This paper describes a method that could generate electric energy from the propagating ocean waves by implementing an actively controlled tuned mass damper on a ship sailing on the ocean. There are three fundamental requirements for any alternative energy method to make it work in practice. The first issue is that there should be affluent energy sources in the nature. Then, we should collect and confine them in a compact space by means of a smart method. Finally, we must convert the renewable energy into electric power as fast as possible. The author discusses the weak points and strong points of the proposed power generating method, while paying attention to these three requirements. The author started an observation project that the vibration data from the vessels sailing on the ocean would be collected under different conditions. The motion data obtained from a ship on the ocean gives the energy density spectrum in the frequency domain, which verifies the first requirement mentioned above. There is the appropriate natural period that determines the performance of the device, or equivalently the power of the generator. The solution for the second requirement is the tuned mass damper method, which indirectly collect the energy from the primal system to the auxiliary system by means of gravity. The last requirement is satisfied by the unique control algorithm known as acceleration feedback method, which enhances the cost performance of the tuned mass damper with the low frequency dynamic property.
This paper reports the scheme of a research project funded by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) from the fiscal year of 2012 to 2014 under the title of "Development of base isolation device complied with the ultimate strength design code." The theoretical prediction tells us a new approach to develop a highly stable laminated rubber bearing that has a constant buckling load even under large lateral displacement. Relatively high shear stiffness makes it more stable and the height of the bearing should be longer than its diameter. They are the newly discovered theoretical buckling stability criteria from the previous studies conducted by the author’s research team. The experimental studies in this project show the compatibility with the theoretical prediction and highly linear loaddisplacement relationship under large deformation. The performance of the newly developed device satisfies the requirement of the ultimate strength design code, if the ground condition of the target building is normally solid enough to prevent liquefaction. The theoretically predicted buckling stability of the laminated rubber bearings has been experimentally verified by the specimens of this project.
This paper discusses the eigenvalue problem of a nonlinear differential equation that governs the stability of a shear
bending column under extremely large deformation. What is taken into consideration is the geometrical nonlinearity
while the material is supposed to be linear. The reason of a superbly stable buckling behavior of a slender rubber bearing
is physically explained by pointing out the analogy that is similar to the nonlinear wave propagation expressed in KdV
equation. The nonlinear boundary condition and the nonlinear term of the differential equation cancel each other and
make the associated eigenvalue rather constant. In other words, as far as the material is supposed to be linear, the column
does not buckle no matter how large the deformation is. This theoretical prediction is experimentally verified and
successfully applied to a base isolation system of a lightweight structure.
Authors propose a method to identify the mass matrix of a large building structure by using a small active dynamic damper, or equivalently, an active tuned mass damper. We modify the acceleration feedback algorithm, which was once developed for improving the dynamic damper's performance, with a different objective. The advantage of the dynamic damper is its size: it is so small that there is a possibility that we could create an extra-small device for measuring the mass of a large structure. We review the physical meaning of the acceleration feedback, and then we use a single-degree-of-freedom model to explain how to operate the device to examine the weight of a primary structure. Then, we extend this method to a multi-degree-of- freedom model so that we can measure its effective modal mass with respect to the location where this device is placed. The identification of the mass matrix of a large structure can be completed as we shift the observing points and determine the associated effective mass. Several numerical studies are also carried out to certify the proposed method.
A new control algorithm to improve a tuned mass damper is proposedand investigated. The feedback gain of the algorithm is linear to the response accel- eration of the primal system and it is optimized in the frequency domain under a har- monic excitation. The optimum feedback gain and the optimum parameters of thetuned mass damper are expressed in a closed form solution.
Conference Committee Involvement (2)
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
15 March 2004 | San Diego, CA, United States
Smart Systems and Nondestructive Evaluation for Civil Infrastructures
3 March 2003 | San Diego, California, United States
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