Scientia Iranica
Volume:17 Issue: 2, 2010

The sloshing phenomena in a partially lled tank can a ect its stability. Modi cations of tank instability due to the movement of the tank carrier, are key design points for the stability of a carrier. Even though the sloshing phenomenon has already been investigated using the BEM-FDM technique, the research in this paper covers this phenomenon in a porous media, which is new in 2-D coordinates. For this purpose, a Laplace equation has been used for potential ow, and kinematic and dynamic boundary conditions have been applied to the free surface. Also, a formulation has been developed for a free surface in porous media. BEM has been used for solving the governing equation and FDM discretization has been used for kinematic and dynamic free surface boundary conditions and for time marching. Theoretical results have been veri ed with experimental data collected in this study. The results show an acceptable agreement between theory and experiment, and the rapid damping property in the sloshing phenomena by using porous material in the water, as expected. Also, these results illustrate that the derived formula in this research are applicable and true.

series of supersonic visualization tests were performed on an airplane model in both static and dynamic pitching cases. After image processing, the wave angles originating from di erent parts of the model were carefully measured and averaged over several oscillation cycles. These ndings were then compared with the corresponding normal force under similar conditions. The results reveal a hysteresis loop in variations of the model shock angles with instantaneous angles of attack during up-stroke and down-stroke motions. In comparison with the normal force hysteresis loop, it has been found that there is an interesting relationship between the shape of the hysteresis loop of the shock angle and the corresponding loop observed in the normal force data. Further, the oscillation frequency has been shown to have similar e ects on both shock angle and aerodynamic force variations with the instantaneous angle of attack.

The transient ow of a compressible gas generated in a pipeline after an accidental rupture is studied numerically. The numerical simulation is performed by solving the conservation equations of an axisymmetric, transient, viscous, subsonic ow in a circular pipe including the breakpoint. The numerical technique is a combined nite element- nite volume method applied on the unstructured grid. A modified  􀀀 " model with a two-layer equation for the near wall region and compressibility correction is used to predict the turbulent viscosity. The results show that, for example, after a time period of 0.16 seconds, the pressure at a distance of 61.5 m upstream of the breakpoint reduces about 8%, while this value for the downstream pressure located at the same distance from the rupture is about 14% at the same time. Also, the mass ow rate released from the rupture point will reach 2.4 times its initial value and become constant when the sonic condition occurs at this point after 0.16 seconds. Also, the average pressure of the rupture reduced to 60% of its initial value and remained constant at the same time and under the same condition. The results are compared with available experimental and numerical studies for steady compressible pipe ow.

In this paper, a nonlinear optimal feedback control law is designed to nd the maximum load carrying capacity of mobile manipulators for a given trajectory task. The optimal state feedback law is given by the solution to the nonlinear Hamilton-Jacobi-Bellman (HJB) equation. An iterative procedure is used to nd a sequence of approximate solutions of the HJB equation. This is done by solving a sequence of Generalized HJB (GHJB) di erential equations. The Galerkin procedure is applied to nd a numerical solution to the GHJB equation. Using this method, a nonlinear feedback is designed for the mobile manipulator and, then, an algorithm is developed to nd the maximum payload. In mobile base manipulators, the maximum allowable load is limited by their joint actuator capacity constraints, nonholonomic constraints and redundancy that arise from base mobility and increased Dofs. To solve the extra Dofs of the system, an extended Jacobian matrix and additional kinematic constraints are used. The validity of the methodology is demonstrated via simulation for a two-link wheeled mobile manipulator and linear tracked Puma arm and the results are discussed.

A series of wind tunnel tests were performed to study the e ects of a canard and its position on the downstream ow eld over the wing surface. The wing surface pressure was measured for both canard-o and canard-on con gurations. In addition, the canard position e ects on the wing were investigated at di erent angles of attack. The canard was installed at three vertical positions and at two di erent horizontal distances from the wing apex. The results show a remarkable increase in the wing suction peak for the canard-on con gurations. At low to moderate angles of attack, among the various con gurations examined in the present experiments, the mid-canard con guration developed a higher suction on the wing while, at high angles of attack, the upper-canard was found to induce the most favorable ow eld on the wing. In addition, higher suctions were achieved on the wing at moderate to high angles of attack, as the wing-canard distance was increased.

Like other o shore structures, oating wind turbines are subjected to stochastic wave and wind loads that cause a dynamic response in the structures. Wind turbines should be designed for di erent conditions, such as Operational and Survival conditions. In high sea states, the response can be quite di erent from the operational condition. The present paper deals with coupled wave and wind induced motion in harsh conditions, up to 15 m signi cant wave height and 50 m/sec average wind speed. There are several ways to deal with the dynamic response of oating wind turbines. The Coupled Time domain dynamic response analysis for a moored spar wind turbine subjected to wave and wind loads is carried out using DeepC. DeepC is well known software for calculating the coupled dynamic response of moored oating structures. The aerodynamic forces on a parked wind turbine are calculated, based on the strip theory, and imported to the DeepC through a MATLAB interface. At each time step, the relative wind velocity, based on the response of the structure, is calculated.