Showing papers on "Minimum weight published in 1974"
TL;DR: In this paper, an efficient automated minimum weight design procedure is presented which is applicable to sizing structural systems that can be idealized by truss, shear panel, and constant strain triangles.
Abstract: An efficient automated minimum weight design procedure is presented which is applicable to sizing structural systems that can be idealized by truss, shear panel, and constant strain triangles. Static stress and displacement constraints under alternative loading conditions are considered. The optimization algorithm is an adaptation of the method of inscribed hyperspheres and high efficiency is achieved by using several approximation concepts including temporary deletion of noncritical constraints, design variable linking, and Taylor series expansions for response variables in terms of design variables. Optimum designs for several planar and space truss examples problems are presented. The results reported support the contention that the innovative use of approximation concepts in structural synthesis can produce significant improvements in efficiency.
570 citations
TL;DR: In this paper, a mathematical optimization problem based on the equilibrium conditions and the stress constraints is formulated to obtain an approximate design which avoids merely local optima, which is close to the exact global optimum obtained by enforcing the compatibility conditions and is therefore a good starting point for an optimizing procedure.
42 citations
TL;DR: In this paper, a procedure based on the force method of analysis and using linear programming is presented for a minimum weight optimum design of stress limited indeterminate trusses, where the problem is initially cast as a linear optimization problem considering only equilibrium conditions and stress limits, and additional approximate linear conditions are annexed to the initial formulation and the solution is repeated yielding a more nearly compatible design.
Abstract: A procedure based on the force method of analysis and using linear programming is presented for a minimum weight optimum design of stress limited indeterminate trusses. The problem is initially cast as a linear optimization problem considering only equilibrium conditions and stress limits. Thereafter, additional approximate linear conditions are annexed to the initial formulation and the solution is repeated yielding a more nearly compatible design. The process is then repeated refining these additional conditions in each iteration until a compatible design is obtained. The simplex method is used to solve the linear programming problem in each iteration cycle. The relatively simple mathematical programming formulation is shown to be efficient as well as having the ability to modify the configuration of the structure by vanishing unnecessary members. A computer program based on this method and the results of some examples are presented.
34 citations
TL;DR: A mathematical formulation is given which results in a minimum weight feedback model and a heuristic is developed similar to the Greedy algorithm for minimum weight spanning trees which requires only one pass through the network.
Abstract: A solution method is given for a class of practical optimization problems requiring the determination of a consistent partial ordering for sets of objects, events, preferences, and the like. These problems are characterized by the existence of “noisy” or contradictory links of varying strengths. The origin of this class of problems is an anthropological study in which it is desired to specify a global chronological ordering of ancient cemetery data. A mathematical formulation is given which results in a minimum weight feedback model. A heuristic is developed similar to the Greedy algorithm for minimum weight spanning trees which requires only one pass through the network.
32 citations
01 Nov 1974
TL;DR: In this paper, a structural synthesis technique was used to determine the optimum hat-stiffened compression panel design using a more accurate analysis, which is a linked plate element program.
Abstract: Optimum hat-stiffened compression panel designs are determined using a structural synthesis technique. Effects of simplifying assumptions made in the buckling analysis for the optimization program are investigated using a more accurate analysis which is a linked plate element program. Optimization results for an aluminum panel are compared with available results. Optimization results for hat-stiffened graphite-epoxy panels show a 50-percent weight savings over optimized aluminum panels. Using the structural synthesis technique, composite panels are shown to possess a variety of proportions at nearly constant weight.
26 citations
Patent•
30 Sep 1974
TL;DR: A plurality of parallel constructed members that have means for securing the two parallel members together along an axis parallel to the longitudinal axis of the members to lend structural support relative to each other as mentioned in this paper.
Abstract: A plurality of parallel constructed members that have means for securing the two parallel members together along an axis parallel to the longitudinal axis of the members to lend structural support of the members relative to each other. This allows the structurally secured members to have structures having high strength to weight ratios and requiring minimum volume for the securing structure.
17 citations
TL;DR: In this paper, the problem of minimum weight design of elastic structures under multiple loading conditions is considered, and it is shown that the problem can be expressed as a search for feasible deflection patterns coupled with repeated searches for structures of the minimum weight for given stiffness.
9 citations
TL;DR: In this article, the authors present a procedure and computer program for the minimum weight design of circular, cylindrical, "T" frame reinforced, submersible shells where all metal thicknesses may be confined to specified gage thickness values.
8 citations
TL;DR: Two mathematical programming procedures for treating nonlinear problems involving mixed variables are presented and are applied to the minimum weight design of stiffened, cylindrical shells where they prove to be effective.
Abstract: : Two mathematical programming procedures for treating nonlinear problems involving mixed variables are presented One involves a relatively simple concept First an optimum is located treating all variables as continuous Adjacent discrete points are then evaluated in order of increasing distance from the all-continuous optimum, each evaluation requiring an optimization of the continuous variables, if any, until a satisfactory design is found The other method utilizes an optimal discrete search to locate the optimum These procedures are applied to the minimum weight design of stiffened, cylindrical shells where they prove to be effective (Author)
8 citations
TL;DR: In this paper, a structural optimization problem is considered in which the design requirements include restrictions on the strength, stability, frequency and flutter characteristics of the structure, and the design problem is formulated as a minimum weight optimization problem and is solved by using nonlinear programming techniques.
Abstract: A structural optimization problem is considered in which the design requirements include restrictions on the strength, stability, frequency and flutter characteristics of the structure. One of the central concerns of this phase of the work has been to overcome the problems inherent in analysing the dynamic and aeroelastic behaviour of structures with many degrees of freedom. The multiweb delta wing structure under supersonic flight conditions is the model upon which this exploratory study is based. The finite element idealization, with three different kinds of elements, is used to model the wing structure. The constant stress triangular plate elements, the rectangular shear panels and the pin-jointed bar elements are used to represent, respectively, the cover skins, webs and stringers of the wing structure. The design problem is formulated as a minimum weight optimization problem and is solved by using non-linear programming techniques. Computationally efficient schemes are developed for the necessary derivatives of the behaviour constraints. Numerical examples are presented to illustrate the feasibility and the computational effectiveness of the method.
7 citations
01 Jul 1974
TL;DR: The pilot program is expanded both in capacity and scope to a new version OPTIM 2 which is compatible with the MAGIC finite element analysis system and a number of special computational features are provided to extend the utility of the program.
Abstract: : A pilot computer program OPTIM was developed previously for the weight optimization of complex finite element models of real structures subject to strength and stiffness constraints The program was developed using optimality criteria to generate a highly efficient iterative optimization procedure with good convergence characteristics which are independent of problem size In the present study, the pilot program is expanded both in capacity and scope to a new version OPTIM 2 which is compatible with the MAGIC finite element analysis system The finite element library is expanded by the addition of five new elements and a number of special computational features are provided to extend the utility of the program The input/output is compatible with MAGIC but OPTIM 2 can be used as a stand-alone analysis program The report presents a complete development of the theoretical basis for stiffness-based optimality criteria along with description of the program features
TL;DR: In this paper, a mathematical programming procedure for the automated optimal structural synthesis of frame stiffened, cylindrical shells is described, where the skin, frame web and frame flange thicknesses and the flange width are treated as continuous variables.
TL;DR: In this paper, the synthesis of anisotropic cylindrical shells of minimum weight is considered; the initial data relate to the characteristics of the reinforcing filaments and binder, the optimum case satisfying the requirements of stability, strength, and geometrical limitations is found by the method of projective gradients.
Abstract: The synthesis of anisotropic cylindrical shells of minimum weight is considered; the initial data relate to the characteristics of the reinforcing filaments and binder. The optimum case satisfying the requirements of stability, strength, and geometrical limitations is found by the method of projective gradients.
TL;DR: In this article, the problem of finding the minimum weight configuration for a statically determinate structure of fixed layout under two alternative load systems, as analysed by Chern and Prager, is re-examined by a special primal-dual formulation known as geometric programming.
01 Jun 1974
TL;DR: In this article, the potential of hybrid methods of structural optimization for dealing with relatively large design problems involving practical complexity was explored, and the reduced basis concept in design space was used to decrease the number of generalized design variables dealt with by the mathematical programming algorithm.
Abstract: The rational use of optimality criteria was investigated for a class of structural synthesis problems where materials, configuration and applied load conditions are specified, and the minimum weight design is to be determined. The potential of hybrid methods of structural optimization for dealing with relatively large design problems involving practical complexity was explored. The reduced basis concept in design space was used to decrease the number of generalized design variables dealt with by the mathematical programming algorithm. Optimality criteria methods for obtaining design vectors associated with displacement, system buckling and natural frequency constraints are presented. A stress ratio method was used to generate a basis design vector representing the stress constraints. The finite element displacement method was used as the basic structural analysis tool. Results for several examples of truss systems subject to stress, displacement and minimum size constraints are presented. An assessment of these results indicates the effectiveness of the hybrid method developed.
Dissertation•
01 Aug 1974
TL;DR: In this article, a technical procedure for designing a fuselage-type stiffened thin circular cylindrical shell to carry a specified uniform axial compression with minimum weight is described.
Abstract: : This report contains a technical procedure by which one may design a fuselage-type stiffened thin circular cylindrical shell to carry safely a specified uniform axial compression with minimum weight.
12 Aug 1974
TL;DR: In this paper, a resizing algorithm was developed that employs a uniform-flutter-velocity-derivative optimality criterion for fluttercritical elements and the fully-stressed-design criterion for strength-critical elements.
Abstract: Several methods for sizing the finite elements of an aircraft structural idealization to achieve minimum-weight design under combined strength and flutter-speed requirements are developed and evaluated. Two basic categories are considered: methods based on a combination of energy principles and optimality criteria; and procedures employing numerical-search techniques. Drawing upon the experience gained from studies of both of these basic methods, a resizing algorithm is developed that employs a uniform-flutter-velocity-derivative optimality criterion for flutter-critical elements and the fully-stressed-design criterion for strength-critical elements. The final result is a practical, automated approach for dealing with large-scale idealizations having both structural and mass-balance design variables.
01 Jun 1974
Abstract: Light weight shafts reduce bearing forces and allow the use of smaller bearings, seals, and supports. The Minimum Principle is used to set up the problem of determining the minimum weight shaft for a specified critical speed of given order. Specific examples include simply supported shafts and cantilevered shafts with and without a disk. The designs are obtained from the solution to a nonlinear multi-point boundary-value-problem. Minimum weight configurations represent a standard against which other designs, such as stepped shafts, can be compared.
30 Jan 1974
01 Jan 1974
TL;DR: In this article, three minimizing techniques are evaluated to determine the most efficient method for minimizing the weight of a thermal protection system and for reducing computer usage time, including numerical optimization and nonlinear least squares.
Abstract: Three minimizing techniques are evaluated to determine the most efficient method for minimizing the weight of a thermal protection system and for reducing computer usage time The methods used (numerical optimization and nonlinear least squares) for solving the minimum-weight problem involving more than one material and more than one constraint are discussed In addition, the one material and one constraint problem is discussed
01 Mar 1974
TL;DR: In this article, Galerkin's method is applied to the design of minimum weight structures with dynamic constraints, and the problems considered include the weight optimization of a simply supported beam and a panel, with the condition that their fundamental frequencies be the same as those of corresponding uniform thickness structures.
Abstract: : Galerkin's method is applied to the design of minimum weight structures with dynamic constraints. The problems considered include the weight optimization of a simply supported beam and a panel, with the condition that their fundamental frequencies be the same as those of corresponding uniform thickness structures. Galerkin's method is also used for the weight optimization of a semi-infinite panel and of a finite square panel, both of which have flutter speed constraints. In addition, the assumption of a symmetric thickness distribution in the flutter problems is investigated. (Modified author abstract)
TL;DR: In this article, the minimum weight of a truss is obtained by approximating the structural behavior as a function of the reciprocal of the characteristic crosssectional property of the finite elements.
Abstract: Design algorithms for obtaining the minimum weight of finite element structure are presented. The procedures are based upon approximating the structural behavior as a function of the reciprocal of the characteristic crosssectional property of the finite elements. In addition, approximations based upon the compatibility equations are employed. This results in simpler and generally more accurate approximations of the deflection and stress changes as compared to present procedures which utilize the size variables and the equilibrium equations. Algorithms based upon linear programming utilizing linear constraints obtained either from the global equilibrium or compatibility equations plus a gradient search procedure with segmented linear constraints are developed. The efficiency of the linear programming with linear (equilibrium) constraints, which utilizes available digital subprograms, was demonstrated by comparison of solutions of 3- and 10-bar truss problems presented in the literature. All solutions were of equal or less weight than published results and generally were obtained with fewer redesign cycles. The other algorithms are potentially more efficient. They require, however, further development and demonstration.