• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.977-979
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• 1996

This paper presents an algorithm to control the undesirable sway of a suspended load in the crane system that has a trade-off between positioning the load and suppressing the sway of the load. The aim is to transport the load to a specified place with small sway angle as quickly as possible. Dynamic model is based on a simple pendulum driven by a velocity drive that is mostly used for actuating a trolley in industry. Proposed algorithm is composed of two parts : one is a off-line optimal trajectory generator, the other on-line tracking control. The former produces optimal trajectories minimizing energy under the speed constraint of velocity drive. The latter controls outputs to track the generated trajectories. Digital simulations and experiments are performed on a pilot crane to demonstrate the performance of the proposed control algorithm.

• Wind and Structures
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• 제38권1호
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• pp.15-42
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• 2024

A flexible-base coupled-two-beam (CTB) discrete model with equivalent tuned mass dampers is used to assess the effect of soil-structure interaction (SSI) and different types of lateral resisting systems on the design of passive dynamic absorbers (PDAs) under the action of along-wind and across-wind loads due to vortex shedding. A total of five different PDAs are considered in this study: (1) tuned mass damper (TMD), (2) circular tuned sloshing damper (C-TSD), (3) rectangular tuned sloshing damper (R-TSD), (4) two-way liquid damper (TWLD) and (5) pendulum tuned mass damper (PTMD). By modifying the non-dimensional lateral stiffness ratio, the CTB model can consider lateral deformations varying from those of a flexural cantilever beam to those of a shear cantilever beam. The Monte Carlo simulation method was used to generate along-wind and across-wind loads correlated along the height of a real shear wall-frame building, which has similar fundamental periods of vibration and different modes of lateral deformation in the xz and yz planes, respectively. Ambient vibration tests were conducted on the building to identify its real lateral behavior and thus choose the most suitable parameters for the CTB model. Both alongwind and across-wind responses of the 144-meter-tall building were computed considering four soil types (hard rock, dense soil, stiff soil and soft soil) and a single PDA on its top, that is, 96 time-history analyses were carried out to assess the effect of SSI and lateral resisting system on the PDAs design. Based on the parametric analyses, the response significantly increases as the soil flexibility increases for both type of lateral wind loads, particularly for flexural-type deformations. The results show a great effectiveness of PDAs in controlling across-wind peak displacements and both along-wind and across-wind RMS accelerations, on the contrary, PDAs were ineffective in controlling along-wind peak displacements on all soil types and different kind of lateral deformation. Generally speaking, the maximum possible value of the PDA mass efficiency index increases as the soil flexibility increases, on the contrary, it decreases as the non-dimensional lateral stiffness ratio of the building increases; therefore, there is a significant increase of the vibration control effectiveness of PDAs for lateral flexural-type deformations on soft soils.

• Safety and Health at Work
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• 제3권1호
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• pp.22-30
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• 2012

Objectives: To challenge the problem of slipperiness, various slipmeters have been developed to assess slip hazard. The performance of in-situ slipmeter is, however, still unclear under the various floor conditions. The main objectives of this study were to evaluate the performance of three kinds of slipmeters under real conditions, and to find their dynamic and kinematic characteristics, which were compared with gait test results. Methods: Four common restaurant floor materials were tested under five contaminants. Slipmeters and human gaits were measured by high speed camera and force plate to find and compare their dynamic and kinematic characteristics. Results: The contact pressures and built-up ratio were below those of subjects. The sliding velocity of British Pendulum Tester was above those of subjects, while those of BOT-3000 and English XL were below those of subjects. From the three meters, the English XL showed the highest overall correlation coefficient (r = 0.964) between slip index and $R_a$, while the rest did not show statistical significance with surface roughness parameters ($R_a$, $R_z$). The English XL only showed statistical significance (p < 0.01) between slip index and contaminants. The static coefficient of friction obtained with the BOT-3000 showed good consistency and repeatability (CV < 0.1) as compared to the results for the BPT (CV > 0.2) and English XL (CV < 0.2). Conclusion: It is unclear whether surface roughness can be a reliable and objective indicator of the friction coefficient under real floor conditions, and the viscosity of contaminants can affect the friction coefficient of the same floors. Therefore, to evaluate slipperiness, the performance of the slipmeters needed to improve.

• 자동차안전학회지
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• 제4권2호
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• pp.37-43
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• 2012

The purpose of this research is to obtain and analyze dynamic responses from human volunteers for the development of the human-like mechanical or mathematical model for Korean males in automotive rear collisions. This paper focused on the introduction to a low-speed rear impact sled test involving Korean male subjects, and the accumulation of the motion of head and neck. A total of 50 dynamic rear impact sled tests were performed with 50 human volunteers, who are 30-50 year-old males. Each subject can be involved in only one case to prevent any injury in which he was exposed to the impulse that was equivalent to a low-speed rear-end collision of cars at 5-8 km/h for change of velocity, so called, ${\Delta}V$. All subjects were examined by an orthopedist to qualify for the test through the medical check-up of their necks and low backs prior to the test. The impact device is the pendulum type, tuned to simulate the crash pulse of a real vehicle. All motions and impulses were captured and measured by motion capture systems and pressure sensors on the seat. Dynamic responses of head and T1 were analyzed in two cases(5 km/h, 8 km/h) to compare with the results in the previous studies. After the experiments, human subjects were examined to check up any change in the post medical analysis. As a result, there was no change in MRI and no injury reported. Six subjects experienced a minor stiffness on their back for no more than 2 days and got back to normal without any medical treatment.

• Earthquakes and Structures
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• 제12권1호
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• pp.135-144
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• 2017

Near-fault ground motions are characterized by high values of the ratio between the peak of vertical and horizontal ground accelerations, which can significantly affect the nonlinear response of a base-isolated structure. To check the effectiveness of different base-isolation systems for retrofitting a r.c. framed structure located in a near-fault area, a numerical investigation is carried out analyzing the nonlinear dynamic response of the fixed-base and isolated structures. For this purpose, a six-storey r.c. framed building is supposed to be retrofitted by insertion of an isolation system at the base for attaining performance levels imposed by current Italian code in a high-risk seismic zone. In particular, elastomeric (e.g., high-damping-laminated-rubber bearings, HDLRBs) and friction (e.g., steel-PTFE sliding bearings, SBs, or friction pendulum bearings, FPBs) isolators are considered, with reference to three cases of base isolation: HDLRBs acting alone (i.e., EBI structures); in-parallel combination of HDLRBs and SBs (i.e., EFBI structures); FPBs acting alone (i.e., FPBI structures). Different values of the stiffness ratio, defined as the ratio between the vertical and horizontal stiffnesses of the HDLRBs, sliding ratio, defined as the global sliding force divided by the maximum sliding force of the SBs, and in-plan distribution of friction coefficient for the FPs are investigated. The EBI, EFBI and FPBI base-isolation systems are designed assuming the same values of the fundamental vibration period and equivalent viscous damping ratio. The nonlinear dynamic analysis is carried out with reference to near-fault earthquakes, selected and scaled on the design hypotheses adopted for the test structures.

• 한국항공우주학회지
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• 제47권10호
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• pp.705-711
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• 2019

전개형 반사판 안테나의 전개거동 특성을 해석적 그리고 실험적 방법으로 분석하고자 한다. Kane 방정식을 이용하여 전개형 안테나의 다물체 운동방정식을 공식화하였다. 복합재료 반사판의 구조변형 특성을 살펴보기 위해 FSDT(First-order Shear Deformation Theory)를 이용하여 빔 모델로 유한요소 정식화 하였다. 역진자 모델을 이용하여 안테나 전개시간에 따른 스프링 상수 그리고 댐핑 계수들을 결정하였다. 다물체 동력학 해석을 통하여 설계변수에 따른 안테나 반사판의 동적구조 특성을 확인하였고, 무중력 모사 전개실험을 통하여 해석결과 검증 및 거동특성을 실험적으로 관찰하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1009-1014
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• 2007

To improve passenger safety, seatbelt systems with pre-tensioner that tightens seatbelt webbing using explosives just before collision are widely adopted. Even though seatbelt must not be unlatched without passenger's operation, release of a buckle due to explosion of pre-tensioner takes place in some situations resulting in serious injury to passengers. To prevent the unintended unlocking, a pendulum like part called anti-g mass is attached to the buckle to block displacement of release button. In this study, the unlocking conditions of anti-g buckle when pre-tensioner explodes has been theoretically investigated. Through multibody model of the seatbelt system incorporating every detailed part of the buckle, dynamic analysis of the seatbelt system with pre-tensioner has been performed including the driver's body model that interacts with seatbelt system. The simulations results has been validated through actual sled test with driver dummy and the seatbelt system.

• 한국항공운항학회지
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• 제18권4호
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• pp.30-37
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• 2010

This paper deals with attitude determination and parameter estimation problems for a lunar module. For this we first derive equations of motion for the lunar module by considering allocation locations (configurations) of reaction thruster and a reaction wheel assembly. The lunar module is assumed as a rigid body. In order to include the effect of fuel sloshing on the dynamics of the lunar module, we model it as a spherical pendulum for a simple analysis. For estimating angular rates and moment of inertia of the module, we employ an extended Kalman filter and the least mean square algorithms, respectively. Finally we construct a dynamical model for the lunar module by combining all these elements.

• 한국항공우주학회지
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• 제45권12호
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• pp.1059-1068
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• 2017

우주 탐사선은 다량의 액체 연료를 탑재하는데, 절반 이상을 넘는 경우가 많다. 이러한 경우, 액체 연료의 슬라슁 현상이 탐사선의 자세 안정성에 영향을 주기 때문에 탐사선 설계에 슬라슁 현상을 고려해야 한다. 본 논문에서는, 액체 연료의 슬라슁 현상과 이와 상호작용하는 탐사선의 동적 거동을 분석한 결과를 제시한다. 이를 위하여 탐사선의 기동이 액체 연료의 슬라슁 현상을 일으키는 모델과 슬라슁에 의한 반력 힘과 모멘트가 탐사선에게 전달되는 모델을 개발하였다. 모델리카 언어로 작성한 시뮬레이션 프로그램을 이용하여 탐사선의 거동을 분석하였다.

• 한국응용과학기술학회지
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• 제20권3호
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• pp.237-242
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• 2003

The high-solid coatings were prepared by blending the synthesized acrylic resin in the previous paper and hexamethylene diisocyanate-trimer and curing it at room temperature. The characterization of the films of the prepared coatings was performed. The impact resistance, $60^{\circ}C$ specular gloss, cross-hatch adhension, and heat resistance of the films proved to be good, and the pencil hardness and drying time proved to be slightly poor. Especially, there was a remarkable improvement in the heat resistance. This improvement may stem from the regular arrangement of ethyl groups introduced into the acrylic resin. From a viscoelastic measurement using a rigid-body pendulum, curing was accelerated with the $T_g$ value. With the increase in $T_g$, log damp value was lowered and dynamic viscoelasic $T_g$ of a cured film was increased.