• 소음진동
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• 제6권1호
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• pp.83-88
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• 1996

The significance of spectral element method is that it can treat the mass and stiffness distribution exactly in contrast to the conventional finite element method, and therefore the dynamic behaviors within each spectral element can be obtained exactly. The present study provides the derivation of the spectral element of a curved beam, while the previous ones presented that of a straight structure. Further, in order to verify the derived spectral element, the natural frequencies of a ring by the spectral element method are compared with those by the analytical method and those by the FEM. From the verification, derived spectral element is admissible. And the dynamic behaviors of curved beam are simulated by using the derived spectral element of a curved beam.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.275-280
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• 2003

This paper discusses on the dynamic responsed of an elastically restrained beam under a moving mass of constant velocity. Governing equations of motion taking into account of all inertia effects of the moving mass were derived by Galerkin's mode summation method, and Runge-Kutta integration method was applied to solve the differential equations. Numerical solutions for dynamic deflections of beams were obtained for the changes of the various parameters (spring stiffness, spring position, mass ratios and velocity ratios of the moving mass). In order to verify the numerical predictions for the dynamic response of the beam, experiments were conducted. Numerical solutions for the dynamic responses of the test beam have a good agreement with experimental ones.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.534-539
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• 2000

A flexible rotating beam test bed has been developed for experimental verification of flexible rotating beam dynamics and vibration. It consists of a flexible arm, harmonic driver reducer, ac servo motor and DSP board with PC. To capture the motion induced stiffening effects of the flexible rotating beam, substructuring model has been established in multibody dynamics simulation. Substructuring model provides better results comparing with experimental data.

• Structural Engineering and Mechanics
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• 제19권5호
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• pp.477-501
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• 2005

In this study, a new smart beam finite element is proposed for the finite element modeling of beam-type smart structures that are equipped with bonded plate-type piezoelectric sensors and actuators. Constitutive equations for the direct piezoelectric effect and converse piezoelectric effect of piezoelectric materials are considered in the formulation. By using a variational principle, the equations of motion for the smart beam finite element are derived. The proposed 2-node beam finite element is an isoparametric element based on Timoshenko beam theory. The proposed smart beam finite element is applied to the free vibration control adopting a constant gain feedback scheme. The electrical force vector, which is obtained in deriving an equation of motion, is the control force equivalent to that in existing literature. Validity of the proposed element is shown through comparing the analytical results of the verification examples with those of other previous researchers. With the use of smart beam finite elements, simulation of free vibration control is demonstrated by sensing the voltage of the piezoelectric sensors and by applying the voltages to the piezoelectric actuators.

• Structural Engineering and Mechanics
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• 제71권2호
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• pp.153-163
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• 2019

Longitudinal fracture behavior of non-linear elastic beam configurations is studied in terms of the strain energy release rate. It is assumed that the beams exhibit continuous material inhomogeneity along the width as well as along the height of the crosssection. The Ramberg-Osgood stress-strain relation is used for describing the non-linear mechanical behavior of the inhomogeneous material. A solution to strain energy release rate is derived that holds for inhomogeneous beams of arbitrary cross-section under combination of axial force and bending moments. Besides, the solution may be applied at any law of continuous distribution of the modulus of elasticity in the beam cross-section. The longitudinal crack may be located arbitrary along the beam height. The solution is used to investigate a longitudinal crack in a beam configuration of rectangular cross-section under four-point bending. The crack is located symmetrically with respect to the beam mid-span. It is assumed that the modulus of elasticity varies continuously according a cosine law in the beam cross-section. The longitudinal fracture behavior of the inhomogeneous beam is studied also by applying the J-integral approach for verification of the non-linear solution to the strain energy release rate derived in the present paper. Effects of material inhomogeneity, crack location along the beam height and non-linear mechanical behavior of the material on the longitudinal fracture behavior are evaluated. Thus, the solution derived in the present paper can be used in engineering design of inhomogeneous non-linear elastic structural members to assess the influence of various material and geometrical parameters on longitudinal fracture.

• 한국의학물리학회지:의학물리
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• 제14권2호
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• pp.99-107
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• 2003

선형가속기(Mitsubishi, ML15MDX)를 이용한 방사선수술시스템인 Photon Knife에서 Linac-gram을 통해 선속-표적 위치를 확인하여 신뢰성 있는 시술을 유지하도록 하였다. 선속-레이저광 교정 기구를 제작하여 레이저광의 입사점과 사출점을 조사하여 빔의 위치결정에 이용하였다. 선형가속기에 부착한 보조 콜리메이터의 고정을 확인하기 위해 Isocenter에서 5 cm 떨어진 위치에 팔각형 필름지지체를 두도록 제작하고 확인용 필름(Kodak X-omat V2)을 설치하였다. 필름에 선형가속기의 지지체를 45$^{\circ}$씩 회전조사 하여 필름에 나타난 거리로 보조 콜리메이터의 이동을 확인한 결과 실험 오차내에서 이동이 없음을 확인하였다. 임상에 이용한 체위 표시기는 10 mm 쇠구슬 제도와 납인형을 두어 PKRS 시술시 환부의 체위를 쉽게 확인할 수 있도록 고안제작되었다. 앙와위 및 우측 측와위로 조사한 방사선수술에서 표적 위치기에 있는 양측 쇠구슬과 콜리메이터 조사면과의 일치를 LINAC-gram에서 확인한 결과 CT 영상의 표적좌표와 비교해서 평균 0.8$\pm$0.26 mm 의 오차범위에서 시술하였음을 보이므로 방사선조사의 정확성을 알 수 있다. 선형가속기의 Couch 에 임의의 힘을 가했을 때 위치변동은 좌우 $\pm$5 mm, Couch 축방향으로 $\pm$1 mm, 상하로 $\pm$2 mm 이동할 수 있음을 확인하였다. 이상의 결과로 Photon knife 방사선 수술 시스템은 방사선수술 전 환부의 표적과 선속의 일치를 LINAC-gram을 통해 확인할 수 있어 시술의 신뢰도를 높일 수 있을 것으로 생각된다.

• Smart Structures and Systems
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• 제4권5호
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• pp.605-628
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• 2008

In bridge structures, damage may induce an additional deflection which may naturally contain essential information about the damage. However, inverse mapping from the damage-induced deflection to the actual damage location and severity is generally complex, particularly for statically indeterminate systems. In this paper, a new load concept, called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location. A PBIL for an inspection region is defined as a load or a system of loads which guarantees the bending moment to be positive in the inspection region. From the theoretical investigations, it was proven that the damage-induced chord-wise deflection (DI-CD) has the maximum value with the abrupt change in its slope at the damage location under a PBIL. Hence, a novel damage localization method is proposed based on the DI-CD under a PBIL. The procedure may be summarized as: (1) identification of the modal flexibility matrices from acceleration measurements, (2) design for a PBIL for an inspection region of interest in a structure, (3) calculation of the chord-wise deflections for the PBIL using the modal flexibility matrices, and (4) damage localization by finding the location with the maximum DI-CD with the abrupt change in its slope within the inspection region. Procedures from (2)-(4) can be repeated for several inspection regions to cover the whole structure complementarily. Numerical verification studies were carried out on a simply supported beam and a three-span continuous beam model. Experimental verification study was also carried out on a two-span continuous beam structure with a steel box-girder. It was found that the proposed method can identify the damage existence and damage location for small damage cases with narrow cuts at the bottom flange.

• Journal of Radiation Protection and Research
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• 제46권2호
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• pp.48-57
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• 2021

Background: In this study, the complexities of step-and-shoot intensity-modulated radiation therapy (IMRT) plans in magnetic resonance-guided radiation therapy systems were evaluated. Materials and Methods: Overall, 194 verification plans from the abdomen, prostate, and breast sites were collected using a ⁶⁰Co-based ViewRay radiotherapy system (ViewRay Inc., Cleveland, OH, USA). Various plan complexity metrics (PCMs) were calculated for each verification plan, including the modulation complexity score (MCS), plan-averaged beam area (PA), plan-averaged beam irregularity, plan-averaged edge (PE), plan-averaged beam modulation, number of segments, average area among all segments (AA/Seg), and total beam-on time (TBT). The plan deliverability was quantified in terms of gamma passing rates (GPRs) with a 1 mm/2% criterion, and the Pearson correlation coefficients between GPRs and various PCMs were analyzed. Results and Discussion: For the abdomen, prostate, and breast groups, the average GPRs with the 1 mm/2% criterion were 77.8 ± 6.0%, 79.8 ± 4.9%, and 84.7 ± 7.3%; PCMs were 0.263, 0.271, and 0.386; PAs were 15.001, 18.779, and 35.683; PEs were 1.575, 1.444, and 1.028; AA/Segs were 15.37, 19.89, and 36.64; and TBTs were 18.86, 19.33, and 5.91 minutes, respectively. The various PCMs, i.e., MCS, PA, PE, AA/Seg, and TBT, showed statistically significant Pearson correlation coefficients of 0.416, 0.627, -0.541, 0.635, and -0.397, respectively, with GPRs. Conclusion: The area-related metrics exhibited strong correlations with GPRs. Moreover, the AA/Seg metric can be used to estimate the IMRT plan accuracy without beam delivery in the ⁶⁰Co-based ViewRay radiotherapy system.

• 한국인터넷방송통신학회논문지
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• 제24권1호
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• pp.23-30
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• 2024

본 논문에서는 광대역 특성을 가지는 능동위상배열 안테나의 설계, 검증 및 분석에 대하여 기술하였다. 능동위상 배열 안테나를 항공기 혹은 미사일에 적용하려면 배열 안테나의 소형화 및 광각 빔조향 특성을 확보하는 것은 피할 수 없는 안테나 설계 고려 사항이 될 수 있다. 특히 전자적으로 광각 빔조향 시 능동반사계수 특성은 시스템의 생존 및 성능 측면에서 최소화되어야 하는 설계 파라미터이다. 광대역 특성 및 광각 빔조향에 적합한 복사 소자로 본 논문에서는 Step Flared Notch(SFN)를 적용한 배열 구조를 설계하고 구좌표계 θ 각도 기준 최대 40° 빔조향에 따른 능동반사계수를 최소화하였다. 복사소자의 대역폭은 Ka대역에서 능동반사 기준으로 3GHz를 확인하였다. 또한 실제 제작된 8by8 배열 안테나는 근접전계 시험을 통해 복사소자의 단일 패턴을 측정하고, 수학적으로 합성하여 탐색기 시스템에 사용하는 송/수신빔을 예측하여 성능을 분석하였다.

• 한국안전학회지
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• 제5권2호
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• pp.50-57
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• 1990

A new technique for the measurement of surface roughness based on the intensity fluctuations of laser light backscattered from a moving surface has been introduced. This paper reports a method of measuring surface roughness using coherent optics and interferometry. Included are both the theory of the technique and experimental verification. The range of surface roughness which can be accurately measured by this method is also reported.