Topology optimization for ship structures with manufacturing constraints

Topology optimization for ship structures with manufacturing constraints

Bos, Dennis (TU Delft Mechanical, Maritime and Materials Engineering)

Walters, C.L. (mentor)

Delft University of Technology

Marine Technology

2021-08-23

Currently, most ships are designed on the basis of rules and reference ships for which often only the critical structural parts are calculated and designed in detail. This process can result in an over-dimensioned ship with the standard structural outcome of longitudinal stiffeners, transverse stiffeners, and bulkheads with a fixed distance due to ease of manufacturing. With the use of finite element analysis (FEA), the complete structure of a ship is analyzed against prescribed loads, which facilitates the determination of the detailed dimensions of all stiffeners and plates within a reasonable lead time and could result in better engineering in the form of a lighter ship. In addition, the most common structural forms could be optimized by replacing them with unique and optimal shapes. Topology optimization (TO) uses FEA, and it facilitates unique structural shapes. TO generates an optimized material distribution for a set of loads and constraints within a given design domain. The result can be used to inform the design of an improved part. Although the results provide helpful insight, they often cannot be used literally, as they are organic and cannot be manufactured with typical steel shipbuilding methods. The objective of this study is to research the possibility to design the structure of a steel midship with TO where the resulting structural form is manufacturable using steel-cut plates and cost-effective from a shipbuilding perspective. However, constraints that result in a manufacturable structure that can be made cost-effectively from steel-cut plates have not been developed and implemented in TO. To meet the objective, this project was initiated in cooperation with C-Job and the University TU Delft. The methodology was established based on a software comparison followed by an extensive trial and errortesting process. The study was executed in a case study for which the domain concerned the midsection of a 203m offshore vessel named Orion, as TO could result in substantial computational time such that analyzing a hull section is more efficient. The optimization was performed in multiple iterations with different design objectives using the method of Solid Isotropic Material with Penalization (SIMP). After a baseline comparison, the manufacturing constraints were implemented and developed. Despite the availability of manufacturability constraints, it is currently not possible with the software used in this study to design the complete structure of a steel midship. However, it can be very useful to employ TO as a suggestion early in the design process, as this can result in manufacturable structures (see Figure 77). The TO software used in this study can help designers with structural suggestions in the basic design phase when there are fewer design limitations. This case study resulted in unusual 45-degree, X-shape components that are highly efficient for sustaining shear loads and which resulted in a weight reduction of the mid-section of 2.4%. In addition, the result shows that unique structural shapes under various angles can result in an optimal strength-weight design rather than in orthogonal structural parts with a fixed span.

Marine Technology
Topology optimization
Ship
Structure
Manufacturing constraints

http://resolver.tudelft.nl/uuid:0926ffde-d641-450f-b800-e993c9ced40e

Student theses

master thesis

© 2021 Dennis Bos