Potential of Optimal Ship Structure Redesign for Minor Collisions

This paper develops an alternative optimization approach for systematic design of a parametrized engine system and illustrates the procedure through application to a novel conversion device, the patented Stiller-Smith mechanism (1, 2). Using simultaneous interplay between a simulation scheme, presented in detail elsewhere (3), and an optimization scheme, the proposed structural design process integrates the multiple objectives of structural design. Developed here in detail, optimization involves intermediate continuous optimization via a penalty function method, and integer or discrete programming through the branch-and-bound algorithm. The ensuing application illustrates the approach by optimizing a 16-cylinder Stiller-Smith engine for minimum weight-power and dimensions-power ratios under several types of constraints. In the context of a multi-objective constrained non-linear programming problem, the design example proceeds through three stages: (a) preliminary, in which the designer applies the simulation scheme to obtain the system response variables from the design requirements to reflect trade-off relationships among multiple design objectives; (b) secondary, the intermediate continuous optimal design stage, in which a penalty function method is used to specify constraints within a general range to allow variation in the choice of parameters; and (c) final, in which the branch-and-bound algorithm constrains integer variables to take integer values and discrete variables to take discrete values, thereby arriving at an optimal design.

According to the geometric meaning of the structural reliability index, an unconstrained optimization model with structural reliability index and design point is obtained by exterior penalty function method. The Powell method, golden section method and extrapolation method are used to solve the unconstrained optimization problem. The proposed method not has to deal with the any derivative of the limited state function, and can been used to obtain structural reliability index and design point of the strong nonlinear limit state function, which first-order reliability method (FORM) may fail to converge. Three examples are given to compare penalty function method with the difference methods. The results show that the given method is simply, effective and precise enough.

This paper presents a dynamic reliability-based optimization technique for the seismic design of structures with tuned mass damper (TMD). Firstly, the governing equation of multi-degree-of-freedom structure with TMD is established. Then, the main structure is unfolded by the first mode. Considering that the damping is non-classical and the total main structure and TMD system is un-symmetric, the complex modal analysis is adopted to uncouple the governing equation and the analytical solutions of stochastic seismic response under the Kanai-Tajimi spectrum loading are obtained. Taking the ratio between the first-order modal displacement standard deviation of the structure with TMD and the one without TMD as the objective function, the dynamic reliability of the TMD system displacement as the constraint, the optimal design parameters of the TMD system are obtained through the penalty function method. A 10-story building with TMD system illustrates the proposed dynamic reliability-based optimization method. It is believed that such an optimization technique provides an effective tool for the seismic design of structures with TMD.

Even with the state-of-the-art technology of computer-aided design and topology optimization, the present structural design still faces the challenges of high dimensionality, multi-objectivity, and multi-constraints, making it knowledge/experience-demanding, labor-intensive, and difficult to achieve or simply lack of global optimality. Structural designers are still searching for new ways to cost-effectively to achieve a possible global optimality in a given structure design, in particular, we are looking for decreasing design knowledge/experience-requirements and reducing design labor and time. In recent years, Artificial Intelligence (AI) technology, characterized by the large language model (LLM) of Machine Learning (ML), for instance Deep Learning (DL), has developed rapidly, fostering the integration of AI technology in structural engineering design and giving rise to the concept and notion of Artificial Intelligence-Aided Design (AIAD). The emergence of AIAD has greatly alleviated the challenges faced by structural design, showing great promise in extrapolative and innovative design concept generation, enhancing efficiency while simplifying the workflow, reducing the design cycle time and cost, and achieving a truly global optimal design. In this article, we present a state-of-the-art overview of applying AIAD to enhance structural design, summarizing the current applications of AIAD in related fields: marine and naval architecture structures, aerospace structures, automotive structures, civil infrastructure structures, topological optimization structure designs, and composite micro-structure design. In addition to discussing of the AIAD application to structural design, the article discusses its current challenges, current development focus, and future perspectives.

Artificial neural networks (ANNs) have powerful function approximation and pattern classification capabilities, but their performance is greatly affected by structural design and parameter selection. Traditional training methods have drawbacks including long training time, over-fitting, premature convergence, etc. Evolutionary optimization algorithms have provided an effective tool for ANN parameter optimization, but simultaneously optimizing ANN structure and parameters remains a difficult problem. This paper adapts a relatively new evolutionary algorithm, water wave optimization (WWO), for both structure design and parameter selection for ANNs. The algorithm uses a variable-dimensional solution representation, and designs new propagation, refraction, and breaking operators to effectively evolve solutions towards the optimum or near-optima. Computational experiments show that the WWO algorithm exhibits significant performance advantages over other popular evolutionary algorithms including genetic algorithm, particle swarm optimization, and biogeography-based optimization, for ANN structure and parameter optimization.

Optimal structural design of stiffened plate structure with multi order modal frequencies objective is discussed. It is a structural reverse design problem for the first several order modal frequencies to reach a set of given value. A new method based on bi-directional evolutionary structural optimization (BESO) and size optimization is presented. To solve the porous and irregular shape problem in the optimized structure, a regular shaped grid-like frame structure optimization model is established. The bars in the frame structure are regarded as basic unites of structure modification. The bars’ sensitivity is discussed, and applied to optimization process based on frequency sensitivity. The structural optimal design process can be described as follows: the frequencies are used as the target, the volume is considered as constraint, adjacent sensitivity redistribution method is adopted to suppress numerical instability. Then size optimization method is adopted to conduct detailed design. Finally this method is applied to a stiffened plate structure. Results show that the proposed approach is feasible to achieve given multi order modal frequencies. The optimized structure consists of regular bars, so a clear structure is obtained.

Structural analysis and design optimization have recently been extended to stochastic approach to take various uncertainties into account. However in areas whwew it is not possible to produce accurate statistical information, the probabilistic method is not appropriate for stochastic structural analysis and design optimization, since improper modeling of uncertainty could cause greater degree of statistical uncertainty than those of physical uncertainty. For uncertainty with insufficient information, possibility-based (or fuzzy set) methods have recently been introduced in stochastic structural analysis and design optimization. The main advantage of the fuzzy analysis is that it preserves the intrinsic random nature of physical variables through their membership functions and, when used for evaluation of designs, yields more conservative design than those from the probabilistic methods. There are two computational aspects in the fuzzy analysis compared to the probability analysis. First, the input fuzzy variables can be defined easier than the input random variables when no or very limited statistical data are available. Secondly, extended fuzzy operations are much simpler than those required to use probability, especially when a number of variables are involved. For possibility-based design optimization (PBDO), like for reliability-based design optimization (RBDO), the performance measure approach (PMA) with an inverse fuzzy analysis is more appropriate than other approaches, such as a possibility index approach. This paper proposes a new formulation of PBDO using PMA. It is also found that PBDO is more desirable than RBDO, since PBDO can inherently handle a system level possibility unlike RBDO. For the inverse fuzzy analysis, the maximal possibility search (MPS) method is proposed to improve numerical efficiency and accuracy comparing with the vertex method and the

A new version of the DNV RP C204 standard for the design of offshore steel structures against accidental loads was released in 2019. The updated recommended practice made considerable changes on the design against ship collisions. The changes addressed the challenge of increasing ship sizes and collision energy and new structural designs. This paper discussed several aspects of the changes in the revised DNV RP C204, including updated design collision energy and force-displacement curves of the standard supply vessel, ship installation interactions, compactness criterion of offshore tubulars and external dynamic models. Examples are given to demonstrate application of the new standards. Potential impact of the new standard on structural design is discussed.

Purpose– Since the use of advanced finite element analysis (FEA) in the design of steel structures has been increasing its popularity in order to avoid unsafe or highly conservative designs, a solid know-how in computer-aided design (CAD) and engineering (CAE) codes is necessary. Therefore the purpose of this paper is to provide an extensive review of useful guidelines concerning modelling, simulation and result validation for the accurate performance of those analyses.Design/methodology/approach– Such guidelines are obtained from international steel design codes like Eurocode 3 and DNV, publications from experienced CAE engineers and renowned FE software companies like Ansys and Altair. Topics like mesh independence, the effect of the load sequence on the load bearing capacity and steel fracture criteria are underlined.Findings– Since the use of advanced FEA in the design of steel structures is becoming more and more traditional due to the increase of its competitiveness when compared to the use of (very) conservative design rules, a solid know-how in CAD and CAE codes is necessary.Practical implications– This work will be quite useful for structural steel stress engineers, contributing for a safer use of FEA in research and design.Originality/value– This work will be quite useful for structural steel stress engineers, contributing for a safer use of FEA in research and design.

Bumper is a structure attached to the vehicle at both front and rear end to dissipate the kinetic energy generated by an impact and protect the vehicle components and its occupants. An ideal bumper energy absorbing system should be crash-worthy at both low-speed and high-speed collisions as well as meet the requirement of pedestrian safety. Energy absorbers are used between the bumper fascia and bumper beam to improve crashworthiness. Key areas of research focused to optimise the bumper energy absorbing systems are the selection of material and the structural design/geometry. Different materials and structural designs are being tried out to optimise the bumper energy absorbing system to meet the requirements. The characteristics, advantages and disadvantages of these materials and structures are reviewed in this paper.

This paper presents an overview of the activities developed by the Structural Integrity Group at the Institute of Aeronautics and Space - IAE, Brazil, as well as the status of ongoing work related to the life extension program for aircraft operated by the Brazilian Air Force BAF. The first BAF-operated airplane to undergo a DTA-based life extension was the F-5 fighter, in the mid 1990s. From 1998 to 2001, BAF worked on a life extension project for the BAF AT- 26 Xavante trainer. All analysis and tests were performed at IAE. The fatigue critical locations (FCLs) were presumed based upon structural design and maintenance data and also from exchange of technical information with other users of the airplane around the world. Following that work, BAF started in 2002 the extension of the operational life of the BAF T-25 “Universal”. The T-25 is the basic training airplane used by AFA - The Brazilian Air Force Academy. This airplane was also designed under the “safe-life” concept. As the T-25 fleet approached its service life limit, the Brazilian Air Force was questioning whether it could be kept in flight safely. The answer came through an extensive Damage Tolerance Analysis (DTA) program, briefly described in this paper. The current work on aircraft structural integrity is being performed for the BAF F-5 E/F that underwent an avionics and weapons system upgrade. Along with the increase in weight, new configurations and mission profiles were established. Again, a DTA program was proposed to be carried out in order to establish the reliability of the upgraded F-5 fleet. As a result of all the work described, the BAF has not reported any accident due to structural failure on aircraft submitted to Damage Tolerance Analysis.

One of the major difficulties in structural shape optimal design is to create a design model by parameterizing a geometric model. Shape design parameterization is more complicated and difficult to handle than sizing design parameterization. First, the optimum shape is highly dependent on the design parameterization selected. An inappropriate design parameterization may result in an impractical design. On the other hand, changing the geometric shape of the design model to reflect successive changes in design parameters is a tedious, complicated, and inefficient process. Manual updates of geometric shape and finite element meshes are quite impractical. In this paper, a shape design parameterization method that is built on the geometric modeler PATRAN is presented. Using this method, a number of geometric entities that represent structural design boundaries are parameterized, and a design parameter linking process can be performed to create geometric features from geometric entities. To support the proposed method in structural shape design, a unified velocity computation method using geometric parametric mapping and an elliptic equation solver is developed for shape design sensitivity computation. The design parameterization and associated velocity Held computation methods are general enough to handle a broad range of engineering applications. Finally, automatic finite element mesh and geometric shape update methods are presented, which can be used to easily perform design changes.

Changes in the design and operational wind due to climate change at the Indian offshore sites

Introduction. The author presents the results of the reliability analysis of the structural systems in spans of bridges.Materials and methods. The analysis of published materials for the purpose of using them in the design of reinforced concrete bridges, in connection with changes in design standards and tightening of regulatory requirements for safety is made by the author.Results. The results of surveys of slab superstructures indicate the reliability and durability of typical structures operated under normal conditions, but in emergency situations there is a danger of progressive collapse. Therefore, in such conditions, split schemes of multi-span structures are unacceptable. The research tasks to ensure the durability of slab superstructures are formulated. In particular, the task of developing the method of durability calculation in case of one of the pillars failure in the continuous span structure, taking into account the dynamic effect is illustrated.Discussion and conclusion. Changes in design of slab structures of bridge cause the necessity to study the reliability and failure in emergency situations.

Methods for finding feasible points are needed in some numerical optimization algorithms to initiate the search for a local minimum. Other methods perform more efficiently if a nearly feasible starting point is used. In addition, a feasible solution may be acceptable as the final design in some practical applications. Therefore, constraint correction methods are quite useful. Such methods based on penalty functions and primal approach are described and discussed. To gain insight into the methods a two-variable problem is used to analyze the methods. Several structural design problems are used to study the numerical behavior of the methods and compare their performance. It is concluded that, in general, the primal methods are more efficient than the penalty function methods. Also, no method has been found that is guaranteed to find a feasible point for general constrained nonlinear problems starting from an arbitrary point. In case a method fails, random points should be used to restart the procedure to search for a feasible point.