نشریه مهندسی مکانیک مدرس
سال دهم شماره 4 (زمستان 1389)

Vehicles are subject to random road excitations due to road unevenness and variable velocity which causes ride discomfort and fatigue. Ride comfort could be improved by decreasing vehicle accelerations. In this paper, to evaluate the vehicle ride comfort, root mean square acceleration response (RMSAR) is calculated using power spectral density (PSD) of road excitations and these quantities are compared with the ISO2631 boundary values. Then by considering ISO2631, the vehicle’s RMSAR is minimized by optimal design of vehicle suspension viscous damping and stiffness parameters. To solve this nonlinear constrained optimization problem, we utilize genetic algorithms. Also, in the design process the physical restrictions are included. Obtained results demonstrate a considerable improvement of vehicle ride comfort and its dynamic response as a result of reduced accelerations. Comparing the obtained results with those obtained by method of nonlinear programming confirms the supremacy of genetic algorithms.

In this paper, an analytical formulation of FGM axisymmetric thick-walled cylinders, based on the first shear deformation theory (FSDT) is presented. The displacements and maximum stress in thick cylindrical shells are calculated. Solutions are obtained under generalized plane strain assumptions. It is assumed that the material is isotropic and heterogeneous with constant Poissn's ratio and radially varying elastic modulu. The results have been compared with findings of the plane elasticity theory (PET).

In this paper, first, a number of emerging technologies for rapid manufacturing of components are introduced and their application in manufacturing aeronautical structural components is discussed. Then, a novel method for generation of sectional contour curves directly from the cloud point data is presented. The proposed method computes contour curves for rapid prototyping model generation through adaptive slicing, data points reducing and B-spline curve fitting. The Proposed procedure was programmed in MATLAB software package to perform all computational effort in a single software system. The method has been applied to a wing-fuselage connector component of an existing fighter aircraft to create its layered model for rapid manufacturing. 3D comparison of the developed model and the digitized cloud point data reveals that 95% of the data points have a maximum deviation of 0.5 mm, which is a reasonable accuracy compared to the component size. The simplicity and effectiveness of the proposed method, as demonestarted by our experiments, confirms that the algorithm can be practically used for rapid prototype manufaturing of aeronautical structural components with an adequate accuracy.

Considering the diverse climates of Iran, the need for architectural design according to climate zones is obvious. Especially in critical thermal conditions this need will be more important and becomes the architect’s most important challenge. Cold climate is one of the important climates which deserve special design. In cold climate, summer is very short and environmental temperature is often below the comfort range, so the most important issue is heating. Since in most of the time we require to increase the temperature up to the comfort range. This article aims to provide solutions for critical climate conditions. So Tabriz with a dry and cold climate was selected and its thermal analysis was done. Through this analysis we find out when there is heating problems and we can design solutions based on these findings. This information will help us to design the selected site conditions.

In this study thermal properties of Woofd Plastic Composite (WPC) were measured using Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG). The investigated specimens were: high density polyethylene (HDPE), wood particle and WPC. DSC test showed that adding wood particle to HDPE matrix cause a decrease in the area under the DSC curve. The result revealed that WPC have a heat of fusion less than unfilled HDPE and are more stable when temperature increases. The melting point temperature did not changed significantly. The heat of capacity of HDPE, wood particle and WPC were obtained using DSC test. An enhancement in the temperature led to a linear increase in the heat of capacity of wood particle. HDPE and WPC showed similar behavior too. But WPC specimen had a heat of capacity more than wood particle and less than HDPE. The heat capacity of WPC by rule of mixture has a good agreement to experimental results. Adding wood to plastic identify higher WPC thermal stability by TG. The extrusion process was modeled and the throughput temperature was calculated using themal equation. The model was used to carry out high throughput by incresing screw speed. These help to produce defectless extruded WPC in continous production.

Urine production and excretion has been one of the intricate problems investigated in the field of biomechanics. However, the mechanism that transports urine from the kidney into the bladder has not been fully understood. Realization of peristalsis in the ureter may be helpful in better understanding of function and abnormalities of this organ of the urinary system and also aid in the design of flow aided devices such as valves and stents to remove these abnormalities. In this paper, urine isolated bolus transportation in the ureter was simulated using ureteral anatomical data during peristalsis. Urine pressure distribution in the ureter, shear stress of ureteral inner wall, bolus dynamic deformations during its propagation and the effect of pressure difference between the kidney and the bladder on the quantity of reflux and efficiency of urine transportation as a result of peristalsis, were investigated. A computational model was presented that used the tools of computational fluid dynamics, Arbitrary Lagrangian-Eulerian formulation, incompressible Navier-Stokes equations and adaptive mesh algorithm in the fluid domain. In the structure domain, it utilized Arruda-Boyce non-linear model and contact condition. The major benefits of this model comparing to previous studies were that the ureteral wall displacements were not pre-determined during peristalsis and luminal pressure variations influenced on it. Finite element equations of fluid and structure were solved using fluid-structure interaction method (FSI) and direct coupling. Results of this research showed that the proximal portions of ureter were under higher magnitudes of shear stress. Moreover, increase of the bladder pressure magnified the quantity of ureteropelvic reflux in the case of dysfunction of ureteropelvic junction, and resulted in a higher peristaltic efficiency transporting ureteral bolus into the bladder.

In this paper, an optimal trajectory planning method is presented for robot manipulators with multiple degrees of freedom in 3D space using a new analytical technique for collision avoidance in the presence of ellipsoidal obstacles. To generate the robot’s trajectory, a genetic algorithm with a fuzzy mutation rate is introduced to have a quick access to optimal solutions in a complex workspace. A cubic spline interpolation polynomial is applied to approximate trajectories in the joint space. In order to optimize the objective function, the genetic algorithm determines a number of interior points for curve fitting using interpolation polynomials. The performance of the proposed technique is demonstrated by simulations.