Current Issue : July - September Volume : 2012 Issue Number : 3 Articles : 5 Articles
The very first step in the simulation of ice accretion on a wind turbine blade is the accurate prediction of the flow field around\r\nit and the performance of the turbine rotor. The paper addresses this prediction using RANS equations with a proper turbulence\r\nmodel. The numerical computation is performed using a commercial CFD code, and the results are validated using experimental\r\ndata for the 3D flow field around the NREL Phase VI HAWT rotor. For the flow simulation, a rotating reference frame method,\r\nwhich calculates the flow properties as time-averaged quantities, has been used to reduce the time spent on the analysis. A basic\r\ngrid convergence study is carried out to select the adequate mesh size. The two-equation turbulence models available in ANSYS\r\nFLUENT are compared for a 7 m/s wind speed, and the one that best represents the flow features is then used to determine\r\nmoments on the turbine rotor at five wind speeds (7 m/s, 10 m/s, 15 m/s, 20 m/s, and 25 m/s). The results are validated against\r\nexperimental data, in terms of shaft torque, bending moment, and pressure coefficients at certain spanwise locations. Streamlines\r\nover the cross-sectional airfoils have also been provided for the stall speed to illustrate the separation locations. In general, results\r\nhave shown good agreement with the experimental data for prestall speeds....
The effect of temperature dependent variable viscosity on magnetohydrodynamic (MHD) natural convection flow of viscous\r\nincompressible fluid along a uniformly heated vertical wavy surface has been investigated. The governing boundary layer equations\r\nare first transformed into a nondimensional form using suitable set of dimensionless variables. The resulting nonlinear system\r\nof partial differential equations are mapped into the domain of a vertical flat plate and then solved numerically employing the\r\nimplicit finite difference method, known as Keller-box scheme. The numerical results of the surface shear stress in terms of skin\r\nfriction coefficient and the rate of heat transfer in terms of local Nusselt number, the stream lines and the isotherms are shown\r\ngraphically for a selection of parameters set consisting of viscosity parameter (e), magnetic parameter (M), and Prandtl number\r\n(Pr). Numerical results of the local skin friction coefficient and the rate of heat transfer for different values are also presented in\r\ntabular form....
This paper provides a general description of a variational graph-theoretic formulation for simulation of flexible multibody systems\r\n(FMSs) which includes a brief review of linear graph principles required to formulate this algorithm. The system is represented by\r\na linear graph, in which nodes represent reference frames on flexible bodies, and edges represent components that connect these\r\nframes. Themethod is based on a simplistic topological approach which casts the dynamic equations of motion into a symmetrical\r\nformat. To generate the equations of motion with elastic deformations, the flexible bodies are discretized using two types of finite\r\nelements. The first is a 2 node 3D beam element based on Mindlin kinematics with quadratic rotation. This element is used to\r\ndiscretize unidirectional bodies such as links of flexible systems. The second consists of a triangular thin shell element based on\r\nthe discrete Kirchhoff criterion and can be used to discretize bidirectional bodies such as high-speed lightweight manipulators,\r\nlarge high precision deployable space structures, and micro/nano-electromechanical systems (MEMSs). Two flexible systems are\r\nanalyzed to illustrate the performance of this new variational graph-theoretic formulation and its ability to generate directly a set\r\nof motion equations for FMS without additional user input....
In this paper the requisite foundational numerical and experimental investigations that are carried out, to model the ââ?¬Å?uncracked\r\nand crackedââ?¬Â shaft and to identify its bending and torsional vibration responses, are reported. The cylindrical shaft used in this experimental\r\nstudy is continuous over two spans (with a cantilever span carrying a propeller) with ball-bearing supports. During\r\nmodal tests the backward end of shaft (away from the propeller end and connecting it to an electric motor, required for online\r\nmonitoring) is fixed to one of the test frame supports; later on this backward end will be connected to an electric motor to carry out\r\nonline modal monitoring for crack identification. In the numerical study, beam elements are used for modeling the bending and\r\ntorsional vibrations of the rotating shaft. The paper describes in detail the numerical ââ?¬Å?linear springââ?¬Â models developed for representing\r\nthe effects of ââ?¬Å?ball bearings and the (experimental test) frame supportsââ?¬Â on the vibration frequencies. Shaft response\r\nparameters are obtained using modal analysis software, LMS Test Lab, for bending vibrations monitored using accelerometers, and\r\nthree ââ?¬Å?setsââ?¬Â of shear strain gages fixed at three different shaft locations measure the torsional vibrations. Effects of different crack\r\ndepths on bending and torsional frequencies and mode shapes are investigated experimentally and numerically, and the results interpreted\r\nto give better comprehension of its vibratory behavior....
Vibrational characteristics of functionally graded cylindrical shells filled with fluid and placed on Winkler and Pasternak elastic\r\nfoundations are investigated. Love�s thin-shell theory is utilized for strain-displacement and curvature-displacement relationships.\r\nShell dynamical equations are solved by using wave propagation approach. Natural frequencies for both empty and fluid-filled\r\nfunctionally graded cylindrical shells based on elastic foundations are determined for simply-supported boundary condition and\r\ncompared to validate the present technique. Results obtained are in good agreement with the previous studies. It is seen that the\r\nfrequencies of the cylindrical shells are affected much when the shells are filled with fluid, placed on elastic foundations, and\r\nstructured with functionally graded materials. The influence of Pasternak foundation is more pronounced than that of Winkler\r\nmodulus....
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