Wyniki wyszukiwania - BazTech

1

Computational fluid dynamics and experimental hydrodynamic analysis of a solar AUV

Asadi Asrami Ehsan, Moonesun Mohammad, Azizi Abi Farhad

Computer Assisted Methods in Engineering and Science

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2021

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Vol. 28, no. 1

57--77

EN

In the present study, the effect of free surface on the hydrodynamic forces acting on themotion of an autonomous underwater vehicle (AUV) has been investigated. The AUVis powered by solar energy. Using computational fluid dynamics, the Reynolds averaged Navier Stokes (RANS) equations for the flow around the AUV are solved, and the freesurface effect is simulated using the volume of fluid (VOF) two-phase flow model. Forthis purpose, the commercial code ANSYS FLUENT 18 was used [1]. The results ofthe numerical solution are compared with experimental results of the AUV model in thesurface motion in the towing tank of the Persian Gulf National Laboratory with a scaleof 1:1. The experiment was performed in a fixed draft and the velocity was ranging from 0.2 m/s to 1.4 m/s (according to Reynolds number 2.4 x 105 to 1.7 x 106).

2

Determination of seakeeping performance for a case study vessel by the strip theory method

Niklas Karol, Karczewski Artur

Polish Maritime Research

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2020

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nr 4

4--16

EN

The increase of seakeeping performance is of particular importance for car and passenger ferries, service ships in the gas and oil extraction industry and offshore wind power farm industry, as well as for special purpose ships (including military applications). In the water areas of the Baltic Sea, North Sea, and Mediterranean Sea, which are characterised by a short and steep wave, the hull shape has a substantial impact on the operational capacity and propulsion efficiency of the ship, as well as on comfort and safety of navigation. The article analyses selected aspects of seakeeping for four variants of a selected case study vessel, indicating practical limitations of the strip method. The analysed aspects included hull heaving and pitching, added resistance, Motion Thickness Indicator (MSI), and Subjective Magnitude (SM). Experimental tests were also performed in the towing tank. Their comparison with the numerical results has indicated high inaccuracy of the strip method. What is more, the simplified representation of hull shape used in the strip method makes it impossible to analyse the effect of hull shape changes on the predicted seakeeping characteristics. Especially for the case of head wave, neglecting highly non-linear phenomena, such as slamming or head wave breaking, in strip method-based computer simulations will significantly decrease the reliability of the obtained results. When using the strip method, the seakeeping analysis should be complemented with model tests in a towing tank, or by another more complex numerical analysis, such as CFD for instance.

3

Generation and propagation of nonlinear waves in a towing tank

Drzewiecki Marcin, Sulisz Wojciech

Polish Maritime Research

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2019

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nr 1

125--133

EN

The paper presents the results of the research focused on linear and nonlinear wave generation and propagation in a deepwater towing tank equipped with a single flap-type wavemaker of variable draft. The problem of wave generation and propagation has been theoretically formulated and solved by applying an analytical method; linear and nonlinear solutions were obtained. The linear solution has been verified experimentally. The laboratory experiments confirmed that a linear model can be applied to predict the generation and propagation of water waves of low steepness. However, according to the analysis, the discrepancies between wave profiles predicted by applying the linear and nonlinear models rapidly increases with increasing wave steepness. Additionally, the secondary phenomena which occur in the towing tank, including: disintegration of wave profile, wave reflections from the beach and wave damping, were analyzed. Knowledge on the nonlinear processes and phenomena is essential for modeling the environmental conditions during tests carried out to secure the safety of the naval and offshore constructions. The theoretical formulation was derived and the solution was obtained by the Institute of Hydroengineering of the Polish Academy of Sciences IBW PAN while the experimental research was carried out in Ship Hydromechanics Division of the Ship Design and Research Centre CTO S.A.

4

Analiza wybranych metod obliczeniowych i eksperymentalnych wyznaczania charakterystyk amplitudowych jachtu żaglowego na fali regularnej

Karczewski A., Szmagliński R.

Prace Wydziału Nawigacyjnego Akademii Morskiej w Gdyni

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2018

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Z. 33

21--32

PL

W artykule zaprezentowano wyniki analizy porównawczej charakterystyk amplitudowych właściwości morskich kadłuba jachtu żaglowego na fali regularnej, uzyskanych trzema metodami. Dwie z nich opierały się na podejściu obliczeniowym, trzecia zaś na klasycznym eksperymencie, przeprowadzonym na basenie modelowym. Zrewidowano użyteczność formuł empirycznych, opracowanych na bazie badań kadłubów jachtowych serii Delft. Wykonano symulacje komputerowe przy użyciu modelu numerycznego według teorii paskowej oraz wykonano badania modelowe w celu walidacji obu metod. Dla wybranych warunków falowania porównano zachowania jachtu, które są charakterystyczne dla jego pływania w warunkach sfalowanej powierzchni akwenu wodnego, czyli nurzanie i kiwanie. Zbadano również przyrost oporu kadłuba od falowania.

EN

This paper presents the results of a comparison analysis for seakeeping performance in regular waves obtained by three methods. Two of them were based on a computational approach, the third was based on an experiment carried out in a model pool. The usefulness of empirical formulas developed on the basis of the Delft yacht hulls has been revised. Computer simulations were performed using a numerical model according to strip theory, and model tests were performed to validate both methods. For selected wave characteristics, heave and pitch motions was compared. The added resistance in waves was also examined.

5

The propagation of the waves in the CTO S.A. towing tank

Drzewiecki M.

Polish Maritime Research

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2018

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S 1

22--28

EN

The paper presents the results of research focused on the wave propagation in the CTO S.A. deepwater towing tank. In the scope of paper, the wavemaker transfer function was determined for regular waves, based on the Biésel Transfer Function and further for irregular waves, based on Hasselman model of nonlinear energy transfer. The phenomena: wave damping, wave breakdown and wave reflection, were measured, analyzed and mathematically modeled. Developed mathematical models allow to calculate the impact of mentioned phenomena on the wave propagation and furthermore to calculate the wave characteristics along the whole measurement area in the CTO S.A. deepwater towing tank, based on wavemaker flap motion control.

6

Modernizacja kaskadowego układu regulacji wywoływacza fal basenu modelowego

Drzewiecki M.

Zeszyty Naukowe Wydziału Elektrotechniki i Automatyki Politechniki Gdańskiej

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2015

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Nr 47

39--42

PL

Artykuł opisuje modernizację stanowiska badawczego w Centrum Techniki Okrętowej (CTO) S.A. – głębokowodnego basenu modelowego z płytowym wywoływaczem fal z płytą mocowaną powyżej dna basenu na pojedynczym przegubie. Modernizacja obejmowała zastąpienie oryginalnego analogowego układu regulacji nowoczesnym cyfrowym układem sterowania, opartym na 8-bitowym mikrokontrolerze AVR. Na podstawie dokonanej identyfikacji poprzedniego układu regulacji zrealizowany został nowy, bardziej przyjazny użytkownikowi układ, który – umożliwiając wdrażanie nowych rozwiązań wykorzystujących nowoczesną technikę cyfrową – zapewnia równocześnie oczekiwaną powtarzalność realizacji fal basenowych.

EN

The paper describes the problem of modernizing a test bench – a deepwater towing tank with a wave maker with a rigid flap articulated above channel bed in the Ship Design and Research Centre (Centrum Techniki Okrętowej S.A.). The modernization was based on the replacement of an analog control system from the 1974 by a modern digital control system based on a 8-bit microcontroller AVR. The scope of this paper includes: identification of the analog control system with a measuring system and an actuating system, design of the digital control system based on the identified analog control system, implementation of the digital controller, start-up and checking of the new control system. The new digital control system meets user expectations, offering extended functionality together with required repeatability. The modernizing of the cascade control system was contribution to start of work on the implementations of new solutions using a modern digital technology.