• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.241-243
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• 1998

This paper describes a new method for the faster shape optimization of the electromagnetic devices. In a conventional iterative method of shape design optimization using design sensitivity based on a finite element method, meshes for a new shape of the model are generated and a discretized system equation is solved using the meshes in each iteration. They cause much design time. To save this time, a polynomial approximation of the finite element solution with respect to the geometric design parameters using Taylor expansion is constructed. This approximate state variable expressed explicitly in terms of design parameters is employed in a gradient-based optimization method. The proposed method is applied to the shape design of quadrupole magnet.

• Journal of Korean Association for Spatial Structures
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• v.19 no.1
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• pp.109-116
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• 2019

In this paper, the shape adjustment algorithm of the spoked wheel cable structures with retractable membrane system is studied. The initial tension of the membrane or cable is necessary to form the structure and its value is determined by the design shape. However, due to internal and external environmental influences, its shape may be different from the initial designed shape. In the case of the cable structures covered in this study, tension adjustment is necessary to maintain the designed shape because it influences the tension of the cable depending on the state of the retractable membrane. Therefore, we proposed an adjustment algorithm of an initial shape based on the force method. The effectiveness and validity of the methodology were examined through the applicable cable structures. The results of the shape adjustment analysis of the symmetric spoked wheel cable model were reliable and accurate results were obtained.

• Journal of computational fluids engineering
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• v.11 no.1 s.32
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• pp.57-66
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• 2006

An optimal shape design approach is presented for a subsonic S-shaped intake using aerodynamic sensitivity analysis. Two-equation turbulence model is employed to capture strong counter vortices in the S-shaped duct more precisely. Sensitivity analysis is performed for the three-dimensional Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method For code validation, the result of the flow solver is compared with experiment data and other computational results of bench marking test. To study the influence oj turbulence models and grid refinement on the duct flow analysis, the results from several turbulence models are compared with one another and the minimum number of grid points, which can yield an accurate solution is investigated The adjoint variable code is validated by comparing the complex step derivative results. To realize a sufficient and flexible design space, NURBS equations are introduced as a geometric representation and a new grid modification technique, Least Square NURBS Grid Approximation is applied With the verified flow solver, the sensitivity analysis code and the geometric modification technique, the optimization of S-shaped intake is carried out and the enhancement of overall intake performance is achieved The designed S-shaped duct is tested in several off-design conditions to confirm the robustness of the current design approach. As a result, the capability and the efficiency of the present design tools are successfully demonstrated in three-dimensional highly turbulent internal flow design and off-design conditions.

• Journal of Ocean Engineering and Technology
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• v.26 no.6
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• pp.66-73
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• 2012

A pressure compensated chamber of a pilot mining robot isolates and protects an electrical-electronic system from the ambient highly pressured water. Since the inner pressure of the chamber is compensated with outer water pressure using hydraulic oil and pressure compensator, there exists a pressure difference, less than 1 bar, between outer and inner surface. The structural safety of the chamber is obtained relatively easier than the canister type which inner pressure is kept as the atmospheric pressure. However, due to the adoption of box shape for space efficiency and usage of the transparent engineering plastic viewport for checking inner circumstance, the viewport can be largely deformed. This large deformation can cause an additional tensile force, called the prying force, to the bolt-flange connection parts of the viewport. In this paper, we suggest the structural design equation considering the prying action for designing the structure of a box-shape pressure compensated chamber.

• Smart Structures and Systems
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• v.24 no.3
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• pp.361-377
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• 2019

The stiffness of shape memory alloy (SMA) spring while in actuation is represented by an empirical model that is derived from the logistic differential equation. This model correlates the stiffness to the alloy temperature and the functionality of SMA spring as active variable stiffness actuator (VSA) is analyzed based on factors that are the input conditions (activation current, duty cycle and excitation frequency) and operating conditions (pre-stress and mechanical connection). The model parameters are estimated by adopting the nonlinear least square method, henceforth, the model is validated experimentally. The average correlation factor of 0.95 between the model response and experimental results validates the proposed model. In furtherance, the justification is augmented from the comparison with existing stiffness models (logistic curve model and polynomial model). The important distinction from several observations regarding the comparison of the model prediction with the experimental states that it is more superior, flexible and adaptable than the existing. The nature of stiffness variation in the SMA spring is assessed also from the Dynamic Mechanical Thermal Analysis (DMTA), which as well proves the proposal. This model advances the ability to use SMA integrated mechanism for enhanced variable stiffness actuation. The investigation proves that the stiffness of SMA spring may be altered under controlled conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.2
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• pp.107-115
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• 1999

In order to develop a convenient method for the estimation of transport distance of settling stones in quiescent water or flowing water, introduced was the simple but relatively accurate equation of drag coefficient. The equation of drag coefficient introduced was confirmed to give relatively accurate evaluation for the drag force of smooth-surface sphere, and the effects of surface roughness and shape can be considered by adjusting empirical parameters. A theoretical equation has been developed for the settling velocity or settling distance of smooth-surface sphere in quiescent fluid, and the computation results have been obtained by adjusting the empirical parameter for the settling distance of stone in quiescent water. The 2nd order ordinary differential equation has been developed for the case of settling stones in flowing fluid, and a numerical model has been developed by using Runge-Kutta method for its solution. A number of cases have been tested by adjusting the empirical parameter.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.401-402
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• 2007

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.833-839
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• 2013

In this study, an experiment was performed to monitor the two-dimensional shape of a cantilever composite structure using fiber Bragg grating (FBG) sensors. To monitor the shape of a composite structure, a deflection equation developed by NASA was applied and a composite beam attached to three FBG sensors was used. In the experiment, the shape of the composite beam was successfully estimated and an error was evaluated by comparing a real deflection. The error increased with real deflection; therefore, it was compensated by using the linear relationship between the error and the real deflection. After compensating the error, the measured deflection shows good agreement with the real deflection. Finally, the experiment shows that the FBG sensor and the deflection equation are suitable for monitoring the deflection curve of the beam structure with compensation of the error.

• Steel and Composite Structures
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• v.21 no.5
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• pp.1157-1182
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• 2016

A newly puzzle shape of crestbond rib shear connector is a type of ductile perfobond rib shear connector. This shear connector has some advantages, including relatively easy rebar installation and cutting, as well as the higher shear resistance strength. Thus, this study proposed a newly puzzle shape of crestbond rib with a "${\mho}$" shape, and its shear resistance behaviors and shear strengths were examined using push-out tests. Five main parameters were considered in the push-out specimens to evaluate the effects of shear resistance parameters such as the dimensions of the crestbond rib, transverse rebars in the crestbond dowel, concrete strength, rebar strength, and dowel action on the shear strength. The shear loading test results were used to compare the changes in the shear behaviors, failure modes, and shear strengths. It was found that the concrete strength and number of transverse rebars in the crestbond rib were significantly related to its shear resistance. After the initial bearing resistance behavior of the concrete dowel, a relative slip occurred in all the specimens. However, its rigid behavior to shear loading decreased the ductility of the shear connection. The cross-sectional area of the crestbond rib was also shown to have a minor effect on the shear resistance of the crestbond rib shear connector. The failure mechanism of the crestbond rib shear connector was complex, and included compression, shear, and tension. As a failure mode, a crack was initiated in the middle of the concrete slab in a vertical direction, and propagated with increasing shear load. Then, horizontal cracks occurred and propagated to the front and rear faces of the specimens. Based on the results of this study, a design shear strength equation was proposed and compared with previously suggested equations.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.2
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• pp.169-173
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• 2010

Because of power consumption increase, global warming, and limitation of installation, not only high reliability and interruption capability but also compact and light power apparatuses are needed. In this paper, E field calculation and experiment were processed to identify the influence of the shape of end shield and gap distance. It is expected that the results of FEM simulation and experiments could be the basic data to develop VI. the results of FEM simulation and experiments are as following. Firstly, maximum E fields were compared by means of finite element method as a function of the shape of end shield. 3 types of models were used to analyze maximum E field of each model and the influence of shape of shield could be identified. As a result, proposed L type shield could reduce the maximum E field by 20%. Secondly, the influence of the gap distance between end shields on E field was analyzed. As the gap distance become short the gap distance between inner walls of ceramic also become short. And the maximum E field concentrated on inner wall of ceramic finally increased. Thirdly, the experiment was conducted by fabricating each prototype. As a result, no creepage occurred in shieldless model. In other words, creepage occurred in the shield-installed models. And creepage inception voltages were different from each other because of the difference of maximum E field. Fourthly, The equation that shows relation between calculated E field and measured creepage inception voltage was proposed as a result of FEM analysis and experiment. It is concluded that when designing VI this equation could be important data to reduce time and cost by identifying indirectly the optimal gap distance and the shape of shield required to prevent creepage.