Three-Dimensional Hydroelastic Dynamic Analyses Including Torsion for a Large Floating Platform in Frequency and Time Domains

2014 ◽  
Author(s):  
H. Y. Kang ◽  
M. H. Kim
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Irregular Waves ◽  
Mode Shapes ◽  
Head Waves ◽  
Time Domains ◽  
Hydroelastic Analysis ◽  
Element Method

Recent increasing demands for more ocean energy and space utilization require larger scale of offshore structures, and the large scale leads to needs for comprehensive hydroelastic analysis to accurately account for the interaction of the floating body’s deformation with waves or other environmental loads. In this study, as generalization of the previous hydroelastic analyses by the present authors [4, 5], the three-dimensional hydroelastic analysis including torsion is achieved. Ocean wave is assumed to be potential flow. The example large-scale floating body studied here is 480 m long and 400 m wide with 8 m draft. It is modeled by 7857 elastic plate elements which have 6 degrees of freedom at each element. Modal analysis by finite element method (FEM) for all free boundary conditions is conducted and provides mode shapes, modal inertia/stiffness, and dry natural frequencies. The mode shapes are verified against experimental results by Leissa [10]. Using the mode expanded boundary element method (BEM), hydroelastic dynamics is first solved in frequency domain. Subsequently, the large flexible platform is applied to irregular waves in time domain. To investigate the three-dimensional dependency of dynamics, a series of oblique waves are applied as well as head waves, and the dynamic responses of the elastic system are systematically analyzed. Considering remarkable effect of added mass due to large submerged volume, its effects on elastic modes and resonance phenomena are also investigated. To validate the accuracy, pertinent verifications are carried out for both frequency and time domains.

scholarly journals Vibration characteristics of triple-gear-rotor system in compressed air energy storage under variable torque load

2021 ◽  
Vol 104 (1) ◽  
pp. 003685042098705
Author(s):  
Xinran Wang ◽  
Yangli Zhu ◽  
Wen Li ◽  
Dongxu Hu ◽  
Xuehui Zhang ◽  
...  
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Element Model ◽  
Rotor System ◽  
Dynamic Responses ◽  
System Response ◽  
Rotating Speed ◽  
Torque Load ◽  
Set Up ◽  
Two Stages

This paper focuses on the effects of the off-design operation of CAES on the dynamic characteristics of the triple-gear-rotor system. A finite element model of the system is set up with unbalanced excitations, torque load excitations, and backlash which lead to variations of tooth contact status. An experiment is carried out to verify the accuracy of the mathematical model. The results show that when the system is subjected to large-scale torque load lifting at a high rotating speed, it has two stages of relatively strong periodicity when the torque load is light, and of chaotic when the torque load is heavy, with the transition between the two states being relatively quick and violent. The analysis of the three-dimensional acceleration spectrum and the meshing force shows that the variation in the meshing state and the fluctuation of the meshing force is the basic reasons for the variation in the system response with the torque load. In addition, the three rotors in the triple-gear-rotor system studied show a strong similarity in the meshing states and meshing force fluctuations, which result in the similarity in the dynamic responses of the three rotors.

Dynamic Analysis of Large-Scale Power House

2012 ◽  
Vol 446-449 ◽  
pp. 837-840
Author(s):  
Yu Zhao ◽  
Shu Fang Yuan ◽  
Jian Wei Zhang
Keyword(s):  
Finite Element ◽  
Dynamic Characteristics ◽  
Large Scale ◽  
Three Dimensional ◽  
Dynamic Responses ◽  
Dynamic Loads ◽  
Element Analysis ◽  
Power House ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

The underwater structure of power house is major structure under the dynamic loads of unit. The vibration problem is very common in operation. So the structures should have sufficient stiffness to resist dynamic loads of unit. This paper establishes three-dimensional finite element models with finite element analysis software—ANSYS. Dynamic characteristics of the power house and dynamic responses of structure under earthquake are analyzed. The results of the computation show that fluid-solid coupling may be ignored when studying dynamic characteristics of structures of the underground power house.

Study on Dynamic Responses of a TLP in Waves

1987 ◽  
Vol 109 (1) ◽  
pp. 61-66 ◽  
Author(s):  
M. Kobayashi ◽  
K. Shimada ◽  
T. Fujihira
Keyword(s):  
Three Dimensional ◽  
Time History ◽  
Dynamic Responses ◽  
Irregular Waves ◽  
Fluid Viscosity ◽  
Regular Waves ◽  
Distribution Method ◽  
Wave Drift ◽  
Drift Force ◽  
Singularity Distribution

The dynamic responses of a TLP (Tension Leg Platform) in regular and irregular waves were investigated by model tests and calculations in both frequency and time domain. Hydrodynamic forces in regular waves were calculated by the three-dimensional singularity distribution method. Furthermore, a contribution of the fluid viscosity to wave drift force was discussed. Usefulness of the time history simulation was confirmed in the comparison between experimental and calculated time traces.

The Asymmetry of the Large-Scale Structures in Turbulent Three-Dimensional Wall Jets Exiting Long Rectangular Channels

2007 ◽  
Vol 129 (7) ◽  
pp. 929-941 ◽  
Author(s):  
J. W. Hall ◽  
D. Ewing
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Wall Pressure ◽  
Mode Shapes ◽  
Wall Jets ◽  
Frequency Dependent ◽  
Large Scale Structures ◽  
Intermediate Field ◽  
Rectangular Channels ◽  
Scale Structures

The development of the large-scale structures in three-dimensional wall jets formed using long rectangular channels with aspect ratios of 1 and 4 was investigated using measurements of the fluctuating wall pressure and point measurements of the turbulent velocity throughout the near and intermediate field. The instantaneous pressure fluctuations in both jets were laterally asymmetric causing the fluctuating wall pressure to be poorly correlated across the jet centerline. A frequency-dependent proper orthogonal decomposition (POD) of the fluctuating pressure measurements indicated that the first two mode shapes were opposite and each mode made similar contributions to the mean square fluctuations at all frequencies in order to capture the instantaneous asymmetry of the pressure field. The mode shapes in the intermediate field of both jets were strongly frequency dependent, and a subsequent wavelet analysis indicated that there are both large-scale horseshoe structures that span one-half of the jet and separate, smaller, near-wall structures located near the jet centerline. The initial development of the large-scale structures in the two jets differed, with the most energetic fluctuations being more antisymmetric in the square jet.

Displacement and Pressure Transfer Between Structural and Fluid Meshes in Fluid-Structure Interaction

2003 ◽  
Author(s):  
L. L. Huang ◽  
H. R. Riggs
Keyword(s):  
Fluid Model ◽  
Fluid Pressure ◽  
Three Dimensional ◽  
Element Model ◽  
Offshore Structures ◽  
Rigid Bodies ◽  
Element Analysis ◽  
General Applicability ◽  
Fluid Structure ◽  
Hydroelastic Analysis

Nonlinear, time-domain hydroelastic analysis of flexible offshore structures requires that the structural motion be transferred to the fluid model and the resulting fluid pressure at the fluid-structure interface be transferred from the fluid model to the structure. When the structural mesh and the fluid mesh describe two distinct three-dimensional surfaces, the transfer of displacement and pressure is both difficult and non-unique. In this paper, a new transfer strategy based on the variational-based smoothing element analysis (SEA) technique is presented. The displacement transfer uses the original formulation of the SEA method, although the application of the procedure to displacement transfer is new. For energy conservation during the reverse pressure transfer, the original functional in the SEA method is enhanced with a new term that attempts to conserve the work done by the hydrodynamic forces when obtaining the global structural nodal forces. To evaluate the transfer methodology, the hydrodynamic response of three rigid bodies are considered. Pressure contours, hydrodynamic coefficients, and motions that are calculated based on the data transferred with the proposed method are compared with the results that are obtained from standard rigid-body hydrodynamics theory that does not include a structural finite element model. The method is shown to work very well. In addition, it has general applicability and it can deal with relatively large geometric differences in the meshes.

Application of Direct Boundary Element Method to Three Dimensional Hydrodynamic Analysis of Interaction Between Waves and Floating Offshore Structures

2004 ◽  
Author(s):  
Saeid Kazemi ◽  
Atilla Incecik
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Three Dimensional ◽  
Offshore Structures ◽  
Sea Waves ◽  
Offshore Structure ◽  
Hydrodynamic Analysis ◽  
Hydrodynamic Behaviour ◽  
Direct Boundary Element Method ◽  
Element Method

A three-dimensional hydrodynamic analysis of interaction between a floating offshore structure and sea waves has been carried out using a novel approach which is based on the weighted residual technique and the direct boundary element method. The main advantage of the direct boundary element method is the fact that one can determine the total velocity potential directly. Direct BEM is more versatile and computationally more efficient than indirect BEM. Besides, the BEM can easily be coupled with other numerical methods, e.g. finite element method (FEM) in order to carry out structural analysis of deck of the platform due to impact. Firstly, the boundary value problem of three-dimensional interaction between regular sea waves and a semi-submersible will be described. Secondly, the direct boundary element method has been applied to predict hydrodynamic behaviour of Khazar Semi-Submersible Drilling Unit (KSSDU), which is the largest semi-submersible drilling platform under construction for a location in the Caspian Sea, North of Iran. The rigid body motion responses in six degrees of freedom of KHAZAR semi-submersible in response to encountering waves have been calculated by using the direct boundary element method. The results obtained from the direct BEM will be compared with those obtained by the results based on the conventional boundary element method (indirect BEM) which were obtained by the designers of KHAZAR semi-submersible.

The Simulation of Ship Motions Using a B-Spline–Based Panel Method in Time Domain

2007 ◽  
Vol 51 (03) ◽  
pp. 267-284
Author(s):  
Ranadev Datta ◽  
Debabrata Sen
Keyword(s):  
Time Domain ◽  
Three Dimensional ◽  
Basis Functions ◽  
The Body ◽  
Irregular Waves ◽  
Ship Motions ◽  
B Spline ◽  
Head Waves ◽  
Wigley Hull ◽  
Spline Basis

In this paper, a B-spline-based higher-order method is developed for simulating three-dimensional ship motions with forward speed. The problem is formulated in time domain using a transient free surface Green function. The body geometry is defined by open uniform or nonuniform B-spline basis functions depending on the hull type, whereas the unknown field variables are described by open uniform B-spline basis functions. The collocation method is applied to discretize the integral equation and then solved for the unknown potentials and source strengths. Motion computations in head waves are carried out for three types of ship hulls: a mathematically defined Wigley hull, a typical containership (S175 hull), and a Series 60 hull. Results are obtained for regular and irregular waves and compared with available experimental and computational results. It is found that the results from the present method are in very good agreement with the published results, and in particular with experimental data. Long-duration simulations have also been carried out with an ordinary desktop PC (PIV with 512 MB RAM) to demonstrate the ability of the method to simulate motions over long periods without any visible deterioration using only modest computational resources.

A FORMULATION OF THE FAST MULTIPOLE BOUNDARY ELEMENT METHOD (FMBEM) FOR ACOUSTIC RADIATION AND SCATTERING FROM THREE-DIMENSIONAL STRUCTURES

2008 ◽  
Vol 16 (02) ◽  
pp. 303-320 ◽  
Author(s):  
Z.-S. CHEN ◽  
H. WAUBKE ◽  
W. KREUZER
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Large Scale ◽  
Acoustic Radiation ◽  
Three Dimensional ◽  
Efficient Computation ◽  
Fast Multipole ◽  
Head Related Transfer Function ◽  
And Storage ◽  
Element Method

Compared to the traditional boundary element method (BEM), the single level fast multipole boundary element method (SLFMBEM) or the multilevel fast multipole boundary element method (MLFMBEM) reduces the computational complexity of a job from O(n2) to O(n3/2) or O(n log 2n), respectively with n being the number of unknowns; this means a dramatical reduction in terms of CPU-time and storage requirement. Large scale problems, unsolvable with the traditional BEM, can be solved by using the FMBEM. In this paper, the traditional BEM, SLFMBEM, and MLFMBEM are formulated within the framework of the Burton–Miller Collocation BEM for acoustic radiation and scattering from 3D structures. Attention is especially paid to the practical aspects of the method in order to get a reliable and efficient computation code. The performance of the method is tested with practical examples, including one for computing the head-related transfer function (HRTF) between 1000 and 18 000 Hz.

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