Reliability-Based Structural Optimization for Positioning of Marine Vessels

2006 ◽  
Author(s):  
Bernt J. Leira ◽  
Per I. B. Berntsen ◽  
Ole Morten Aamo
Keyword(s):  
Control System ◽  
Control Algorithm ◽  
Structural Reliability ◽  
Mooring System ◽  
Response Model ◽  
Marine Structures ◽  
Mooring Lines ◽  
Control Schemes ◽  
Marine Vessels

The present paper is concerned with floating marine structures that are kept in position by means of mooring lines in addition to a thruster system. Different options relevant for construction of automatic control schemes for the thruster system are first investigated based on a simplified response model. In particular, the role of structural reliability criteria applied to the mooring system is investigated. Subsequently, a more refined control algorithm based on such reliability criteria is introduced. The performance of this control system is demonstrated by numerical simulations.

Structural Reliability Criteria for Control of Large-Scale Interconnected Marine Structures

2004 ◽  
Author(s):  
Per Ivar Barth Berntsen ◽  
Bernt J. Leira ◽  
Ole Morten Aamo ◽  
Asgeir J. So̸rensen
Keyword(s):  
Control System ◽  
Large Scale ◽  
Structural Reliability ◽  
Fish Farming ◽  
Current Control ◽  
Mooring System ◽  
Marine Structures ◽  
Mooring Cable ◽  
A Chain ◽  
Configuration Control

In this paper, we develop a model of a futuristic fish farming structure, and study problems related to interconnected marine structures and strategies for configuration control with focus on structural reliability. Configuration control refers to positioning of individual modules or the entire structure as a whole. The structure is a chain of surface vessels, moored to the seabed via a spread mooring system connected to the front vessel. In this paper we design a control system that: 1) Ensures limited loading of the mooring system in order to avoid mooring cable failure and;2) Ensures positive strain in the connectors between vessels in order to avoid buckling effects due to variations in for instance the current. Control actuation is by means of a thruster mounted on the first module. The performance of the control system is demonstrated by simulations.

Value of information of in situ inspections of mooring lines

2021 ◽  
pp. 1748006X2098740
Author(s):  
Jorge Mendoza ◽  
Jacopo Paglia ◽  
Jo Eidsvik ◽  
Jochen Köhler
Keyword(s):  
Pitting Corrosion ◽  
Value Of Information ◽  
Structural Reliability ◽  
Structural Safety ◽  
Statistical Dependence ◽  
Mooring System ◽  
Mooring Lines ◽  
Corrosion Condition ◽  
Chain Links

Mooring systems that are used to secure position keeping of floating offshore oil and gas facilities are subject to deterioration processes, such as pitting corrosion and fatigue crack growth. Past investigations show that pitting corrosion has a significant effect on reducing the fatigue resistance of mooring chain links. In situ inspections are essential to monitor the development of the corrosion condition of the components of mooring systems and ensure sufficient structural safety. Unfortunately, offshore inspection campaigns require large financial commitments. As a consequence, inspecting all structural components is unfeasible. This article proposes to use value of information analysis to rank identified inspection alternatives. A Bayesian Network is proposed to model the statistical dependence of the corrosion deterioration among chain links at different locations of the mooring system. This is used to efficiently update the estimation of the corrosion condition of the complete mooring system given evidence from local observations and to reassess the structural reliability of the system. A case study is presented to illustrate the application of the framework.

A Control System on Soil Temperature

2014 ◽  
Vol 599-601 ◽  
pp. 673-679
Author(s):  
Shi Guo Chen ◽  
Li Hua Hu ◽  
Dong Sheng Wu ◽  
Xue Yong Chen
Keyword(s):  
Mathematical Model ◽  
Control System ◽  
Soil Temperature ◽  
Control Algorithm ◽  
Soil Ecology ◽  
Control Soil ◽  
Pid Algorithm ◽  
And Control ◽  
The Mathematical Model

The soil’s temperature plays an important role of soil ecology research. In order to gain and control soil’ temperature. A control system is proposed for soil’s temperature. And a new control algorithm which is based on the PID algorithm is designed in the control system to handle the complex change of the soil’s temperature. It does not need to know the mathematical model of soil’s temperature. At last, the control result is analyzed in this paper. The result shows that the soil’s temperature is controlled ideal by this control system which is accurate to 0.5°C.

Real-time FEM Control System for Connected Piezoelectric Actuators

2000 ◽  
Vol 12 (2) ◽  
pp. 172-179
Author(s):  
Daigoro Isobe ◽  
◽  
Hiroshi Nakamura ◽  
Ryuta Shimizu ◽  
◽  
...  
Keyword(s):  
Control System ◽  
Finite Elements ◽  
Real Time ◽  
Control Algorithm ◽  
Piezoelectric Actuators ◽  
Real Time Control ◽  
Time Control ◽  
Control Schemes ◽  
In Series ◽  
Realtime Control

In this paper, the Finite Element Method (FEM) and the previously proposed inverse theory for bimorph piezoelectric actuators are applied into a real time control algorithm of connected piezoelectric actuators. Most control schemes handle an entire system in series, which becomes a drawback when some elements lose their function in a higher redundant system. On the other hand, the FEM can handle the system in parallel by subdividing it into discrete finite elements, and can cope with flexibility in the change of form and material properties. Noncompatible finite elements are used to express the actuators in the control algorithm, and empirical formulae considering time-dependent characteristics such as creep and residual strain, are also implemented. A real-time FEM control system, which consists of a PC, a bipolar DC unit and a signal-distributing controller, is developed. The system is verified by experiments on quasi-static displacement control of connected piezoelectric actuators. The results show the possibility of highly accurate, realtime control of the actuators using the FEM.

Structural Reliability-Based Control for Moored Vessels: Experimental Results

2007 ◽  
Author(s):  
Per I. B. Berntsen ◽  
Ole M. Aamo ◽  
Bernt J. Leira
Keyword(s):  
Structural Properties ◽  
Reliability Index ◽  
Laboratory Experiments ◽  
Structural Reliability ◽  
Weather Conditions ◽  
Dynamic Positioning ◽  
Mooring System ◽  
Reliability Measures ◽  
Mooring Lines ◽  
Surface Vessels

This paper addresses dynamic positioning of surface vessels moored to the seabed via a turret based spread mooring system, referred to as position mooring. The controller utilize a reliability index to determine the actuator force needed to operate safely. The structural reliability measures become an intrinsic part of the controller, automatically adjusting the allowed geographical region based on current weather conditions and structural properties of the mooring lines. The performance of the controller is demonstrated through laboratory experiments on a model vessel named CyberShip III.

Consistent Design Codes for Anchors and Mooring Lines

2002 ◽  
Author(s):  
Rune Dahlberg ◽  
Jan Mathisen
Keyword(s):  
Structural Reliability ◽  
Mooring System ◽  
Design Codes ◽  
Safety Factors ◽  
Design Code ◽  
Mooring Lines ◽  
Safety Level ◽  
Industry Standard ◽  
Partial Safety Factors ◽  
Anchor Design

As the water depth of hydrocarbon discoveries becomes deeper, the technological challenges related to the design of mooring systems increases. Changing from steel catenary mooring systems (CMS) to fibre rope taut mooring systems (TMS) has been accompanied by an immense focus on how to qualify and approve fibre rope material for use in a TMS. This involves items related to specifications for manufacturing, handling and testing fibre ropes, as well as calibration of safety factors to use in the design of TMSs. One consequence of moving to a TMS is that the anchors will have to take more uplift load than in a conventional CMS, which makes the anchors a more critical component of the mooring system than before. The types of anchor normally available to the designer of a TMS are pile anchors, suction anchors and various types of plate anchors. Anchors of all types are designed and installed in ever-deeper water, but the safety of the designed mooring systems varies with the design code adopted. There is thus an obvious need for an industry standard, a design code for each anchor type that is calibrated based on structural reliability analysis using the current experience and knowledge in the industry. This paper compares anchor design codes that use total safety factors (TSF) with the DNV design code that uses partial safety factors and failure consequence classes. Examples of design codes for station-keeping systems that adopt the TSF format are API RP2SK and (assumed herein) the ISO code, which is under development. The comparison demonstrates that use of the safety format adopted in the DNV code provides more flexibility and ensures a uniform safety level of all components in a mooring system than the TSF format. If all types of anchor were designed to the same safety level it would be possible to compare anchors without worrying about differences in safety. A typical approach for calibration of a design code is described.

scholarly journals Controller Analysis in Real-Time Hybrid Model Testing of an Offshore Floating System

2018 ◽  
Author(s):  
Stefan A. Vilsen ◽  
Thomas Sauder ◽  
Martin Føre ◽  
Asgeir J. Sørensen
Keyword(s):  
Control System ◽  
Real Time ◽  
Hybrid Model ◽  
Low Frequency ◽  
Experimental Tests ◽  
Mooring System ◽  
Wave Excitation ◽  
Marine Structures ◽  
Wave Basin ◽  
Floating System

This paper presents an experimental study using Real-Time Hybrid Model (ReaTHM) testing of a moored floating cylindrical buoy, conducted in a wave basin. ReaTHM testing is a method for studying the dynamics of marine structures by partitioning the system into numerical and physical substructures that are then coupled in real-time using a control system. In this study, the floating cylinder buoy is modelled physically, and the mooring system modelled numerically. In this paper, the effect of selected controller parameters on the performance of the control system is studied, for both wave frequency and low-frequency ranges. The architecture/design of the control system is presented in the first part of the paper, while results from experimental tests with wave excitation on the physical substructure are presented in the second part of the paper.

scholarly journals Transient Responses Evaluation of FPSO with Different Failure Scenarios of Mooring Lines

2021 ◽  
Vol 9 (2) ◽  
pp. 103
Author(s):  
Dongsheng Qiao ◽  
Binbin Li ◽  
Jun Yan ◽  
Yu Qin ◽  
Haizhi Liang ◽  
...  
Keyword(s):  
Service Condition ◽  
Mooring Line ◽  
Mooring System ◽  
Transient Effects ◽  
Floating Platform ◽  
Transient Responses ◽  
Mooring Lines ◽  
Performance Deterioration ◽  
Steady State Responses ◽  
Influence Process

During the long-term service condition, the mooring line of the deep-water floating platform may fail due to various reasons, such as overloading caused by an accidental condition or performance deterioration. Therefore, the safety performance under the transient responses process should be evaluated in advance, during the design phase. A series of time-domain numerical simulations for evaluating the performance changes of a Floating Production Storage and Offloading (FPSO) with different broken modes of mooring lines was carried out. The broken conditions include the single mooring line or two mooring lines failure under ipsilateral, opposite, and adjacent sides. The resulting transient and following steady-state responses of the vessel and the mooring line tensions were analyzed, and the corresponding influence mechanism was investigated. The accidental failure of a single or two mooring lines changes the watch circle of the vessel and the tension redistribution of the remaining mooring lines. The results indicated that the failure of mooring lines mainly influences the responses of sway, surge, and yaw, and the change rule is closely related to the stiffness and symmetry of the mooring system. The simulation results could give a profound understanding of the transient-effects influence process of mooring line failure, and the suggestions are given to account for the transient effects in the design of the mooring system.

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