• 한국음향학회지
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• 제37권2호
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• pp.99-109
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• 2018

현존하는 진동 측정 센서는 정밀도 면에서는 대부분의 진동을 측정하기에 충분하나, 센서 한 개로 하나의 지점이나 방향에 한정하여 측정할 수밖에 없다는 단점을 갖고 있다. 반면 카메라의 경우, 정밀도나 측정 가능한 주파수 영역의 면에서는 다소 불리하지만, 한 번에 광범위한 영역의 진동을 측정할 수 있고 가격 면에서 유리하며 다자유도의 진동을 동시에 측정할 수 있다는 큰 장점을 갖고 있다. 본 연구에서는 저가의 머신 비전 카메라가 진동 측정 센서로서 어느 정도의 오차 범위 내에서 진동을 측정할 수 있는지 알아본 후, 실제 외팔보의 진동을 측정하였다. 카메라의 2차원 평면 이미지는 두 방향의 직선 운동과 한 방향의 회전 운동을 나타낼 수 있다. 먼저 단일 점의 진동을 카메라로 측정하고, LDV(Laser Doppler Vibrometer) 측정을 기준으로 한 카메라 측정의 오차를 실험적으로 교정하였다. 다음으로 다중점의 진동을 한 번에 측정하여 회전 진동과 외팔보 전체 형상의 진동을 측정하였다. 외팔보 전체 형상 진동은 주파수와 시간 영역 모두에 대하여 분석하였다.

• 한국전산구조공학회논문집
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• 제17권1호
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• pp.21-30
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• 2004

본 연구에서는 유한요소법을 이용한 채널단면을 갖는 복합재료 적층 구조물의 자유진동을 다룬다. 복합적층 절판구조물에 고차항 판이론을 적용하기 위하여 개발된 유한요소 프로그램은 Lagrangian 및 Hermite 보간함수를 병용하여 면내회전각 자유도를 포함한 절점 당 8개의 자유도를 갖는다. 전단보정계수의 가정을 필요로 하지 않고 전단변형의 3차항 비선형 특성이 고려된 본 논문의 절판 요소는 국부좌표계와 전체좌표계에 대한 좌표변환행렬에 의하여 요소 당 32×32의 국부요소행렬로 구성된다. 본 해석 프로그램의 결과는 기존의 고전적 이론 및 일차항 이론에 의한 문헌 결과와 비교ㆍ분석하였으며, 화이버 보강각도, 길이-두께비, 기하학적 형상 변화 등의 다양한 매개변수 연구를 수행하였다. 본 연구에서는 특히 경계조건 및 길이-두께비 변화에 따라 예측하기 힘든 복잡한 거동을 보이는 복합적층 채널단면 구조물의 자유진동에 대하여 정밀한 고차항 이론 적용에 의한 엄밀 해석의 필요성을 제기하였다.

• 대한기계학회논문집A
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• 제34권5호
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• pp.597-604
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• 2010

본 논문에서는 모바일하버의 하역 시스템으로 특화되어 개발한 제로 모멘트 크레인에 적용되는 조인트를 설계하고자 한다. 해당 조인트는 제로 모멘트 포인트의 개념에 기반하여 제로 모멘트 크레인을 안정화시키는데 중요한 역할을 수행한다. 이 목적을 위해서는 크고 다양한 형태의 하중을 견딜 수 있으며, 또한 2 방향의 자유도를 허용할 수 있어야 한다. 통상적인 설계 과정을 거쳐, 유니버셜 조인트와 스피리컬 조인트를 결합한 후 가변형 구름 요소를 적용한 새 디자인을 제안하였다. 구름 요소는 하중을 분산시키며 하역 과정 동안의 동력 손실을 줄여준다. 시스템의 복잡성과 최적화 과정의 효율성을 고려하여, 크리깅 기반 근사 최적화 기법을 선정하였다. 설계된 조인트를 검증하기 위해, 구조 해석을 수행하고, 축소 시제품을 제작하였다.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1126-1134
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• 2003

The signals obtained from the $5^{th}$-order (two-dimensional) Raman spectrum of a liquid can depend dramatically on the polarizations of the various light beams, but to date there has been no evidence presented that different polarization conditions probe any fundamentally different aspects of liquid dynamics. In order to explore the molecular significance of polarization we have carried out a molecular dynamics simulation of the $5^{th}$-order spectrum of a dilute solution of CS₂ in liquid Xe, perhaps the simplest system capable of displaying a full range of polarization dependencies. By focusing on the 5 distinct rotational invariants revealed by the different polarizations and by comparing our results with those from liquid Xe, a liquid whose spectrum has no significant polarization dependence, we discovered that the polarization experiments do, in fact, yield valuable microscopic information. With different linear combinations of the experimental response functions one can separate the part of the signal derived from the purely interaction-induced part of the many-body polarizability from the portion with the largest contributions from single-molecule polarizabilities. This division does not directly address the underlying liquid dynamics, but it significantly simplifies the interpretation of the theoretical calculations which do address this issue. We find that the different linear combinations differ as well in whether they exhibit nodal lines. Despite the absence of nodes with the atomic liquid Xe, observing the resilience of our solution's nodes when we artificially remove the anisotropy of our solute leads us to conclude that there is no direct connection between nodes and specifically molecular degrees of freedom.

• 한국유기농업학회지
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• 제6권2호
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• pp.127-140
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• 1998

Organic farming excludes any use of the herbicide. The present paper reviews what can be done for effective weed control with existing weed control technology by farmers crop-ping paddy rice, field crops, vegetables, and fruit trees. If condition of the crop-land-al-lows diversified rotational use of the paddy land as paddy and upland field would minimize weed problem. Practising this is limited in acreage due to extremely limited governmental investment to the land for the purpose. Secondly, rotation of crops in the upland field breaking life cycles of various weeds adapted to each crop should reduce the weed problem. This is also limited as only a few crops are making the farmer profitable. In addition climate and tolerance of crops to high and low temperature. Monsoon rains and poor drainage restrict the freedom of choice. For any crop land year-round multiple cropping in denser planting shall lessen the weed problem, this multiple cropping practiced by 1960s has been abandoned due to laborshortage and increased production cost. Deep flooding the rice is impractical at present in Korean. Mulching crop with transparent, black , or combinated polyethylene sheet, hs been in-creasingly used. Progresses in development and use of mulch with allelopathic crop residues. inexpensive paper mulch, allelopathic crop residues, inexpensive paper mulch, allelopathic crop cultivar development, recently developed ex-perimental weeding machinaries, flamers, microbial herbicides, biological control organisms, soil sterilization techniques have been critically reviewed for their adoption into existing in-tegrated weeding system. Unfortunately, information on cost-benifit, and labor-benefit, for the various methods above mentioned are lacking. Urgent need for the research on rational weeding in organic farming, and herbicide low-input farming is emphasized.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.859-865
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• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.

• Structural Engineering and Mechanics
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• 제54권1호
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• pp.169-188
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• 2015

This study presents the effects of the spatial variation of ground motions in a hard rock site on the seismic responses of a base-isolated nuclear power plant (BI-NPP). Three structural models were studied for the BI-NPP supported by different number of lead rubber bearing (LRB) base isolators with different base mat dimensions. The seismic responses of the BI-NPP were analyzed and investigated under the uniform and spatial varying excitation of El Centro ground motion. In addition, the rotational degrees of freedom (DOFs) of the base mat nodes were taken to consider the flexural behavior of the base mat on the seismic responses under both uniform and spatial varying excitation. Finally, the seismic response results for all the analysis cases of the BI-NPP were investigated in terms of the vibration periods and mode shapes, lateral displacements, and base shear forces. The analysis results indicate that: (1) considering the flexural behavior of the base mat has a negligible effect on the lateral displacements of base isolators regardless of the number of the isolators or the type of excitation used; (2) considering the spatial variation of ground motions has a substantial influence on the lateral displacements of base isolators and the NPP stick model; (3) the ground motion spatial variation effect is more prominent on lateral displacements than base shear forces, particularly with increasing numbers of base isolators and neglecting flexural behavior of the base mat.

• Journal of Biosystems Engineering
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• 제32권5호
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• pp.339-347
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• 2007

A hexapod walking robot had been developed for gathering information in the field. The developed robot was $260{\times}260{\times}130$ ($W{\times}L{\times}H$, mm) in size and 14.7 N in weight. The legs had nineteen degrees of freedom. A leg has three rotational joints actuated by small servomotors. Two servomotors placed at ankle and knee played the roles of vertical joint for up and down motions of the leg and the other one placed at coxa played the role of horizontal joint for forward and backward motions. In addition, a servomotor placed at thorax between the front legs and the middle legs played the role of vertical joint for pumping the two front legs to climb stair or inclination. Walking motion of the robot was executed by tripod gait. The robot was controlled by manual remote-controller communicated by an infrared ray. Two controllers were equipped to control the walking of the robot. The sub-controller using PIC microcomputer (Microchips, PIC16F84A) received the 16 bit command signal from the manual remote controller, decoded it to 8bit and transmitted it to the main microcomputer (RENESAS, SH2/7045), which controlled the 19 servomotors using the PWM command signals. Walking speeds were controlled by adjusting the period of command cycle and the stride. Forward walking speed were within 100 cm/min to 300 cm/min. However, experimental walking speed had the error of 4-40 cm/min to compare with the theoretical one, because of slippage of the leg and the circular arc motion of servomotor of coxa.

• Journal of Biosystems Engineering
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• 제39권4호
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• pp.389-399
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• 2014

Purpose: This study was aimed at developing a tractor-driving simulator for the safety training of agricultural tractor operators. Methods: The developed simulator consists of five principal components: mock operator control devices, a data acquisition and processing device, a motion platform, a visual system that displays a computer model of the tractor, a motion platform, and a virtual environment. The control devices of a real tractor cabin were successfully converted into mock operator control devices in which sensors were used for relevant measurements. A 3D computer model of the tractor was also implemented using 3ds Max, tractor dynamics, and the physics of Unity 3D. The visual system consisted of two graphic cards and four monitors for the simultaneous display of the four different sides of a 3D object to the operator. The motion platform was designed with two rotational degrees of freedom to reduce cost, and inverse kinematics was used to calculate the required motor positions and to rotate the platform. The generated virtual environment consisted of roads, traffic signals, buildings, rice paddies, and fields. Results: The effectiveness of the simulator was evaluated by a performance test survey administered to 128 agricultural machinery instructors, 116 of whom considered the simulator as having potential for improving safety training. Conclusions: From the study results, it is concluded that the developed simulator can be effectively used for the safety training of agricultural tractor operators.

• Structural Engineering and Mechanics
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• 제68권3호
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• pp.299-312
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• 2018

In this paper, an extended finite element method is proposed to analyze both geometric and material non-linear behavior of general Functionally Graded Material (FGM) plate-shell type structures. A user defined subroutine (UMAT) is developed and implemented in Abaqus/Standard to study the elastoplastic behavior of the ceramic particle-reinforced metal-matrix FGM plates-shells. The standard quadrilateral 4-nodes shell element with three rotational and three translational degrees of freedom per node, S4, is extended in the present study, to deal with elasto-plastic analysis of geometrically non-linear FGM plate-shell structures. The elastoplastic material properties are assumed to vary smoothly through the thickness of the plate-shell type structures. The nonlinear approach is based on Mori-Tanaka model to underline micromechanics and locally determine the effective FGM properties and self-consistent method of Suquet for the homogenization of the stress-field. The elasto-plastic behavior of the ceramic/metal FGM is assumed to follow Ludwik hardening law. An incremental formulation of the elasto-plastic constitutive relation is developed to predict the tangent operator. In order to to highlight the effectiveness and the accuracy of the present finite element procedure, numerical examples of geometrically non-linear elastoplastic functionally graded plates and shells are presented. The effects of the geometrical parameters and the volume fraction index on nonlinear responses are performed.