The MIROSmc is a new system for full scale verification of the rig response amplitude operators. This paper reviews the basic principles of operation of MIROSmc. Wave and motion data collected by the system during the water '85/'86 are presented and theoretical and measured transfer functions are compared.
The lack of convenient, reliable and accurate instrumentation has been a severe limitation for the full scale evaluation of rig performance. Combining microwave remote sensing principles and inertial navigation techniques the recently developed MIROSmc concept represents a new and powerful tool for full scale determination of the rig response operators.
This paper reviews the basic MIROSmc concept and presents comparisons of theoretical and measured transfer functions based on data collected during the water '85/'86 from the Deepsea Bergen semisub (type: Aker H3.2). The rig is owned by Odfjell Drilling and was operated by Statoil as in the North Sea.
The results presented m this report originate from a development project sponsored by Statoil a. s. and Saga Petroleum a. s. In addition to the sponsors the following parties participated in the project: Odfjell Drilling, Marintek a.s. and MIROS A/S.
In the following a brief description of the MIROSmc system and the rig installation is given. A comprehensive review of the basic measurement principles of the MIROS system is given in Appendix 1.
Floating structures are exposed to environmental forces due to wind, waves and current MIROSmc (Microwave Remote sensor for the Ocean Surface, motion compensated) measures the directional wave height spectrum, surface current and the resulting rig motion due to the environmental forces. A block diagram is presented in Fig. 1. The system comprises(Fig 1 is available in full paper)
SENSOR HEAD containing the microwave transceiver operating at 5.8 GHz and the antenna assembly
MIREF (Marine Inertial Reference) measuring the rig motion with SIX degrees of freedom.
CENTRAL PROCESSOR containing the signal processing electronics the system computer and the cassette tape logger.
In a typical installation, the sensor head is mounted about 50m above the sea, and scans the sea surface at a radius of 500m over a 180 degree arc, in six 30 degree sectors
The sensor head receives echoes from the sea surface containing information about the dynamic processes of the upper layer of the ocean. This information is processed in the central processor giving the wave height spectrum and the radial surface current for each sector. Integration over all sectors provides the conventional nondirectional wave spectrum and parameters such as the significant wave height and peak period. The total current vector is calculated from the radial components using a least squares algorithm.
MIREF is a compact inertial navigation unit providing information of the rig motion with six degrees of freedom. The rig heading is obtained from the gyro compass. The motion data collected by MIREF and the wave and current data collected simultaneously by the sensor head give the basis for the calculation of the response amplitude operators of the floating structure for any sea state and loading condition.