علی عبداللهی فر

The bottom of floats and flying boat should be strong against impact loads such as low velocity impact despite being light weight. In this article, we will investigate the dynamic behavior of the structure of meta-sandwich panels with different cores under low velocity impact loading using analytical and numerical methods. Four different core samples including honeycomb, auxetic, square and triangular made of polylactic acid under impact, a hemispherical steel projectile with a radius of 15 mm with fixed boundary conditions have been investigated. The interaction between the impactor and the meta-sandwich panel has been modeled using a two-degree-of-freedom mass and spring system using finite element software such as ANSYS Workbench. The maximum impact contact force is also analytically and numerically compared with each other and the results show a good match between these two methods. Considering the importance of the effective parameters in the dynamic response of the sandwich panel structure, the effect of some parameters, including the velocity and mass of the impactor, on the maximum contact force, the maximum displacement and the maximum Von Mises stress were numerically investigated and evaluated. The results show that impactor velocity effects are a more important factor in increasing and decreasing contact force, displacement, Von Mises stress and impact time compared to impactor mass. In the end, by comparing the different cores presented in this article, the auxetic core is introduced as the best core among other cores.

The main goal of this research is to study of interaction between the propulsion system and the WIG Craft main parts. Therefore, the effects of some parameters such as the propeller rotation direction and the propulsion system location on the aerodynamic quality of the WIG craft have been studied deeply. Using ANSYS-CFX Software, The SIMPLE algorithm has been utilized to consider the pressure-velocity coupling, additionally the k-ω SST model has been applied as a turbulence model to take the account of the flow separation. The numerical approach is verified by comparing its results with experimental data of a three-blade aerial propeller. These comparisons indicated that there was a good agreement between present numerical results and experimental ones. The results revealed that the propeller rotation direction has no significant effect on the aerodynamic quality of the WIG craft and at α=3o, the highest aerodynamic quality is achieved. Moreover, as the propulsion system approached closer to the WIG craft center line, the drag and lift forces on the horizontal tail are respectively enhanced and decreased, subsequently in this situation the longitudinal stability of the vehicle is decreased; whereas by changing the vertical position of the propulsion system, the drag and lift forces on the horizontal tail are correspondingly reduced and increased, Thus the longitudinal stability of the WIG craft is increased.

In this paper, at fist two-degree-of-freedom quarter-vehicle model and four-degree-of-freedom half-vehicle model of two vehicles with passive suspension systems and linear characteristics are developed. Then responses of these models to a road unevenness which is modeled as an impulse function with 100 mm amplitude, are investigated. For analyzing the dynamic behavior of vehicle, State Space Method in Matlab/Workspace, Matlab/Simulink and Finite Element Method were developed. For validation, the results are compared to previous works with the same data. The simulation results of these two models are compared with results of a fullvehicle model in another article. Finally, the effect of the suspension parameters on the maximum displacement and acceleration of body is investigated. Obtained diagrams show that while crossing a vehicle over an impulse and 100 mm amplitude road unevenness, softer springs always improve ride quality and Stronger dampers, reduce ride quality but make requirement of having more space between body and tires.

The crankshaft is one of the most critically loaded components as it experiences cyclic loads in the form of bending and torsion during its service life. Its failure will cause serious damage to the engine so it’s important at the time of design to verify fatigue strength. More challenges in crankshaft design due to increasing vehicle payloads, lower weight requirement, higher efficiency and longer durability life. In this study a dynamic simulation was conducted on a crankshaft from a V8 diesel four stroke engine. Finite element analysis was performed to obtain and analysis the variation of the stress magnitude at every location of crankshaft especially at critical points. Results obtained from the aforementioned analysis were then used in optimization of the crankshaft. Also accumulated fatigue damage caused by the change in loading in different crankshaft speeds was determined. The goal of this study is designing crankshaft with suitable and optimum dimensions which can serve the longer durability life without any failures.

In this paper, elasto-plastic time dependent impact of high-speed projectile on water surface is simulated numerically using Arbitrary Lagrangian- Eulerian (ALE) method. The projectile is considered as elasto-plastic solid and its mesh is generated by Lagrangian approach. The water is also assumed as compressible fluid so its mesh is produced by Eulerian method. Three steps simulation are performed in this research; static, dynamic stress analysis and also impact analysis of full degrees of freedom (DOF) projectile on water surface using ALE method. The effects of fluid compressibility and cavitation are considered in last analysis. In order to validate results, the stress wave propagation produced in the projectile due to water impact is compared with exact ones. The results show that the maximum error compare with exact ones is 5%. Also the magnitude of maximum stress and location/path of fracture in the projectile are compared with experimental data. The good agreement between the predicted and analytical/experimental values shows the accuracy of this numerical algorithm. The impact of projectile on water surface is simulated with different angles. The results show that the safe zone of impact angle for present projectile is ±0.5°.

In this paper 3D mixed-mode crack analysis of gas turbine blade is performedby using the finite element method and the path independent J integral.The effect of different parameters like rotation speed ofthe blade, fluid pressure, crack angle, crack position on the blade and crack length on the stress intensity factors of mode I, II, III and effective are investigated.Moreover critical rotational speed and critical crack length, height and angle are estimated too.Results are alsoshow, the edge cracks might grow form surface crack tip, so Surveillance of crack outer surface assurance the safety in the blade.

In this paper، the mixed-Mode dynamic fracture analysis of a FGM plate is performed using MLPG method also the effect of changes in value and angle of material gradation on the dynamic Stress Intensity Fctor (SIF) of Mode I، II، and effective are investigated. To solve time dependent equations that discretized by MLPG method، the Central Difference Method (CDM) and the Newmark method are used. Although the J integral is one of the most common methods to calculate the SIF، but in general، it is not applicable for FGMs. So، in this paper the path independent integral، J*، which is formulated for the non-homogeneous material is used to calculate stress intensity factor. Results show that the present method has good agreement with the exact and other existent solutions. Results also، show the maximum and minimum values of effective stress intensity factor for E2/E1>1 are occurred at material gradation angle equal to 0 and 90 respectively، and for E2/E1

In this paper، the Meshless Local Petrov-Galerkin (MLPG) method is used to analyze the fracture of an isotropic FGM plate. The stress intensity factor of Mode I and Mode II are determined under the influence of various non-homogeneity ratios، crack length and material gradation angle. Both the moving least square (MLS) and the direct method have been applied to estimate the shape function and to impose the essential boundary conditions. The enriched weight function method is used to simulate the displacement and stress field around the crack tip. Normalized stress intensity factors (NDSIF) are calculated using the path independent integral، J*، which is formulated for the non-homogeneous material. The Edge-Cracked FGM plate is considered here and analyzed under the uniform load and uniform fixed grip conditions. To validate results، at first، homogeneous and FGM plate with material gradation along crack length was analyzed and compared with exact solution. Results showed good agreement between MLPG and exact solution.