• Water for future
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• v.29 no.1
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• pp.163-179
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• 1996

Flood flow characteristics of the Han River (from Goan to Indo Bridge) are analyzed using 1-dimensional St. Venant equations. NETWORK, a finite difference model, is used to calculate each term (local acceleration term, convective acceleration term, pressure force term, gravity force term, and friction force term) of the momentum equation and to analyze the flow characteristics. By the result of the study, as the general characteristics of flow in a channel that acceleration terms are very small and the other three terms are much greater is presented, three terms(pressure force term, gravity force term, friction force term) are to be main terms which decide the characteristics of flow. Specially in this region the acceleration term is noted so large that it cannot be ignored according to the shape of hydrograph and the region.

• Physical Therapy Korea
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• v.13 no.3
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• pp.1-9
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• 2006

The purpose of this study was to assess the influence of spine orthosis and sit-to-stand motor strategies on ground reaction force (GRF) and lower extremity muscle activity. Twenty healthy adult men participated, and subjects randomly performed sit-to-stand motions in three different conditions: Momentum-transfer strategy (MTS); MTS with spine orthosis; and zero-momentum strategy (ZMS) with spine orthosis. GRF data, onset time, and muscle activity were determined and compared using force plate and electromyography. Data were statistically analyzed by the SPSS version 13.0. One-way repeated analysis of variance (ANOVA) was used to determine the statistical significance, and least significant difference was used as a post hoc test. The level of significance was .05. The results of this study were as follows: 1. Peak GRF and relative time to peak GRF were not significantly different in the three different conditions (p>.05). 2. Onset time of four muscles, tibialis anterior, gastrocnemius, biceps femoris and rectus femoris, in the three different conditions were significantly different (p<.05). 3. The tibialis anterior and rectus femoris muscle activity before hip-off and tibialis anterior, gastrocnemius, and rectus fermoris muscle activity after hip-off were significantly different in the three different conditions (p<.05).

• Korean Journal of Applied Biomechanics
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• v.16 no.4
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• pp.153-164
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• 2006

This thesis is focused on kinematical and kinematical analysis of each types(Type #1 : use both swing of arm and reaction of knee, Type #2 : Use only swing of arm, not reaction of knee, type #3 : Neither use of swing of arm nor reaction of knee) of vertical jumps according to gender of High School Students. The subjects of this study is High School Student's male and female, 5 each, for analyzation of actions 3D image analyzing and GRF machines were used. To identify the differences of analyzed variables, an independent T-test on gender, an One-way ANOVA on types were used. Summery of the results are stated below. first of all, female students showed differences on Hip Joint angle and Joint Velocity from male students on Kimentic Variable. So training on hip joint force of flection and extension of female students is needed. Both male and female students showed relatively bigger result of arm's Angular Momentum than thigh's Angular Momentum on Type #1. This is regarded of faster Joint Velocity of Arm. Bigger result of female students of arm's contribution on Type #1 than male students can be said as Female student's weaker hip joint's angular muscle force than male student's, so the dependency of arm is heavier than male students. In Kinetic variable, GRF showed bigger result on male students than female students. So female students need to enhance joint's torque to increase GRF than male students. On vertical Impulse, high numeric data of last two reaction of tiptoe of vertical GRF and antero-posterior GRF helped increasing impulse by extending action time of force.

• 한국기계연구소 소보
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• s.14
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• pp.135-144
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• 1985

A method is described to obtain the first order force and second order steady force on the fixed two dimensional submerged or semisubmerged cylinders at infinite depth of water due to regular waves. The first order diffraction wave velocity potential which describes the flow diffracted by a body is obtained numerically using source distribution method on the mean wetted surface. And a technique to remove the irregular frequency phenomena of the source distribution method is also applied. The second order steady force is calculates by means of direct integration of the pressures on the body as derived from the first order velocity potential and is also computed by means of reflection wave height derives from momentum conservation theory. The results are compared with those of published works, and show good agreement.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.4
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• pp.9-18
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• 2002

In this paper, we have studied the characteristics of a perforated muzzle brake. The main purpose of a muzzle brake is to reduce the momentum being applied to the recoil system. Muzzle brake redirect a portion of the exiting gases to the side exerting a forward force on the brake, thus reducing recoil. So it also reduces the recoil force which acts on the turret and vehicle. First of all, we analyzed the flow-field characteristics of muzzle brake using RAMPANT software. Then we investigated the influence of design parameters of perforated muzzle brake. Sixteen muzzle brakes were tested and evaluated for analyzing their influence on the muzzle brake efficiency. The muzzle brakes were designed to fit on a 40mm gun barrel. The strong dependent parameters of muzzle brake efficiency were the wall thickness(L/d ratio) and the area ratio AR. We designed the perforated muzzle brakes which have 10-20% efficiency. And we proposed a design method of perforated muzzle brake.

• Korean Journal of Applied Biomechanics
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• v.18 no.4
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• pp.201-207
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• 2008

The purpose of this study was to examine the Roche technique performed by three male subjects in 2003 Taegu World Students Game. Conclusions are as followed. If the angular momentum was increased to counter-clockwise on voulting, the momentum acted like an interrupting factor of body spinning force. The biggest body angle was at VTD phase and the smallest was at BTO phase. At the phase of contacting on vaulting board and taking off from the vaulting board, the biggest personal angle difference between VTD and BTO was found. As the Roche technique was needed not only to fly high but also to increase body spinning rate, the projection angles of Roche technique were showed smaller than those of Cuervo technique. The angular velocity was peak during 2 times forward turn phase. The angular momentum was influenced by angular velocity from BTO and VTD phase.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.347-355
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• 2016

This study presents a Lattice Boltzmann Method (LBM) coupled with a momentum-exchange approach/fictitious domain (MEA/FD) method for the simulation of particle suspensions. The method combines the advantages of the LB and the FD methods by using two unrelated meshes, namely, a Eulerian mesh for the flow domain and a Lagrangian mesh for the solid domain. The rigid body conditions are enforced by the momentum-exchange scheme in which the desired value of velocity is imposed directly in the particle inner domain by introducing a pseudo body force to satisfy the constraint of rigid body motion, which is the key idea of a fictitious domain (FD) method. The LB-MEA/FD method has been validated by simulating two different cases, and the results have been compared with those through other methods. The numerical evidence illustrated the capability and robustness of the present method for simulating particle suspensions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.11
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• pp.861-871
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• 2020

Raising the speed of the momentum wheel in the CMG increases the unintended force and torque caused by mass imbalance. This unintended force and torque should be minimized to get the better quality of satellite SAR image because they lead to the vibration of the output image. This paper shows the works on compensating the static imbalance and couple mass imbalance in the CMG wheel. First, the force and torque at the center of mass generated by the mass imbalance were predicted through M&S analysis. Second, the force and torque were estimated similarly through the M&S analysis when the measurement point was moved from the rotation center. Third, the measurement configuration for the force and torque by the mass imbalance was described. Fourth, the change of the force and torque by adding the specified mass to the momentum wheel was observed after comparing the measurements with the results of the M&S. And finally, the effect of the compensation was analyzed by comparing the force and torque before and after the correction while 24Nm class CMG was running in the standby mode.

• Journal of Korean Society of Disaster and Security
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• v.16 no.2
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• pp.57-63
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• 2023

Recently, Heavy rains and super typhoons occurred by climate change cause a lot of damage in Korea. In order to reduce such damage, various types of river maintenance projects are being promoted, but it is difficult to maintain the balance of rivers in Korea with distinct flood and dry seasons. In particular, river structures installed as a river maintenance project cause various problems such as scouring of structures and their foundations during floods and river bed changes. In order to reduce such bed scour, various vanes are installed in the bend of the river, and various bed scour reduction effects appear depending on the size, arrangement, and shape of the vanes. The vane regenerates the secondary flow in the opposite direction to the secondary flow generated by the centrifugal force, thereby reducing scour around the outer bed and promoting deposition. The theory of this study uses the governing equation applying the continuity equation that satisfies the law of conservation of mass and the momentum equation that satisfies the conservation of momentum, and measures the overall average flow velocity change rate according to design factors to investigate the effect of vanes under various conditions. Both the average and cross-sectional flow velocities decreased in both the trapezoidal vane and the square vane. In addition, vanes installed perpendicularly or inclined to the direction of river flow generate a secondary flow in the opposite direction to the secondary flow generated by centrifugal force, thereby canceling the secondary flow of centrifugal force, so the effect of the vane appears.

• Tribology and Lubricants
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• v.20 no.5
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• pp.284-291
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• 2004

We present a three-dimensional average flow model considering elastic deformation of pad asperities for chemical mechanical planarization. To consider the contact deformation of pad asperities in the calculation of the flow factor, three-dimensional contact analysis of a semi-infinite solid based on the use of influence functions is conducted from computer generated three dimensional roughness data. The average Reynolds equation and the boundary condition of both force and momentum balance are used to investigate the effect of pad roughness and external pressure conditions on film thickness and wafer position angle.