Shahrood University of TechnologyJournal of Solid and Fluid Mechanics2251-94752220130518Investigation of the fundamental period for the moment resistant frameInvestigation of the fundamental period for the moment resistant frame11113310.22044/jsfm.2013.133FAHamidBeiraghiMohsenGeramiJournal Article20120603The experimental equation of the codes for the fundamental period usually do not consider exactly the effect of infilled frame with masonry material, This issue may affect severely the fundamental period of the moment resistant frame. It appears that the review and assessment of the experimental formulas for the fundamental period is necessary. In this paper, by modeling of infill walls as compression diagonal element in the steel frame of 3,5,7,9 and 11-storey, effect of different infill percent from 0 to 80, variable modulus of elasticity and different bay length are studied. The results show that the error between the standard no. 2800 of Iran and the curve which is interpolated on the total results is less than 5 percent, but the R squared of the regression curve on the standard no. 2800 is 0.65 which show the poor capability of estimation. A new formula for the time period of the moment resistant frames is also derived from the resultsThe experimental equation of the codes for the fundamental period usually do not consider exactly the effect of infilled frame with masonry material, This issue may affect severely the fundamental period of the moment resistant frame. It appears that the review and assessment of the experimental formulas for the fundamental period is necessary. In this paper, by modeling of infill walls as compression diagonal element in the steel frame of 3,5,7,9 and 11-storey, effect of different infill percent from 0 to 80, variable modulus of elasticity and different bay length are studied. The results show that the error between the standard no. 2800 of Iran and the curve which is interpolated on the total results is less than 5 percent, but the R squared of the regression curve on the standard no. 2800 is 0.65 which show the poor capability of estimation. A new formula for the time period of the moment resistant frames is also derived from the resultshttps://jsfm.shahroodut.ac.ir/article_133_41e61051abb2c979f5fbb418e3bc72a6.pdfShahrood University of TechnologyJournal of Solid and Fluid Mechanics2251-94752220130518Stress Recovery and Error Estimation by Using Forces Induced on Patches of Isogeometric AnalysisStress Recovery and Error Estimation by Using Forces Induced on Patches of Isogeometric Analysis132913410.22044/jsfm.2013.134FABehroozHassaniAhmadGanjaliJournal Article20120604In this paper, a new method is introduced for calculation of stress field in the isogeometric analysis (IGA) method. In this technique, by considering the forces induced on the patches of IGA, the surface denoting the variations of each component of the stress tensor is approximated by the same order of NURBS’ shape functions that are used for approximation of the displacements. This new surface is more accurate compared to the stress surfaces obtained from isogeometric analysis, thereby, can be used error estimation of the IGA. It is shown that this method, which falls in the category of stress recovery methods, is superior to the stress recovery based on the superconvergent points in the IGA. To verify the performance of the method, three examples are taken into consideration and their solutions with this approach as well as the method based on superconvergent points are compared with their exact solutions. The obtained results of these examples indicate the effectiveness of the proposed method and therefore can be considered as a simple and efficient method for error estimation and stress recovery.In this paper, a new method is introduced for calculation of stress field in the isogeometric analysis (IGA) method. In this technique, by considering the forces induced on the patches of IGA, the surface denoting the variations of each component of the stress tensor is approximated by the same order of NURBS’ shape functions that are used for approximation of the displacements. This new surface is more accurate compared to the stress surfaces obtained from isogeometric analysis, thereby, can be used error estimation of the IGA. It is shown that this method, which falls in the category of stress recovery methods, is superior to the stress recovery based on the superconvergent points in the IGA. To verify the performance of the method, three examples are taken into consideration and their solutions with this approach as well as the method based on superconvergent points are compared with their exact solutions. The obtained results of these examples indicate the effectiveness of the proposed method and therefore can be considered as a simple and efficient method for error estimation and stress recovery.https://jsfm.shahroodut.ac.ir/article_134_d45cfbd855c8a3de2b7a0eb052abfc23.pdfShahrood University of TechnologyJournal of Solid and Fluid Mechanics2251-94752220130518Indirect type-2 fuzzy control of flexible-joint robotsIndirect type-2 fuzzy control of flexible-joint robots314313510.22044/jsfm.2013.135FAMohammad MehdiFatehMahdiAliyariJournal Article20121225Since the properties of flexible-joint robots such as nonlinearity, being time variable, coupling and high order, an accurate modelling of its dynamics is complicate. Therefore, model-free control methods are a suitable choise to control flexible-joint robots. In this paper, an indirect type-2 fuzzy control is presented for flexible-joint robots. The proposed scheme has the advantage that is computationally simple ، decoupled and free from manipulator dynamics. This advantage is for adopting voltage control strategy instead of common torque control strategy. The proposed method includes two interior loops: the inner loop controls the motor position using indirect type-2 fuzzy control while the outer loop controls the joint angle of the robot. To do this, an adaptive proportional-integral-derivative (PID) controller is used and by defining proper sliding condition using gradient descent there PID control gains are updated. Stability analysis is presented to verify the effectiveness of the proposed method. A three-joint articulated flexible-joint robot is simulated and simulation results show the superior of the indirect adaptive type-2 fuzzy system to nonlinear control method.Since the properties of flexible-joint robots such as nonlinearity, being time variable, coupling and high order, an accurate modelling of its dynamics is complicate. Therefore, model-free control methods are a suitable choise to control flexible-joint robots. In this paper, an indirect type-2 fuzzy control is presented for flexible-joint robots. The proposed scheme has the advantage that is computationally simple ، decoupled and free from manipulator dynamics. This advantage is for adopting voltage control strategy instead of common torque control strategy. The proposed method includes two interior loops: the inner loop controls the motor position using indirect type-2 fuzzy control while the outer loop controls the joint angle of the robot. To do this, an adaptive proportional-integral-derivative (PID) controller is used and by defining proper sliding condition using gradient descent there PID control gains are updated. Stability analysis is presented to verify the effectiveness of the proposed method. A three-joint articulated flexible-joint robot is simulated and simulation results show the superior of the indirect adaptive type-2 fuzzy system to nonlinear control method.https://jsfm.shahroodut.ac.ir/article_135_e9df6f8577fcf6324962b3ad3a2b8f79.pdfShahrood University of TechnologyJournal of Solid and Fluid Mechanics2251-94752220130518Tank shape designing method for reducing fluid tank sloshing based on using bspline and penalty functionTank shape designing method for reducing fluid tank sloshing based on using bspline and penalty function455413610.22044/jsfm.2013.136FAJournal Article20120912In this paper, a theory based on genetic evolution has been proposed to optimize the tank cross-section. Other tank functions such as controlling the sloshing, enhancing stability and preventing overturning moment have been enhanced. The proposed algorithm is used to increase rollover threshold in oval-shaped tanks based on bspline function. Then the optimization method continues with applying the penalty function. The presented diagram is based on bspline function of order 4 with 10 control points. This function is obtained after developing bspline function of 3rd order with 8 control points. In this algorithm, control points and their bands are modified over 100 samples and the optimization parameter such as population number and mutation rate are analyzed. The optimized mutation rate is proposed approximately 4 to 6 percent with the minimum population number of 40. The comparison of optimized results with the numerical methods confirms that optimized cross-sections enhance roll stability and reduce tank sloshing.In this paper, a theory based on genetic evolution has been proposed to optimize the tank cross-section. Other tank functions such as controlling the sloshing, enhancing stability and preventing overturning moment have been enhanced. The proposed algorithm is used to increase rollover threshold in oval-shaped tanks based on bspline function. Then the optimization method continues with applying the penalty function. The presented diagram is based on bspline function of order 4 with 10 control points. This function is obtained after developing bspline function of 3rd order with 8 control points. In this algorithm, control points and their bands are modified over 100 samples and the optimization parameter such as population number and mutation rate are analyzed. The optimized mutation rate is proposed approximately 4 to 6 percent with the minimum population number of 40. The comparison of optimized results with the numerical methods confirms that optimized cross-sections enhance roll stability and reduce tank sloshing.https://jsfm.shahroodut.ac.ir/article_136_1eef3395fce1d602a44212164e3f2fbf.pdfShahrood University of TechnologyJournal of Solid and Fluid Mechanics2251-94752220130518Parametric Study & Performance Improvement of Centrifugal Compressor Impeller of a Turbo-shaft Engine Using 3D Numerical SimulationParametric Study & Performance Improvement of Centrifugal Compressor Impeller of a Turbo-shaft Engine Using 3D Numerical Simulation556813710.22044/jsfm.2013.137FAMohammadJafariJournal Article20120619In this research, the centrifugal compressor impeller of a turbo-shaft engine is studied. For this purpose, at first, its geometric specifications are exactly measured and then, the impeller geometric model is generated in the Blade-Gen module of Ansys software. This geometry is then reticulated in Turbo-Grid module and is numerically analyzed by applying the boundary conditions that can be obtained from the engine performance. The results are presented in the form of pressure ratio and efficiency curves versus the mass flow. After grid independency, some geometrical parameters (e.g. meridional profiles pages, the axial length and so on) that affect the performance of the compressor are investigated. Finally, the effects of geometric changes on the compressor performance curves are considered and the optimum compressor geometry equivalent to one with higher ratio of pressure and efficiency is introduced. In the modified compressor, the radial region of impeller to the whole ratio is 0.22 and the angle between the end of shroud wall and the vertical line is 6 degrees; moreover, the axial length of impeller increases by 5mm. By applying these modifications to the current compressor, the compressor efficiency and pressure ratio increases by 2.4 and 0.86 percent, respectively.In this research, the centrifugal compressor impeller of a turbo-shaft engine is studied. For this purpose, at first, its geometric specifications are exactly measured and then, the impeller geometric model is generated in the Blade-Gen module of Ansys software. This geometry is then reticulated in Turbo-Grid module and is numerically analyzed by applying the boundary conditions that can be obtained from the engine performance. The results are presented in the form of pressure ratio and efficiency curves versus the mass flow. After grid independency, some geometrical parameters (e.g. meridional profiles pages, the axial length and so on) that affect the performance of the compressor are investigated. Finally, the effects of geometric changes on the compressor performance curves are considered and the optimum compressor geometry equivalent to one with higher ratio of pressure and efficiency is introduced. In the modified compressor, the radial region of impeller to the whole ratio is 0.22 and the angle between the end of shroud wall and the vertical line is 6 degrees; moreover, the axial length of impeller increases by 5mm. By applying these modifications to the current compressor, the compressor efficiency and pressure ratio increases by 2.4 and 0.86 percent, respectively.https://jsfm.shahroodut.ac.ir/article_137_11d95160b81c5ace745078c5fd2a1997.pdfShahrood University of TechnologyJournal of Solid and Fluid Mechanics2251-94752220130518Numerical Investigation of Optimized Cooling of Square ObstacleNumerical Investigation of Optimized Cooling of Square Obstacle698013810.22044/jsfm.2013.138FAJournal Article20121028In this paper, natural convection heat transfer in a cavity induced by an isothermal obstacle is investigated. This paper is an extension of our previous paper [1] so that the effects of geometrical parameters and position of the obstacle are considered precisely. Air is chosen as a working fluid and the flow is assumed to be two-dimensional, steady and incompressible. Lattice Boltzmann method is employed for numerical analysis and the results are compared with finite volume results. A scale analysis is also performed for both numerical methods which have not been presented in the literature. With the representation, the Navier-Stokes equation can be derived from the lattice Boltzmann equation through the Chapman-Enskog expansion. The study is performed for different aspect ratios and different values of Rayleigh number. Heat transfer rate increases by either way of increasing the Ra number from 103 to 105 and increasing the aspect ratio from 0.1 to 0.4. At last, the Nusselt number versus the obstacle’s position, for different aspect ratios and Rayleigh numbers is shown and the position of the obstacle in which heat transfer rate is maximum is investigated.In this paper, natural convection heat transfer in a cavity induced by an isothermal obstacle is investigated. This paper is an extension of our previous paper [1] so that the effects of geometrical parameters and position of the obstacle are considered precisely. Air is chosen as a working fluid and the flow is assumed to be two-dimensional, steady and incompressible. Lattice Boltzmann method is employed for numerical analysis and the results are compared with finite volume results. A scale analysis is also performed for both numerical methods which have not been presented in the literature. With the representation, the Navier-Stokes equation can be derived from the lattice Boltzmann equation through the Chapman-Enskog expansion. The study is performed for different aspect ratios and different values of Rayleigh number. Heat transfer rate increases by either way of increasing the Ra number from 103 to 105 and increasing the aspect ratio from 0.1 to 0.4. At last, the Nusselt number versus the obstacle’s position, for different aspect ratios and Rayleigh numbers is shown and the position of the obstacle in which heat transfer rate is maximum is investigated.https://jsfm.shahroodut.ac.ir/article_138_b5c7f61da858f90004be3bf92199cb37.pdfShahrood University of TechnologyJournal of Solid and Fluid Mechanics2251-94752220130518Experimental investigation on drag coefficient reduction due to tripping wire on a cylinderExperimental investigation on drag coefficient reduction due to tripping wire on a cylinder819013910.22044/jsfm.2013.139FAFarzanehForoozeshGraduated M.Sc.MohsenVahidihakim sabzevari universityJournal Article20120515An experimental investigation is conducted in the wake of a circular cylinder with two tripwires attached at angle of 140 and 40 degrees measured from the forward stagnation point at Reynolds numbers, Re = 30000. The tripwire diameter is 0.5, 1, 1.5 mm. The effects of the tripwires on drag reduction, mean velocity profile and velocity defect and half width, turbulence intensity profiles and Strouhal number have been examined. The results reveal that for Re=3000, there exits optimum case where the drag coefficients acting on the cylinder all reach some of the drag coefficient of a plain cylinder. At the optimum case the drag coefficient of cylinder is reduced for two-wire cylinder with two different diameters. The results reveal that when we get far from cylinder, the procedure of changes of the peak of mean velocity (w0), and peak of turbulence intensity profiles decrease–increase and increase–decrease, respectively. Also the results of experiment are shown that with a plain cylinder the values of peak of turbulence intensity profiles and velocity defect (w0) are generally decreased compared with those values for tripping wires cylinder.An experimental investigation is conducted in the wake of a circular cylinder with two tripwires attached at angle of 140 and 40 degrees measured from the forward stagnation point at Reynolds numbers, Re = 30000. The tripwire diameter is 0.5, 1, 1.5 mm. The effects of the tripwires on drag reduction, mean velocity profile and velocity defect and half width, turbulence intensity profiles and Strouhal number have been examined. The results reveal that for Re=3000, there exits optimum case where the drag coefficients acting on the cylinder all reach some of the drag coefficient of a plain cylinder. At the optimum case the drag coefficient of cylinder is reduced for two-wire cylinder with two different diameters. The results reveal that when we get far from cylinder, the procedure of changes of the peak of mean velocity (w0), and peak of turbulence intensity profiles decrease–increase and increase–decrease, respectively. Also the results of experiment are shown that with a plain cylinder the values of peak of turbulence intensity profiles and velocity defect (w0) are generally decreased compared with those values for tripping wires cylinder.https://jsfm.shahroodut.ac.ir/article_139_9a37b604917a4f2ed34344a05045f64b.pdf