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.

An Innovative Synthetic Mooring Solution for an Octagonal FPSO in Shallow Waters

2010 ◽  
Author(s):  
Mo Fan ◽  
Da Li ◽  
Tuanjie Liu ◽  
Alex Ran ◽  
Wei Ye
Keyword(s):  
Oil And Gas ◽  
Shallow Waters ◽  
Manufacturing Processes ◽  
Mooring System ◽  
Oil And Gas Development ◽  
Mooring Lines ◽  
Environmental Loads ◽  
Design And Manufacturing ◽  
Full Production ◽  
Three Bundles

An octagonal FPSO has been proposed for marginal oil and gas development in shallow waters. A shuttle tanker will be deployed near the FPSO during offloading operations. This new concept simplifies the design and manufacturing processes, yet maintains full production, storage, and offloading functions of a conventional ship-shaped FPSO. However, design of the mooring system for this floating unit imposes technical challenges due to: 1) high environmental loads expected on this unit, 2) large dynamic offsets of the unit in shallow waters, and 3) inadequate performance of catenary mooring systems in shallow waters. Thus, development of a viable station keeping solution becomes a key issue to the new concept FPSO design. In this paper, an innovative mooring system is designed to meet the challenges. The FPSO mooring system consists of pile anchors, bridle chains, anchorage buoys, and polyester ropes. Nine mooring lines are grouped into three bundles which evenly spread around the FPSO. The shuttle tanker is attached to the FPSO with a nylon rope hawser at the bow and secured to pre-installed anchorage buoys at the stern with two other nylon ropes. Analyses have been performed for the FPSO mooring system. It is concluded that the proposed mooring system is fully functional and effective.

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.

Dynamic Load Reduction and Station Keeping Mooring System for Floating Offshore Wind

2018 ◽  
Author(s):  
Magnus J. Harrold ◽  
Philipp R. Thies ◽  
Lars Johanning ◽  
David Newsam ◽  
Michael Checkley ◽  
...  
Keyword(s):  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Extreme Conditions ◽  
Mooring System ◽  
Load Reduction ◽  
Station Keeping ◽  
Physical Test ◽  
Peak Loads ◽  
Non Linear

The mooring system for a floating offshore wind turbine ensures that the platform stays within pre-defined station keeping limits during operation, while it provides sufficient restraining forces in storm events to guarantee survival. This presents a challenge during the design process, since the cost of the mooring system is proportional to the peak loads, i.e. those that occur infrequently in extreme conditions. Mooring designs are governed by extreme and fatigue loads which determine the required Minimum Breaking Load (MBL) of the system. If uncertainties in the environmental loading or hydrodynamic coupled response exist, additional safety factors are required. This paper explores the application of a hydraulic based mooring system that enables a variable, non-linear line stiffness characteristic that cannot be achieved with conventional designs. This non-linear load-response behavior could function like a ‘shock absorber’ in the mooring system, and thus reduce the line tensions, enabling a more efficient mooring system that necessitates a lower MBL and thus lower cost. These claims are evaluated through numerical modelling of the NREL OC3 spar buoy and OC4 semi-submersible offshore wind platforms using the FAST-OrcaFlex interface. The simulations compare the dynamics with and without the inclusion of the hydraulic mooring component. The results suggest that mean mooring line loads can be reduced in the region of 9–17% through a combination of lower static and dynamic loads, while the peak loads observed in extreme conditions were reduced by 17–18%. These load reductions, however, come at the expense of some additional platform motion. The paper also provides an outlook to an upcoming physical test campaign that will aim to better understand the performance and reliability of the mooring component, which will provide the necessary evidence to support these load reduction claims.

scholarly journals Research on a Visual Servo Method of a Manipulator Based on Velocity Feedforward

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Rui Wang ◽  
Changchun Liang ◽  
Dong Pan ◽  
Xiaodong Zhang ◽  
Pengfei Xin ◽  
...  
Keyword(s):  
Coordinate System ◽  
Control Method ◽  
Tracking Error ◽  
Target Prediction ◽  
Target Velocity ◽  
Visual Servo ◽  
Integral Control ◽  
Motion State ◽  
Simulation And Experiment ◽  
Velocity Prediction

In this paper, a method of predicting the motion state of a moving target in the base coordinate system by hand-eye vision and the position and attitude of the end is proposed. The predicted value is used as the velocity feedforward, and the position-based visual servo method is used to plan the velocity of the end of the manipulator. It overcomes the influence of end coordinate system motion on target prediction in a discrete system and introduces an integral control method to compensate for the prediction velocity, eliminating the end tracking error caused by target velocity prediction error. The effectiveness of this method is verified by simulation and experiment.

Mixing on the Boundaries of Layers of Multilayer Nanoperiod Coatings of the TiNх/ZrNх System: Simulation and Experiment

2017 ◽  
Vol 9 (6) ◽  
pp. 06021-1-06021-6
Author(s):  
O. V. Sobol ◽  
◽  
A. A. Meylekhov ◽  
R. P. Mygushchenko ◽  
А. А. Postelnyk ◽  
...  
Keyword(s):  
System Simulation ◽  
Simulation And Experiment

scholarly journals An Analysis on the Spread Mooring of the Belida FSO Induced by Squall Loads

Kapal ◽  
2020 ◽  
Vol 17 (1) ◽  
pp. 15-27
Author(s):  
M Murdjito ◽  
Inneke Yulistanty Pravitasari ◽  
Eko Budi Djatmiko
Keyword(s):  
Wind Speed ◽  
Water Depth ◽  
Time Domain ◽  
Sharp Increase ◽  
Diffraction Theory ◽  
Mooring System ◽  
Environmental Loads ◽  
Minute Duration ◽  
Axis Offset ◽  
D Wave

Squall is the occurrence of a sudden sharp increase in wind speed, thus amplifies sea environmental loads. In the South of Natuna Sea, squall can reach an intensity of up to 50 m/s or close to 100 knots. In this water, the Belida FSO operates at a water depth of 77.0 m, tethered to the seabed by a spread mooring system. Squall’s impacts on the FSO mooring system has been examined by implementing time-domain simulations accommodated in a numerical model based on the 3-D wave diffraction theory. The simulations were performed by varying the squall duration of escalation, i.e. 2.5, 5.0, and 10.0 minutes, for the load cases of 1-year extreme operational and 100-year extreme survival conditions propagating at 0°, 45°, 90°, 135°, 180°. The three squall durations of escalation substantially increase the significant wave height Hs by averagely 60%, 50% and 34%, respectively. The largest of the maximum mooring tension due to the sea load directions is found to be brought about the 45° load when magnified by the squall with a 2.5-minute duration of escalation. In this respect, the largest intensities of the operational and survival tension loads may reach some 2,027 kN and 3,318 kN, respectively, which are eventually far below the MBL of 7,685 kN. The largest x-axis offsets in operational and survival conditions are 3.94 m and 10.21 m, respectively. Whereas the largest y-axis offsets for operational and survival loads are found to be 13.31 m and 15.48 m. These y-axis offset intensities are larger than the limiting criteria, i.e. 15% of the water depth or 11.55 m.

Modeling, Parameter Identification and Thruster-Assisted Position Mooring of C/S Inocean Cat I Drillship

2017 ◽  
Author(s):  
Jon Bjørnø ◽  
Hans-Martin Heyn ◽  
Roger Skjetne ◽  
Andreas R. Dahl ◽  
Preben Frederich
Keyword(s):  
Parameter Identification ◽  
Control Algorithm ◽  
State Of The Art ◽  
Control Algorithms ◽  
Model Parameters ◽  
Mooring System ◽  
Environmental Loads ◽  
Control Functions ◽  
Vessel Motion ◽  
And Control

A thruster-assisted position mooring (TAPM) system includes different control functions for stationkeeping and motion damping for a moored offshore vessel with assist from thrusters. It consists of a conventional mooring system and a dynamic positioning (DP) system. The thrusters are used to provide damping and some restoring to the vessel motion and compensate if line breakage occurs. The mooring system absorbs the main loads to keep the vessel in place. This paper presents a complete modeling, parameter identification, and control design for a 1:90 scaled TAPM model vessel. The numerical values for the different model parameters are identified from towing tests. State-of-the-art TAPM control algorithms have been tested on the vessel in the Marine Control Laboratory (MC Lab), to see the behavior resulting from the different control algorithms. The presented experiments focus on the setpoint chasing algorithm, where the position setpoint slowly moves to the equilibrium position where the environmental loads are balanced by the mooring loads. This avoids conflicts between the mooring system and the control actions. If the environmental loads are too large so that the setpoint exceeds a user-defined safety radius, the setpoint is set to this radius and thruster forces grow to support the mooring system in counteracting the environmental loads to avoid line breakage. The experiments show that the vessel and setpoint chasing control algorithm behaves as expected, minimizing thruster usage and maximizing utilization of mooring system.

Experimental Study of Energy Saving Effect of Building Envelope in Winter

2011 ◽  
Vol 121-126 ◽  
pp. 2741-2747
Author(s):  
Hou Hua Wang ◽  
Tao Zhang ◽  
Qiu Lian Xiao
Keyword(s):  
Experimental Study ◽  
Energy Saving ◽  
Temperature Difference ◽  
Average Energy ◽  
Internal Surface ◽  
Mean Value ◽  
Building Envelope ◽  
Simulation And Experiment ◽  
The Mean ◽  
Saving Effect

This paper presents an experimental study on the energy saving effect of building envelope in winter in Chongqing city. The basic cubicle was adopted for comparison. Experiments show that when energy saving measurements are applied in the external walls and windows, energy saving cubicle has an average energy efficiency rate of 32.68%, 7.68% over the target value of the standard. The indoor temperature of the energy saving cubicle is higher than the basic one’s. The internal surface temperature and the temperature difference between the exterior and interior of the insulation wall of the energy saving cubicle are both higher than that of the basic cubicle, the mean value is 1.28°C and 1.90°C respectively. And the temperature difference of the insulation glass is higher than that of the single glass, with a maximum value of 6.32°C. Daily simulation of the two cubicles is addressed by VisualDOE-4.0, the mean error between simulation and experiment is 16.16%, illustrating the effectivity and the accurateness of the VisualDOE-4.0.

Numerical Simulation of a Spar Interacting With a Polyester Mooring System

2004 ◽  
Author(s):  
Minsuk Kim ◽  
Yu Ding ◽  
Jun Zhang
Keyword(s):  
Energy Dissipation ◽  
Cyclic Loads ◽  
Mooring System ◽  
Floating Structure ◽  
Mooring Lines ◽  
Floating Structures ◽  
System A ◽  
Large Elongation ◽  
The Mean ◽  
Offset Curve

A numerical scheme, known as CABLE3D, originally developed for the simulation of dynamics of steel mooring lines is extended to allow for special properties pertaining to polyester ropes, such as relatively large elongation under tension, dependence of the modulus on loads, and energy dissipation under cyclic loads. The modified CABLE3D is then integrated into a numerical package, known as COUPLE6D, for computing the interaction between a floating structure and its polyester mooring system. A classical SPAR is chosen in this study as a representative of deepwater floating structures. By considering large elongation in polyester ropes, the static offset curve of a polyester mooring system is softer than that calculated under the assumption of small elongation. The effects of the mean loads on the modulus of polyester ropes are much greater than those of the dynamic loads. The energy dissipation in polyester ropes under cyclic loading does not play a significant role in the responses of the SPAR and tensions in a polyester mooring system. The above observations though made based on a classical SPAR may still have important implications to other floating structures moored by a polyester mooring system.

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