Scientia Iranica
Volume:26 Issue: 1, Jan-Feb 2019

In the current paper, numerical simulations of Fluid structure interaction (FSI) of a SP (Surface Piercing) hydrofoil are conducted in order to study the influence of elasticity on the initial water entry ventilation. Using ANSYS multi physics solvers, two-way FSI analyses are conducted by the implicit coupled URANS (Unsteady Reynolds averaged Navier–Stokes) equations and finite element method. Numerical result is validated by the well known rigid and elastic wedge water entry problems. Subsequently, computational results are presented for different velocity ratios range [0.38, 0.64] and elasticity factor range [0, 4]. Similar to the Surface Piercing Propeller (SPP), performance curves of a wedge water entry are defined. The obtained similar trend of propeller and wedge performance curves in fully ventilated, transition, and partially cavitated operation modes shows that the adopted approach (2D-study) can be appropriate for future related studies. FSI simulation results indicate that structural deformation can highly affect the location of transition point and shifts it toward the fully ventilated part at high Froude number and elasticity factor. The overall efficiency loss due to increase of foil elasticity is observed and overshoot time of the foil deformation related to the variation of Froude number and elasticity factor, is evaluated.

Based on optimal Latin hypercube design for computer experiments, blind Kriging surrogate model and sequential quadratic programming method, the optimal design of the aerodynamic configuration of a 30mm tubular projectile is carried out with the use of commercial softwares, such as UG, ICEM CFD, FLUENT etc. The aerodynamic configuration has been optimized to minimize the drag coefficients at different Mach numbers and maximize the kinetic energies at given flight ranges. The optimal configuration is obtained and discussed. Finally, the similarities and differences of the flow structure and aerodynamic characteristics between the original and optimal tubular projectiles are compared. The numerical optimal method proposed in this paper for optimizing the tubular projectile can provide important guidances for the aerodynamic configuration design of projectiles.

This investigation presents the characteristics of Cattaneo-Christov heat flux model for the boundary layer flow of Burgers’ fluid model. Instead of simple Fourier’s law of heat conduction, we presented the Cattaneo-Christov model to analyze the thermal relaxation properties when the heat source/sink is present in the system. Mathematical modeling the laws of momentum and energy are presented under the order analysis approach. It is revealed that the term “” is for the hydro-magnetic rheology of the Newtonian model whereas the generalized magnetic field term (as mentioned in Eq. 2) is for the Burgers’ model which is incorporated in the current analysis. Suitable transformations are utilized for the conversion of partial differential system into coupled nonlinear set of ordinary differential equations which are tackled analytically through homotopy analysis technique. The plots of various physical quantities are presented showing the dynamics of the considered analysis. Streamlines for Burgers’ and Newtonian model are presented which show a difference of rheology. Numerical values for skin friction and surface heat transfer rate are presented in the form of tables.

The Clean room is a controlled space and is used in various industries such as electronics, medical and military industries. One of the most important tests to evaluate the performance of the cleanroom is recovery test. Recovery test determines the time period during which a clean room returns to its designated cleanliness level after an instant or a period of deliberate or unintentional contamination. In this paper, a thorough investigation of recovery period has been implemented. In this study, air change rate and its pattern were studied using the Eulerian and Lagrangian approaches and LES, DES and k-ω SST turbulent models. Simulation results were evaluated against control volume analysis. Parameters such as the air change rate, the number of particles, and pressure and energy consumption in various radial and tangential angles of diffusers were studied Results showed that radial angle had little positive and occasionally negative effect on recovery period. On the contrary, tangential angle improved decontamination rate, at maximum performance (β=45°), it could reduce recovery period as much as 25% which in turn reduces energy consumption. In addition the DES model provides the best and most coinciding answers between all turbulence models.

A novel spatial parallel manipulator designed to assemble diagnostic instruments in SG-III is introduced in this paper. Firstly, resorting to screw theory, mobility analysis of this manipulator is investigated. Then the inverse kinematics problem is determined by the method of RPY transformation, with the singularity analyzed. As a key issue in parallel manipulators, it is more difficult to solve the forward kinematics problem, since it is highly nonlinear and coupled. In this work, three different approaches are presented to deal with this issue, which include the back propagation neural network, the simplified ant colony optimization and the proposed improved Newton iterative method. Simulation of each approach is conducted, and their merits and demerits are compared in detail. It is concluded that the improved Newton iterative method which can provide good initial iteration values possesses the best performance to estimate the nonlinear forward kinematic mapping of the considered parallel manipulator

Use of spike on a hemispherical body changes the flow field and hence the aerodynamic drag. Computational studies have been made to obtain the flow field around a hemispherical body with spikes at a hypersonic Mach number of 6. The effect of shape of spike tip and length has been studied. Laminar computations have been made adopting structured grid using commercial software Fluent. It is observed that use of a sharp spike itself reduces the drag signicantly. However the use of a hemispherical head spike further reduces the drag. Contribution of dierent components towards drag indicate that the increase in length of a spike do not change the spike contribution. However the flow field on main body is altered which leads to reduction in drag with change in length. Estimated maximum drag obtained is found to be highest in comparison to any reported drag value in literatures with any spike shape and length.

Variations in loadings of rolling contact components lead to a change in contact forces between surfaces. These forces are the main cause of rolling contact damages such as fatigue. Residual stresses are a major issue in railway wheel structures and it is appropriate to reduce such stresses. The aim of this paper is to estimate residual stresses in railway wheel due to hub to rim and axle to hub fitting process. a nonlinear three-dimensional model of stress is applied for analyzing stress field during press fitting process. An elastic-plastic finite element model is developed to model variable thermal loading in railway wheel. Finally, results of three dimensional finite element analysis showed a good agreement to field observations.

With an ability to mimic the human behaviour, humanoid robots have become a topic of major interest among research fellows dealing with robotic investigation. The current work is focussed on the design of a novel navigational controller based on the logic of the regression analysis to be used in the path planning and navigation of humanoid robots. In the current investigation, static and dynamic path planning of humanoid NAOs are encountered. The static path planning represents a single NAO navigating through random static obstacles. The dynamic path planning represents multiple humanoid NAOs navigating through random static obstacles and acting as dynamic obstacles for each other. A Petri-Net controller is designed to avoid the collision among the multiple NAOs in dynamic path planning. To reduce the path length and time travel and to provide the shortest possible path, an advanced regression controller is implemented in the NAOs in both simulation and experimental environments. Finally, a comparison has been performed between the simulation and experimental results, and a good agreement is observed between both the results with a minimal percentage of error. The proposed navigational controller is also tested against other existing navigational technologies to validate better efficiency.

Machining of ceramics often involves many challenges due to their high hardness, brittleness, and low thermal conductivity. Laser assisted machining (LAM) is a promising technology for improving the machinability of hard-to-cut materials. In this work, the effect of laser heating in the LAM process on slip cast fused silica (SCFS) ceramics is investigated by presenting a numerical thermal analysis of laser effects on material behavior. A transient three-dimensional heat transfer analysis for laser assisted turning (LAT) of SCFS is performed using finite element method. Temperature distributions in SCFS cylindrical specimens are obtained. Moreover, the influence of laser parameters such as power, translational speed, and feed rate on the temperature field are studied. To increase the absorptivity of the ceramic surface, a coating is applied, and the absorptivity of the coated surface is determined by carrying out a series of experiments. Experiments are performed to validate the numerical transient heat transfer finite element model. In addition, the effects of spot overlapping of pulsed laser on temperature distribution and absorptivity of SCFS workpiece are studied. It is for the first time that effect of laser beam overlapping on low frequency pulsed laser heating in LAT is formulated and completely investigated.

One of the important functionality of liver cells is ammonia detoxification and urea production. In this study, a numerical model of urea cycle in hepatocytes have been developed. Navier Stokes along with convection equations have been employed to study the process of ammonia elimination and urea production using a microfluidic channel.The concentration of urea and ammonia throughout the channel were obtained. Furthermore, the urea cycle was modeled regarding its four main enzymes. This resulted in twelve rate equations which were solved to determine the concentration of each metabolites participating in the urea cycle. Application of results were implied to common disorders such as Hyperammonemia type I and II and argininosuccinicaciduria type I and II. Result of this study indicated that there is 80% of reduction in concentration of Citrulline, Argininosuccinate, Arginin, Carbamoyl phosphate, Phosphate and Fumarate in hyperammonemia type II. A 10 fold increase of Argininosuccinate concentration was observed in both argininosuccinicaciduria I and II. The predicted result may be useful in better understanding and control of metabolite deficiencies in patient abnormalities.

In the present study, the effective parameters of centrifugal pumps are investigated using the EFAST Sensitivity Analysis (SA) method. The SA is performed using GMDH type artificial neural networks (ANN) which are based on validated numerical data of flow field in centrifugal pumps. There are four design variables namely: leading edge angle of blades on hub section (β1 Hub), leading edge angle of blades on shroud section (β1 Shroud), trailing edge angle of blades (β2), and the stagger angle of blades on mid span (γ mid) and there are two objective functions namely: efficiency (h) and the required NPSH of impeller. The results show that among design variables, β2 has the highest effect on variations of h (46%) and NPSH (45%). Except β2, β1 Hub and γ mid has the highest effect on NPSH (33%) and h (28%) respectively. The effects of all of the design variables on objective functions are shown in the results.

In this paper, the general analysis of two-dimensional steady-state thermal and mechanical stresses for a hollow thick cylinder made of functionally graded piezoelectric materials (2D-FGPMs) is developed.The general form of thermal ,mechanical and electrical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations, using the complex Fourier series and the power law functions method.The material properties are assumed to depend on the radial and circumferential variables and are expressed as power law functions along the radial and circumferential direction.

In this investigation repetitive upsetting-extrusion (RUE) process was used to investigate the effect of severe plastic deformation on the microstructural changes and flow behavior of commercial pure copper. Initial material together with two passes, four passes and eight passes of RUE in annealed and non-annealed condition were studied. Results show that grain refinement, in the scale of nano meter, has mostly been achieved only after two passes of RUE which is essentially a combination of one upsetting and one extrusion path. Increasing the number of passes after four passes of RUE did not have discernible effect on the grain refinement. Such a behavior is explained to be due to saturation of dislocations and the formation of high angle grain boundaries after only two passes of RUE. The grains after eight passes of RUE process even became slightly larger than the two and the four passes of RUE. This was related to restoration phenomena occurring during high number of passes of RUE. Flow strength of the material after different passes substantially increased, though the rate at which the flow stress increased declined by increasing the number of passes. ETMB model were used to explain the deformation behavior of the RUE samples.