Boots – shoes – and leggings
Patent
1989-08-08
1990-04-17
Chin, Gary
Boots, shoes, and leggings
364550, 364559, 364463, 340623, 340689, 73451, 73453, 114123, G06F 1520, B63B 4304
Patent
active
049186280
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the assessment of stability of floating objects and assessment of the transverse metacentric height of the object, for example a ship.
It is known to try to assess a vessel's stability from a measure of its rolling frequency. This is derived by counting the number of rolls of the vessel over a measured period of time.
The Wesmar SC44 stability computer, manufactured by Western Marine Electronics Inc., calculates the transverse metacentric height (GM) of a vessel from its predominant roll frequency as derived from a simple timing of the roll period of the vessel. A count of a plurality of rolls is taken in order to arrive at an average figure for the roll period. This count is recommended to take place over a period of thirty minutes or more for a large vessel. Thus, a long interval may elapse before a change in GM is recognized. Furthermore, the inconsistent nature of the waves causing the vessel to roll and the finite time over which the roll period can be averaged leads to errors and spurious readings.
According to the present invention, there is provided apparatus for assessing the stability of a floating object. The apparatus comprises a roll sensor which is sensitive to the component of gravitational force along a working axis of the sensor, the roll sensor being mounted in use on the object with the working axis horizontal when the object is floating in an upright position, and processing means, including analyzing means, for sampling the output of the roll sensor at predetermined intervals of time over a period, the analyzing means being adapted to determine the frequency components of the roll motion of the object from the samples for identification of the dominant roll frequency of the object.
The natural rolling frequency of a vessel can normally be identified as the frequency at which the roll power of the spectral function is largest.
The invention will now be described in more detail with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of an apparatus incorporating the present invention;
FIG. 2 is a schematic diagram of the analog interface in FIG. 1;
FIG. 3 is a flow chart of the method of computation of the metacentric height under free rolling conditions incorporated in one aspect of the present invention;
FIG. 4 is a graph of a typical roll power spectrum of a vessel under free rolling conditions;
FIG. 5 is a graph of a weighting function used in the embodiment of the present invention;
FIG. 6 is a flow chart of the method of computation of metacentric height under forced rolling conditions incorporated in another embodiment of the present invention; and
FIGS. 7a, b and c are graphs of typical roll gain of a vessel under forced rolling conditions.
Referring to FIGS. 1 and 2, the apparatus comprises a transducer and an electronics unit 2. The transducer serves as a roll sensor and is a translational accelerometer 1, which in this embodiment is a Setra Model 141 translational accelerometer which is, in use, fixed to a bulkhead of a vessel in a vertical fore-and-aft plane thereof by a magnetic mount so that the sensitive axis of the accelerometer is in the lateral axis of the vessel. With the accelerometer working axis thus horizontally mounted, it is insensitive to acceleration due to gravity when the vessel is in the upright position. As the vessel rolls away from the upright position, the accelerometer is increasingly affected by this acceleration in proportion to the sine of the angle of roll of the vessel. Alternatively, the translational accelerometer 1 could be replaced by a gyroscopic sensor or a rotational accelerometer.
The electronics unit 2 comprises a display 8, a thermal printer 9, a keyboard 10 with which to enter commands, a microprocessor controller 12, an analog interface 3, a real time clock 14, a complementary metal oxide semiconductor (CMOS) memory unit 16 and a power supply 18. The electronics unit 2 is mounted in a portable steel case which can be closed to protect against the elements. In a preferred embodiment,
REFERENCES:
patent: 3633003 (1972-01-01), Talwani
patent: 4317174 (1982-02-01), Dean
patent: 4401888 (1983-08-01), West et al.
patent: 4549627 (1985-10-01), Drabouski Jr.
patent: 4647928 (1987-03-01), Casey et al.
Griffin Michael J.
Lawther Anthony
Lewis Christopher
Chin Gary
Mattson Brian M.
University of Southampton
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