Author(s): J. Pukki; K. Simomaa
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Abstract: An instrument for registering ice loads in an offshore structure has been designed and constructed in the Instrument Laboratory of the Technical Research Centre of Finland. The instrument is intended for the investigation of new methods and structures for offshore engineering and also the development of new types of lighthouses for severe environments, to give just two examples. The device consists of two stress-measuring channels, two acceleration-measuring channels, a magnetic tape recorder, plus time-keeping and control electronic circuitry. The instrument is designed to operate unattended for a period of several months in an offshore structure, without an external power supply, and subject to the environmental stresses met in the northernmost part of the Gulf of Bothnia, Finland. To save electrical energy, most parts of the instrument are normally inoperative. The time-keeping circuit, the acceleration measurement channels and an activating circuit are functioning all the time. At predetermined time intervals, the time-keeping circuit activates the device. If the acceleration signal level on either acceleration measurement channel exceeds a predetermined limit value, the wake-up circuit activates the device. The activating time interval and the acceleration limit value are determined by the user before instrument operation is started. When activated, the instrument performs a set of measurements. Each of the four channels is measured simultaneously. The processing unit then calculates some criterion values from the measurements, and if they satisfy the criteria it has in its memory, the measurement series (of values) is stored on a magnetic cassette tape in digital form. The computer then updates the criterion 1imit values, taking into account the newest measurements and the amount of tape left on the cassette. Then the device deactivates itself. The device has been tested in KEMI II lighthouse at the northern end of the Gulf of Bothnia in late winter 1982, and again in late winter 1983, The total testing time was about six months, during which the device operated correctly.
Year: 1984