• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.146-153
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• 2005

In this paper, a multi-step optimization using genetic algorithm with variable penalty function is introduced to the structural design optimization of a grinding machine. The design problem, in this study, is to find out the optimum configuration and dimensions of structural members which minimize the static compliance, the dynamic compliance, and the weight of the machine structure simultaneously under several design constraints such as dimensional constraints, maximum deflection limit, safety criterion, and maximum vibration amplitude limit. The first step is shape optimization, in which the best structural configuration is found by getting rid of structural members that have no contributions to the design objectives from the given initial design configuration. The second and third steps are sizing optimization. The second design step gives a set of good design solutions having higher fitness for lightweight and minimum static compliance. Finally the best solution, which has minimum dynamic compliance and weight, is extracted from the good solution set. The proposed design optimization method was successfully applied to the structural design optimization of a grinding machine. After optimization, both static and dynamic compliances are reduced more than 58.4% compared with the initial design, which was designed empirically by experienced engineers. Moreover the weight of the optimized structure are also slightly reduced than before.

• Journal of Ocean Engineering and Technology
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• v.17 no.5 s.54
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• pp.57-65
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• 2003

This paper proposes an optimum design method of structural and control systems, using a 2-D truss structure as an example. The structure is subjected to initial static loads and disturbances. For the structure, a FEM model is formed. Using modal transformation, the equation of motion is transformed into modal coordinates, in order to decrease D.O.F. of the FEM model. To suppress the effect of the disturbances, the structure is controlled by an output feedback $H_{\infty}$ controller. The design variables of the combined optimal design of the control-structure systems are the cross sectional areas of truss members. The structural objective function is the structural weight. The control objective function is the $H_{\infty}$ norm, the performance index of control. The second structural objective function is the energy of the response related to the initial state, which is derived from the time integration of the quadratic form of the state in the closed-loop system. In a numerical example, simulations have been perform. Through the consideration of structural weight and $H_{\infty}$ norm, an advantage of the combined optimum design of structural and control systems is shown. Moreover, since the performance index of control is almost nearly optimiz, we can acquire better design of structural strength.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.6 no.1
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• pp.60-68
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• 2003

This paper proposes an optimum design method of structural and control systems, using a 2-D truss structure as an example. The structure is subjected to initial static loads and disturbances. For the structure, a FEM model is formed. Using modal transformation, the equation of motion is transformed into modal coordinates, in order to decrease D.O.F. of the FEM model. To suppress the effect of the disturbances, the structure is controlled by an output feedback $H_{\infty}$ controller. The design variables of the combined optimal design of the control-structure systems are the cross sectional areas of truss members. The structural objective function is the structural weight. The control objective function is the $H_{\infty}$ norm, the performance index of control. The second structural objective function is the energy of the response related to the initial state, which is derived from the time integration of the quadratic form of the state in the closed-loop system. In a numerical example, simulations have been perform. Through the consideration of structural weight and $H_{\infty}$ norm, an advantage of the combined optimum design of structural and control systems is shown. Moreover, since the performance index of control is almost nearly optimiz, we can acquire better design of structural strength.

• Special Issue of the Society of Naval Architects of Korea
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• 2009.09a
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• pp.47-51
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• 2009

It is well known that a rudder is influential devices to help ship maintain its stable performances, such as a course-keeping and maneuverability. In the procedures of a commercial ship design proper rudder dimensions (area and shape) ensuring better ship maneuverability have been settled in an initial concept design stage performed by a preceding department, without little structural consideration. It is true that there are time discrepancy between an initial design and a structural analysis stage. Therefore structural analysis results would sometimes cause a rudder to modify its dimensions. Most of these cases, however, ship design and performance tests had been finished. In this matter, only limited modifications of redder could be carried out. Besides, these could also cause bad effects on productivity. Finally, it is necessary to develop a new program considering co-relationship between an initial rudder design and a following work, a structural strength analysis, in order to enhance productivity and minimize a rate of redesign procedures.

• Journal of Ocean Engineering and Technology
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• v.23 no.2
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• pp.104-109
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• 2009

In the view of the importance of material reduction due to the jump in oil and steel prices, an optimized structural system for lifting lugs was developed. Such a system is needed hundreds of thousands of times a year. A direct design process was added to this developed optimized system to increase the design efficiency and provide a way of directly inserting a designer's decisions into the design system process. In order to verify the system efficiency and convenience, several new prototype lug shapes were suggested using the developed system. From these research results, it was found that the slope of the main plate of the lug structure has a tendency to move from about 45 degrees to about 60 degrees and the design weight was reduced from an initial value of about 32kgf to about $15{\sim}19kg_f$ after the redesign. Based on these initial research results, an efficient reduction in steel weight was expected considering the enormous consumption of lug structures per year. Additionally, a more detail structural analysis through local strength evaluations will be performed to verify the efficiency of the optimum structural design for a lug structure.

• Structural Engineering and Mechanics
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• v.29 no.5
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• pp.469-488
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• 2008

Finite element methods have often been used for structural analyses of various mechanical problems. When finite element analyses are utilized to resolve mechanical systems, numerical uncertainties in the initial data such as structural parameters and loading conditions may result in uncertainties in the structural responses. Therefore the initial data have to be as accurate as possible in order to obtain reliable structural analysis results. The typical finite element method may not properly represent discrete systems when using uncertain data, since all input data of material properties and applied loads are defined by nominal values. An interval finite element analysis, which uses the interval arithmetic as introduced by Moore (1966) is proposed as a non-stochastic method in this study and serves a new numerical tool for evaluating the uncertainties of the initial data in structural analyses. According to this method, the element stiffness matrix includes interval terms of the lower and upper bounds of the structural parameters, and interval change functions are devised. Numerical uncertainties in the initial data are described as a tolerance error and tree graphs of uncertain data are constructed by numerical uncertainty combinations of each parameter. The structural responses calculated by all uncertainty cases can be easily estimated so that structural safety can be included in the design. Numerical applications of truss and frame structures demonstrate the efficiency of the present method with respect to numerical analyses of structural uncertainties.

• Journal of Power System Engineering
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• v.7 no.4
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• pp.38-43
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• 2003

This paper proposes an optimum design problem of structural and control systems. taking a 3-D truss structure as an example. The structure is supposed to be subjected to initial static loads and time-varying disturbances. The structure is controlled by a state feedback $H_{\infty}$ controller to suppress the effect of the disturbances. The design variables are the cross sectional areas of truss members. The structural objective function is the structural weight. As the control objective, we consider two types of performance indices. The first function represents the effect of the initial loads. The second one is the norm of the feedback gain. These objective functions are in conflict with each other. Then, first, two control objective functions are transformed into one control objective by the weighting method. Next, the structural objective is treated as the constraint. By introducing the second control objective which considers the magnitude of the feedback gain, we can per limn the design which is robust in modeling errors.

• Journal of Ocean Engineering and Technology
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• v.17 no.4
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• pp.66-72
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• 2003

This paper proposes an optimum, problematic design for structural and control systems, taking a 3-D truss structure as an example. The structure is subjected to initial static loads and time-varying disturbances. The structure is controlled by a state feedback H$_{\infty}$ controller which suppress the effects of disturbances. The design variables are the cross sectional areas of truss members. The structural objective function is the structural weight. For the control objective, we consider two types of performance indices, The first function represents the effect of the initial loads. The second function is the norm of the feedback gain, These objective functions are in conflict with each other but are transformed into one control objective by the weighting method. The structural objectives is treated as the constraint, By introducing the second control objective which considers the magnitude of the feedback gain, we can create a design to model errors.

• Journal of Ocean Engineering and Technology
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• v.28 no.2
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• pp.147-151
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• 2014

This research presents a method for the initial structural design of a multi-megawatt wind turbine blade. The structural data for a 2-MW blade were applied as the blade structural characteristic data of the reference blade. Tenkinds of blade models were newly designed by replacing the spar cap axial GRRP with a GFRP and CFRP These terms should be defined. at different orientations. The axial stiffness coefficients of the newly designed models were made equal to the coefficient of the reference blade. The required numbers of layers in each section of blades were calculated, and the lay-up designs were based on these numbers. Verification results showed that the design method that used the structural data of the reference blade was appropriate for the initial structural design of a wind turbine blade.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.6
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• pp.521-526
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• 2018

The doubler plate design system for the reinforcement of the ship plate members was developed considering various loads that subjected to the in-plane biaxial load, the in-plane shear load and out-of-plane load. The author summarized the accuracy of the development formula and equations through the equivalent plate thickness concept and finally introduced the new design system of doubler plate reinforcement. Through this study, it can be considered as an initial design guideline based on ship doubler plate reinforcement strength at areas without repeated load, or an initial structure analysis model for final structural design.