• Wind and Structures
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• v.31 no.3
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• pp.229-240
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• 2020

In the present work, the main features of primary vortices and the vorticity concentrations downstream of vortex bursting in crossflow plane of a delta wing with a sweep angle of Λ=70° were investigated under the variation of the sideslip angles, β. For the pre-review of flow structures, dye visualization was conducted. In connection with a qualitative observation, a quantitative flow analysis was performed by employing Particle Image Velocimetry (PIV). The sideslip angles, β were varied with four different angles, such as 0°, 4°, 12°, and 20° while angles of attack, α were altered between 25° and 35°. This study mainly focused on the instantaneous flow features sequentially located at different crossflow planes such as x/C=0.6, 0.8 and 1.0. As a summary, time-averaged and instantaneous non-uniformity of turbulent flow structures are altered considerably resulting in non-homogeneous delta wing surface loading as a function of the sideslip angle. The vortex bursting location on the windward side of the delta wing advances towards the leading-edge point of the delta wing. The trajectory of the primary vortex on the leeward side slides towards sideways along the span of the delta wing. Besides, the uniformity of the lift coefficient, C_L over the delta wing plane was severely affected due to unbalanced distribution of buffet loading over the same plane caused by the variation of the sideslip angle, β. Consequently, dissimilarities of the leading-edge vortices result in deterioration of the mean value of the lift coefficient, C_L.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.2
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• pp.179-187
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• 2000

When one considers the property of the axisymmetry, an analysis of an axisymmetric shell subjected to unaxisymmetric loading can be employed to save time and computer memory space. If one considers the Fourier series of the circumference direction of loads and displacements, an axisymmetric tank subjected to a nonaxisymmetric load can be treated as a frame element. Using the Fourier series, the authors derived the stiffness matrix of the cylindrical shell subjected to unaxisymmetric loading by the usual finite element method, and converted the stiffness matrix of a frame element into a transfer matrix by rearranging the stiffness matrix to apply the transfer matrix method. Here the most significant purpose of this paper is to achieve the fewest number of simultaneous equations for analysing an axisymmetric shell subjected to a nonaxisymmetric load. The results of the proposed method of the analysis of the cylindrical shell subjected to a wind load and a water load show no differences when compared to the other methods.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.1
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• pp.27-36
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• 2012

The mobile harbor is a new concept system to solve the problems of a port. These problems are that container ships cannot be anchored at the dock because they have become larger or the waiting times of anchoring the ships are increased due to heavy container traffic. A new system is designed to carry out the loading and unloading of containers between the mobile harbor and the container ship using the mobile harbor crane at sea. The crane plays an important role when transferring the containers. In this research, various types of the mobile harbor crane are proposed and structural optimization for each type of the crane is carried out. The loading conditions consider the rolling and pitching conditions of the unstable sea state and the wind force are considered. The constraints are mainly the regulations made by the Korean Register of Shipping. The structure of the crane is optimized to minimize the mass while various constraints are satisfied.

• Journal of the Korean GEO-environmental Society
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• v.23 no.12
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• pp.25-31
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• 2022

Unlike structures installed on land, the structures installed on the offshore ground must consider long-term cyclic loads such as wave loads, wind loads and tidal loads at sea. Therefore, it is important to analyze the behavior of the ground subjected to long-term cyclic loads in order to design a structure installed on the ocean ground. In this paper, cyclic simple shear tests were performed to analyze the ground behavior for long-term cyclic loads according to the confining pressure, and a three-dimensional design failure curve was prepared that can easily check the failure characteristics according to the confining pressure. As a result of the analysis, it was confirmed that the position of the design failure curve is different depending on the confining pressure even under the same conditions of the cyclic shear stress ratio and the average shear stress ratio, and the number of cyclic loads reaching failure is affected by the confining pressure. From the created 3-D design failure curve under different confining pressure, the tendency and approximate value of the design failure curve according to the confining pressure can be estimated.

• Geomechanics and Engineering
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• v.32 no.3
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• pp.255-270
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• 2023

One of the main parameters that affect the design of suction caisson-supported offshore structures is uplift behavior. Pull-out of suction caissons is profoundly utilized as the offshore wind turbine foundations accompany by a tensile resistance that is a function of a complex interaction between the caisson dimensions, geometry, wall roughness, soil type, load history, pull-out rate, and many other parameters. In this paper, a parametric study using a 3-D finite element model (FEM) of a single offshore suction caisson (SOSC) surrounded by saturated soil is performed to examine the effect of some key factors on the tensile resistance of the suction bucket foundation. Among the aforementioned parameters, caisson geometry and uplift loading as well as the difference between the tensile resistance and suction pressure on the behavior of the soil-foundation system including tensile capacity are investigated. For this purpose, a full model including 3-D suction caisson, soil, and soil-structure interaction (SSI) is developed in Abaqus based on the u-p formulation accounting for soil displacement (u) and pore pressure, P.The dynamic responses of foundations are compared and validated with the known results from the literature. The paper has focused on the effect of geometry change of 3-D SOSC to present the soil-structure interaction and the tensile capacity. Different 3-D caisson models such as triangular, pentagonal, hexagonal, and octagonal are employed. It is observed that regardless of the caisson geometry, by increasing the uplift loading rate, the tensile resistance increases. More specifically, it is found that the resistance to pull-out of the cylinder is higher than the other geometries and this geometry is the optimum one for designing caissons.

• Journal of Korean Society of Steel Construction
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• v.18 no.1
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• pp.11-22
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• 2006

Message Signs (VMS) structures offer an increase in traffic safety through their ability to relay massages to motorists for warnings of hazards ahead, traffic congestion, accidents, and lane closings. The geometry of these signs sometimes results in the significant cyclic loading of the supports structure due to wind gusts, which can result from passing trucks or from natural wind. This study presents the results of analytical and experimental investigations of VMS structures. The commercially available softwareGTSTRUDL (2003) was used to perform space-frame structural analyses of these welded tubular structures. Fatigue evaluations were performed using stress ranges from field measurements and from structural analyses. Based on the results of the structural analyses that were conducted, where fatigue design loadings that had been derived from AASHTO Specifications for Structural Supports for Highway Signs, Luminaries, and Traffic Signals (2001) were used, the structures that had been studied were found not to have infinite fatigue life. According to the limited measurements that were made in this study, the fatigue design loadings derived from AASHTO Specifications (2001) appear to be conservative, but they are not overly conservative. The results of this study should be used to make a reasonable design of VMS structures, and to maintain their standards.

• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.17-25
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• 2014

Offshore wind turbine foundations are subjected to wind, current and wave loadings. Hence, both static and cyclic behaviors of foundation's soil are important for the design of offshore wind turbine foundation. Undrained cyclic behaviors of soils depend upon the number of loading cycles, vertical effective stress, cyclic shear strain, relative density, and the combination of cyclic and average shear stresses. In order to evaluate the effect of average and cyclic shear stresses on the undrained cyclic behavior of marine silty sand, cyclic direct simple shear (CDSS) tests are performed with relative density of 85%, vertical effective stress of 200 and 300 kPa, and failure criteria of either 15% double amplitude cyclic shear strain (${\gamma}_{cyc}$) or permanent shear strain (${\gamma}_{p}$). The results are presented in the form of design graphs or contour diagrams. The undrained cyclic behavior of marine silty sand is found to be dependent on cyclic and average shear stresses and/or the combination of both shear stresses. It is found that when significant average shear stress exists the permanent or progressive shear strain is the govering failure criteria instead of cyclic shear strain.

• Journal of Korean Society of Steel Construction
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• v.25 no.4
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• pp.421-430
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• 2013

To predict behaviors of offshore wind turbines which are highly laterally loaded structures and to design them rationally, evaluating the soil-foundation interaction is important. Nowadays, there are many soil modeling methods for structural analysis of general structures subjected to vertical loads, but using the methods without any consideration for design of a monopile foundation is eschewed because it might cause wrong structural design due to the deferent loading state. In this paper, we identify the differences of the member forces and displacements by design methods. The results show that fixed end method is barely suitable for monopile design in terms of checking the serviceability because it underestimate the lateral displacement. Fixed end method and stiffness matrix method underestimate the member forces, whereas virtual fixed end method overestimates them. The results of p-y curve method and coefficient of subgrade reaction method are similar to the results of 3D soil modeling method, and 2D soil modeling method overestimates the displacement and member forces as compared with other methods.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.3
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• pp.194-202
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• 2016

This study aims to review a topology optimization based on finite element analysis (FEA) for conceptual design of platform in the 10MW class floating type wave-wind hybrid power generation system (WHPGS). Two topology optimization theories, density method (DM) and homogenization design method (HDM) were used to check which one is more effective for a simplified structural design problem prior to the topology optimization of platform of WHPGS. From the results of the simplified design problem, the HDM was applied to the topology optimization of platform of WHPGS. For the conceptual platform design of WHPGS, FEA model was created and then the structural analysis was performed considering offshore environmental loads at installation site. Hydrodynamics analysis was carried out to calculate pressure on platform and tension forces in mooring lines induced from the offshore environmental loads such as design wave and current. Loading conditions for the structural analysis included the analysis results from the hydrodynamic analysis and the weights of WHPGS. Boundary condition was realized using inertia relief method. The topology optimization of WHPGS platform was performed using the HDM, and then the conceptual arrangement of main structural members was suggested. From the results, it was confirmed that the topology optimization might be a useful tool to design the conceptual arrangement of main structural members for a newly developed offshore structure such as the floating type WHPGS.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.1-7
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• 2013

Structural design and analysis of a coiling arm unloading machine for submarine cable have been originally conducted in this study. Three-dimensional CAD modeling process is practically applied for the structural design in detail. Finite element method(FEM) and multi-body dynamics(MBD) analyses are also used to verify the safety and required motions of the designed coiling arm structure. The effective moving functions of the designed coiling arm with respect to rotational and radial motions are achieved by adopting bearing-roller mechanical parts and hydraulic system. Critical design loading conditions due to its self weight, carrying cables, offshore wind, and hydraulic system over operation conditions are considered for the present structural analyses. In addition, possible inclined ground conditions for the installation of the designed coiling arm are also considered to verify overturn stability. The present hydraulic type coiling arm system is originally designed and developed in this study. The developed coiling arm has been installed at a harbor, successfully tested its operational functions, and finished practical unloading mission of the submarine cable.