• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.41-51
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• 2018

Downwash from helicopter rotor blades and external winds from various maneuvering make an unguided rocket change its trajectory and range. For the prediction of the trajectory and range, it is essential to consider the downwash effect. In this study, an algorithm was developed to calculate 6-Degree-Of-Freedom(6 DOF) forces and moments exerting on the rocket, and total flight trajectory of a 2.75-inch unguided rocket in a helicopter downwash flow field. Using Actuator Disk Model(ADM) analysis result, the algorithm could analyze the entire trajectory in various initial launch condition such as launch angle, launch velocity, and external wind. The algorithm that considered the interference between a fuselage and external winds could predict the trajectory change more precisely than inflow model analysis. Using the developed algorithm, the attitude and trajectory change mechanism by the downwash effect were investigated analyzing the effective angle of attack change and characteristics of pitching stability of the unguided rocket. Also, the trajectory and range changes were analyzed by considering the downwash effect with external winds. As a result, it was concluded that the key factors of the rocket range change were downwash area and magnitude which effect on the rocket, and the secondary factors were the dynamic pressure of the rocket and the interference between a fuselage and external winds. In tailwind case which was much influential on the range characteristics than other wind cases, the range of the rocket rose as increasing the tailwind velocity. However, there was a limit that the range of the rocket did not increase more than the specific tailwind velocity.

• Korean Journal of Applied Biomechanics
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• v.15 no.1
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• pp.75-89
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• 2005

D. K. LEE, J. S. LEE, B. J. LEE, H. S. LEE, Y. J. KIM, S. B. PARK, J. P. JOO. Plantar foot pressure analysis during golf swing motion using plantar foot pressure measurement system. Korean Journal of Sport Biomechanics, Vol. 15, No. 1, pp. 75-89, 2005. In this study, weight carrying pattern analysis and comparison method of four foot region were suggested. We used three types of club(driver, iron7, pitching wedge). This analysis method can compare between top class golfer and beginner. And the comparison data can be used to correct the swing pose of trainee. If motion analysis system, which can measure the swing speed and instantaneous acceleration at the point of hitting a ball, is combined with this plantar foot force analysis method, new design development of golf shoes to increase comfort and ball flight distance will be available. 1. Address acting, forces concentrated in rare foot regions and lateral foot of right foot. Back swing top acting, relatively high force occurred in medial forefoot region of left foot and forefoot region of right foot. Impact acting, high force value observed in the lateral rarefoot region of left foot and medial forefoot region of right foot. Finish acting, force concentration observed on the lateral region and rarefoot region of left foot. 2. Forces were increased in address of right foot with clubs length increased. All clubs, back swing top acting, high force value observed in the lateral forefoot region of right foot. All clubs, in impact, high force value observed in the lateral rarefoot region of left foot and medial forefoot region of right foot. Finish acting, force concentration observed on the rarefoot region in driver and lateral foot region in iron on left foot. 3. Right foot forces distribution were increased in address, back swing top and left foot force distribution were increased in impact, finnish

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.15 no.3
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• pp.83-91
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• 2009

It is very difficult to export the fresh agricultural products to long distance countries such as USA and EU without any damage. Fresh products exporting would overcome very severe conditions such as hot and cold weather changes, heavy vibrations with rolling and pitching during the target distribution period, therefore, the packaging needs the immobility of products in the container and the keeping its quality by packaging materials or methods under any surrounding environments, especially. The physical strength of outer box should be designated according to its own characteristics for agricultural product packaging. Packaging dimension which would be fit to standard pallet is also very important factor to reduce the distribution cost. There have been many agricultural products researches for export packaging to the USA so far. However they have never got desirable results which enough to apply it in real. The main purpose of this research is to develop optimum compressive strength and optimum dimension of corrugated fiberboard box which would be used to USA export packaging of fresh melon as well as Japan.

• Journal of Korean Orthopaedic Sports Medicine
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• v.2 no.1
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• pp.62-70
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• 2003

Purpose: We examined the kinematics and kinetics of the shoulder in youth baseball pitchers in light of the mechanisms of development of little league shoulder and humeral retrotorsion. Materials and Methods: The joint kinematics and the net force and torque acting on the humerus were calculated in fourteen youth pitchers throwing in a simulated game. Results: The major force component acting on the humerus was a tensile force of 378$\pm$81 N that peaked just after ball release. The predominant torque on the humerus was an external rotation torque about the long axis of the humerus. This torque reached a peak value of 35.3$\pm$6.7 Nm about 73$\%$through the pitching motion. This torque is approximately 66$\%$ of the torque required to fracture of the adult humerus. Conclusions: The direction of the humeral torque was consistent with the development of increased humeral retrotorsion in the throwing arm. Shear stress arising from the high torque during the late cocking phase likely leads to deformation the relatively weak proximal humeral epiphysis. The external rotation torque applied to the humerus during the pitch also agrees with the proposed mechanism for development little league shoulder, which has been hypothesized to be due to rotational stresses acting on the epiphysis during the throwing motion.

• Journal of Korean Orthopaedic Sports Medicine
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• v.4 no.1
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• pp.36-42
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• 2005

Purpose: To investigate the arthroscopic findings, and to evaluate the clinical outcomes of the treatment of posterior internal impingement of the shoulder in baseball players. Materials and Methods: We followed up 5 cases who were diagnosed as posterior internal impingement for the mean 15 months. All of the cases complained of the pain in the posterior shoulder at late cocking, and were positive in the relocation test added by hyper-horizontal abduction at $120^{\circ}$ abduction of the arm. We sutured posterior labral tear and SLAP lesion arthroscopically, and conducted debridement for rotator cuff. Three cases were performed of anterior capsular plication and the other two were performed of thermal capsular shrinkage. Pain, range of motion, and level of return to sports activity were assessed for the results. Results: As to the arthroscopic findings, all the five cases showed the fraying in posterosuperior labrum, and two of them was accompanied with the flap tear in posterosuperior labrum and the other one was accompanied with type 2 SLAP lesion. All the cases showed the fraying in supraspinatus, and one case showed partial tear. Meanwhile, in all the cases, the rotator cuff was impinged to the labrum at $90^{\circ}{\sim}120^{\circ}$ of abduction and external rotation. As to the postoperative results, all the cases did not complain of pain or instability while pitching, and the competition was recovered to be the mean 88%($80{\sim}100%$) of that before the injury. Conclusion: Definite diagnosis for the posterior internal impingement would be possible through arthroscopic examination. Favorable outcomes could be obtained with capsular plication or shrinkage for anterior microinstability and stretching exercise for posterior capsule tightness inducing the internal impingement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.373-381
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• 2017

Kyeonggi Provincial Government is considering double decker bus service to solve the problem of heavy rush hour traffic. However, the height-to-width ratio is more than 1.16 times larger than that of a general high-speed single decker bus, and the center of gravity is higher. This could cause driving stability problems, such as turnover and breakaway from the lane, especially under strong side-wind conditions at high speed. In this numerical study, the driving characteristics of a model double decker bus were reviewed under side-wind and superelevation conditions at high driving speed. The rolling, pitching, and yawing moment of the model bus were calculated with CFD numerical simulation, and the results were compared to the recovery angular moments of the model bus to evaluate the dynamic stability under given driving conditions. As the model vehicle moves on a straight level road, it is stable under any side-wind conditions. However, on a curved road under side-wind conditions, it could reach unstable conditions dynamically. There is a chance that the bus will turn over when it moves on a curved road with a radius of gyration less than 100 m under side-wind (15 m/s). However, there is a very small chance of breakaway from the lane under any driving conditions.

• Journal of the Korean Society for Railway
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• v.16 no.1
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• pp.7-13
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• 2013

A scaled version of a roller rig is developed to demonstrate the dynamic characteristics of a railway vehicle for academic purposes. This rig is designed based on Jaschinski's similarity law. It is scaled to 1/10 of actual size and allows 9-DOF motion to examine the up and down vibration of a train set. The test rig consists of three sub-hardware components: (i) a driving roller mechanism with a three-phase AC motor and an inverter, (ii) a bogie structure with first and second suspensions, and (iii) the vehicle body. The motor of the rig is capable of 3,600rpm, allowing the test to simulate a vehicle up to a maximum speed of 400Km/hr. Because bearings and joints are properly connected to the sub-structures, various motion analyses, such as a lateral, pitching, and yawing motion, are allowed. The slip motion between the rail and the wheel set is also monitored by several sensors mounted in the rig. After the construction of the hardware, an experiment is conducted to obtain the natural frequencies of the dynamic behavior of the specimen. First, the test rig is run and data are collected from six sets of accelerometers. Then, a numerical analysis of the model based on the ADAMS program is derived. Finally, the measurement data of the first three fundamental frequencies are compared to the analytical result and the validation of the test rig is conducted. The results show that the developed roller rig provides good accuracy in simulating the dynamic behavior of the vehicle motion. Although the roller rig designed in this paper is intended for academia, it can easily be implemented as part of a dynamic experiment of a bogie and a vehicle body for a high-speed train as part of the research efforts in this area.

• Journal of Korean Society of Forest Science
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• v.101 no.2
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• pp.251-258
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• 2012

This study was conducted to analyze field inspection results of erosion control facilities within national forests and to suggest maintenance and management plan of erosion control facilities. The objects amounted to a total of 1,628 locations, comprising 308 erosion control dams and 1,320 erosion control areas (1,269.05 ha). The field inspections were conducted during March-June each year. The erosion control dams inspected were constructed during 1991-2005, with 96.4% of them, or 297 dams, constructed in or after 2000. The erosion control areas were constructed during 1986-2005, with 68.6% of them, or 903 areas, constructed in or after 2000. As for erosion control dams, there were 205 concrete erosion control dams and 68 concrete with boulder pitching erosion control dams, respectively, with 296 out of a total of 308 erosion control dams in a good condition. As for erosion control areas, there were many erosion control structures using stone masonry works and gabions, with 1,245 out of a total of 1,320 (94.3%) erosion control areas in a good condition. Overall, erosion control facilities within national forests were in a good condition, amply fulfilling their functions. As for erosion control facilities in a bad condition, they must be made to accomplish the goals of erosion control works through supplementation and repairs without fail. In addition, for the systematic maintenance and management of existing erosion control facilities and erosion control facilities constructed in the future as part of erosion control works, the construction of an erosion control facility management system is urgently needed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.711-719
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• 2016

In this study, we derived an theoretical equation, using a simplified spring-mass model for the rolling stock, to obtain the overriding behavior of a leading vehicle, which is considered as the main factor in train accidents. To verify the derived equation, we created a simple 2D model based on the theoretical model, and a simple 3D model considering the characteristics of the power bogie. We then compared the theoretical results with the simulation results obtained using LS-DYNA. The maximum relative derivations in the vertical displacements at the first end-buffer, which is the most important point in overriding, were 3.5 [%] and 1.7 [%] between the two results. Further, we evaluated collision-induced overriding displacements using the theoretical equation for a rubber draft gear, a hydraulic buffer under various collision conditions. We have suggested a theoretical approach for the realization of overriding collision accidents or the energy absorption design of the front end of trains.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.146-153
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• 2000

The rubber crawler system for farm machine is composed of driving units such as track rollers, driving sprockets and rubber crawlers. Vibration characteristics of the rubber crawler system varies by driving speed, center of gravity, mass□moment of inertial□location arrangement of track rollers and dynamic parameters such as dynamic spring constant (k) and viscous damping coefficient (c) of a rubber crawler. In general, vibration of the rubber crawler system occurs by reason for mechanical interaction between the rubber crawler and track rollers. Because the dynamic spring constant and viscous damping coefficient vary periodically by mechanical characteristics(deformation characteristics) of the rubber crawler when track rollers drive on the between lugs of the rubber crawler. Therefore, both dynamic parameters k and c were expressed as Fourier series by authors through the shaking test of the rubber crawler and further, vibration characteristics of the rubber crawler system could be simulated analytically. However, actual values of dynamic parameters k and c are different from those obtained by the shaking test because dynamic characteristics of the rubber crawler vary by the effect of variable tension and driving resistance of track rollers. So, actual values of k and c should be identified in the condition of actual driving test. In this study, dynamic parameters such as k and c of the rubber crawler system, which are expressed as Fourier series, were identified using the Gauss-Newton Method. Therefore, validity of identified parameters k and c was discussed through the simulation using experimental data of actual driving test. As a result, in the Fourier series of dynamic parameters of spring constant k and viscous damping coefficient c, excellent parameter convergence and simulation were observed using the Fourier series' zero order and first term of the dynamic model. Furthermore, it was clarified that identification for model parameters which are fitted to actual dynamic motion (vibration) wave of the crawler system was possible by using the time series data observed in vertical and pitching motion of the crawler system.