Design, Analysis and Verification of Moored Floating Caisson System

2004 ◽  
Author(s):  
Partha Chakrabarti ◽  
Subrata K. Chakrabarti ◽  
Adinarayana Mukkamala ◽  
Nagaraj Anavekar ◽  
Shen Qiang ◽  
...  
Keyword(s):  
Bottom Topography ◽  
Suspension Bridge ◽  
Design Tool ◽  
Mooring System ◽  
Mooring Lines ◽  
Hydrodynamic Analysis ◽  
Analysis And Design ◽  
Dynamic Forces ◽  
Tacoma Narrows Bridge ◽  
Line Loads

Tacoma Narrows Constructors (TNC) is building a new suspension bridge in Tacoma, close to Seattle, Washington State, USA. The new bridge will be built just south of the existing bridge mounted on two caissons, referred to as East Caisson (Tacoma side) and West Caisson (Gig Harbor side). Each pier is about 80’ wide and 130’ long in plan. The mooring system for each caisson consists of two sets of mooring lines: lower and upper. Each set consists of 16 mooring lines. The lower 16 lines consist of anchors that form a radius of about 300 feet. The fairlead locations for these lower 16 lines are kept constant throughout the construction process. These 16 lines are hooked-up after the caisson is towed from the harbor and positioned at the site. For the upper 16 lines (except three lines on East Pier), the anchor locations form a radius of 600’. The fairlead locations for these upper 16 lines vary based on the draft. Due to the proximity of the proposed caissons to the existing piers and the varying bottom topography, considerable turbulence and vortex shedding is expected which will cause current induced dynamic forces on the caissons. This paper describes the design and analysis of this multi-line mooring system for Tacoma Narrows Bridge caissons, based on the construction sequence in the floating condition. The analysis involved optimizing the anchor locations and the line pretensions, determining the dynamic motions of the caissons, maximum line loads, and corresponding safety factors. The paper includes the hydrodynamic analysis for added mass, and damping, the methodology used for the nonlinear moored caisson analysis (MOTSIM), and the validation of the design tool with other similar models (e.g., StruCAD*3D). The results of the analysis and design are discussed.

Design Analysis of Moored Floating Caisson System

2004 ◽  
Vol 127 (2) ◽  
pp. 75-82 ◽  
Author(s):  
Partha Chakrabarti ◽  
Subrata K. Chakrabarti ◽  
Adinarayana Mukkamala ◽  
Nagaraj Anavekar ◽  
Shen Qiang ◽  
...  
Keyword(s):  
Bottom Topography ◽  
Suspension Bridge ◽  
Design Tool ◽  
Mooring System ◽  
Mooring Lines ◽  
Hydrodynamic Analysis ◽  
Construction Sequence ◽  
Close Proximity ◽  
Dynamic Forces ◽  
Line Loads

Tacoma Narrows Constructors (TNC) are building a new suspension bridge in Tacoma, close to Seattle, Washington State, USA. The new bridge is being built just south of the existing bridge mounted on two caissons. The caissons are constructed on location after the shallow draft caissons are towed to site. During the construction sequence, the mooring system for each caisson consists of two sets of 16 mooring lines. The lower 16 lines are hooked-up after the shallow draft caisson is towed from the harbor and positioned at the site. The fairlead locations for these lines are kept constant throughout the construction process. The fairlead locations for the upper 16 lines (except three lines on the East Caisson) vary based on the caisson draft. The caissons are subject to a high current from the ebb and flood tide flow in the Narrows. The new caissons are in close proximity to the existing piers and the bottom topography at the site is varying. Therefore, considerable turbulence and vortex shedding is expected in the prevailing current, which will cause current-induced dynamic forces on the caissons. This paper describes the design and analysis of this multiline mooring system for Tacoma Narrows Bridge caissons, based on the construction sequence in the floating condition. The analysis involved optimizing the anchor locations and the line pretensions, determining the dynamic motions of the caissons, the maximum line loads, and the corresponding safety factors. The paper also describes the hydrodynamic analysis for added mass, and damping, the methodology used for the nonlinear moored caisson analysis (MOTSIM), and the validation of the design tool with other similar models (e.g., STRUCAD*3D). The results of the analysis and the design of the system are discussed.

Overview of Tacoma Narrows Bridge Floating Caisson Design

2004 ◽  
Author(s):  
M. Sri Krishna ◽  
Partha Chakrabarti ◽  
Subrata K. Chakrabarti ◽  
Adinarayana Mukkamala ◽  
Nagaraj Anavekar
Keyword(s):  
Design Procedure ◽  
Suspension Bridge ◽  
Offshore Structures ◽  
Mooring Lines ◽  
Critical Areas ◽  
Dynamic Forces ◽  
Order Of Magnitude ◽  
Associated Design ◽  
Tacoma Narrows Bridge ◽  
Full Height

Tacoma Narrows Constructors is building a new suspension bridge in Tacoma, close to Seattle, Washington State, USA next to an existing bridge at the location. The new bridge is being built just south of the existing bridge. This new bridge will be built on towers mounted on two caissons. The caissons are towed to the site from the harbor with the cutting edge, first full lift, and the second and third exterior lifts. The piers are constructed on site up to their full height as floating caissons at varying drafts. During the construction, the floating caissons on both ends of the new bridge are moored in place with 32 catenary mooring lines. The current flow due to ebb and flood tide in the narrows is very high. This high current and the consequent vortex-induced dynamic forces provided a technical challenge in the design of the caisson and its mooring system whose dimensions are of similar order of magnitude as typical offshore structures exposed to severe environment. This paper provides an overview of this challenge, and describes the steps taken in overcoming these difficulties. The design procedure adopted of the moored caisson system and the piers in the overall scheme of the Tacoma Narrows Bridge are summarized. This overview stresses the practical side of towing, mooring and in place construction of the caissons. Some of the critical areas of associated design challenges and their solution techniques are highlighted.

Validation of Mooring Simulations (for Mooring Integrity Assessment) With In-Service Tension Measurements

2021 ◽  
Author(s):  
Willemijn Pauw ◽  
Remco Hageman ◽  
Joris van den Berg ◽  
Pieter Aalberts ◽  
Hironori Yamaji ◽  
...  
Keyword(s):  
Numerical Models ◽  
Weather Conditions ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Data Set ◽  
Integrity Assessment ◽  
Motion Data ◽  
Load Cells ◽  
Line Loads

Abstract Integrity of mooring system is of high importance in the offshore industry. In-service assessment of loads in the mooring lines is however very challenging. Direct monitoring of mooring line loads through load cells or inclinometers requires subsea installation work and continuous data transmission. Other solutions based on GPS and motion monitoring have been presented as solutions to overcome these limitations [1]. Monitoring solutions based on GPS and motion data provide good practical benefits, because monitoring can be conducted from accessible area. The procedure relies on accurate numerical models to model the relation between global motions and response of the mooring system. In this paper, validation of this monitoring approach for a single unit will be presented. The unit under consideration is a turret-moored unit operating in Australia. In-service measurements of motions, GPS and line tensions are available. A numerical time-domain model of the mooring system was created. This model was used to simulate mooring line tensions due to measured FPSO motions. Using the measured unit response avoids the uncertainty resulting from a prediction of the hydrodynamic response. Measurements from load cells in various mooring lines are available. These measurements were compared against the results obtained from the simulations for validation of the approach. Three different periods, comprising a total of five weeks of data, were examined in more detail. Two periods are mild weather conditions with different dominant wave directions. The third period features heavy weather conditions. In this paper, the data set and numerical model are presented. A comparison between the measured and numerically calculated mooring line forces will be presented. Differences between the calculated and measured forces are examined. This validation study has shown that in-service monitoring of mooring line loads through GPS and motion data provides a new opportunity for mooring integrity assessment with reduced monitoring system complexity.

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

2004 ◽  
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.

Station-Keeping Tests of Moored Caisson in Strong Current

2005 ◽  
Vol 127 (4) ◽  
pp. 315-321 ◽  
Author(s):  
Subrata K. Chakrabarti ◽  
Mark McBride
Keyword(s):  
Suspension Bridge ◽  
Mooring Line ◽  
Mooring Lines ◽  
Construction Period ◽  
Physical Model Tests ◽  
Strong Current ◽  
Highly Nonlinear ◽  
Flow Directions ◽  
Flow Interference ◽  
Line Loads

A new suspension bridge is being built over the Tacoma Narrows, Washington. The bridge will be placed on a structure mounted on two large concrete caissons. The caissons are being constructed in a floating position by pouring concrete at site. During this construction period, the floating caissons are moored in place and will be subject to high currents in the Narrows at a range of drafts. In order to investigate the motions of the caisson and the mooring line loads, physical model tests were performed at a scale of 1:100 at HR Wallingford (HRW). The actual bottom contours of the Narrows near the construction site were duplicated in the model. The catenary mooring lines were highly nonlinear. The current forces and moments on the floating caisson included steady and oscillating components due to flow separation and vortex shedding. There is an existing bridge mounted on two piers in the vicinity of the new caissons, which introduced an appreciable flow interference effect. The tests were conducted in both the ebb and flood flow directions so that the effect of the shadowing of the caisson-pier pair could be studied in the tests. The recorded results of the elastic mooring tests were compared in terms of the maximum measured tensions with a time-domain dynamic motion simulation program, MOTSIM. The results of this comparison are presented in this paper.

Coupled Mooring Analysis for a Deep Water CALM Buoy

2004 ◽  
Author(s):  
J. L. Cozijn ◽  
T. H. J. Bunnik
Keyword(s):  
Model Tests ◽  
Mooring Line ◽  
Mooring System ◽  
Test Results ◽  
Mooring Lines ◽  
Restoring Force ◽  
Small Water ◽  
Force Components ◽  
Force Characteristics ◽  
Line Loads

The effect of the mooring loads on floator motions can be significant for small water plane are floaters like CALM buoys. Not only does the mooring system contribute to the static restoring force components, but the dynamic behaviour of the mooring lines also affects the inertia and damping of the moored CALM buoy. The results from model tests with a moored CALM buoy were compared with the results from two series of time-domain computer simulations. First, fully dynamic coupled simulations were carried out, in which the interaction between the floater motions and the dynamic mooring line loads was modelled for all 6 modes of motion. Second, quasi-static simulations were carried out, in which only the (non-linear) static restoring force characteristics of the mooring system were taken into account. The comparison of results from the simulations and the model tests clearly indicates that the fully dynamic coupled simulations show a much better correspondence with the model test results than the quasi-static simulations. It is concluded that for the simulation of the behavior of a moored CALM buoy in waves a fully dynamic coupled mooring analysis is essential.

Motion Responses of a Catenary-Taut-Hybrid Moored Single Module of a Semisubmersible Very Large Floating Structure in Multisloped Seabed

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Yiting Wang ◽  
Xuefeng Wang ◽  
Shengwen Xu ◽  
Lei Wang
Keyword(s):  
Shallow Water ◽  
Time Domain ◽  
Large Scale ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Low Frequency ◽  
Mooring System ◽  
Floating Structure ◽  
Mooring Lines ◽  
Motion Responses

Motion responses of moored very large floating structures (VLFSs) in coastal regions are remarkably influenced by shallow water, seabed topography, and mooring system, which were given particular focus in this paper. A three-dimensional (3D) numerical model of a moored semisubmersible single module (SMOD) was described, and time domain simulated and experimentally validated. A catenary-taut-hybrid mooring system was adopted considering coastal space limitations. Large-scale catenary mooring lines were deployed on the deep water side, while taut chains were used on the shore side to decrease the anchor radius. Although the mooring system may induce a stiffness difference between the two sides, the effectiveness of the mooring system was demonstrated by time-domain simulation and model tests. The moored semisubmersible SMOD in shallow water exhibits significant low frequency characteristics. Water depth, asymmetric stiffness, and bottom topography effects were investigated by a series of sensitivity studies. The results show that these factors play an important role in motion responses of the moored SMOD, which can further conduce to better understandings on the hydrodynamic of the semisubmersible-type VLFSs.

Station-Keeping Tests of Moored Caisson in Strong Current

2004 ◽  
Author(s):  
Subrata K. Chakrabarti ◽  
Mark McBride
Keyword(s):  
Suspension Bridge ◽  
Mooring Line ◽  
Mooring Lines ◽  
Construction Period ◽  
Physical Model Tests ◽  
Strong Current ◽  
Highly Nonlinear ◽  
Flow Directions ◽  
Flow Interference ◽  
Line Loads

A new suspension bridge is being built over the Tacoma Narrows, Washington. The bridge will be placed on a structure mounted on two large concrete caissons. The caissons are being constructed in a floating position by pouring concrete at site. During this construction period, the floating caissons are moored in place and will be subject to high currents in the Narrows at a range of drafts. In order to investigate the motions of the caisson and the mooring line loads, physical model tests were performed at a scale of 1:100 at HR Wallingford (HRW). The actual bottom contours of the Narrows near the construction site was duplicated in the model. The catenary mooring lines were highly nonlinear. The current forces and moments on the floating caisson included steady and oscillating components due to flow separation and vortex shedding. There is an existing bridge mounted on two piers in the vicinity of the new caissons, which introduced an appreciable flow interference effect. The tests were conducted in both the ebb and flood flow directions so that the effect of the shadowing of the caisson-pier pair could be studied in the tests. The recorded results of the elastic mooring tests were compared in terms of the maximum measured tensions with a time-domain dynamic motion simulation program, MOTSIM. The results of this comparison are presented in this 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.

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.

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