Safety as Objective in Multicriterial Structural Optimization

2010 ◽  
Author(s):  
Vedran Zanic ◽  
Stanislav Kitarovic ◽  
Pero Prebeg
Keyword(s):  
Failure Modes ◽  
Design Procedure ◽  
Material Design ◽  
Design System ◽  
Stiffened Panel ◽  
Safety Measures ◽  
Multicriterial Optimization ◽  
Design Variables ◽  
Standard Design ◽  
Longitudinal Strength

Multicriterial design methodology with safety as one of the design objectives is presented. The aim of the paper is to analyze the influence of safety based design objectives on generated nondominated designs on the Pareto frontier. Possible improvements in nondominated designs are investigated by comparison to ones obtained with the standard design procedure when safety criteria are used as design constraints only. It is assumed that safety based objectives and targets act as attractors, driving nondominated designs along the constant cost/weight contours in design space towards its safer regions. Global safety objectives (for hogging/sagging modes), are based on the maximization of ultimate longitudinal strength in vertical bending calculated via the extended IACS incremental-iterative method. Applied compound safety measures for gross-panel (stiffened panel with associated girders) are based upon 34 failure modes, belonging to serviceability/collapse subsets. Objectives based on the maximization of safety measures are applied together with standard design objectives such as minimization of initial cost and weight. The following problems were solved with different sets of objectives: (a) minimize cost and weight objectives subject to safety constraints (used for reference), (b) only the maximization of local safety measures is added to (a) as additional objectives, (c) only the maximization of global safety measures is added to (a) as additional objectives, (d) maximization of safety measures ad (b) and (c) are added to (a) as additional objectives. For each of the problems (a–d) the developed design procedure is executed. It contains two basic tasks for structural design of realistic (non-academic) problems: (1) multicriterial optimization with topology / geometry design variables; (2) multicriterial optimization of gross-panels with scantling / material design variables. Design procedure steps are executed using a fast and balanced collection of analysis and synthesis modules/methods of the OCTOPUS design system: • Determination of design load sets; • MOGA / MOPSO based generation of nondominated designs for the selected ship structure; • For each design the following analysis blocks are executed: – calculation of ship’s primary and racking response fields, – calculation of ship’s ultimate longitudinal strength, – calculation of serviceability and collapse safety criteria on the gross-panel level. Comparisons of results, based on generated Pareto hyper-surfaces and on subset of preferred designs, are given for problems (a–d). Insights into the results of optimization process, using 5-D graphics for design and attribute spaces, are also presented. Design problems of modern RoPax and SWATH structures are used in case studies.

Reliability and Robustness Based Design Attributes for Multi-Criteria Decision Making

2013 ◽  
Author(s):  
Vedran Žanić ◽  
Karlo Pirić ◽  
Stanislav Kitarović
Keyword(s):  
Design Methodology ◽  
Structural Model ◽  
Design Procedure ◽  
Design Parameters ◽  
Design System ◽  
Concept Design ◽  
Design Attributes ◽  
Standard Design ◽  
Reliability And Robustness ◽  
Panel Design

Novel design methodology with inclusion of reliability and robustness-based design criteria is presented. Robustness is defined as the insensitivity of a design attribute to uncontrollable design parameters. The developed design procedure for the concept design phase is divided into two basic, coordinated tasks: (1) multi-criteria topology/geometry optimization of the ship structural model; (2) scantlings / material multi-criteria optimization of structural panels. Reliability criteria and robustness of design attributes are applied as relative measures of quality, besides standard design attributes such as costs and weight. They are used in generation of Pareto-optimal design variants. Reliability attributes used for the panel design are compared with respect to fidelity and computational efficiency. A novel method for fast reliability calculations is presented using dimension reduction method (DRM) as implemented into FASTREL software. The method is verified with respect to accuracy and speed on the box girder design and panel design with CalREL methods (MC, FORM). The design procedure steps are executed in the predefined sequence of design sub-problems, using the fast and balanced collection of analysis and synthesis modules/methods of the MAESTRO/OCTOPUS design system. They are as follows: • Probabilistic determination of design loads; • Calculation of the structural serviceability and ultimate strength criteria on the panel (macro-element) level; • Calculation of the cross section ultimate longitudinal strength criterion; • Calculation of reliability and robustness measures on the panel level (safety) and on the global level. Other design attributes (initial cost, structural weight, etc.) are also determined; • Generation of the Pareto frontier for the selected test structure based upon the cost–safety design paradigm; • Generation of insight into the multilevel optimization process with graphic presentation of designs in design and attribute spaces. Practical application of the developed concept design methodology and of the design environment to the structural design of modern multi-deck ship elements (panels) is presented for verification/validation of accuracy and speed of FASTREL module.

Bending Stiffener Design Through Structural Optimization

2009 ◽  
Author(s):  
Rafael Loureiro Tanaka ◽  
Lauro Massao Yamada da Silveira ◽  
Joa˜o Paulo Zi´lio Novaes ◽  
Eduardo Esterqui de Barros ◽  
Clo´vis de Arruda Martins
Keyword(s):  
Optimization Problem ◽  
Design Procedure ◽  
Complex Task ◽  
Load Case ◽  
Shear Forces ◽  
Design Variables ◽  
Curvilinear Coordinate ◽  
Regular Design ◽  
Curvature Deformation ◽  
Flexible Risers

Bending stiffeners are very important ancillary equipments of umbilicals or flexible risers, since they protect the lines from overbending. Their design however is a complex task, since many load cases must be taken into account; the structure itself has a section that is variable with curvilinear coordinate. To aid the designer in this task, optimization algorithms can be used to automate the search for the best design. In this work an optimization algorithm is applied to the design of the bending stiffener. First, a bending stiffener model is created, which is capable of simulating different load case conditions and provide, as output, results of interest such as maximum curvature, deformation along the stiffener, shear forces and so on. Then, a bending stiffener design procedure is written as an optimization problem and, for that, objective function, restrictions and design variables defined. Study cases were performed, comparing a regular design with its optimized counterpart, under varying conditions.

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

Analysis of Stresses and Strains in Packed Stuffing-Boxes

2014 ◽  
Author(s):  
Mehdi Kazeminia ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Design Procedure ◽  
Standard Test ◽  
Packing Material ◽  
Test Procedures ◽  
Analytical Methodology ◽  
Packing Materials ◽  
Standard Design ◽  
Packing Rings ◽  
Leak Tightness ◽  
Side Walls

Packed stuffing-boxes are mechanical sealing systems that are extensively used in pressurized valves and pumps. Yet there is no standard design procedure that could be used to verify their mechanical integrity and leak tightness. It is only recently that standard test procedures to qualify the packing material have been suggested for adoption in both North America and Europe. While the packing contact stress with the side walls is predictable using existing models there is no analytical methodology to verify the stresses and strains in the stuffing-box housing. This paper presents an analytical model that analyzes the stresses and strains of all the stuffing box components including the packing rings. The developed model will be validated both numerically using FEM and experimentally on an instrumented packed stuffing box rig that is specially designed to test the mechanical and leakage performance of different packing materials.

STAEBL/General Composites With Hygrothermal Effects (STAEBL/GENCOM)

1988 ◽  
Vol 110 (2) ◽  
pp. 301-305
Author(s):  
R. Rubinstein
Keyword(s):  
Composite Laminates ◽  
Fiber Composite ◽  
Thickness Distribution ◽  
Turbine Blades ◽  
Material Design ◽  
Computer Code ◽  
Forced Response ◽  
General Description ◽  
Blade Thickness ◽  
Design Variables

A computer code has been developed to perform structural optimization of turbine blades made from angle ply fiber composite laminates. Design variables available for optimization include geometric parameters such as blade thickness distribution and root chord, and composite material parameters such as ply angles and numbers of plies of each constituent material. Design constraints include resonance margins, forced response margins, maximum stress, and maximum ply combined stress. A general description of this code is given. Design optimization studies for typical blades are presented.

scholarly journals An Innovative Optimization Design Procedure for Mechatronic Systems with a Multi-Criteria Formulation

2021 ◽  
Vol 11 (19) ◽  
pp. 8900
Author(s):  
Cuauhtémoc Morales-Cruz ◽  
Marco Ceccarelli ◽  
Edgar Alfredo Portilla-Flores
Keyword(s):  
Optimization Design ◽  
Optimization Problem ◽  
Heuristic Algorithms ◽  
Design Procedure ◽  
Concurrent Design ◽  
Mechatronic Systems ◽  
Design Variables ◽  
One Step ◽  
Task Oriented ◽  
And Task

This paper presents an innovative Mechatronic Concurrent Design procedure to address multidisciplinary issues in Mechatronics systems that can concurrently include traditional and new aspects. This approach considers multiple criteria and design variables such as mechanical aspects, control issues, and task-oriented features to formulate a concurrent design optimization problem that is solved using but not limited to heuristic algorithms. Furthermore, as an innovation, this procedure address all considered aspects in one step instead of multiple sequential stages. Finally, this work discusses an example referring to Mechatronic Design to show the procedure performed and the results show its capability.

scholarly journals Design and Optimization of Lug Bracket Assembly

2021 ◽  
Vol 13 (1) ◽  
pp. 55-67
Author(s):  
G. GOWTHAM ◽  
G. SHIVA SAM KUMAR SHIVA SAM KUMAR ◽  
AASA DARA
Keyword(s):  
Static Loading ◽  
Design Procedure ◽  
Initial Model ◽  
Stress Concentrations ◽  
Fighter Aircraft ◽  
Design And Optimization ◽  
High Speeds ◽  
Cantilever Structure ◽  
Standard Design ◽  
Optimized Model

An aircraft is an advanced mechanical structure made by man which has been dominating the skies from the early 19th centuries. It has been used for transportation of cargo/ passengers from one place to another in a shorter period of time. Advances in aeronautics lead to the development of fighter aircrafts with exciting and dominating characteristics. A fighter aircraft is to be designed in such a way that it can withstand heavy loadings on the wing due to its high manoeuvrability. A fighter aircraft is designed to be marginally unstable, which makes control easier and better during manoeuvrability at high speeds, but in this state there is a heavy fluctuating load acting on the wing. The wing is connected to the fuselage using wing fuselage lug attachment bracket. Since the wing is a cantilever structure, the load acting on the wing is concentrated on the hinge (lug bracket assembly). In this paper, a lug bracket is designed according to the standard design procedure and is validated using Finite Element Methods to ensure the static loading capability and stress concentrations in lug bracket. The validated model has been optimized using Altair Optistruct. The optimized model has been validated under static loading condition for the stress concentration and displacement and is compared with initial model in order to study and understand its behaviour under various conditions.

Ultimate Longitudinal Strength of Ship Hulls of Composite Materials

2008 ◽  
Vol 52 (03) ◽  
pp. 184-193
Author(s):  
Nian-Zhong Chen ◽  
C. Guedes Soares
Keyword(s):  
Composite Materials ◽  
Cross Section ◽  
Reaction Force ◽  
Strain Curve ◽  
Ship Hull ◽  
Stiffened Panel ◽  
Average Strain ◽  
Ship Hulls ◽  
Longitudinal Strength ◽  
Load Average

A progressive collapse analysis method is proposed to predict the ultimate longitudinal strength of ship hulls of composite materials. The load-average strain curve derived from a progressive failure nonlinear finite element analysis is adopted for representing the behavior of each stiffened composite panel forming a hull cross section. The bending moment of the ship hull under a prescribed curvature is achieved by integrating the reaction force of each stiffened panel over a hull cross section based on the load-average strain curves. The ultimate longitudinal strength of a ship hull is obtained from the moment-curvature relationship of the ship hull, which is established by imposing progressively increasing curvatures of a hull cross section. An all-composite ship is analyzed as an application.

INTEGRATED MATERIAL DESIGN SYSTEM FOR NEW GLASSES

1991 ◽  
pp. 109-112
Author(s):  
Akira Takada ◽  
Kazuko Adachi ◽  
Misae Keitora ◽  
Fujiko Mitsuhashi ◽  
Toshiyasu Kawaguchi
Keyword(s):  
Material Design ◽  
Design System

Code Development for Ship Structures—A Demonstration

1997 ◽  
Vol 119 (2) ◽  
pp. 114-119 ◽  
Author(s):  
A. E. Mansour ◽  
P. H. Wirsching ◽  
B. Ayyub ◽  
G. White
Keyword(s):  
Failure Modes ◽  
Safety Margin ◽  
Limit States ◽  
Hull Girder ◽  
Load Combination ◽  
Plate Buckling ◽  
Design Variables ◽  
Critical Detail ◽  
Safe Side ◽  
Future Publication

A demonstration summary of a reliability-based structural design code for ships is presented for two ship types: a cruiser and a tanker. One reason for the development of such a code is to provide specifications which produce ship structure having a weight savings and/or improvement in reliability relative to structure designed by traditional methods. Another reason is to provide uniform safety margin for ships within each type. For both ship types, code requirements cover four failure modes: hull girder bulkling, unstiffened plate yielding and buckling, stiffened plate buckling, and fatigue of critical detail. Both serviceability and ultimate limit states are considered. Because of limitation on the length, only hull girder modes are presented in this paper. Code requirements for other modes will be presented in future publication. A specific provision of the code will be safety check expression, which, for example, for three bending moments (still water Ms, wave Mw, and dynamic Md), and strength Mu, might have the form, following the partial safety factor format: γsMs+γwMw+γdMd≤φMu γs, γw, γd, and φ are the partial safety factors. The design variables (M’s) are to be taken at their nominal values, typically values in the safe side of the respective distributions. Other safety check expressions for hull girder failure that include load combination factors, as well as consequence of failure factors, are considered. This paper provides a summary of safety check expressions for the hull girder modes.

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