Numerical Research on Mooring System of Wave Measuring Buoy

2013 ◽  
Vol 787 ◽  
pp. 439-444 ◽  
Author(s):  
Xiu Tao Fan ◽  
Meng Shao ◽  
Jin Wei Sun ◽  
Shan Shan Zheng ◽  
Yong Qi
Keyword(s):  
Line Tension ◽  
Static Characteristic ◽  
Mooring System ◽  
Large Current ◽  
Numerical Research ◽  
Design Requirements ◽  
The Mean ◽  
Response Amplitude Operators ◽  
Sea Area ◽  
Drift Forces

The static characteristic of a horizontal composite mooring system for wave measuring buoy is studied using 3D potential theory and catenary theory. The 3D hydrodynamic model is built for surface pontoon and wave measuring buoy to calculate the mean steady drift forces and response amplitude operators. Combined with extreme environmental conditions and catenary theory, static analysis of the mooring system is done, obtaining the results of line tension, catenary shape and safety factor etc. The research results show that the horizontal composite mooring system meets the design requirements and it is proven to be an effective mooring method for the sea area with large current velocity.

Calibration of Hydrodynamic Coefficients for a Semi-Submersible 10 MW Wind Turbine

2018 ◽  
Author(s):  
Marit I. Kvittem ◽  
Petter Andreas Berthelsen ◽  
Lene Eliassen ◽  
Maxime Thys
Keyword(s):  
Numerical Model ◽  
Line Tension ◽  
Offshore Wind ◽  
Scale Model ◽  
Viscous Drag ◽  
Mooring System ◽  
Drag Coefficients ◽  
Damping Coefficients ◽  
Decay Tests ◽  
Drift Forces

Hydrodynamic model tests and numerical simulations may be combined in a complementary manner during the design and qualification of new offshore structures. In the EU H2020 project LIFES50+ (lifes50plus.eu), a model test campaign of floating offshore wind turbines using Real-Time Hybrid Model (ReaTHM) testing techniques was carried out at SINTEF Ocean in fall 2017. The present paper focuses on the process of calibrating a numerical model to the experimental results. The concepts tested in the experimental campaign was a 1:36 scale model of the public version of the 10MW OO-Star Wind Floater semi-submersible offshore wind turbine. A time-domain numerical model was developed based on the as-built scale model. The hull was considered as rigid, while bar elements were used to model the mooring system and tower in a coupled finite element approach. First-order frequency-dependent added mass, potential damping, and excitation forces/moments were evaluated across a range of frequencies using a panel method. Distributed viscous forces on the hull and mooring lines were added to the numerical model according to Morison’s equation. Potential difference-frequency excitation forces were also included by applying Newman’s approximation. The quasi static properties of the mooring system were assessed by comparing the restoring force and maximum line tension with the pull-out test. Drag coefficients for the line segments were estimated by imposing the measured fairlead motion from model tests as forced displacement and comparing the calculated and measured dynamic line tension. The linear and viscous damping coefficients were first estimated based on the decay tests, and the tuned damping coefficients were compared to initial guesses based on the Reynolds and Keulegan-Carpenter number at model scale. The results were then applied in the numerical model, and simulations in extreme irregular waves were compared to the experiments. It was found that second order drift forces proved to be significant, particularly for the severe irregular seastate. These could not be modelled correctly applying the potential drift forces together with quadratic damping matrix tuned to the free decay test. And the model with viscous drag coefficients tuned to decay tests also underestimated the slow drift motions. Thus, new viscous drag coefficients were determined to match the low frequency platform response. To inverstigate the performance of the tuned model, comparisons were made for a moderate seastate and for a simulation with both waves and wind on an operating turbine. In the end, possible further improvements to the modelling were suggested.

Analysis of Wave Drift Forces on a Floating Wave Energy Converter

2008 ◽  
Author(s):  
Nuno Fonseca ◽  
Ricardo Pascoal ◽  
Joa˜o Marinho ◽  
Tiago Morais
Keyword(s):  
Transfer Function ◽  
Wave Energy ◽  
Time History ◽  
Wave Energy Converter ◽  
Mooring System ◽  
Energy Converter ◽  
Wave Drift ◽  
The Mean ◽  
Wave Drift Forces ◽  
Drift Forces

Wave drift forces acting on floating wave energy converters (WEC) are often the most important loading component for the design of the mooring system. On one hand these forces may be, at least, one order of magnitude larger than wind and current forces, and on the other hand the floating structure and mooring system may respond dynamically to the slowly varying wave drift forces. The paper presents an analysis of the wave drift forces on an articulated floating wave energy converter. Particular attention is given to the effects of the wave energy extraction on the time history of the horizontal drift forces. The hydrodynamic calculations are carried out by a frequency domain Green function panel method, resulting on the transfer function of the WEC motions as well as the transfer function of the mean drift forces. The power takeoff system is represented by a simple linear model where the extracted power is related to the relative velocity in the articulation and the damper of the PTO. With the transfer function of the mean drift forces, the variance spectrum of these same forces is calculated for stationary irregular seastates, and finally time histories of the drift forces are produced for typical operational conditions.

Drift Forces on a Floating Body of Simple Geometry Due to Second Order Interactions Between Pairs of Harmonics With Different Frequencies

2009 ◽  
Author(s):  
Joa˜o Pessoa ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Vertical Cylinder ◽  
Vertical Axis ◽  
Second Order ◽  
The Body ◽  
Floating Body ◽  
Order Problem ◽  
Simple Geometry ◽  
The Mean ◽  
Order Quantities ◽  
Drift Forces

The paper presents an investigation of the slowly varying second order drift forces on a floating body of simple geometry. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom and a ratio of diameter to draft of 3.25. The hydrodynamic problem is solved with a second order boundary element method. The second order problem is due to interactions between pairs of incident harmonic waves with different frequencies, therefore the calculations are carried out for several difference frequencies with the mean frequency covering the whole frequency range of interest. Results include the surge drift force and pitch drift moment. The results are presented in several stages in order to assess the influence of different phenomena contributing to the global second order responses. Firstly the body is restrained and secondly it is free to move at the wave frequency. The second order results include the contribution associated with quadratic products of first order quantities, the total second order force, and the contribution associated to the free surface forcing.

Lightweight Materials for Mooring Lines of Deepwater Tension Leg Platforms

1984 ◽  
Vol 21 (03) ◽  
pp. 234-241
Author(s):  
Mamdouh M. Salama
Keyword(s):  
Carbon Fiber ◽  
Water Depth ◽  
Hybrid Composites ◽  
Medium Size ◽  
Mooring System ◽  
Basic Design ◽  
High Modulus ◽  
Mooring Lines ◽  
Lightweight Materials ◽  
Design Requirements

The design of a mooring system for tension leg platforms (TLPs) becomes more complicated as water depth increases. The use of steel mooring lines requires complicated tensioning, handling, and flotation systems. This paper discusses the basic design requirements for the TLP mooring system and identifies several advanced fiber-reinforced lightweight materials as alternatives to steel. High-modulus carbon fiber/KevlarcircleR fiber hybrid composites and Kevlar ropes appear to offer the optimum mooring systems for TLPs used in the development of large and medium-size reservoirs, respectively.

scholarly journals Radiographic Outcomes after Fixation of Distal Metatarsal Osteotomy for Hallux Valgus Using a Tension Band Construct

2019 ◽  
Vol 4 (4) ◽  
pp. 2473011419S0042
Author(s):  
Alexander Volpi ◽  
Robert Zbeda ◽  
Christopher Katchis ◽  
Lon Weiner ◽  
Stuart Katchis
Keyword(s):  
Hallux Valgus ◽  
Postoperative Period ◽  
Weight Bearing ◽  
Line Tension ◽  
Tension Band ◽  
Metatarsal Osteotomy ◽  
First Metatarsal ◽  
Distal Metatarsal Osteotomy ◽  
The Mean

Category: Bunion Introduction/Purpose: Hallux valgus is a common deformity of the forefoot. There are over 130 procedures described to correct hallux valgus. Classically, the treatment of mild to moderate hallux valgus is with a distal metatarsal osteotomy. A variety of fixation techniques have been described for use with this osteotomy most of which require partial or non-weight bearing until the osteotomy is healed. Tension Band fixation is a well-known principle in orthopedic surgery. The goal of the present study is to radiographically assess the maintenance of distal first metatarsal osteotomy fixation using a novel tension band device (Re+Line tension band bunion plate system, Nextremity Solutions) with immediate post-operative weight-bearing. Methods: The patient database for one surgeon was retrospectively reviewed for patients that underwent hallux valgus correction with the Re+Line tension band device between 2014 and 2017. Postoperative protocol included a soft dressing, firm surgical shoe, and weight-bearing as tolerated with a cane. Patients were excluded if fixation was achieved with something other than a tension band construct. Radiographs were obtained and reviewed retrospectively by 3 authors. Pre and postoperative hallux valgus (HVA) and intermetatarsal angles (IMA) were measured as described previously in the literature, and the changes in correction compared. Maintenance of correction and hardware integrity were assessed at final follow-up after weight bearing as tolerated in a surgical shoe in the postoperative period. Statistical analysis was performed using a Wilcoxon signed-rank test for the changes in HVA and IMA. Results: There was a total of 72 patients and 76 toes that underwent hallux valgus correction with a tension band construct, at a mean follow-up of 4.36 months. 68 of 72 patients were female. The average age was 60.8 years old. The mean preoperative HVA was 27.1 degrees. The mean postoperative HVA was 6.14 degrees, with a mean correction of 20.22 degrees (p<0.001). The mean preoperative IMA was 14.14 degrees. The mean postoperative IMA was 6.10 degrees, with a mean correction of 7.98 degrees (p<0.001). There was loss of reduction found in 6 of 76 toes (7.89%).There were zero cases of hardware failure. All osteotomies healed at final follow-up. Conclusion: This study shows successful radiographic outcome after hallux valgus correction using a tension band construct and allowing immediate full weight-bearing in a surgical shoe in the postoperative period. Significant deformity correction was achieved and maintained and all osteotomies healed. The Re+Line tension band bunion correction system can be safely used as a successful option to fix distal first metatarsal osteotomies, while allowing patients to fully weight bear in a surgical shoe postoperatively and potentially return to activities faster than when using traditional fixation methods. Future studies are needed to assess functional outcomes and patient satisfaction with this novel technique.

Stochastic Response and Stability Analysis of Two-Point Mooring System

2011 ◽  
Author(s):  
A. K. Banik ◽  
T. K. Datta
Keyword(s):  
Stability Analysis ◽  
Probability Density Function ◽  
Probability Density ◽  
Mooring System ◽  
Mean Square ◽  
Stochastic Response ◽  
Sea State ◽  
Mean Square Response ◽  
Linear Damping ◽  
The Mean

The stochastic response and stability of a two-point mooring system are investigated for random sea state represented by the P-M sea spectrum. The two point mooring system is modeled as a SDOF system having only stiffness nonlinearity; drag nonlinearity is represented by an equivalent linear damping. Since no parametric excitation exists and only the linear damping is assumed to be present in the system, only a local stability analysis is sufficient for the system. This is performed using a perturbation technique and the Infante’s method. The analysis requires the mean square response of the system, which may be obtained in various ways. In the present study, the method using van-der-Pol transformation and F-P-K equation is used to obtain the probability density function of the response under the random wave forces. From the moment of the probability density function, the mean square response is obtained. Stability of the system is represented by an inequality condition expressed as a function of some important parameters. A two point mooring system is analysed as an illustrative example for a water depth of 141.5 m and a sea state represented by PM spectrum with 16 m significant height. It is shown that for certain combinations of parameter values, stability of two point mooring system may not be achieved.

Setpoint Chasing for Thruster-Assisted Position Mooring

2007 ◽  
Author(s):  
Dong T. Nguyen ◽  
Asgeir J. So̸rensen
Keyword(s):  
Force Control ◽  
System Simulation ◽  
Extreme Conditions ◽  
Mooring System ◽  
Integral Control ◽  
Proportional Control ◽  
Environmental Loads ◽  
Damping Control ◽  
Simulation And Experiment ◽  
The Mean

This paper presents a new concept for control of thruster-assisted position moored vessel using setpoint chasing. The mooring system is designed to compensate the mean environmental loads up to a certain limit of the environmental conditions. In the present industrial position mooring (PM) system, the thrusters are used to damp the vessel’s dynamical motions and to provide compensation of any line break. The main contribution in this paper is to extend the damping control used in industrial PM system with improved restoring and mean force control. In order to avoid conflicting control action with the mooring system, the equilibrium position of the uncontrolled vessel will be found using setpoint chasing. The setpoint chasing with proportional control will be developed to prevent a possible resonance situation by shifting the natural frequency of the moored vessel out of the bandwidth of the excitation loads. The setpoint chasing with integral control will improve the ability to prevent line break in extreme conditions by compensating the mean drift loads together with the mooring system. Simulation and experiment will be carried out to verify the advantages of the setpoint chasing strategies.

scholarly journals Prediction of the Side Drift Force of Full Ships Advancing in Waves at Low Speeds

2020 ◽  
Vol 8 (5) ◽  
pp. 377 ◽  
Author(s):  
Shukui Liu ◽  
Apostolos Papanikolaou
Keyword(s):  
Empirical Formula ◽  
Experimental Results ◽  
Regular Waves ◽  
Short Waves ◽  
Wave Parameters ◽  
Preliminary Validation ◽  
The Mean ◽  
Drift Force ◽  
Low Speeds ◽  
Drift Forces

In this study, we analyze the experimental results of the mean sway (side drift) forces of six full type ships at low speeds in regular waves of various directions and compare them with numerical results of the in-house 3D panel code NEWDRIFT. It is noted that the mean sway force is most significant in relatively short waves, with the peak being observed at λ/LPP ≈ 0.5–0.6. For λ/LPP > 1.0, the corresponding value is rather small. We also observe a solid recurring pattern of the mean sway force acting on the analyzed full type ships. On this basis, we proceed to approximate the mean sway force with an empirical formula, in which only the main ship particulars and wave parameters are used. Preliminary validation results show that the developed empirical formula, which is readily applicable in practice, can accurately predict the mean sway force acting on a full ship, at both zero and non-zero speeds.

Design and Calculation of Double Buoys Mooring System in Estuary of Yalu River

2012 ◽  
Vol 253-255 ◽  
pp. 2071-2075
Author(s):  
Guo You Shi ◽  
Jia Xuan Yang ◽  
Wei Feng Li
Keyword(s):  
Calculation Result ◽  
Meteorological Condition ◽  
Wave Force ◽  
Good Effect ◽  
Total Force ◽  
Mooring System ◽  
Wind Force ◽  
Method Of Calculation ◽  
Yalu River ◽  
Sea Area

In order to design a double buoys mooring system in the estuary of Yalu River for loading work of 40,000 tons of bulk cargo ship, the article mainly based on the practicality of the meteorological condition of this sea area and the data of the vessel as well as the national criterion, do some calculations of wind force, current force, wave force as well as the total force on the ship, with the calculation result to make a designation of double mooring buoy system, decide the size of the mooring buoy, the size and length of the chain, the size and the depth of the Deadman. The construction according to the designation has a good effect; the method of calculation and the designation are proved useful.

The Dynamic Motion of the OC4 Floating Turbine with Different Incident Wave and Wind Directions in a Mooring System Failure Condition in Numerical Model

2020 ◽  
Author(s):  
Tzu-Ching Chuang ◽  
Wen-Hsuan Yang ◽  
Yi-Hong Chen ◽  
Ray-Yeng Yang
Keyword(s):  
Steady State ◽  
Line Tension ◽  
Time Domain Analysis ◽  
Mooring Line ◽  
Second Phase ◽  
Mooring System ◽  
System Failure ◽  
Floating Platform ◽  
Initial Tension ◽  
Wave Condition

&lt;p&gt;&lt;span&gt;In this paper, the commercial software Orcaflex is used to simulate the motion behavior of the OC4 floating platform, and the floater stability and mooring line tension after the mooring system failure. In the time domain analysis, the discussion is divided into three phases&amp;#8212;the first phase (before the tether failure), the second phase (before the tether failure, before reaching the new steady-state), and the third phase (after reaching the new steady-state). The motion characteristics and tension values at different stages were observed. In this study, only a 50-year return period wave condition is used as an input condition and simulating 11 different incident wind and wave directions. The numerical results are presented in the trajectory map and the table. About the tension of the mooring line, after the mooring system fails, it is notable that the mooring line tension will first decrease and then increase slightly above the initial tension value. In other words, the mooring system may survive after the failure of one mooring line and got a new balance of it. However, the tension amplitude will be higher than the first stage in the new balance and it will likely increase the risk of mooring line fatigue.&lt;/span&gt;&lt;/p&gt;

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