numerically reliable computational methods are proposed for the stabilization of a linear descriptor system with or without simultaneous elimination of its impulsive behavior. Two basic stabilization approaches are di...
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numerically reliable computational methods are proposed for the stabilization of a linear descriptor system with or without simultaneous elimination of its impulsive behavior. Two basic stabilization approaches are discussed. The first approach relies on methods which represent generalizations of direct stabilization techniques for standard state-space systems. The second approach is based on a recursive generalized Schur algorithm for pole assignment. Both approaches are based exclusively on numerically reliable procedures and can serve for robust software implementations.
We analyze the behavior of common indices used in numerical linear algebra, analysis, and optimization to measure rates of convergence of an algorithm. A simple consistent axiomatic structure is used to uniquely defin...
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We analyze the behavior of common indices used in numerical linear algebra, analysis, and optimization to measure rates of convergence of an algorithm. A simple consistent axiomatic structure is used to uniquely define convergence rate measures on the basic linear, superlinear, and sublinear scales in terms of standard comparison sequences. Agreement with previously utilized indices and related measures is discussed.
The dynamic buckling global response of a nonlinear, 3-degree-of-freedom dissipative model under a step loading of infinite duration is thoroughly discussed. Geometrically imperfect models with symmetric or antisymmet...
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The dynamic buckling global response of a nonlinear, 3-degree-of-freedom dissipative model under a step loading of infinite duration is thoroughly discussed. Geometrically imperfect models with symmetric or antisymmetric imperfections losing their static stability through a limit point and an asymmetric bifurcation point, respectively, are considered. Emphasis is given to the combined effect of nonlinearities (geometric and/or material) and damping. Exact, approximate, and lower/upper bound estimates based on energy criteria for establishing the dynamic buckling response of such autonomous models without solving the highly nonlinear initial-value problem are assessed. The reliability and efficiency of the proposed readily obtained estimates is illustrated via numerical simulation, the accuracy of which is checked using energy balanced considerations. Certain interesting byproducts associated with a postlimit point bifurcation and breakdown of the symmetry of deformation are also revealed.
numerical simulations of high-angle-of-attach flows around slender bodies of revolution are earned out using four different numerical algorithms: a partially flux-split algorithm, the Beam and Warming algorithm in its...
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numerical simulations of high-angle-of-attach flows around slender bodies of revolution are earned out using four different numerical algorithms: a partially flux-split algorithm, the Beam and Warming algorithm in its original and diagonal forms, and an algorithm combining block and diagonal forms. Comparisons of laminar flows at alpha = 20 and 40 deg reveal that the diagonal algorithm fails to conserve symmetry at high angles of attack and a spurious asymmetry is developed, The source of the spurious asymmetry has been traced and found to be inherent to the diagonalization process.
Product complexity is increasing rapidly to address the demanding requirements driven by customers, regulations and safety. More complex designs and an increasing number of design options must be evaluated whilst cont...
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Product complexity is increasing rapidly to address the demanding requirements driven by customers, regulations and safety. More complex designs and an increasing number of design options must be evaluated whilst controlling the cost and length of the design cycle. The engineering requirements come from different disciplines, such as aerodynamics, structures and electromagnetics. The division of engineering into separate disciplines is not recognised by nature, with the result that addressing requirements within one discipline can compromise requirements in other disciplines. Product complexity is now such that requirements from multiple engineering disciplines need to be simultaneously addressed at an early stage of the design cycle to avoid costly re-design. These problems have placed strong demands on computational design, driving key trends in numerically intensive modelling, as well as the requirement for more computational resource. The requirement for more computational resource arises in many disciplines and is compounded by the need for multi-disciplinary design. This results from the increased product complexity which has to be matched by increasing the mathematical complexity of the model providing the underlying framework for the computational design tools. The availability of increased computational resource via parallel platforms at affordable prices enables these problems to be addressed facilitating computational analyses of more complex problems simultaneous computational analyses of multiple design and planning options multi-disciplinary analyses, i.e. simultaneously address requirements in different disciplines. The continual growth in computational design and computational resource provides the potential for the end-user engineer to carry out far more design more rapidly and accurately. However this potential can only be exploited if the end-user can efficiently define more complex problems, multiple problems, multi-disciplinary problems and also
An investigation of the use of piezoceramics as sensors and actuators for controlling the deflection of the centroid of a rectangular plate suddenly subjected to a uniformly distributed load. The formulated problem w...
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An investigation of the use of piezoceramics as sensors and actuators for controlling the deflection of the centroid of a rectangular plate suddenly subjected to a uniformly distributed load. The formulated problem was analyzed using a finite element code that utilizes 4-noded Lagrangian elements and a consistent mass matrix. The results indicate that these actuators are effective in controlling the vertical deflection of the centroid of the plate when a displacement type controller with a gain of 5 × 1024 V/C-mm is used.
To study multidimensional unstable detonation waves, we have developed a high-order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves. The numerical...
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To study multidimensional unstable detonation waves, we have developed a high-order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves. The numerical algorithm uses a multidomain approach so that different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A --> B. Several cases of unstable two-dimensional detonation waves are simulated, and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity to obtain the correct cellular patterns.
This article presents an exact inverse method that generates the airfoil shape, satisfying all fluid dynamic and geometric constraints imposed by prescribing any input velocity distribution (or contour at the hodograp...
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This article presents an exact inverse method that generates the airfoil shape, satisfying all fluid dynamic and geometric constraints imposed by prescribing any input velocity distribution (or contour at the hodograph), with the only restriction that it does not take the same vector velocity at two different points of the boundary. The method is supported with a successive conformal mapping technique that can also be used in other problems as the one of grid-generation. The method may be a valuable general tool to obtain optimized designs with excellent performance. It can be extended to generate high-lift airfoils for compressible subsonic flow velocities.
A computational procedure suitable for simulating the flowfield, performance, and interference of a curved-bladed, three-dimensional Darrieus wind turbine is presented. The rotor blades are modeled as time-averaged so...
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A computational procedure suitable for simulating the flowfield, performance, and interference of a curved-bladed, three-dimensional Darrieus wind turbine is presented. The rotor blades are modeled as time-averaged sources in the steady, laminar momentum equations solved on a Cartesian grid. As an illustration of the potential of the method, terrain and generator box influence on the behavior of the turbine are simulated in a uniform freestream wind. The generator box of the turbine is modeled as a solid cube and viscous no-slip boundary conditions are prescribed on the generator box and the ground plane, The influence of the terrain on the flowfield of the turbine is considered for two hypothetical, two-dimensional ridge-lines. Computed turbine performance, such as the power coefficient and the normal force coefficient, are compared with results from Sandia field tests and a theoretical method based on stream-tube momentum balance for a stand-alone turbine. Quantitative differences in the performance of the Sandia 17-m turbine with and without the hypothetical terrains are discussed. Qualitative behavior of the flowfield under the influence of the ground plane is also presented with the help of velocity vector plots acid path lines.
In this paper, a new sufficient condition for robust stability of perturbed large-scale systems is presented. If the given matrix equations are solved, their solutions can be applied to obtain the bounds on the uncert...
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In this paper, a new sufficient condition for robust stability of perturbed large-scale systems is presented. If the given matrix equations are solved, their solutions can be applied to obtain the bounds on the uncertain parameters to guarantee the stability of the system. Furthermore, we discuss the existence of the solutions of the matrix equations and numerical algorithms. The application of the proposed method is illustrated by an example.
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