[Vol. 2] A recent trend in the marine industry is that manufacturers are striving to quickly develop eco-friendly devices. Nakashima Propeller manufactures marine propellers for domestic and international shipbuilders. They are also actively involved in developing and manufacturing energy saving propellers and appendages. Software Cradle’s SC/Tetra has been an indispensable tool for their development.
Function to Identify Erosion RisksOne of the achievements accomplished by introducing SC/Tetra was the evaluation of erosion risk using the erosion index function. The first task Mr. Hasuike wanted to examine, after introducing the fluid analysis tool, was the evaluation of erosion risk. Fig 1 shows contours of the erosion index. The white bubbles represent cavitation. The six blades were given different shapes, and the shape of the blade on top had the least erosion risk. Cavitation occurs where the flow slows down as the propeller moves towards the top, and diminishes completely by the time it moves to the side. With efficient blades, cavitation moves smoothly towards the top and diminishes without causing any damages to the blade.
Ultimate Rudder is an improved version of a rudder valve. The valve is attached to the propeller head instead of the rudder, where it is normally located. Attaching the valve near the propeller creates two favorable effects. First the hub vortex is better dispersed. Second, wake gain is improved. “Our intention is to slow down the incoming flow toward the propeller by locating the head, which was at the rudder edge, closer to the propeller. The head shape is our invention,” says Mr. Okazaki. As the propeller is most efficient when rotating slowly in the slowest possible flow, the wake gain can be improved by obstructing the incoming flow toward the propeller faces (Fig 2).
“Using CFD, we have been able to develop new energy saving devices over the years,” says Mr. Hasuike. Applying CFD enables optimization of an entire ship, including the propeller and the rudder, instead of only the propeller. Prior to introducing CFD, Nakashima Propeller used prototype appendages and rotating propellers in water tank experiments. “Thanks to CFD, we can now determine the optimal device shape easily and quickly at low cost. We were also able to reduce the number of experiments,” says Mr. Hasuike.
Mr. Hasuike says: “We found SC/Tetra easily operable. It is well integrated, from mesh generation to solver execution.” Easy mesh generation is also helpful. “It didn’t take long to get the hang of using SC/Tetra. Our design engineers now perform analyses just as regular tasks,” says Mr. Hasuike.
Next year, Nakashima Propeller plans to manufacture a CFRP propeller scaling six meters in diameter. By applying lightweight CFRP, it is possible to manufacture propellers in a larger scale compared to using metals. This can also improve energy efficiency. “CFRP is flexible unlike metals. If we can tailor this material skillfully, cavitation and vibrations can be controlled,” explains Mr. Hasuike. SC/Tetra is used extensively for these complicated analyses, where structural and fluid analyses must be coupled. “SC/Tetra is all-in-one software, which is useful even when we need to use several different functions,” says Mr. Hasuike.
Mr. Hasuike remarks that minimizing noise is becoming a requirement in the marine industry. Propeller noise from a marine vessel is a disturbance to sea animals, such as whales, that use sounds to communicate with each other. The need to regulate ship noise is being discussed. To prepare for these changes, Nakashima Propeller will start to focus on noise reduction.
Nakashima Propeller is also exploring optimization of overall ship design, instead of solely focusing on propellers. “Design optimization was done separately up until now. Propeller manufacturers focused on propellers, just as shipbuilders were only concerned with ship bodies. However, improving total energy efficiency for the entire ship requires analyzing it as a whole. To achieve this, we intend to construct a virtual towing tank,” says Mr. Hasuike.
Nakashima Propeller is working on upgrading their computational hardware environment for parallel computation in preparation for the virtual towing tank project (Picture 4). Their machine parallelism is now 3,000 degrees but was increased to 5,000. “Processing dozens of millions of mesh elements used to take two weeks, but it can now be done in just one day,” says Mr .Hasuike. Nakashima Propeller suggests the possibility of using the virtual towing tank for future EEDI certification. “We hope to facilitate a better simulation environment though the support from Software Cradle,” says Mr. Hasuike.
Nakashima Propeller has always been an industry leader. Software Cradle will continue to offer solutions that assist their development.
|Businesses||Development, manufacturing and sales of marine equipment, environmental improvement devices, and exterior products|
|Head Office||Jotokitagata, Okayama Higashi-ku, Okayama, Japan|
|Representative||Motoyoshi Nakashima, President|
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