• Structural Engineering and Mechanics
• /
• v.65 no.6
• /
• pp.645-656
• /
• 2018

Importance of procuring adequate knowledge about the mechanical behavior of double-layered graphene sheets (DLGSs) incensed the authors to investigate wave propagation responses of mentioned element while rested on a visco-Pasternak medium under hygro-thermal loading. A nonlocal strain gradient theory (NSGT) is exploited to present a more reliable size-dependent mechanical analysis by capturing both softening and hardening effects of small scale. Furthermore, in the framework of a classical plate theory the kinematic relations are developed. Incorporating kinematic relations with the definition of Hamilton's principle, the Euler-Lagrange equations of each of the layers are derived separately. Afterwards, combining Euler-Lagrange equations with those of the NSGT the nonlocal governing equations are written in terms of displacement fields. Interaction of the each of the graphene sheets with another one is regarded by the means of vdW model. Then, a widespread analytical solution is employed to solve the derived equations and obtain wave frequency values. Subsequently, influence of each participant variable containing nonlocal parameter, length scale parameter, foundation parameters, temperature gradient and moisture concentration is studied by plotting various figures.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.32 no.E
• /
• pp.33-46
• /
• 1990

Abstract Over 700/0 of the rural land area in Korea is mountainous and small watersheds provide most of the water resources for agricutural use. To provide an appropriate tool for the agricultural water resource development project, SNUA2, a mathematical model for simulating the physical processes governing the precipitation-runoff relationships and predicting the storm and long-term runoff quantities from the small mountainous watersheds was developed. The hydrological characteristics of small mountainous watersheds were reviewed to select appropriate theories for the simulation of the runoff processes, and a deterministic and distributed model was developed. In this, subsurface flows are routed by solving Richard's two dimensional equation, the dynamics of soil moisture contents are simulated by the consideration of phenological factors of canopy plants and surface flows are routed by solving the kinematic wave theory by numerical analysis. As a result of an application test of the model to the Sanglim watershed, peak flow rates of storm runoff were over-estimated by up to 184.2%. The occurence time of peak flow and total runoff volume of storm runoffs simulated were consistent with observed values and the annual runoff volumes were simulated in the error range of less than 5.8%.

• Korean Journal of Applied Biomechanics
• /
• v.30 no.3
• /
• pp.217-223
• /
• 2020

Objective: The purpose of this study was to analyze the effect of postural sway on the kinematic variables of the putter head during golf putting and to provide information to the importance of postural sway control in the putting stroke for novice golfers. Method: The center of pressure (CoP) and Kinematics variables of the putter head were calculated during 2 m flat golf putting using 8 motion capture cameras (250 Hz) and 2 force plate (1,000 Hz). SPSS 24.0 was used to perform Pearson's correlation coefficient and simple regression analysis, and the statistically significance level was set to .05. Results: As a result of analyzing the correlation between CoP variables and the putter head rotation angle, the CoP moving length, CoP moving range (ML direction), and CoP moving velocity (ML direction) showed a positive correlation with the putter head rotation angle (yaw axis) and were statistically significant. Conclusion: Therefore, In order to perform the accurate putting stroke maintaining the ball's directionality, it is determined that it is important to control posture sway in the ML directions by minimizing the movement and velocity of the CoP.

• Transactions of Materials Processing
• /
• v.33 no.1
• /
• pp.18-35
• /
• 2024

In the present work, the evolution rules for the internal variables including continuum damage factors are obtained using the thermodynamic framework, which are in turn facilitated to derive the elastic-plastic constitutive relation for the particulate composites. Using the Mori-Tanaka scheme, the homogenization on state and internal variables such as back-stress and damage factors is carried out to procure the rate independent plasticity relations. Moreover, the degradation of mechanical properties of constituents is depicted by the distinctive damages such that the phase and interfacial damages are treated individually accordingly, whereas the kinematic hardening is depicted by combining the Armstrong-Frederick and Phillips' back-stress evolutions. On the other hand, the present constitutive relation for each phase is expressed in terms of the respective damage-free effective quantities, then, followed by transformation into the damage affected overall nominal relations using the aforementioned homogenization concentration factors. An emphasis is placed on the qualitative analyses for strain localization by observing the perturbation growth instead of the conventional bifurcation analyses. It turns out that the proposed constitutive model offers a wide range of strain localization behavior depending on the evolution of various internal variable descriptions.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.17 no.5 s.122
• /
• pp.415-426
• /
• 2007

In a link motion punch press, numerous links are interconnected and each link executes a constrained motion at high speed. As a consequence, dynamic unbalance force and moment are transmitted to the main frame of the press, which results in unwanted vibration. This degrades productivity and precise stamping work of the press. This paper presents an effective method for reducing dynamic unbalance in a link motion punch press based upon kinematic and dynamic analyses. Firstly, the kinematic analysis is carried out in order to understand the fundamental characteristics of the link motion mechanism. Then design variable approach is presented in order to automate the model setup for the mechanism whenever design changes are necessary. To obtain the inertia properties of the links such as mass, mass moment of inertia, and the center of mass, 3-dimensional CAD software was utilized. Dynamic simulations were carried out for various combinations of design changes on some links having significant influences on kinematic and dynamic behavior of the mechanism.

• Korean Journal of Applied Biomechanics
• /
• v.18 no.4
• /
• pp.209-216
• /
• 2008

The purposes of this study were to describe the techniques used by the university male's triple jumpers and to examine the characteristics of the kinematic and the kinetic factors of the three phases of a triple jump. The subjects were the five finalists with 16.70m over in the triple jump at the 2003 World Student Games. After analyzing the kinematic and the kinetic data during the whole triple jump, the following findings are obtained. The heights of the center of gravity of takeoff and touchdown for the three phases of the triple jump were medium-law-high pattern and the same height pattern as hop and step, respectively. Mean values for the average forces exerted on the subjects ranged from 0.6 to 0.7 times body weight to the horizontal direction and about 2.8 to 3.0 times body weight to the vertical direction.

• Korean Journal of Applied Biomechanics
• /
• v.14 no.1
• /
• pp.27-40
• /
• 2004

The purpose of this study was to provide basic data for improving athletic performances by analyzing the kinematic variables of the Double Backward Somersault on the Parallel Bars through the 3D motion analysis. The subjects in this study were 5 male gymnasts who were ranked as national athletes. The results are as follows. 1. A total time(Mean Time) of performance showed $2.72{\pm}0.82\;sec$. and flight time to landing after releasing was 0.87sec.(mean). In order to perform better stable flying movement, the flight time should be increased. 2. In the change of velocity of the center of mass, when the increasing ascension velocity of the upper point was high, the position in the top point was high on releasing. 3. In the position variable of the center of mass, the mean of upper-bottom position in horizontal posture was $242.1{\pm}6.5cm$, $232.8{\pm}6.4cm$ in releasing, and $265.0{\pm}5.6cm$ in the highest point. This result is explained that the position of center of mass can be raised by using elastic power when wrist raised the bar in the releasing movement. 4. The angle of shoulder joint was $271.1{\pm}14.0$. Such a big angle influences a negative effect on the releasing velocity, because trunk is not a position in the enough vertical direction. 5. The ankle of hip joint in hand-standing was $191.1{\pm}5.9$, $118.8{\pm}5.3$ in releasing, and $122.3{\pm}5.3$ in taking on. Therefore, the result suggests that trunk should be straightly raised in taking on.

• Korean Journal of Applied Biomechanics
• /
• v.31 no.4
• /
• pp.259-269
• /
• 2021

Objective: The purpose of this systematic review and meta-analysis was to investigate age-related bimanual coordination functions in older adults. Method: Thirteen studies that compared bimanual coordination functions in older adults with those in healthy young adults qualified for this meta-analysis. We additionally categorized 21 total comparisons from the 13 qualified studies into two types of task-related moderator variables: (1) kinematic versus kinetic movements and (2) symmetry versus asymmetry movements. Results: Random effects model meta-analysis found that older adults revealed significant bimanual coordination impairments as compared with young adults (Hedges's g = -0.771; p < .0001; I² = 74.437%). We additionally confirmed specific bimanual coordination deficits using two moderator variables: 1) kinematic (Hedges's g = -0.884; p < .0001; I² = 0.000%) and kinetic (Hedges's g = -0.666; p = .023; I² = 86.170%). 2) symmetry (Hedges's g = -0.712; p = .001; I² = 74.291%) and asymmetry (Hedges's g = -0.817; p < .0001; I² = 76.322%). The moderator variable analysis indicated older adults indicated bimanual coordination deficits in the upper extremities than healthy young adults while performing kinematic bimanual coordination tasks and asymmetry coordination tasks. Conclusion: These findings suggest that developing motor rehabilitation programs based on asymmetric bimanual movement task for enhancing interlimb coordination functions of older adults may be crucial for increasing their independence in everyday activities. Given that elderly revealed the deficits in lower extremities coordination when older adults perform gait, posture, and balance, future studies should estimate lower limb coordination functions in elderly people.

• Korean Journal of Applied Biomechanics
• /
• v.17 no.2
• /
• pp.11-21
• /
• 2007

The study was undertaken to present the quantitative materials available in underwater industries, underwater rehabilitation & physical training through comparison & analysis of effects contributing to propulsion of COG by types of fin-kick in underwater activities. For this 3D cinematography was performed for the skilled subjective and conclusions obtained on the basis of analysis of kinematic variables were as follows. In temporal variable the delay in the order of flutter>side>dolphin kick in elapsed time by total & phase resulted in longer sliding phase by larger fin kick of extension & flexion of both leg and thus more contributed in propulsion of COG. than those of the otherwise. In linear variable the contribution ratio to the result of propulsion of COG in both propulsive(mean $35.39{\pm}7.93cm$ in Y axis) and sliding phases(mean $66.36{\pm}11.01cm$ in Y axis)was shown to be order of flutter>dolphin>side fin kick. the maximum velocity of COG in Y direction was showed in both propulsive and sliding phases, and the contribution ratio to the propulsion of COG was in the order of flutter$\geq$dolphin>side fin kick. In angular variable the Significant difference in angle of leg joint by types of fin kick in both leg was showed but no routine order. The Significant difference in angular velocity of leg joint by types of fin kick in both leg was showed in the order of flutter>dolphin$\geq$side fin kick in propulsive but no in sliding phase. The Fluid resistance by tilting angle of trunk in both propulsive and sliding phase was decreased in the order of flutter>dolphin$\geq$side fin kick and tilting angle of trunk of the skilled was smaller than that of the unskilled in difference of maximum mean 7.97degree and minium mean 2.06degree. In summary of the above, It will desirable fin kick type because of more contribution to COG propulsion by the velocity & displacement in Y-axis and less fluid resistance by tilting angle of trunk and larger angular velocity in the case of more delayed in elapsed time of propulsive phase than that of the otherwise.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.50 no.8
• /
• pp.531-540
• /
• 2022

In this paper, we present an algorithm that identifies artillery type and rapidly predicts the impact point based on the IMM filter. The ballistic trajectory equation is used as a system model, and three models with different ballistic coefficient values are used. Acceleration was divided into three components of gravity, air resistance, and lift. And lift acceleration was added as a new state variable. The kinematic condition that the velocity vector and lift acceleration are perpendicular was used as a pseudo-measurement value. The impact point was predicted based on the state variable estimated through the IMM filter and the ballistic coefficient of the model with the highest mode probability. Instead of the commonly used Runge-Kutta numerical integration for impact point prediction, a semi-analytic method was used to predict impact point with a small amount of calculation. Finally, a state variable initialization method using the least-square method was proposed. An integrated algorithm including artillery type identification, impact point prediction and initialization was presented, and the validity of the proposed method was verified through simulation.