• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 2002.02a
• /
• pp.471-478
• /
• 2002

초음파를 사과의 비파괴 품질판정에 이용하기 위한 기초연구로서 계측된 저장기간에 따른 사과의 초음파 특성과 본 연구에서 계측된 사과의 기계적 특성을 이용하여 초음파에 의한 사과의 탄성계수 및 생물체항복강도 예측모델을 개발하고자 하였으며, 결론은 다음과 같다. 1. UTM을 이용하여 사과의 기계적 특성치를 분석하여 생물체항복점, 생물체항복변형량, 생물체항복강도, 파괴점, 극한변형량, 극한강도 및 탄성계수 등을 구하였다. 2. 사과의 기본 물성, 초음파 특성과 기계적 특성값 들을 분석한 결과 사과의 질량, 체적, 시간영역의 진폭(PTP), 제3영역 에너지 스펙트럼 밀도함수가 기계적 특성 중 생물체항복강도, 탄성계수와 높은 상관성이 있는 것으로 나타났다. 3. 사과의 저장 기간, 질량, 체적, Peak-to-peak, 제3영역의 에너지값 등 5개의 독립변수를 가지는 다중선형회귀모형으로 사과의 탄성계수 및 생물체 항복강도 예측모형을 개발하였다.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1997.05b
• /
• pp.23-29
• /
• 1997

유한요소법을 이용하여 경수로형 핵연료집합체에서 냉각수 유동에 의한 수직 상승력으로부터 핵연료를 지지하는 판형 HDS의 강성도를 수치해석적으로 평가할 수 있는 방법을 제안하였다 I-DEAS code의 8 node brick element를 사용하고 판스프링들간의 간섭 부위에 접촉요소를 사용한 유한요소 모델링 및 해석기법으로 평가한 탄성강성도가 변형 에너지법에 근거하여 유도된 탄성강성도 평가식으로부터 얻은 결과와 잘 일치하고 있어서 제안된 유한요소 모델링 및 해석기법은 판형 HDS의 거동 분석에 유용하게 이용될 수 있다.

• Geophysics and Geophysical Exploration
• /
• v.25 no.4
• /
• pp.214-216
• /
• 2022

Distributed acoustic sensing (DAS), an increasingly growing acquisition technique in the oil and gas exploration and seismology fields, has been used to record seismic signals using optical cables as receivers. With the development of imaging methods for DAS data, full waveform inversion (FWI) is been applied to DAS data to obtain high-resolution property models such as P- and S-velocity. However, because the DAS systems measure strain from the phase distortion between two points along optical cables, DAS data must be transformed from strain to particle velocity for FWI algorithms. In this study, a plane-wave FWI algorithm based on the relationship between strain and horizontal particle velocity in the plane-wave assumption is proposed to apply FWI to DAS data. Under the plane-wave assumption, strain equals the horizontal particle velocity, which is scaled by the velocity at the receiver position. This relationship was confirmed using a numerical experiment. Furthermore, 4-layer and modified Marmousi-2 velocity models were used to verify the applicability of the proposed FWI algorithm in various survey environments. The proposed FWI was implemented in land and marine survey environments and provided high-resolution P- and S-velocity models.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.10
• /
• pp.193-202
• /
• 1998

본 논문에서는 비선형 고체역학 이론에 대하여 특히 시간에 무관한 변형을 하는 초탄성 및 탄소성고체물질의 비선형 변형이론에 대하여 철저한 분석을 수행하였다 특히 비선형 변형의 해석방범론에 대하여 특별한 관심을 가지고 분석하였다. 비선형 변형해석 방법론으로 널리 논의되고 있는 증분뉴튼랩슨 방법에 대하여 수정된 개념을 제시하여 비선형 변형 해석의 정 확성을 향상시켰다.

• Journal of the Korea Concrete Institute
• /
• v.14 no.5
• /
• pp.689-697
• /
• 2002

The dynamic loads and load-point displacements of concrete three-point bend (TPB) specimens had been measured. The average crack velocities measured with strain gages were 0.16 ㎜/sec ∼ 66 m/sec. The fracture energy for crack extension was determined from the difference of the kinetic energy for the load-point velocity and the strain energy without permanent deformation from the measure external work. For all crack velocities, there were micro-cracking for 23 ㎜ crack extension, stable cracking for 61 ㎜ crack extension at the maximum strain energy, and then unstable cracking. The unstable crack extension was arrested at 80 ㎜ crack extension except the tests of 66 m/sec crack velocity. The tests less than 13 ㎜/sec crack velocity and faster than 1.9 m/sec showed static and dynamic fracture behaviors, respectively. In spite of much difference of the load and load-point displacement relations for the crack velocities, the crack velocities of dynamic tests did not affect on fracture energy rate during the stable crack extension due to the reciprocal action of kinetic force, crack extension and strain energy. During stable crack extension, the maximum fracture resistances of the dynamic tests was 147％ larger than that of the static tests.

• Composites Research
• /
• v.12 no.1
• /
• pp.68-75
• /
• 1999

This study has observed that the dynamic behavior of Metal Matrix Composites (MMCs) in low velocity impact varies with impact velocity. MMCs with 15 fiber volume percent were fabricated by using the squeeze casting method. The AC8A was used as the matrix, and the alumina and the carbon were used as reinforcements. The tensile and vibration tests conducted yielded the yielded the tensile stress and elastic modulus of MMCs The low pass filter and instrumented impact test machine was adopted to study dynamic behaviors of MMCs corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact energy of unreinforced alloy and MM s increased as the impact velocity increased. The increase of crack propagation energy was especially prominent, but the dynamic toughness of each material did not change much. To show the relation between crack initiation energy and dynamic fracture toughness, a simple model was proposed by using the strain energy and stress distribution at notch. The model revealed that crack initiation energy is proportional to the square of dynamic fracture toughness and inversely proportional to elastic modulus.

• Journal of the Korean Society for Railway
• /
• v.16 no.3
• /
• pp.202-206
• /
• 2013

A submerged floating railway is an innovative tunnel infrastructure passing through the deep sea independent of wave and wind so that high speed trains can run on it. It doesn't depend on water depth and is cost effective due to modular construction on land. The construction period can be reduced drastically. This paper introduces the concept design of a submerged floating railway, and for securing safety, proposes a method to analyze the structural behavior of the body in case of collision with a submarine. The theory of a beam with an elastic foundation was used to calculate the equivalent mass of the body so that the perfect elastic collision could be applied to calculate the collision velocity. The maximum deformation and bending moment was analyzed based on energy conservation. To verify the results, a collision analysis using a finite element analysis code was made. Comparing the results confirmed that this simplified collision analysis method gives enough accurate deformation and bending moment to be used for actual estimation in the initial design stage.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.44 no.1
• /
• pp.11-17
• /
• 2024

A seismic structure is an earthquake-resistant design that dissipates seismic energy by equipping the structure with a device called a damper. As research efforts to reduce earthquake damage continue to rise, technology for isolating vibrations in structures has evolved by altering the materials and shapes of dampers. However, due to the inherent nature of the damper, there are an unescapable restrictions on the extent of plastic deformation that occurs in the material to effectively dissipate energy. Therefore, in this study, we proposed a long-life damper that offers semi-permanently usage and enhances structural performance by applying additional tension which is achieved by utilizing super elastic shape memory alloy (SSMA), a material that self-recovers after deformation. To comprehensively understand the behavior of long-life dampers, finite element analysis was performed considering the design variables such as material, wire diameter, and presence of tension, and response behavior was derived to analyze characteristics such as load resistance, energy dissipation, and residual displacement to determine the performance of long-life dampers in seismic structure. Excellence has been proven from finite element analysis results.

• Journal of Aerospace System Engineering
• /
• v.11 no.6
• /
• pp.34-41
• /
• 2017

As an alternative of the existing honeycomb shock absorbing device, the new approach on shock absorbing design using the extrusion of hyper-viscoelastic material such as silicon rubber is studied in this paper. The strain energy and stress-strain characteristic of viscoelastic material at extrusion process through the metered orifice has a similarity with the honeycomb core for maximizing shock absorbing capability. And in order to evaluate the design feasibility of this device and to understand the shock absorbing mechanism of energy transformation, finite element analysis and quasi-static compression test of the multi-stage extrusion shock absorber are examined in this paper.

• Journal of the Korean Ceramic Society
• /
• v.39 no.7
• /
• pp.675-679
• /
• 2002

To produce a strengthened glass, single ion exchange properties such as three-point bend strength and residual stress were investigated in soda-lime-silicate substrate glass for display use. The present work showed that the maximum value of strength was 62.5${\times}$10$\sub$6/ kg/㎡ after, the two-step single ion exchange process at 470$^{\circ}C$ for 1 h and 450$^{\circ}C$ for 24 h. As the result of the fracture analysis after bending test, the residual stress on the fractured surface of the strengthened glass increased the flexibility by means of absorbing the elastic deformation energy in the glass. Also, the effects of absorbing the elastic deformation energy were analysed by curvature change, number of multiple crack branches and brittleness.