Composite structures are currently being designed to make use of multiple layers of fiber-reinforced material. The fibers in each layer are aligned straight and parallel with each other. Within a particular layer, the...
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Composite structures are currently being designed to make use of multiple layers of fiber-reinforced material. The fibers in each layer are aligned straight and parallel with each other. Within a particular layer, the fiber orientation is fixed. This is opposed to having a fiber orientation that varies from point to point within a layer or group of layers. The idea of using fibers in anything other than a straightline format has been hampered by the inability to implement such a design. However, comtemporary fiber handling techniques, such as multiaxis tow placement devices may eliminate this barrier. As such, it is worthwhile to consider the gains, or losses, that accompany the use of curvilinear fiber formats. This paper begins to discuss the notion of a curvilinear fiber format for the specific problem of a plate with a hole. It should be noted that some work has been done in the area of curvilinear reinforcement.
During the service of an aerospace structure, its configuration may vary for different operating conditions. When we restrict the word 'configuration' to structural geometry, the structures with multiple confi...
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During the service of an aerospace structure, its configuration may vary for different operating conditions. When we restrict the word 'configuration' to structural geometry, the structures with multiple configurations that come to mind are, for example, a tilt-rotor aircraft in airplane or helicopter mode and a stowed vs deployed solar array system for a spacecraft. If we generalize the word configuration to encompass boundary conditions and mass distribution, then all aerospace vehicles can be considered to be structures with multiple configurations. In application, design specifications may impose specific natural frequency constraints for different configurations. For a structure with a single configuration, the minimum weight design with frequency constraints can be found readily. However, the resulting optimum design may not satisfy frequency constraints for the structure in other configurations. This often leads to design iterations among various configurations. After many design iterations, the final design may be feasible but not optimum. The purpose of this paper is to develop an approach for minimum weight design of structures with several configurations under natural frequency constraints. In the optimum design problem, frequency constraints for all configurations are considered simultaneously. In each design cycle, the constrained minimum weight design problem is solved iteratively by a combined analysis/optimization procedure. To increase the computational efficiency, the iterative analysis is approximated by using reduced-order modal space models. sequential linear programming (SLP) for optimization procedure is considered. In SLP, the optimum design problem is linearized at each design iteration. Together with a strategy to compute move limits, the resulting linear optimization problem is solved as a linearprogramming problem. The combination of finite element analysis together with optimization method (SLP) constitutes an effective and reliable app
The paper treats a piping system, where the layout of the network is given but the diameters of the pipes should be chosen among a small number of different values. The cost of realizing the system should be minimized...
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The paper treats a piping system, where the layout of the network is given but the diameters of the pipes should be chosen among a small number of different values. The cost of realizing the system should be minimized while keeping the energy heads at the nodes above some lower limits. A new algorithm using successive linearprogramming is presented. The performance of the algorithm is illustrated by optimizing a network with 201 pipes and 172 nodes. It is concluded that the new algorithm seems to be very efficient and stable, and that it always finds a solution with a cost near the best possible.
A design approach that combines iterative structural analysis with a traditional iterative optimization algorithm is applied to the optimum design of the shape of a hole in a plate in tension. The plate is modeled by ...
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A design approach that combines iterative structural analysis with a traditional iterative optimization algorithm is applied to the optimum design of the shape of a hole in a plate in tension. The plate is modeled by three-dimensional finite elements, and an element-by-element preconditioned conjugate gradient iterative algorithm is used for solving the equations of equilibrium. Several parameterizations of the optimum shape are considered, and it is shown that a sine series can describe the optimum shape with only three design variables, whereas other series require seven variables for similar results. The optimum shape compares well with an experimental optimum obtained by A. J. Durelli. An investigation is performed to determine the best way of obtaining finite-difference derivatives of the stresses with respect to design variables. It is shown that a method based on modifying the equations of equilibrium for the perturbed problem performs best. The benefit of the integrated approach is determined by comparing convergence with different initial iterates for the displacement field. It is shown that using the final iterate of the previous solution can reduce the number of analysis iterations by about 40% compared to starting with a zero initial iterate.
An improved method is developed for eigenvalue and eigenvector placement of a closed-loop control system using either state or output feedback. The method basically consists of three steps. First, the singular value o...
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An improved method is developed for eigenvalue and eigenvector placement of a closed-loop control system using either state or output feedback. The method basically consists of three steps. First, the singular value or QR decomposition is used to generate an orthonormal basis that spans admissible eigenvector space corresponding to each assigned eigenvalue. Second, given a unitary matrix, the eigenvector set that best approximates the given matrix in the least-square sense and still satisfies eigenvalue constraints is determined. Third, a unitary matrix is sought to minimize the error between the unitary matrix and the assignable eigenvector matrix. For use as the desired eigenvector set, two matrices, namely, the open-loop eigenvector matrix and its closest unitary matrix, are proposed.
Several novel ideas in the definition and optimization of robustness for structures and structural controllers are presented. A robustness bound attributable to Patel and Toda is developed using eigenvalue conditionin...
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Several novel ideas in the definition and optimization of robustness for structures and structural controllers are presented. A robustness bound attributable to Patel and Toda is developed using eigenvalue conditioning analysis. Homotopy and sequential linear programming algorithms are used in lieu of conventional nonlinearprogramming to implement these ideas for an illustrative example. The numerical results confirm the conservatism of the stability robustness bound but nevertheless support the hypothesis that maximizing the robustness measure does significantly increase the true robustness of a closed-loop system. The results also indicate that maximizing the stability robustness measure produces more robust designs than minimizing eigenvalue sensitivity directly.
A numerical method is presented for the solution of nonlinear discrete optimization problems. The applicability of discrete optimization to engineering design is discussed, and several standard structural optimization...
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The requirements for extremely precise and powerful large space antenna reflectors have motivated the development of a procedure for static shape control of the reflector surface. A mathematical optimization procedure...
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Automated design of large aerospace structures requires efficient optimization algorithms because of a large number of design variables and design constraints. Most of the difficulties associated with large structural...
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A numerical procedure for obtaining optimal vehicle suspensions has been studied. The vehicle has been modelled by dynamic systems of linear springs and dampers. Several optimizations were accomplished using different...
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A numerical procedure for obtaining optimal vehicle suspensions has been studied. The vehicle has been modelled by dynamic systems of linear springs and dampers. Several optimizations were accomplished using different irregularities and speeds.
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