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.

Numerical Evaluation of Ship Maneuvering Performance in Waves

2018 ◽  
Author(s):  
Min-Guk Seo ◽  
Bo Woo Nam ◽  
Yeon-gyu Kim
Keyword(s):  
Irregular Waves ◽  
Time Signal ◽  
Regular Waves ◽  
Ship Maneuvering ◽  
Wave Drift ◽  
Mmg Model ◽  
Free Running ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

This paper considers a numerical computation of ship maneuvering performance in waves. For this purpose, modular-type maneuvering model (MMG model) is adopted and wave drift forces and moments are included in maneuvering equation of motion. Wave drift forces ware calculated using a seakeeping program based on higher-order Rankine panel method. When calculating the wave drift force acting on a ship, the forward speed, wave heading, wave period and drift angle of the ship are considered as key parameters. It means that ship’s lateral speed is also included to calculate wave drift force. Numerical simulations are carried out in regular waves using S175 containership and computation results are validated by comparing them with results of free-running model test. Using the developed program, numerical simulation in irregular waves are, also, conducted and discussion is made on the sensitivities of time signal of wave elevation on turning performance.

Numerical Evaluation of Ship Turning Performance in Regular and Irregular Waves

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Min-Guk Seo ◽  
Bo Woo Nam ◽  
Yeon-Gyu Kim
Keyword(s):  
Experimental Data ◽  
Degrees Of Freedom ◽  
Irregular Waves ◽  
Time Signal ◽  
Group Model ◽  
Frequency Wave ◽  
Wave Condition ◽  
Wave Drift ◽  
Mmg Model ◽  
Drift Force

Abstract In this study, ship's maneuvering performance in waves is evaluated using numerical computation. To this end, three degrees-of-freedom (3DOF) planar motions are considered, and modular-type maneuvering model (maneuvering modeling group model (MMG model)) is applied. As external force of the equation of motion, hull force, propulsion force, rudder force, and wave drift force are adopted. In order to calculate wave drift force, seakeeping program which is based on a higher-order Rankine panel method is used by considering wave frequency, wave heading, ship's forward speed, and ship's lateral speed. This wave drift force is pre-calculated, made into database, and used in time domain simulation. The developed simulation program is validated by comparing the computation results of a turning test in regular waves with experimental data. Using this program, turning performance in irregular waves is evaluated and sensitivities for time signal of wave elevation are investigated. Through this study, it is confirmed that the simplified method based on the MMG model including wave drift force can provide good agreement with experimental data in a practical point of view. It can be observed that the simulation results considering the lateral speed show better agreement with the experimental data than those without consideration. In the case of irregular wave condition, the turning performance can be affected by wave random phases. When the ship encounters the beam sea during the turning operation, the wave elevations at that time play an essential role in the change of ship speed and turning trajectory.

Comment on Oppenheim and Wilson: "Continuous Digital Simulation of the Second-Order Slowly Varying Wave Drift Force”

1982 ◽  
Vol 26 (01) ◽  
pp. 36-37
Author(s):  
Paul Kaplan
Keyword(s):  
Digital Simulation ◽  
Time History ◽  
Second Order ◽  
Main Concern ◽  
Integration Technique ◽  
Time Step ◽  
Variable Time ◽  
Wave Drift ◽  
Drift Force ◽  
Variable Time Step

The title paper [1] 2 is intended to provide a method for simulating (via digital computation) the second-order slowly varying wave drift force acting on a ship in waves. The Oppenheim and Wilson method is based upon obtaining a digital time history representation when using known information about the power spectrum of this drift force. The main concern indicated in their paper is the requirement to provide the drift force time history for use in a digital simulation of a moored floating vessel which makes use of a variable time step integration technique. The necessity for obtaining such disturbing forces in the proper form when applying a variable time step integration technique is well understood, in view of similar experience using such variable time step integration procedures in different simulation studies covering both high-frequency and relatively low-frequency motion phenomena (for example, [2, 8]).

A Strip Method for Lateral Drift Force of a Semisubmersible

1985 ◽  
Vol 107 (3) ◽  
pp. 329-334
Author(s):  
C. H. Kim ◽  
W. Bao
Keyword(s):  
Experimental Data ◽  
Hydrodynamic Interaction ◽  
Three Dimensional ◽  
Source Distribution ◽  
Regular Waves ◽  
Dimensional Theory ◽  
Lateral Drift ◽  
Drift Force ◽  
Twin Hulls ◽  
Drift Forces

This paper presents the results of an application of a strip technique for the prediction of the lateral drift forces on a semisubmersible platform floating in oblique regular waves. The method employs Maruo’s formula and source distribution technique, without taking account of the hydrodynamic interaction between the twin hulls and columns of the semisubmersible. Overall the strip technique shows a more favorable correlation with the experimental data than the three-dimensional theory. It is, however, premature to conclude that the technique has been fully validated.

Reciprocal Form of the Wave Drift Force and Moment Acting on Floating Body

2008 ◽  
Author(s):  
Takashi Tsubogo
Keyword(s):  
Body Surface ◽  
Near Field ◽  
Floating Body ◽  
Far Field ◽  
Regular Waves ◽  
Momentum Theory ◽  
Wave Drift ◽  
Drift Force

This paper provides the reciprocal form on wave drift force and moment from the momentum theory. The author in Japan has transformed from the pressure integration on the wetted body surface oscillating in regular waves into the reciprocal form at the near field, then transformed into the form at the far field owing to Green’s second identity, and transformed into Maruo’s and Newman’s formulas. But in this paper the start point is the momentum theory and the goal is the reciprocal form. The obtained reciprocal form at the far field can be transformed into the integration over the wetted floating body surface owing to Green’s second identity.

An Experimental Study of Negative Drift Force Acting on a Floating OWC “Backward Bent Duct Buoy”

2008 ◽  
Author(s):  
Yasutaka Imai ◽  
Kazutaka Toyota ◽  
Shuichi Nagata ◽  
Toshiaki Setoguchi ◽  
Junko Oda ◽  
...  
Keyword(s):  
Wave Energy ◽  
Fluid Velocity ◽  
Wave Energy Converter ◽  
Wave Direction ◽  
Regular Waves ◽  
Energy Converter ◽  
Negative Wave ◽  
Wave Drift ◽  
Negative Drift ◽  
Drift Force

The utilization of renewable energy is required immediately since emissions of carbon dioxide are being restricted. To this end, we are investigating the ocean wave energy converter, especially the floating OWC “Backward Bent Duct Buoy” (BBDB). The BBDB, proposed by Masuda in 1986, is a wave energy converter of the ‘moored floating oscillating water column’ type that is composed of an air chamber, an L-shaped bent duct, a buoyancy chamber, and a turbine. The BBDB has certain positive characteristics. Firstly, the primary conversion performance of the BBDB is better than other floating OWCs. Secondly, the length of the BBDB is shorter than other floating OWCs. Thirdly, as the BBDB advances in the incident wave direction with slow speed waves because of the negative wave drift force, the mooring cost can be reduced. In this research, experiments under a various wave periods were carried out to clarify the characteristics and cause of the generation of negative drift force acting on a BBDB in regular waves with a two-dimensional wave tank at Saga University. The length of the BBDB model is 85cm. To measure the wave drift force, the model is moored with horizontal wire-springs. The motions of the BBDB, such as surge, heave, and pitch, are measured by remotely using image processing. The fluid velocity around the BBDB is measured by using particle image velocimetry (PIV). Motion tests of the BBDB without mooring are also carried out to measure the horizontal velocity of the BBDB in waves. From the experimental results, the characteristics and causes of the generation of negative drift force acting on the BBDB in regular waves are discussed.

A Time-Domain Method for Hydroelasticity of a Curved Floating Bridge in Inhomogeneous Waves

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Wei Wei ◽  
Shixiao Fu ◽  
Torgeir Moan ◽  
Chunhui Song ◽  
Shi Deng ◽  
...  
Keyword(s):  
Time Domain ◽  
Time History ◽  
Dynamic Responses ◽  
Irregular Waves ◽  
Inhomogeneous Wave ◽  
Inhomogeneous Waves ◽  
Hydroelastic Analysis ◽  
History Of ◽  
Floating Bridge ◽  
The Time Domain

This paper presents a time-domain hydroelastic analysis method for bridges supported by floating pontoons in inhomogeneous wave conditions. The inhomogeneous wave effect is accounted for by adopting different wave spectra over different regions along the structure, then the time history of inhomogeneous first-order wave excitation forces on the floating pontoons can be obtained. The frequency-domain hydrodynamic coefficients are transformed into the time-domain hydroelastic model using Cummins' equations. The linear hydroelastic responses of a curved floating bridge with end supports, subjected to irregular waves with spatially varying significant wave heights and peak periods, are investigated. Moreover, sensitive analyses are performed to study the effects of the inhomogeneity on the hydroelastic responses. The primary results indicate that the inhomogeneity of the waves has a significant effect on the dynamic responses of the floating bridge.

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.

Macroorganisation and flexibility of thylakoid membranes

2019 ◽  
Vol 476 (20) ◽  
pp. 2981-3018 ◽  
Author(s):  
Petar H. Lambrev ◽  
Parveen Akhtar
Keyword(s):  
Light Harvesting ◽  
Current Knowledge ◽  
Three Dimensional ◽  
Photosynthetic Apparatus ◽  
Dynamic Responses ◽  
State Transitions ◽  
Photochemical Quenching ◽  
Light Harvesting Complex ◽  
Complex Ii ◽  
Light Harvesting Complex Ii

Abstract The light reactions of photosynthesis are hosted and regulated by the chloroplast thylakoid membrane (TM) — the central structural component of the photosynthetic apparatus of plants and algae. The two-dimensional and three-dimensional arrangement of the lipid–protein assemblies, aka macroorganisation, and its dynamic responses to the fluctuating physiological environment, aka flexibility, are the subject of this review. An emphasis is given on the information obtainable by spectroscopic approaches, especially circular dichroism (CD). We briefly summarise the current knowledge of the composition and three-dimensional architecture of the granal TMs in plants and the supramolecular organisation of Photosystem II and light-harvesting complex II therein. We next acquaint the non-specialist reader with the fundamentals of CD spectroscopy, recent advances such as anisotropic CD, and applications for studying the structure and macroorganisation of photosynthetic complexes and membranes. Special attention is given to the structural and functional flexibility of light-harvesting complex II in vitro as revealed by CD and fluorescence spectroscopy. We give an account of the dynamic changes in membrane macroorganisation associated with the light-adaptation of the photosynthetic apparatus and the regulation of the excitation energy flow by state transitions and non-photochemical quenching.

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.

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