• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.574-582
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• 1999

This paper discusses the multi-level optimization method in dynamic optimization problems through stiffened plate of ship structures. In structural optimization the computational cost increases rapidly as the number of design variables increases. And we need a great amount of cal-culation and time on problems of modified dynamic characteristics of large and complicated struc-tures. In this paper the multi-level optimization is proposed which decreases computational time and cost. the dynamic optimum designs of stiffened plate that control the natural frequency and minimize weight subjected to constraints condition are derived. The way to apply the multi-level optimization methods in this study follow: In the first step the dynamic characteristics is controlled for the two-dimensional model of stiffened plate by sensitivity analysis and quasi-least squares methods. In the second step the cross-section of the stiffener is decided so that the weight is minimized under needed constraints by the steepest descent or ascent method. In the third the three-dimensional model is made based on the results of the first step and the second step confirmation and finer tuning of the objective function are carried out. It is shown that the results are effective in the optimum modification for dynamic characteristics of the stiffened plate.

• Journal of Welding and Joining
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• v.15 no.4
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• pp.63-69
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• 1997

Welding distortion is more serious problem than any other problems caused by welding process, especially, in the heavy-industrial place. These welding distortions are caused by nonuniform heating and cooling of metal during and after welding operations. And these distortion quantities are must be known to worker in production line because distorions are important role in assembling part. Therefore an analytical model to explain and predict the welding distortion are needed. A numerical analysis of welding distortion which is inelastic behavior of weldment would require the three dimensional calculation. But computing time and memory would be very large, and the resulting cost might be unacceptable. Therefore we use a numerical technique for two dimensional analysis in the section normal to the weld direction of weldment under an assumption of quasi-stationary conditions. But the result of the calculation under two dimensional(plane strain) assumption was not satisfied as compared with experimental result. This paper proposed a technique for analysing the welding angular distortion by using a constraint boundary condition on the two dimensional finite element model. The simulation results revealed that the constraint boundary model could more reasonably describe the welding distortion than the plane strain model did.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.317-328
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• 2018

In this paper, a new refined quasi-three-dimensional (3D) shear deformation theory for the bending analysis of functionally graded plate is presented. The number of unknown functions involved in this theory is only four against five or more in the case of the other shear and normal deformation theories. Due to its quasi-3D nature, the stretching effect is taken into account in the formulation of governing equations. In addition, the effect of different micromechanical models on the bending response of these plates is studied. Various micromechanical models are used to evaluate the mechanical characteristics of the FG plates whose properties vary continuously across the thickness according to a simple power law. The present theory accounts for both shear deformation and thickness stretching effects by a parabolic variation of displacements across the thickness, and the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The problem is solved for a plate simply supported on its edges and the Navier solution is used. The results of the present method are compared with others from the literature where a good agreement has been found. A detailed parametric study is presented to show the effect of different micromechanical models on the flexural response of a simply supported FG plates.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1294-1306
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• 1992

In order to determine the design parameters and processing conditions in injection molding, it is very important to establish the theoretical model with scientific base. In this study, a two dimensional model has been developed for the purpose and flow simulations of filling process are carried out. The moving boundary transient flow problem along the flat plane is solved efficiently by the Iterative Boundary Pressure Reflection Method which rearranges the impinged melt front along the physical boundary in scientific manner. The two dimensional modeling of filling process is applied to two examples : a three dimensional cover with two screw holes and a two-gated flat cavity with unbalanced runners. The numerical results show good agreement with experimental short shots, especially for the weldline locations and the pressure traces at various locations. They also provide the temperature, clamp force, and velocity field in the mold at different times during filling of cavity.

• Journal of Korea Foundry Society
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• v.9 no.1
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• pp.39-48
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• 1989

A basic three dimensional thermal model has been developed to simulate the solidification sequence for gravity die casting process. The finite difference method was used to analyze the solidification process during all the casting cycles. The prediction of die temperature in the quasi-steady state was analyzed by the boundary element method. The influence of die cooling on the heat flow in the cast/mold system was also investigated. Predictions of the computer simulation on temperature profiles and location of shrinkage defects were in good agreement with those observed in experimental die castings. Models of computer simulation which is developed by this work can be useful for the design and process control of die casting.

• International Journal of Fluid Machinery and Systems
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• v.6 no.1
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• pp.18-24
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• 2013

In order to apply the design method of diagonal flow fan based on axial flow design to the design of radial-outflow type diagonal flow fan which has lower specific speed of 600-700 [$min^{-1}$, $m^3/min$, m], radial-outflow type diagonal flow fan which specific speed was 670 [$min^{-1}$, $m^3/min$, m] was designed by a quasi three-dimensional design method. Experimental investigations were conducted by fan characteristics test, flow surveys by a five-hole probe and a hot wire probe. Fan characteristics test agreed well with the design values. In the flow survey at rotor outlet, the characteristic region was observed. Two flow phenomena are considered as the cause of the characteristic region, one is tip leakage vortex near rotor tip and another is pressure surface separation on the rotor blade.

• Steel and Composite Structures
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• v.32 no.1
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• pp.37-57
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• 2019

This paper presents experimental and analytical studies to evaluate the cyclic behaviour of Circular Reinforced Concrete column Steel beam (CRCS) connections. Two 3/4-scale CRCS specimens are tested under quasi-static reversed cyclic loading. Specimens were strengthened with a tube plate (TP) and a steel doubler plate (SDP). Furthermore; nine interior beam-through type RCS connections are simulated using nonlinear three-dimensional finite element method using ABAQUS software and are verified with experimental results. The results revealed that using the TP improves the performance of the panel zone by providing better confinement to the concrete. Utilizing the TP at the panel zone may absorb and distribute stress in this region. Results demonstrate that TP can be used instead of SDP. Test records indicate that specimens with TP, with and without SDP maintained their maximum strength up to 4% drift angle, satisfying the recommendation given by AISC341-2016 for composite special moment-resisting frames.

• Structural Engineering and Mechanics
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• v.85 no.4
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• pp.485-500
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• 2023

The non-linear static analysis of reinforced concrete (RC) structures using the three-dimensional (3D) finite element method is a time-consuming and challenging task. Moreover, this type of analysis encounters numerical problems such as the lack of convergence of results in the stages of growth and propagation of cracks in the structure. The time integration analysis along with the mass scaling (MS) technique is usually used to overcome these limitations. Despite the use of this method in the 3D finite element analysis of RC structures, a comprehensive study has not been conducted so far to assess the effects of the MS method on the accuracy of results. This study aims to evaluate the accuracy of the MS method in the non-linear quasi-static finite element analysis of RC structures. To this aim, different types of RC structures were simulated using the finite element approach based on the implicit time integration method and the mass scaling technique. The influences of effective parameters of the MS method (i.e., the allowable values of increase in the mass of the RC structure, the relationship between the duration of the applied load and fundamental vibration period of the RC structure, and the pattern of applied loads) on the accuracy of the simulated results were investigated. The accuracy of numerical simulation results has been evaluated through comparison with existing experimental data. The results of this study show that the achievement of accurate structural responses in the implicit time integration analyses using the MS method involves the appropriate selection of the effective parameters of the MS method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2585-2596
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• 1994

Many particle filled materials like Poweder/Binder mixtures for poweder injection moldings, have complicated rheological behaviors such as an yield stress and slip phenomena. In the present study, numerical simulation programs via a finite element method and a finite difference method were developed for the quasi-three-dimensional flows and the two-dimensional flow models, respectively, with the slip phenomena taken into account in terms of a slip velocity. In order to qualitatively understand the slip effects, typical numerical results such as vector plots, pressure contours in the cross-channel plane, and isovelocity controus for the down-channel direction were discussed with respect to various slip coefficients. Slip velocities along the boudary surfaces were also investigated to find the effects of the slip coefficient and processing conditions on the overall flow behavior. Based on extensive numerical calculations varying the slip coefficients, pressure gradient, aspect ratio, and power law index, the screw characteristics of the extrusion process were studied in particular with comparisons between the slip model and non-slip model.

• Ocean Systems Engineering
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• v.8 no.3
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• pp.329-343
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• 2018

The inclination of seabed profile (sloped seabed) is one of the known topographic features which can be observed at different seabed level in the large offshore basin. A mooring system connected between the platform and global seabed is an integral part of the floating structure which tries to keep the floating platform settled in its own position against hostile sea environment. This paper deals with an investigation of the motion responses of an FPSO platform moored on the sloped seabed under the combined action of wave, wind and current loads. A three-dimensional panel discretization method has been used to model the floating body. To introduce the connection of multi-segmented non-linear elastic catenary mooring cables with the sloped seabed, a quasi-static composite catenary model is employed. The model and analysis have been completed by using hydrodynamic diffraction code AQWA. Validation of the numerical model has been successfully carried out with an experimental work published in the latest literature. The analysis procedure in this study has been followed time domain analysis. The study involves an objective oriented investigation on platform motions, in order to identify the effects of the slopped seabed, the action of the wave, wind and current loads and the presence of riser system. In the end, an effective analysis has been performed to identify a stable mooring model in demand of reducing structural responses of the FPSO.