One of the principle objectives of the project is to reduce construction weight of the CVN(x) and similar naval vessels. With this in mind, it is important to consider all loads influencing members scantlings. Some of the member scantlings are governed by local rather than global loads. Because of this concern, both local and global environmental loads will be investigated in this project if awarded to Mansour Engineering, Inc. In Phase I of the project, an operational profile will be constructed for the CVN (x) in consultation with NAVSEA and NSWCCD personnel, consistent with her service life requirements. Based on the operational profile and wave statistics in areas of operation, a multi-dimensional matrix of sea state (H1/3, Ta), heading angle (0), ship speed (V) and loading condition (W) will be established. A probability of occurrence of each "cell", i.e., each combination of (H1/3, Ta, q, V, W) will be estimated. The time domain computer program LAMB will be used to obtain the response of the ship in each "cell". The response shall include ship motion, global loads such as vertical and lateral bending moments as well as local loads in the various regions of the hull. As much as possible, slamming loads will be included. Long term distribution of ship motion and global and local loads will be determined, and from these, life time extreme values will be estimated. These values may be used as design loads or for guidance in determining member scantlings. Mansour Engineering, Inc. has been awarded and successfully conducted similar work in SBIR project "Reliability of Ship Structures," SBIR N00024-94-C- 4059. In Phase II of the project, the strength aspects will be developed, including appropriate limit state equations for global and local structure requirements. As much as possible, the effect of fabrication imperfections on member strength will be included in the limit state equations. Mansour Engineering, Inc. has been awarded and has successfully conducted an SBIR project on this subject, "Structural Fabrication Tolerances and Structural Details," SBIR contract no. N00024-96-C-4123. In Phase III of the project, a weight optimization of the midship section will be conducted based on the extreme loads developed in Phase I and the limit state equations developed in Phase II. The proposed principal investigator, Dr. Alaa E. Mansour has conducted a similar study titled "Reliability-Based Method for Optimal Structural Design of Stiffened Panels," Journal of Marine Structures, Vol. 10, No. 4, June 1997. In addition to the principal investigator, there will be co-workers specialized in Naval ship technology including Dr. Robert Sieleski and Dr. Woei-Min Lin who was responsible for the development of the LAMP software at the Science Applications International Corporation.
Benefits: Significant weight savings in construction of the CVN (x) and similar USN ships are expected if it is demonstrated that an optimized midship section can be achieved with no decrease in structural integrity relative to an existing carrier. This has been demonstrated in other engineering fields (offshore, civil and mechanical) where weight savings can be accomplished when reliability-based structural design methods and optimization techniques are used. The proposed principal investigator is currently conducting a reliability-based study for ABS to reduce structural weight in the design of bulk carriers in order to modify Safe Hull Rules.
Keywords: Long term load distribution, Ship structural design, Structural weight optimization , Life time extreme loads, Reliability
