• International Journal of Aeronautical and Space Sciences
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• v.2 no.2
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• pp.1-18
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• 2001

A numerical technique for simulating the separation dynamics of strap-on boosters jettisoned in the dense atmosphere is presented. Six degree of freedom rigid body equations of motion are integrated into the three-dimensional unsteady Navier-Stokes solution procedure to determine the dynamic motions of strap-ons. An automated Chimera overlaid grid technique is introduced to achieve maximum efficiency for multi-body dynamic motion and a domain division technique is implemented in order to reduce the computational cost required to find interpolation points in the Chimera grids. The flow solver is validated by comparing the computed results around the Titan IV launch vehicle with experimental data. The complete analysis process is then applied to the. H-II launch vehicle, the central rocket in japans space program, the CZ-3C launch vehicle developed in China and the KSR-III, a three-stage sounding rocket being developed in Korea. From the analyses, separation trajectories of strap-on boosters are predicted and aerodynamic characteristics around the vehicles at every time interval are examined. In addition, separation-impulse devices generally introduced for safe separation of strap-ons are properly modeled in the present paper and the jettisoning force requirements are examined quantitatively.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.306-313
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• 2004

The microwave discharge ion engine generates plasmas of both the main ion source and the neutralizer using 4㎓ microwave without discharge electrodes and hollow cathodes, so that long life and durability against oxygen and air are expected. The MUSES-C “HAYABUSA” asteroid explorer installing four microwave discharge ion engines “$\mu$10s” was launched into deep space by M-V rocket No.5 on May 9, 2003. After vacuum exposure and several runs of baking for reduction of residual gas the ion engine system established the continuous acceleration of the spacecraft toward the asteroid “ITOKAWA”. The Doppler shift measurement of the communication microwave revealed the performance of ion engines, which is 8mN thrust force for a single unit with 3,200sec specific impulse at 23mN/㎾ thrust power ratio. At the end of 2003 the accumulated operational time exceeded 8,000 hour and unit. HAYABUSA will execute the Earth swing-by on June 2004 and arrive at the asteroid in 2005 and return to Earth in 2007.

• Korean Journal of Applied Biomechanics
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• v.20 no.4
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• pp.365-372
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• 2010

The purpose of this study were to analyze the changes in kinematic and kinetic parameters and to find biomechanical benefits of Nordic Walking and normal gait performed under the same velocity. Nine participants(age: $26.73{\pm}3.28$ year, height: $182.45{\pm}4.62\;cm$, weight: $76.59{\pm}6.84\;kg$) was chosen. The velocity of gait was set by 5.75 km/h which was made by a Nordic Walking professional. The data were collected by using VICON with 8 cameras to analyze kinematic variables with 200 Hz and force platform to analyze kinetic variables with 2000 Hz. The results of this study were as follows. First, when compared with Normal gait, Nordic Walking group showed decreased Plantarflexion angle and ROM. Second, Nordic Walking group showed decreased knee flexion angle and ROM. Third, Nordic Walking group showed increased hip joint movement. Fourth, Nordic Walking group showed higher active GRF but decreased loading rate from delayed Peak Vertical GRF time and increased impulse. Fifth, Nordic Walking group showed longer ground contact time. Through this study, we found that Nordic Walking showed higher stability and efficiency during gait than normal gait and that Nordic Walking may help people who have walking difficulties.

• Korean Journal of Applied Biomechanics
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• v.23 no.2
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• pp.131-139
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• 2013

Naejirgi is one of the fastest, most forceful and most often being used kicks in Taekkyon games, The purpose of this study was to investigate kinetic factors on two types of Naejirgi kick, one of which uses knee bending of supporting leg and the other uses little it. 12 taekkyoners (11 males and one female) who are the students of Y University participated in this study. They have been practicing on Taekkyon for five years or more. Positions of CoM, the elapsed time of each phase, vertical ground reaction forces, joint moments and impulses of supporting leg were analyzed for this study. The results were as follows; in Naejirgi with knee bending of supporting leg than without knee bending of supporting leg, the vertical motion range of whole body CoM was larger during phase 2 and 3, the elapsed time of phase 4 were longer, players stayed longer in the nearest location to opponent, during phase 4 the vertical ground reaction forces of supporting foot were larger, and joint extension moments and angular impulses of supporting leg (especially knee) were larger. In conclusion supporting knee bending is not a useful strategy for Naejirgi, because players stay longer in the nearest position to opponent and consumed more muscle force and energy for producing the vertical momentum which is unnecessary for pushing down the opponent.

• Journal of Institute of Convergence Technology
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• v.7 no.2
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• pp.25-30
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• 2017

This paper presents the effects of a virtual mass with a low-pass filter on the stability boundary of a virtual spring in the haptic system. In general, a haptic system consists of a haptic device, a sampler, a virtual impedance model and zero-order-hold. The virtual impedance is modeled as a virtual spring and a virtual mass. However the high-frequency noise due to the sampling time and the quantization error of sampled data may be generated when an acceleration is measured to compute the inertia force of the virtual mass. So a low-pass filter is needed to prevent the unstable behavior due to the high-frequency noise. A finite impulse response (FIR) filter is added to the measurement process of the acceleration and the effects on the haptic stability are simulated. According to the virtual mass with the FIR filter and the sampling time, the stability boundary of the virtual spring is analyzed through the simulation. The maximum available stiffness to guarantee the stable behavior is reduced, but simulation results still show that the stability boundary of the haptic system with the virtual mass is larger than that of the haptic system without the virtual mass.

• Smart Structures and Systems
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• v.24 no.4
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• pp.525-539
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• 2019

In this study, vibration characteristics of a gravity-based caisson-foundation breakwater system are investigated for ambient and geometric parameters such as various waves, sea levels, and foundation conditions. To achieve the objective, following approaches are implemented. Firstly, operational modal analysis methods are selected to identify vibration modes from output-only dynamic responses. Secondly, a finite element model of an existing caisson-foundation breakwater system is established by using a structural analysis program, ANSYS. Thirdly, forced vibration analyses are performed on the caisson-foundation system for two types of external forces such as controlled impacts and wave-induced dynamic pressures. For the ideal impact, the wave force is converted to a triangular impulse function. For the wave flow, the wave pressure acting on the system is obtained from wave field analysis. Fourthly, vibration modes of the caisson-foundation system are identified from the forced vibration responses by combined use of the operational modal analysis methods. Finally, vibration characteristics of the caisson-foundation system are investigated under various waves, sea levels, and foundations. Relative effects of foundation conditions on vibration characteristics are distinguished from that induced by waves and sea levels.

• Journal of Practical Engineering Education
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• v.13 no.3
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• pp.497-505
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• 2021

Test equipment for strain and vibration measurement was designed for educational purposes. Widely available and affordable materials were put into making this device. Three strain gauges placed on an iron ruler made cantilevered beam were used to measure values according to external load. An electromagnet triggered excitation and a function generator created vibration of the beam. We present three different tests conducted with this equipment regarding production of scales, measurement of resonant frequency, and calculation of the difference between excitation frequency and measured frequency. Overall, this paper presents a piece of simple yet inexpensive test equipment and its corresponding portfolio with expectations of being applied to the educational field for efficient measurement of load and vibration.

• Physical Therapy Rehabilitation Science
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• v.11 no.3
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• pp.279-284
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• 2022

Objective: This study was conducted to confirm the effect of physiotherapy on the balance and walking in dog with sciatic nerve injury and degenerative arthritis of stifle joints. Design: Single case study Methods: The dog walked abnormally for six months and was administrated in S animal hospital. The dog's right hindlimb was operated for cranial cruciate ligament repair and the dog had been taking a nonsteroidal anti-inflammatory analgesic before being refered. There was severe degenerated osteoarthritis in the right hindlimb. During stance and walking, the right hindlimb was often shown partial weight bearing. The dog's left hindlimb was shown plantigrade stance and walking. The radiograph was shown an intact calcaneal tendon in the left hindlimb. In the neurologic examination, sciatic nerve injury in the left hindlimb was confirmed. The dog was treated using muscle strengthening, proprioceptive exercise, underwater treadmill and Laser therapy two, or three times a week for 3 months. At the 10th and 17th treatment, it was evaluated through stance and gait analyzer system to measure dog's balance and walking. Results: 3 months following physiotherapy, the dog's balance was improved in center of pressure(COP). And peak vertical force(PVF), vertical impulse(VI) was increased in right hindlimb and double stance was decreased. Conclusions: Physiotherapy may have improved the prognosis in this dog with severe osteoarthritis and sciatic nerve injury. This study suggested that animal physiotherapy is a valuable way to improve balance and walking.

• Smart Structures and Systems
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• v.30 no.4
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• pp.397-410
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• 2022

It is essential to monitor the working conditions of bolt-connected joints, which are widely used in various kinds of steel structures. The looseness of bolts may directly affect the stability and safety of the entire structure. In this study, a guided wave-based method for bolt looseness detection and localization is presented for a joint structure with multiple bolts. SH waves generated and received by a small number (two pairs) of magnetostrictive transducers were used. The bolt looseness index was proposed based on the changes in the reconstructed responses excited by the time reversal signals of the measured unit impulse responses. The damage locations and local damage severities were estimated using the damage indices from several wave propagation paths. The back propagation neural network (BPNN) technique was employed to identify the local damages. Numerical and experimental studies were conducted on a lap joint with eight bolts. The results show that the total damage severity can be successfully detected under the effect of external force and measurement noise. The local damage severity can be estimated reasonably for the experimental data using the BPNN constructed by the training patterns generated from the finite element simulations.

• Journal of Institute of Convergence Technology
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• v.13 no.1
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• pp.29-34
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• 2023

This paper presents the effects of a virtual mass with a low-pass filter on stability boundaries of a virtual spring in the haptic system with first-order hold. A virtual mass is required to improve the realism of a virtual environment. However the second derivative of a displacement of a haptic device is needed while the inertia forces are computed, which causes the reflective force to change quickly and then makes the haptic system unstable. A low pass filter is added to resolve this problem and the stability region of a haptic system depends on the characteristics of the filter. In this paper the finite impulse response filter (FIR filter) is applied as one of low pass filters and the effect of the FIR filter on the stable region of a haptic system with first order hold is analyzed. When compared to stable region of the system without the FIR filter, the region of available virtual mass is increased by 20% and the maximum of the stable virtual spring is reduced by 32%, irrespective of the sampling time. Besides it is shown that the stable region of a virtual spring is proportional to the inverse square of the sampling period.