Position determining and dynamic positioning method and system for floating marine well drill platforms and the like

A system for determining the relative horizontal positions in terms of a cartesian coordinate system having a vertical Z axis and horizontal X and Y axes of the upper and lower ends of a flexible connecting line suspended from a floating marine platform, comprising:

• angle sensing means including upper and lower connecting line angle sensors for producing angle signals representing the vertical slope angles of the upper and lower ends of said connecting line measured in vertical X planes parallel to said X and Z axes and vertical Y planes parallel to said X and Z axes and vertical Y planes parallel to said Y and Z axes,
• signal processing means for combining said angle signals in accordance with the following equations (1) and (2) to provide an output signal representing the relative horizontal positions of said connecting line ends in terms of the X and Y coordinates of the upper end relative to the lower end
• X=K.sub.1 (.alpha..sub.x).sub.TOP +K.sub.2 (.alpha..sub.x).sub.BOTTOM
• Y=K.sub.1 (.alpha..sub.y).sub.TOP +K.sub.2 (.alpha..sub.y).sub.BOTTOM
• where:
• (.alpha..sub.x).sub.TOP, (.alpha..sub.x).sub.BOTTOM are the upper and lower vertical slope angles of the connecting line measured in said X planes, respectively,
• (.alpha..sub.y).sub.TOP, (.alpha..sub.y).sub.BOTTOM are the upper and lower vertical slope angles of the connecting line measured in said Y planes, respectively,
• K.sub.1, K.sub.2 are scale factors which are dependent upon at least some of the following:
• surface wave spectrum;
• physical characteristics of the connecting line including tension, modulus of elasticity, moment of inertia, drilling mud weight if used, and transit time of platform motion induced stress waves through the connecting line;
• physical characteristics of the platform;
• water current, and
• a positioning system adapted to correct said relative horizontal displacement of said platform in response to said output signal.

The method of determining the relative horizontal positions in terms of a cartesian coordinate system having a vertical Z axis and horizontal X and Y axes of the upper and lower ends of a flexible connecting line suspended from a floating marine platform comprising:

• sensing and producing angle signals representing the vertical slope angles of the upper and lower ends of said connecting line measured in vertical X planes parallel to said X and Z axes and vertical Y planes parallel to said Y and Z axes,
• combining said angle signals in accordance with the following equations (1) and (2) to provide an output signal representing the relative horizontal positions of said connecting line ends in terms of the X and Y coordinates of the upper end relative to the lower end
• X=K.sub.1 (.alpha..sub.x).sub.TOP +K.sub.2 (.alpha..sub.x).sub.BOTTOM
• Y=K.sub.1 (.alpha..sub.y).sub.TOP +K.sub.2 (.alpha..sub.y).sub.BOTTOM
• where:
• (.alpha..sub.x).sub.TOP, (.alpha..sub.x).sub.BOTTOM are the upper and lower vertical slope angles of the connecting line measured in said X planes, respectively,
• (.alpha..sub.y).sub.TOP, (.alpha..sub.y).sub.BOTTOM are the upper and lower vertical slope angles of the connecting line measured in said Y planes, respectively,
• K.sub.1, K.sub.2 are scale factors which are dependent upon at least some of the following:
• surface wave spectrum;
• physical characteristics of the connecting line including tension, modulus of elasticity, moment of inertia, drilling mud weight if used, and transit time of platform motion induced stress waves through the connecting line;
• physical characteristics of the platform;
• water current, and
• supplying said output signal to a positioning system adapted to correct said relative horizontal displacement of said platform.

A system of positioning a floating marine platform relative to a reference position on the ocean floor comprising:

• a flexible connecting line extending between said platform and reference position,
• angle sensing means including upper and lower connecting line angle sensors for sensing and producing angle signals representing the vertical slope angles and azimuth angles of the upper and lower ends of said connecting line,
• signal processing means for combining said signals in accordance with a predetermined relationship and producing an output signal representing the horizontal position of said platform relative to said reference position, and
• means for horizontally positioning said platform in response to said signal.

A signal processing system adapted to determine the relative horizontal displacement of a floating marine platform from a predetermined point, said system being adapted to receive input signals representing the vertical slope angles and azimuth angles of the upper and lower ends of a flexible connecting line suspended from a floating marine platform, said system comprising:

• a first analog-to-digital converter means for receiving, combining, and converting an upper angle signal to provide a converted upper angle signal,
• a d.c. power supply means for providing a calibration signal;
• a timing and control logic means for providing first, second, and third timing and control signals respectively;
• an analog multiplexer means for receiving and combining said calibration signal, said first timing and control signal, and a lower angle signal to provide a composite signal;
• a second analog-to-digital converter means for receiving and combining said composite signal and said second timing and control signal to provide a converted lower angle signal;
• a modem means for receiving and combining said converted lower angle signal and said third timing and control signal to provide a digital information signal;
• a conditioning means for receiving and conditioning said converted upper angle signal and said digital information signal to provide a conditioned data signal and a data ready signal, respectively, to said signal processing means;
• a keyboard means for entry of cable, platform, and marine parameters to provide a system parameter signal to said signal processing means;
• said processing means providing an output signal to said positioning system and a read out signal to a digital read out.