Numerical Model of Towing Line in Sea Transport

2014 ◽  
Author(s):  
Ivan Ćatipović ◽  
Nastia Degiuli ◽  
Andreja Werner ◽  
Većeslav Čorić ◽  
Jadranka Radanović
Keyword(s):  
Numerical Model ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Vertical Plane ◽  
Cost Effective ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Sea Transport ◽  
Nonlinear Properties ◽  
Wave Induced

Towing as a specific type of sea transport is often used for installing objects for drilling and exploitation of underwater gas and oil wells. Also, towing proved to be a cost-effective solution for the installation of the offshore wind turbine electric generators at sea locations. Because of the mass of these objects the need for towing increases progressively. Time domain numerical model for the wave-induced motions of a towed ship and the towline tension in regular head seas is presented in this paper. For the sake of simplicity, one end of the towing line is attached to ship’s bow and another end has prescribed straight line motion. All considerations are done in the vertical plane so the ship is modeled as a rigid body with three degrees of freedom. Hydrodynamic loadings due to waves are taken into account along with added mass and damping. Dynamics of the towing line is described by finite elements. Due to the nonlinear properties of the problem calculations are done in time domain. Comparison of the obtained numerical results is made with previously published results.

scholarly journals Wave Induced Effects on the Hydrodynamic Coefficients of an Oscillating Heave Plate in Offshore Wind Turbines

2020 ◽  
Vol 8 (8) ◽  
pp. 622
Author(s):  
Krish Thiagarajan ◽  
Javier Moreno
Keyword(s):  
Free Surface ◽  
Vertical Plane ◽  
Research Problem ◽  
Added Mass ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Hydrodynamic Coefficients ◽  
Offshore Wind Turbines ◽  
Turbine Design ◽  
Wave Induced

The research problem discussed in this paper is of relevance to floating offshore wind turbine design, where heave plates are attached to the columns of a semi-submersible in order to improve vertical plane stability and the power output. Because of the shallow draft of these structures, the heave plates are proximal to the water surface. When subject to vertical plane motions the flow around a plate is altered by the presence of the free surface, resulting in changes in added mass and damping forces. In this paper, we present the experimental results for the added mass and damping coefficients for circular heave plates attached to a column, when oscillating in heave in the presence of oncoming waves. The results tend to indicate that applying the hydrodynamic coefficients obtained from still water experiments for a structure moving in waves may only be an approximation. For different relative phases of the wave and the motion, large variations could occur. We define a modified Keulegan—Carpenter (KC) number that depends on the relative amplitude of motion with respect to the wave. With this definition, the added mass and damping values are seen to be closer to the still water trends. However, at lower KC values, the added mass coefficients could differ by 30%, which can affect natural frequency estimates. Thus, caution needs to be exerted in the selection of hydrodynamic coefficients for heave plates oscillating in proximity to the free surface.

Coupled Dynamic Analysis for Multi-Unit Floating Offshore Wind Turbine in Maximum Operational and Survival Conditions

2015 ◽  
Author(s):  
H. K. Jang ◽  
H. C. Kim ◽  
M. H. Kim ◽  
K. H. Kim
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Time Domain ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Random Waves ◽  
Mooring Lines ◽  
Floating Offshore Wind Turbine ◽  
Coupled Dynamic Analysis ◽  
Floating Offshore Wind Turbines

Numerical tools for a single floating offshore wind turbine (FOWT) have been developed by a number of researchers, while the investigation of multi-unit floating offshore wind turbines (MUFOWT) has rarely been performed. Recently, a numerical simulator was developed by TAMU to analyze the coupled dynamics of MUFOWT including multi-rotor-floater-mooring coupled effects. In the present study, the behavior of MUFOWT in time domain is described through the comparison of two load cases in maximum operational and survival conditions. A semi-submersible floater with four 2MW wind turbines, moored by eight mooring lines is selected as an example. The combination of irregular random waves, steady currents and dynamic turbulent winds are applied as environmental loads. As a result, the global motion and kinetic responses of the system are assessed in time domain. Kane’s dynamic theory is employed to formulate the global coupled dynamic equation of the whole system. The coupling terms are carefully considered to address the interactions among multiple turbines. This newly developed tool will be helpful in the future to evaluate the performance of MUFOWT under diverse environmental scenarios. In the present study, the aerodynamic interactions among multiple turbines including wake/array effect are not considered due to the complexity and uncertainty.

Optimization of O&M for Offshore Wind Farms Modelling for WMTC Conferences

2015 ◽  
Author(s):  
Thomas Nivet ◽  
Ema Muk-Pavic
Keyword(s):  
Wind Farm ◽  
Wind Farms ◽  
Cost Effective ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Wind Farms ◽  
Climate Conditions ◽  
Operation Analysis ◽  
Cost Effective Approach ◽  
Failure Evaluation

Offshore wind energy is one of the most upcoming sources of energy, and it is already partially replacing the fossil fuelled power production. However, offshore wind turbine technology is also associated with harsher weather environment. Indeed, it experiences more challenging wind and wave conditions, which in turn limits the vessels capabilities to access the wind farms. Additionally, with the constant rise of power utilization, improvements in the Operation Maintenance (O&M) planning are crucial for the development of large isolated offshore wind farms. Improvements in the planning of the O&M for offshore wind farms could lead to considerable reduction in costs. For this reason, the interest of this research paper is the investigation of the most cost effective approach to offshore turbine maintenance strategies. This objective is achieved by implementing a simulation approach that includes a climate conditions analysis, an operation analysis, a failure evaluation and a simulation of the repairs. This paper points out how different O&M strategies can influence the sustainability of a wind farm.

scholarly journals A Comparative Study between Three-Legged and Tripod Sub-structures in Design of Offshore Wind Turbines in the Transition Water Depth

2018 ◽  
Vol 7 (3.36) ◽  
pp. 23
Author(s):  
Aliakbar Khosravi ◽  
Tuck Wai Yeong ◽  
Mohammed Parvez Anwar ◽  
Jayaprakash Jaganathana ◽  
Teck Leong Lau ◽  
...  
Keyword(s):  
Water Depth ◽  
Limit State ◽  
Cost Effective ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Ultimate Limit State ◽  
Offshore Wind Turbines ◽  
Welding Joints ◽  
Fatigue Limit State ◽  
Ultimate Limit

This research aimed at investigating tripod and three-legged offshore wind turbine substructures. A comparison between the two substructures based on their weight as well as the installation method of piles, i.e. pre-piling and post-piling, was carried out. The in-place (Ultimate Limit State), Dynamic, natural frequency check and fatigue (Fatigue Limit State) analyses were conducted considering aerodynamic and hydrodynamic loads imposed on substructures in 50m water depth. An optimisation process was carried out in order to reduce the mass of substructures. The results revealed that the three-legged substructure is more cost effective with 25% lesser structure mass. However, the construction of the three-legged structure usually takes more time due to increased number of members and subsequently welding joints. The results, furthermore, showed that the pre-piling method reduces the time and cost of offshore installation, and reduces the weight of piles by 50%.  

Structural Control of an Ultra-Large Semi-Submersible Floating Offshore Wind Turbine

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Zhixin Zhao ◽  
Wenhua Wang ◽  
Dongdong Han ◽  
Wei Shi ◽  
Yulin Si ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Dynamic Model ◽  
Structural Control ◽  
Degrees Of Freedom ◽  
Vibration Suppression ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Floating Platform ◽  
Floating Offshore Wind Turbine ◽  
Proposed Model

Abstract A braceless semi-submersible floating platform is proposed for a Technical University of Denmark (DTU) 10-MW wind turbine at moderate water depths with reference to an existing National Renewable Energy Laboratory (NREL) 5-MW braceless semi-submersible floating platform, and a servo control system for a 10-MW semi-submersible floating offshore wind turbine (FOWT) is introduced. To control the ultimate and fatigue loads of the FOWT, a fore-aft tuned mass damper (TMD) installed in the nacelle of the 10-MW semi-submersible FOWT was investigated for vibration alleviation and load reduction. Considering the hydrodynamic and mooring effect, a four degrees-of-freedom (DOFs) (platform surge and pitch motions, tower fore-aft bending, and TMD translation) simplified dynamic model for the 10-MW semi-submersible FOWT is established based on D’Alembert’s principle. Then, the parameter estimation is conducted based on the Levenberg–Marquardt (LM) algorithm, and the simplified dynamic model was further verified by comparing the output responses with FAST and the proposed model. Furthermore, the exhaustive search (ES) and genetic algorithm (GA) are embedded into the simplified dynamic model to optimize the TMD parameters. Finally, a fully coupled time-domain simulation for all the selected environmental conditions is conducted in FAST, and the vibration suppression performance of the optimized TMD design for the 10-W semi-submersible FOWT was further examined and analyzed.

Underactuated Part Alignment System (UPAS) for Industrial Assembly Tasks

2011 ◽  
Author(s):  
Brian J. Slaboch ◽  
Philip Voglewede
Keyword(s):  
Degrees Of Freedom ◽  
Vertical Plane ◽  
Cost Effective ◽  
Robotic Assembly ◽  
Robot Arm ◽  
Planning Techniques ◽  
Alignment System ◽  
Compliant Assembly ◽  
Industrial Assembly ◽  
Assembly Tasks

This paper introduces the Underactuated Part Alignment System (UPAS) as a cost-effective and flexible approach to aligning parts in the vertical plane prior to an industrial robotic assembly task. The advantage of the UPAS is that it utilizes the degrees of freedom (DOFs) of a SCARA (Selective Compliant Assembly Robot Arm) type robot in conjunction with an external fixed post to achieve the desired part alignment. Three path planning techniques will be presented that can be used with the UPAS to achieve the proper part rotation.

A Comparison of Time Domain Seismic Analysis Methods for Offshore Wind Turbine Structures: Using a Superelement Approach

2019 ◽  
Author(s):  
Laurens Alblas ◽  
Corine de Winter
Keyword(s):  
Rigid Body ◽  
Wind Turbine ◽  
Time Domain ◽  
Wind Farm ◽  
Assessment Tool ◽  
Seismic Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Rigid Body Motions ◽  
Seismic Accelerations

Abstract Recently, wind farm development has gained more traction in Asian countries such as Taiwan, which are seismically active. Compared to Europe, the offshore wind structures need to be designed for these additional extreme environmental conditions. For monopiles, these calculations can typically be performed in an integrated way in the wind turbine load calculation, but for jackets the superelement (SE) approach remains preferred. At the time of writing different approaches are being applied in the industry to apply the SE approach for seismic time domain analysis. This work explains and compares three different methods, based on calculations performed in offshore strength assessment tool Sesam and aeroelastic tool BHawC. When including additional interface nodes at the foundation model bottom into the SE to which the seismic accelerations can be applied in BHawC similarly as in the re-tracking run in Sesam, the results between BHawC and Sesam are nearidentical. Using a normal SE, which only includes an interface node for the connection to the wind turbine tower bottom, and including the response due to seismic displacements into the SE load file gives a match between BHawC and Sesam, and closely matches the results of the case with additional interface nodes. Doing the same but only including the dynamic response of the interface point relative to a frame of reference moving with the rigid body motions as caused by the seismic accelerations into the SE load file, significant differences occur. This is due to the lack of the loading effect of rigid body motions. The same conclusions on how these methods compare can be drawn when using different wind and wave cases. The presented results give insights into the differences between the methods and how the choice of method may influence the results.

scholarly journals Design Optimization and Coupled Dynamics Analysis of an Offshore Wind Turbine with a Single Swivel Connected Tether

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3526 ◽  
Author(s):  
Jieyan Chen ◽  
Chengxi Li
Keyword(s):  
Wind Turbine ◽  
Design Optimization ◽  
Time Domain ◽  
Dynamic Performance ◽  
Coupled Systems ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Elastic Model ◽  
Dynamics Analysis ◽  
Coupled Dynamics

The increased interest in renewable wind energy has stimulated many offshore wind turbine concepts. This paper presents a design optimization and a coupled dynamics analysis of a platform with a single tether anchored to the seabed supported for a 5 MW baseline wind turbine. The design is based on a concept named SWAY. We conduct a parametric optimization process that accounts for important design considerations in the static and dynamic view, such as the stability, natural frequency, performance requirements, and cost feasibility. Through these optimization processes, we obtain and present the optimized model. We then establish the fully coupled aero-hydro-servo-elastic model by the time-domain simulation tool FAST (Fatigue, Aerodynamics, Structures, and Turbulence) with the hydrodynamic coefficients from an indoor program HydroGen. We conduct extensive time-domain simulations with various wind and wave conditions to explore the effects of wind speed and wave significant height on the dynamic performance of the optimized SWAY model in various water depths. The swivel connection between the platform and tether is the most special design for the SWAY model. Thus, we compare the performance of models with different tether connection designs, based on the platform motions, nacelle velocity, nacelle accelerations, resonant behaviors, and the damping of the coupled systems. The results of these comparisons demonstrate the advantage of the optimized SWAY model with the swivel connection. From these analyses, we prove that the optimized SWAY model is a good candidate for deep water deployment.

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