1,720,978 research outputs found
Topology optimization for ship structures with manufacturing constraints
No full textCurrently, 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 Technolog
Load Capacity of Low Speed Steel Wheels
No full textSteel wheels are often essential parts for heavy construction equipment, such as constructed by Huisman. These steel wheels must endure heavy loads. In order to prevent downtime, costs and to guarantee safety, it is important that the steel wheels do not fail. One important failure mode is failure resulting from subsurface initiated cracks. This research is focused calculating the allowable load for steel wheels with initial cracks as a function of the number of cycles.The allowable load will be calculated using four different methods. Fracture mechanics will be applied, which uses an initial crack size and a load case to calculate the number of cycles until failure. The three other methods that will be discussed are described by fabrication standard, which are used during design of steel wheels. An analytical model will be used which applies all four methods to calculate the allowable load as a function of lifetime. The results will be analyzed in order to understand the differences between the methods. Also, parametric research will be done in order to understand the effects of the fracture mechanics input parameters. Furthermore, experimental data will be used in order to estimate which method is most realistic. It can be concluded that fracture mechanics can be used to calculate the allowable load for steel wheels if the correct values for the input parameters are known. The acquired data is very limited, however, which indicates that more data must be gathered in order to specify the input parameters for specific situations and materials.Mechanical Engineering | Multi-Machine Engineerin
Effect of strain hardening on the rotation capacity of welded I-section high-strength steel beams
No full textHigh-strength steel beams are known to have less plastic rotation capacity than beams with lower yield strengths. This has been related to the decreased strain-hardening ability of high-strength steels, and various rules and standards for steel structures stipulate maximum limits on the allowable yield-to-tensile strength ratio ((Formula presented.)), which indirectly acts as a measure of strain hardening. While the literature suggests that there is an interdependence between strain hardening ability, yield strength, cross-sectional slenderness and rotation capacity, the presently prescribed limits on (Formula presented.) (e.g. 0.91, 0.94, 0.95) are typically constant for a given material regardless of the other parameters mentioned. This computational study hence investigates how the rotation capacity is simultaneously dependent on yield strength, strain hardening ability and cross-sectional slenderness, and how each parameter affects the relationship between the others. The results show that, with the geometrical aspect kept constant through the use of normalised slenderness parameters, a higher yield strength leads to higher rotation capacity for a given (Formula presented.), while the well-known decrease of rotation capacity with higher (Formula presented.) is confirmed. This suggests the possibility of more efficient use of high-strength steels with high (Formula presented.) when the interdependence of all the variables are accounted for. The results also suggest the importance of accounting for the relative slendernesses of the web and the flange and whether the buckling behaviour is web- or flange-dominated, since a switch between a web- and flange- dominated buckling response could lead to a reverse in the trend between the rotation capacity and the overall cross-sectional slenderness.</p
Inexpensive Fracture Toughness Testing of Welded Steel
No full textIn a prior project, TNO has presented a low-cost way of finding fracture toughness of base materials for cleavage fracture. That method features a small-scale CTOD specimen, combined with simplified sensors, less fatigue pre-cracking, faster testing, and no need for a temperature chamber. This method has been extended to welds by considering the effect of pop-ins. This paper summarizes the prior method and the justifications for it before extending it to welded structures by introducing adjustments for pop-ins for small-scale specimens.Accepted Author ManuscriptShip Hydromechanics and StructuresBUS/TNO STAF
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
On Ship Structure Risk and Total Ownership Cost Management Assisted by Prognostic Hull Structure Monitoring
No full textShips must perform their missions with a high degree of reliability to maximize availability through their service life. The ultimate safety of the hull structure is time-dependent with degradation caused by the operational environment. Achieving the fore mentioned reliability and mission availability requirements are complicated because ships operate in random seaways producing random loading on the hull structure. The subsequent strength degradation also involves random processes including the material properties themselves. Furthermore, the models used to estimate the loading and responses are not perfect and result in additional randomness and related uncertainty. The potential Risks involved are very high, given the combination of uncertainties and high value of the assets, crews, and related resources. The primary research questions posed by this dissertation include; 1) what approaches are needed to make Risk informed decisions in Ship Structure Life Cycle Management (SSLCM) and, 2) how can Hull Structural Monitoring (HSM) be used effectively to support these decisions? This dissertation addresses these research questions by building on the fundamentals of hull structural loading and failure mechanisms on both component and systems-levels that are unique to ship structure. This fundamental research includes a correlation analysis of the system loading to support new definitions of ship structural system response. This new definition of structural system response provides insights into definitions of serviceability failure, reserve strength, and redundancy. Following the structural systems definition development, this dissertation proposes a Risk and Total Ownership Cost (TOC) trade-space perspective for making informed decisions and managing both Risk and costs associated with SSLCM and fundamental characterization of Risk and uncertainty. The development of Risk-TOC approach provides tangible and relatable benefits for understanding uncertainty in Risk terms required to make informed decisions. The Risk-TOC approach provides a more informed perspective than prior proposals for Decision Theory-based Optimal Inspection approaches with assumptions and parameters that do not fully quantify the uncertainties involved in the SSLCM processes. The Risk-TOC approach also provides a quantitative means for assessing the consequences of different failure modes (i.e., fatigue cracking and corrosion). The Risk-TOC approach provides a quantified basis for comparing Risk and costs given the magnitude of resources at Risk by monetizing uncertainty. In this manner, the Risk - TOC approach provides a framework for fundamental definitions, including monetized uncertainty, analysis of alternatives (AoAs), Return on Investment (RoI), and Value of Information (VoI). The benefits of prognostic HSM are presented in the context of reduction of uncertainty in the SSLCM processes; thereby, reducing Risk and TOC with favorable RoI and VoI. The Risk-TOC approach is verified as demonstrated in example applications involving a US Coast Guard Cutter. A discussion is provided on the implications of the Risk-TOC approach on SSLCM and sustainability. Conclusions and recommendations are presented for further development of the Risk-TOC approach for SSLCM.Ship Hydromechanics and Structure
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Marriage record of Vedmore, Reginald and Walters, Majorie
No full textMarriage license for Reginald Vedmore and Majorie Walters. C.L. Jackson was the Justice of the Peace
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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