نشریه مهندسی مکانیک و ارتعاشات
سال دوم شماره 2 (پیاپی 3، تابستان 1390)

Mechanisms with flexible joints transfer displacement, force and energy by using flexure hinges instead of Simple hinge joints. Reduction of manufacturing costs, increasing the accuracy of these mechanisms, absence of error caused by being loose and lack of joint wear and vibration problems resulting from their movements are among the advantages of these types of mechanisms. In this article for analyzing these mechanisms, a quasi-rigid model was used. Then, by introducing and evaluating a number of mechanical magnification mechanisms which were used to increase the movement of piezoelectric actuator, a new model is also provided and analyzed. This new model offers a high ratio in compact dimensions that is pretty good compared to previous models. The natural frequency of the model and the lack of lateral movements are among advantages of this model compared to the models introduced. We will review and determine the design parameters for the analytical solution for the optimal work condition of the quasi-rigid mode. Also, by using finite element analysis and comparison of its results with analytical solutions, the effect of various parameters on the performance of this mechanism have been identified and at the end an optimal mechanism is offered.

Optimization techniques based on basic structure and the minimum growth ground method and stationary nodes, are among useful and effective methods in finding optimal discrete structures. But the slow optimization process of the base structure method for two-dimensional Large-scale structures and the large number of basic structural elements, waste a lot of time to solve problems. The fixed nodes of the truss in minimum growth ground method with fixed nodes, which in some cases makes structures to find a local optimum. In this article we have tried to provide a new method, optimization of cross section and truss topology are in a way that the aforementioned problems are solved as far as possible and for this purpose the algorithm of growth ground method with floating nodes are suggested. In this method, instead of starting with the base structure with the most possible members of the structure, we start with a structure with minimum members and the basic structure grows until it satisfies the conditions and all nodes are added to the structure in a floating mode. Then, in this paper several standard example are used which are coded using MATLAB software and the obtained results in the form of growth ground  method  with floating nodes using optimization algorithm of particle swarm is compared to other methods. The results show that growth ground method with floating nodes has a very high Convergence rate compared to growth ground method and more Absolute optimization compared to the minimum growth ground method with fixed nodes.

Vibration of floating structures under the effect of propeller excitation is One of the main issues in the design of floating structures and not paying attention to this issue and the placement Super structure at the bottom of the float, vibrations caused by the stimulus of the fan can cause problems for crews and individuals and the vibrations from the propeller make noise and also reduce the life of existing machines in the bottom of the float. In this paper the vibrations caused by the propeller stimulation, using a numerical analysis of fluid-structure on a commercial vessel is studied and the results are discussed. First with respect to the geometry and condition a suitable propeller was chosen for the float and the numerical solution for different speeds of the float and the angular velocity of the impeller is done. The floating structure is designed based on the standard and discretization is conducted using finite element.  Pressure distribution on the propeller and hull obtained from the numerical solution of fluid flow, has been applied to floating structures in the structural analysis and floating structures due to harmonic loading induced by the rotation of the propeller is investigated and modal analysis of floating structures has been performed And the results of its analysis in a frequency range including natural frequencies that canaries in different modes and rotational speeds  of the propeller were recorded. The Results show that in some rotational speeds of the propeller excitation frequency in rotational speed can lead to vibration increase and resonance amplitude The results are compared with the standard range, the results show that with accurate choosing of the propeller And the range of allowable angular velocity and optimization of the structure, we can provide the Requirements for vibration exposure in the limited range.

The safety of the car is one of the high attentions of car customers. Then, automobile manufactures make a lot of effort to improve safety. Because of the high attention of buyers towards the safety of car, car manufacturers make a huge effort to improve this safety. Among them, we can refer to the airbag, which in turn is the most important safety component on a vehicle. In this paper, the mathematical analysis of a simple mechanical system is discussed which is lightweight, low cost, and can be reasonably accurate. The system consists of a cantilever beam in which a  Current-carrying wire is placed .when  occur accidents due to the high acceleration shock, the beam is broken and the current will be out of circuit. So, secondary factors such as cutting of the petrol circuit, unlocking the doors and deactivation of the alarm system may happen. The Analysis is performed using Laplace technique. . The results show that the accidents with speeds above 40 miles per hour, choosing   a beam with a height of 8 cm and a cross-section of 3* 0.3cm2, the system will work smoothly and efficiently.  Keywords: Mathematical modeling, safety, airbags, Laplace transformations, bending of beam

In this article, prediction of lobe stability diagram is presented with the new method of 3th degree of full discretization that is based on direct integral. First, the dynamic model of milling with delay is developed from condition form to integral form. Then every period is discretized in limited time sections. Full discretization method is used for manual calculation of system integral. In every small time interval, the Lagrange 3th degree multi term is applied to interpolate the condition part. Furthermore the Lagrange linear multi term is also used for interpolation of delay- and period parts. A discrete dynamic design is achieved.  Now it is possible to determine the matrix of condition transition in a time interval. Using this matrix by Floquet theory, lets to predict the stability lobe diagram. A basic example provides verifying of this method by comparison with results from literatures. The MATLAB program to calculate the problem is attached.

In this paper, the effect of polyurethane foam and initiator are investigated on axial crushing response of cylindrical aluminum external grooved tubes. For this purpose, an initiator is placed at the top of the foam-filled tube to prevent a sudden applied force to the main part of the structure when the accident occurs. In this new idea, several numerical simulations using ABAQUS 5.6 finite element explicit code are carried out to study of crashworthiness characteristics of the foam-filled thin-walled cylindrical grooved tubes. In order to verify these numerical results, a series of quasi-static axial compression tests are performed. Moreover, load-displacement curves, deformation mechanism of the structure with different number of annular rings are described. The results show that the initiator reduces the intensity of damage to the main structure and occupants.

Promotion of security level in urban roads network has important role in increasing confidence and efficiency and competence in transportation network and it is one of the most impressive and effective parameters in increasing immunity and safety, speed control of automobile, so as to it causes number decrease and severity of accidents between vehicles and security increase for passenger. In this case, speed bump and speed humps play important role in speed decrease of vehicles in city. Unfortunately in Iran some reasons as have because of incorrect designs, unlimited and excessive usage of speed bumps and also determining erection place  optionally without observing  global standards it caused that these tools and instruments have little effect on speed control and this case caused maximum loss and damage to automobile suspension system and it follows discomfort of all automobile’s passengers as an example vehicles that move with permissible speed while passing from speed bumps. One of the most important objections for these speed bumps is delay in giving agency vehicles and firefighting automobiles. In this article first of all, existing speed bumps is introduced and by designing and constructing pride automobile quarter model with Simulink software in MATLAB software, their effects on automobile and their passengers has been investigated. Then using ISO 2361-1 Standard, vertical acceleration in which the vehicle passenger feel comfortable is obtained and using Genetic Algorithms, a new design compatible with this standard is also obtained for the speed bump and hump. Using the speed bump and hump optimal design in urban roads network, passengers of the cars which pass them with permissible speed are in the most comfortable area and passengers of the cars which pass them with impermissible speed are in the least comfortable area.