Fluid-structure interaction models on the hydroelastic analysis of containerships in waves

Commercial vessels have recently been increasing in size to meet the fast-growing demand for transportation and operations. However, this trend may result in more flexible or "softer" hulls. The flexible hull structure and high operational speed requirements bring the ship's natural frequency closer to the wave encounter frequency, increasing the probability of resonance or high-frequency vibrations. Therefore, hydroelastic effects and relevant loads should be considered when designing wave loads and evaluating the strength of large ships. A robust numerical model is in search of ship designers and regulators, intended to predict the impact of hydroelasticity in the initial stages of design as per the design regulations, where there exists a greater opportunity to make modifications and utilise high-fidelity tools to verify the performance of advanced designs. This study aims to fill this gap by performing robust numerical investigations based on open-source software on the seakeeping and hydroelastic analysis of a monohull under wave excitations. Firstly, a detailed literature review is presented to overview the previous theoretical and numerical methods for ship hydroelasticity. This review also includes a general comparison between these hydroelastic techniques and discusses the differences. Following this, two fully coupled CFD-based unsteady FSI numerical frameworks are established: coupled CFD-FEA and CFD-DMB methods, respectively. The physical principle of these FSI models is to treat a ship’s surface hull as an elastic body and interact with its surrounding flow field to form a fully coupled system. Taking advantage of the present numerical models, the hydroelastic behaviours of a containership, such as its vertical bending displacement and corresponding bending moment, can be quantified, and the “springing” and “whipping” behaviour can be measured. It is believed that the present FSI model will exhibit more advantages over the traditional rigid-body method in the ship seakeeping field. Later, the presented CFD-DMB model is further extended for its application to irregular extreme waves and damaged ship conditions. The results achieved from these studies could also help to assess the structural integrity and longitudinal strength of a ship (intact or damaged), which serves as an improved technique for regulations to evaluate conventional ship designs. Finally, the results drawn from each chapter of this thesis are summarised and discussed, and recommendations are made for future research.Commercial vessels have recently been increasing in size to meet the fast-growing demand for transportation and operations. However, this trend may result in more flexible or "softer" hulls. The flexible hull structure and high operational speed requirements bring the ship's natural frequency closer to the wave encounter frequency, increasing the probability of resonance or high-frequency vibrations. Therefore, hydroelastic effects and relevant loads should be considered when designing wave loads and evaluating the strength of large ships. A robust numerical model is in search of ship designers and regulators, intended to predict the impact of hydroelasticity in the initial stages of design as per the design regulations, where there exists a greater opportunity to make modifications and utilise high-fidelity tools to verify the performance of advanced designs. This study aims to fill this gap by performing robust numerical investigations based on open-source software on the seakeeping and hydroelastic analysis of a monohull under wave excitations. Firstly, a detailed literature review is presented to overview the previous theoretical and numerical methods for ship hydroelasticity. This review also includes a general comparison between these hydroelastic techniques and discusses the differences. Following this, two fully coupled CFD-based unsteady FSI numerical frameworks are established: coupled CFD-FEA and CFD-DMB methods, respectively. The physical principle of these FSI models is to treat a ship’s surface hull as an elastic body and interact with its surrounding flow field to form a fully coupled system. Taking advantage of the present numerical models, the hydroelastic behaviours of a containership, such as its vertical bending displacement and corresponding bending moment, can be quantified, and the “springing” and “whipping” behaviour can be measured. It is believed that the present FSI model will exhibit more advantages over the traditional rigid-body method in the ship seakeeping field. Later, the presented CFD-DMB model is further extended for its application to irregular extreme waves and damaged ship conditions. The results achieved from these studies could also help to assess the structural integrity and longitudinal strength of a ship (intact or damaged), which serves as an improved technique for regulations to evaluate conventional ship designs. Finally, the results drawn from each chapter of this thesis are summarised and discussed, and recommendations are made for future research

3D Face Synthesis Driven by Personality Impression

Synthesizing 3D faces that give certain personality impressions is commonly needed in computer games, animations, and virtual world applications for producing realistic virtual characters. In this paper, we propose a novel approach to synthesize 3D faces based on personality impression for creating virtual characters. Our approach consists of two major steps. In the first step, we train classifiers using deep convolutional neural networks on a dataset of images with personality impression annotations, which are capable of predicting the personality impression of a face. In the second step, given a 3D face and a desired personality impression type as user inputs, our approach optimizes the facial details against the trained classifiers, so as to synthesize a face which gives the desired personality impression. We demonstrate our approach for synthesizing 3D faces giving desired personality impressions on a variety of 3D face models. Perceptual studies show that the perceived personality impressions of the synthesized faces agree with the target personality impressions specified for synthesizing the faces. Please refer to the supplementary materials for all results.Comment: 8pages;6 figure

Robust multi-clue face tracking system

In this paper we present a multi-clue face tracking system, based on the combination of a face detector and two independent trackers. The detector, a variant of the Viola-Jones algorithm, is set to generate very low false positive error rate. It initiates the tracking system and updates its state. The trackers, based on 3DRS and optical flow respectively, have been chosen to complement each other in different conditions. The main focus of this work is the integration of the two trackers and the design of a closed loop detector-tracker system, aiming at achieving superior robustness at real-time operation on a PC platform. Tests were carried out to assess the actual performance of the system. With an average of about 95% correct face location rate and no significant false positives, the proposed approach appears to be particularly robust to complex backgrounds, ambient light variation, face orientation and scale changes, partial occlusions, different\ud facial expressions and presence of other unwanted faces

Multi-wavelength afterglow emission from bursts associated with magnetar flares and fast radio bursts

Magnetars have been considered as progenitors of magnetar giant flares (MGFs) and fast radio bursts (FRBs). We present detailed studies on afterglow emissions caused by bursts that occur in their wind nebulae and surrounding baryonic ejecta. In particular, following the bursts-in-bubble model proposed by Murase, Kashiyama \& M\'esz\'aros, we analytically and numerically calculate spectra and light curves of such afterglow emission. We scan parameter space for the detectability of radio signals, and find that a burst with $\sim10^{45}~{\rm erg}$ is detectable with the Very Large Array or other next-generation radio facilities. The detection of multi-wavelength afterglow emission from MGFs and/or FRBs is of great significance for their localization and revealing their progenitors, and we estimate the number of detectable afterglow events.Comment: 12 pages, 8 figures, 4 tables, accepted for publication in MNRA

Yelp Reviews and Food Types: A Comparative Analysis of Ratings, Sentiments, and Topics

This study examines the relationship between Yelp reviews and food types, investigating how ratings, sentiments, and topics vary across different types of food. Specifically, we analyze how ratings and sentiments of reviews vary across food types, cluster food types based on ratings and sentiments, infer review topics using machine learning models, and compare topic distributions among different food types. Our analyses reveal that some food types have similar ratings, sentiments, and topics distributions, while others have distinct patterns. We identify four clusters of food types based on ratings and sentiments and find that reviewers tend to focus on different topics when reviewing certain food types. These findings have important implications for understanding user behavior and cultural influence on digital media platforms and promoting cross-cultural understanding and appreciation

A CFD study of the behavior of a crew transfer vessel in head seas using OpenFOAM

Crew transfer vessels (CTV) were a fast means of transportation, providing inspection and maintenance services by transferring technicians from shore to offshore structures. These vessels had been designed to be efficient and effective at high speeds, though this means the ship motions were highly sensitive to the sea conditions. Accordingly, it was critical to be able to estimate a ship’s response among different wave conditions in the time domain. In this study, a Computational Fluid Dynamics (CFD) method was used for the analysis of Fluid-Structure interactions with a crew transfer vessel as a case study. The CFD codes were formulated to solve the unsteady Reynolds-Averaged Navier–Stokes equations using the finite-volume method with OpenFOAM, an open-source CFD software program. OpenFOAM offered high accuracy of ship motion predictions and high resolution of infield flow phenomena, taking into consideration both viscous and rotational effects in the flow and free surface waves. A comprehensive uncertainty analysis was presented, including verification and validation studies. The cases performed demonstrate that the results were found to be in good agreement with the available experimental results and showed the importance of a seakeeping analysis for such vessels

A fluid-structure interaction model on the hydroelastic analysis of a container ship using PRECICE

Commercial vessels have recently shown a common trend in increasing their sizes to meet the growing demand for transportation and operations. This trend may however result in more flexible or 'softer' hulls. The flexible hull structure reduces the ship natural frequency close to the wave encounter frequency, increasing the probability of resonance or high-frequency vibrations. Meanwhile, the resulting structural deformations from flexible hull could significantly affect the flow field and the hydrodynamic loads cannot be estimated accurately. Hence, it is important to treat a flexible hull and its surrounding flow field as an interacting system to predict a ship's dynamic behaviour based on the hydroelastic theory. In this study, a novel fluid-structure interactions coupling scheme using the "preCICE" library to communicate with the fluid solver "OpenFOAM" and structure solver "calculiX" was first proposed to study the hydroelastic behavior of a container ship with a forward speed in regular waves. With the advantage of this numerical model, the flexible behaviour of this ship, such as its vertical bending displacement and corresponding bending moment can be quantified, and the "springing" and "whipping" responses can be calculated. It is believed that the present FSI model will exhibit more advantages over the traditional rigid-body methods currently used in the ship seakeeping field

Research on Online Reviews Reliability

This study examines the factors that have an impact on online reviews reliability. A theoretical framework was built and empirically tested with a sample of 200 interviewees. Results of structural equation model show that the online reviews quality and perceived risk have positive impact on online review reliability. Accordingly, online review value and number have positive impact on online review quality, customer involvement and reviewer acception have positive impact on perceived risk. The results of this study also suggest that the character of online review and reviewer indirectly impact review reliability by impacting intermediate variables