Unsteady hydrodynamics of ships moving in confined waterways

When a ship is navigating on water surface, its resistance can be divided into three components: frictional resistance, eddy resistance, and wave-making resistance (Havelock, 1909). While in many cases, the steady component dominates the wave-making resistance, there are still certain instances where unsteady effects cannot be ignored. For example: • Sudden changes of boundaries, such as the width and depth of the waterway. This may occur when ships navigate in port, harbor or lock environments. It will potentially increase the risk of collisions or grounding incidents. • When a ship is overtaking (or being overtaken) or passing other vessels in busy waterways, the unsteady effects of the free surface can generate horizontal unsteady forces between the two ships. This can result in collisions between the vessels and lead to the blockage of the waterway. • Another typical scenario is when a ship keeps accelerating in open area, particularly in extremely shallow depths. In this case, the unsteady effects will significantly increase after the ship’s velocity exceeds the critical speed. At this point, the unsteady effects alter the flow field around the ship, resulting in changes in wave-making resistance. This thesis posits that the aforementioned unsteady effects are closely correlated with unsteady waves on the free surface. Hence, the primary objectives of this research are two-fold: 1) To develop a linear unsteady numerical program which is capable of simulating the unsteady free surface effects. This program will accurately capture the formation and evolution of unsteady waves. 2) To devise a real-time updating mesh method that handles changes in waterway boundaries and depths encountered during the simulation process. Additionally, it ensures temporal continuity for all cells on the free surface. In this thesis, Chapter 1 will be an introduction and literature review of the research topic. Chapter 2 introduces the methodology used in this research. Chapters 3 to 5 constitute the main body of this thesis. Specifically, Chapter 3 presents the simulation of unsteady waves generated by a single object, with particular focus on the simulation of the previously mentioned scenario of a ship accelerating in shallow water. Chapter 4 aims to simulate multiple objects. In this chapter, the ship-to-ship problem and the unsteady bank effect within a confined waterway will be investigated. Due to the presence of interacting objects, the grid is required to be updated in real-time to accommodate changes in the boundary conditions. The simulation results will be compared with experimental data to validate their accuracy. Chapter 5 will build upon the foundation established in Chapter 3 by extending the grid handling techniques to account for unsteady banks. Additionally, the unsteady hydrodynamic model developed in Chapter 2 will also be incorporated. This integration will enable the simulation of the intricate wave phenomena that occurs during the process of a vessel entering a lock. The simulation results will be compared against experimental data as well as computational fluid dynamics (CFD) results to validate their accuracy. This comparative analysis serves to ensure the reliability and fidelity of the simulation outcomes. By undertaking these efforts, Chapter 4 aims to provide a comprehensive understanding of the wave behaviour within the lock chamber during vessel entry, contributing to the advancement of knowledge in the field of unsteady water dynamics. Finally, Chapter 6 serves as the conclusion which summarizing all the achievements of this thesis and also proposing future directions for research.When a ship is navigating on water surface, its resistance can be divided into three components: frictional resistance, eddy resistance, and wave-making resistance (Havelock, 1909). While in many cases, the steady component dominates the wave-making resistance, there are still certain instances where unsteady effects cannot be ignored. For example: • Sudden changes of boundaries, such as the width and depth of the waterway. This may occur when ships navigate in port, harbor or lock environments. It will potentially increase the risk of collisions or grounding incidents. • When a ship is overtaking (or being overtaken) or passing other vessels in busy waterways, the unsteady effects of the free surface can generate horizontal unsteady forces between the two ships. This can result in collisions between the vessels and lead to the blockage of the waterway. • Another typical scenario is when a ship keeps accelerating in open area, particularly in extremely shallow depths. In this case, the unsteady effects will significantly increase after the ship’s velocity exceeds the critical speed. At this point, the unsteady effects alter the flow field around the ship, resulting in changes in wave-making resistance. This thesis posits that the aforementioned unsteady effects are closely correlated with unsteady waves on the free surface. Hence, the primary objectives of this research are two-fold: 1) To develop a linear unsteady numerical program which is capable of simulating the unsteady free surface effects. This program will accurately capture the formation and evolution of unsteady waves. 2) To devise a real-time updating mesh method that handles changes in waterway boundaries and depths encountered during the simulation process. Additionally, it ensures temporal continuity for all cells on the free surface. In this thesis, Chapter 1 will be an introduction and literature review of the research topic. Chapter 2 introduces the methodology used in this research. Chapters 3 to 5 constitute the main body of this thesis. Specifically, Chapter 3 presents the simulation of unsteady waves generated by a single object, with particular focus on the simulation of the previously mentioned scenario of a ship accelerating in shallow water. Chapter 4 aims to simulate multiple objects. In this chapter, the ship-to-ship problem and the unsteady bank effect within a confined waterway will be investigated. Due to the presence of interacting objects, the grid is required to be updated in real-time to accommodate changes in the boundary conditions. The simulation results will be compared with experimental data to validate their accuracy. Chapter 5 will build upon the foundation established in Chapter 3 by extending the grid handling techniques to account for unsteady banks. Additionally, the unsteady hydrodynamic model developed in Chapter 2 will also be incorporated. This integration will enable the simulation of the intricate wave phenomena that occurs during the process of a vessel entering a lock. The simulation results will be compared against experimental data as well as computational fluid dynamics (CFD) results to validate their accuracy. This comparative analysis serves to ensure the reliability and fidelity of the simulation outcomes. By undertaking these efforts, Chapter 4 aims to provide a comprehensive understanding of the wave behaviour within the lock chamber during vessel entry, contributing to the advancement of knowledge in the field of unsteady water dynamics. Finally, Chapter 6 serves as the conclusion which summarizing all the achievements of this thesis and also proposing future directions for research

History, gendered space and organizational identity:An archival study of a university building

How do buildings contribute to an organization’s sense of what it is? In this article, we present the findings of a major archival study of an iconic university building to answer this question. Founded in the 19th century as a college for women, the building is analysed as a gendered space that embodies meanings that are selectively deployed and adapted by the present-day, now co-educational, university. By bringing together concepts of space and history so as to examine ‘space in history’ we show how over long periods of time what buildings ‘say’ about an organization change so that the past is both a legacy and a resource for shifting organizational identity

History, gendered space and organizational identity:An archival study of a university building

How do buildings contribute to an organization’s sense of what it is? In this article, we present the findings of a major archival study of an iconic university building to answer this question. Founded in the 19th century as a college for women, the building is analysed as a gendered space that embodies meanings that are selectively deployed and adapted by the present-day, now co-educational, university. By bringing together concepts of space and history so as to examine ‘space in history’ we show how over long periods of time what buildings ‘say’ about an organization change so that the past is both a legacy and a resource for shifting organizational identity

Factorization of the Hückel Hamiltonian Matrix for Highly Symmetrical Molecules

A simple approach to the group-theoretical factorizing of the Hamiltonian matrix of highly symmetrical molecules is presented. This approach, which is based on the Lanczos method, requires only a symmetry-adapted linear combination (SALC) for each category of irreducible representation (IR) of the molecular point-group, while it reduces the size of the problem by more than one order of magnitude. We demonstrate the treatment by applying it to the study of electronic structures of the Goldberg type-II fullerenes, Cgo, C1go, C320, C50o and Cggo within the Hückel tight-binding framework. The results, in terms of the factor characteristic polynomial (or the subspectrum) for each category of irreducible representation, are presented for these giant molecules

Deconvolution approach for floating wind turbines

Green renewable energy is produced by floating offshore wind turbines (FOWT), a crucial component of the modern offshore wind energy industry. It is a safety concern to accurately evaluate excessive weights while the FOWT operates in adverse weather conditions. Under certain water conditions, dangerous structural bending moments may result in operational concerns. Using commercial FAST software, the study's hydrodynamic ambient wave loads were calculated and converted into FOWT structural loads. This article suggests a Monte Carlo-based engineering technique that, depending on simulations or observations, is computationally effective for predicting extreme statistics of either the load or the response process. The innovative deconvolution technique has been thoroughly explained. The suggested approach effectively uses the entire set of data to produce a clear but accurate estimate for severe response values and fatigue life. In this study, estimated extreme values obtained using a novel deconvolution approach were compared to identical values produced using the modified Weibull technique. It is expected that the enhanced new de-convolution methodology may offer a dependable and correct forecast of severe structural loads based on the overall performance of the advised de-convolution approach due to environmental wave loading.publishedVersio

Decoding secrecy as multiple temporal processes : Co-constitution of concealment and revelation in archival stories

How can we understand secrecy as temporal processes in organization? How can we address the inherent dynamics between concealment and revelation over time? In this article, we build on an inherent and yet overlooked character of secrecy as temporal, and explore temporalization processes of secrecy. We suggest that secrecy should be reconceptualized as processes of simultaneous concealment and revelation in multiple temporalities. Drawing on such temporal sensitivity, we apply a history-laden analysis of four examples of archival stories as ongoingly completing processes of secrecy. The analysis sheds light on the paradoxical dynamics of secrecy in three interconnected ways: first, writing archival stories offer opportunities to mask and attack the concealed. Therefore, second, archival stories as the site and process that sustain secrecy can become the site where secrecy is revealed. In this sense, as the third way, secrecy is ongoingly and fragmentally formed, producing multiple and subjective experiences of time. This article also contributes to the methodological potential for using archival stories in organizational studies

Efficient Parallel Output-Sensitive Edit Distance

Given two strings $A[1..n]$ and $B[1..m]$, and a set of operations allowed to edit the strings, the edit distance between $A$ and $B$ is the minimum number of operations required to transform $A$ into $B$. Sequentially, a standard Dynamic Programming (DP) algorithm solves edit distance with $\Theta(nm)$ cost. In many real-world applications, the strings to be compared are similar and have small edit distances. To achieve highly practical implementations, we focus on output-sensitive parallel edit-distance algorithms, i.e., to achieve asymptotically better cost bounds than the standard $\Theta(nm)$ algorithm when the edit distance is small. We study four algorithms in the paper, including three algorithms based on Breadth-First Search (BFS) and one algorithm based on Divide-and-Conquer (DaC). Our BFS-based solution is based on the Landau-Vishkin algorithm. We implement three different data structures for the longest common prefix (LCP) queries needed in the algorithm: the classic solution using parallel suffix array, and two hash-based solutions proposed in this paper. Our DaC-based solution is inspired by the output-insensitive solution proposed by Apostolico et al., and we propose a non-trivial adaption to make it output-sensitive. All our algorithms have good theoretical guarantees, and they achieve different tradeoffs between work (total number of operations), span (longest dependence chain in the computation), and space. We test and compare our algorithms on both synthetic data and real-world data. Our BFS-based algorithms outperform the existing parallel edit-distance implementation in ParlayLib in all test cases. By comparing our algorithms, we also provide a better understanding of the choice of algorithms for different input patterns. We believe that our paper is the first systematic study in the theory and practice of parallel edit distance

Voucher Abuse Detection with Prompt-based Fine-tuning on Graph Neural Networks

Voucher abuse detection is an important anomaly detection problem in E-commerce. While many GNN-based solutions have emerged, the supervised paradigm depends on a large quantity of labeled data. A popular alternative is to adopt self-supervised pre-training using label-free data, and further fine-tune on a downstream task with limited labels. Nevertheless, the "pre-train, fine-tune" paradigm is often plagued by the objective gap between pre-training and downstream tasks. Hence, we propose VPGNN, a prompt-based fine-tuning framework on GNNs for voucher abuse detection. We design a novel graph prompting function to reformulate the downstream task into a similar template as the pretext task in pre-training, thereby narrowing the objective gap. Extensive experiments on both proprietary and public datasets demonstrate the strength of VPGNN in both few-shot and semi-supervised scenarios. Moreover, an online deployment of VPGNN in a production environment shows a 23.4% improvement over two existing deployed models.Comment: 7 pages, Accepted by CIKM23 Applied Research Trac