Design Considerations for Polyester Construction Stretch Removal and its Impact on Mooring System Design

Abstract Polyester based mooring systems offer unique challenges from design, analysis and installation perspective. Non-linear elongation behavior of the fiber is key to these challenges. A good understanding of the fiber elongation characteristics is critical to the design of a robust and efficient mooring system. Mooring systems are one of the primary contributors to the CAPEX of the Floating Production Units (FPU) and the drive to develop cost effective systems has led to improvements/changes to mooring systems. Off-vessel tensioning has been in use for several years, but the option has recently received more in-depth consideration. Off-vessel tensioning is becoming the standard for floating systems with the elimination of on-vessel tensioning systems. The elimination of on-vessel tensioning system brings upon new challenges in terms of mooring line installation and tensioning. A key driver for these systems is the polyester rope pre-load criteria primarily used to remove construction stretch and jump the creep curve that the system may experience. The challenges to each project are unique, however, understanding and assessing the key design impacts will be beneficial to the industry. This paper focuses on the design of a polyester based mooring system with focus on polyester fiber elongation characteristics and its impact on the design and installation. A polyester test program is established to understand the rope elongation behavior and impact of various pre-load levels. Installation assessment is also performed to understand the installation vessel requirements to achieve various pre-loads. Based on the studies, design updates are made to the mooring system and a novel two tension regime mooring system is proposed. Design impact of the two pre-tension system on various design criterions are evaluated and presented in this paper. The paper also makes recommendations on target pre-load and elongation to be considered in systems that do not plan to re-tension their system post installation. Authors appreciate that recommendations and observations reported may not be applicable for all types of floaters and mooring system.

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Sensitivity of Mooring Line Pretension in the Design Cycle for Floating Caissons

23rd International Conference on Offshore Mechanics and Arctic Engineering, Volume 1, Parts A and B ◽

10.1115/omae2004-51237 ◽

2004 ◽

Cited By ~ 1

Author(s):

Adinarayana Mukkamala ◽

Partha Chakrabarti ◽

Subrata K. Chakrabarti

Keyword(s):

Reinforced Concrete ◽

System Design ◽

Mooring Line ◽

Mooring System ◽

Mooring Lines ◽

Design Cycle ◽

Overall Performance ◽

The Difference ◽

Tacoma Narrows Bridge ◽

System Layout

The new parallel Tacoma Narrows Bridge being constructed by Tacoma Narrows Constructors will be mounted on two towers and these towers in turn will be supported by reinforced concrete caissons referred to as East Caisson (Tacoma side) and West Caisson (Gig Harbor side). Each Caisson is towed to the location and several stages of construction will take place at the actual site. During construction, the floating caissons will be moored in place to hold it against the flood and ebb currents in the Narrows. During the mooring system design, a desired pretension is established for the lines at each draft. However, due to practical limitations in the field some variations to this design pretension value may be expected. It is important to study the effect of this variation on the overall performance of the mooring system. In this paper, the sensitivity of the mooring line pretension on the overall performance of the mooring system for the above caisson is presented. During this study, all the variables that affect the mooring system design such as mooring system layout, mooring line makeup, anchor positions, fairlead departure angles, and fairlead locations are kept constant. The only variable changed is the pretension of the mooring lines. Two approaches for defining the variations in the pretension have been studied in this paper. In the first approach, the pretension is changed in a systematic way (predicted approach). In the second method the pretension is changed randomly. The latter is considered more likely to occur in the field for this type of complex mooring system. Both sets of results are presented for some selected drafts attained by the caisson during its construction. The difference in the results from the two methods is discussed.

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Mooring with Multicomponent Cable Systems

Journal of Energy Resources Technology ◽

10.1115/1.3227853 ◽

1980 ◽

Vol 102 (2) ◽

pp. 62-69 ◽

Cited By ~ 9

Author(s):

K. A. Ansari

Keyword(s):

Dynamic Response ◽

System Design ◽

Mooring Line ◽

Analysis Tool ◽

Mooring System ◽

Practical Application ◽

Analysis Techniques ◽

Anchoring System ◽

Cable Systems ◽

Stiffness Characteristics

Relative to the present-day need for offshore operations involving the use of moored vessels, mooring system design has become quite complex. Since a proper choice of mooring line components in the form of anchors, clump weights, chains and cables is vital for vessel station-keeping and mooring system survival, the adequacy of the mooring system under consideration must be checked out by suitable analysis techniques. This paper gives a general discussion of the various mooring line components available for use, presents an analysis tool to determine the stiffness characteristics of a multicomponent cable including the effect of line stretch, and demonstrates how these could be included in the dynamic analysis of an offshore construction vessel moored by a multileg anchoring system. The maximum limiting tension of the mooring line considered, which is a combination of anchors, clump weights, chains and cables is determined from the several breaking strengths and anchor capacities associated with the various cable configurations that can occur. Finally, in order to illustrate a practical application, the dynamic response of a moored production barge subjected to external environmental forces is examined.

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Modeling of a Shared Mooring System for a Dual-Spar Configuration

Volume 9: Ocean Renewable Energy ◽

10.1115/omae2020-18467 ◽

2020 ◽

Author(s):

Guodong Liang ◽

Karl Merz ◽

Zhiyu Jiang

Keyword(s):

Wind Turbines ◽

Wind Farms ◽

Cost Effective ◽

Sensitivity Study ◽

Design Stage ◽

Mooring Line ◽

Mooring System ◽

Preliminary Design ◽

Simulation Tool ◽

Preliminary Design Stage

Abstract As floating wind turbines become more technically mature, the development of floating wind farms is under way. Cost-effective solutions are desired to reduce the mooring costs. The concept of a shared mooring system has been proposed for this purpose. This work presents a method to model the shared mooring system for a dual-spar configuration. By applying the theory in elastic catenary of cable structures, a shared line can be modelled. To verify the method, a dual-spar system is modelled in a multibody simulation tool, in which two floating wind turbines are connected via a shared line. Static analyses are performed by using the present method and the simulation tool. Further, a sensitivity study is applied to the shared line properties. Different mooring line properties have been investigated. The influence of the shared line properties is shown on the mooring restoring properties of the dual-spar system. The present modeling method can be applied in the preliminary design stage of shared mooring systems.

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Global analysis of floating offshore wind turbines with shared mooring system

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/1201/1/012024 ◽

2021 ◽

Vol 1201 (1) ◽

pp. 012024

Author(s):

H Munir ◽

C F Lee ◽

M C Ong

Keyword(s):

Wind Turbines ◽

Time Domain ◽

Global Analysis ◽

Cost Effective ◽

Offshore Wind ◽

Mooring Line ◽

Mooring System ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Restoring Stiffness

Abstract Floating wind turbines (FWTs) with shared mooring systems can be one of the most cost- effective solutions in reducing mooring costs. First, the static configuration of a shared line is estimated using the elastic catenary equation. The present study investigates the global responses of two FWT with a shared mooring system. Two shared mooring configurations with different horizontal distances between the FWTs are considered. In the first configuration, the FWTs are placed 750m apart; and in the second configuration, they are placed 1000m apart. Two different environmental conditions (ECs) are used to simulate the global responses of the system in time domain. The shared mooring line results in higher extreme motions in surge and sway (degree of freedoms) DOFs due to the reduction of mooring restoring stiffness. The lower mooring restoring stiffness can be attributed to the reduction of one seabed anchoring point for each FWT as compared to a single FWT with three anchors installed. In the rotational DOFs, the shared mooring line configurations result in slight mean offset in each direction and significant increase in the motion standard deviations. This is caused by the reduced mooring stiffness associated with the change in platform orientation.

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Design Considerations and Selection of Cost-Effective Switched Reluctance Drive for Radiator Cooling Fans

Electronics ◽

10.3390/electronics10080917 ◽

2021 ◽

Vol 10 (8) ◽

pp. 917

Author(s):

Ickjin Son ◽

Grace Firsta Lukman ◽

Mazahir Hussain Shah ◽

Kwang-Il Jeong ◽

Jin-Woo Ahn

Keyword(s):

Low Cost ◽

Cost Effective ◽

Magnetic Characteristics ◽

Switched Reluctance Motors ◽

Switched Reluctance ◽

Design Considerations ◽

Cooling Fan ◽

Cooling Fans ◽

Power Switches ◽

Selection Of

Switched reluctance motors (SRMs) are simple in structure, easy to manufacture, magnet-less, brushless, and highly robust compared to other AC motors which makes them a good option for applications that operate in harsh environment. However, the motor has non-linear magnetic characteristics, and it comes with various pole-phase combinations and circuit topologies that causes many difficulties in deciding on which type to choose. In this paper, the viability of SRM as a low-cost, rugged machine for vehicle radiator cooling fan is considered. First, necessary design considerations are presented, then three commonly use types of SRM are analyzed: A 3-phase 6/4, 3-phase 12/8, and a 4-phase 8/6 to find their static and dynamic characteristics so the most suitable type can be selected. Simulation results show that the 8/6 SRM produces the highest efficiency with less phase current which reduces the converter burden. However, with asymmetric half bridge converter, eight power switches are required for 8/6 SRM and thus put a burden on the overall drive cost. As a solution, the Miller converter with only six switches for four phase SRM. To verify the proposed idea, the 8/6 SRM was manufactured and tested. The results show that Miller converter can be used for the proposed SRM with slightly reduced efficiency at 80.4%.

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

Journal of Marine Science and Engineering ◽

10.3390/jmse9020103 ◽

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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Multicriterial Optimization of Technical Systems Considering Multiple Load and Availability Scenarios

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.807.247 ◽

2015 ◽

Vol 807 ◽

pp. 247-256 ◽

Cited By ~ 2

Author(s):

Lena C. Altherr ◽

Thorsten Ederer ◽

Philipp Pöttgen ◽

Ulf Lorenz ◽

Peter F. Pelz

Keyword(s):

System Design ◽

Cost Effective ◽

Optimization Methods ◽

Technical System ◽

Multicriterial Optimization ◽

Fluid Systems ◽

Rule Number ◽

Technical Systems ◽

Multiple Load ◽

Modern Optimization

Cheap does not imply cost-effective -- this is rule number one of zeitgeisty system design. The initial investment accounts only for a small portion of the lifecycle costs of a technical system. In fluid systems, about ninety percent of the total costs are caused by other factors like power consumption and maintenance. With modern optimization methods, it is already possible to plan an optimal technical system considering multiple objectives. In this paper, we focus on an often neglected contribution to the lifecycle costs: downtime costs due to spontaneous failures. Consequently, availability becomes an issue.

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Design and Automated Optimization of an Internal Turret Mooring System in the Frequency and Time Domain

Journal of Marine Science and Engineering ◽

10.3390/jmse9060581 ◽

2021 ◽

Vol 9 (6) ◽

pp. 581

Author(s):

Hongrae Park ◽

Sungjun Jung

Keyword(s):

System Design ◽

Time Domain ◽

Initial Conditions ◽

Minimum Weight ◽

Optimization Algorithms ◽

Local Optimization ◽

Mooring System ◽

Floating Offshore Wind Turbines ◽

Global And Local Optimization ◽

Global And Local

A cost-effective mooring system design has been emphasized for traditional offshore industry applications and in the design of floating offshore wind turbines. The industry consensus regarding mooring system design is mainly inhibited by previous project experience. The design of the mooring system also requires a significant number of design cycles. To take aim at these challenges, this paper studies the application of an optimization algorithm to the Floating Production Storage and Offloading (FPSO) mooring system design with an internal turret system at deep-water locations. The goal is to minimize mooring system costs by satisfying constraints, and an objective function is defined as the minimum weight of the mooring system. Anchor loads, a floating body offset and mooring line tensions are defined as constraints. In the process of optimization, the mooring system is analyzed in terms of the frequency domain and time domain, and global and local optimization algorithms are also deployed towards reaching the optimum solution. Three cases are studied with the same initial conditions. The global and local optimization algorithms successfully find a feasible mooring system by reducing the mooring system cost by up to 52%.

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