At Todd Shipyard we use MAESTRO to plan heavy or unusual lifts on our drydocks, to plan lifting and turning of large structural modules, and especially to plan maintenance of our drydocks. The ability to model corrosion helps us get the most bang for our maintenance bucks. And their tech support
can’t be beat.
~ Esther Schmall
Guido Perla & Associates, Inc. (GPA) has been using MAESTRO since 1999 for a number of vessel designs that have been constructed and placed into service.
The initial project, also used for instruction and training in MAESTRO, was the SWATH AGOR ocean class research vessel, M/V KILO MOANA. This is a 182-foot, steel SWATH hull form currently operated by the University of Hawaii. The vessel is classed with the American Bureau of Shipping (ABS). Due to limited experience with this hull form, SWATH vessels require a “first principles” type of analysis for review and approval of the hull structure and deck house by the classification society.
The MAESTRO model of the hull and deck house, with all major structure, was developed from initial scantling calculations. Seaway loads were developed by a separate hydrodynamic code (WAMIT) and input to the MAESTRO model for several wave loading scenarios. The resulting global model was analyzed and numerous fine mesh models developed for critical areas. The analyses included detail stress concentration areas, areas requiring fatigue analysis, and buckling. Reports were submitted for review and approval by ABS.
A second project was a unique, 300-foot sternwheel passenger vessel, with full SOLAS compliance, for passage on the Inside Passage from Seattle to SE Alaska. Due to exposure to ocean wave conditions, a finite element analysis of the hull and superstructure was required to obtain a restricted ocean rating for this vessel from ABS and US Coast Guard. A full model of the hull, with sternwheel outrigger supports, and superstructure was developed. MAESTRO’s ability for imposing various wave profiles on the hull from any direction was used to develop the quasi-hydrodynamic loading conditions. Both global and fine mesh models were used in designing the hull and superstructure, particularly in way of large openings.
MAESTRO was also used on this project to evaluate vessel launching and dry docking. This vessel was also subject to several grounding accidents in the years following delivery. MAESTRO was instrumental in evaluating the damaged hull bottom structure, temporary repairs, and dry docking arrangements to the satisfaction of the US Coast Guard oversight salvage team.
Most recently, MAESTRO was instrumental in evaluating the structural design of a unique catamaran/SWATH hull form using only forward and aft crossbeams between the demi-hulls (instead of a typical cross deck structure along the length of the demihulls). The vessel is capable of reducing its draft by lowering a center barge section that provides additional displacement.
Because of the different vessel configurations, more than one FEA model of the vessel was required. Using appropriate substructures within MAESTRO, these multiple models could be readily developed.
MAESTRO’s hydrostatic balancing routines are able to handle multiple displacement bodies, which was necessary when evaluating the various components of the barge lifting and lowering system.
Wave loads were imported from a hydrodynamic code (WASIM) for 14 load cases, in addition to still water load cases, for analysis of the SWATH mode of operation.
The fine mesh modeler was used extensively in evaluating high stress areas including fatigue calculations. Also used was the Ultimate Limit State Analysis of Plated Structures (ULSAP) to evaluate a range of limit states (panel buckling, web tripping, etc.) throughout the structure.
Also unique to this vessel is ice navigation in the SWATH (twin hull) mode. Since classification rules for ice navigation are intended for monohulls, engineering evaluation was required in determining structural adequacy during ice navigation. Model tests in ice were undertaken and the measured loads applied in the MAESTRO SWATH model of the vessel.
All analyses were reviewed abd approved by ABS.
MAESTRO has also been used in evaluating the structure of a double-ended passenger/vehicle ferry for protected waters. In this project, there was a requirement to evaluate the hull and deck house in specified design wave conditions, which was readily undertaken with MAESTRO. Natural frequency models were also investigated and, based on the results, further evaluation was deemed necessary. The MAESTRO model was readily exported to a NASTRAN-type finite element program for forced vibration analyses.
Ship design is becoming more directed towards a “first principles” approach as opposed to a “rules” based approach. This has been found to be true for conventional hull forms in addition to the more unique vessel types that are evolving. MAESTRO has been found to be a unique tool in evaluating ship structures. In particular, the orthotropic stiffened plate structure that characterizes most vessels is readily handled by MAESTRO’s plate and beam elements. The ability to impose wave loads, from the program’s internal code or from imported loads, and balance the model with those loads, is important to accurately evaluate the “free body” that is a typical ship. MAESTRO incorporates a wide range of structure analysis, from calculated forces to various stresses, limit states, and natural frequency modes. The ability to develop a global model and proceed to fine mesh stress analysis facilitates evaluation of entire hulls and superstructures. This is a highly recommended program for any naval architecture/marine engineering firm.
~ Guido Perla & Associates, Inc. MAESTRO Experience
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