• 한국재료학회지
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• 제11권9호
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• pp.763-768
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• 2001

Molybdenum-based thermal spray powder is widely used for coating the moving parts of the internal combustion engines due to its excellent wear resistance. A composite powder of the $Mo_{40}(Al_{1-x}Si_x)_{60}$ system was synthesized using the SHS method. The synthesized bulk was pulverized and specially treated to produce thermal spray powder. It was found that the synthesis reaction consisted of two-steps: the formation of $Al_8/Mo_3$ and the formation of Mo(Al,Si)$_2$. Both the temperature and the rate of the SHS reaction linearly increased with the increase of the value of x in $Mo_{40}(Al_{1-x}Si_x)_{60}$, The temperature and the rate of the reaction were also affected by the compacting density of the specimens, exhibiting the maximum valves at 62% and 60%, respectively. Since spherical shape is advantageous to the thermal spraying process, shape-control of the powder was attempted with PVA as a binding additive, resulting in the successful production of almost perfectly spherical powder of 80 $\mu\textrm{m}$ Ø$(d_{50})$ mean particle size.

• 한국항공우주학회지
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• 제49권4호
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• pp.301-309
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• 2021

펄스개수측정방법은 반작용휠의 속도를 측정하는 고전적인 방법이다. 본 연구에서는 펄스개수측정방법을 수식으로 표현하였다. 반작용휠의 회전을 속도가 아니라 샘플링 시간 동안의 회전각도로 모델링하였다. 제안된 모델의 유효성은 모델에서 얻어진 펄스개수 변화와 이동평균의 효과가 기존 연구결과와 동일함을 확인하는 방법으로 검증하였다. 이렇게 검증된 모델에 타코펄스 불균일성을 추가하고 펄스개수측정방법의 오차에 대해서 살펴보았다. 불균일성으로 인해서 증가하는 측정오차의 크기를 수식으로 표현하였으며, 측정오차를 상쇄하기 위해서 취해야 하는 이동평균의 개수 조건을 제시하였다.

• 한국전문물리치료학회지
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• 제27권2호
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• pp.155-161
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• 2020

Background: The consequences of falls are often debilitating, and prevention is important. In theory, the lower the center of mass (COM), the greater postural stability during standing, and a weight belt at the waist level may help to lower the COM and improve the standing balance. Objects: We examined how the limit of stability (LOS) was affected by the lowered center of mass with the weight belt. Methods: Twenty healthy individuals participated in the LOS test. After calculating each participant's COM, a weight belt was fastened ten centimeters below the COM. Trials were acquired with five weight belt conditions: 0%, 2%, 4%, 6%, and 8% of body weight. Outcome measures included reaction time, movement velocity, endpoint excursion, maximum excursion, and directional control in 4 cardinal moving directions. Results: None of our outcome variables were associated with a weight belt (p > 0.075), but all of them were associated with moving direction (p < 0.01). On average, movement velocity of the COM and maximum excursion were 31% and 18% greater, respectively, in mediolateral than anteroposterior direction (5.4°/s vs. 4.1°/s; 97.5% vs. 82.6%). Conclusion: Our results suggest that postural stability was not affected by the weight-induced lowered COM, informing the development and improvement of balance training strategies.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.426-432
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• 2000

The hydraulic loading system real-time simulator using a PC and I/O interface board is developed to simulate the dynamic characteristics of hydraulic loading system in real time. The simulator receives the digital on-off control signals generated by the operator through the D/I channels, updates the state and output variables of the hydraulic loading system responding to the input signals and draw the moving pictuters of the lift cylinder, lift arm and loading box on the PC monitor in real time. Also, the operator can observe the displacement and pressure of cylinder, the rotatinal angle, reaction force, and safety factors of lift arm representing the operation of hydraulic loading system through the PC monitor in real time. The real-time simulator can be a very useful tool to design industrial dynamic systems and feel the goodness of the system operation since the operator can observe the moving pictures of the operating system in real time as he operates the real time simulator.

• 제어로봇시스템학회논문지
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• 제8권11호
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• pp.954-962
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• 2002

In a park or street, we can see many people jogging or walking with their dogs tracking their masters. In this study, an entertainment robot that imitates a dog's behavior is created. The robot's task is tracking a moving target that is recognized as the master. In order to design the robot, the ecological approach. in which the robot's goals and surroundings heavily influence its design, is used. A three-wheel type locomotion system is designed as the robot's physical structure which can follow a human jogging in outdoor space like a park. A sensor system which can detect the position of a master for the robot in the outdoor space, is developed. This sensor system consists of a signal transmitter which is at the hand of a master and some sensors which are mounted on the robot. The transmitter emits RF(radio frequency) and ultrasonic signals and the sensors detect the direction and distance from the robot to the transmitter by using the received signals. For the control architecture of the robot, a purely reactive behavior-based method is used in order to increase speed of response. The developed robot is evaluated through experiments conducted in indoor and outdoor environments.

• Steel and Composite Structures
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• 제50권1호
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• pp.15-24
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• 2024

This research presents dynamical reaction investigation of pore-dependent and nano-thickness beams having functional gradation (FG) constituents exposed to a movable particle. The nano-thickness beam formulation has been appointed with the benefits of refined high orders beam paradigm and nonlocal strain gradient theory (NSGT) comprising two scale moduli entitled nonlocality and strains gradient modulus. The graded pore-dependent constituents have been designed through pore factor based power-law relations comprising pore volumes pursuant to even or uneven pore scattering. Therewith, variable scale modulus has been thought-out until process a more accurate designing of scale effects on graded nano-thickness beams. The motion equations have been appointed to be solved via Ritz method with the benefits of Chebyshev polynomials in cosine form. Also, Laplace transform techniques help Ritz-Chebyshev method to obtain the dynamical response in time domain. All factors such as particle speed, pores and variable scale modulus affect the dynamical response.

• 한국해양공학회지
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• 제22권4호
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• pp.90-96
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• 2008

In general, the swing motions of a crane are controlled and suppressed by controlling the trolley motion. In many of our previous studies, we suggested a new type of anti-sway control system for a crane. In this proposed control system, a small auxiliary mass (moving-mass) is installed on the spreader and moving this auxiliary mass controls tire swing motion. The actuator reaction against the auxiliary mass applies inertial control forces to the container in order to reduce the swing motion in the desired manner. However, measuring systems based on a laser sensor or other means are not veryuseful in real-worldapplications. So, in this paper, animage sensor is used to measure the motions of the spreader and the measured data are fed back to the controller in real time. The applied image processing technique is a kind of robust template matching method called Vector Code Correlation (VCC), which was devised to consider real environmental conditions. The H $\infty$ based control technique is applied to suppress the swing motion of the crane. Experimental results showed that the proposed measurement and control system based on an image sensor is useful and robust to disturbances.

• 한국운동역학회지
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• 제12권2호
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• pp.179-195
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• 2002

본 연구의 목적은 현대 스포츠가 점점 스피디하고 격렬한 상황의 연출을 요구하고 있는 상황에서 순간적으로 신속 정확한 판단력과 그에 따른 재빠르고 민첩한 행동이 필요할 때가 많으므로 준비동작에 대한 운동역학적 메카니즘의 이해가 필요하다고 판단되어 연구를 실시하였다. 따라서 본 연구에서는 준비동작의 형태 변화(open stance & cross stance)에 따른 신체움직임을 운동역학적인 분석을 통하여 바람직한 준비동작의 모델을 제시하는데 있으며, 이러한 연구 목적을 달성하기 위하여 연구대상자는 부산 B대학교 핸드볼 선수인 남학생 5명과 부산 S대학교 사격 선수인 여학생 5명을 선정하여 실험하였다. 준비자세에서의 좌 우 전방향으로 이동시의 동작을 2대의 고속 비디오 카메라와 2대의 지면반력기 그리고 전신반응측정 장비를 이용하여 자료를 수집하였고, 준비자세에서의 좌 우 전방향 이동시의 메카니즘을 분석한 결과 다음과 같은 결론을 얻었다. 첫째, 준비자세에서 좌 우 전방향 이동시 cross stance 자세가 open stance 자세 보다 신체중심이동 속도가 빠른 것으로 분석되었으며, Take-off시 슬관절의 굴곡각은 약 $175^{\circ}$의 각도를 유지하고, 고관절의 굴곡각은 약 $172^{\circ}$의 각도를 유지하여 준비자세를 취하는 것이 바람직한 것으로 분석되었다. 둘째, 준비자세에서의 좌 우 전방향으로 이동시 지지시간과 지면반력분석 결과를 종합해 보면 준비동작에서 왼쪽방향으로 이동시 가장 빠른 신체중심이동 속도를 나타냈다. 셋째, 준비자세에서 좌 우 전방향 이동시 지면반력 분석 결과에서도 cross stance 자세가 open stance 자세보다는 왼발과 오른발에 체중을 적절히 분산시켜 준비동작을 수행할 수 있도록 하여 상해를 예방할 수 있으므로 cross stance 준비자세가 바람직한 것으로 분석되었다. 따라서 준비자세의 역학적인 메가니즘은 cross stance 자세가 open stance 자세보다 보다 바람직한 준비자세라고 할 수 있으나 반드시 개인차도 고려되어져야 할 것이다.

• 자원리싸이클링
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• 제18권1호
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• pp.22-29
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• 2009

중유회를 효율적으로 소각 처리할 수 있는 이동상식 스토카로를 설계, 제작하기 위해 중유회가 노상을 이동하면서 겪는 조건들을 회분식 노에서 모사(模寫)하여 열중량분석법으로 중유회의 소각실험을 수행하였다. 이 결과로부터 이동상식 스토카로의 운전조건 및 노상면적 등을 구하였다. 중유회의 연소과정은 연소속도 차이에 의해 3단계로 구별되며, 각 단계별로 효과적인 연소가 이루어질 수 있도록 해야 한다. 비산방지 및 체적감소를 위하여 소각 전 첨가되는 수분 함량은 20 wt.%가 적절하였다. 중유회의 연소속도는 산소농도에 크게 의존하므로, 소각로는 연소공기의 조절 기능이 필요하다. 저융점 금속화합물의 용착 및 증발을 방지하고, 소각잔사의 불용화 및 유가금속 회수를 위해 소각온도는 $750^{\circ}C{\sim}800^{\circ}C$가 적절하고, 중유회의 균일한 연소반응과 연소속도의 향상을 위해 소각 중 중유회의 교반이 요구된다. 최적 조건에서 단위면적당 소각속도는 $12.53kg/m^{2}hr$이며 1일 18 ton의 중유회를 소각처리하기 위해서는 $60m^2$의 노상면적이 필요하다.

• Computers and Concrete
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• 제19권3호
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• pp.315-323
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• 2017

Within the context of continuum mechanics, inelastic behaviours of constitutive responses are usually modelled by using phenomenological approaches. Elasto-plastic damage modelling is extensively used for concrete material in the case of progressive strength and stiffness deterioration. In this paper, a review of the main features of elasto-plastic damage modelling is presented for uniaxial stress-strain relationship. It has been reported in literature that the influence of Alkali-Silica Reaction (ASR) can lead to severe degradations in the modulus of elasticity and compression strength of the concrete material. In order to incorporate the effects of ASR related degradation, in this paper the constitutive model of concrete is based on the coupled damage-plasticity approach where degradation in concrete properties can be captured by adjusting the yield and damage criteria as well as the hardening moduli related parameters within the model. These parameters are adjusted according to results of concrete behaviour from the literature. The effect of ASR on the dynamic behaviour of a beam and a column are illustrated under moving load and cyclic load cases.