Marine Structures Research Recommendations Recommendations for the Interagency Ship Structure Committee's FYs 1998-1999 Research Program (1997) / Chapter Skim
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ACTIVE AND PENDING PROJECTS
ACTIVE AND PENDING PROJECTS
Pages 21-56
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From page 21... ...
A major barrier to more extensive use of composites in marine structures is uncertainty over their performance in a fire. Recommended for FY 95 is a program to address fire and safety issues associated with nonmetallic materials, Project 95-14, "Assessment of Fire, Smoke and Toxicity Characteristics of Composite Materials Proposed for Manne Applications." In a parallel effort focused on structural monitoring and safety, a program centered on Smart structures'' is recommended Project 95M-C' ''Intelligent Composite Structure Development for Marine Applications." A program is also recommended to address long-term durability effects of composites in the marine environment, Project 95M-S, "Long Terser Durability of Polymer-Based Composites and Corrosion at MetalComposite Interfaces." A parallel effort is recommended to develop the analytical tools and design methods needed to achieve the full benefits of using composite materials, Project 95M-T, "Analysis and Design Techno~o~r Development for Manne Composite Structures." Fracture The recent failures of bulk carriers, weld cracking of structural members of TransAlaska Pipeline Service trade tankers, and the large number of SSC projects related to reliability of marine structures are cause for the CMS to recommend a hands-on workshop addressing fracture assessments and the application of reliability methods to real design problems.
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From page 22... ...
Another elastic-plastic fracture assessment method, the Failure Assessment Diagram, is presented as part of Project 95-1O, "A Guide to Damage Tolerance Analysis of Marine Structures." Further evaluation is required regarding how these methods apply to some of the more complicated details found in ship structures. Project SR-1349, "Evaluation of Ductile Fracture Models for the Prediction of Fracture Behavior of Ship Structure Details," is considering various ductile fracture methodologies by testing complex model components.
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From page 23... ...
Project 95-3, entitled "Commercial Ship Design and Fabncation for Corrosion Control (Phase I) ," addresses these issues and wall indicate the capability to improve competitiveness of the shipbuilding industry and result in cost savings to owners/operators.
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From page 24... ...
This is the subject of Project 95M-A, "Retrofit of Marine Cathodic Protection Systems." The Oil Pollution Act of 1990 mandates double hulls for all tankers that operate in U.S. terntonal waters.
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With this in mind, a 2-day symposium and workshop has been proposed—Project 95-l, "Symposium/Workshop: Higher Order Prediction Methods for Hydrodynamic Loads and Response of Manne Structures"- by which these experts can be brought together to discuss the pros and cons of their methods and progress to date. Project 95-5, "Combined Load Effects for Design and Strength Assessment of Ship Structures" (94D-~)
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From page 26... ...
Design Methods The need to maintain a pipeline of well-trained structural designers, versed In the pnnciples of structural integrity, requires support to the technical education community. Accordingly, the CMS recommends Project 95-16, ''Evaluation of Manne Structures Education in North Amenca" and Project 95D-F, "Design of Innovative Marine Stn~ctures." The thrust of these projects is to get more schools and students interested In stn~ctural design in naval architecture and marine eng~neenng and to provide an opportunity for several students to obtain grants for senior or graduate studies in the area of structural concepts for a practical marine structure and to present their Endings.
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From page 27... ...
However, the design of these ships is generally based on the concept of single-skin design. Project 93-3, ~Double-Hull Vessel Assessment Methods for Collision and Grounding Protection," proposed in FY 1993 Recommendations, was combined into a joint industry project under Project SR-1354, "Grounding Protection of Tankers." To expand this work to include the effect of collisions, the CMS recommends Project 95-12, "Rupture Resistance Cargo Tanks of Double Hull Tankers to Low-Energy Impact." Project 95-~l, "Alternative Stiffening Systems for Double Skin Tankers," should produce concepts that wall reduce the cost of these ships.
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From page 28... ...
The project wiD be able to build upon the results of the recently initiated Project SR-1343, "Optunized Weld Metal Properties for Ship Structures," which is a project to develop guidelines to improve productivity by optimizing weld metal properties for use with high-strength steels. Potential for increases in productivity is offered by incorporation of these new high-strength, high-performance steels into ship designs.
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From page 29... ...
There has been continuing concern with the problems resulting from corrosion of ship structures. As discussed earlier, in recognition of that concern, Project 95-3, "Commercial Ship Design and Fabrication for Corrosion Control," was recommended.
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These technologies cannot be implemented in isolation but rather require an interdisciplinary approach involving design, material delivery, cutting and forming operations, joining, assembly, inspection, and coating methods. As methods are developed to increase productivity, the structural integrity has to be maintained.
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In this regard, Project 95-4, "Detection Probability Assessment of Visual Inspection of Ships," is proposed. Another project to standardize inspection procedure is proposed under Project 95TC-B, "Standardized Approach to Methodology and Analysis of Ultrasonic Inspection of Ship Structures." The CMS is promoting these new analytical techniques in the marine structures industry.
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From page 32... ...
Decisions on design and maintenance of ship structures hinge on the effectiveness and cost of inspection. Project SR-1355, YInspection of Marine Structures, was initiated to quantify inspection performance and address inspection cost.
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Further, the Amencan Petroleum Institute has recommended this technology for offshore structures with their publication RP2A, unrecommended Practice for Design, Fabrication, and Installation of Fixed Offshore Structures." The development of probability-based design codes in other areas appears to have stimulated important advances in structural design. In addition, the codes become a living document that can be revised to include new sources of information and to reflect additional statistical data on loads and load effects.
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Probability-hased Design Approach for Ship Structures Phase 1: Demo,~stranon Project A demonstration project ~Probability-based Ship Design Procedures: A Demonstrations (SSC-368) was completed in 1993.
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From page 35... ...
Rel~abdity of Existing Ship Structures Knowledge of the risks associated with important failure modes, which have been tolerated by existing marine structures, would be useful in developing rational probability-based design cnteria. This information could be used on an ad hoc basis to review or revise present procedures or to develop an entire design-cnteria document.
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From page 36... ...
The first phase, Project SR-1344, Assessment of Reliability of Existing Ship Structures (Phase If, is now complete, and it will be useful for the Phase 3 project, Implementation of Design Guideiir~es for Shiest (SR-1343~. Phase 2 of Project SR1344 wall begin in 1994.
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standards. Other international standards should also be considered, including the International Institute of Welding fatigue design S-N cumes (Eurocode 3)
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Reduce marine environmental risks. SSC Strateeies Improved engineering analysis and evaluation Development of better design tools and information systems Prevention research including damage-tolerant structures Background Criteria for fracture-resistant design, fatigue-damage repair, and damage tolerance and structural integrity analyses require laboratory-generated elastic-plastic fracture-toughness data from fracture-mechanics-based tests, e.g., I-integral or crack-tip opening displacement (CTOD)
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Detection Probability Assessment of Visual Inspection of Ships Combined Load Effects for Design and Strength Assessment of Ship Structures (94D-~)
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maritime industry in shipbuilding, maintenance, and repair. SSC Strategies · Development of better design tools · Improved engineering analysis and evaluation Background Linear techniques have played a central role in the design of ship and marine structures.
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· For distribution to the ship-structure community, prepare a written report on the symposiumEvorkshop that addresses current capan~t~es short and long term research needs, Duration 1,000 labor hours over ~ year gS-2 Methodology to Establish the Adequapy of Weld Repairs (94-~) , ongomg researc :1, Objective Experimentally evaluate the adequacy of weld repairs so that a decision whether to repair at all, to repair further, or to operate without such repairs can be made on a technical basis.
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From page 42... ...
· Coordinate these activities with similar ones at Defense Research Establishment Atlantic of Canada, American Welding Society, and National Shipbuilding Research Program. Duration 2,000 labor hours over 1.5 years 95-3 Commercial Ship Design and Fabrication for Corrosion Control (Phase I)
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From page 43... ...
Duration 1,000 labor hours over 6 months 95-4 Detection Probability Assessment of Visual Inspection of Ships Objective Develop a probabilistic model, based on inspection data, that wall help eliminate uncertainties associated with the use of visual methods for the detection of fatigue cracks. Background Numerous probabilistic methods have been developed to make inspection results more meaningful when the inspection results are used in fatigue analysis.
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From page 44... ...
SSC Strategies · Structural reliability engineering · Improved structural inspection techniques Recommendations Perform the following tasks: · Review the literature and compile available statistical data for visual inspection and detection of cracks on ship structures, emphasizing welds and joints. Coordinate with research underway in the ongoing Project SR-1355.
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From page 45... ...
loads for design and strength assessment of ship structures. · Perform a pilot study for a selected ship type, considering a group of representative locations and structural components, to determine the most probable combined effects of the global and local loads, using long-te~m prediction techniques of time-domain simulations.
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From page 46... ...
maritime industry in shipbuilding, maintenance, and repair. SSC Strategy Development of reliability design techniques to optimize material use Background Crack initiation at discontinuities in welded connection details are a primary cause of fatigue failures.
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From page 47... ...
Duration 1,500 labor hours over ~ year 95-7 Structural Design Guide for Twin Hull Vessels Objective Provide the designers of twin-hull vessel structure with a practical design guide reflecting the knowledge gained by the U.S. Navy and the American Bureau of Shipping on the subject in recent years.
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Recommendations Perform the following tasks: · Develop a structural-design guide for twin-hull vessels that: · reflects the knowledge gained by the U.S. Navy and the Amencan Bureau of Shipping in the subject area in recent years; · focuses on practical information of direct value to the twin-hull ship designer; · presents design procedures, data, and algorithms; and · emphasizes loads prediction and present methods appropriate for early stage design in the absence of mode]
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Benefit The project will result in improved structural integrity and operational efficiency under extreme or unusual external loadings. SSC National Goals · Improve the safety and integrity of marine structures.
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· Review and recommend requirements for bridge information display and mon~tonng systems operation. Duration 1,000 labor hours over ~ year so
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-- a -A fir ~ Do ~ ~ ~ r ~~SSC Strategy Improved engineering analysis and evaluation Background The rational approach to structural design is based on a recognition of possible failure modes of a flawed member and determination of the margin of safety between the ultimate response of a member and its state at the time of analysis. Currently, techniques are available to estimate, quantitatively, the durability of a flawed structural member for a given service environment (load history, corrosive medium, and service temperature)
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From page 52... ...
The Failure Assessment Diagram compares the ultimate response of the i: i member with its state at the tune of analysis and estimates the margin of safety. Recommendations Perform the following tasks: · Develop a guide for engineers to perform damage tolerance assessment of potentially or actually flawed members in marine structures.
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From page 53... ...
This should include close coordination with Project SR-1354, "Grounding Protection of Tankers," the British Mantime Technology computer program for computing damage, and related research under the shipbuilding program and the double-hull investigations at the Carderock Division of the Naval Surface Warfare Center. · Derive guidelines from past and current studies for ma~miz~ng the structural resistance to seaway loads.
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From page 54... ...
SSC Strategies · Research of double-hull vessel technology · Prevention research including damage-tolerant structures · Improved eng~neenng analysis and evaluation Background: To reduce the risk of environmental pollution due to grounding and collision, the Oil Pollution Act of 1990 and the International Mantime Organisation mandated that new tankers be either double hulled or, according to the organization, equivalent Tom an of] outflow standpoint.
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From page 55... ...
The design of double-hull tankers to date has been based largely on conventional s~ngle-hull design practices, without optimizing the structural design to reduce risks of damage to outer hulls and pollution due to inner-hull rupture. There is a need to evaluate the damage resistance of current double-hull designs and to develop double-hull structural arrangements and details that minimize the possibility of premature hull rupture under low-energy collision and grounding impacts.
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From page 56... ...
Duration 2,000 labor hours over I.5 years 95-13 Two-parameter Approach to Fracture Prediction in Ship Structures Objective Explore the use of the two-parameter fracture-mechanics approach as it applies to ship structure components. Benefit The two-parameter fracture-mechanics approach allows the incorporation of planar constraint conditions into the fracture-prediction capability and allows a more accurate transfer of laboratory test results to the prediction of component fracture behavior.
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