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FlagShip’s structural design capability is based
on MAESTRO, an integrated ship structural modeling, analysis, and optimization
system. MAESTRO combines rapid ship-oriented ship structural modeling, large scale
global and fine mesh finite element analysis, structural failure evaluation, and
structural optimization in an integrated yet modular software package. MAESTRO’s
core capabilities represent a system for rationally-based optimum design of large, complex
thin-walled structures, although MAESTRO is also capable of
performing local analyses. In essence, MAESTRO is a synthesis of finite element
analysis, failure, or limit state, analysis, and mathematical optimization, all of which
is smoothly integrated under a user-friendly graphical interface.
MAESTRO is fully integrated with the ALPS system of limit state analysis,
developed by Professor Jeom Paik from the Pusan National University. Please
click here for further information on the
ALPS software.
MAESTRO can be used to analyze and design many types of thin-wall stiffened
structures, and has been used for virtually every type of ship from large tankers,
container ships and bulk carriers to high speed ferries, multi-hull vessels, and SWATHs,
as well as smaller vessels such as fishing vessels and patrol craft. MAESTRO’s
modeling and analysis capabilities are not geometrically limited in any sense so that any
type of geometry or structural configuration can be accommodated by MAESTRO.
MAESTRO’s basic capabilities fall into
seven categories:
Rapid Structural Modeling
The MAESTRO Modeler is an interactive graphics tool that
allows a rapid creation of a full ship or other structure finite element model, typically
in days rather than weeks or months. The MAESTRO Modeler uses the
notion of a stiffened panel as the basic building block for the model.
Stiffened panels typically span frame to frame and from one primary
longitudinal member to the next. Any element in the model (stiffener,
girder, plate, stanchion, etc.) can be chosen from a customizable library of
standard parts. The properties of any element can be changed at any point in
the modeling process; for example, if the analysis shows an area of
unacceptably high stress, the user can simply right-click on the affected
elements, and change the properties of those elements. The analysis is then
re-run, and in a matter of seconds, the effects of the design change can be
seen. During the design process, this ability to rapidly modify the
scantlings can save many hours.
back
Ship-Based Loading
MAESTRO offers a
ship-oriented, flexible and highly automated specification of loads which are
realistically applied by MAESTRO to the structural model. The MAESTRO
modeler allows the user to define multiple load cases with various
combinations of any of the following load types:
-
Lightship Mass Distribution: The Lightship Weight
Distribution curve may be easily matched by specifying the weight per unit
section which can vary along the length of the ship.
-
Hydrostatic Loads: The user may specify any waterline,
optionally with a wave profile and heading, and MAESTRO will
automatically apply the hydrostatic pressure to the hull.
-
Tank Loads: Tanks may have their loads specified by various
methods, including percentage full, head, soundings, or by simply specifying
the mass.
-
Cargo Masses: The user may define the footprint and specific
mass of cargo and other significant load items.
-
Accelerations: In addition to the acceleration due to
gravity, MAESTRO allows the user to apply a rotational or
translational acceleration to model.
-
Pressure Loads: A constant pressure plane or linearly
varying pressures can be applied to the model.
-
External Bending Moments and Shear Forces: If only a portion
of the ship is being analyzed (e.g. 3 holds), the user can apply external
bending moments and shear forces to the ends of the model.
-
Boundary Conditions: The model can be restrained in 6
degrees of freedom to prevent rigid body motion.back
Finite Element Analysis
This is
usually applied to the complete structure, and deflections and stresses are determined for
all principle structural members and for all load cases. The results of
MAESTRO's FE solver have been
verified against various
other industry-standard solvers, and for most ship models will produce
results more quickly.back
Structural Evaluation
The next major capability of MAESTRO is the structural evaluation, or failure analysis, where each of the
principal structural members are evaluated subsequent to the finite element analysis for
all possible failure modes. The principal structural members of the global MAESTRO
model typically includes all of the stiffened panels and their associated beams,
transverse frame segments and longitudinal girders. These failure modes address yielding,
buckling, plastic hinge formation, and other major failure modes and design limits such as
deflections. There are a total of 25 failure modes at the individual principal structural
member level, and 10 at the overall or multi-member level. The failure analysis provides a
quantified evaluation of each of these failure modes for each principal structural member,
for each load case that is being analyzed. This is the most powerful such failure
evaluation capability available to the ship structural engineer, and results in a high
level of information that identifies structural problems associated with events such as
buckling. These structural failure evaluations are used by the structural engineer to
assess the adequacy or degree of conservatism that is represented by the design, and are
also used by MAESTRO as constraints for the structural optimization.
MAESTRO offers two failure mode calculation methods; the first is
based on Professor Owen Hughes' "Ship
Structural Design: A Rationally-Based, Computer-Aided Optimization Approach"
textbook, while the second, known as ULSAP, is based on theory presented in
the book "Ultimate Limit State
Design of Steel-Plated Structures", by Professor Jeom Paik and A.K.
Thayamballi. Professor Hughes' method is suitable for panels with stiffeners
in one direction, while Professor Paik's method is suitable for a true
grillage.
back
Optimization
The next major capability of MAESTRO is its structural optimization,
which is based on a designer-specified optimization objective of least
weight, least cost, scantling limit, or any weighted combination of these. MAESTRO
interactively revises the structural design at the level of the principal member
scantlings to achieve the optimum solution. The optimized design provides the required
safety margins against all of the structural failure modes. These safety margins are
controlled and specified by the user.back
Fine-Mesh Analysis
The Fine-Mesh Analysis feature offers two options to meet your fine-mesh
analysis needs: Top-down and Embedded.
The Top-down option is a two-step analysis that creates a
separate fine-mesh model with imposed boundary displacements via the
MAESTRO global coarse mesh results. The user can create multiple
fine-mesh models within one global model, allowing the user to review
design-change decisions without re-loading other models.
The Embedded option is a one-step analysis that “embeds” the
fine-mesh model into the coarse-mesh model via rigid spline connections.
During this process the “master elements” are deleted and replaced with a
fine-mesh model. Therefore, the coarse-mesh and fine-mesh models are solved
together. The embedded analysis is more accurate than the top-down analysis
because the global results are closely coupled with the fine-mesh model.back
Natural Frequency Analysis
MAESTRO can compute the natural frequency of the ship in either air
or water. When the analysis is done in water, the added mass of the water is
automatically applied to the wetted elements.back
A further capability of MAESTRO is the translation of the global finite element
model to other formats, such as translation of the structural model into a NASTRAN model.
MAESTRO’s output consists of graphics associated with the structural
models, displacements and stress data associated with finite element analysis, structural
evaluation adequacy parameters which are quantified evaluations of each of the 35 limit
state evaluations conducted by MAESTRO, as well as deformation and stress data
associated with the detailed stress analysis module. All of this data is available both
graphically and in tabular formats. The MAESTRO graphics system allows immediate
user access to all of this data, and full flexibility for searching against various
criteria for stress and failure evaluation data.
MAESTRO uniquely combines rapid structural modeling, ship-based
loading, ship oriented finite
element analysis, limit state or failure mode evaluations and structural optimization in a
highly integrated form that represents a unique, efficient and powerful system for
designing ship structures.
MAESTRO is intended to introduce structural analysis, failure evaluation, and
optimization into the ship design process at much earlier stages than finite element
analysis has routinely been used. The structural model and MAESTRO’s global,
as well as fine mesh analysis capabilities, can then support each phase of design
through final design and even then into detail level design. MAESTRO is also being
used extensively for repair design, as well as life-cycle structural maintenance. |
