In CAD, the shape of a design is often described by an interpolating curve. In this paper, an automated method for finding the optimal geometry of such a curve is used to study the blade geometry of vertical axis wind...
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In CAD, the shape of a design is often described by an interpolating curve. In this paper, an automated method for finding the optimal geometry of such a curve is used to study the blade geometry of vertical axis wind turbines. To minimize bending moments due to centrifugal loads during rotation the blades are often curved in the shape of the troposkien (Greek for ‘turning rope’). From a fabrication point of view a simpler shape is preferred. An optimal number of interpolating points along the curve are used as design variables and their movements controlled by an optimization algorithm. During the optimization, the shape of the curve is successively recomputed and current objective and constraint functions are analysed. Stresses along the beam are computed using the finite element method by regarding the curve as a plane elastic beam.
Developments of a general multilevel optimization capability and results for a three-level structural optimization are described. The latter is considered a major stage in the method development because the addition o...
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An efficient structural optimization methodology is presented for the design of minimum-weight space frames subject to multiple natural frequency constraints. A powerful class of generalized hybrid constraint approxim...
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A method is described for designing time-invariant controllers to minimize root-mean-square target-tracking errors with root-mean-square control constraints in the presence of random initial conditions, target motions...
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The ability to maneuver within the atmosphere during orbital return is a major advantage of high-lift vehicles. For example, a maximum lift/drag ratio of nearly 2 affords the Space Shuttle orbiter a choice of several ...
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The ability to maneuver within the atmosphere during orbital return is a major advantage of high-lift vehicles. For example, a maximum lift/drag ratio of nearly 2 affords the Space Shuttle orbiter a choice of several landing sites. In addition, the Shuttle can be rolled during entry while still maintaining a shallow glide trajectory. This roll maneuver during entry reduces the descent time and, therefore, the total heat input, although the heating rate is increased. One typical measure of maneuvering capability is the maximum lateral range that a vehicle can achieve;the solution to this problem was originally given. Another important maneuver consists of performing turns that change the vehicle's heading. This paper contains a brief analysis of turning maneuvers during gliding flight, including lateral distances traversed, at velocities up to circular satellite speed.
A reliable and fast transonic wing flowfield analysis program, TWING, has been coupled with a modified quasi-Newton unconstrained optimization algorithm, QNMDIF, to create a new design tool. Because of the high comput...
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A reliable and fast transonic wing flowfield analysis program, TWING, has been coupled with a modified quasi-Newton unconstrained optimization algorithm, QNMDIF, to create a new design tool. Because of the high computational efficiency of the design code, in particular, the efficiency of TWING on the Cray X-MP vector computer, the computer time required for a typical wing design is significantly reduced over previous methods. The lift-to-drag ratio, previously thought to be too unreliable for numerical optimization, was used as the objective function to be minimized. This, coupled with a new cubic-spline wing parameterization, produced great success, yielding wing designs with nearly shock-free (zero-wave-drag) pressure distributions and reasonable wing section shapes.
In the direct method of shape optimum design, mesh regridding is a necessary step in avoiding the distortion of finite element grids. The effect of internal-nodal movements on the shape design sensitivity associated w...
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A method for generating and optimizing arbitrary three-dimensional boundary-conforming computational grids has been developed. The smoothness and local orthogonality of the grid are maximized using a fast iterative pr...
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A method for generating and optimizing arbitrary three-dimensional boundary-conforming computational grids has been developed. The smoothness and local orthogonality of the grid are maximized using a fast iterative procedure, and provision is made for clustering the optimized grid in selected regions. An optimal grid can be obtained iteratively, irrespective of the method used to generate the initial grid. Unacceptable grids and even singular grids (i. e. , grids containing regions of overlap) can be made useful for computation using this method. Application of the method to several test cases shows that grids containing regions of overlap are typically untangled in 2-5 iterations and that the conjugate gradient optimization procedure converges to an optimized grid within 25 iterations. Taking advantage of the original properties of this method, a new concept for generating optimal three-dimensional computational grids is proposed. It consists in optimizing a first guess of the desired grid, using an imperfect grid generated by a simple, inexpensive method as input.
Positive definite and positive semidefinite (also called nonnegative definite) real quadratic and Hermitian forms play important roles in many control and dynamics applications. A practical test for positive definiten...
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Positive definite and positive semidefinite (also called nonnegative definite) real quadratic and Hermitian forms play important roles in many control and dynamics applications. A practical test for positive definiteness that does not require explicit calculation of the eigenvalues is the principal minor test. The note formulates the correct necessary and sufficient condition for the positive semidefinite matrix.
Described is a new equivalent plate analysis formulation that is capable of modeling aircraft wing structures with a general-planform such as cranked wing boxes. Multiple trapezoidal segments are used to represent suc...
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