• Coupled systems mechanics
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• v.9 no.4
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• pp.311-323
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• 2020

This paper deals with the effect of the mode shapes on the dynamic response of a multi-storey frame subjected to moving train loads which are modelled as loads of constant intervals with constant velocity using the finite element method. The multi-storey frame is modelled as a number of Bernoulli-Euler beam elements. First, the first few modes of the multi-storey frame are determined. Then, the effects of force span length to beam length ratio and velocity on dynamic magnification factor (DMF) are evaluated via 3D velocity-force span length to beam length ratio-DMF graphics and its 2D projections. By using 3D and 2D graphics, the directions of critical speeds that force the structure under resonance conditions are determined. Last, the mode shapes related to these directions are determined by the time history and frequency response graphs. This study has been limited by the vibration of the frame in the vertical direction.

• Korean Journal of Applied Biomechanics
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• v.29 no.3
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• pp.173-183
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• 2019

Objective: The aim of this study was to investigate the correlation coefficients between anthropometric parameters of the foot and kinetic variables during running. Method: This study was conducted on 21 healthy young adults (age: $24.8{\pm}2.1yes$, height: $177.2{\pm}5.8cm$, body mass: $73.3{\pm}7.3kg$, foot length: $256.5{\pm}12.3mm$) with normal foot type and heel strike running. To measure the anthropometric parameters, radiographs were taken on the frontal and sagittal planes, and determined the length and width of each segment and the navicular height. Barefoot running was performed at a preferred velocity ($3.0{\pm}0.2m/s$) and a fixed velocity (4.0 m/s) on treadmill (Bertec, USA) in order to measure the kinetic variables. The vertical impact peak force, the vertical active peak force, the braking peak force, the propulsion peak force, the vertical force at mid-stance (vertical ground reaction when the foot is fully landed in mid-stance or at the point where the weight was uniformly distributed on the foot) and the impact loading rate were calculated. Pearson's correlation coefficient was used to investigate the relationship between anthropometric variables and kinetical variables. The significance level was set to ${\alpha}=.05$. Results: At the preferred velocity running, the runner with longer forefoot had lower active force (r=-.448, p=.041) than the runner with short forefoot. At the fixed velocity, as the navicular height increases, the vertical force at full landing moment increases (r= .671, p= .001) and as the rearfoot length increases, the impact loading rate decreases (r=- .469, p= .032). Conclusion: There was a statistically significant difference in the length of fore-foot and rearfoot, and navicular height. Therefore it was conclude that anthropometric properties need to be considered in the foot study. It was expected that the relationship between anthropometric parameters and kinetical variables of foot during running can be used as scientific criteria and data in various fields including performance, injury and equipment development.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.8
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• pp.1046-1053
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• 1999

The musculotendon model is presented to show the declines in muscle force and shortening velocity during muscle fatigue due to the repeated functional electrical stimulation (FES). It consists of the nonlinear activation and contraction dynamics including physiological concepts of muscle fatigue. The activation dynamics represents $Ca^{2+}$ binding and unbinding mechanism with troponins of cross-bridges in sarcoplasm. It has the constant binding rate or activation time constant and two step nonlinear unbinding rate or inactivation time constant. The contraction dynamics is the modified Hill type model to represent muscle force - length and muscle force - velocity relations. A muscle fatigue profile as a function of the intracellular acidification, pH is applied into the contraction dynamics to represent the force decline. The computer simulation shows that muscle force and shortening velocity decline in stimulation time. And we validate the model. The model can predicts the proper muscle force without changing its parameters even when existing the estimation errors of the optimal fiber length. The change in the estimate of the optimal fiber length has an effect only on muscle time constant in transient period not on the tetanic force in the steady-state and relaxation periods.

• Journal of the korean Society of Automotive Engineers
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• v.4 no.3
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• pp.56-68
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• 1982

This paper presents analytic solutions of defection and their resonance diagrams for a uniform beam of infinite length subjected to an constant axial force and moving transverse load simultaneously. Steady solutions are obtained by a time-independent coordinate moving with the load. The supporting foundation includes damping effects. The influences of the axial force, the damping coefficient and the load velocity on the beam response are studied. The limiting cases of no damping and critical damping are also investigate. The profiles of the deflection of the beam are shown graphically for several values of the load speed, the axial force and damping parameters. Form the results, following conclusions have been reached. 1. The critical velocity .THETA.cr decreases as the axial compressive force increases, but increases as the axial tensile force increase. 2. At the critical velocity .THETA.cr the deflection have a tendency to decrease as the axial tensile force increases and to increase gradually as the axial compressive force increases. 3. In case if relatively small dampings, the deflection increases suddenly as the velocity of the moving load approaches the critical velocity, and it reachs its maximum at the critical velocity, and it decreases and become greatly affected by the axial force as the velocity increases further. 4. in case of relatively large dampings, as the velocity increases the deflection decreases gradually and it is affected little by the axial load.

• Wind and Structures
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• v.32 no.4
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• pp.371-391
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• 2021

Tornadoes are the most devastating meteorological natural hazards. Many empirical and theoretical numerical models of tornado vortex have been proposed, because it is difficult to carry out direct measurements of tornado velocity components. However, most of existing numerical models fail to explain the physical structure of tornado vortices. The present paper proposes a new empirical numerical model for a tornado vortex, and its load effects on a low-rise and a tall building are calculated and compared with those for existing numerical models. The velocity components of the proposed model show clear variations with radius and height, showing good agreement with the results of field measurements, wind tunnel experiments and computational fluid dynamics. Normal stresses in the columns of a low-rise building obtained from the proposed model show intermediate values when compared with those obtained from existing numerical models. Local forces on a tall building show clear variation with height and the largest local forces show similar values to most existing numerical models. Local forces increase with increasing turbulence intensity and are found to depend mainly on reference velocity Uref and moving velocity Umov. However, they collapse to one curve for the same normalized velocity Uref / Umov. The effects of reference radius and reference height are found to be small. Resultant fluctuating force of generalized forces obtained from the modified Rankine model is considered to be larger than those obtained from the proposed model. Fluctuating force increases as the integral length scale increases for the modified Rankine model, while they remain almost constant regardless of the integral length scale for the proposed model.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1996.04a
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• pp.137-140
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• 1996

This study investigated the length-tension and velocity-force relations of the torso erectors. A myoelectric based approach was used wherein a dynamic biomechanical model incorporating active and passive tissue charactreistics provided music kinematic estimates during controlled sagittal plan extension motions. A double linear optimization formulation from the literatured provided muscle tension estimates. The data supported a linear length-tension relation toward full flexion for both the erector spinae and latissimus muscles. Velocity trends agreed with that predicted by Hill's exponential relation. The results have implications for muscle tension estimation in biomechanical torso modeling, and suggest a possible low back pain injury mechanism.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.3
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• pp.209-216
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• 2001

A numerical study is peformed to investigate the effect of circumferential velocity generated by the guide vane on the nozzle flow of a jet fan, s a way of increasing the penetration force of jet fan with nozzle of 175mm diameter. For the validation of numerical results. the velocity is measured by a 5-hole pitot tube and flow visualization is conducted by the tuft method. Under the inlet condition that the maximum circumferential velocity in the stator outlet of the present jet fan is 1.8m/s, the axial velocity in the nozzle outlet has the feature that the velocity at the axis is low and the velocity near the wall high. Therefore, to increase the throw length of the jet fan, the configuration of the fairing and nozzle needs to be developed and the precise revise of the stator angle is required, In addition, the bigger the circumferential velocity, the smaller the axial velocity at the axis and the bigger non-uniformity of the flow distribution.

• The Journal of the Korea Contents Association
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• v.12 no.9
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• pp.389-395
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• 2012

This research analyzed the peak impulsive force, maximum velocity and a spot of fist's maximum velocity comparing stop-jirugi and push-jirugi. 7 males volunteered for this experiment. peak impulsive force was measured by PS2142 force platform[10], and maximum velocity of fist was measured by PS2103A motion sensor[12]. All of data was collected in the data studio and t-test was applied using SAS 9.1 package. The following conclusions were drawn. First, stop-jirugi's peak impulsive force was greater (P<.01) than that of push-jirugi. Second, push-jirugi's maximum velocity of fist was greater (P<.01) than that of stop-jirugi. Third, stop-jirugi's maximum velocity of fist was occurred on 69.14% of arm's length and that of push-jirugi was occurred on 75.66%. This maximum velocity spot was statistically significant difference(p<.001).

• Journal of the Korean Society of Visualization
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• v.19 no.1
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• pp.12-17
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• 2021

A three-dimensional slope valve component is used for controlling micro volume of liquid on a centrifugal force-based microfluidic disk platform, also called a lab-on-a-disk. The modeling factor of the slope valve component is determined to centrifugal force for liquid passing the crest of a slope valve via variation of slope length and angle as well as the radius to start point of slope valve. The centrifugal force is calculated by the equilibrium equation of the capillary and gravitational forces according to the microchannel surface roughness and the liquid volume, respectively. As a result, the slope valve is analyzed by the minimum angular velocity for liquid passing at crest point and the ratio between the length of micro liquid and slope length to obtain the factors for optimal slope angle modeling.

• Journal of Sensor Science and Technology
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• v.32 no.5
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• pp.307-312
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• 2023

To measure the flow velocity and direction in the near field of an unmanned underwater vehicle, an optical measurement unit containing an image sensor and a phosphor-integrated pillar that mimics the neuromasts of a fish was constructed. To analyze pillar movement, which changes with fluid flow, fluorescence image analysis was conducted. To analyze the flow velocity, mean force analysis, which could determine the relationship between the light intensity of a fluorescence image and an external force, and length-force analysis, which could determine the distance between the center points of two fluorescence images, were employed. Additionally, angle analysis that can determine the angles at which pixels of a digital image change was selected to analyze the direction of fluid flow. The flow velocity analysis results showed a high correlation of 0.977 between the external force and the light intensity of the fluorescence image, and in the case of direction analysis, omnidirectional movement could be analyzed. Through this study, we confirmed the effectiveness of optical flow sensors equipped with phosphor-integrated pillars.