In this paper, a nonlinear optimal feedback control law is designed to find 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 find a sequence of approximate solutions of the HJB equation. This is done by solving a sequence of Generalized HJB (GHJB) differential equations. Galerkin procedure is applied to find a numerical solution to the GHJB equation. Using this method, a nonlinear feedback is designed for mobile manipulator and then, an algorithm is developed to find 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 increase Dofs. To solve the extra Dofs of the system, 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. Key Words: Maximum Payload, Manipulator, Optimal Control, Closed Loop Controller, HJB

A transient flow 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 flow in a circular pipe including the breakpoint. The numerical technique is a combined finite-element finite-volume method applied on the unstructured grid. A modified model with a two-layer equation for 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 61.5m upstream of the breakpoint reduces about 8%, while this value for the downstream pressure located in the same distance from the rupture is about 14% at the same time. Also the mass flow rate released from the rupture point will reach 2.4 times of its initial value and becomes 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 remains constant at the same time and condition. The results are compared with available experimental and numerical studies for steady compressible pipe flow.

Keywords:
Transient compressible flow, Gas pipeline, Numerical modeling, Sudden rupture, Combined finite element-finite volume method

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

Keywords:
Offshore, Floating Wind Turbine, Stochastic Dynamic Response, Aero-hydro-elastic

A series of wind tunnel tests were performed to study the effects of canard and its position on the downstream flowfield over the wing surface. The wing surface pressure was measured for both canard-off and canard-on configurations. In addition, the canard position effects on the wing were investigated at different angles of attack. The canard was installed at three vertical positions and at two different horizontal distances from the wing apex. The results show a remarkable increase in the wing suction peak for the canard-on configurations. At low to moderate angles of attack, among the various configurations examined in the present experiments, the mid-canard configuration developed a higher suction on the wing, while at high angles of attack, the upper-canard was found to induce the most favorable flow field 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. Key Words: Canard, Delta Wing, Downwash, Leading Edge Vortex

One of the important challenges in the automotive industry is to reduce the mass of the vehicle while meeting structural performance requirements for Crashworthiness, Noise, Vibration and Harshness (NVH) etc. In this paper, a multidisciplinary optimization (MDO) of a car back-bonnet is investigated by using the Response Surface Method (RSM). Firstly, a car body is fully surface modeled in CATIA and meshed in HYPERMESH software. Then, modal analysis of the finite element model is performed by NASTRAN software to find natural frequencies. Frequency map of that component is extracted and compared with a reference map to detect defects. Design of Experiments (DOE) methodologies is used for a screening of the design space and for the generation of approximation models using RSM techniques. Therefore, to optimize the model, improvement of the NVH behavior and minimization of the weight are imposed.

Keywords:
multidisciplinary optimization, modal analysis, NVH, weight, RSM, back-bonnet

A 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 different parts of the model have been carefully measured and averaged over several oscillation cycles. These findings were then compared with the corresponding normal force at similar conditions. The results reveal a hysteresis loop in the variations of the model shock angles with instantaneous angle of attack during upstroke and down stroke motions. Having compared with the normal force hysteresis loop, it has been found that there is an interesting relationship between the shape of the hysteresis loops of the shock angle and the corresponding loop observed in the normal force data. Further, the oscillation frequency has been shown to have similar effects on both the shock angle and the aerodynamic force variations with the instantaneous angle of attack. Key Words: Hysteresis, Pitching Motion, Vortex Bursting, Reduced Frequency, Schlieren, Upstroke

In this study the fluid dynamics and convective heat transfer for turbulent flows through a 3 sub channels of rod bundle which is representative of those used in VVER-1000 are examined. The rod bundle is constructed from parallel rods in a hexagonal array. The rods are on constant pitch by spacer grids spaced axially along the rod bundle. The geometry details of the bundle and heat flux from the fuel rod are similar to that of the Iranian nuclear reactor under construction. A numerical study using Computational Fluid Dynamics (CFD) was carried out to estimate the flow field, pressure loss and heat transfer coefficients in spacer grids and rod bundles. Turbulence has been modeled using the turbulence model. In distance of 2 from the beginning of the spacer grids in direction of flow because fluid enthalpy and Nusselt number have maximum and minimum values respectively, therefore the probability of nucleate boiling (DNB) is very higher and two phase flow will occur. Predicted results are found to be in close agreement with that of the experimental results reported in literature.

Keywords:
Sub channel, Rod bundle, Spacer grid, Computational fluid dynamics (CFD), Turbulent flow, Nusselt number

The most suitable and widely used numerical integration method for boundary integrals in BEM method is Gauss-Legendre integration. But this integration method is not appropriate for singular and nearly singular integrations in BEM. In this study, some criteria are introduced for recognizing the nearly singular integrals in integral form of Laplace equation. At the first stage, a criterion is obtained for constant element and in the later stages higher order elements are investigated. In the present research, the Romberg integration method is used for nearly singular integrals. The results of this numerical method have a good agreement with analytical integration. The singular integrals are solved by composing the Romberg method and midpoint rule. Constant, linear and other interpolation functions of potentials over an element are a category of BEM elements. In those elements, the Gauss-Legendre integration will be accurate, if the source point is placed out of the circle with a diameter equal to element length and its center matched to midpoint of element.

Keywords:
Boundary element method, Gauss-Legendre integration, Laplace equation, nearly singular integrals, Romberg integration.

Abstract: - A series of low speed wind tunnel tests were conducted on a section of a 660 kW wind turbine blade to examine the effects of the distributed surface contamination on its performance characteristics. The selected airfoil was tested with a clean surface, two types of zigzag roughness, strip tape roughness, and distributed contamination roughness. The straight and zigzag leading edge roughness models simplify the contamination results in an early turbulence transition. In this study the surface contamination was simulated by applying 0.5 mm height roughness over the entire upper surface of the airfoil. The distribution density varied from the leading edge to the trailing edge of the model. Our data show that this particular airfoil was very sensitive to the surface contamination and its maximum lift coefficient decreased up to 35% while the stall angle of attack increased slightly. The surface contamination, however, caused a very smooth stall characteristics and less lift drop in the post stall region. In contrast to the clean model, the maximum lift coefficient of the roughened airfoil increased by the Reynolds number. The effects of zigzag roughness and strip tape roughness were less than that of the distributed contamination roughness.

Keywords:
Wind turbine

Contamination model
Performance drop
Experimental test
Pressure distribution
Roughness effects.