Iranian Journal of Science and Technology Transactions of Mechanical Engineering
Volume:37 Issue: 1, 2013

The ability of mesh design in arbitrary Lagrangian-Eulerian finite element method (ALE-FEM) makes it a generally efficient device for simulating engineering problems. In this paper, ALE-FEM is used to model the static deflection and instability of beam-type cantilever nano-actuators using plain element. Effects of electrostatic fields are taken into account through first-order fringing field corrected model. In addition, the influence of quantum vacuum fluctuations is considered via attractive Casimir and van der Waals force depending on the range of application. The instability parameters, i.e. pull-in voltage and deflection of the nano-actuator are computed. The obtained results are compared with those reported in literature using numerical method as well as Lagrangian FEM. The findings indicate that ALE method can be used as a powerful technique for modeling beam type nano-actuator.

Natural convection of an electrically conducting fluid under the different directions of magnetic field in a horizontal cylindrical annulus is numerically studied using lattice Boltzmann method (LBM). The inner and outer cylinders are maintained at uniform temperatures. Detailed numerical results of heat transfer rate, temperature and velocity fields have been presented for salt water with Pr=13.2, Ra=105 to 106 and Ha=0 to 100 for three directions of magnetic field. The computational results reveal that in horizontal cylindrical annulus the flow and heat transfer are suppressed more effectively by direction and intensity of magnetic field. It is also found that the flow oscillations can be suppressed effectively by imposing an external horizontal magnetic field. The average Nusselt number increases with rise in radius ratio but decreases with the Hartmann number. Furthermore, it can be observed that there is a good agreement between the present result and those predicted by available benchmark solutions under the limiting conditions.

This research paper provides a mathematical modeling of heat transfer enhancement during melting process in a square cavity through dispersion of nanoparticles. The enthalpy-based lattice Boltzmann method (LBM) with a combination of D2Q9 and D2Q5 lattice models is used to solve density, velocity and temperature fields. The nano-enhanced phase change material (NEPCM) is composed of a dilute suspension of copper particles in water (ice) and is melted from the left. Also, in this study the sub-cooling case is neglected. Conduction heat transfer has been taken into account in the solid phase as well as natural convection in the liquid phase. Numerical simulations are performed for various volume fractions of nanoparticles and Rayleigh numbers ranging from 104 to 106. The validation of results is carried out by comparing the present results of natural convection and convection-dominated melting in a square cavity with those of existing earlier numerical studies. Predicated results illustrate that by suspending the nanoparticles in the fluid the thermal conductivity of NEPCM is increased in comparison with PCM. Also, by enhancing thermal conductivity and decreasing latent heat of fusion higher rates of heat release can be obtained.

Heat transfer augmentation and pressure loss penalty caused by vortex generators (VGs) are numerically studied for finned flat/round tube heat exchangers and compared with available experimental results. The simulations are performed with the steady three-dimensional incompressible conditions and a RNG K-ε turbulence model is used. The Reynolds numbers based on the bulk velocity and the height of channel are selected from 600 to 4050. To compare the effectiveness of VGs on the round and flat tubes for tube-fin heat exchangers, two different configurations are investigated with two and four delta winglet vortex generators for each tube. The streamlines, vorticity, the averaged Nusselt number, the friction factor and the performance factor (JF) are provided to evaluate the effectiveness of VGs for the heat exchangers employed. It is found that the flat tube with VGs provides better thermal performance than the round one, especially at the lower Reynolds numbers.

This paper presents a solution to the boundary stabilization of a vibrating composite plate under fluid loading. The fluid is considered to be compressible, barotropic and inviscid. A linear control law is constructed to suppress the composite plate vibration. The control forces and moments consist of feedbacks of the velocity and normal derivative of the velocity at the boundaries of the composite plate. The novel features of the proposed method are that (1) it asymptotically stabilizes vibrations of a composite plate in contact with fluid (the fluid has a free surface) via boundary control and without truncation of the model; and (2) the stabilization of both the composite plate vibrations and fluid motion are simultaneously achieved by using only a linear feedback from the composite plate boundaries.

In this study, an experimental and numerical analysis is done to study the flow characteristics of an offset and non-offset axisymmetric jet impingement on a circular cylinder. The purpose of this study is investigation of the behavior of the cutting gas jets and finding the optimum distance between nozzle and cylinder to achieve maximum cutting performance. Finite volume approach is used to solve the governing equations for a turbulent, incompressible jet numerically. According to the literature the suitable turbulence model for this purpose is realizable k-ε. Velocity and pressure fields around the cylinder and pressure and shear stress distribution on the cylinder surface are determined for various cases. Also, some experiments are done to validate repeatability of experiments and numerical results. Comparisons between numerical results and experimental measurements validate the accuracy of numerical results. Also, results show that if the horizontal distance between the nozzle outlet and the stagnation point of cylinder is 2.5D, the shear stress on the cylinder surface has maximum value. Therefore in this situation jet has a maximum performance in cutting procedure.

In the current work, two-dimensional simulations are presented for incompressible laminar mixed convection flow of a radiating gas over a recess including two backward and forward facing steps in a vertical duct. The continuity, momentum and energy equations for fluid flow are solved by the computational fluid dynamic (CFD) techniques. The fluid is treated as a gray, absorbing, emitting and scattering medium. For computation of the radiative term in the energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM). The effects of Grashof number, radiation-conduction parameter and ptical thickness on heat transfer behavior of the system are studied.

A CVT push-belt, composed of 12 layers of bands and a number of segments, is modeled for vibration analysis. Predefined compression and tension loads are applied to segments and bands respectively. Continuous and discrete beams composed of segments are used to investigate contact properties between segments. Three models of band contacts have been established based on complexity and various modeling approaches in ABAQUS. Contacts between bands are modeled by a frictionless contact between shell elements tied together in the first model and in the second model. To improve the accuracy, a composite shell with special interface layers is utilized as third model. By using the segment models, it has been concluded that a group of segments can be considered as a continuous beam at high compression loads and as individual rigid masses in low compression loads. The results of composite shell model show better prediction of the vibration properties of bands pack model. Separate cases of loading are considered for tension and compression spans.