• Structural Engineering and Mechanics
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• v.29 no.3
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• pp.289-300
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• 2008

The use of metric trial functions to represent the real stress field in what is called the unsymmetric finite element formulation is an effective way to improve predictions from distorted finite elements. This approach works surprisingly well because the use of parametric functions for the test functions satisfies the continuity conditions while the use of metric (Cartesian) shape functions for the trial functions attempts to ensure that the stress representation during finite element computation can retrieve in a best-fit manner, the actual variation of stress in the metric space. However, the issue of how to handle situations where there is locking along with mesh distortion has never been addressed. In this paper, we show that the use of a consistent definition of the constrained strain field in the metric space can ensure a lock-free solution even when there is mesh distortion. The three-noded Timoshenko beam element is used to illustrate the principles. Some significant conclusions are drawn regarding the optimal strategy for finite element modelling where distortion effects and field-consistency requirements have to be reconciled simultaneously.

• Journal of Ocean Engineering and Technology
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• v.38 no.3
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• pp.124-136
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• 2024

As the number of offshore wind-power installations increases, collision accidents with vessels occur more frequently. This study investigates the risk of collision damage with operating vessels that may occur during the operation of an offshore wind turbine. The floater used in the collision study is a 15 MW UMaine VolturnUS-S (semi-submersible type), and the colliding ships are selected as multi-purpose vessels, service operation vessels, or anchor-handling tug ships based on their operational purpose. Collision analysis is performed using ABAQUS and substantiation is performed via a drop impact test. The collision analyses are conducted by varying the ship velocity, displacement, collision angle, and ship shape. By applying this numerical model, the extent of damage and deformation of the collision area is confirmed. The analysis results show that a vessel with a bulbous bow can cause flooding, depending on the collision conditions. For damage caused by collision, various collision angles must be considered based on the internal stiffener arrangement. Additionally, the floater can be flooded with relatively small collision energy when the colliding vessel has a bulbous bow.

• The Journal of the Acoustical Society of Korea
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• v.28 no.1
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• pp.25-31
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• 2009

This paper introduces a spectrally formulated element method (SEM) for the beams treated with passive constrained layer damping (PCLD). The viscoelastic core of the beams has a complex modulus that varies with frequency. The SEM is formulated in the frequency domain using dynamic shape functions based on the exact displacement solutions from progressive wave methods, which implicitly account for the frequency-dependent complex modulus of the viscoelastic core. The frequency response function and dynamic responses obtained by the SEM and the conventional finite element method (CFEM) are compared to evaluate the validity and accuracy of the present spectral PCLD beam element model. The spectral PCLD beam element model is found to provide very reliable results when compared with the conventional finite element model.

• Journal of Korean Association for Spatial Structures
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• v.4 no.3 s.13
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• pp.77-84
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• 2004

This study presents an effective stiffness-based optimal technique to control quantitatively lateral drift for tall frameworks using composit member subject to lateral loads. To this end, displacement sensitivity depending on behavior characteristics of tall frameworks is established and approximation concept that preserves the generality of the mathematical programming and can efficiently solve large scale problems is introduced. Specifically, under the 'constant-shape' assumption, resizing techniqe of composite member is developed. Two types of 50 story frameworks are presented to illustrate the features of the quantitative lateral drift control technique proposed in this study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.273-278
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• 2013

This paper presents optimal design procedures of mount based on a magnetorheological (MR) fluid to isolate the vibration in heavy diesel engine system. At first, frequency response and force-displacement transmissibility methods are used to get required damping force that is necessary for effective vibration isolation. From this result, a new type of high damping force engine mount is proposed and the governing equation of Bingham plastic behavior of MR fluid in flow path is mathematically derived under cylindrical coordinates. Finally, parametric design optimization featuring finite element is performed using ANSYS software to get the required damping force in MR mount system which can be used to reduce engine vibration. Damping force of the MR mount is then determined as an objective function in this analysis based on ANSYS. Furthermore, Magnetic analysis is then applied in this process.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.2
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• pp.73-78
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• 2004

By modeling the block matching algorithm as a function of the correlation of image blocks, we derive search patterns for fast block matching motion estimation. The proposed approach provides an analytical support lot the diamond-shape search pattern, which is widely used in fast block matching algorithms. We also propose a new fast motion estimation algorithm using adaptive search patterns and statistical properties of the object displacement. In order to select an appropriate search pattern, we exploit the relationship between the motion vector and the block differences. By changing the search pattern adaptively, we improve motion prediction accuracy while reducing required computational complexity compared to other fast block matching algorithms.

• Journal of Korean Association for Spatial Structures
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• v.5 no.3 s.17
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• pp.123-130
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• 2005

This study presents an effective stiffness-based optimal technique to control quantitatively lateral drift and evaluate the structural behavior characteristics and efficiency for tall outrigger system subject to lateral loads. To this end, displacement sensitivity depending on behavior characteristics of outrigger system is established and approximation concept that preserves the generality of the mathematical programming and can efficiently solve large scale problems is introduced. Specifically, under the 'constant-shape' assumption, resizing technique of member is developed. Four types of 50 story frameworks are presented to illustrate the features of the quantitative lateral drift control technique proposed in this study.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.5-12
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• 2014

Organic Rankine Cycle is widely used to convert the low-grade thermal energy to the electrical energy. However, usually available thermal energy is not supplied constantly. This makes hard to use positive displacement expanders. Hence, turbo-expander has merits to apply as an expander in ORC because it can operate well off-design points even though the mass flowrate is fluctuated. The thermal energy fluctuation causes the turbo-expander to operate in partial admission. In addition, supersonic nozzles are required so that the partially admitted turbine operates efficiently. In this study, R245fa was chosen as a working fluid of ORC. A design method and an analysis technique of supersonic nozzle based on R245fa were developed. The shape of the nozzle was designed by the characteristic method. The thermal properties within the nozzle were estimated and the predicted results were agreed well with the computed results.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.725-726
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• 2008

This paper proposes elastic stress intensity factors and crack opening displacements (CODs) for a slanted axial through-wall cracked cylinder under an internal pressure based on detailed 3-dimensional (3-D) elastic finite element (FE) analyses. Based on the elastic FE results, the stress intensity factors along the crack front and CODs through the thickness at the center of the crack were provided. These values were also tabulated for three selected points, i.e., the inner and outer surfaces and at the mid-thickness. The present results can be used to evaluate the crack growth rate and leak rate of a slanted axial through-wall crack due to stress corrosion cracking and fatigue. Moreover, the present results can be used to perform a detailed Leak-Before-Break analysis considering more realistic crack shape development.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1135-1141
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• 2006

Air foil bearing supports the rotating journal using hydrodynamic force generated at thin air film. The bearing performance, stiffness, damping coefficient and load capacity, depends on the rotating speed and the performance of the elastic foundation, bump foil. The main focus of this study is to decide the dynamic performance of corrugated bump foil, structural stiffness and Coulomb damping caused by friction between bump foil and top foil/bump foil and housing. Structural stiffness is determined by the bump shape (bump height, pitch and bump thickness), dry-friction, and interacting force filed up to fixed end. So, the change of the characteristics was considered as the parameters change. The air foil bearing specification for analysis follows the general size; diameter 38.1 mm and length 38.1mm (L/D=1.0). The results show that the stiffness at the fixed end is more than the stiffness at the free end, Coulomb damping is more at the fixed end due to the small displacement, and two dynamic characteristics are dependent on each other.