Fluid Control Research Group

 


For the development of eco-friendly and energy-saving ships, we are engaged in research and development of advanced technologies for computational fluid dynamics (CFD) applications and tank testing, and are developing fundamental ship design tools based on the results of these studies. Furthermore, by applying and developing the results of basic research and development, we are developing hull forms, propellers, and energy-saving devices that are more closely aligned with our products and embodying new energy-saving concepts to meet the needs of our customers (ship owners, shipyards, etc.) through collaborative or contracted research projects.

Fluid Control Research Group Logo


 

  

Roman,
Vision,
Mission

Roman
  • The oceans are the frontier of the 21st century, a place to meet new discoveries.



Vision
  • Becoming the world's admired group of engineers on marine fluid control.
  • To contribute to strengthening the international competitiveness of the Japanese maritime industry.



Mission
  • Development of zero GHG emission ships.
  • Advancement of energy-saving devices to improve propulsive performance.
  • Development of predictive technology for underwater noise emission from ships and low noise and high efficiency propellers.
  • Development of optical measurement technology for interfering flow field around hull and propeller and cavitation.

  

Overview of Research

1.  Skin-friction drag reduction and its evaluation methods
 The skin-friction drag accounts for about 60 to 80% of the total resistance of the displacement-type vessels. Therefore, a high energy saving effect can be expected by reducing it. We research the air lubrication method that reduces skin-friction drag by covering the ship bottom with bubble and develop the evaluation method of the skin-friction drag increase due to the hull coating and fouling.


Skin-friction drag reduction measurements by air lubrication method
using 36m length flat plate model at high reynolds number (Towing speed 8 m/s)



Skin-friction measurements of hull coating using 14m length flat plate
(Towing speed 4 m/s)




2.  Design of High Energy Efficiency Ship

Maritime Industry is making significant efforts to alleviate the global warming issue, ex. Since 2013, a regulation of the Energy-Efficiency Design Index was introduced to address the issue. For this reason, the development of environmentally friendly ships plays an essential role in solving the issue. Our group is developing eco-friendly ships and energy-saving additions by applying a detailed analysis of the flow around the hull using computational fluid dynamics (CFD) and a highly efficient water tank test method using a 3D printer.


EEDI certification test (ISO 9001 certified) (left)
and the energy-saving device WAD installed on a ship (right)



Results of CFD analysis of the energy-saving device USTD (left)
and a model made with a 3D printer (right)


Our developed hull forms and the energy-saving devices have been adopted by the shipyard and are actually working on the sea.


Actual vessel with an energy-saving hull form that reduces CO2 emissions
by more than 16% compared to conventional vessels




3.  Propeller Cavitation

In recent years, demands for lower hull vibration and noise of ships has been increasing. The main cause of the hull vibration is engine and propeller cavitation. A high accuracy estimation method of the pressure fluctuation caused by cavitation is required. It is important for the estimation method to accurately calculate the second-order time variation of the cavity volume of the unsteady cavitation on the propeller blade. However, current theoretical prediction methods are not accurate enough, and verification of theoretical prediction methods using the results of cavity shape measurements is essential to further improve accuracy. Our group has developed a 3D shape measurement system using a combination line CCD camera method. This system enables fast and accurate shape measurement underwater. Our group have been developing a measurement method for the cavity shapes on a propeller blade using the developed 3D shape measurement system. This system can measure the cavity shapes that have been difficult to measure with high accuracy and resolution. In addition, the high-precision cavity shape measurement data obtained by our measurement system can contribute to the validation of the theoretical estimation method of the pressure fluctuation induced by cavitation.

Combination line CCD camera method



Cavitation volume measured by Combination line CCD camera method




4.   Development of a novel ship design method utilizing AI technology

Our group is building a hull form and flow field database and developing a novel ship design method utilizing AI technology.


Conceptual diagram of a new ship design method using AI technology


To utilize AI tech. to hull form design, hull form representation method which can express complex 3D curved surface on the hull with AI tech. friendliness is essential. Our group has been developing an image-based Curved Surface Representation (ICSR) for the purpose of applying image recognition technology to hull design, and has been promoting the application of AI technology to hull design.



Database construction method is one of the key technologies to apply the AI technology to ship design. Our group is developing a database construction method by utilizing a hull form blending (morphing) method which can generate new hull forms automatically while retaining the genes of excellent hull shapes which are difficult to be parameterized.



Conceptual diagram of a hull form blending


Hull form design has been developed based on the experience of expert engineers, and the transfer of these skills has been a challenge. Our research group has been studying to visualize the relationship between hull form and stern flow field, which has been tacitly known by experienced engineers, by utilizing the hull form database.

Visualization of changes in stern flow field due to ship shape change (formal knowledge of tacit knowledge)


An example of a new hull form design method using AI technology is the development of an optimal hull form for energy-saving additives using the Wake Design System. In this example, we have developed a system that automatically guides the interference design between the hull form and the energy-saving device from the database, which had been done through trial and error by skilled engineers. As a result of tank tests, it was confirmed that the hull form output from the system is actually more effective for energy-saving devices, and is 2.2% more effective than the initial hull shape.



Energy saving effect of hull form suitable for energy saving duct designed by wake design system


HOPE Light, a hull form optimization program, is one of the systems widely used by shipyards and shipping companies to analyze the database in Japan, and it can evaluate a ship's propulsive performance from the main dimensions of a ship based on the database of tank tests conducted by NMRI. It is a program that can be used in practical applications such as initial hull form studies.
Click here for detailed instructions



Sample of HOPE Light Output





5.   Flow filed measurements

In order to clarify complicated fluid phenomena such as gas-liquid two-phase flow and high Reynolds number flow around a real ship, we are developing advanced flow field measurement technology applying visualization technology such as laser.


Two-phase flow filed measurements using Particle Tracking Velocimetry and Shadowgprahy


Hull pressure fluctuation measurements in wave by Fiber Bragg Gating pressure sensor


Flow filed measurements around model ship stern
by Underwater Stereo Particle Image Velocimetry system


Measured flow filed and pressure distribution around ship stern
by Stereo PIV and FBG sensor


PIV measurements around energy saving device of actual ship
(Collaborate with KED Photonics (Germany) )