JOURNAL OF MECHANICAL RESEARCH AND APPLICATION (JMRA)
Year:2009 | Volume:1 | Issue:1|Papers Count:7

In this article a new and an accurate method for kinematic and dynamic analysis of a parallel robot 3PRS and a hybrid robot (parallel and serial) 3PRSRRP are presented, which is based on the Denavit-Hartenberg transformation matrix algebra. First, basic properties of various kinds of robots are compared, and then the Denavit-Hartenberg parameters and their table are introduced. Next, the methods of forward and inverse kinematic are explained and system dynamic equations are obtained by Lagrange method. Finally for defined sizes and with imagination of a rotational movement for the center point of the moving plate of parallel robot and two input kinematic for serial robot, a few kinematic and dynamic results for parallel and serial robot by Newton and Lagrange methods are presented for singularity consideration. Generally, the forward kinematic solution of parallel robots and inverse kinematic solution of serial robots are difficult. For these hybrid robots, it would be better to use parallel robots, which have linear movement on the moving plate in the forward mode to increase the space and strength, or the two robots be time independent.

This paper presents an overview of model updating and particularly its application for updating of frame model. In this article a mathematical model of the frame was produced with finite element method. The frame was subjected to hammer modal testing. Then the results of the modal testing were compared with those predicted with the model. This comparison revealed discrepancies between these two sets of results. It is a commonly known fact that incorrect values of parameters in a model, among other things, do cause these discrepancies. In order to improve the correlation between the measured and the predicted results and hence improve the reliability of the model, the model was subjected to finite element model updating. In this updating process, incorrect values of parameters in a model are adjusted. Also it is important in updating that the FE model be simple and in the same time can give good results. The objective of this article is to use direct and sensitivity-base methods for frame and also compare these methods.

Modeling of crack propagation by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture mechanics. Crack growth process is simulated by an incremental crack-extension analysis based on the maximum principal stress criterion, which is expressed in terms of the stress intensity factor.In this paper, a procedure to correct the direction of crack propagation in the analysis of finite element is presented to ensure that a unique final crack path is achieved for different analysis of a problem by using different increments of crack. For each increment of crack extension, finite element method is applied to perform a single region stress analysis of the cracked structure. Results of this incremental crack extension analysis are presented for several geometries.

In this paper, the axisymmetric corrugated diaphragm using finite element method will be discussed, so that half of these diaphragms’ cross sections and later the applied pressure will be considered.Following this, using the consequent equations and visual basic software, a computer program will be provided which receives the diaphragms’ particulars such as diameter, thickness, pressure and the form of object’s cross section as AutoCAD file and then it measures the maximal stress and displacement. Finally, the calculated values will be compared with the experimental values and Theoretical results using the above program and then it will become clear that the results of this research enjoy the acceptable precision. Then, the various parameters which have an influence on the displacement and stress are changed and the results of these changes will be investigated.

In this paper, the finite element analysis of stability problem of vehicle composite drive shafts subjected to torsional loading is studied. First, using the minimum total potential energy principle, the governing equations are derived and then they are solved by finite element method. The initial geometrical imperfection which is usually in the form of radial displacement is taken into consideration in the formulation and the displacement field is expressed according to the third order shear deformation theory. Finally, Budyanski’s criterion is employed for determination of the critical buckling load and the effect of different parameters on the buckling behavior is studied. The results show that the stacking sequence has a significant effect on the buckling torque. Furthermore, the buckling torque increases as the initial imperfection amplitude decreases.

The new non-conventional cutting process by the use of thermal shock is a convenient procedure for cutting the brittle materials such as glasses and ceramics. This method is based on the application of localized thermal shock to brittle materials by the use of hot air jet, which induces thermal stresses at the tip of an existed pre-crack. Due to the thermo-elastic behavior of materials, the pre-crack is propagated in the material. By the use of this process, the glass and brittle materials can be cut to any shape without the use of cutting tools. In this paper, based on the presented phenomena and the induced time-dependent thermal shock, the tip of an existed pre-crack in a glass sheet is heated by a moveable point heat source. The effect of parameters such as cutting speed, nozzle orifice diameter, cutting temperature, macroscopic quality of cutting surface on cutting the brittle materials were studied. The results indicated that as far as a pre-defined distance is developed between the moveable heating point and the tip of the existed pre-crack, the crack is propagated in stable manner and under complete control, and hence better cutting surface quality. Based on this distance, the effective cutting parameters are investigated and set to get better cutting process.

This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodynamic characteristics and then design the optimum operational condition to be installed on two different large bulk carriers and VLCC. The method is based on boundary element method (BEM) to obtain the hydrodynamic performance of any complicated configuration such as CRP system, and then the optimum propeller data is obtained by the systematic method at the design condition. The researchers prepared a software package code, namely SPD, which has model mesh generation, solver and numerical output results. The comparison of the propulsive performance was made between the propeller alone and CRP arrangement. Major finding include optimal agreement between predictions using the numerical code and experimental data for both ships.