Investigation of unrestrained cylinders rolling in steady uniform flows     

Jack E. Davis  Billy L. Edge  Hamn-Ching Chen 《Ocean Engineering》2007,34(10):1431-1448

The goal of this study is to understand the movement of unexploded ordnance that may become unburied and forced by currents. Symmetrical, smooth, finite-length, unrestrained cylinders were studied in steady, uniform flows over a range of Reynolds numbers in a smooth-bottomed, horizontal flume. The study uses PIV tracking methods in the laboratory to identify the movement of ordnance simulated by unrestrained cylinders. The PIV is supported with a numerical analysis using a RANS flow solver. The simulations showed that at low Reynolds numbers the cylinders should roll at speeds near 70% of the free-stream flow.  相似文献   

Analysis of roll motion and stability of a fishing vessel in head seas   总被引：1，自引：0，他引：1  

M. A. Santos Neves  N. Prez  O. Lorca 《Ocean Engineering》2003,30(7):921-935

The present paper describes an investigation on the relevance of parametric resonance for a typical fishing vessel in head seas. Results for different Froude numbers are discussed based on experimental, numerical and analytical studies.The first region of resonance is investigated. Distinct wave amplitudes are considered. Some intense resonances are found to occur. The paper compares the experimental results with non-linear time simulations of the roll motion. Very good agreement is found, even when large motions take place.Finally, in order to analyze the experimental/numerical results, analytic consideration is given to distinct parameters affecting the dynamic process of roll amplification. The influence of heave, pitch, wave passage effect, speed and roll restoring characteristics are discussed.  相似文献   

The influence of some ship parameters on manoeuvrability studied at the design stage     

Francisco Lzaro Prez  Juan Antonio Clemente 《Ocean Engineering》2007,34(3-4):518-525

Collision and grounding are the most common accidents in ship operation. Some accidents are due to human failure, but several research projects have shown that a high percentage of these accidents could have been avoided if the ship have had better manoeuvrability characteristics. This paper describes how, when the shipyard select some important ship parameters and dimensions at the design stage, these set of parameters influence manoeuvrability characteristics. To obtain these effects, some IMO manoeuvres have been numerically simulated for a sample ship and a non-linear numerical model proposed by the authors to study ship manoeuvrability is described in this work. The day to day practice of a shipyard where fast modelisation and calculations are required, and modifications to the original design are quite common at the preliminary design stage, requires fast but accurate numerical models.  相似文献   

Theoretical and Experimental Studies of Radiative Shocks     

C. Michaut  T. Vinci  L. Boireau  M. Koenig  S. Bouquet  A. Benuzzi-Mounaix  N. Osaki  G. Herpe  E. Falize  B. Loupias  S. Atzeni 《Astrophysics and Space Science》2007,307(1-3):159-164

This paper deals with the radiative shock from both theoretical and numerical points of view. It is based on the whole experimental results obtained at Laboratoire d'Utilisation des Lasers Intenses (LULI, école Polytechnique). Radiative shocks are high-Mach number shocks with a strong coupling between radiation and hydrodynamics which leads to a structure governed by a radiative precursor. These shocks are involved in various astrophysical systems: stellar accretion shocks, pulsating stars, interaction between supernovae and the interstellar medium. In laboratory, these radiative shocks are generated using high power lasers. New diagnostics have been implemented to study the geometrical shape of the shock and the front shock density. Data were obtained varying initial conditions for different laser intensities and temperature. The modeling of these phenomena is mainly performed through numerical simulations (1D and 2D) and analytical studies. We exhibit results obtained from several radiative hydrodynamics codes. As a result, it is possible to discuss about the influence of the geometry and physical parameters introduced in the 1D and 2D models.  相似文献   

Hydrodynamics of Supernova Evolution in the Winds of Massive Stars     

Vikram V. Dwarkadas 《Astrophysics and Space Science》2007,307(1-3):153-158

Core-Collapse supernovae arise from stars greater than 8 M_⊙. These stars lose a considerable amount of mass during their lifetime, which accumulates around the star forming wind-blown bubbles. Upon the death of the star in a spectacular explosion, the resulting SN shock wave will interact with this modified medium. We study the evolution of the shock wave, and investigate the properties of this interaction. We concentrate on the evolution of the SN shock wave in the medium around a 35 solar mass star. We discuss the hydrodynamics of the resulting interaction, the formation and growth of instabilities, and deviations from sphericity.  相似文献   

Intelligent ship traffic monitoring for oil spill prevention: risk based decision support building on AIS     

Eide MS  Endresen O  Brett PO  Ervik JL  Røang K 《Marine pollution bulletin》2007,54(2):145-148

The paper describes a model, which estimates the risk levels of individual crude oil tankers. The intended use of the model, which is ready for trial implementation at The Norwegian Coastal Administrations new Vard? VTS (Vessel Traffic Service) centre, is to facilitate the comparison of ships and to support a risk based decision on which ships to focus attention on. For a VTS operator, tasked with monitoring hundreds of ships, this is a valuable decision support tool. The model answers the question, "Which ships are likely to produce an oil spill accident, and how much is it likely to spill?".  相似文献   

The phosphoric acid leak from the wreck of the MV Ece in the English Channel in 2006: Assessment with a ship of opportunity, an operational ecosystem model and historical data     

Kelly-Gerreyn BA  Hydes DJ  Hartman MC  Siddorn J  Hyder P  Holt MW 《Marine pollution bulletin》2007,54(7):850-862

This study evaluates the ship of opportunity (Ferrybox) concept for both sustained monitoring of UK shelf sea waters and numerical model validation. Release of phosphate from the wreck of a chemical tanker (MV Ece) in the western English Channel (49.73 degrees N, 3.25 degrees W) in March 2006 is used to demonstrate the importance of sustained observations in decision support systems and policy development. The Ferrybox system continuously collects sea surface (5m) data from a suite of autonomous electronic sensors installed on a passenger ferry operating year-round between Portsmouth (UK) and Bilbao (Spain). The detection of anomalously high concentrations of phosphate (1.54mmolm(-3), four times the usual level) and onset of phytoplankton growth close to the wreck site in March 2006 was placed in the context of multiple years of measurements (phosphate, nitrate, silicate and chlorophyll) collected from the Ferrybox system (2003-2006) and the long-term time series station E1 (50.03 degrees N, 4.65 degrees W, 1930-1987) in the English Channel. With regard to decision support, release of phosphate from the tanker is unlikely to pose a threat as phytoplankton growth at the end of winter is not unusual in this region and dissolved inorganic nitrogen rather than phosphate (DIN:DIP=10-18) is likely to ultimately limit algal growth in spring 2006. With regard to policy development, the Oslo and Paris (OSPAR) commissions recommendation of sampling every three years in "non-problem areas" is likely to provide statistically inadequate data, given the interannual and decadal variability identified in the Ferrybox and E1 data: the Ferrybox data show that oceanic winter nutrient concentrations varied by 35-50% between 2003/2004 and 2005/2006 due to deeper mixing of water off-shelf in early 2005/2006 and comparisons between the Ferrybox and E1 years show that the western English Channel is currently experiencing a low in phosphate concentrations similar to those in the 1960s. The importance of Ferrybox data in evaluating the reliability of predictive operational models needed in decision support is also demonstrated, by highlighting both strengths and weaknesses in a state-of-the-art ecosystem model designed for UK shelf waters.  相似文献   

Dynamic evolution model of isothermal voids and shocks     

Yu-Qing Lou  Xiang Zhai 《Astrophysics and Space Science》2009,323(1):17-40

We explore self-similar hydrodynamic evolution of central voids embedded in an isothermal gas of spherical symmetry under the self-gravity. More specifically, we study voids expanding at constant radial speeds in an isothermal gas and construct all types of possible void solutions without or with shocks in surrounding envelopes. We examine properties of void boundaries and outer envelopes. Voids without shocks are all bounded by overdense shells and either inflows or outflows in the outer envelope may occur. These solutions, referred to as type void solutions, are further divided into subtypes and according to their characteristic behaviours across the sonic critical line (SCL). Void solutions with shocks in envelopes are referred to as type voids and can have both dense and quasi-smooth edges. Asymptotically, outflows, breezes, inflows, accretions and static outer envelopes may all surround such type voids. Both cases of constant and varying temperatures across isothermal shock fronts are analyzed; they are referred to as types and void shock solutions. We apply the ‘phase net matching procedure’ to construct various self-similar void solutions. We also present analysis on void generation mechanisms and describe several astrophysical applications. By including self-gravity, gas pressure and shocks, our isothermal self-similar void (ISSV) model is adaptable to various astrophysical systems such as planetary nebulae, hot bubbles and superbubbles in the interstellar medium as well as supernova remnants.   相似文献   

European Venus Explorer (EVE): an in-situ mission to Venus   总被引：1，自引：0，他引：1  

E. Chassefière  O. Korablev  T. Imamura  K. H. Baines  C. F. Wilson  D. V. Titov  K. L. Aplin  T. Balint  J. E. Blamont  C. G. Cochrane  Cs. Ferencz  F. Ferri  M. Gerasimov  J. J. Leitner  J. Lopez-Moreno  B. Marty  M. Martynov  S. V. Pogrebenko  A. Rodin  J. A. Whiteway  L. V. Zasova  J. Michaud  R. Bertrand  J.-M. Charbonnier  D. Carbonne  P. Raizonville 《Experimental Astronomy》2009,23(3):741-760

The European Venus Explorer (EVE) mission was proposed to the European Space Agency in 2007, as an M-class mission under the Cosmic Vision Programme. Although it has not been chosen in the 2007 selection round for programmatic reasons, the EVE mission may serve as a useful reference point for future missions, so it is described here. It consists of one balloon platform floating at an altitude of 50–60 km, one descent probe provided by Russia, and an orbiter with a polar orbit which will relay data from the balloon and descent probe, and perform science observations. The balloon type preferred for scientific goals is one which oscillates in altitude through the cloud deck. To achieve this flight profile, the balloon envelope contains a phase change fluid, which results in a flight profile which oscillates in height. The nominal balloon lifetime is 7 days—enough for one full circumnavigation of the planet. The descent probe’s fall through the atmosphere takes 60 min, followed by 30 min of operation on the surface. The key measurement objectives of EVE are: (1) in situ measurement from the balloon of noble gas abundances and stable isotope ratios, to study the record of the evolution of Venus; (2) in situ balloon-borne measurement of cloud particle and gas composition, and their spatial variation, to understand the complex cloud-level chemistry; (3) in situ measurements of environmental parameters and winds (from tracking of the balloon) for one rotation around the planet, to understand atmospheric dynamics and radiative balance in this crucial region. The portfolio of key measurements is complemented by the Russian descent probe, which enables the investigation of the deep atmosphere and surface.  相似文献   

Astrophysical smooth particle hydrodynamics     

Stephan Rosswog   《New Astronomy Reviews》2009,53(4-6):78-104

The paper presents a detailed review of the smooth particle hydrodynamics (SPH) method with particular focus on its astrophysical applications. We start by introducing the basic ideas and concepts and thereby outline all ingredients that are necessary for a practical implementation of the method in a working SPH code. Much of SPH’s success relies on its excellent conservation properties and therefore the numerical conservation of physical invariants receives much attention throughout this review. The self-consistent derivation of the SPH equations from the Lagrangian of an ideal fluid is the common theme of the remainder of the text. We derive a modern, Newtonian SPH formulation from the Lagrangian of an ideal fluid. It accounts for changes of the local resolution lengths which result in corrective, so-called “grad-h-terms”. We extend this strategy to special relativity for which we derive the corresponding grad-h equation set. The variational approach is further applied to a general-relativistic fluid evolving in a fixed, curved background space-time. Particular care is taken to explicitly derive all relevant equations in a coherent way.  相似文献