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In practice, clearances in the joints are inevitable due to tolerances and defects arising from design and manufacturing. It is well-known that in the presence of clearance at one joint, the linkage gains an additional uncontrollable degree of freedom which is the source of error. Moreover, these joints undergo wear and backlash, resulting in poor accuracy and repeatability, and so cannot be used in precision mechanisms. The model of continuous contact is used for clearance model. Therefore, joint clearance was modeled as a small link with the length equals to the clearance. In this paper, a method is proposed to alleviate the undesirable effects of joints clearances. This improvement implemented using compliant joints. The compliances are introduced locally in the form of flexural hinges at the two oscillating revolute joints of a four-bar crank-rocker linkage. pseudo-rigid body model is used for modeling the flexures. An optimum design of the flexural hinge for minimum objective function is deduced and used to modify the conventional mechanism. The PSO method is used for optimization process. An example is included in which we show that introduction of compliance will modify the dynamics performances of the linkage.

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In this study, a Lattice Boltzmann Method (LBM) has been developed to calculate the distribution of a scalar quantity, like temperature, in a natural convection flow field under the condition of varying fluid thermal conductivity. The standard form of an LBM usually considers the fluid properties to be constant without any source term in conservation equations. The model developed is to account for variation of thermal conductivity with temperature in the presence of an external heat source. The proposed model has been examined against various case studies. It is shown that it is capable of modeling the extremely nonlinear problems. To magnify the nonlinear term in the natural convection case of under study, the radiation and other thermal sources have been used. The multiple relaxation time scheme has been applied to assure the solution stability. Using Chapman-Enskog analysis, the error associated with the proposed model has been estimated. The part of error which was not due to variations in the fluid properties, may be eliminated by introducing a correction term in higher order terms in Chapman-Enskog analysis. In addition, it has been shown that the correction term associated with the fluid conductivity variations, create an error of second order in terms of Knudsen number and is negligible. The present LBM model has an error of the second order of magnitude with respect to time.

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Solar humidification-dehumidification desalination is one of the most practical methods for water desalination in small scale for regions far from cities and low population. The aim of this study is manufacturing and simulation of a solar humidification-dehumidification desalination system with capacity of 20 lit/day. This system consists of humidification and dehumidification units, solar air and water heaters. To this end, at first this system is explained and modeled. Then, manufacturing process of solar air heaters, and different parts of desalination system is investigated. After the manufacturing process of the desalination system, this system is experimentally tested and the effect of pertinent parameters, such as the temperature of inlet water and air to humidifier; inlet water temperature and flow rate to dehumidifier on the performance of the system and distillate product is investigated. The results show that the effect of water temperature on the fresh water produced in more than air temperature. Moreover, using the chilled water, which its temperature in the range of well temperature, in the dehumidifier inlet leads to an increase of 31 % in the fresh water produced. Also, the best water flow rate to the dehumidifier inlet is 0.12 kg/s. Finally, experimental and simulation results are compared with each other and good consistency is seen.