In this study, theoretical analyses are performed to investigate the characteristics of the static and dynamic stiffness of a nonlinear vibration isolator system. The vibration isolator system is modeled as an equivalent nonlinear oscillator. Based on the model, the static equilibrium and frequency response solutions are obtained with the variations of external static load and/or system parameters. It is shown that the static stiffness of the nonlinear vibration isolator tends to be hardened with the increase of external static load, which prevents the occurrence of excessively large deflection. This static stiffness-hardening effect is more remarkable with a larger spring constant ratio. The dynamic stiffness is also strengthened when the spring constant ratio increases, which enlarges the force transmissibility and reduces the isolation frequency bandwidth. Thus, the static stiffness- hardening improves the robustness of the nonlinear vibration isolator, whereas the dynamic stiffness-hardening rather degrades its performance. Thus, the opposite tendency of the static and dynamic stiffness-hardening effects should be considered in the design process of the nonlinear vibration isolator.

In this paper, the instability of the domed spatial truss structure using wood and the characteristics of the buckling critical load were studied. Hexagonal space truss was adopted as the model to be analyzed, and two boundary conditions were considered. In the first case, the deformation of the inclined member is only considered, and in the second case, the deformation of the horizontal member is also considered. The materials of the model adopted in this paper are steel and timbers, and the considered timbers are spruce, pine, and larch. Here, the inelastic properties of the material are not considered. The instability of the target structure was observed through non-linear incremental analysis, and the buckling critical load was calculated through the singularities and eigenvalues of the tangential stiffness matrix at each incremental step. From the analysis results, in the example of the boundary condition considering only the inclined member, the critical buckling load was lower when using timber than when using steel, and the critical buckling load was determined according to the modulus of elasticity of timber. In the case of boundary conditions considering the effect of the horizontal member, using a mixture of steel and timber case had a lower buckling critical load than the steel case. But, the result showed that it was more effective in structural stability than only timber was used.

In this study, structural characteristics were analyzed by combining gravity load and lateral loads such as seismic loads through static analysis of example structures, and the static characteristics of the twisted structure according to the plane rotation angle were also analyzed. Example structures were selected as regular structure, and twisted structures; 1.0, 2.0, and 3.0 degree angle of rotation per story, and static analysis was performed by the load combination case 1 and case 2. As a result the story drift ratio of the twisted-shaped structure also increased as the plane rotation angle per story increased. The eccentricity according to the load combination was the highest in the lower stories of all analysis models, and the eccentricity was found to be larger as the rotation angle decreased. The twisted-shaped structure was more responsible for the bending moment of the column than the regular structure, and the vertical member axial force of all analysis models was almost similar.

This paper aims to experimentally and numerically explore fracture mechanism characteristics of ultra-thin chopped carbon fiber tape-reinforced thermoplastics (UT-CTT) hat-shaped hollow beam under transverse static and impact loadings. Three distinct failure modes were observed in the impact bending tests, whereas only one similar progressive collapse mode was observed in the transverse bending tests. The numerical model was to incorporate some hypothetical inter-layers in UT-CTT and assign them with the failure model as cohesive zone model, which can perform non-linear characteristics with failure criterion for representing delamination failure. The dynamic material parameters for the impact model were theoretically predicted with consideration of strain-rate dependency. It shows that the proposed modeling approach for interacting damage modes can serve as a benchmark for modeling damage coupling in composite materials.

The main object of this study is to investigate the collection characteristics of an electro-static multi-staged impaction system, experimentally. The experiment is carried out to analyze the characteristics of pressure drop and collection efficiency for the present system with the experimental parameters such as the inlet velocity, stage number, applied voltage and shape of discharge electrode, etc. In results, the pressure drop is shown below 148 mmH2O lower than that of the conventional bag filter at inlet velocity 3.46 m/s and 5 stage. For 5 stage , the collection efficiencies are to be 97.4, 99.0% with the applied voltage 0 kV at the inlet velocity 2.07, 3.46 m/s, while 98.4, 99.9% with 40 kV of a sharp edge discharge electrode. Additionally, the present system is to be considered as an effective compact system for a removal of particulate pollutants from marine diesel engines due to much higher collection efficiency and appropriate pressure drop.

이 논문에서는 곡선 프리스트레스트 콘크리트 사장교의 풍하중에 의한 정적 횡방향 휨거동 해석에 비선형 해석 모델 특성들이 미치는 영향을 검토하여 곡선 프리스트레스트 콘크리트 사장교의 풍하중에 의한 정적 휨거동을 정당하게 예측할 수 있는 해석방법을 제시하였다. 곡선 프리스트레스트 콘크리트(PSC) 사장교의 시공단계별 풍하중에 의한 횡방향 휨거동 해석 시 재료의 비선형성은 물론 기하학적 비선형성을 모두 고려하였고 재료의 시간의존적 특성의 영향으로 콘크리트의 크리프, 건조수축, 강도증가와 프리스트레싱(PS) 강재와 케이블의 이완을 고려하였다. 곡선 PSC 사장교의 풍하중에 의한 휨거동을 다양한 비선형 해석 모델 특성들을 조합해서 고려하여 해석을 수행한 결과, 교량 상판의 인장균열 및 이에 따른 처짐의 증가를 정확히 예측하기 위해서는 재료의 비선형 응력-변형률 관계는 물론 콘크리트의 인장균열을 모두 포함한 재료 비선형성과 기하강성도 매트릭스는 물론 대변위에 의한 변형률의 비선형항 및 부재의 위상변화를 모두 포함하는 기하학적 비선형성을 고려한 해석이 반드시 필요함을 확인하였다. 부가적으로, 콘크리트의 인장증강효과 및 뼈대요소의 축력에 의한 기하강성도 매트릭스의 고려여부는 교량의 풍하중에 의한 정적 휨거동을 예측하는 데 영향을 크게 미치지 않는 것으로 나타났다. 또한 풍하중에 의한 곡선 PSC 사장교의 횡방향 휨거동은 상판의 횡방향 변위의 상당한 증가 및 거더 단면의 인장균열로 인해 상판이 폐합되기 직전단계가 폐합된 이후 단계보다 크게 불리함을 확인하였다.

The purpose of this study was to compare the static balance of standing position between adolescent idiopathic scoliosis (AIS) and a normal group that were aged-matched. There were forty subjects included in this study. Twenty-seven healthy subjects (age, 13.9±1.2 yrs; height, 161.9±7.5 ㎝; weight, 52.2±7.7 ㎏) and thirteen AIS subjects (age, 14.2±2.2 yrs; height, 161.5±8.7 ㎝; weight, 48.1±8.1 ㎏) were participated in the study. The thirteen subjects in the AIS group had a major Cobb angle between 20.1° and 49°. Each group was tested with the Balance Performance Monitor (BPM). The parameters for static balance were sway area, sway path, max velocity, mean balance, anterior-posterior angle, and left-right angle of each group with their eyes opened and again with their eyes closed. Both sides of the forward reach test and the lateral reach test were also performed on each group. Results from the BPM tested showed significantly increases in all parameters of static balance with those patients with AIS under the conditions where eyes were opened and closed. In the right and left forward reach test, there was no significant difference between normal and AIS groups. However, in the lateral reach test with right and left direction, there were significant differences between normal and AIS groups. For the normal subjects, there were significant differences in the parameters with sway path and anterior-posterior sway angle between the eyes opened and closed. However, there were no significant differences in the all parameters between eyes opened and closed for the AIS subjects. These results suggest that, balance programs could be used in the rehabilitation setting for intervention of AIS and evaluation of AIS. Further study is needed to measure many patients with AIS and other functional balance scales for clinical application.

대공간 구조는 3차원적인 힘의 흐름과 면내력에 의해 외부하중에 대한 저항능력을 확보하는 형태저항형 구조로서 기본적인 구조저항 메커니즘은 구조물 자체의 곡률을 이용하여 면외방향으로 작용하는 외력을 주로 면내력으로 저항할 수 있게 한 구조시스템이다. 따라서 최소의 재료로, 가볍고 얇게 대공간을 만들 수 있는 장점이 있다. 대공간 구조시스템 중 연성 구조물의 일종인 막 구조, 케이블 구조 또는 복합 구조체로서의 막-케이블 구조물의 비약적인 발전이 최근 주목을 끌고 있다. 즉, 기존의 일반 구조재보다 가볍고 축 강성은 강하나 휨 강성은 매우 작은 막 및 케이블을 사용하여 대공간 구조물을 보다 효과적으로 구축할 수 있는 구조시스템을 말한다. 그러나, 이러한 구조물은 하중 레벨이 어느 임계값에 도달하면 구조물의 형상에 따라 뜀좌굴(snap-through) 또는 분기좌굴(bifurcation)에 의한 불안정 현상이 일어나며, 이로 인한 파괴 메커니즘의 파악은 구조설계에서 매우 중요하다. 본 연구에서는 텐세그리티형 케이블 돔 구조물의 구조시스템에 따른 정적 불안정 거동 특성을 파악하기 위해 먼저, 형상해석을 통해 복합 케이블 돔 구조물인 Geiger형, Zetlin형 및 Flower형 케이블 돔 구조물의 초기응력에 의한 형상을 결정하고, 형상해석 결과를 기준으로 하여 정적 외력에 의한 불안정 문제를 파악하고자 한다.

인위적인 산성스트레스가 담수산 소백옆새우(Gammarus sobaegensis Ueno)에 미치는 영향을 정체성 수조건 하에서 급, 만성 생태독성실험을 통해 알아보았다. 급성독성 실험 시 pH 3 대역에서의 반수치사시간(LT50)은 평균 0.271(±0.146)day로 개체의 크기 또는 먹이의 유무 그리고 주변 환경에 대한 적응능력에 관계없이 일정한 모습을 나타내고 있었다. pH4.0대역에서의 LT50은 0.812(±0.

쉘형 구조물의 불안정 현상은 크게 뜀좌굴과 분기좌굴로 분류할 수 있다. 이들은 구조물의 형상특성, 특히 형상 초기불완전에 대해 매우 민감하게 반응한다. 본 연구에서는, 형상 초기불완전을 가진 쉘형 구조물의 불안정 거동을 파악하기 위해 양단이 힌지로 고정된 얕은 정현형 아치의 평형경로를 조사한다. 비선형 방정식을 얻기 위해 Galerkin법을 이용하였으며, 증분형 방정식으로의 변환은 섭동법을 이용하였다.

본 연구에서는 유량제어 조직밸브의 기초특성을 집중정수계 모델을 사용하여, 해석하고, 이것을 실험적으로 확인하였다. 그 결과를 요약하면 아래와 같다. 1. 로직밸브의 주밸브 유량은, 그것보다 매우 소유량인 파일럿 유량에 의하여 제어할 수 있다. 2. 주밸브(파핏밸브)~파일럿실간의 개구면적이 주밸브 변위에 비례하도록 밸브를 설계함으로써 주밸브변위(혹은 면적)와 부하유량사이에 양호한 직선성이 얻어진다. 3. 유량제어 로직밸브에서 주밸브 유량의 제어범위의 상한은 기름홈의 개구면적의 최대치에 의하여 결정한다.

We investigated the quality characteristics of brewing brown rice vinegar through a traditional static fermentation process. Accordingly, we decided to compare the physicochemical characteristics of brewing vinegar at different temperatures and filtration methods. In four to five weeks’ time, the acetic acid fermentation exhibited the highest titratable acidity and then it eventually decreased. The titratable acidity was affected by the filtration method. It was revealed that the titratable acidity was higher in the forced filtration than the traditional filtration method. Various organic acids were detected in order to initialize the fermentation stage and as the fermentation progressed, only the acetic acid could be detected. The total free amino acid content was higher at a temperature of 30℃ than at 20℃. Moreover, the free amino acid content was dependent on the acetate content during the acetic fermentation process. The main bioactive substance of the γ-aminobutyric acid content was more than twice at a fermentation temperature of 30℃ compared to the fermentation temperature of 20℃. Furthermore, the total amino acid and essential amino acid content at a temperature of 30℃ was excellent. The quality of the brown rice vinegar via forced filtration method at a temperature of 30℃ was the most excellent. Based on these results, the fermentation temperature and the use of nuruks (fermenting agent) affected the quality of the brown rice vinegar, and an appropriate method to consider its purpose is required.

This study analyzes descriptive statistics and tests homogeneity hypothesis, and applies a posteriori comparison procedures among treatment levels for the response characteristics such as static response ratios, impact factors, natural frequencies of bridges according to structural types and service periods. This study is expected to help understand the difference among response characteristics of groups and provides the practical information for safety assessment and structural design.

최근 건설 산업에서 CFRP는 재료적 장점들 때문에 구조물의 보강재로서 많이 사용되어 지고 있다. 본 논문에서 CFRP Plate가 보강된 철근콘크리트 보의 보강 효율과 설계 기초자료를 제공하려 한다. 정적 실험은 실험체의 파괴양상, 보강성능을 평가하였으며, 피로 실험은 처짐, 철근 변형률, CFRP Plate의 변형률을 분석하고, 에너지 소산과 보강성능을 평가하였다. 실험한 결과, 보강량이 증가할수록 단부 박리 파괴를 일으켰다. 그리고, 단부를 보강한 경우는 휨균열로 인한 박리파괴를 나타내는 파괴양상을 보였다. 피로 실험을 통하여 일정한 반복하중 횟수가 되면 처짐, 철근 변형률, CFRP Plate의 변형률 값이 일정한 값으로 수렴하였다. CFRP Plate가 보강된 보는 피로하중에 대해 사용성 확보가 가능했다.