Velusamy Subramaniam | National University of Singapore (original) (raw)

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Papers by Velusamy Subramaniam

Dynamics and Control, 2000

In this paper, a new guidancelaw known as the all-aspect proportional navigation (AAPN) guidancel... more In this paper, a new guidancelaw known as the all-aspect proportional navigation (AAPN) guidancelaw is formulated. AAPN is a modification of traditional proportionalnavigation, with an additional term added to improve performanceat large heading error angles. The missile guidance problem isfirst formulated as an optimal control problem and solved usinga combined genetic algorithm-shooting method. The problem isrepeatedly solved at various heading error angles. By employingChebychev polynomial fitting, we can then determine the parametersof the AAPN. Subsequently, AAPN is compared against the proportionalnavigation guidance law as well as the optimal solution. Theresults clearly show that AAPN outperforms PN at large headingerror angles. Also, its performance is only slightly inferiorto the optimal solution.

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International Journal of Systems Science, 2000

In this paper, an alternative method for solving optimal control problems is presented. By applyi... more In this paper, an alternative method for solving optimal control problems is presented. By applying calculus of variations, the optimal control problem can be reduced to solving a two-point boundary value problem. Here, the solution is generated with a combination of two methods genetic algorithms (GA) and the shooting method. An estimate of the optimal solution is first obtained using GA. This solution is in turn used as the initial guess for the shooting method. This combined method is applied to an optimal missile guidance problem. The performances of the combined method and GA are evaluated by simulation and compared. The results clearly show that the proposed combined method is able to locate the optimal solution more efficiently than GA. The results also show that the combined method never fails to correctly determine the optimal solution. Therefore, it proves to be more robust than the shooting method whose convergence is not always guaranteed.

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Fuel and Energy Abstracts

The phenomena of machine failures, defects, multiple rework loops, etc., results in much difficul... more The phenomena of machine failures, defects, multiple rework loops, etc., results in much difficulty in modeling rework systems, and therefore the performance analysis of such systems has been investigated limitedly in the past. We propose an analytical method for the performance evaluation of rework systems with unreliable machines and finite buffers. To characterize the rework flow in the system, a new 3M1B (three-machine and one-buffer) Markov model is first presented. Unlike previous models, it is capable of representing multiple rework loops, and the rework fraction of each loop is calculated based on the quality of material flow in the system. A decomposition method is then developed for multistage rework systems using the proposed 3M1B model as one of the building blocks. The experimental results demonstrate that the decomposition method provides accurate estimates of performance measures such as throughput and Work-In-Process (WIP). We have applied this method to several problems, such as the determination of the optimal inspection location and the identification of bottleneck machines in rework systems.► We propose an analytical model for manufacturing systems with multiple rework loops. ► We solve problems such as inspection allocation and bottleneck identification. ► Bottlenecks of rework systems migrate differently compared to systems without rework. ► We propose a continuous improvement strategy in the paper.

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Quantity modeling has long been studied separately from quality modeling of production lines. The... more Quantity modeling has long been studied separately from quality modeling of production lines. The quantitative and qualitative objectives are highly coupled, and hence it is desirable to formulate a model to achieve these objectives simultaneously. We therefore propose a two-machine line model known as the machine-buffer-inspection model, that will be used as the building block for the eventual integration of quality and quantity modeling of production lines with assignable cause quality failures. A Markov model with additional quality states is presented for the machine-buffer-inspection system. Unlike traditional models, this machine-buffer-inspection model enables inspection for quality failures, and is capable of approximating both quality and quantity performance measures. Numerical experiments demonstrate that the model provides good accuracy.

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Dynamics and Control, 2000

In this paper, a new guidancelaw known as the all-aspect proportional navigation (AAPN) guidancel... more In this paper, a new guidancelaw known as the all-aspect proportional navigation (AAPN) guidancelaw is formulated. AAPN is a modification of traditional proportionalnavigation, with an additional term added to improve performanceat large heading error angles. The missile guidance problem isfirst formulated as an optimal control problem and solved usinga combined genetic algorithm-shooting method. The problem isrepeatedly solved at various heading error angles. By employingChebychev polynomial fitting, we can then determine the parametersof the AAPN. Subsequently, AAPN is compared against the proportionalnavigation guidance law as well as the optimal solution. Theresults clearly show that AAPN outperforms PN at large headingerror angles. Also, its performance is only slightly inferiorto the optimal solution.

Bookmarks Related papers MentionsView impact

International Journal of Systems Science, 2000

In this paper, an alternative method for solving optimal control problems is presented. By applyi... more In this paper, an alternative method for solving optimal control problems is presented. By applying calculus of variations, the optimal control problem can be reduced to solving a two-point boundary value problem. Here, the solution is generated with a combination of two methods genetic algorithms (GA) and the shooting method. An estimate of the optimal solution is first obtained using GA. This solution is in turn used as the initial guess for the shooting method. This combined method is applied to an optimal missile guidance problem. The performances of the combined method and GA are evaluated by simulation and compared. The results clearly show that the proposed combined method is able to locate the optimal solution more efficiently than GA. The results also show that the combined method never fails to correctly determine the optimal solution. Therefore, it proves to be more robust than the shooting method whose convergence is not always guaranteed.

Bookmarks Related papers MentionsView impact

Fuel and Energy Abstracts

The phenomena of machine failures, defects, multiple rework loops, etc., results in much difficul... more The phenomena of machine failures, defects, multiple rework loops, etc., results in much difficulty in modeling rework systems, and therefore the performance analysis of such systems has been investigated limitedly in the past. We propose an analytical method for the performance evaluation of rework systems with unreliable machines and finite buffers. To characterize the rework flow in the system, a new 3M1B (three-machine and one-buffer) Markov model is first presented. Unlike previous models, it is capable of representing multiple rework loops, and the rework fraction of each loop is calculated based on the quality of material flow in the system. A decomposition method is then developed for multistage rework systems using the proposed 3M1B model as one of the building blocks. The experimental results demonstrate that the decomposition method provides accurate estimates of performance measures such as throughput and Work-In-Process (WIP). We have applied this method to several problems, such as the determination of the optimal inspection location and the identification of bottleneck machines in rework systems.► We propose an analytical model for manufacturing systems with multiple rework loops. ► We solve problems such as inspection allocation and bottleneck identification. ► Bottlenecks of rework systems migrate differently compared to systems without rework. ► We propose a continuous improvement strategy in the paper.

Bookmarks Related papers MentionsView impact

Quantity modeling has long been studied separately from quality modeling of production lines. The... more Quantity modeling has long been studied separately from quality modeling of production lines. The quantitative and qualitative objectives are highly coupled, and hence it is desirable to formulate a model to achieve these objectives simultaneously. We therefore propose a two-machine line model known as the machine-buffer-inspection model, that will be used as the building block for the eventual integration of quality and quantity modeling of production lines with assignable cause quality failures. A Markov model with additional quality states is presented for the machine-buffer-inspection system. Unlike traditional models, this machine-buffer-inspection model enables inspection for quality failures, and is capable of approximating both quality and quantity performance measures. Numerical experiments demonstrate that the model provides good accuracy.

Bookmarks Related papers MentionsView impact