• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.2
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• pp.227-235
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• 2016

Heavy-weight high speed underwater vehicle(HSUV) is launched from the submerged mother ship. For the safety point of view, it is important to confirm whether the HSUV would touch the launching mother ship. In this paper, the hydrodynamic force and moment were modeled by the polynomials of motion variables and the simple lift and drag acting on a plate and cylinder which consist of the HSUV's several parts. The mother ship was assumed as the Rankine half body to consider the flow field near the moving ship. Such hydrodynamic force and moment were included in the 6 DOF equations of motion of the HSUV and the dynamic simulations for the various conditions of the HSUV until the propeller activation were performed. Developed simulation program is expected to reduce the number of expensive sea trial test to develop safety logic of the HSUV at the initial firing stage.

• The Journal of Korean Physical Therapy
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• v.34 no.4
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• pp.175-180
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• 2022

Purpose: Leg length discrepancy causes the posture deformation, gait asymmetry, and lower back pain. The purpose of this study is to investigate the correlation among functional leg length discrepancy (FLLD), muscle activity, muscle contraction onset time and vertical ground reaction force (vGRF) during simple lifting task. Methods: Thirty-nine subjects participated in this study. FLLD was measured from the umbilicus to medial malleolus of left and right leg using a tape. The subjects performed to lift a 10 kg box from the floor to chest. The muscle activity and muscle contraction onset time of rectus abdominis, erector spinae and rectus femoris was measured using EMG system and vGRF was measured by two force plate. Pearson correlation was used to fine out the correlation among FDDL, muscle activity, muscle contraction onset time and vGRF during simple lifting task. Results: Correlation between FLLD and difference of muscle activity of short-long side was very high (r>0.9) during simple lifting task. Correlation between FLLD and difference of muscle contraction onset time of short-long side was very high (r>0.9) during simple lifting task. And correlation between FLLD and difference of vGRF of short-long side was high (r>0.7) during simple lifting task. Conclusion: This study suggests that there is high correlation between FLLD and muscle activity, muscle contraction onset time, and ground reaction force during simple lifting task. Therefore, FLLD could negatively affect the postural balance.

• Korean Journal of Materials Research
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• v.19 no.1
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• pp.28-32
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• 2009

Silicon carbide (SiC) is a promising material for power device applications due to its wide band gap (3.26 eV for 4H-SiC), high critical electric field and excellent thermal conductivity. The Schottky barrier diode is the representative high-power device that is currently available commercially. A field plate edge-terminated 4H-SiC was fabricated using a lift-off process for opening the Schottky contacts. In this case, Ni/Ti dual-metal contacts were unintentionally formed at the edge of the Schottky contacts and resulted in the degradation of the electrical properties of the diodes. The breakdown voltage and Schottky barrier height (SBH, ${\Phi}_B$) was 107 V and 0.67 eV, respectively. To form homogeneous single-metal Ni/4H-SiC Schottky contacts, a deposition and etching method was employed, and the electrical properties of the diodes were improved. The modified SBDs showed enhanced electrical properties, as witnessed by a breakdown voltage of 635 V, a Schottky barrier height of ${\Phi}_B$=1.48 eV, an ideality factor of n=1.04 (close to one), a forward voltage drop of $V_F$=1.6 V, a specific on resistance of $R_{on}=2.1m{\Omega}-cm^2$ and a power loss of $P_L=79.6Wcm^{-2}$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.120-127
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• 2016

This study examined the dynamic characteristics of the gate to identify the optimal gate installation direction according to the installation direction. A 1:31 scale model was constructed for a 47.5m prototype gate using acrylic. The scaled weights were tuned by adding lead weights. The first step was to measure the natural frequencies of the model gates, and compare them with finite-element analysis of the prototypes as a calibration. The scaled model was tested in a 1.6 m wide concrete flume for two orientations to determine the effects of the gate orientation on structural vibrations. Vertical vibrations were measured under a range of operational conditions, including a range of bottom opening heights and different upstream and downstream water levels. For large bottom opening heights in the normal direction, relatively large vibrations were induced by vortices shed at the plate bottom that would strike the horizontal truss member. This phenomenon was avoided in the reverse direction. For small bottom opening heights in the normal direction, these vibrations were caused by a suction force that developed at the gate bottom. The gate model in the reverse direction was preferred because of its low overall vibrational response under general gate opening and flow level combinations.

• Korean Journal of Applied Biomechanics
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• v.15 no.3
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• pp.143-152
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• 2005

The purpose of this study was to predict the failure or success of the Snatch-lifting trial as a consequence of the stand-up phase simulated in Kane's equation of motion that was effective for the dynamic analysis of multi-segment. This experiment was a case study in which one male athlete (age: 23yrs, height: 154.4cm, weight: 64.5kg) from K University was selected The system of a simulation included a multi-segment system that had one degree of freedom and one generalized coordinate for the shank segment angle. The reference frame was fixed by the Nonlinear Trans formation (NLT) method in order to set up a fixed Cartesian coordinate system in space. A weightlifter lifted a 90kg-barbell that was 75% of subject's maximum lifting capability (120kg). For this study, six cameras (Qualisys Proreflex MCU240s) and two force-plates (Kistler 9286AAs) were used for collecting data. The motion tracks of 11 land markers were attached on the major joints of the body and barbell. The sampling rates of cameras and force-plates were set up 100Hz and 1000Hz, respectively. Data were processed via the Qualisys Track manager (QTM) software. Landmark positions and force-plate amplitudes were simultaneously integrated by Qualisys system The coordinate data were filtered using a fourth-order Butterworth low pass filtering with an estimated optimum cut-off frequency of 9Hz calculated with Andrew & Yu's formula. The input data of the model were derived from experimental data processed in Matlab6.5 and the solution of a model made in Kane's method was solved in Matematica5.0. The conclusions were as follows; 1. The torque motor of the shank with 246Nm from this experiment could lift a maximum barbell weight (158.98kg) which was about 246 times as much as subject's body weight (64.5kg). 2. The torque motor with 166.5 Nm, simulated by angular displacement of the shank matched to the experimental result, could lift a maximum barbell weight (90kg) which was about 1.4 times as much as subject's body weight (64.5kg). 3. Comparing subject's maximum barbell weight (120kg) with a modeling maximum barbell weight (155.51kg) and with an experimental maximum barbell weight (90kg), the differences between these were about +35.7kg and -30kg. These results strongly suggest that if the maximum barbell weight is decided, coaches will be able to provide further knowledge and information to weightlifters for the performance improvement and then prevent injuries from training of weightlifters. It hopes to apply Kane's method to other sports skill as well as weightlifting to simulate its motion in the future study.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.45-56
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• 2020

In this paper, intelligent compaction (IC) technology and the earthwork quality control specifications based on IC were analyzed, and the field study was conducted to investigate the relationship between the representative IC value CMV (Compaction Meter Value) and spot test results (plate bearing test and field density test). As the number of roller passes increased, both the CMV and spot test results increased. However, point-by-point comparison between CMV and spot test results yielded poor quality correlations; this is because the ununiform stiffness of the underlying layer and the moisture content of the lift layer affected the CMV and spot test results, respectively. Most international specifications related to IC requires knowledge of the IC values and their relationships with the soil properties obtained by the traditional spot tests. Therefore, for the successful implementation of intelligent compaction technology into earthwork construction practice, the number of roller passes as well as the lift thickness and the moisture content of the soil should be carefully considered.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.648-656
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• 2022

As environmental regulations such as the International Maritime Organization (IMO)'s strategy to reduce greenhouse gases(GHG) are strengthened, technology development such as eco-friendly ships and alternative fuels is expanding. As part of this, ship propulsion technology using energy reduction and wind propulsion technology is emerging, especially in shipping companies and shipbuilders. By securing wind propulsion technology and introducing empirical research into shipbuilding and shipping, a high value-added market using eco-friendly technology can be created. Moreover, by reducing the fuel consumption rate of operating ships, GHG can be reduced by 6-8%. Rotor Sail (RS) technology is to generate a hydrodynamic lift in the vertical direction of the cylinder when the circular cylinder rotates at a constant speed and passes through the fluid. This is called the Magnus effect, and this study attempted to propose a plan to increase propulsion efficiency through a numerical analysis study on turbulence flow characteristics around RS, a wind power assistance propulsion system installed on a ship. Therefore, C_L and C_D values according to SR and AR changes were derived as parameters that affect the aerodynamic force of the RS, and the flow characteristics around the rotor sail were compared according to EP application.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.5
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• pp.487-494
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• 2011

The safety valve used in LNG/LNG-FPSO ships plays an important role in maintaining a fixed level of pressure by emitting LNG gas out of the pipes in the LNG piping system. The discharge coefficient is regarded as the most important factor in the valve performance. To satisfy the ship's classification, the discharge coefficient of the safety valve must usually be over 0.8. Despite the importance of understanding the flow phenomena inside the safety valve, the valve design is usually based on experience and experiments. We carried out a computational fluid dynamics (CFD) investigation using the ANSYS-CFX software. We observed the flow phenomena inside the valve and measured the discharge coefficients according to changes in the valve lift, which is the distance between the exit of the nozzle and the lower part of the disc plate. We verified our CFD results for the discharge coefficients using available experimental data.

• The Research Journal of the Costume Culture
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• v.28 no.3
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• pp.299-312
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• 2020

The purpose of this study is to create a shirt sloper suitable for an elderly male body shape by producing virtual models using a 3D-virtualization program, making a torso prototype using the Yuka CAD system, and employing 3D simulation to virtualize and calibrate the model. First, the following three types of obese dummies are implemented through the CLO 3D program: Type 1 exhibits body fat in the lower body; Type 2 exhibits an obese abdomen; and Type 3 displays a balanced form of obesity. Second, for the design of the shirt pattern, the waist back length (measured value+1), back armhole depth (C/10+12+3+0.5~1.5), front armhole depth (back armhole depth 0~1), front interscye (2C/10-1+0.5-0.5), armscye depth (C/10+2+3.5+ 0.5), back interscye (2C/10-1+1), front chest C (C/4+2.5+1), back chest C (C/4+2.5-1), front hem C (C/4+2.5+1(+2)), back hem C (C/4+2.5-1(+2)), cap height (AH/3-5), and biceps width (Front AH-1, Back AH-1) are calculated. Third, the virtual attachment of the shirt pattern is resolved by increasing the front and back armhole depths, and the front and rear wrinkles are improved by adding a back armhole dart. The front hem lift and lateral pull caused by the protrusion of the abdomen are amended by increasing the margin of the chest, waist C, and hip C, with the appearance improved by balanced margin distribution in the front, back, and side panels. The improved retail pattern with an increase in the front armholes C was balanced on the torso plate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.97-108
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• 2015

In the design of sailing yachts, para-glider, or high-sky wind power, etc., the analysis of side-wind aerodynamic forces exerted on a cambered 3-D model is very important to predict the performance of various machinery systems. To understand the essential flow physics around the three-dimensional shape, simplified rigid-body models are proposed in this study. Four parameters such as free stream velocity, angle of attack, aspect ratio, and camber are considered as the independent variables. Lift and drag coefficients are computed with CFD technique using ANSYS-CFX, and the results with the visualization of post-processed flow fields are analyzed in the viewpoint of fluid dynamics.