• Wind and Structures
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• v.16 no.5
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• pp.411-431
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• 2013

A computational study of vortex-induced transverse vibrations of a cylinder with low mass-damping is presented. An Arbitrary Lagrangian-Eulerian (ALE) formulation of the Unsteady Reynolds-Averaged Navier-Stokes equations (URANS), along with the Spalart-Allmaras (SA) one-equation turbulence model, are coupled conservatively with rigid body motion equations of the cylinder mounted on elastic supports in order to study the amplitude and frequency response of a freely vibrating cylinder, its flow-induced motion, Vortex Street, near-wake flow structure, and unsteady loading in a moderate range of Reynolds numbers. The time accurate response of the cylinder from rest to its limit cycle is studied to explore the effects of Reynolds number on the start of large displacements, motion amplitude, and frequency. The computational results are compared with published physical experiments and numerical studies. The maximum amplitudes of displacements computed for various Reynolds numbers are smaller than the experimental values; however, the overall agreement of the results is quite satisfactory, and the upper branch of the limit-cycle displacement amplitude vs. reduced velocity response is captured, a feature that was missed by other studies. Vortex shedding modes, lock-in phenomena, frequency response, and phase angles are also in agreement with experiments.

• Journal of Navigation and Port Research
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• v.30 no.5 s.111
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• pp.315-320
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• 2006

It is well known that the ship manoeuvring motion is greatly affected by hydrodynamic forces and moments acting between two vessels passing too close to each other in confined waters, such as in a harbour or narrow channel. This interaction between two vessels could be assumed to be the functions of the longitudinal distance, transverse distance and their speeds. The aim of this study is to calculate the interaction between two vessels passing close to each other on parallel courses by simulation, and to estimate the effect of rudder action and time at collision through simulation under the condition of various longitudinal distances and different speed-ratios of the two vessels.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.06b
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• pp.55-60
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• 2006

It is well known tint the ship manoeuvring motion is greatly affected by hydrodynamic forces and moments acting between two vessels passing too close to each other in confined waters, such as in a harbour or narrow channel. This interaction between two vessels could be assumed to be the functions of the longitudinal distance, transverse distance and their speeds. The aim of this study is to calculate the interaction between two vessels passing close to each other on parallel courses by simulation, and to estimate the effect of rudder action and time of collision through simulation under the condition of various longitudinal distances and different speed-ratios of the two vessels.

• Smart Structures and Systems
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• v.16 no.1
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• pp.141-162
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• 2015

The magneto-rheological visco-elastomer (MRVE) is used as a smart core to control the stochastic micro-vibration of a sandwich plate with supported mass. The micro-vibration response of the sandwich plate with MRVE core and supported mass under stochastic support motion excitations is studied and compared to evaluate the vibration suppression capability. The effects of the supported mass and localized magnetic field on the stochastic micro-vibration response of the MRVE sandwich plate are taken into account. The dynamic characteristics of the MRVE core in micro-vibration are described by a non-homogeneous complex modulus dependent on vibration frequency and controllable by applied magnetic fields. The partial differential equations for the coupled transverse and longitudinal motions of the MRVE sandwich plate with supported mass are derived from the dynamic equilibrium, constitutive and geometric relations. The simplified ordinary differential equations are obtained for the transverse vibration of the MRVE sandwich plate under localized magnetic fields. A frequency-domain solution method for the stochastic micro-vibration response of sandwich plates with supported mass is developed based on the Galerkin method and random vibration theory. The expressions of frequency-response functions, response power spectral densities and root-mean-square velocity responses of the plate in terms of the one-third octave frequency band are obtained for micro-vibration evaluation. Finally, numerical results are given to illustrate the large response reduction capacity of the MRVE sandwich plate with supported mass under stochastic support motion excitations, and the influences of MRVE parameters, supported mass and localized magnetic field placement on the micro-vibration response.

• Steel and Composite Structures
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• v.19 no.2
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• pp.369-384
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• 2015

This work presents a free vibration analysis of functionally graded metal-ceramic (FG) beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. For this purpose, a simple displacement field based on higher order shear deformation theory is implemented. The proposed theory is based on the assumption that the transverse displacements consist of bending and shear components in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The most interesting feature of this theory is that it accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the beam without using shear correction factors. In addition, it has strong similarities with Euler-Bernoulli beam theory in some aspects such as equations of motion, boundary conditions, and stress resultant expressions. The rule of mixture is modified to describe and approximate material properties of the FG beams with porosity phases. By employing the Hamilton's principle, governing equations of motion for coupled axial-shear-flexural response are determined. The validity of the present theory is investigated by comparing some of the present results with those of the first-order and the other higher-order theories reported in the literature. Illustrative examples are given also to show the effects of varying gradients, porosity volume fraction, aspect ratios, and thickness to length ratios on the free vibration of the FG beams.

• Korean Journal of Applied Biomechanics
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• v.16 no.4
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• pp.115-124
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• 2006

This study was conducted to investigate the running motion in the max-velocity phase(150-160m) and the fatigue phase(350-360m) during 400m sprint by performed elementary school athletes. Eighteen elementary school male athletes who achieved at least the 3rd place in the sprint at the Korea Gangwon-Do elementary school track and field meetings during 2004 and 2005 were selected as subjects. The running motions performed by the subjects were recorded using two 8mm high speed cameras at the nominal speed of 100 frames per second. The Direct Linear Transformation technique was adopted from the beginning of filming to the final stage of data extraction. KWON 3D motion analysis package program was used to compute the 3 Dimensional coordinates, smoothing factor in which lowpass filtering method was used and cutoff frequency was 6.0 Hz. The movement patterns during foot touchdown and takeoff for the running stride were related with the biomechanical consideration. Within the limitations of this study it is concluded: In order to increase running velocity, several conditions must be fullfilled at the instant of leg touchdown and takeoff during the fatigue phase(350-360m). First, the body C.O.G(Center of Gravity) height should be raised at the instant of leg touchdown and takeoff during the fatigue phase. Second, the foot contact time should be shortened and the takeoff distance should be increased at the foot takeoff during the fatigue phase. Third, the shank angular velocity with respect to a transverse axis through the center of gravity should be increased during the leg touchdown and takeoff in the fatigue phase. Forth, the active landing style described as clawing the ground with the sole of the foot should be performed during the leg touchdown and takeoff in the fatigue phase) phase. Fifth, In order to increase running velocity in the fatigue phase while taking a slightly greater leg knee angle and body lean angle within the range of the subject's running motion during the fatigue phase would result in greater flight distance.

• Journal of the Korean Society of Physical Medicine
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• v.17 no.3
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• pp.23-30
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• 2022

PURPOSE: This study was designed to investigate the effects of keeping contraction of abdominal and pelvic floor muscles on 3D pelvic stability in individuals with nonspecific chronic low back pain (CLBP) during normal speed walking. METHODS: The subjects were 20 adults with CLBP deformity and had moderate pain intensity of the visual analog scale. A three-dimensional camera capture system was used to collect kinematic pelvic motion data with and without contraction of the abdominal and pelvic floor muscles during gait. The subjects were asked to walk on a walkway in the lab room and they were attached 40 reflective markers to their pelvic segment and lower extremities. A Visual3D Professional V6 program and Vicon Nexus software were used to analyze 3D pelvic kinematic data. RESULTS: There were significant differences between with and without contraction of the abdominal and pelvic floor muscles of the pelvic depression and the total pelvic motion in coronal plane during gait (p < .05). However, there were no significant differences in any of the maximal motion of the pelvic segment in sagittal and transverse motion plane according to the different muscle contraction conditions (p > .05). CONCLUSION: The results of this study suggest that maintaining co-contraction of the abdominal and pelvic floor muscles in individuals with CLBP increased pelvic stability and contributed to preventing excessive pelvic movements during gait.

• Journal of Chest Surgery
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• v.13 no.4
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• pp.455-461
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• 1980

This is one case report of surgically treated ventricular septal defect [VSD] with aortic insufficiency [AI] at department of thoracic and cardiovascular surgery, Hanyang university hospital. He had had progressive dyspnea on exertion and palpitation for 3 years prior to admission to our hospital. On examination, the blood pressure was 120/0 mmHg and the pulse rate 88 times/min. Bobbing motion of the head, Water hammer pulse, Corringan`s pulse, Quincke`s pulse and to and fro murmur were present. The heart murmur was consistent with .VSD and AI. Cardiomegaly was seen in chest X-ray. EKG, echocardiogram, aortogram and right heart catheterization was performed. On Sep. 9, 1980, open heart surgery was performed under the impression of VSD with AI. Infracrystal type VSD measuring 2 x 1.5 cm in diameter was closed with Teflon patch graft through the transverse ventriculotomy. AI was due to prolapsed, elongated right coronary and noncoronary cusp, especially noncoronary cusp. The prolapsed, elongated aortic leaflets were plicated by placing three 8-figure sutures between the free edge and the base of the leaflet [Frater`s method] through a transverse aortotomy. Postoperatively, he made an uneventful recovery, his blood pressure was 120/70 mmHg and showed no signs AI or residual shunt at discharge.

• Earthquakes and Structures
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• v.1 no.1
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• pp.21-41
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• 2010

Multi-span steel-concrete composite (SCC) bridges are very sensitive to earthquake loading. Extensive damage may occur not only in the substructures (piers), which are expected to yield, but also in the other components (e.g., deck, abutments) involved in carrying the seismic loads. Current seismic codes allow the design of regular bridges by means of linear elastic analysis based on inelastic design spectra. In bridges with superstructure transverse motion restrained at the abutments, a dual load path behavior is observed. The sequential yielding of the piers can lead to a substantial change in the stiffness distribution. Thus, force distributions and displacement demand can significantly differ from linear elastic analysis predictions. The objectives of this study are assessing the influence of piers-deck stiffness ratio and of soil-structure interaction effects on the seismic behavior of continuous SCC bridges with dual load path, and evaluating the suitability of linear elastic analysis in predicting the actual seismic behavior of these bridges. Parametric analysis results are presented and discussed for a common bridge typology. The response dependence on the parameters is studied by nonlinear multi-record incremental dynamic analysis (IDA). Comparisons are made with linear time history analysis results. The results presented suggest that simplified linear elastic analysis based on inelastic design spectra could produce very inaccurate estimates of the structural behavior of SCC bridges with dual load path.

• Structural Engineering and Mechanics
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• v.73 no.3
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• pp.319-330
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• 2020

This paper investigates the free vibrations of cylindrical shells made of time-dependent materials for different viscoelastic models under various boundary conditions. During the extraction of equations, the displacement field is estimated through the first-order shear deformation theory taking into account the transverse normal strain effect. The constitutive equations follow Hooke's Law, and the kinematic relations are linear. The assumption of axisymmetric is included in the problem. The governing equations of thick viscoelastic cylindrical shell are determined for Maxwell, Kelvin-Voigt and the first and second types of Zener's models based on Hamilton's principle. The motion equations involve four coupled partial differential equations and an analytical method based on the elementary theory of differential equations is used for its solution. Relying on the results, the natural frequencies and mode shapes of viscoelastic shells are identified. Conducting a parametric study, we examine the effects of geometric and mechanical properties and boundary conditions, as well as the effect of transverse normal strain on natural frequencies. The results in this paper are compared against the results obtained from the finite elements analysis. The results suggest that solutions achieved from the two methods are ideally consistent in a special range.