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In general, in dynamic analysis of mechanical systems, joints are assumed to be ideal. However, due to errors in fabrication and assembly of components, existence of joints clearances is an inevitable issue that caused frequent collisions between the journal and bearing and stable periodic behavior of system becomes chaotic. Degradation the dynamic performance of the system, reduction in fatigue life of components and produce undesirable vibrations are all of the factors resulted from impact- contact forces due to joint clearance. First, different contact force models for two surfaces has been introduced and dynamical models of revolute joint with clearance for two modes, namely, dry contact model and lubricated joint model is then presented. In this paper, the dynamic behavior of a slider- crank mechanism with a revolute joint clearance between the slider and connecting rod, using the Lankarani-Nikravesh contact force model is studied and compared to the ideal case. Considering the effect of friction between journal and bearing, governing equations of motion of the system for two phase, contact and non-contact modes are extracted and it is shown that system exhibits chaotic behavior under specified size of clearance. A fluid lubricant is used in clearance between journal and bearing for stabilizing an unstable periodic orbit embedded in the chaotic attractor.

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In order to avoid unpleasant incidents, it is crucial to maintain the stability for a high-speed railway vehicle. In this research, a high-speed railway vehicle dynamics with 38 degrees of freedom was investigated, adding longitudinal movement equations. Another innovation of this investigation is to determine the critical velocity for the studied railway vehicle and using nonlinear elastic rail for the wheel and rail contact. In this study, the stable and hunting behavior of the system was investigated. To identify the chaotic motion of the system, frequency analysis has been performed. Also, by plotting the Poincaré map, dynamic behavior of the system is illustrated in a discrete state space, which could be a good criteria for the chaotic or periodic behavior of the system. Long-term behavior reveals that at Speeds lower than the critical speed, the system oscillates until it reaches the steady-state of the system. In steady motion, the oscillation continues until the critical speed When the system reaches the critical velocity, the motion on the limit cycle occurs for the first time and when the speed is higher than critical speed, the vibration amplitude increased smoothly. It was observed from the frequency response plot that the hunting frequency evaluated via the linear elastic rail is higher than that of derived using a nonlinear model.

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In this research the designed mechanism for chasing and repoussé of sheet metal is studied. This mechanism is similar to incremental sheet metal forming. In this kind of sheet metal forming, sheet is fixed and forming tool pastes desired pattern incrementally. The major difference between designed mechanism and traditional incremental forming is as follows: control on the punch energy and sequence, and fixing sheet by using protectant material behind it instead of clamping sheet sides. In this mechanism, the solenoid is used as a hammer. The plunger moves to the center of the coil while energized. Striking energy could be controlled by controlling the excitement voltage and punching sequence thus could be adjusted by manipulating the excitement algorithm. In this paper, the utilized solenoid is simulated. The mechanical and magnetic relations are merged for this. And the effect of core head geometry and plunger mass and coil covers on the strike energy and hence power is studied.

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The design of a robust controller for the automatic landing system is investigated for an unmanned fixed-wing aircraft based on an external navigation system. Since landing is the most difficult phase of flight, the major accidents are occurring in the phase. So, providing a high-precision automatic landing system in presence of environmental disturbances is very important for UAVs landing. The used landing navigation system is founded on a portable land-based laser-optics system which can track the UAV and calculate the altitude and direction of it toward the center of runway. However, the navigation system is external; sending them to the UAV can be done with a delay. In this regard, UAV’s control systems must be designed such that the stability of aircraft is satisfied based on information of navigation system with considering the model uncertainty, noises, disturbance and navigation delay. So in this paper, a new robust stabilizer controller is suggested for UAVs to overcome these challenges with considering some limitation in the structure of the controller. Finally, simulation results based on laboratory software in the loop been presented. The results are indicating the capability of using proposed method for automatically landing of UAVs.

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In the present study, the usability of high-density polyethylene (HDPE) based composites in medical applications under impact loads was investigated. Due to the importance of biocompatibility of composites in the medical applications and body environment, zinc oxide nanoparticles (ZnO) were selected as reinforcements. ZnO nanoparticles are generally safe and have superior antibacterial properties. A finite element simulation process with a new approach were used to study the impact properties of the composites in the standard Charpy impact test; moreover, in the experimental procedure, a new method was introduced for the production of HDPE/ZnO composites without use of the compatibilizers. Fourier-transform infrared spectroscopy (FTIR) test was used to check the diffusion of particles in composites. Field emission scanning electron microscopy (FESEM) was utilized to examine the presence of particles in composites. The results of the simulation showed that the HDPE/1%ZnO composites have the best impact resistance in comparison to other composites. Experimental results also showed that HDPE/1%ZnO composites have the best performance in terms of impact strength with an error of about 11% compared to simulation results and are economical. Moreover, the results of antibacterial test of HDPE/1%ZnO composites confirm the excellent performance of this composites against gram-positive and negative strains.