Acoustic observation, identification, and scattering intensity measurement of cold seep based on bubble resonance

The active “cold seep” is indisputable evidence to identify the existence of submarine gas hydrate. Due to the difference in acoustic properties between cold seep bubbles and surrounding seawater, measuring scattering intensity is a new means to detect active cold seep. Cold seep bubbles are the main cause of acoustic scattering, and the scattering ability is closely related to the frequency of the incident sound wave, the radius of the bubble, and the depth of the bubble. This article introduces a ship-borne cold seep sonar system, which uses the resonance principle of bubbles to measure the scattering intensity at various depths underwater and display it with an intuitive acoustic image. Through the investigation and measurement of the cold seep located in the South China Sea, it is proven that the cold seep sonar system can well identify the submarine cold seep. The measured data are consistent with the theoretical simulation results, confirming that the cold seep bubbles have frequency-selective characteristics for incident sound waves. Compared with other detection methods, it has the characteristics of lossless, fast, and high efficiency.info:eu-repo/semantics/publishedVersio

Concept design of a fast sail assisted feeder container ship

A fast sail assisted feeder container ship concept has been developed for the 2020 container market in the South East Asian and Caribbean regions.The design presented has met the requirements of an initial economic study, with a cargo capacity of 1270 twenty-foot equivalent unit containers, meeting the predictions of container throughput derived from historical data. In determining suitable vessel dimensions, account has also been taken for port and berthing restrictions, and considering hydrodynamic performance. The vessel has been designed for a maximum speed of 25 knots, allowing it to meet the demand for trade whilst reducing the number of ships operating on the routes considered.The design development of the fast feeder concept has involved rigorous analyses in a number of areas to improve the robustness of the final design. Model testing has been key to the development of the concept, by increasing confidence in the final result. This is due to the fact that other analysis techniques are not always appropriate or accurate. Two hull forms have been developed to meet requirements whilst utilising different propulsor combinations. This has enabled evaluation of efficiency gains resulting from different hydrodynamic phenomena for each design. This includes an evaluation of the hydrodynamic performance when utilising the sail system. This has been done using a combination of model test results and data from regression analysis. The final propulsor chosen is a contra-rotating podded drive arrangement. Wind tunnel testing has been used to maximise the performance of a Multi-wing sail system by investigating the effects of wing spacing, stagger and sail-container interactions. This has led to an increase in lift coefficient of 32% from initial predictions. The savings in power requirement due to the sail system are lower than initially predicted. However, another benefit of their installation, motion damping, has been identified. Whilst this has not been fully investigated, additional fuel savings are possible as well as improved seakeeping performance.The design is shown to be environmentally sustainable when compared to existing vessels operating on the proposed routes. This is largely due to the use of low-carbon and zero-sulphur fuel (liquefied natural gas) and improvements in efficiency regarding operation. This especially relates to cargo handling and scheduling. Green house gas emissions have been predicted to fall by 42% and 40% in the two regions should the design be adopted. These savings are also due to the use of the Multi-wing sail system, which contributes to reductions in power requirement of up to 6% when the vessel operates at its lower speed of 15 knots. It is demonstrated that the fast feeder is also economically feasible, with predicted daily cost savings of 27% and 33% in the South East Asian and Caribbean regions respectively. Thus the fast feeder container ship concept is a viable solution for the future of container transhipment. <br/

An Investigation into Dynamic Stability of Waterborne Aircraft on Take-off and Landing

This research contributes to the knowledge of dynamic stability of waterborne aircraft and ground effect phenomenon. Hereto an analytical and computational study has been performed during which the motion of waterborne aircraft in take-off and landing is predicted. An analytical tool that can be used to predict the nonlinear heaving and pitching motions of seaplanes is presented. First, the heaving and pitching equations of motion are presented in their general Lagrangian form. Then, the equations are simplified to a form of nonlinear equations known as the forced Duffing equations with cubic nonlinearity. The system of motion is assumed to be driven by a sinusoidal head sea wave. The equations are then solved using the Poincare-Lindstedt perturbation method. The analytical solution is verified with CFD simulations performed on Ansys Fluent and AQWA. The solution is used to extend Savitsky’s method to predict porpoising which is a form of dynamic instability found in high-speed boats and seaplanes. The results of the analytical tool are in very good agreement with the results obtained from Fluent and AQWA. However, as the motion is assumed to be 2D in Fluent, heaving amplitude is slightly over predicted. Moreover, the frequency of oscillations of the 2D simulations is found to be unsteady. The unsteadiness in frequency increases with the increase of the length of the hull. Nevertheless, the amplitude of the pitch motion is slightly less than the amplitude predicted analytically. The discrepancy in the results is due to the characteristics of the 2D simulations that assumes that sea water will only pass underneath the hull which will make the buoyancy force greater as less damping is experienced. This is also a consequence of the fact that parameters within the analytical model of heave and pitch are calculated using a strip theory which considers only hydrodynamic effects, while Fluent also incorporate aerodynamic contributions. Similarly, AQWA is a 3D platform that only takes in consideration hydrodynamic effects. Hence, the results of AQWA are slightly less in amplitude than that predicted analytically. In addition, it was found that the frequency of oscillations obtained using AQWA increases with time while in the analytical approach, the frequency of oscillations can only be assumed to be constant for the whole period of motion. The increment in the oscillations indicates that porpoising is taking place. Nevertheless, it was found that heaving terms control the amplitude of motion and pitching terms control frequency of oscillations. The pitching nonlinear term has an effect on the amplitude of motion but not significant. Finally, the analytical method of Savitsky that is used to predict the porpoising stability limit is extended to find the porpoising limit for a wider range of pitch angles. In addition, the porpoising limit is predicted for a planing hull that is moving under the effect of head sea waves. When the seaplane is moving through head sea waves at a fixed pitch angle, porpoising takes place at a lower speed than what Savitsky has predicted

5 European & African Conference on Wind Engineering

The 5th European-African Conference of Wind Engineering is hosted in Florence, Tuscany, the city and the region where, in the early 15th century, pioneers moved the first steps, laying down the foundation stones of Mechanics and Applied Sciences (including fluid mechanics). These origins are well reflected by the astonishing visionary and revolutionary studies of Leonardo Da Vinci, whose kaleidoscopic genius intended the human being to become able to fly even 500 years ago… This is why the Organising Committee has decided to pay tribute to such a Genius by choosing Leonardo's "flying sphere" as the brand of 5th EACWE

A study on green water problem with dam break model and the BIV technique

The green water generated by extreme waves is primarily an air-water mixture, which includes a continuous phase and a dispersed phase. The continuous phase is explored with the dam break model by three main approaches, namely analytical, experimental and numerical. Analytically, both the Eulerian and Lagrangian Stoker solutions are introduced to study the dam break wave in a dry horizontal channel. The two Stoker solutions have an intersection point at the dam section at instant t ∗ 1 = √ 10 3 . In the initial stages, the “sudden dam break” concept is revised. The dam may be considered break suddenly when the dimensionless gate removal period is smaller than 3t ∗ 1 5 ≈ 0.63. To include the bottom friction effects and the bed slope effects for green water problem, we proposed a simplified piecewise solution (PS). Numerically, the two fluid model with the Volume of Fluid (VOF) method implemented in the interFoam solver is used to simulate the dam break wave. The interFoam solves the RANS equations with a k − ε turbulence model. Experimentally, different dam break cases are carried out including one horizontal bed and four different downstream slope beds (upward 10◦ and 5◦ , downward 10◦ and 5◦ ). Each bed is tested with two different water levels (110 mm and 220 mm). By introducing a time compensation factor t ∗ c = t ∗ 1 3 into PS, the predicted downstream wave agree well with the experimental data and numerical results. In the dispersed phase, the present study mainly focus on the BIV technique. The special properties of bubbles are taken into consideration and a test BIV experiment is carried out to evaluate the BIV system capacity. Finally, the BIV technique is applied to the dam break experiment.A água verde gerada por ondas extremas é principalmente uma mistura ar-água, que inclui uma fase contínua e uma fase dispersa. A fase contínua é estudado principalmente com o modelo de quebra de barragem (QB) por três abordagens principais, a saber analítica, experimental e numérica. Analiticamente, as duas soluções de Stoker são introduzidas para estudar a onda de QB em um canal horizontal seco. Nas fases iniciais, o conceito de “ruptura repentina de barragens” é revisto. A barragem pode ser considerada quebra repentinamente quando o período de remoção adimensional é menor que 3t ∗ 1 5 ≈ 0.63. Para incluírem os efeitos de atrito e de inclinação de fundo, propusemos uma solução fragmentada simplificada (PS). Numericamente, o modelo de dois fluidos com o método Volume of Fluid (VOF) implementado no solver interFoam é usado para simular a onda de QB. O solucionador interFoam resolve as equações de RANS com um modelo de turbulência k − ε. Experimentalmente, diferentes casos de são realizadas incluindo um leito horizontal e quatro leito como diferentes ângulo de inclinação (ascendente 10◦ e 5 ◦ , descendente 10◦ e 5◦ ). Ao introduzir um fator de compensação de tempo t ∗ c = t ∗ 1 3 em PS, a onda de downstream prevista concorda bem com os dados experimentais e os resultados numéricos. Na fase dispersa, os casos presentes aplicaram principalmente a técnica BIV. Para melhorar a compreensão da técnica BIV, são consideradas as propriedades especiais das bolhas e é realizado um experimento BIV de teste para avaliar a capacidade do sistema BIV. Finalmente, a técnica é aplicada no experimento de ruptura da barragem

Mathematical Modelling of LNG Dispersion Under Various Conditions

The global demand of liquefied natural gas (LNG) has risen rapidly in recent years. A new modelling method, direct CFD simulation method, was developed, due to the risks associated in handling, storage and transport of LNG. This method was shown to accurately model a LNG spill, pool formation and dispersion; and has been used to study the effect of (a) Impoundments, (b) Sea and air temperature and; (c) Sea and air stability

Fluid Structure Interaction: A Community View

Conducting fluid-structure interaction (FSI) experiments and simulations is a critical naval engineering capability for the U.S. Navy. However, past workshops on FSI problems have revealed that the FSI community is split into different technical groups. Furthermore, the user communities — practicing engineers and platform teams — are also separate. In July 2016, a cross-community working group of almost 60 people was convened at the University of Michigan Ann Arbor. This working group explored current and anticipated use cases for FSI simulation. Research challenges were also discussed. From this cross-community discussion, it was also possible to start to develop a common taxonomy of FSI problems and modeling approaches. This report documents the state of practice revealed by this working group.Office of Naval Researchhttp://deepblue.lib.umich.edu/bitstream/2027.42/136170/1/2016_003.pdfDescription of 2016_003.pdf : Main repor