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.
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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Correct necessary and sufficient conditions are given for positive semidefiniteness. Positive definite and positive semidefinite real quadratic and Hermitian forms play important roles in many control and dynamics app...
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Correct necessary and sufficient conditions are given for positive semidefiniteness. Positive definite and positive semidefinite real quadratic and Hermitian forms play important roles in many control and dynamics applications. The correct necessary and sufficient condition is that all possible principal minors of the matrix be nonnegative. Examples are given that disprove the conditions set forth by Greenwood (1965), Brogan (1974), and Wiberg (1971). (D.H.)
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.
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.
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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An eigenspace optimization approach is proposed and demonstrated for the design of feedback controllers for the maneuvers/vibration arrests of flexible structures. The algorithm developed is shown to be equally useful...
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An eigenspace optimization approach is proposed and demonstrated for the design of feedback controllers for the maneuvers/vibration arrests of flexible structures. The algorithm developed is shown to be equally useful in sequential or simultaneous design iterations that modify the structural parameters, sensor/actuator locations, and control feedback gains. The approach is demonstrated using a differential equation model for the 'Draper /RPL configuration'. This model corresponds to the hardware used for experimental verification of large flexible spacecraft maneuver controls. A number of sensor/actuator configurations are studied vis-a-vis the degree of controllability. Linear output feedback gains are determined using a novel optimization strategy. The feasibility of the approach is established, but more research and numerical studies are required to extend these ideas to truly high-dimensioned systems. (Author)
A method for decomposing an optimization problem into a set of subproblems and a coordination problem that preserves coupling between the subproblems is described. The decomposition is achieved by separating the struc...
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The article investigates the treatment of pointwise state variable constraints for the dynamic response optimization problems. A suggested alternate treatment is to impose constraints at the two grid points that brack...
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The article investigates the treatment of pointwise state variable constraints for the dynamic response optimization problems. A suggested alternate treatment is to impose constraints at the two grid points that bracket a local max-point. This procedure could result in an optimization algorithm that would be more efficient and effective than previous algorithms. The performance of this procedure is studied.
The imaging of positron-emitting isotopes using a gamma camera requires special collimators. A ray-tracing method for simulating the point-spread function of collimators and, therefore, the total gamma camera system i...
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The imaging of positron-emitting isotopes using a gamma camera requires special collimators. A ray-tracing method for simulating the point-spread function of collimators and, therefore, the total gamma camera system is presented. Simulated data obtained by this method showed good agreement with experimental data. Using this method, optimal lead and tungsten collimators for positron emitters were devised;at an object distance of B = 100 mm, these yielded a point-spread function with an FWHMtot = 9.1 mm using an intrinsic resolution of FWHMintr = 8.0 mm.
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