• Steel and Composite Structures
• /
• 제24권6호
• /
• pp.727-740
• /
• 2017

The present paper studies the stability analysis of the continuously graded CNT-Reinforced Composite (CNTRC) panel stiffened by rings and stringers. The Stiffened Panel (SP) subjected to axial and lateral loads is reinforced by agglomerated CNTs smoothly graded through the thickness. A two-parameter Eshelby-Mori-Tanaka (EMT) model is adopted to derive the effective material moduli of the CNTRC. The stability equations of the CNRTC SP are obtained by means of the adjacent equilibrium criterion. Notwithstanding most available literature in which the stiffener effects were smeared out over the respective stiffener spacing, in the present work, the stiffeners are modeled as Euler-Bernoulli beams. The Generalized Differential Quadrature Method (GDQM) is employed to discretize the stability equations. A numerical study is performed to investigate the influences of different types of parameters involved on the critical buckling of the SP reinforced by agglomerated CNTs. The results achieved reveal that continuously distributing of CNTs adjacent to the inner and outer panel's surface results in improving the stiffness of the SP and, as a consequence, inclining the critical buckling load. Furthermore, it has been concluded that the decline rate of buckling load intensity factor owing to the increase of the panel angle is significantly more sensible for the smaller values of panel angle.

• Structural Engineering and Mechanics
• /
• 제35권4호
• /
• pp.459-478
• /
• 2010

This paper contains detailed descriptions of a dynamic time-history modal analysis to calculate deflection, inter-storey drift and storey shear demand in single-storey and multi-storey buildings using an EXCEL spreadsheet. The developed spreadsheets can be used to obtain estimates of the dynamic response parameters with minimum input information, and is therefore ideal for supporting the conceptual design of tall building structures, or any other structures, in the early stages of the design process. No commercial packages, when customised, could compete with spreadsheets in terms of simplicity, portability, versatility and transparency. An innovative method for developing the stiffness matrix for the lateral load resistant elements in medium-rise and high-rise buildings is also introduced. The method involves minimal use of memory space and computational time, and yet allows for variations in the sectional properties of the lateral load resisting elements up the height of the building and the coupling of moment frames with structural walls by diaphragm action. Numerical examples are used throughout the paper to illustrate the development and use of the spreadsheet programs.

• Steel and Composite Structures
• /
• 제49권4호
• /
• pp.407-417
• /
• 2023

After a disaster like the catastrophic earthquake, the government have to use rapid assessment of the condition (or damage) of bridges, buildings and other infrastructures is mandatory for rapid feedbacks, rescue and post-event management. Many domain schemes based on the measured vibration computations, including least squares estimation and neural fuzzy logic control, have been studied and found to be effective for online/offline monitoring of structural damage. Traditional strategies require all external stimulus data (input data) which have been measured available, but this may not be the generalized for all structures. In this article, a new method with unknown inputs (excitations) is provided to identify structural matrix such as stiffness, mass, damping and other nonlinear parts, unknown disturbances for example. An analytical solution is thus constructed and presented because the solution in the existing literature has not been available. The goals of this paper are towards access to adequate, safe and affordable housing and basic services, promotion of inclusive and sustainable urbanization and participation, implementation of sustainable and disaster-resilient buildings, sustainable human settlement planning and manage. Simulation results of linear and nonlinear structures show that the proposed method is able to identify structural parameters and their changes due to damage and unknown excitations. Therefore, the goal is believed to achieved in the near future by the ongoing development of AI and control theory.

• Steel and Composite Structures
• /
• 제50권4호
• /
• pp.429-441
• /
• 2024

This paper studies the free vibration behavior of trapezoidal shaped coupled double-layered graphene sheets (DLGS) system using first-order shear deformation theory (FSDT) and incorporating nonlocal elasticity theory. Two nanoplates are assumed to be bonded by an interlayer van der walls force and surrounded by an external kelvin-voight viscoelastic medium. The governing equations together with related boundary condition are discretized using a mapping-differential quadrature method (DQM) in the spatial domain. Then the natural frequency of the system is obtained by solving the eigen value matrix equation. The validity of the current study is evaluated by comparing its numerical results with those available in the literature and then a parametric study is thoroughly performed, concentrating on the series effects of angles and aspect ratio of GS, viscoelastic medium, and nonlocal parameter. The model is used to study the vibration of DLGS for two typical deformation modes, the in-phase and out-of-phase vibrations, which are investigated. Numerical results indicate that due to Increasing the damping parameter of the viscoelastic medium has reduced the frequency of both modes and this medium has been able to overdamped the oscillations and by increasing stiffness parameters both in-phase and out-of-phase vibration frequencies increased.

• Advances in Computational Design
• /
• 제2권3호
• /
• pp.123-141
• /
• 2017

Solving a system of linear or non-linear equations is required to analyze any kind of structures. There are many ways to solve a system of equations, and they can be classified as implicit and explicit techniques. The explicit methods eliminate round-off errors and use less memory. The dynamic relaxation method (DR) is one of the powerful and simple explicit processes. The important point is that the DR does not require to store the global stiffness matrix, for which it just uses the residual loads vector. In this paper, a new approach to the DR method is expressed. In this approach, the damping, mass and time steps are similar to those of the traditional method of dynamic relaxation. The difference of this proposed method is focused on the method of calculating the damping. The proposed method is expressed such that the time step is constant, damping is equal to zero except in steps with maximum energy and the concentrated damping can be applied to minimize the energy of system in this step. In this condition, the calculation of damping in all steps is not required. Then the volume of computation is reduced. The DR method for form-finding of membrane structures is employed in this paper. The form-finding of the three plans related to the membrane structures with different loading is considered to investigate the efficiency of the proposed method. The numerical results show that the convergence rate based on the proposed method increases in all cases than other methods.

• Steel and Composite Structures
• /
• 제35권1호
• /
• pp.77-92
• /
• 2020

The present paper outlined a procedure for geometrically nonlinear dynamic analysis of functionally graded graphene platelets-reinforced (GPLR-FG) nanocomposite cylinder subjected to mechanical shock loading. The governing equation of motion for large deformation problems is derived using meshless local Petrov-Galerkin (MLPG) method based on total lagrangian approach. In the MLPG method, the radial point interpolation technique is employed to construct the shape functions. A micromechanical model based on the Halpin-Tsai model and rule of mixture is used for formulation the nonlinear functionally graded distribution of GPLs in polymer matrix of composites. Energy dissipation in analyses of the structure responding to dynamic loads is considered using the Rayleigh damping. The Newmark-Newton/Raphson method which is an incremental-iterative approach is implemented to solve the nonlinear dynamic equations. The results of the proposed method for homogenous material are compared with the finite element ones. A very good agreement is achieved between the MLPG and FEM with very fine meshing. In addition, the results have demonstrated that the MLPG method is more effective method compared with the FEM for very large deformation problems due to avoiding mesh distortion issues. Finally, the effect of GPLs distribution on strength, stiffness and dynamic characteristics of the cylinder are discussed in details. The obtained results show that the distribution of GPLs changed the mechanical properties, so a classification of different types and volume fraction exponent is established. Indeed by comparing the obtained results, the best compromise of nanocomposite cylinder is determined in terms of mechanical and dynamic properties for different load patterns. All these applications have shown that the present MLPG method is very effective for geometrically nonlinear analyses of GPLR-FG nanocomposite cylinder because of vanishing mesh distortion issue in large deformation problems. In addition, since in proposed method the distributed nodes are used for discretization the problem domain (rather than the meshing), modeling the functionally graded media yields to more accurate results.

• 대한조선학회논문집
• /
• 제39권1호
• /
• pp.28-37
• /
• 2002

본 연구에서는 저장력 예인케이블의 비선형 동적거동을 수치적으로 해석하였다. 고장력 케이블해석에서는 흔히 무시되는 굽힘강성의 효과가 저장력 케이블에서는 중요한 역할을 하므로 본 연구에서는 이를 고려하였다. 또한 저장력 케이블에서는 대변위가 발생하기 쉬우므로 기하학적인 비선형 및 유체 비선형 효과가 크므로 이를 고려하였다. 저장력 예인케이블에 대한 3차원 비선형 운동방정식을 수립하고 유한차분법을 적용하여 이산화 시켰다. 시간적분에 있어서 안정적인 해를 얻을 수 있는 음해법(implicit method)을 적용하였으며 비선형 해를 구하기 위하여 Newton-Raphson 반복법을 사용하였다. 케이블과 같이 양단경계조건을 갖고 대각선 주변 성분만 있는 행렬식을 계산하는 경우에는 Gauss-Jordan 방법 등과 같이 일반적인 방법 보다 블록삼중대각행렬 풀이법이 계산시간을 상당히 줄일 수 있음을 알 수 있었다. 몇 가지 예제해석을 수행하였으며 실해역 실험결과에 의해 이미 검증되어 있는 케이블 해석프로그램인 WHOI Cable 프로그램의 해석결과와 비교 검토한 결과 서로 잘 일치함을 알 수 있었다.

• 한국강구조학회 논문집
• /
• 제16권6호통권73호
• /
• pp.833-846
• /
• 2004

포스트-노스리지 연결부를 사용하는 강재 보의 탄성거동을 모델하기 위한 부등 단면 보 요소가 제안된다. 감소 단면 (RBS) 연결부를 갖는 부등단면 부재에 대한 탄성 강성 매트릭스는 수치적분이 필요치 않는 수식으로 표현되고 전단 효과를 포함하고 있다. 또한 균일 단면 보 요소를 사용하여 RBS 연결부를 갖는 보를 모델 하는 간략 방법이 제안된다. 이 방법의 장점은 기존의 보 요소를 사용하여 RBS 연결부를 사용하는 강재 모멘트 골조의 최대 층간 상대 변위 비를 상당히 정확하게 예측할 수 있다는데 있다. 강재 모멘트 골조의 탄성 강성에 감소 단면 연결부가 미치는 영향이 조사되었고, 절점에서의 변형을 고려하기 위한 적절한 모델 선정이 골조의 최대 층간 상대변위 비를 정확히 예측하는데 감소 단면 연결부보다 중요한 역할을 하였다.

• Ocean Systems Engineering
• /
• 제4권4호
• /
• pp.327-342
• /
• 2014

The tension leg platform (TLP) is one of the compliant structures which are generally used for deep water oil exploration. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to the vertical degrees of freedom, it is stiff and resembles a fixed structure and is not allowed to float freely. In the current study, a numerical study for square TLP using modified Morison equation was carried out in the time domain with water particle kinematics using Airy's linear wave theory to investigate the effect of changing the tether tension force on the stiffness matrix of TLP's, the dynamic behavior of TLP's; and on the fatigue stresses in the cables. The effect was investigated for different parameters of the hydrodynamic forces such as wave periods, and wave heights. The numerical study takes into consideration the effect of coupling between various degrees of freedom. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables. Nonlinear equation was solved using Newmark's beta integration method. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e., 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether tension force, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations that is significantly dependent on wave height, and that special attention should be given to tethers fatigue because of their high tensile static and dynamic stress.

• 한국소음진동공학회논문집
• /
• 제23권3호
• /
• pp.240-248
• /
• 2013

자동차 수동변속기 내 래틀과 같은 회전체 진동은 엔진 연소폭발 주기와 연동하여 발생한다. 이러한 충격형 진동 특성은 선형 시간 불변 분석법을 적용하여 살펴볼 수 있다. 기어의 동적 특성을 이해하기 위해, 특정 형태의 앞 바퀴 굴림 방식 수동 변속기에 대한 연구를 수행하였다. 첫째, 동특성 고유값과 주파수 응답함수를 기반으로 자유도를 줄이는 방법을 제시하였는데, 이는 행렬의 크기를 줄이는 효과적인 역할을 한다. 둘째, 단일 질량 플라이휠과 이중 질량 플라이휠의 동적 특성을 비교하였다. 모빌리티 분석을 기반으로 한 이중 질량 플라이휠의 효과를 검토하였는데, 이로부터 진동에 의해 가진되는 충격을 회피하기 위한 기본 개념을 이해 할 수 있다. 마지막으로, 두 단계 클러치 댐퍼로부터 유효 강성 값을 도출하여 선형 불변형 시스템 모델을 연구하였다. 두 단계의 서로 다른 클러치 강성조합을 이용하여 클러치 댐퍼의 동적특성에 대한 관계를 예측할 수 있다.