STRUCTURAL ENGINEERING AND DESIGN

Structural Engineering and Design

Structural Engineering and Finite Element Analysis

Gibbs & Cox, Inc.'s experience in performing surface ship structural analysis is probably the most extensive available. Gibbs & Cox, Inc. has worked closely with shipyards, NAVSEA technical codes and Direct Reporting Program Managers (DRPMs) to provide support in all areas of structural analysis. Our corporate structural analysis experience covers concept, feasibility, contract, and detail design work, including design and producibility trade-off studies. Our experience is supplemented by extensive interaction with the NAVSEA structures code and in direct support of the PMS directorates to resolve emergent structural problems which develop over the lives of in-service ships throughout the fleet. Our capability is extended to commercial (ABS, AISC, DNV) design practices as well.

Our engineers have extensive capabilities in analyzing complex structures using state-of-the-art Finite Element modeling software. This capability includes use of structural analysis software such as MSC/NASTRAN, STRUDL, FEMAP, ANSYS, STARDYNE, and NISA to enhance proven engineering methods for the assessment of structural integrity.

Analytic capabilities include a wide range of finite element analyses and first principles engineering for steel, aluminum and composite materials including the following:

Vibration.

Gibbs & Cox, Inc. has extensive experience in vibration analysis, routinely using finite element models to evaluate multi-mass systems. Examples include, but are not limited to:

• DDG51 foundations; vibration analysis for input to noise and shock analysis and to ensure absence of resonance with equipment or propeller forcing functions. Development of compound mounting for noise and vibration attenuation.
• DDG51 mast analysis for global mast structure and equipment foundations.
• DDG51 VLS foundation, involving interaction with Martin Marietta's model for the VLS structure and fine-tuning foundation frequency characteristics to mitigate shock loads.
• CG47 mast analysis, to correlate measured shock trial data with analytical predictions.
• T-AGM 23 OBSERVATION ISLAND - vibration analysis of COBRA JUDY rotating phased array radar turret and ship support structure as well as smaller radar installations on the deckhouse.

Ship Structures Committee Project.

Gibbs &: Cox, Inc. investigated the effect of high strength steels on the design of construction details of ships for the Ship Structures Committee under contract to the U.S. Coast Guard. The task concentrated on commercial vessels and naval ships to catalog specific structural details with problems; examine the details for workmanship, ability to construct and response to in-service loads; evaluate stress patterns for the failure modes of yielding, buckling and fatigue; and provide improved details and the methodology to examine other details. By identifying the problems associated with the use of HSS, design guidelines were established for new construction that will reduce the number of failures. Structural design details and construction practices were presented to reduce these failures.

Composite Structures.

In addition to our background in conventional ship structures, Gibbs &: Cox, Inc. has extensive experience and capability in the analysis, development, and design of composite materials for general marine structural applications. The company authored a design manual on composite applications for small boats and undertook a number of design studies investigating composite structures for larger ships including a cargo ship. In a completed study for the U.S. Navy, we assessed the feasibility of using state-of-the-art FRP technology to fabricate a surface combatant in the 100 meter, 1200 ton size range. The company has been a principal in the assessment and design of composite structure and outfit items for naval ship applications. These range from maintenance enclosures and masts to entire deckhouses. Also included in these efforts is the development of a detail design for a filament-wound motor whaleboat as a prototype for applications of technology to larger hulls. Gibbs &: Cox, Inc. is recognized as an authority on the use of fiber reinforced plastics in the marine industry.

Structural Design

Gibbs & Cox, Inc. expertise in the field of structural design concentrates on, but is not limited to, the following major areas:

• Design of primary hull girder for longitudinal bending, local loading and nuclear airblast
• Design of decks, bulkheads, superstructure and other hull structure for applied static and dynamic loads, including airblast, helicopter landing and weapons effects
• Structural arrangement, framing and details of shell plating, decks and platforms, structural bulkheads, joiner work and stanchions
• Preparation of welding schedules and typical details
• Castings, such as bow chocks, anchor bolsters, shaft struts, etc.
• Foundation development considering operating loads, shock, noise and vibration
• Masts
• False decks and gratings.
• Hull appendages such as Sonar Domes, Fairwaters and Fairleads, Stern Flaps and Bilge Keels

Structural design is accomplished in accordance with the unique Ship Specifications, contract level documentation, project peculiar documents and design standards such as MIL-standards and Design Data Sheets (DDS). Close interfacing with structural engineering personnel is obviously essential. Gibbs & Cox, Inc. has extensive structural design experience using various types of structural materials including steel, aluminum and bi-metallics. Structural steels used in design include Ordinary Strength (OS), High Strength (HS), High Yield (HY-80 and HY-100) and High Strength Low Alloy (HSLA) steels. Aluminums include the 5086, 5454, 5486, 6061 and 6063 series.

Our designs are usually developed using 2-D and 3-D CAD modeling tools which includes AutoCAD, Computervision,

Recent Structural Design Efforts have included the following:

Littoral Combat Ship preliminary design Gulf Coast Regional Tech Center MAFO doors shipboard integration In-service structural damage assessment of CG 47 class cruisers FFG 7 class frigate derivative detail design (Taiwan, Australia) Structural design of double-hull product tanker Structural design of 150,000 Cubic Foot Sludge Vessel Design of shock-mounted platforms to isolate commercial-off-the-shelf equipment from shock loads Studies of composite structural applications for surface combatants, including design of a 1200 Ton composite corvette