|
FOR IMMEDIATE RELEASE July 15, 1999 | ||||||||||||||||
| ||||||||||||||||
NTT, The University of Tokyo and GH Craft Ltd. have worked together to construct the Fiberoptic Sensor Hull Damage Detection System (Figure 1) to detect deformation in and damage to the hull of Nippon Challenge, Japan's entry in the America's Cup 2000[1], the king of yacht races. Yachts entered in the America's Cup have hulls shaped to provide minimum resistance and formed of light and very strong sandwich compound materials. Because they are designed at close to the limits of the strength of the materials used, technology was needed which allowed early detection of the location of deformation and damage (cracks or debonding) leading to hull break-down. The Fiberoptic Sensor Hull Damage Detection System jointly designed by the above parties combines NTT's BOTDR[2] technology, the structural analysis technology of the Department of Environmental & Ocean Engineering at The University of Tokyo, and GH Craft Ltd.'s composite design and manufacturing technology. This is a radical new detection system which can measure the location of deformation in and damage to the hull automatically or by remote control by analyzing the continuous strain data which is obtained by the fiberoptic sensor attached to the hull. | ||||||||||||||||
Main Features | ||||||||||||||||
This system allows (1) structural design verification, (2) detection of the location of deformation and damage and (3) diagnosis through automatic measurement and remote control. | ||||||||||||||||
Technology Points | ||||||||||||||||
1)Feedback on hull structural design This system produces three-dimensional strain data on the entire hull on the basis of the continuous strain measurement results by the fiberoptic sensors attached to the yacht rather than the point data by conventional sensors such as strain gauges[3]. Moreover, the system not only detects damage but allows checks on hull deformation. Nippon Challenge and the other yachts are designed so that the rigidity in the longitudinal direction line is high to resist deformation, because the great force acts in the line direction. We practically measured strain produced in the both on the water and land, and analysed the change in their strain using the Detection System (Figure2). These results indicate that the hull has an ideal structure, and they were consistent with the structural analysis produced through simulations, proving that the hull has an ideal structure. This bears out the value of the Detection System in structural design verification. | ||||||||||||||||
2)Establishment of damage (cracks or debonding) detection methods The point where cracks or debonding have actually occurred can be detected from the continuous strain distribution measured by the fiberoptic sensors (Figure 3). By comparing the strains shown by two fiberoptic sensors attached along the bonded joints between hull and bulkhead, it is possible to detect failure of the structure by comparing the stress distribution whether the cause of strains appearing between material layers are the result of deformation or material cracks or debonding. Further, by altering the type of optical fibers used in the sensors and elsewhere, their boundary can be used as a mark to correspond position between the fiberoptic sensor and the hull. | ||||||||||||||||
3)Diagnosis through automatic measurement and remote control Automatic operation of the system makes it easier to detect damage which occurred in the yacht in New Zealand base camp. The system can also be operated by remote control using telecommunication lines, etc. During the America's Cup 2000, remote diagnoses will be carried out from Japan while Nippon Challenge is in its base camp in New Zealand. | ||||||||||||||||
Next Steps The next steps planned by the three parties which worked on the Detection System are as follows. To clarify the relationship between strain and damage (cracks or debonding), we perform simulation employing the finite element method which can calculate approximately deformation, abd an experiment using a model. In addition, we plan to collect fundamental strain data of the yacht while applying this system practically. | ||||||||||||||||
Glossary
| ||||||||||||||||
Inquiries
Mr. Kurashima, Mr. Sano, Mr. Ozaki | ||||||||||||||||
 NTT NEWS RELEASE |