A study on the optimal configuration of harbor structure under the combined loads

조규남 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.3

Response of harbor structure to environmental loads such as wave load, impact load, ship’s contacting load, is a fundamental factor in designing of the structure’s optimal configuration. In this paper, typical environmental loads against coastal structures are investigated for designing of the optimal harbor structure. Loads to be considered here are wave load, impact load and contacting load due to ship mooring. Statistical analysis for several harbor structure types under the corresponding loads is carried out, followed by investigation of effect of individual environmental load. Based on these, the optimal configuration for the harbor structure is obtained after considerable engineering process. Estimation of contacting load of the ship is suggested using effective energy concepts for the load, and analysis of structural behavior is done for the optimal designing of the structure in the particular load. A guideline for the design process of the harbor structure is established, and safety of the structure is examined by proposed scheme. For verification of the analytical approach, various steel-piled coastal structures and caissons are chosen and relevant structural analyses are carried out using the Finite Element Methods combined with MIDAS/GTS and ANSYS code. It is found using the Morison equation that impact load cannot be a major load in the typical harbor structure compared with the original wave load, and that configuration shape of the structure may play an important role in consideration of the response criteria.

Optimization of a structure with contact conditions using equivalent loads

Sang-Il Yi,이현아,박경진 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.3

Engineering structures consist of various components, and the components interact with each other through contact. Engineers tend to consider the interaction in analysis and design. Interactions of the components have nonlinearity because of the friction force and boundary conditions. Nonlinear analysis has been developed to accommodate the contact condition. However, structural optimization using nonlinear analysis is fairly expensive, and sensitivity information is difficult to calculate. Therefore, an efficient optimization method using nonlinear analysis is needed to consider the contact condition in design. Nonlinear Response Optimization using Equivalent Loads (NROEL) has been proposed for nonlinear response structural optimization. The method was originally developed for optimization problems considering geometric/material nonlinearities. The method is modified to consider the contact nonlinearity in this research. Equivalent loads are defined as the loads for linear analysis, which generate the same response field as that of nonlinear analysis. A nonlinear response optimization problem is converted to linear response optimization with equivalent loads. The modified NROEL is verified through three examples with contact conditions. Three structural examples using the finite element method are demonstrated. They are shape optimization with stress constraints, size optimization with stress/displacement constraints and topology optimization. Reasonable results are obtained in the optimization process.

A study on the optimal configuration of harbor structure under the combined loads

Cho, Kyu-Nam Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.3

Response of harbor structure to environmental loads such as wave load, impact load, ship's contacting load, is a fundamental factor in designing of the structure's optimal configuration. In this paper, typical environmental loads against coastal structures are investigated for designing of the optimal harbor structure. Loads to be considered here are wave load, impact load and contacting load due to ship mooring. Statistical analysis for several harbor structure types under the corresponding loads is carried out, followed by investigation of effect of individual environmental load. Based on these, the optimal configuration for the harbor structure is obtained after considerable engineering process. Estimation of contacting load of the ship is suggested using effective energy concepts for the load, and analysis of structural behavior is done for the optimal designing of the structure in the particular load. A guideline for the design process of the harbor structure is established, and safety of the structure is examined by proposed scheme. For verification of the analytical approach, various steel-piled coastal structures and caissons are chosen and relevant structural analyses are carried out using the Finite Element Methods combined with MIDAS/GTS and ANSYS code. It is found using the Morison equation that impact load cannot be a major load in the typical harbor structure compared with the original wave load, and that configuration shape of the structure may play an important role in consideration of the response criteria.

A Novel Structural Optimization Method and a Case Study Based on a CHS X-Joint

Xingqi Liu,Weitong Yi,Hailin Sun,Lei Zhu,Xi Chen 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.4

In this paper, a new structural optimization method, “percentage structure optimization”, is presented. This method is obtained by using fi nite element method (FEM) to reduce a specifi c proportion of the stress ineffi cient element reduction, which is called the "structural optimization percentage index". In addition, an evaluation index of the optimized structure, “economic benefi t index”, is introduced. Compared with the existing structural optimization methods, the optimization process is smoother and the results are more controllable. Moreover, the method of evaluating the optimization results through the “economic benefi t index” pays more attention to the economic benefi ts of the project, and can achieve the balance between the minimization of material and the detention of bearing capacity to maximize the economic benefi ts. On the basis of the existing experiment, using ANSYS 17.0 software, two Circular Hollow Sections (CHS) X-joints are optimized by "structural optimization percentage index" of 5, 10 and 15%, and "economic benefi t index" is adopted as the judgment condition of the optimization results. The results show that the method can not only guarantee the bearing capacity, but also save materials as much as possible, and verify the reliability of the new structural optimization method.

The structure optimization of tracked ambulance nonlinear vibration reduction system

Xinxi Xu,Meng Yang,Nan Jia,Deguang Duan 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.2

Our aim was to improve the performance of tracked ambulance nonlinear vibration reduction system by structure optimization design. The structure optimization focuses on the stretcher base. Two structure optimization schemes are proposed based on the mechanism of Dynamic vibration absorber (DVA): Linear and nonlinear structure. The linear structure optimization scheme is finally adopted by comparison of the two schemes under random vibration, and the performance of linear scheme is also verified under shock vibration. Then the global sensitivity analysis method is applied to calculate the parameter sensitivity of nonlinear vibration reduction system. Finally, the Nondominated sorting genetic algorithm II (NSGA-II) is used to optimize the performance of the nonlinear vibration reduction system. It shows that the vibration energy of the supine human body on a stretcher is reduced after above studies, which proves the validity and feasibility of the structure optimization schemes proposed and the optimization studies applied in this paper.

Discrete Sizing Optimization of Truss Structures Using Continuous Optimization and Machine Learning Tools

이권희 한국산학기술학회 2022 한국산학기술학회논문지 Vol.23 No.9

This research proposes a series of design procedures for discrete sizing optimization of truss structures. Most discrete sizing optimization methods for truss structures adopt stochastic approaches using metaheuristic algorithms. However, such methods involve many structural analyses until they find a discrete optimal solution, which is expensive. The primary motivation of this research is to suggest a discrete design while reducing the number of structural analyses as many as possible. First, the structural optimization software GENESIS performs sizing optimization in a continuous design space using proven techniques. This provides an excellent optimal solution, and the proposed method is applied while assuming that the discrete optimal solution exists near the continuous optimum design. For discrete sizing optimization of a truss structure, approximate models are generated near the continuous optimum point using the scikit-learn-one capability of machine learning libraries, leading to a simple optimization problem. Then, the python library, PyGAD, is used to obtain a discrete optimal solution. Compared with existing methods, this research provides discrete designs requiring only 0.38-52.0% of the number of structural analyses performed in other studies.

3D Topology Optimization of Fixed Offshore Structure and Experimental Validation

김현석,Hyun-Sung Kim,박병재,Kangsu Lee 한국해양공학회 2020 韓國海洋工學會誌 Vol.34 No.4

In this study, we performed a three-dimensional (3D) topology optimization of a fixed offshore structure to enhance its structural stiffness. The proposed topology optimization is based on the solid isotropic material with penalization (SIMP) method, where a volume constraint is applied to utilize an equivalent amount of material as that used for the rule-based scantling design. To investigate the effects of the main legs of the fixed offshore structure on its structural stiffness, the leg region is selectively considered in the design domain of the topology optimization problem. The obtained optimal designs and the rule-based scantling design of the structure are manufactured by 3D metal printing technology to experimentally validate the topology optimization. The behaviors under compressive loading of the obtained optimal designs are compared with those of the rule-based scantling design using a universal testing machine (UTM). Based on the structural experiments, we concluded that by employing the topology optimization method, the structural stiffness of the structure was enhanced compared to that of the rule-based scantling design for an equal amount of the fabrication material. Furthermore, by effectively combining the topology optimization and rule-based scantling methods, we succeeded in enhancing the structural stiffness and improving the breaking load of the fixed offshore structure.

Policy research and energy structure optimization under the constraint of low carbon emissions of Hebei Province in China

Wei Sun,Minquan Ye,Yanfeng Xu 대한환경공학회 2016 Environmental Engineering Research Vol.21 No.4

As a major energy consumption province, the issue about the carbon emissions in Hebei Province, China has been concerned by the government. The carbon emissions can be effectively reduced due to a more rational energy consumption structure. Thus, in this paper the constraint of low carbon emissions is considered as a foundation and four energies--coal, petroleum, natural gas and electricity including wind power, nuclear power and hydro-power etc are selected as the main analysis objects of the adjustment of energy structure. This paper takes energy cost minimum and carbon trading cost minimum as the objective functions based on the economic growth, energy saving and emission reduction targets and constructs an optimization model of energy consumption structure. And empirical research about energy consumption structure optimization in 2015 and 2020 is carried out based on the energy consumption data in Hebei Province, China during the period 1995-2013, which indicates that the energy consumption in Hebei dominated by coal cannot be replaced in the next seven years, from 2014 to 2020, when the coal consumption proportion is still up to 85.93%. Finally, the corresponding policy suggestions are put forward, according to the results of the energy structure optimization in Hebei Province.

Structural Design and Optimization of the Crossbeam of a Computer Numerical Controlled Milling-Machine Tool Using Sensitivity Theory and NSGA-II Algorithm

Xueguang Li,Chongqing Li,Penghui Li,Huizhong Hu,Xiansheng Sui 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.2

The crossbeam plays a vital role in computer numerical controlled milling machines, especially in machines with a gantry structure, as it directly influences the machining precision. In this study, a machine tool crossbeam was designed, and the modal frequency of the crossbeam was analyzed using the finite element model (FEM) analysis. In the improved structure obtained through FEM analysis, the X-type structure of the internal unit of the crossbeam was replaced by an O-type structure. The specific structure dimensions were further optimized using a neural-network algorithm and a nondominated sorting genetic algorithm. Finally, we calculated the effect of each crossbeam dimension on the mass, deformation, and frequency in a sensitivity analysis. After optimizing the crossbeam dimensions with respect to deformation, modal frequency, and mass, the structural characteristics of the original and optimized crossbeams were compared. After optimization, the mass and deformation were reduced by 7.45% and 3.08%, respectively, and the modal frequency was increased by 0.42%. These results confirm that the optimization improved the performance of the crossbeam structure.

Structural optimization of an automobile transmission case to minimize radiation noise using the model reduction technique

최중선,이현아,이지영,박경진,박준홍,Chae-Hong Lim,박기종 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.5

Vehicles should provide a comfortable environment for passengers. The noise from the transmission case is one of the causes of an uncomfortable environment. The transmission is composed of gears, shafts, bearing and cases. When transmission activity occurs, noise is transferred to the passengers through the transmission case. Design of the transmission case is performed in order to reduce the transmission noise. Acoustic analysis is carried out and structural optimization is utilized for the design to reduce the noise. Generally, the boundary element method (BEM) has been utilized for acoustic analysis. However, it is difficult to utilize the boundary element method in structural optimization because the cost to calculate the sensitivity information is fairly expensive. Instead, the finite element method (FEM) is employed for calculating the radiation noise of the transmission. Radiation noise is considered as the total noise from the transmission. Radiation noise is calculated at the outside of the transmission case and it can be expressed indirectly by multiplication of the velocity in the normal direction of the finite elements, the radiation efficiency and the characteristic acoustic impedance. The high frequencies are dominant for the transmission noise and the radiation efficiency is 1 at the high frequency range. Since the characteristic acoustic impedance has a constant value, the noise is the same as the norm of the velocity. The velocity of each finite element is calculated from modal analysis and the noise is expressed based on the average velocity of the vibrating structure. However, a long computation time is required to calculate the noise in a large scale structure such as a transmission. Thus, the entire model of transmission is condensed into the reduced model by the model reduction technique. The component mode synthesis (CMS) method is employed for the model reduction technique. The CMS method is an effective method for dynamic analysis of large and/or complex structures. The reduced model keeps the dynamic characteristics of the entire structure and it is used for structural optimization. In structural optimization,the design variables are the thicknesses of the groups of the transmission cases, the objective function is the mass of the structure and a constraint is imposed on the noise. An alternative formulation is made by exchanging the objective and constraint functions. The optimization results are discussed in terms of practical application.