Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program (1995)

The Committee on Marine Structures (CMS) annual report outlines a coordinated research plan for the interagency Ship Structure Committee (SSC). The SSC is an interagency body through which the U.S. Coast Guard, Naval Sea Systems Command, Maritime Administration, Military Sealift Command, American Bureau of Shipping, Transport Canada, and Canadian Department of Defence coordinate their research on the structural integrity of marine structures. Technical coordination of the SSC is performed by the Ship Structure Subcommittee (SSSC). The SSSC is composed of four members from each member agency of the SSC. The research program of the SSC is intended to accommodate advanced concepts and long-range planning, as well as research in technology areas of materials criteria, loads and response, design methods, fabrication and maintenance, and reliability. The SSC has maintained a strong research program in ship structures for almost 50 years. This combined action and consensus of government agencies represents an indication of the importance to those agencies of continued research in ship structures.

The CMS recommendations embody a multiyear research planning program that makes recommendations for the research program of the SSC for fiscal year (FY) 1996 and FY 1997 (FYs 1996–97) and later and reviews research activities from FY 1995 and earlier years. The projects, though capable of standing alone as specific technology enhancements, are grouped into four thrust areas: producibility/competitiveness, reliability, inspection/maintenance, and composites. In addition, in order to maximize knowledge of potential follow-on projects, Appendix A describes those projects considered for out-year support of specific thrust areas.

The report contains five color-coded sections that comprise:

1. introduction, recommendations for the research program, and appendices B and C—white;

2. FYs 1996–97 project recommendations—green;

3. active and pending projects—yellow;

4. completed projects—blue; and

5. potential future-year projects (Appendix A)—beige.

The CMS provides advice that is independent and objective in accordance with the National Research Council process. However, the CMS does meet regularly with the SSC to ensure that the marine structures research that the SSC considers most important is considered in the recommendations of the CMS. The responsibilities of the CMS and its relationship to the SSC are more fully described in Appendix B. The CMS keeps abreast of major technical issues of interest to federal agencies and national programs in which marine structures research can have significant positive impacts. During its 1994 meetings, the committee discussed agency research and development programs that were presented at the Ship Structure Subcommittee spring meeting; the areas of national

interest that might be affected by CMS research recommendations; and special technical topics concerned with safety, reliability, structural maintenance, industry competitiveness, and advanced-materials technology. In order to provide proper visibility to the recommended projects, they are related as parts of total-program thrust areas that support SSC goals.

In September 1994, the CMS held its annual joint meeting with the Ship Structure Subcommittee to discuss research areas of most interest to sponsoring agencies, the strategic plan, and the future financial status of the SSC and its potential effect on CMS efforts. The CMS recognizes that research in ship structures is being sponsored independently by agencies with relatively large funds compared with those available to the SSC. The challenge to the CMS thus becomes one of developing and recommending meaningful and timely research programs that are complementary to these funded major programs and that will fill in gaps and provide initial guidance for, or otherwise enhance, sponsoring agency efforts. (In addition, the CMS recognizes that its recommendations can become the basis for establishing agency research programs.) For example, the Navy's Reliability-Based Structural Design Program stems from, and is supported by, the reliability thrust of the CMS.

In order to properly support the SSC, the CMS strives to maintain a balanced composition of expertise on the design and materials work groups. To ensure broad appeal among the sponsoring agencies and secure the benefits of relevant technologies and technology transfer, representation is obtained from all relevant technical disciplines, academia, the research community, and the marine industry.

The SSC unanimously endorsed a strategic plan on June 5, 1992, and this approved plan as amended in May 1994 is reproduced in its entirety in Appendix C. The CMS project recommendations are keyed to the national goals and specific strategies addressed in the SSC Strategic Plan. However, periodic review and revision of the strategic plan by the SSC will keep the plan abreast of changing circumstances.

In November 1993, the SSC approved publishing a biennial, rather than an annual, report of research recommendations. This step had two potential benefits: first, encouragement of multiyear contracts, thus streamlining the contracting process; and second, a potential for advice that is more cost-effective. This document is the first biennial report.

For the SSC research program for FYs 1996–1997, the current report recommends 20 research projects that fully support the strategic plan and its stated goals and strategies. Also included (in Appendix A) are 19 potential follow-on projects for later years in the 4 specific thrust areas.

In the following sections, projects designated with an “SSC-” prefix are published SSC reports; those designated with an “SR-” prefix are currently being funded; those with a “96-” prefix are recommended for FYs 1996–97, those with a “96D-” prefix are out-year potential projects proposed by the Design work Group, and those with a “96M-” prefix are out-year potential projects proposed by the Materials work Group

that are recommended in this FYs 1996–97 report. Many of these proposed projects are recommendations from the CMS reports for FYs 1994 and 1995 that have been reviewed and either were found to be relevant as written or were rewritten to reflect changes in the technology. These continued projects have their previous number appended to their titles. The designation “TC” refers to projects recommended by Transport Canada rather than by the work groups.

The approved SSC Strategic Plan is reproduced in its entirety in Appendix C. This section of the report presents the considerations of the CMS in focusing on the national goals as defined in the strategic plan and in supporting the strategies for the 1990s as defined in the plan. As mentioned earlier, each project recommended herein is related to at least one specific goal and strategy. But more significantly, rather than present a group of isolated projects, the CMS has grouped the recommended projects into thrust areas that support the overall strategic plan, thus providing a framework to consolidate and focus the efforts. The thrust areas were developed to support the three SSC national goals:

Goal 1. Improve the safety and integrity of marine structures;

Goal 2. Reduce marine environmental risks; and

Goal 3. Support the U.S. and Canadian maritime industries in shipbuilding, maintenance, and repair.

As expressed in the strategic plan, the SSC is interested in leveraging its limited funds by means of joint-industry projects and by independent support. Industries, agencies, and research committees should contact the executive director of the SSC if they are interested in projects listed in this report and are willing to sponsor and fund a project, or cosponsor and share costs.

The research projects proposed herein are all capable of standing alone. However, in order to exploit synergy and make the whole greater than the sum of the parts, they are grouped into thrust areas representing total program approaches to the specific area under consideration. The committee recognizes that in light of funding constraints completion of all phases of a thrust area may require a number of years of research. Also, technology advances can accelerate completion or indicate the need for additional projects over time for a specific thrust area. The successful completion of all necessary projects for a thrust area should result in a specific, defined deliverable that can be implemented by the technical community as a criterion/standard.

All thrust areas in the recommended research plan support at least two national goals of the SSC Strategic Plan, and one supports all three goals. The specific thrust areas and the goals they support are shown in the following figure, where the shaded area represents the SSC national goals addressed by each thrust area.

The SSC Strategic Plan identified a decline in the North American merchant marine industry and developed the goal to “support the U.S. and Canadian maritime industry in shipbuilding, maintenance, and repair.” Past recommendations of the CMS and research projects conducted by the SSC included projects to increase the ease of fabrication and to improve productivity. In the recommendations for FY 1994, the CMS developed a thrust area in producibility/competitiveness. This thrust area seeks to improve industry competitiveness in ship design, construction, and repair. The ship design process needs to be changed to reduce design time and cost; to improve design quality, including producibility; to reduce design errors; and to produce ships that yield enhanced producibility, performance, and operability at lower life-cycle costs.

Recent surveys project a steady growth in world trade during the 1990s. As a leading industrial nation, the United States will benefit from increased export and import of raw materials and manufactured products. At the same time, world shipbuilding costs have risen, and the delivery dates for new ships have been extended as building berths have become filled. Increasing demand for merchant ships presents an opportunity for the United States as a shipbuilder to regain its stature as a leading maritime nation. In this regard, the President of the United States has initiated a plan to provide a transition from the military to the international commercial market.¹

In support of Goal 1—to improve safety and integrity—certain producibility/competitiveness capabilities are required to ensure that safety and integrity

are improved while keeping the cost the same or reducing the costof ship structural design and construction:

• Improved design tools and information systems need to be developed, including computer-aided design, design and manufacturing information, and expert systems.

• Regulations need to be continuously reviewed and upgraded to reflect technological advances.

• Reliability-based design techniques to optimize material use need to be developed.

• Principles of design for production need to be adopted.

• Research on design tools, producibility, production processes, reliability-based design, and damage-tolerant structures needs to be sponsored, and professional education in these fields needs to be enhanced.

In support of Goal 3—to support the U.S. and Canadian maritime industries in shipbuilding, maintenance, and repair—the preceding items as well as the following producibility/competitiveness items are needed:

• Ship repair and construction capability need to be made viable. Repair time and material costs must be reduced and labor efficiency improved.

• The maritime industry needs to adopt the worldwide measurement standard System International to become competitive in the world market. Research is needed to identify and take advantage of that change so as to improve the competitive position of the United States in U.S. ship design and construction.

• Labor hours and material costs for construction need to be drastically reduced to restore a viable production capability for new merchant ships. To achieve this, improvements in production technology and production processes must be developed. Examples of these improvements include laser alignment, faster welding techniques, improved accuracy control, the use of robotics, automated material handling, and automated storage equipment.

On June 17, 1987, the CMS convened an ad hoc committee with experts in the subject areas of marine structures and structural reliability. The consensus of that group was that the SSC should have a long-range program in reliability to develop a probability-based design approach for ship structures. Following that meeting, the CMS formulated a four-phase program, which began in FY 1989. This program has been modified since that time to reflect the results of the first phases and to add a fifth and a sixth phase, but it remains a principal thrust area of the CMS.

The SSC also is committed to supporting the reliability thrust. The goal is development of technology to support preparation of a probability-based design code for ships. The program is described later in the section on reliability in the chapter on research program development. Because reliability-based design criteria promise to

improve structural efficiency, a U.S. Navy panel is studying this approach. Reliability projects proposed for SSC funding provide a sound basis for a much larger, three-pronged effort that would include computer simulation, towing-tank tests, and full-scale trials. Predicting environmental loads and the responses of complex marine structures is extremely difficult. Because assumptions and simplifications are frequently introduced, uncertainty and risk can follow. A research program initiated by the SSC to develop design criteria for marine structures is addressing uncertainties in loads. Many other research projects in structural reliability supported by the SSC either have been or are being completed. At this time, it would be advantageous to provide a synthesis of the projects in the reliability thrust area, as well as in other related SSC projects, and the most recent developments in structural-reliability technology that are likely to impact analysis and design of marine structures. This thrust area is expected to develop the fundamental reference for (1) the development of a probability-based ship-structure design code, (2) the definition of procedures for performing failure analysis, and (3) reliability analysis for existing ships.

In order to ascertain the large uncertainties associated with visual inspection data, and thus improve the ability to make fatigue reliability assessments, Project SR-1375, Detection Probability Assessment of Visual Inspection of Ships," will develop a probabilistic model of visual inspection. Completion of this project will improve the use of fatigue reliability in design and supplement the research project on ship inspection issues under Project SR-1355, “Inspection of Marine Structures.”

In support of Goal 1—to improve safety and integrity—reliability research goals should include:

• improved methods of predicting hydrodynamic loads and structural response of ships in extreme seas;

• improved methods of predicting fatigue stresses in structural components and details;

• improved descriptions of material properties, including fracture, corrosion, and fatigue of common marine steels; and

• development of structural-reliability theory, application to existing designs, and development of probability-based design criteria.

In support of Goal 2—to reduce environmental risks—reliability marine activities must be based on environmental-protection criteria and procedures that will remain effective throughout the life cycle of a structure or project. In the past, inadequate criteria and procedures resulted in environmental damage and loss of natural resources, public support, and productivity.

Enhanced environmental protection can be realized with improved criteria and improved procedures for designing, fabricating, operating, inspecting, and maintaining ships, offshore structures, and marine systems. Structural-research projects that will enhance environmental protection must be pursued in the areas of:

• double-hull technology;

• damage-tolerant structures; and

• the effect of human factors on the reliability of marine structures.

With the increasing number of aging ships and concomitant greater need for repair, life-cycle maintenance of ships grew to equal importance. As a result, the CMS incorporated a thrust area on inspection/maintenance in its recommendations for FY 1994.

Recommended research efforts will focus on inspection and repair strategies for aging ships. Development of improved inspection techniques for in-service structural monitoring is needed, as well as analytical methods for assessing the effects of corrosion, flaws, and other strength defects. Also, development of effective localized repair methods for critical defect areas is needed.

In support of Goal 1—to improve safety and integrity—inspection/maintenance research is needed in the areas of:

• determination of performance properties of coatings and other structural preservation techniques; and

• determination of corrosion rates for materials under various marine environmental conditions.

In support of Goal 2—to reduce environmental risks—inspection/maintenance research is needed in the areas of:

• structural monitoring; and

• blasting and coating application techniques.

In support of Goal 3—support the U.S. and Canadian maritime industries in shipbuilding, maintenance, and repair—the following inspection/maintenance items are needed:

• Ship repair and construction capability must be made more economically viable through improved inspection techniques.

• Repair time and material costs must be reduced and labor efficiency improvedthrough improved repair techniques such as new methods of underwater wet welding.

• Better ship inspection and repair methods must be developed such as better means of assessment of coating systems and and the extent of corrosion.

On September 25–26, 1990, the Marine Board of the National Research Council convened a National Conference on the Use of Composite Materials in Load-Bearing Marine Structures. This conference brought together leaders from industry, government,

and academia to exchange ideas and lay the groundwork for future marine applications of composite materials by U.S. industry. The conference drew enthusiastic participation and was highly productive. Its recommendations are reported in a two volume report of the National Research Council.² As a result, the CMS adopted a thrust area in composites in its recommendations for FY 1994, so that the advantages of composites may be more fully realized in marine structures.

New materials and variations on existing materials offer opportunities for improving marine structures. Current emphasis is on fiber-reinforced plastics and related composites. In recent years, the use of these materials in the primary structures of vessels less than 60 meters long has increased substantially, and many navies are introducing a new class of fiber-reinforced plastic coastal minehunters. New composite materials may have potential applications to larger marine structures, which would take advantage of their increased specific stiffness and strength and resistance to corrosion. Graphite, ceramic, and aramid composites, in addition to glass, should be evaluated for special structural components.

The use of composite materials presents a special challenge to the designer. The many material parameters that can be varied, including the basic fiber and matrix materials, require engineering analysis to determine the most efficient design. The use of composites and their design methodologies is relatively well documented in the aerospace industry. Report SSC-360, “Use of Fiber Reinforced Plastics in the Marine Industry,” provides a survey and assessment of the uses of fiber-reinforced plastic materials. As newer generations of materials, such as fiber-reinforced plastics, are introduced into the marine industry, new analytical techniques need to be developed and verified to address structural integrity. The structural integrity of novel materials is strongly affected by processing. Understanding the necessary interrelationships may require material-property data beyond that which has been historically available.

To expand understanding of these interrelationships requires further evaluation of expertise and design techniques used in aerospace and other industries and of ways to adapt them to marine structures. To accomplish this, the CMS prepared project descriptions in response to the recommendations of the proceedings of the National Conference on the Use of Composite Materials in Load-Bearing Marine Structures. The first of these, Project SR-1367, “Design Guide for Marine Applications of Composites,” was recommended by the CMS in 1993 as the initial project in this thrust area.

In support of Goal 1—to improve safety and integrity—research in composites is needed to address safety and integrity with respect to corrosion, fire, and toxicity.

In support of Goal 3—to support the U.S. and Canadian maritime industries in shipbuilding, maintenance, and repair—research in composites needs to be coordinated and advanced for the determination of performance properties of anisotropic composite materials that will be used increasingly by the marine industry.

Table 1 relates the recommended projects for FYs 1996–97 to the thrust areas and identifies the technology area under which they will be discussed in the section on research program development. The individual project recommendations were developed by the work groups on the basis of technology area, but the process of evaluation by the CMS reflects concern for the thrust areas. For this and other reasons, an individual project may address more than one technology area, as well as more than one thrust area, SSC national goal, and SSC strategy. This may lead to some confusion in reading the report, but the effort has been to develop an integrated program that addresses multiple objectives.

In Table 1, and all other tables, a project that has been carried over from last year's recommended research has the previous project number indicated following the title of the project.