• Applied Science and Convergence Technology
• /
• 제23권3호
• /
• pp.103-112
• /
• 2014

The Korea Research Institute of Standards and Science (KRISS) has three major vacuum systems: an ultrasonic interferometer manometer (UIM; Section II, Figs. 1 and 2) for a low vacuum, a static expansion system (SES; Section III, Figs. 3 and 4) for a medium vacuum, and an orifice-type dynamic expansion system (DES, Section IV, Figs. 5 and 6) for high and ultra-high vacuum systems. For each system, explicit measurement model equations with multiple variables are given. According to ISO standards, all of these system variable errors were used to calculate the expanded uncertainty (U). For each system, the expanded uncertainties (k = 1, confidence level = 95%) and relative expanded uncertainty (expanded uncertainty/generated pressure) levels are summarized in Table 4. Within the uncertainty limits, our bilateral and key comparisons [CCM.P-K4 (10 Pa to 1 kPa)] are extensive and in good agreement with those of other nations (Fig. 8 and Table 5).

• Steel and Composite Structures
• /
• 제17권5호
• /
• pp.641-665
• /
• 2014

This paper presents the analytical solutions for the size-dependent static analysis of the functionally graded (FG) beams with various boundary conditions based on the nonlocal continuum model. The nonlocal behavior is described by the differential constitutive model of Eringen, which enables to this model to become effective in the analysis and design of nanostructures. The elastic modulus of beam is assumed to vary through the thickness or longitudinal directions according to the power law. The governing equations are derived by using the nonlocal continuum theory incorporated with Euler-Bernoulli beam theory. The explicit solutions are derived for the static behavior of the transversely or axially FG beams with various boundary conditions. The verification of the model is obtained by comparing the current results with previously published works and a good agreement is observed. Numerical results are presented to show the significance of the nonlocal effect, the material distribution profile, the boundary conditions, and the length of beams on the bending behavior of nonlocal FG beams.

• 한국콘텐츠학회논문지
• /
• 제5권3호
• /
• pp.73-81
• /
• 2005

CTOC(Classes To Optimized Classes)는 자바 바이트코드의 최적화와 분석을 위해 현재 개발 중인 프레임워크이다. CTOC는 스택 기반인 바이트코드를 최적화와 분석을 쉽게 하기 위해 3-주소 형태로 변환한다. 바이트코드가 타입에 관한 정보를 포함하지만 스택 기반의 동작을 수행하기 때문에 지역 변수를 위한 명시적인 타입을 갖지 못하는 경우가 발생한다. 따라서 바이트코드에서 3-주소 형태로 변환하는 과정에 사용되는 모든 변수는 정적 타입을 가져야 하는 문제점이 발생한다. 왜냐하면, 프로그램의 최적화나 분석을 위해서는 지역 변수의 타입을 알아야 하기 때문이다. 본 논문은 CTOC 프레임워크의 전반부로 바이트코드를 스택을 사용하지 않는 3-주소 형태로 변환하는 과정을 수행한다. 이 과정에서 스택 코드 형태인 CTOC-B 코드를 생성하고, 제어 흐름 그래프를 생성하여 바이트코드 수준에서 분석을 수행한다. 또한 정적 타입을 제공하기 위한 중간 과정으로 타입을 갖지 않는 CTOC-T 코드를 생성한다. 이를 위해 정적 단일 배정문 형태(Static Single Assignment Form)를 사용하여 모든 변수를 분리하고 각 변수에 새로운 이름으로 재명명하는 동작을 수행한다. 분리된 변수들은 추후 정적 타입 추론을 위한 준비 단계로 사용된다.

• Structural Engineering and Mechanics
• /
• 제60권1호
• /
• pp.111-130
• /
• 2016

Two new elements with six degrees of freedom are proposed by applying the equilibrium conditions and strain-displacement equations. The first element is formulated for the infinite ratio of beam radius to thickness. In the second one, theory of the thick beam is used. Advantage of these elements is that by utilizing only one element, the exact solution will be obtained. Due to incorporating equilibrium conditions in the presented formulations, both proposed elements gave the precise internal forces. By solving some numerical tests, the high performance of the recommended formulations and also, interaction effects of the bending and axial forces will be demonstrated. While the second element has less error than the first one in thick regimes, the first element can be used for all regimes due to simplicity and good convergence. Based on static responses, it can be deduced that the first element is efficient for all the range of structural characteristics. The free vibration analysis will be performed using the first element. The results of static and dynamic tests show no deficiency, such as, shear and membrane locking and excessive stiff structural behavior.

• Structural Engineering and Mechanics
• /
• 제59권3호
• /
• pp.579-599
• /
• 2016

In this study, static bending of edge cracked micro beams is studied analytically under uniformly distributed transverse loading based on modified couple stress theory. The cracked beam is modelled using a proper modification of the classical cracked-beam theory consisting of two sub-beams connected through a massless elastic rotational spring. The deflection curve expressions of the edge cracked microbeam segments separated by the rotational spring are determined by the Integration method. The elastic curve functions of the edge cracked micro beams are obtained in explicit form for cantilever and simply supported beams. In order to establish the accuracy of the present formulation and results, the deflections are obtained, and compared with the published results available in the literature. Good agreement is observed. In the numerical study, the elastic deflections of the edge cracked micro beams are calculated and discussed for different crack positions, different lengths of the beam, different length scale parameter, different crack depths, and some typical boundary conditions. Also, the difference between the classical beam theory and modified couple stress theory is investigated for static bending of edge cracked microbeams. It is believed that the tabulated results will be a reference with which other researchers can compare their results.

• Advances in nano research
• /
• 제12권2호
• /
• pp.139-150
• /
• 2022

This paper presents sets of explicit analytical equations that compute the static displacements of nanobeams by adopting the nonlocal elasticity theory of Eringen within the framework of Euler Bernoulli and Timoshenko beam theories. Castigliano's theorem is applied to an equivalent Virtual Local Beam (VLB) made up of linear elastic material to compute the displacements. The first derivative of the complementary energy of the VLB with respect to a virtual point load provides displacements. The displacements of the VLB are assumed equal to those of the nonlocal beam if nonlocal effects are superposed as additional stress resultants on the VLB. The illustrative equations of displacements are relevant to a few types of loadings combined with a few common boundary conditions. Several equations of displacements, thus derived, matched precisely in similar cases with the equations obtained by other analytical methods found in the literature. Furthermore, magnitudes of maximum displacements are also in excellent agreement with those computed by other numerical methods. These validated the superposition of nonlocal effects on the VLB and the accuracy of the derived equations.

• Steel and Composite Structures
• /
• 제45권3호
• /
• pp.349-367
• /
• 2022

In this research, an approach combining a semi-analytical method and an analytical method is presented to investigate the static and dynamic post-buckling behavior of the sandwich functionally graded (FG) porous cylindrical shells exposed to external pressure. The sandwich cylindrical shell considered is composed of a viscoelastic core and two FG porous (FGP) face layers. The viscoelastic core is made of Kelvin-Voigt-type material. The material properties of the FG porous face layer are considered continuous through each face thickness according to a porosity coefficient and a volume fraction index. Two types of sandwich FG porous viscoelastic cylindrical shells named Type A and Type B are considered in the research. Type A shell has the porosity evenly distributed across the thickness direction, and Type B has the porosity unevenly distributes across the thickness direction. The FG face layers are considered in two cases: outside metal surface, inside ceramic surface (OMS-ICS), and inside metal surface, outside ceramic surface (IMS-OCS). According to Donnell shell theory, von-Karman equation, and Galerkin's method, a discretized nonlinear governing equation is derived for analyzing the behavior of the shells. The explicit expressions for static and dynamic critical buckling loading are thus developed. To study the dynamic buckling of the shells, the governing equation is examined via a numerical approach implementing the fourth-order Runge-Kutta method. With a procedure presented by Budiansky-Roth, the critical load for dynamic post-buckling is obtained. The effects of various parameters, such as material and geometrical parameters, on the post-buckling behaviors are investigated.

• 에너지공학
• /
• 제12권1호
• /
• pp.11-16
• /
• 2003

지상 정적 상태에 있는 항공기내 연료온도의 변화가 유한차분식에 의하여 해석되었다. 수정 Dufort-Frankel 기법의 explicit 방법에 의해 수치계산이 수행되었다. 항공기는 지상 정적상태에서 1% hot day 대기조건에 따른 태양의 복사 및 바람의 속도와 함께 반복되는 일일주기의 공기온도에 노출되어 있다고 가정되었다. 항공기는 난류유동장내에 있는 것으로 가정되었다. 항공기 표면과 외부대기사이의 열전달을 계산하기 위하여 Eckert에 의해 제안된 평판위의 난류 열전달계수가 사용되었다. 본 해석에 사용된 지배방정식은 연료에 대한 에너지방정식이다. 본 해석으로부터, 주익탱크의 연료온도가 다른 탱크들 가운데 가장 높게 나타났으며 온도변화율 또한 가장 크게 나타났다. 본 온도해석에 대한 결과는 여러 비행임무에 있어서 항공기내의 연료온도 변화 해석을 위한 초기치로서 사용될 수 있다. 또한, 본 해석방법은 항공기 열에너지 관리시스템의 해석 및 설계에 사용될 수 있다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제8권4호
• /
• pp.107-114
• /
• 2004

본 논문에서는 복합적층판의 유한요소해석을 위해 직접수정법으로 간단히 개선된 8절점 유한요소를 제안하였다. 우선, 9절점 등매개변수 요소와 동일한 조건하에서 이차다항식을 표현할 수 있도록 형상함수를 수정하며, 이를 외시적(explicit)으로 표현하였다. 전단보정계수를 갖는 1차전단변형이론을 고차전단변형이론에 근거하여 간단히 개선함으로써 두께방향으로 전단응력 및 변형률이 포물선 분포를 가지도록 하였다. 더 이상의 전단보정계수가 필요하지 않다. 따라서 간단한 직접수정법 즉, 형상함수의 수정, 1차전단변형이론의 개선 및 가정변형률을 조합함으로써 8절점 유한요소의 성능을 개선하였다. 제안된 유한요소를 이용하여 복합적층판의 정적, 좌굴 및 자유진동 수치해석을 실시하여 비교 검증하였다.

• 한국정밀공학회지
• /
• 제22권8호
• /
• pp.92-99
• /
• 2005

Tungsten heavy metal is characterized by a high density and novel combination of strength and ductility. Among them, 90W-7Ni-3Fe is used for applications, where the high specific weight of the material plays an important role. They are used as counterweights, rotating inertia members, as well as fur defense purposes(kinetic energy Penetrators, etc.). Because of these applications, it is essential to detemine the dynamic characteristics of tungsten alloy. In this paper, Explicit FEM(finite element method) is employed to investigate the dynamic characteristics of tungsten heavy metal under base of stress wave propagation theory for SHPB, and the model of specimen is divided into two parts to understand the phenomenon that stress wave penetrates through each tungsten base and matrix. This simulation results were compared to experimental one and through this program, the dynamic stress-strain curve of tungsten heavy metal can be obtained using quasi static stress-strain curve of pure tungsten and matrix.