Computer-aided Design Optimization Research Articles

Optimisation of dose distribution for linear accelerator-based stereotactic radiosurgery

The work presented in the paper addresses a method for obtaining the optimal dose distribution for LINAC-based stereotactic radiosurgery. As many targets have nonspherical or irregular shapes and three-dimensional dose calculations included in dose optimisation, long computation times are required to determine the optimum isocentre separation and collimator sizes to shape the irregular target using the multiple-isocentre approach, by trial-and-error types of method. The simple approach, using a computer-aided design optimisation technique and a fast approximate dose model, has been developed to find the optimum isocentre positions and collimator sizes quickly and automatically. A spherical dose model has been developed to represent the dose for a standard arc system with a single isocentre. The implementation of computer-aided design algorithms with the spherical dose model and their application to several cases are discussed. It is shown that the spherical dose model gives dose distribution similar to that of the exact dose model, which makes this simple dose model more efficient, with computer-aided design optimisation, in finding optimum isocentre positions and collimator sizes used in stereotactic radiosurgery.

Computer-aided optimal design via modified adaptive random-search algorithm

A modified adaptive random-search algorithm for the design of helical gears has been developed. The proposed methodology allows for the implementation of nonlinear design functions and constraints without the need for linearization. In addition, the technique has the capability of starting from either feasible regions or infeasible regions of the design domain. Application examples demonstrate the feasibility of the proposed technique as a practical method for design optimization. The viability is further illustrated in a performance test against the conjugategradient search method.

Optimization of Filtration for Reduction of Lung Dose from Rn Decay Products

A theoretical model was developed for the optimization of filter characteristics that would minimize the dose from the inhalation of Rn decay products. Modified forms of the Jacobi-Porstendorfer room model and the Jacobi-Eisfeld lung dose model were chosen for use in the mathematical simulation. Optimized parameters of the filter were the thickness, solidity, and fiber diameter. For purposes of the calculations, the room dimensions, air exchange rate, particle-size distribution and concentration, and the Rn concentration were specified. The resulting computer-aided optimal design was a thin filter (the minimum thickness used in the computer model was 0.1 mm) having low solidity (the minimum solidity used was 0.5%) and large diameter fibers (the maximum diameter used was 100 microns). The simulation implies that a significant reduction in the dose rate can be achieved using a well-designed recirculating filter system. The theoretical model, using the assumption of ideal mixing, predicts an 80% reduction in the dose rate, although inherent in this assumption is the movement of 230 room volumes per hour through the fan.

THREE-PHASE INDUCTION MOTOR DESIGN OPTIMIZATION USING THE MODIFIED HOOKE-JEEVES METHOD

ABSTRACT A new method of computer-aided design optimization of a three-phase induction motor is proposed. Due to the highly non-linear nature of the design optimization problem an approach using the modified Hooke-Jeeves method is employed. The optimization of the objective function (motor efficiency) is deduced in terms of eight independent motor design variables which are then used to predict seven performance indices and the cost index of the machine. The method is applied to optimize the design of a 5-HP motor. The results obtained are compared with those of an optimally designed motor [3].

A Computer-Aided Design Technique for the Synthesis of Planar Four Bar Mechanisms Satisfying Specified Kinematic and Dynamic Conditions

This paper presents a computer-aided design optimization method for synthesizing planar four bar mechanisms which satisfy specified kinematic and dynamic conditions. The method can be used for path, motion, and function generation as well as for combinations of these. The kinematic conditions consist of combinations of specifications on the position, velocity, and acceleration of the coupler point and the rotations of the coupler and follower links. The dynamic conditions consist of the minimization of the average power consumed by the mechanism as well as a limit on the maximum input torque. The external loads consist of variable forces and moments at the coupler point as well as variable torques on the follower link. The Selective Precision Synthesis (SPS) method is used to express each kinematic condition in terms of a specification plus an allowable deviation or tolerance from the specification. In this manner, the synthesis problem is converted into a nonlinear optimization problem which is solved using the Generalized Reduced Gradient (GRG) method. In addition, two force balancing routines are included to help the dynamic performance of the mechanism. The mathematical formulation and derivation as well as numerical examples are presented in this paper.

Computer-aided optimal design of a polar-based template digitizer-NC contouring system—I. Synthesis and contouring error minimization

This paper presents the computer-aided optimal design of a template digitizer-NC contouring system which utilizes a set of polar coordinates. The system can operate both as a copying machine or as a numerical control (NC) machine. Part I of the paper describes the proposed system and its salient features. It also analyzes the contouring error due to the incremental approximation of the contour. This error is dependent on the relative location of the contour pole from the machine pole. An objective function relating the area error to the position of the contour is derived and an optimization procedure to minimize this error is outlined. Test results of an attempt to locate the poles of three test contours for minimum error are then presented.

Computer-aided optimal design of a polar-based template digitizer-NC contouring system—II. Dynamic analysis

This paper presents the computer-aided optimal design of a template digitizer-NC contouring system which utilizes a set of polar coordinates. Part I of the paper deals with synthesis and with the minimization of contouring error. Part II studies the dynamics of the polar NC machine. The NC machine operates on an open loop control scheme. Consequently, the changes in the torque needed and the torque available as machining conditions change should be thoroughly understood to avoid overloading and contouring failure. The ratio of the torque needed to that available from an axis-drive is used as a measure of the success or failure of the contouring operation. This paper discusses how the contour, the contouring speed, the magnitude and type of machining load and the relative location of the contour pole from the machine pole affect the torque ratio.

Database management concepts in computer-aided design optimization

This paper deals with database management concepts in computer-aided design optimization. Complex nature of engineering data and the need to organize them are emphasized. Database management concepts applicable to finite element analysis and design optimization are explained. Various aspects associated with the development of data models, such as conceptual, internal and external models are discussed. Suitability of external models, like hierarchical, network and relational, are discussed with reference to design optimization requirements. Some techniques to organize data of large matrices for efficient numerical computations are given. Concepts of normalization of data, global and local databases are described. Details of a suitable database management system are described in a separate paper.

SADDLE: A computer-aided structural analysis and dynamic design language—Part I. design system

The SADDLE system is a tool for computer-aided optimal design of structural and mechanical systems. The system is divided into four parts—the preprocessor, the ‘analyzer’, the ‘synthesizer’, and the postprocessor. The structural model and the design data are generated by the preprocessor. The analyzer uses the finite-element method to compute deflections and stresses in the structure. The synthesizer solves the design problem that is cast into a nonlinear programming format. The postprocessor is used to examine the analysis and design results. Different parts of the system interact via a global database. This study presents the design system configuration. In a companion study, the data management part is presented in detail. The user-interface for design is examined first. The design problem formulation, in the nonlinear programming problem context, is presented. The use of utility libraries to achieve this objective with a minimum programming effort is also explained. The article concludes with two numerical examples that belong to two different classes of design problems—a minimum weight design problem and a min-max problem.

SADDLE: A computer-aided structural analysis and dynamic design language—part II. database management system

The SADDLE program is a tool for computer-aided optimal design of structural and mechanical systems. The system is divided into four parts; the pre-processor, the “analyzer”, the “synthesizer” and the post-processor. The structural model and the design data are generated by the preprocessor. The analyzer used the finite-element method to compute deflections and stresses in the structure. The synthesizer solves the design problem that is cast into a nonlinear programming format. The post-processor is used to examine the analysis and design results. Different parts of the system interact via a global database. The database management system is presented in detail, in this part of a two part paper. The data manager has three distinct parts: the data model processor, the resource manager and the I/O manager. Both the relational and hierarchical data models are supported. Tuning parameters are provided to enhance computational efficiency on different computers. The emphasis is on friendlier user-system interaction; free-format input, error recoveries, and easy means to create, edit, and update information.

Computer-aided design optimization of polyphase induction motors

The design of squirrel-cage induction motors is formulated as a nonlinear programming problem, to predict a computer-aided optimum design. The cost of active materials is taken as an objective function. A constrained optimization method called the Complex Method is used to predict optimum design while meeting the specification requirements, formulated as constraints. The flow-chart diagram and design procedure is given.

Erratum: “Computer-Aided Optimal Design of Compressed Air Energy Storage Systems” (Journal of Mechanical Design, 1980, 102, pp. 437–445)

Erratum: “Computer-Aided Optimal Design of Compressed Air Energy Storage Systems” (Journal of Mechanical Design, 1980, 102, pp. 437–445)

Future Trends in Optimization

The purpose of this article is to provide a permanent record of the major ideas and questions raised during the panel session entitled “Future Trends in Optimization” at the 1980 Design Engineering Technical Conference in Beverly Hills, California. The panel members were Professors D. J. Wilde of Stanford University, E. J. Haug of the University of Iowa, K. M. Ragsdell of Purdue University, J. N. Siddall of McMaster University, and F. Freudenstein of Columbia University. They spoke, respectively, on Optimal Design Under Uncertainty; Computer-aided Design Sensitivity Analysis and Optimization of Dynamic Systems; Optimization: The Future of Design, Integration of Optimization with the Design Process; and Optimization in Mechanisms: Past, Present, and Future. It is hoped that the article will prove useful in guiding future efforts in the area of optimal mechanical design.

Interdisciplinary design optimization: A search method

The design of architectural structures frequently involves interdisciplinary aspects and aesthetic considerations which, being of subjective nature, are difficult to quantify. The computer-aided design optimization model presented here, therefore, is an attempt to optimize, in an interdisciplinary context, quantifiable parameters only. The objective function is graphically illustrated to give the designer a means to evaluate the impact of esoteric design decisions on performance variables, such as costs. A search method is used, i.e., evaluation of a discrete number of designs and nonlinear interpolation. The model's system of computer programs is demonstrated on the sample of an anticlastic cable roof structure.

Practical Least pth Optimization of Networks

A new and practical approach to computer-aided design optimization is presented. Central to the process is the application of least pth approximation using extremely large values of p, typically 1000 to 1 000 000. It is shown how suitable and reasonably well conditioned objective functions can be formulated, giving particular emphasis to more general approximation problems as, for example, in filter design. It is demonstrated how easily and efficiently extremely near minimax results can be achieved on a discrete set of sample points. Highly efficient gradient methods can be employed and, in network design problems, the use of the adjoint network approach for evaluating gradients results in greater savings in computer effort. A comparison between the Fletcher-Powell method and the more recent Fletcher method is made on the application of least pth approximation, using a range of values of p up to 1 000 000 000 000 on transmission-line transformer problems for which optimal minimax solutions are known. This is followed by filter design examples subject to certain constraints.

Satellite attitude control with a gimbaled reaction wheel digital control system

In this paper, the analysis, design, implementation and testing of an accurate satellite attitude control system is presented. The control system function is to provide three axis inertial stabilization and accurate earth pointing automatically, over a period of 5 years or more. Of primary concern in the design of the overall control system was the minimization of compensation complexity and control logic without compromising the stabilization requirements and pointing accuracy of the system. In addition to fulfilling the above requirements, the design presented here provides exceptional capability for including nonredundant multi-mode operation; thereby providing additional reliability and highly versatile performance for a wide range of satellite and experiment pointing requirements. The design logic, fabrication problems, and a computeraided design optimization method are described in this paper. Both the theoretically predicted and numerically simulated performance was verified by testing the implemented control system on a spherical air bearing platform and comparing several sets of attitude response data. In addition to the primary control modes, other operating modes are briefly described such as the initial acquisition mode, and a coarse back-up mode that uses thrusters to provide the control torque.

Correction to "Computer-aided design optimization of FDM-FM communication systems"

Equations (10) and (12) of the above-named article are corrected. the original article appears in ibid., vol. COM-17, pp. 403-412, June 1969.

Computer-Aided Design Optimization of FDM-FM Communication Systems

A technique to determine the optimal design of an FDM-FM communications link considering both dollar cost and system performance is established. The four major items of a communications system, transmitter, receiver, transmitting antenna, and receiving antenna, are considered to be stages of a serial-multistage system with the signal-to-noise power ratio as a final boundary value and threshold as a constraint. For eyery combination of the four equipment items, an rms channel modulation index is computed, which for median performance and the system constraint minimizes the required received carrier power. The cost of those combinations of equipment meeting or exceeding the system requirements are computed and compared. Single variable search optimization techniques are used. Rigorous rapid design of analog communications systems is provided. The least cost system and other selected qualifying systems are explicitly determined.