Seasonal Variations in Vegetation Indices derived from in situ Type Vegetation Monitoring System at typical landcovers in Japan : From the Observation Results in PGLIERC and Lake Biwa Project

研究概要:本研究では光学センサー搭載衛星データの検証及び地表面フラックスとの対応関係を調べるために簡易式の地上設置型植生モニタリングシステムを日本を代表する土地被覆上(草地,水田,アカマツ林,落葉広葉樹)に設置し,それぞれの土地被覆から得られる植生指標の季節変化について示した.その結果,以下の知見が得られた;1.草原系(草地・水田)では各植生の季節変化特性を良好にモニターすることが可能である,2.森林系(アカマツ林・落葉広葉樹)ではセンサーとキャノピーの距離が近すぎるため,思うような結果を得ることが出来なかった.3.ただし全般としては各土地被覆特性を示す連続したデータを取得することができ,システムの妥当性を示すことができた

Benchmark study on simulation of flooding progression

Several time-domain flooding simulation codes have been developed and improved over the past decade, after the previous international benchmark study in 2007. Consequently, within the ongoing EU Horizon 2020 project FLARE, a new benchmark study was organized. The first part of this study focuses on different fundamental flooding mechanisms, characteristic for progressive flooding in damaged passenger ships, including up- and down-flooding, as well as extensive horizontal flooding along a typical deck layout. Numerical results are carefully compared against measured water levels at different locations. Similarities and differences between the codes and applied modelling practices are discussed, and the reasons for observed deviations are analysed

Ein schnelles und explizites Verfahren zur Simulation von Flutungs- und Sinkvorgängen von Schiffen

Zahlreiche schwere Seeunfälle von Schiffen wurden in der Vergangenheit ausgelöst durch Wassereinbruch und anschließender weitergehender Flutung der wasserdichten Unterteilung, welche zum Sinken und dem Totalverlust der Schiffe führte. Daher besteht ein hoher Bedarf an numerischen Simulationsmethoden, mit denen diese Flutungsvorgänge genauer untersucht werden könnten. Dadurch könnten solche Unfälle in Zukunft vermieden werden und sicherere Schiffsentwürfe entwickelt werden. Die Rekonstruktion der Unfallvorgänge wird erschwert durch die hohe Komplexität der inneren Unterteilung von Schiffen und der daraus resultierenden großen Anzahl an Flutungswegen. Aus diesem Grund wird ein numerisches Berechnungsprogramm entwickelt, welches in der Lage ist, diese Vorgänge schnell und direkt zu analysieren und vorhersagen zu können, um so auch Kenntnisse über die einzelnen Zwischenflutungszustände zu erlangen. Die Validierung der Methode erfolgt anhand von drei Testfällen eines Modellversuches und drei realen Unfällen, die bereits umfangreich untersuchten wurden: Die Unfällen der European Gateway, der Heraklion und der Estonia. Die Ergebnisse der neuen Methode in diesen Anwendungen sind sehr vielversprechend. Die quasi-statische Methode ermittelt den zeitlichen Verlauf der Flutung des Schiffes und die daraus resultierenden Schwimmlagen. Die Beschreibung des Flutungssystems, welches aus den Öffnungen und Räumen gebildet wird, erfolgt mit Hilfe gerichteter Graphen. Die Strömungen durch die Öffnungen der komplexen Unterteilung eines Schiffes werden idealisiert mit Hilfe der inkompressiblen Bernoulli-Gleichung berechnet. Teilgetauchte, große Öffnungen werden ebenso berücksichtigt wie zeitlich veränderliche Öffnungen, deren Eigenschaften im Laufe der Simulation unter bestimmten Bedingungen verändert werden. Somit können zum Beispiel berstende Fenster modelliert werden, die erst ab einem bestimmten Druckniveau durchlässig werden. Optional kann der Einfluss der Kompression von eingeschlossener Luft berücksichtigt werden. Nach Bestimmung der neuen Verteilung des Wassers und der Ermittlung der Füllstände in den einzelnen Räumen wird die korrespondierende hydrostatische Gleichgewichts-Schwimmlage bestimmt. Die Simulation wird fortgeführt, bis sich entweder diese Schwimmlage nicht mehr ändert oder das Schiff keine Auftriebsreserve mehr hat und von der Wasseroberfläche verschwindet. Durch die direkte Integration der Simulationsmethode in das schiffbauliche Entwurfssystem E4 ist eine konsistente Datenmodellierung gewährleistet und eine Kopplung mit bestehenden und neuen Methoden möglich. Es wird Wert darauf gelegt, die entscheidenden Effekte hinreichend genau abzubilden, ohne die Komplexität unnötig zu erhöhen und damit die Geschwindigkeit der Simulation zu verringern. Dies erlaubt dem Anwender, verschiedene mögliche Varianten des Unfallhergangs innerhalb kürzester Zeit zu berechnen, um zum Beispiel den Einfluss einer eventuell geöffneten wasserdichten Tür auf einen Unfallhergang untersuchen zu können.Many severe ship accidents in the past were caused by a large water ingress followed by the progressive flooding of the watertight integrity of the ships and finally resulted in the sinking and total loss of the vessels. These accidents show a high demand for a better understanding of the flooding of ships with the help of numerical methods. This would allow to avoid such accidents in the future and to find new designs with an increased capability to withstand flooding. The circumstances of the accidents, which involve flooding are difficult to understand due to the complexity of the inner subdivision and the large number of resulting flooding paths. Hence, a fast numerical simulation method is developed in this thesis to analyse and predict such flooding events. The validation of the method comprises the comparison with experimental results from three test cases of a model test and the re-investigation of three severe ship accidents, which have been carefully investigated before: The accident of the European Gateway, the Heraklion and the Estonia. The results obtained with the new method in these applications are very promising. A quasi-static approach in the time domain is chosen to compute the flooding of the inner subdivision and the resulting equilibrium floating position at each intermediate time step. The flooding paths are modelled with the help of directed graphs. The water fluxes through the openings are computed by a hydraulic model based on the Bernoulli equation. Large and partly flooded holes are taken into account, as well as conditional openings like breaking windows or the flooding through completely filled compartments. The effect of air compression can be taken into account as well if this is required for a certain case. After the determination of the new flood water distribution and the corresponding filling levels in each compartment, the resulting equilibrium floating position is computed. The simulation ends, either if the intermediate floating position does not change any more or if all buoyancy reserve is lost and the ship starts to submerge below the sea surface. The method is developed within the ship design system E4, which ensures a consistent data model and allows the direct coupling with existing and new methods. All essential effects are taken into account without unnecessarily increasing the complexity of the model as this would lower the performance of the simulation method. The method enables the user to study many flooding scenarios within a short period, for example to investigate the influence of watertight doors that were left open

Investigation of the Mighty Servant 3 accident by a progressive flooding method

The semi-submersible heavy-lift vessel MIGHTY SERVANT 3 sank off the port of Luanda, Angola in the morning of December 6th, 2006 during a ballast operation to offload the drilling platform Aleutian Key. The official investigations carried out after the accident identified an error in the control of the submerging ballast operations as the direct cause of the sinking. However, the detailed phenomenons and reasons for the sudden excessive trim development has not been investigated further. This paper intends to identify the most likely sceneario which lead to the hydrostatic stability failure during the discharge operation by computing the flooding process during the ballast operation in the time domain. A numerical progressive flooding simulation method is presented for applications like accident investigations or damage stability assessments. This method is modified to fit the special requirements of simulating the operational procedures of semi-submersible vessels in the time domain. Extensions like the inclusion of pump elements but also the multi-body interaction of the cargo and the vessel with regard to the hydrostatics is presented. The direct flooding simulation computes the flux between the compartments based on the Bernoulli equation and the current pressure heads at each intermediate step. Large and partly flooded holes are taken into account as well as optional air compression and flooding through completely filled rooms. Pressure losses due to viscous effects are taken into account by applying semi-empirical discharge coefficients to each opening. The flooding paths are modeled by directed graphs. A detailed investigation of the MIGHTY SERVANT 3 accident and an identification of the possible failure modes leading to the sinking of the vessel is presented. This will help to better understand the phenomenons leading to critical situations during the submerging procedure of semi-submersible heavy-lift vessels and to avoid such accidents in the future. Applying time domain flooding simulations allows to predict the ship behavior during ballast operations to identify critical situations and to better schedule the different steps of such an operation in advance. Copyright © 2013 by ASME

A Monte Carlo based simulation method for damage stability problems

To cope with future developments of the SOLAS 2009 B1, damage stability investigations must become a central part of the initial design phase. If damage stability calculations are performed in the classical way, they are very time consuming with respect to both modelling and computational time. To overcome this problem, damage stability can be treated as a stochastic process, where the probability of a damage case and the survivability of that particular damage case need to be determined. This task can be solved by direct numerical simulations based on the Monte Carlo principle. If statistical damage distributions are once known, the Monte Carlo simulation delivers a population of damages which can be automatically related to certain damage cases. These damage cases can then be investigated with respect to their survivability. Applying this principle to SOLAS 2009 damage stability calculations leads to a number of implementation problems which must be solved to guarantee that the MC simulation delivers exactly the same results as the manual, zone based damaged stability calculation. If these problems are solved, the MC based damage stability calculations can be used during the initial design phase until the damage stability approval. The proposed method reduces the computational effort drastically which supports the initial design phase of the ship's compartmentation. The method further leads to higher attained indices and consequently to a safer and more efficient design

Calculation of the hydrostatic and structural integrity of docking sequences

The conditions of competition within ship yards are changing. The current market situation requires a new orientation of the Pella Sietas ship yard with flexible solutions for new ship types. Complex, heavy and ice-going ships show one way for future designs. In view of all the technical difficulties involved in such challenging projects, the first question must be how to handle these heavy constructions with the yards building facilities available. The Pella Sietas yard is using a floating platform for newbuildings. The question arises whether or not this platform is still capable and suited for this kind of ship types. The docking procedure is a complex multi-body interaction that copes with hydrostatic and structural challenges. The docking operation is regulated by the sequence of flooding and emptying ballast water tanks of the dock. At any time of this dynamic operation the hydrostatic stable equilibrium of ship and dock must be ensured. When the ship becomes afloat the keel block system transfers the ships weight on the structure of the dock. It must be ensured that the resulting tensions and deformations do not exceed the maximum permissible values. This paper describes a fast calculation method that determines the mentioned hydrostatic as well as the structural investigations during the docking procedures. The method implies a numerical progressive flooding simulation that calculates the hydrostatics of ship and dock under consideration of their interaction by dock blocks together with the ballasting sequence in the time domain. Furthermore it calculates the block forces distribution by applying the deformation method. In the calculation process ship and dock are modeled as Timoshenko beams and the dock blocks as nonlinear spring elements. Moreover the shear force and bending moment distributions of ship and dock are calculated and the deflection lines are presented. Therefore, the described method enables the ship yard to evaluate quickly the possibility of building new types of ships on the existing building platform and allows evaluating which modifications are useful to enlarge the capacity of the platform even further. It provides a useful tool to minimize local and global stresses and deformations of the interacting bodies during the whole docking procedure by fast optimization of the block system arrangement and the ballasting sequences. As a result the described method could expand the range of flexibility of a given floating dock structure. In addition, the whole hydrostatic and structural integrity of docking sequences can be computed faster and more accurate even at a very early project stage

A fast numerical method for internal flood water dynamics to simulate water on deck and flooding scenarios of ships

The paper reports the extension of a Lattice Boltzmann model for the nonlinear viscous shallow water equations (NSW) and its application to the simulation of internal flood water dynamics. The solver is accelerated with the help of NVIDIAs CUDA framework to access the computational power of graphics processing units (GPGPUs). The model is validated with typical tank sloshing and cross flooding scenarios and the results are compared to analytical solutions and the results of a state-of the art shallow water solver on the basis of Glimm's method. Copyright © 2013 by ASME

Dritter Interdisziplinärer Workshop Maritime Systeme : aktuelle Ergebnisse aus laufenden Promotionsprojekten an der TUHH

Kurzberichte zum Dritten Interdisziplinären Workshop Maritime System

Zweiter Interdisziplinärer Workshop Maritime Systeme : aktuelle Ergebnisse aus laufenden Promotionsprojekten an der TUHH

Kurzberichte zum Zweiten Interdisziplinären Workshop Maritime SystemeProceedings of the Second Interdisciplinary Workshop Maritime System

Numerical prediction of ship-ice interaction-a project presentation

It is inevitable that commercial shipping and oil and gas resource exploitation activities in the Arctic will increase due to decreasing sea ice extent caused by global climate changes. Significantly more demanding and at the same time less well known environmental conditions create a need for reliable methods to assess icebreaking performance guaranteeing safe performance of the ships operating in this area subjected to various ice conditions. The classic approach of assessing ice-going performance, which combines class rules, experience and model tests, may not be applicable for the Arctic region in full. Furthermore, ship yards experience difficulties due to decreasing time frames and financial restrictions. Therefore this paper seeks to introduce a new development for a realistic and validated direct simulation approach for prediction of the hull load and icebreaking resistance that covers all aspects of the industrial design process and allows a more comprehensive analysis. The breaking model will provide a variable breaking pattern and is able to mimic the influence of the vessel speed and the environment on the ice loading and the predicted breaking length. In order to predict the extreme representative conditions to be simulated, a reverse extreme load prediction methodology is incorporated. An efficient, time dependent dynamic coupling between broken ice fragments, ice features, the 3D flow field and the ship's hull provides resistance values for performance calculations. The computational model will be validated against full-scale data and class rules using deterministic and probabilistic measures. This simulation approach is developed within international research collaboration between Pella Sietas, Rolls Royce Marine, TUHH and NTNU. An overview of the project together with the current status of the ongoing work including first results is presented