The goal of this paper is to provide a comparative analysis of two commonly used approaches to discretize offshore fish cages： the lumped-mass approach and the finite element technique. Two case studies are chosen to...The goal of this paper is to provide a comparative analysis of two commonly used approaches to discretize offshore fish cages： the lumped-mass approach and the finite element technique. Two case studies are chosen to compare predictions of the LMA（lumped-mass approach） and FEA（finite element analysis） based numerical modeling techniques. In both case studies, we consider several loading conditions consisting of different uniform currents and monochromatic waves. We investigate motion of the cage, its deformation, and the resultant tension in the mooring lines. Both model predictions are sufficient close to the experimental data, but for the first experiment, the DUT-Flex Sim predictions are slightly more accurate than the ones provided by Aqua-FETM. According to the comparisons, both models can be successfully utilized to the design and analysis of the offshore fish cages provided that an appropriate safety factor is chosen.展开更多
The real-time computer-controlled actuators are used to connect the truncated parts of moorings and risers in the active hybrid model testing system. This must be able to work in model-scale real time, based on feedba...The real-time computer-controlled actuators are used to connect the truncated parts of moorings and risers in the active hybrid model testing system. This must be able to work in model-scale real time, based on feedback input from the floater motions. Thus, mooring line dynamics and damping effects are artificially simulated in real time, based on a computer-based model of the problem. In consideration of the nonlinear characteristics of the sea platform catenary mooring line, the equations of the mooring line motion are formulated by using the lumped-mass method and the dynamic response of several points on the mooring line is investigated by the time and frequency domain analysis method. The dynamic response of the representative point on the mooring line is analyzed under the condition of two different corresponding upper endpoint movements namely sine wave excitation and random wave excitation. The corresponding laws of the dynamic response between the equivalent water depth truncated points at different locations and the upper endpoint are obtained, which can provide technical support for further study of the active hybrid model test.展开更多
Although a detailed finite element(FE) model provides more precise results, a lumped-mass stick(LMS) model is preferred because of its simplicity and rapid computational time. However, the reliability of LMS models ha...Although a detailed finite element(FE) model provides more precise results, a lumped-mass stick(LMS) model is preferred because of its simplicity and rapid computational time. However, the reliability of LMS models has been questioned especially for structures dominated by higher modes and seismic inputs. Normally, the natural frequencies and dynamic responses of a LMS model based on tributary area mass consideration are different from the results of the FE model. This study proposes a basic updating technique to overcome these discrepancies; the technique employs the identical modal response, D(t), to the detailed FE model. The parameter D(t) is a time variable function in the dynamic response composition and it depends on frequency and damping ratio for each mode, independent of the structure's mode shapes. The identical response D(t) for each mode is obtained from the frequency adaptive LMS model; the adaptive LMS model which can provide identical modal frequencies as the detailed FE model. Theoretical backgrounds and formulations of the updating technique are proposed. To validate the updating technique, two types of structures(a symmetric straight column and an unsymmetric T-shaped structure) are considered. From the seismic response results including base shear and base moment, the updating technique considerably improves the seismic response accuracy of the tributary area-based LMS model.展开更多
Dynamic modeling and simulation of the mooring system are the key technologies in anchor handling simulator(AHS).Built up the mooring line’s dynamics model based on lumped-mass method(LMM),and fourth-order Runge–Kut...Dynamic modeling and simulation of the mooring system are the key technologies in anchor handling simulator(AHS).Built up the mooring line’s dynamics model based on lumped-mass method(LMM),and fourth-order Runge–Kutta method was used to solve the model;because of the huge amounts of calculation in the model’s solving,the very time-consuming process brings great impact on the real-time,fidelity and immersed feeling in the anchor handling scene simulation,seriously hindered its application in AHS.A novel parallel algorithm was proposed to speed-up the model’s solving process by taking the advantages of graphic processing units(GPU’s)massive parallel computing and float point computing capability.The model’s solving process was implemented on vertex shader based on the transform feedback(TF)mechanism in modern GPU.Experimental results show that,the new algorithm reduced the calculating time largely without losing accuracy,and can finally realize the real-time solving and simulation.展开更多
该文实现了一种半无限域SH波散射问题的数值分析方法。采用传递矩阵法得到SH波斜入射时的自由场,将其作为输入;采用集中质量显式有限元方法计算区域内节点的位移;采用透射人工边界计算人工边界点的位移;通过编写的FORTRAN程序实现计算...该文实现了一种半无限域SH波散射问题的数值分析方法。采用传递矩阵法得到SH波斜入射时的自由场,将其作为输入;采用集中质量显式有限元方法计算区域内节点的位移;采用透射人工边界计算人工边界点的位移;通过编写的FORTRAN程序实现计算过程。运用该方法对均匀半空间内半圆柱型沉积盆地在SH波入射下的散射进行了分析,与Trifunac M D的解析解进行了对比,验证了该文方法的有效性,分析了不同入射角对地表位移和位移谱放大系数的影响。最后,对成层半空间内半圆柱型沉积盆地在SH波入射下的散射进行了分析。相对于解析方法而言,该方法可以考虑更为复杂地形情况。展开更多
In this study, a new lumped-mass-stick model （LMSM） is developed based on the modal characteristics of a structure such as eigenvalues and eigenvectors. The simplified model, named the ＂frequency adaptive lumped-ma...In this study, a new lumped-mass-stick model （LMSM） is developed based on the modal characteristics of a structure such as eigenvalues and eigenvectors. The simplified model, named the ＂frequency adaptive lumped-massstick model,＂ hasonly a small number of stick elements and nodes to provide the same natural frequencies of the structure and is applied to a nuclear containment building. To investigate the numerical performance of the LMSM, a time history analysis is carried out on both the LMSM and the finite element model （FEM） for a nuclear containment building. A comparison of the results shows that the dynamic responses of the LMSM in terms of displacement and acceleration are almost identical to those of the FEM. In addition, the results in terms of floor response spectra at certain elevations are also in good agreement.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51239002 and 51221961)Cultivation Plan for Youth Agricultural Science and Technology Innovative Talents of Liaoning Province(Grant No.2014008)
文摘The goal of this paper is to provide a comparative analysis of two commonly used approaches to discretize offshore fish cages： the lumped-mass approach and the finite element technique. Two case studies are chosen to compare predictions of the LMA（lumped-mass approach） and FEA（finite element analysis） based numerical modeling techniques. In both case studies, we consider several loading conditions consisting of different uniform currents and monochromatic waves. We investigate motion of the cage, its deformation, and the resultant tension in the mooring lines. Both model predictions are sufficient close to the experimental data, but for the first experiment, the DUT-Flex Sim predictions are slightly more accurate than the ones provided by Aqua-FETM. According to the comparisons, both models can be successfully utilized to the design and analysis of the offshore fish cages provided that an appropriate safety factor is chosen.
基金financially supported by the Natural Science Foundation of Zhejiang Province(Grant Nos.Y14E090034 and Y13F020140)the Young Scientist Training Program in Zhejiang Province(Grant No.2013R60G7160040)+1 种基金the State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University for the Open Fund Project(Grant No.1516)the Open Fund Project of Second Institute of Oceanography(Grant No.SOED1706)
文摘The real-time computer-controlled actuators are used to connect the truncated parts of moorings and risers in the active hybrid model testing system. This must be able to work in model-scale real time, based on feedback input from the floater motions. Thus, mooring line dynamics and damping effects are artificially simulated in real time, based on a computer-based model of the problem. In consideration of the nonlinear characteristics of the sea platform catenary mooring line, the equations of the mooring line motion are formulated by using the lumped-mass method and the dynamic response of several points on the mooring line is investigated by the time and frequency domain analysis method. The dynamic response of the representative point on the mooring line is analyzed under the condition of two different corresponding upper endpoint movements namely sine wave excitation and random wave excitation. The corresponding laws of the dynamic response between the equivalent water depth truncated points at different locations and the upper endpoint are obtained, which can provide technical support for further study of the active hybrid model test.
基金Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education,Science and Technology under Grant No.20151D1A3A01020017
文摘Although a detailed finite element(FE) model provides more precise results, a lumped-mass stick(LMS) model is preferred because of its simplicity and rapid computational time. However, the reliability of LMS models has been questioned especially for structures dominated by higher modes and seismic inputs. Normally, the natural frequencies and dynamic responses of a LMS model based on tributary area mass consideration are different from the results of the FE model. This study proposes a basic updating technique to overcome these discrepancies; the technique employs the identical modal response, D(t), to the detailed FE model. The parameter D(t) is a time variable function in the dynamic response composition and it depends on frequency and damping ratio for each mode, independent of the structure's mode shapes. The identical response D(t) for each mode is obtained from the frequency adaptive LMS model; the adaptive LMS model which can provide identical modal frequencies as the detailed FE model. Theoretical backgrounds and formulations of the updating technique are proposed. To validate the updating technique, two types of structures(a symmetric straight column and an unsymmetric T-shaped structure) are considered. From the seismic response results including base shear and base moment, the updating technique considerably improves the seismic response accuracy of the tributary area-based LMS model.
基金the National High Technology Research and Development Program of China(“863”Program)(Grant No.2015AA016404)the Fundamental Research Funds for the Central Universities(Grant No.3132016310).
文摘Dynamic modeling and simulation of the mooring system are the key technologies in anchor handling simulator(AHS).Built up the mooring line’s dynamics model based on lumped-mass method(LMM),and fourth-order Runge–Kutta method was used to solve the model;because of the huge amounts of calculation in the model’s solving,the very time-consuming process brings great impact on the real-time,fidelity and immersed feeling in the anchor handling scene simulation,seriously hindered its application in AHS.A novel parallel algorithm was proposed to speed-up the model’s solving process by taking the advantages of graphic processing units(GPU’s)massive parallel computing and float point computing capability.The model’s solving process was implemented on vertex shader based on the transform feedback(TF)mechanism in modern GPU.Experimental results show that,the new algorithm reduced the calculating time largely without losing accuracy,and can finally realize the real-time solving and simulation.
文摘该文实现了一种半无限域SH波散射问题的数值分析方法。采用传递矩阵法得到SH波斜入射时的自由场,将其作为输入;采用集中质量显式有限元方法计算区域内节点的位移;采用透射人工边界计算人工边界点的位移;通过编写的FORTRAN程序实现计算过程。运用该方法对均匀半空间内半圆柱型沉积盆地在SH波入射下的散射进行了分析,与Trifunac M D的解析解进行了对比,验证了该文方法的有效性,分析了不同入射角对地表位移和位移谱放大系数的影响。最后,对成层半空间内半圆柱型沉积盆地在SH波入射下的散射进行了分析。相对于解析方法而言,该方法可以考虑更为复杂地形情况。
基金Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), Ministry of Knowledge Economy, Republic of Korea under Grant No. 2010T100101066
文摘In this study, a new lumped-mass-stick model （LMSM） is developed based on the modal characteristics of a structure such as eigenvalues and eigenvectors. The simplified model, named the ＂frequency adaptive lumped-massstick model,＂ hasonly a small number of stick elements and nodes to provide the same natural frequencies of the structure and is applied to a nuclear containment building. To investigate the numerical performance of the LMSM, a time history analysis is carried out on both the LMSM and the finite element model （FEM） for a nuclear containment building. A comparison of the results shows that the dynamic responses of the LMSM in terms of displacement and acceleration are almost identical to those of the FEM. In addition, the results in terms of floor response spectra at certain elevations are also in good agreement.
