DRUM :: Browsing by Author "Azarm, Shapour"

Browsing by Author "Azarm, Shapour"

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An Approach for Building a Rule-Based System for Design Optimization.
(1986) Azarm, Shapour; Pecht, M.; ISR
A strategy for design optimization for nonlinearly constrained problems is presented. The strategy combines techniques used in production rule systems with an optimization procedure dealing with local monotonicity and sequential quadratic programming techniques. The rule system is based on observations obtained by applying the optimization procedure to different classes of test problems. The observations made may be incorporated in a rule- based system in such a way that if its premise is true, then the action part of the rule is concluded. This is the first step at developing such a rule-based system for design optimization.
An Approach for Building a Rule-Based System for Design Optimization.
(1985) Azarm, Shapour; Pecht, M.; ISR
A strategy for design optimization of nonlinearly constrained problems is presented. The strategy combines techniques used in production rule systems with an optimization procedure dealing with local monotonicity and sequential quadratic programming techniques. The rule system is based on observations obtained by applying the optimization procedure to different classes of test problems. The observations made may be incorporated in a rule- based system in such a way that if its premise is true, then the action part of the rule is concluded. This is the first step at developing such a rule-based system for design optimization.
Design of a Crank-and-Rocker Driven Pantograph: A Leg Mechanism for the University of Maryland's 1991 Walking Robot
(1991) Williams, R.P.; Tsai, L-W.; Azarm, Shapour; ISR
The National Aeronautics and Space Administration has been funding university research into flexible, six-legged walking machines capable of exploring alien terrain. This research has led to a progressive new look at standard four bar mechanisms.
Four bar mechanisms, by definition, consist of a crank link, coupler link, rocker link and fixed (ground) link. The passive role of the coupler link, in traditional four bar mechanisms, can be reversed so that the coupler becomes the transmission link. This is achieved by replacing the coupler with an oblique triangular link. The internal angles of the modified coupler can be varied to create an array of continuous, ovoid paths at the disjointed vertex of the triangle.
Attaching a pantograph mechanism to the modified coupler's trace point amplifiers and translates the ovoid path. The combination of these two mechanisms provides a stable, one degree of freedom walking path which emulates that of humans. This mechanism can therefore be used as a robotic leg.
A second degree of freedom is obtained by attaching an adjacent link to the pantograph mechanism which raises or lowers the walking path without effecting its shape or magnitude. This is used for climbing and maneuvering amidst rugged terrain.
The Design of a Three-Degrees-of-Freedom Walking Machine.
(1989) Tsai, L.W.; Chen, Jie; Azarm, Shapour; ISR
The walking machine presented in this paper consists of six walking legs arranged in a triangular configuration. Each leg may have two modes of operation: an elliptical mode for walking on a flat plane and a circular mode for stair climbing. The six legs are mechanically coupled to a single drive motor through the use of chains and sprockets. the coupling is arranged in such a way that three of the six legs, one from each corner of the triangle, are always in phase while the other three are 180 degrees out of phase. When walking, three of the six legs are always on the ground propelling the machine forward, while the other three are in the air in an opposing position rotating forward. Turning is achieved through the use of a two degres-of-freedom mechanism. Through the use of a prismatic joint, the body of the machine can be lifted up-anddown, and through the use of a revolute pint, it can be rotated to any desirable orientation. The result is a simple, three degrees of freedom, walking machine that is capable of walking on a flat plane and performing some limited stair climbing. Because of the simple construction, the control system is also extremely simple and fast locomotion may be achieved for a small sacrifice of flexibility.
Design Optimization of Spur Gear Sets.
(1986) Azarm, Shapour; Hassan, S.S.; ISR
Design optimization problems are typically characterized by a large number of inequality constraints, many of them satisfied as equalities at the optimum. To take advantage of this tact, we have used an augmented Lagrangian approach together with monotonicity analysis to optimize the design of spur gear sets. Two examples are included: namely, minimizing the pinion diameter of a gear set and minimizing the weight of a gear reducer.
Distributed Task Allocation Algorithms for Multi-Agent Systems with Very Low Communication
(IEEE, 2022-11-23) Bapat, Akshay; Bora, Bharath Reddy; Herrmann, Jeffrey W.; Azarm, Shapour; Xu, Huan; Otte, Michael W.
In this paper we explore the problem of task allocation when communication is very low, e.g., when the probability of a successful message between agents is ≪0.01 . Such situations may occur when agents choose not to communicate for reasons of stealth or when agent-to-agent communication is actively jammed by an adversary. In such cases, agents may need to divide tasks without knowing the locations of each other. Given the assumption that agents know the total number of agents in the workspace, we investigate solutions that ensure all tasks are eventually completed—even if some of the agents are destroyed. We present two task allocation algorithms that assume communication may not happen, but that benefit whenever communications are successful. (1) The Spatial Division Playbook Algorithm divides task among agents based on an area decomposition. (2) The Traveling Salesman Playbook Algorithm considers mission travel distance by leveraging Christofides’ 3/2 approximation algorithm. These algorithms have task completion runtime complexity of O(mlogm) and O(m3) , respectively, where m refers to the total number of tasks. We compare both algorithms to four state-of-the-art task allocation algorithms — ACBBA, DHBA, PIA and GA — across multiple communication levels and multiple numbers of targets, and using three different communication models. The new algorithms perform favorably, in terms of the time required to ensure all targets are visited, in the special case when communication is very low.
An Experimental versus Numerical Shape Optimization Method.
(1988) Azarm, Shapour; Bhandarkar, Sarvotham M.; Durelli, A.J.; ISR
This paper describes and compares an experimental and a numerical method for shape optimization of continuum structures. The experimental method is based on a systematic application of photoelasticity. The numerical method is based on coupling of a finite element analysis and an optimization method. The paper demonstrates the importance of designer's interaction during the shape optimization process. The discussion is made taking shape optimization of a hole in a tall beam as an example.
Heuristic Optimization of Rough-Mill Yield with Production Priorities
(1990) Azarm, Shapour; Harhalakis, George; Srinivasan, M.; Statton, P., Jr.; ISR
Efficient lumber utilization at the saw has become a key issue in the woodworking industry. This is because of shrinking supply and increasing raw material prices. In this paper, formulation of the cross-cut first method of cutting defects out of lumber, as a one-dimensional stock cutting problem is discussed. A Monte-Carlo simulation method has been used for generating boards of a given grade. This simulation greatly aids in comparing alternate solution procedures proposed in the paper. To facilitate real- time application, a fast heuristic for the digital computer is introduced. This is followed by a discussion of cutting length priority allocation. The heuristic solution is compared with the optimal solution obtained using Kolesar's knapsack algorithm.
Monotonicity-Based Decomposition Methods for Design Optimization.
(1988) Azarm, Shapour; Li, Wei-Chu; ISR
This paper describes applications of global and local monotonicity analysis within a decomposition framework. We present a general formulation and solution procedure, based on a bottom-level global monotoncity analysis, for a design optimization problem which is decomposed into three levels of subproblems. We then perform an optimality test to prove that the optimality conditions for the decomposed subproblems will form the optimality conditions of the overall problem. Furthermore, applications of a two-level decomposition method is presented in which an overall global monotonicity analysis or first-level local monotonicity analysis is performed. Well-known examples illustrate applications of the methods.
Multi-Level Design Optimization Using Global Monotonicity.
(1988) Azarm, Shapour; Li, Wei-Chu; ISR
This paper describes application of global monotonicity analysis within a multi-level design optimization framework. We present a general formulation and solution procedure, based on a bottom- level global monotonicity analysis, for a design optimization problem which is decomposed into three levels of subproblems. A well known gear reducer example illustrates application of the method.
Multiobjective Optimization of a Leg Mechanism with Various Spring Configurations for Force Reduction
(1996) Shieh, W-B.; Azarm, Shapour; Tsai, L-W.; Tits, A.L.; ISR
In this paper, the design of a two degree-of-freedom leg mechanism is accomplished by a two-stage optimization process. In the first stage, leg dimensions are optimized with respect to three design objectives: minimize (i) leg size, (ii) vertical actuating force, and (iii) peak crank torque for an entire walking cycle. Following the optimization of leg dimensions, in the second stage, spring elements with various placement configurations are considered for further reduction of the actuating force and crank torque. Several tradeoff solutions are obtained and a comparison between variously spring configurations is made. It is shown that the inclusion of spring elements can significantly reduce the actuating force and crank torque.
A New Class of Six-Bar Mechanisms with Symmetrical Coupler Curves
(1996) Shieh, W-B.; Azarm, Shapour; Tsai, L-W.; Tits, A.L.; ISR
A new class of six-bar mechanisms with symmetrical coupler-point curves is presented. This class of mechanisms is made up of a four-bar linkage with an additional dyad to form an embedded regular or skew pantograph. Because the coupler curve generated at an output point is amplified from that of a four-bar, a compact mechanism with a relatively large coupler curve can be obtained. In addition, due to their structure arrangement, the analysis and synthesis of such mechanisms can be easily achieved. It is shown that the admissible range of transmission angle for such mechanisms is smaller than that of a four-bar mechanism. It is also shown that mechanisms with an embedded skew pantograph exhibit better design flexibility than those with an embedded regular pantograph. Finally, an example mechanism from this class is illustrated and compared with a four-bar linkage with the same coupler curve.
Optimal Design Using a Two-Level Monotonicity-Based Decomposition Method.
(1987) Azarm, Shapour; Li, Wei-Chu; ISR
In this paper, a two-level decomposition method for optimal design is described. Using this method, an optimal design problem is decomposed into several subproblems in the first-level and a coordinating problem in the second-level. In the first level, the subproblems are analyzed using the global monotonicity concepts, then in the second level the analyses of the subproblems are coordinated to obtain the optimal solution. Two engineering design examples, namely a gear reducer (formulated and solved in the literature) and a flywheel (formulated and solved here), illustrate applications of the developed method.
Optimal Design Using Decomposition Methods.
(1986) Azarm, Shapour; Li, Wei-Chu; ISR
In this paper, a unified review of eight decomposition methods is presented. A two-level decomposition method is proposed, which is an extension of feasible model coordination methods. The method couples the global monotonicity analysis of the first- level subproblem(s) with an optimization method (single-level method) of the second-level. Three classes of problems are considered where in the first-level they have (1) one subproblem with one local variable, (2) several subproblems with one local variable, and (3) several subproblems with several local variables. Some test results have been presented which show the substantially improved performance of the proposed approach over a single-level optimization method.
Optimality and Constrained Derivatives in Two-Level Design Optimization.
(1989) Azarm, Shapour; Li, Wei-Chu; ISR
The objective of this paper is twofold. First, an optimality test is presented to show that the optimality conditions for a two- level design optimization problem before and after its decomposition are the same. Second, based on identification of active constraints and exploitation of problem structure, a simple approach for calculating the gradient of a "second-level" problem is presented. This gradient is an important piece of information which is needed for solution of two-level design optimization problems. Three examples are given to demonstrate applications of the approach.
Optimization of Injection Molding Operational Conditions
(1987) Pandelidis, I.; Smith, T.; Azarm, Shapour; Gupta, Sonjai K.; ISR
A major goal of the injection molding process is to produce complex parts to a relatively high degree of accuracy. To do this, one must be able to control the warpage that often occurs in injection molded products. We have developed a methodology to minimize product deformation. Pressure and temperature distributions obtained from flow simulation software are used as an indirect measure of the quality of the molded product. Optimization theory is then used to determine the optimal molding conditions to minimize product deformation.
Optimized Hole Shapes in a Tall Beam.
(1988) Durelli, A.J.; Azarm, Shapour; Bhandarkar, Sarvotham M.; ISR
This paper follows a recent paper in Experimental Mechanics, also dealing with optimization. The objectives besides the attempt at optimizations of the design of in-plane loaded tall beams are 1) to discuss the properties of some of the designs Obtained; and 2) to compare and evaluate experimental and numerical methods. The optimal hole shape introduced in the beam decreases its weight, has an approximately uniform tangential stress along its boundary and does not increase the maximum tensile stress present originally in the solid beam. The numerical method used is based on finite element analysis and non-linear programming. The experimental method is based on photoelasticity. Emphasis is placed on the results obtained rather than on the description of the methodologies. Practical difficulties, assumptions, accuracy, and the applicability of the two methods are also discussed.
Optimized Redundancy Allocation for Electronic Equipment.
(1987) Pecht, M.G.; Azarm, Shapour; Praharaj, S.Y.; ISR
This paper describes a methodology for optimizing the temperature dependent reliability of electronic equipment using active redundancy, while satisfying an area constraint. The process consists of transforming the objective unreliability function by adding to it a suitable penalty term so as to force the optimum solution to an almost integer" value, and minimizing the transformed objective function by a sequential quadratic programming technique. A sensitivity analysis, which avoids "perturb-and-reoptimize" methods, is then conducted to show how an incremental change in an input parameter affects the optimum solution.
Towards Intelligent Design Optimization.
(1985) Azarm, Shapour; Pecht, M.; ISR
A strategy for design optimization of nonlinearly constrained problems is presented. The strategy combines techniques used in production rule systems with an optimization procedure dealing with local monotonicity and with sequential quadratic programming techniques. The production rule system is based on the observations obtained by applying the optimization program to different classes of test problems. The observations made are incorporated in the rule-based system in such a way that if its premise is true, then the action part of the rule is concluded. This is the first attempt at developing such a microcomputer rule-based system for design optimization.
Walking Robot (Terrapin 1).
(1987) Azarm, Shapour; Chen, R.J.; Tsai, L.W.; ISR
The University of Maryland's entry to the walking robot competition is composed of three parts: body, leg, and control. The body is a tripod design in which one of the two sets of three legs is always on the ground. Each leg is mounted at the corner of one of two triangles which are stacked and able to rotate one relative to the other. The legs are modelled after a pantograph and are driven by "acme" screws in both the horizontal and vertical directions. The robot is controlled by a system that employs both integrated circuits with pulse-width modulation and "class-b" transistors, amplifiers, and relays.

Browsing by Author "Azarm, Shapour"

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