Author: pa

Towing Tank

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SR_Schlepprinne_Zeichnung

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SR_SUBPMM_Traeger

The SVA Potsdam operates a towing tank which is 280 m long and has a rectangular cross-section of 9 m width and 4.5 m depth. The maximum towing speed is 7.5 m/s with an accuracy of 0.6 mm/s. The towing carriage is driven via two double stator linear motors.

At the front of the tank there is a wave generator which can produce regular and irregular waves and also wave packets up to a wave height of 0.30 m. At the back, the towing tank ends in a beach as a wave absorber.

In the towing tank, free running tests are carried out with propellers and propulsion systems as well as resistance and propulsion tests, wake field measurements and paint flow tests. Additional elements of the testing spectrum include maneuvering, seakeeping tests and experiments with submersibles.

The towing carriage is provided with a flexible carrier system that can accommodate all equipment and experiments. The support at the rear of the towing vehicle is hydraulically adjustable in height. For example, the open water dynamometer and the submarine planar motion system (SUBPMM) or the PIV system can be installed there.

The equipment of the towing carriage is completed with cameras for the QualiSys optical tracking system and video cameras as well as cameras for recording experiments and images of wave systems.

Technical Specifications
Towing Tank
Length [m] 280
Width [m] 9
Depth [m] 4.5
Towing Carriage
Max. Towing Velocity [m/s] 7.5
Precision Carriage Velocity [mm/s] 0.6
Wave Generator
Max. Wave Height [m] 0.3
Types of Waves regular, irregular, wave trains  

Sea Trial Evaluation

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Prior to delivery and acceptance of new ships, the achievable speed for a given power and the power consumption for a given speed is determined in a trial (measured mile) with the full-scale version. Primarily, it is checked as to whether the contractual parameters have been achieved and, secondarily, whether the required EEDI is fulfilled.

To determine the delivered power, the torque and rotational velocity of the propeller for a given speed can be measured. This measurement can be carried out by the SVA onboard the ship with own measurement equipment.

Unlike model tests, the conditions in a measured mile are only in the rarest cases ideal. It can hardly be avoided that measured miles must be carried out in wind and waves, with shallow water effects, in areas of current, etc. To convert the environmental influences on the contract or experimental conditions, the measured mile results must be evaluated. The SVA Potsdam offers such calculations which are performed in accordance to the current standards of IMO and ITTC.

 

Power Measurement at Full-Scale

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Performance measurements on the propeller shaft are performed during measured miles, acceptance of new ships and, in case of problems, in the area of propeller/engine tuning to determine the power consumption of the propeller at full-scale. For this, the torque and speed of the propeller shaft or gear coupling shafts and intermediate shafts are measured. The torque measurement is carried out with strain gauges and the speed measurement with a magnet-hall sensor system. With a Bluetooth measurement module, the signals are processed and transmitted digitally to a measuring computer. Additional metrics like speed, heading, rudder angle and trim of the vessel may be time equidistantly recorded. For this purpose, GPS / DGPS systems, gyroscopes and other instrumentation are available.

Manoeuvering

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The use of numerical calculation methods offers many possibilities to investigate ship manoeuvres. In general, numerical calculations analogous to PMM-experiments (Planar Motion Mechanism) are carried out in which static and dynamic simulations are performed to determine the forces and moments as a function of a specific movement of the ship. From this, the hydrodynamic coefficients can be derived and fed into a mathematical model. With the calculation of a complete set of hydrodynamic coefficients, any manoeuvre can be simulated. To verify the quality of the numerical calculations, the calculation results are continually validated with the corresponding measured values.

Numerical simulations allow to:

  • Simulate manoeuvring behaviour in model and full-scale
  • Simulation of static and dynamic tests
  • Visualisation of flow, detection of separating flow
  • Design of control elements such as rudders, thrusters, etc.

The rudder is by far the most frequently used control element; it operates in the wash of the propeller. Below, the pressure distribution on the rudder for a rudder angle of δR = 20° with a rotating propeller is shown.

 

  

CFD_man_abb2_m_RahmenCFD_man_diag_m_Rahmen

 

Context Related References / Research Projects

[1] Lübke, L.: Investigation of a Semi-Balanced Rudder, 10th Numerical Towing Tank Symposium, Hamburg, 24.09.2007
[2] Lübke, L.: Investigation of a Semi-Balanced Rudder, 14. SVA Forum, Potsdam, 07.11.2007
[3] Lübke, L.: Investigation of a Semi-Balanced Rudder, ANSYS Conference & 25th CADFEM Users Meeting 2007, Dresden, 21. – 23.11.2007
[4] Lübke, L.: Numerische und experimentelle Untersuchungen an einem Halbschweberuder, STG-Sprechtag, Verbesserung der Propulsions- und Manövriereigenschaften von Schiffen, Papenburg, 18.09.2008
[5] Lübke, L.: Numerische PMM-Tests für Unterwasserfahrzeuge, ANSYS Seminar, Simulationswerkzeuge für die Marine und Offshore Industrie, Hamburg, 05.11.2008
[6] El Moctar, O., Brehm, A., Lübke, L.: Hydrodynamische und strukturmechanische Untersuchung von Rudern großer, schneller Schiffe (XXL-Ruder), PTJ Statustagung, Warnemünde, 11.12.2008
[7] Lübke, L.: Numerische und experimentelle Untersuchungen der effektiven Ruderzuströmung beim Manövrieren, 2. SVA Forschungsforum „Theoria cum praxi“, Potsdam, 29.01.2009
[8] Lübke, L.: Manoeuvering Simulations of Underwater Vehicles, 12th Numerical Towing Tank Symposium, Cortona Italy, 04.-06.10.2009
[9] Lübke, L.: Investigation of a Semi-balanced Rudder, Ship Technology Research, Vol. 56, No. 2, 2009

Seakeeping

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The use of numerical methods offers many opportunities to examine ships at sea. The SVA can use the program system UTHLANDE or RANSE Method depending on the application. UTHLANDE provides the ability to perform seaway calculations based on linear and non-linear strip method. Using this method, monohulls and catamarans can be studied over a wide range of applications and short- and long-term statistics can be calculated. For special cases or the simulation of non-linear applications, RANSE Method (ANSYS Fluent) is used.

With numerical calculations, issues can be examined in terms of added resistance or the acceleration and motion behavior of ships. Added resistance at sea is an essential aspect in order to determine power requirements and operating costs of vessels correctly. The motion behaviour at sea, however, is an essential aspect of comfort and determines the operating limits of ships.

The numerical seaway simulations with RANSE procedures include the following applications:

  • Seaway from any direction, stationary and in motion
  • Calculation of regular and irregular sea states, with the focus on the calculation of regular seaway
  • Determination of the added resistance
  • Determination of accelerations

 

Energy Saving Devices

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