithm in LS-DYNA code is conducted. In order to simulate the nonlinear responses of the elastomeric bearing under the compression and shear, a hyperviscoelastic rubber model such as The MAT_77_H (MAT_HYPERVISCOELASTIC_RUBBER) in LS- DYNA code is adopted. Based on the proposed material model for the SLEB, the interaction effects of the SLEB under compression, bending, and torsion are analyzed. Analytical results are compared with the test results of the SLEBs. A set of material parameters is proposed for 3D FEM analysis of SLEBs. The proposed material model demon- strates its accuracy.
TL;DR: In this article, the authors presented the fluid temperature measurement at a 90-degree sharp bend inside a microchannel using molecule-based temperature sensor technique, which provides both detailed and global information for temperature investigation in microfluidic research.
Abstract: This study presents the fluid temperature measurement at a 90-degree sharp bend inside a microchannel using molecule-based temperature sensor technique. This technique provides both detailed and global information for temperature investigation in microfluidic research. Rhodamine B was selected as the molecule-based temperature probe in the experiment to provide non-invasive and straightforward measurements. To resolve the luminescence deviation in the microscale temperature measurements introduced by the corner structure, in-situ calibration method and pixel-by-pixel correction were applied during the data reduction. The temperature measurement was performed in a 200μm wide, 67μm deep and 2cm long PDMS microchannel with a 90-degree sharp bend at the center. The temperature profile was measured at a Reynolds number of 27.66 using Rhodamine B in DI water while the bottom of channel was heated at 50°C. As revealed by the molecule-based temperature sensor, the temperature variation along the central line increased 2°C while passing the corner. Additionally, the lateral temperature distributions upstream of the corner show the temperature increase near the outer side of microchannel and decreased near the inner side. The velocity profiles around the 90-degree sharp bend were acquired to analyze the flow after corner. Secondary flow structure after the corner was observed in the velocity profiles along the depth of the microchannel. This study analyzes the thermal flow fields in the microchannel with a 90-degree sharp bend and reveals that regardless of the low Reynolds number, the flow mixing after the corner resulted in the increase of temperature downstream of the bend.
TL;DR: In this paper, the authors proposed a specific method using ANSYS including the birth and death method and combined with the optimal method (SCGM) to reduce the residual stresses during the CMOS fabrication process.
Abstract: Residual stress in MEMS is of inherent importance in various respects. This study proposes a specific method using ANSYS including the birth and death method and combined with the optimal method (SCGM) to reduce the residual stresses during the CMOS fabrication process. The suitable cooling temperature for decreasing the residual stress is proposed and available. It demonstrates that the suitable parameter on the fabrication can reduce the residual stress in MEMS devices without any extra manufacturing process or external apparatus. The proposed method can expand to simulate the realistic MEMS model effectively.
TL;DR: In this article, the geometry and kinematics of the worm-gear pair were established to derive its meshing properties which have been further verified by the finite element simulation, and the contact area of this worm-german pair was shown to be a point or an ellipse instead of a line.
Abstract: With the increasing use of plastic gears in substitution of conventional steel ones, a plastic involute helical gear has been introduced to engage with a steel involute worm thus forming a novel plastic-steel worm-gear pair. The geometry and kinematics of this kind of worm-gear pair has been established first to derive its meshing properties which have been further verified by the finite element simulation. And it turns out that the contact area of this worm-gear pair is a point or an ellipse instead of a line. Further, a discrete dynamic model has been applied to investigate the dynamic transmission of motion and power of this worm-gear pair through the dynamic mesh force and the driven plastic involute helical gear. And the effects of angular and distance assembling errors have also been included.
TL;DR: In this article, a numerical study has been carried out to analyze the constant heat flux, internal heat generation, variable viscosity and thermal radiation effects on the flow and heat transfer of a Newtonian fluid over an exponentially stretching porous sheet.
Abstract: A numerical study has been carried out to analyze the constant heat flux, internal heat generation, variable viscosity and thermal radiation effects on the flow and heat transfer of a Newtonian fluid over an exponentially stretching porous sheet. Using a similarity transformation, the governing partial differential equations are transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by using an efficient Chebyshev spectral method. The effects of various physical parameters such as viscosity parameter, the suction parameter, the radiation parameter, internal heat generation or absorption parameter and the Prandtl number on velocity and temperature are discussed by using graphical approach. Moreover, numerical results indicate that in the presence of constant heat flux, the skin-friction coefficient as well as Nusselt number is strongly affected by the viscosity parameter, suction parameter, radiation parameter and the internal heat generation parameter.
TL;DR: In this paper, a numerical investigation has been conducted to study the unsteady oscillatory flow of a viscous fluid induced by a swirling disk, where the disk stretches radially with the time-based sinusoidal os-cillations.
Abstract: In this work a numerical investigation has been conducted to study the unsteady oscillatory flow of a viscous fluid induced by a swirling disk. The disk stretches radially with the time-based sinusoidal os-cillations. The governing equations for the three-dimensional boundary layer-flow are normalized using a suitable set of similarity transformations. The normalized partial differential equations are then solved numerically using a finite difference scheme by altering the semi-infinite domain to a finite domain. The effects of various imperative parameters on the oscillatory flow are discussed with graphs and tables. Keywords: Oscillatory flow, Viscous fluid, Rotating disk, Numerical solution. 1. INTRODUCTION The behavior of boundary-layer flows over the ro-tating and stretching surfaces is one of the interesting topics to be studied as it has great practical importance in engineering and industrial processes. Such type of flow phenomena occur in fuel and aerodynamic indus-tries, biomechanics, extrusion and condensation pro-cesses, thermal-power generating systems, gas turbines, medical equipment,
TL;DR: In this article, the deformation of a plastic package due to moisture absorption first, then hygro-thermo-mechanical stress of the plastic package and its evolution during a period of three months were investigated with finite element method, user development was performed for this investigation.
Abstract: Plastic packaging materials tend to absorb moisture from ambient environment and get swollen, this may raise hygro-stress in plastic electronic package and redistribute the internal stress. In this paper, we reviewed the dramatic deformation of a plastic package (Flip Chip Plastic Ball Grid Array-FCPBGA) due to moisture absorption first, then hygro-thermo-mechanical stress of the plastic package and its evolution during a period of three months were investigated with finite element method, user development was performed for this investigation. The finite element model was verified with hygro-thermal deformation of the FCPBGA measured with a 3-D moire interferometry system. Following findings were obtained: A. Thermal stress field was changed a lot due to moisture absorption; B. Thermal stress of chip was released to some extent, but peal stress up to 62.2MPa occurred to the solder bump, thus the danger of Under Bump Metal (UBM) opening increased.
TL;DR: In this article, the nonlinear characteristics of a simply-supported three-layer circular piezoelectric plate-like power harvester near resonance were examined, where the energy-scavenging structure consists of two properly poled piezoceramic layers separated by a central metallic layer.
Abstract: The nonlinear characteristics of a simply-supported three-layer circular piezoelectric plate-like power harvester near resonance are examined in the paper, where the energy-scavenging structure consists of two properly poled piezoceramic layers separated by a central metallic layer. The structure is subjected to a uniform harmonic pressure on the upper surface. Nonlinear effects of large deflection near resonance to induce the incidental in-plane extension are considered. Results on output powers are presented, which exhibit multi-valuedness and jump phenomena.
TL;DR: In this paper, a dynamic formulation of the boundary element method for stress and failure criterion analyses of anisotropic thin plates is presented, where elastostatic fundamental solutions are used in the formulations and inertia terms are treated as body forces.
Abstract: This paper presents a dynamic formulation of the boundary element method for stress and failure criterion analyses of anisotropic thin plates. The elastostatic fundamental solutions are used in the formulations and inertia terms are treated as body forces. The radial integration method (RIM) is used to obtain a boundary element formulationithout any domain integral for general anisotropic plate problems. In the RIM, the augmented thin plate spline is used as the approximation function. A formulation for transient analysis is implemented. The time integration is carried out using the Houbolt method. Integral equations for the second derivatives of deflection are developed and all derivatives of fundamental solutions are computed analytically. Only the boundary is discretized in the formulation. Numerical results show good agreement with results available in literature as well as finite element results.
TL;DR: In this paper, the effect of vaned diffuser on the performance of an auto-motive turbo charger has been analyzed using a numerical simulation that was made in the three-dimensional flow carried out in a modified centrifugal compressor.
Abstract: This paper is a numerical simulation that was made in the three-dimensional flow, carried out in a modified centrifugal compressor, having vaned diffuser stage, used as an auto-motive turbo charger. Moreover, the performance of the centrifugal compressor was dependent on the proper matching between compressor impeller and vaned diffuser, influencing significantly surge and the efficiency of centrifugal compressor stages. In addition, a modified compressor impeller, coupled with vane and vaneless diffuser, has been found to have similar internal flow patterns for both the vaneless and vaned diffuser design. The vaned diffuser effect has been paid particular attention in terms of better analysis where the diffuser was designed for high sub-sonic inlet conditions. Another aim of this research was to study and simulate the effect of vaned diffuser on the performance of a centrifugal compressor. The simulation was undertaken by using a commercial software, the so-called ANSYS CFX, to predict numerically the performance in terms of pressure ratio, poly tropic efficiency and mass flow rate for the centrifugal compressor stage. The results were generated from CFD and were analyzed for better understanding of the fluid flow through centrifugal compressor stage. Conclusively, it was observed that the effect of the vaned diffuser is to convert the kinetic energy into a high static pressure after analyzing the results of the simulation.
TL;DR: An axisymmetric layerwise finite element formulation for dynamic analysis of laminated structures with embedded viscoelastic material whose constitutive behavior is represented by the Prony-generalized Maxwell series is presented.
Abstract: This paper presents an axisymmetric layerwise finite element formulation for dynamic analysis of laminated structures with embedded viscoelastic material whose constitutive behavior is represented by the Prony-generalized Maxwell series. To account the time dependence of the constitutive relations of linear viscoelastic materials, the incremental formulation in the temporal domain is used. Layerwise finite element has been shown to provide an efficient and accurate tool for the simulation of laminated structure. Most of the previous work on numerical simulation of laminated structures has been limited to elastic material behavior. Thus, the current work focuses on layerwise finite element analysis of laminated structures with embedded viscoelastic material. A computer code based on the presented formulation has been developed to provide the numerical results. The present approach is verified by studying its convergence behavior and comparing the numerical results with those obtained using the ABAQUS software. Finally, and as an application of the presented formulation, the effects of load duration on the dynamic structural responses of multilayered pavements are studied.
TL;DR: In this paper, the authors investigated the adsorption-induced surface stress of self-assembled alkanethiolate monolayers on a Au(111) surface as a function of the alkyl chain length.
Abstract: First-principles calculations were employed to investigate the adsorption-induced surface stress of self-assembled alkanethiolate monolayers on a Au(111) surface as a function of the alkyl chain length. A recently developed fully nonlocal van der Waals density functional was used to accurately account for the chain-chain interactions. We found that surface charge redistribution produces compressive surface stress, while chain-chain interactions produce tensile surface stress. The stress induced by surface charge redistribution is about one order of magnitude greater than that of chain-chain interactions. We observed that the chain-chain interactions play an important role in determining the molecular configuration during adsorptions, and also contribute significantly to the induced anisotropic tensile (positive) surface stress. As the chain length increases the tensile stress increases at a rate of ∼ 0.32 (∼ 0.18) N/m for the direction perpendicular (parallel) to the chain tilt direction.
TL;DR: The accuracy and robustness of the utilized LB models are improved for inviscid compressible flows by implementation of the numerical filters on primitive variables by demonstrating that the proposed complementary scheme is practical.
Abstract: The stability of the lattice Boltzmann model (LBM) is a challenging problem in the simulation of compressible flows with different types of embedded discontinuities. This study, proposes a complementary scheme for simulation of inviscid compressible flows by the lattice Boltzmann models using the numerical filters to improve the stability. The advantages and disadvantages of the implementation of numerical filters on the primitive and conservative variables, in addition to, mesoscopic and macroscopic variables are investigated. Moreover, a shock-detecting sensor, which activates a second-order linear filter near the discontinuities and a higher-order linear filter in smooth regions, is described and assessed. This study demonstrates that the proposed complementary scheme is practical. Also the accuracy and robustness of the utilized LB models are improved for inviscid compressible flows by implementation of the numerical filters on primitive variables. The validity of the procedure to capture shocks and to resolve contact discontinuity and rarefaction waves in well-known benchmarks is investigated and good agreements are obtained for all test cases.
TL;DR: In this article, a numerical study is carried out to investigate the mixed convection flow and heat transfer in a parallel-plate channel with an anisotropic permeable porous medium, where the principal axis of the porous medium is orientated in a direction which is oblique to the gravity vector.
Abstract: In this paper, a numerical study is carried out to investigate the mixed convection flow and heat transfer in a parallel-plate channel with an anisotropic permeable porous medium. The principal axis of the porous medium is orientated in a direction which is oblique to the gravity vector. Both clear (Newtonian) fluid dissipation and Darcy viscous dissipation are considered in the heat transport equation. In this model, the temperature dependent fluid properties are considered and their influence on the flow and heat transfer characteristics is brought out. The governing non-linear equations (in non-dimensional form) are solved numerically by a second order finite difference scheme. The directional permeability ratio A1 is defined to combine the effects of the permeability ratio parameter K* = (K1 / K2) and the orientation angle Φ1. The effects of the anisotropic permeability ratio, the orientation angle of the principal axis, and the temperature dependent variable properties on the mixed convection flow and heat transfer are investigated. It is demonstrated that both the anisotropic permeability of the porous medium and the variable transport properties have strong effects on the flow and heat transfer characteristics.
TL;DR: In this article, a study of steady hydromagnetic fluid flow with heat and mass transfer over an inclined nonlinear shrinking porous sheet in the presence of thermophoresis and heat generation is presented.
Abstract: The paper is devoted to a study of steady hydromagnetic fluid flow with heat and mass transfer over an inclined nonlinear shrinking porous sheet in the presence of thermophoresis and heat generation. The problem is formulated as a non-linear boundary value problem. A numerical method is developed to solve the problem. The surface velocity of the shrinking sheet and the applied transverse magnetic field are considered as power functions of the distance from the origin. The viscosity and thermal conductivity of the fluid are considered temperature-dependent. The viscosity is taken to be an inverse function of temperature, while the thermal conductivity is supposed to vary linearly with temperature. By using suitable transformation, the equations governing the flow, temperature and concentration fields are reduced to a system of coupled non-linear ordinary differential equations, which are solved numerically by developing an appropriate numerical method. Velocity, temperature and concentration profiles as well as the skin-friction coefficient and wall heat transfer are studied with particular emphasis. Their variations with different parameters are investigated. The computed numerical results are presented graphically.
TL;DR: In this paper, the effect of the surface inclination on the hydrodynamics and heat transfer of droplets impinging on very hot surfaces is studied, based on the accurate calculation of the vaporization rate in the simulation process using a combination of the level set and ghost fluid methods.
Abstract: In this research, the effect of the surface inclination on the hydrodynamics and heat transfer of droplets impinging on very hot surfaces is studied. The applied numerical algorithm is based on the accurate calculation of the vaporization rate in the simulation process using a combination of the level set and ghost fluid methods. Also a mesh clustering technique is utilized to create sufficient mesh resolution near the surface in order to take into account the effect of the thin vapor layer between droplet and very hot surface. The results are verified against available experiments. The effect of the surface inclination on the droplet maximum spreading radius, droplet contact time and total heat removal from the surface is considered. Results show that for the studied regime, the maximum spreading radius of the droplet is decreased with an increase in the surface inclination while the droplet contact time on the surface is independent from the surface inclination. For inclinations greater than 45°, the total heat removal is decreased considerably with an increase in the inclination angle. For smaller inclinations, the dependency of the total heat removal on the surface inclination is not strong.
TL;DR: In this paper, the torsional instability of an elastic structure due to hydrodynamic loads into the water current was studied, and the results confirmed that the structure becomes dynamically unstable due to the hydrodynamynamic moment applied on it beyond the critical velocity.
Abstract: The present work studies the torsional instability of an elastic structure due to hydrodynamic loads into the water current. The structure applied here is a rectangular flat plate with an elastic axis in its mid-chord length. The elasticity in the structure is provided by torsion spring. The flat plate has only one degree of freedom which is rotation in pure yaw about its axis. Through the free vibration experiments, it is observed that as the current speed exceeds a critical velocity, the flat plate becomes unstable. Two different chord lengths are tested and the instability occurs for a chord base range of Reynolds number, 0.75 × 105 < Rec < 1.5 × 105. As a result of the instability, the flat plate begins to yaw about the elastic axis. The hydrodynamic moment acting on the flat plate is modeled by means of the flutter derivatives. As an identification technique to extract flutter derivatives, a curve fitting scheme called General Least-Square (GLS) theory is applied on the results of the free vibration experiments. The results confirm that the structure becomes dynamically unstable due to the hydrodynamic moment applied on it beyond the critical velocity. The super-critical Hopf bifurcation is also discussed in the light of the analysis.