• The KSFM Journal of Fluid Machinery
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• v.14 no.5
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• pp.48-54
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• 2011

Structural modifications of a ship may cause a fatal accident such as sinking and wrecking of ship. Especially, barge ship can be easily reconstructed to load more bulk cargo. In this study, for a real accident case, change of mooring force due to structural modification was analyzed to evaluate accident risk. A two dimensional dynamic model for the barge ship was constructed to compute mooring forces with related to floating motion. The equation of motion was established in Matlab code and buoyancy was calculated by using direct integration of submerged volume. The results showed that wind force, current force, and mooring force after rebuilding was approximately 4.3 kN, 14 kN, 1,561 kN respectively. The maximum force of mooring force according to the length of mooring cable were 1,614 kN at 30 m of mooring cable. Thus, an arbitrary modification of ship lead instability and unreliable result so that illegal rebuilding of ship should be avoided.

• Ocean Systems Engineering
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• v.4 no.1
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• pp.1-19
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• 2014

Hydrodynamic coefficients strongly affect the dynamic performance of autonomous underwater vehicles (AUVs). A novel kind of underwater vehicle (Heavier-than-water AUV) with higher density than water is presented, which is different from conventional ones. RANS method and overlapping grids are used to simulate the flow field around the vehicle. Lifts, drags and moments of different attack and drift angles in steady state are calculated. The hydrodynamic performances and how the forces change with the attitude are analyzed according to the flow field structure. The steady-state results using overlapping grid method are compared with those of software FLUENT and wind tunnel tests. The calculation results show that the overlapping grid method can well simulate the viscous flow field around the underwater vehicle. Overlapping grid skills have also been used to figure out the planar-motion-mechanism (PMM) problem of Heavier-than-water AUV and forecast its hydrodynamic performance, verifying its effectiveness in dealing with the dynamic problems, which would be quite helpful for design and control of Heavier-than-water AUV and other underwater vehicles.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.43-46
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• 2008

Quad-Rotor, which consists of four blades, performs a flight task by controling each rotation speed of the four blades. Quad-Rotor blade making no use of cyclic pitch or collective one is a type of fixed-wing as different from helicopter blade. Although, Quad-Rotor is simple and easy to control for those reasons, blade configuration of the fixed wing is one of the critical factors in determining the performance of Quad-Rotor. In the present study, coefficients for thrust and power of Quad-Rotor blade were derived from the data acquired by using 6-component balances. Firstly, Measurements for aerodynamic force were conducted at various pitch angles (i.e., from 0$^{\circ}$ to 90$^{\circ}$ with the interval of 10$^{\circ}$). The blade used in this experiment has aspect ratio of 6 and chord length of 35.5 mm. Secondly, assembled-blade, which was an integral blade but divided into many pieces, was used in order to test aerodynamic forces along twist angles. The curve of thrust coefficient along pitch angle indicates a parabola form. Stall which occurs during wind tunnel test to calculate lift coefficient of airfoil does not generate. When deciding the blade twist angle, structural stability of blade should be considered together with coefficients of thrust and power. Those aerodynamic force data based on experimental study will be provided as a firm basis for the design of brand-new Quad-Rotor blade.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.11-20
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• 1992

In general, the cross-section of a girder of a bridge has only one axis of symmetry. Therefore, lateral forces such as earthquake and wind may cause torsion coupled with lateral bending in the gider. This induces additional stresses especially in cables arranged in double-planes. Since this effect cannot be considered by using the conventional frame elements, the stiffness and the mass matrices of the geometrically nonlinear thin-walled frame element have to be used in order to model the girder. Theoretical development and verification of the frame element used in this study were made through a-previously presented paper. In this paper, seismic analysis of a three dimensional cable-stayed bridge considering the unsymmetry of the girder cross-section is performed to investigate the coupled flexural-torsional behaviors.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1252-1257
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• 2009

Off-line 6-DOF simulation program for store separation analysis has been developed. The developed program enables to predict a trajectory of a store from the database which was constructed by wind tunnel testing or CFD analysis. The flow angle method was applied to the program for predicting aerodynamic coefficients from the database and the ejector forces and constraints were enabled to incorporate the equations of motion for computing the trajectory. Using the program, the trajectories were calculated and the results are compared with the CTS results.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.5-11
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• 2015

Ocean waves have huge amounts of energy, even larger than wind or solar, which can be extracted by some mechanical device. This can be done by creating a system of reacting forces, in which two or more bodies move relative to each other, while at least one body interacts with the waves. This moves the floater up and down. The floaters are connected to an arm structure, which are mounted on a fixed hull structure. Hence, the structure of the floater is very important. A static structural analysis with FSI (Fluid-Structure Interaction) analysis is conducted. To achieve the pressure load for the FSI analysis, the floater is simulated on a wave generator using rigid body motion. The structural analysis is done to examine the stresses on the whole system, and four types of flange and floater are optimized. The result shows that the structure of floater with wood support is the safest.

• Structural Engineering and Mechanics
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• v.59 no.3
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• pp.539-558
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• 2016

Minarets are almost the inevitable part of Mosques in Islam and according to some, from a philosophical point of view, today they symbolize the spiritual elevation of man towards God. Due to slenderness, minarets are susceptible to earthquakes and wind loads. They are mostly built in a masonry style by using cut limestone blocks or occasionally by using bricks. In this study, one minaret (M1 Minaret) of one of the charmest mosques of Turkey, Sultan Ahmed Mosque, popularly known as Blue Mosque, built between 1609 and 1616 on the order of Sultan Ahmed by the architect Mehmet Agha is investigated under some registered earthquake loads. According to historical records, a great earthquake hit Istanbul and/or its close proximity approximately every 250 years. Ottomans tackled with the problem of building earthquake resistant, slender minarets by starting to use forged iron connectors with lead as a filler to fix them to the upper and lower and to adjacent stones instead of using traditional mortar only. Thus, the discrete stones are able to transfer tensile forces in some sense. This study investigates the contribution of lead to the energy absorption capacity of the minaret under extensive earthquakes occurred in the region. By using the software ANSYS/LS-DYNA in modelling and investigating the minaret nonlinearly, it is found out that under very big recorded earthquakes, the connectors of vertical cast iron-lead mechanism play very important role and help to keep the structure safe.

• Steel and Composite Structures
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• v.19 no.6
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• pp.1581-1598
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• 2015

A concentric braced steel frame is a very efficient structural system because it requires relatively smaller amount of materials to resist lateral forces. However, primarily developed as a structural system to resist wind loads based on an assumption that the structure behaves elastically, a concentric braced frame possibly experiences the deterioration in energy dissipation after brace buckling and the brittle failure of braces and connections when earthquake loads cause inelastic behavior. Consequently, plastic deformation is concentrated in the floor where brace buckling occurs first, which can lead to the rupture of the structure. This study suggests reinforcing H-shaped braces with non-welded cold-formed stiffeners to restrain flexure and buckling and resist tensile force and compressive force equally. Weak-axis reinforcing members (2 pieces) developed from those suggested in previous studies (4 pieces) were used to reinforce the H-shaped braces in an inverted V-type braced frame. Monotonic loading tests, finite element analysis and cyclic loading tests were carried out to evaluate the structural performance of the reinforced braces and frames. The reinforced braces satisfied the AISC requirement. The reinforcement suggested in this study is expected to prevent the rupture of beams caused by the unbalanced resistance of the braces.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.263-276
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• 2013

Most yacht sails are made of thin fabric, and they have a cambered shape to generate lift force; however, their shape can be easily deformed by wind pressure. Deformation of the sail shape changes the flow characteristics over the sail, which in turn further deforms the sail shape. Therefore, fluid-structure interaction (FSI) analysis is applied for the precise evaluation or optimization of the sail design. In this study, fluid flow analyses are performed for the main sail of a 30-foot yacht, and the results are applied to loading conditions for structural analyses. By applying the supporting forces from the rig, such as the mast and boom-end outhaul, as boundary conditions for structural analysis, the deformed sail shape is identified. Both the flow analyses and the structural analyses are iteratively carried out for the deformed sail shape. A comparison of the flow characteristics and surface pressures over the deformed sail shape with those over the initial shape shows that a considerable difference exists between the two and that FSI analysis is suitable for application to sail design.

• Journal of Korean Association for Spatial Structures
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• v.17 no.3
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• pp.45-55
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• 2017

The objective of this study is to estimate the mechanical characteristics and nonlinear behaviors on the geometric nonlinear analysis of curved cable-membrane roof systems for long span lightweight roof structures. The weight of a cable-membrane roof dramatically can reduce, but the single layer cable-membrane roof systems are too flexible and difficult to achieve the required structural stiffness. A curved cable roof system with reverse curvature works more effectively as a load bearing system, the pretension of cables can easily increase the structural stiffness. The curved cable roof system can transmit vertical loads in up and downward direction, and work effectively as a load bearing structure to resists self-weights, snow and wind loads. The nonlinear behavior and mechanical characteristics of a cable roof system has greatly an affect by the sag and pretension. This paper is carried out analyzing and comparing the tensile forces and deflection of curved roof systems by vertical loads. The elements for analysis uses a tension only cable element and a triangular membrane element with 3 degree of freedom in each node. The authors will show that the curved cable-membrane roof system with reverse curvature is a very lightweight and small deformation roof for external loads.