• 디지털융복합연구
• /
• 제17권7호
• /
• pp.125-130
• /
• 2019

민감도 해석은 어떤 설계 변수의 변화가 전체 시스템에 미치는 영향을 확인하기 위한 방법으로, 계산된 민감도는 구조개선 시 중요한 지표가 된다. 본 연구에서는 유한요소해석을 이용하여 설계 변수에 대한 민감도 도출 및 분석 방법과, 민감도 결과를 활용한 구조개선 방법을 제안하였다. 구조 개선이 필요한 실제 반도체 검사 장비를 이용하여 경량화를 위한 설계 변수를 선정하고 설계 변수에 대한 민감도를 유한요소법과 유한차분법을 활용하여 계산하였으며, 장비가 요구하는 과도응답(Transient Response)은 유지하면서도 무게 감소가 가능한 개선 방안을 제시하였다. 유한요소해석과 유한차분법을 이용한 민감도 분석 결과를 이용한다면 구조물의 설계 개선 시 원하는 응력 또는 변위는 만족하면서도 구조적으로 향상된 설계를 할 수 있고, 이는 반도체 검사 장비뿐만 아니라 다양한 분야에서 활용이 가능하다.

• Structural Engineering and Mechanics
• /
• 제86권2호
• /
• pp.167-180
• /
• 2023

This work applies a four-known quasi-3D shear deformation theory to investigate the bending behavior of a functionally graded plate resting on a viscoelastic foundation and subjected to hygro-thermo-mechanical loading. The theory utilizes a hyperbolic shape function to predict the transverse shear stress, and the transverse stretching effect of the plate is considered. The principle of virtual displacement is applied to obtain the governing differential equations, and the Navier method, which comprises an exponential term, is used to obtain the solution. Novel to the current study, the impact of the viscoelastic foundation model, which includes a time-dependent viscosity parameter in addition to Winkler's and Pasternak parameters, is carefully investigated. Numerical examples are presented to validate the theory. A parametric study is conducted to study the effect of the damping coefficient, the linear and nonlinear loadings, the power-law index, and the plate width-tothickness ratio on the plate bending response. The results show that the presence of the viscoelastic foundation causes an 18% decrease in the plate deflection and about a 10% increase in transverse shear stresses under both linear and nonlinear loading conditions. Additionally, nonlinear loading causes a one-and-a-half times increase in horizontal stresses and a nearly two-times increase in normal transverse stresses compared to linear loading. Based on the article's findings, it can be concluded that the viscosity effect plays a significant role in the bending response of plates in hygrothermal environments. Hence it shall be considered in the design.

• 대한기계학회논문집A
• /
• 제35권3호
• /
• pp.309-316
• /
• 2011

일반적으로 카누는 목재나 FRP 등으로 제작된다. 그러나 소비자들은 기존의 재료에 비하여 염가이면서 친환경 재료를 선호한다. 특히, 선진국에서는 일부 선박에 대하여 FRP 선체 제조를 금지하는 법안을 발표하고 이에 따른 국제협약을 제정하였다. 폴리에틸렌은 식료품 용기나 의료용 용기로 널리 사용되는 재료로서 리사이클 가능한 재료이다. 본 연구에서는 카누 선체 재료로 폴리에틸렌으로 선정하였으며 선형설계는 상용 선형 설계 프로그램인 3D Boat Design을 이용하여 수행하였다. 카누 구조하중은 우선 ANSYS CFX R12.1을 이용하여 선체에 작용되는 압력 분포를 구하고 이것을 ANSYS WORKBENCH R12.1로 넘겨 선체 압력 하중과 패들러 하중을 동시에 고려하였다. 카누 각 치수를 설계변수화하여 응력과 무게를 최소화하는 최적화 과정을 반응표면방법과 만족도 함수를 이용하여 수행하였다. 개발된 카누는 운항시험에서 직진성이나 안정성은 우수하나 운반성과 선회성 및 속도는 보통인 것으로 판단된다.

• 한국산학기술학회논문지
• /
• 제12권4호
• /
• pp.1495-1501
• /
• 2011

본 연구는 동력전달 장치인 추진축이 차량 주행중 상하운동에 따라 생기는 자재이음의 내구성에 대한 강도 해석을 하였다. 유니버설 조인트에서의 최대 등가 응력과 전변형량은 요크 부분에서 $1.3177{\times}10^3$Pa및 $3.6148{\times}10^{-4}$m로 크게 나타났다. 'SAE bracket', 'SAE transmission' 및 Sample history'의 불규칙 피로 하중들 중에서는 하중의 변화가 극심한 SAE bracket'의 경우가 사용 가능 수명이 15951 Cycle 정도로 가장 짧은 것을 볼 수가 있고 하중의 변화가 가장 완만한 Sample history'에서 사용가능 수명이 $2{\times}10^7$ Cycle 정도로 가장 긴 것을 알 수 있었다. 피로 하중의 빈도수로서는 SAE Bracket history'가 80% 정도로서 가장 높게 나타나 파손의 가능성이 큼을 알 수 있었고 Sample history'가 5%로서 가장 낮게 나타났다. 그리고 구속 조건을 가하여 한 Harmonic response 해석에서의 최대 변위는 58Hz에서 일어났다. 이러한 진동수에서의 최대 변위는 0.00261m가 되었다. 본 연구의 결과를 종합하여 동력전달 장치인 추진축에 응용한다면 그 파손 방지 및 내구성을 예측하는데 활용이 클 것으로 사료된다.

• Structural Engineering and Mechanics
• /
• 제91권2호
• /
• pp.211-225
• /
• 2024

Soft bending actuators have gained significant interest in robotic applications due to their compliance and lightweight nature. Their compliance allows for safer and more natural interactions with humans or other objects, reducing the risk of injury or damage. However, the nonlinear behaviour of soft actuators presents challenges in accurately predicting their bending motion and force exertion. In this research, a new comprehensive study has been conducted by employing a developed 3D finite element model (FEM) to investigate the effect of geometrical and material parameters on the bending behaviour of a soft pneumatic actuator reinforced with Kevlar fibres. A series of experiments are designed to validate the FE model, and the FE model investigates the improvement of actuator performance. The material used for fabricating the actuator is RTV-2 silicone rubber. In this study, the Cauchy stress was expanded for hyperelastic models and the best model to express the stress-strain behaviour based on ASTM D412 Type C tensile test for this material has been obtained. The results show that the greatest bending angle was achieved for the semi-elliptical actuator made of RTV2 material with a pitch of 1.5 mm and second layer thickness of 1 mm. In comparison, the maximum response force was obtained for the semi-elliptical actuator made of RTV2 material with a pitch of 6 mm and a second layer thickness of 2 mm. Additionally, this research opens up new possibilities for development of safer and more efficient robotic systems that can interact seamlessly with humans and their environment.

• Steel and Composite Structures
• /
• 제48권2호
• /
• pp.113-130
• /
• 2023

The present manuscript aims to investigate the deviation between the middle surface (MS) and neutral surface (NS) formulations on the static response of bi-directionally functionally graded (BDFG) porous plate. The higher order shear deformation plate theory with a four variable is exploited to define the displacement field of BDFG plate. The displacement field variables based on both NS and on MS are presented in detail. These relations tend to get and derive a new set of boundary conditions (BCs). The porosity distribution is portrayed by cosine function including three different configurations, center, bottom, and top distributions. The elastic foundation including shear and normal stiffnesses by Winkler-Pasternak model is included. The equilibrium equations based on MS and NS are derived by using Hamilton's principles and expressed by variable coefficient partial differential equations. The numerical differential quadrature method (DQM) is adopted to solve the derived partial differential equations with variable coefficient. Rigidities coefficients and stress resultants for both MS and NS formulations are derived. The mathematical formulation is proved with previous published work. Additional numerical and parametric results are developed to present the influences of modified boundary conditions, NS and MS formulations, gradation parameters, elastic foundations coefficients, porosity type and porosity coefficient on the static response of BDFG porous plate. The following model can be used in design and analysis of BDFG structure used in aerospace, vehicle, dental, bio-structure, civil and nuclear structures.

• Steel and Composite Structures
• /
• 재36권6호
• /
• pp.643-656
• /
• 2020

This article presents a comprehensive static analysis of simply supported cross-ply carbon nanotubes reinforced composite (CNTRC) laminated nanobeams under various loading profiles. The nonlocal strain gradient constitutive relation is exploited to present the size-dependence of nano-scale. New higher shear deformation beam theory with hyperbolic function is proposed to satisfy the zero-shear effect at boundaries and parabolic variation through the thickness. Carbon nanotubes (CNTs), as the reinforced elements, are distributed through the beam thickness with different distribution functions, which are, uniform distribution (UD-CNTRC), V- distribution (FG-V CNTRC), O- distribution (FG-O CNTRC) and X- distribution (FG-X CNTRC). The equilibrium equations are derived, and Fourier series function are used to solve the obtained differential equation and get the response of nanobeam under uniform, linear or sinusoidal mechanical loadings. Numerical results are obtained to present influences of CNTs reinforcement patterns, composite laminate structure, nonlocal parameter, length scale parameter, geometric parameters on center deflection ad stresses of CNTRC laminated nanobeams. The proposed model is effective in analysis and design of composite structure ranging from macro-scale to nano-scale.

• Structural Engineering and Mechanics
• /
• 제57권4호
• /
• pp.617-639
• /
• 2016

In this work, an analytical formulation based on both hyperbolic shear deformation theory and stress function, is presented to study the nonlinear post-buckling response of symmetric functionally graded plates supported by elastic foundations and subjected to in-plane compressive, thermal and thermo-mechanical loads. Elastic properties of material are based on sigmoid power law and varying across the thickness of the plate (S-FGM). In the present formulation, Von Karman nonlinearity and initial geometrical imperfection of plate are also taken into account. By utilizing Galerkin procedure, closed-form expressions of buckling loads and post-buckling equilibrium paths for simply supported plates are obtained. The effects of different parameters such as material and geometrical characteristics, temperature, boundary conditions, foundation stiffness and imperfection on the mechanical and thermal buckling and post-buckling loading capacity of the S-FGM plates are investigated.

• 한국추진공학회지
• /
• 제19권2호
• /
• pp.29-37
• /
• 2015

본 연구는 케로신 연료를 사용하는 액체로켓엔진에서 발생할 수 있는 연소불안정으로 인하여 파괴될 수 있는 연소기의 손상을 수치적으로 모사하는 해석 모델의 기초연구이다. 연소불안정으로부터 야기 될 수 있는 케로신의 데토네이션은 1단계 아레니우스 식의 화학 반응식을 이용하였고, 구조체는 Johnson-Cook 강성모델을 활용하여 데토네이션으로 인한 금속관의 소성 변형을 모델링하였다. 금속관의 소성 변형에 의해 변화하는 유동장과 구조체의 스트레스를 노즐 형상과 관의 두께변화에 따라 해석하였다.

• 한국정밀공학회지
• /
• 제33권8호
• /
• pp.617-622
• /
• 2016

The article describes the determination of the dynamic stability for an observation antenna, considering the rotational speed by the payload driving motor. A finite element model of the observation antenna was made using the solid and beam elements. The connecting parts between the solid and the beam was adequately coupled. The boundary conditions were made by restriction of the degree of freedoms in the supporting points. With the comparison between the modal analysis results and the rotating speed of the payload driving motor, no resonance for the structure of antenna was identified and first natural frequency was determined under 33 Hz (Seismic Cut-Off Frequency). Therefore, the dynamic stability of the antenna was confirmed by the comparism between the seismic safety criterion and the stress results of the dynamic analysis applied the loading conditions and required response spectrum (RRS).