. Development and evaluation of a motion compensating lift system for deep ocean construction. Underwater construction; Marine engineering; Civil engineering. MlZ+Kr^ Z = K^-jix Z(t) X(t) J_ MZ + KZ = KX where M = Mi K= Ku L,/L (a) Figure 1. Single-degree-of-freedom model of MCLS. of the uncertainty of the coefficients at the time the model was developed, they were omitted; this model was intended to produce only gross approximations. Physically, the MCLS (Motion Compensating Lift System) is arranged as shown in Figure la with the boom, pivoted at one end, supported by the spring Kg at a dista
. Development and evaluation of a motion compensating lift system for deep ocean construction. Underwater construction; Marine engineering; Civil engineering. MlZ+Kr^ Z = K^-jix Z(t) X(t) J_ MZ + KZ = KX where M = Mi K= Ku L,/L (a) Figure 1. Single-degree-of-freedom model of MCLS. of the uncertainty of the coefficients at the time the model was developed, they were omitted; this model was intended to produce only gross approximations. Physically, the MCLS (Motion Compensating Lift System) is arranged as shown in Figure la with the boom, pivoted at one end, supported by the spring Kg at a distance Lj from the pivot point. The boom supports a payload Mj^ on a rigid cable suspended from the outer end at a distance L from the pivot point. Motion of the support platform is represented by X(t) and motion of the payload by Z(t). This model is mathematically equivalent to the simple spring/mass system of Figure lb in which the input motion is X(t) and the response Z(t). The ratio of the amplitude of the load motion Z(t) to the input motion X(t) (that is, the response of this system) is shown in Figure 2 as a function of the period of the input T divided by the resonance period T^. Damping, or drag, forces present at the payload tend to decrease system response while damping in the com- pensator mechanism tends to increase system response by increasing the magnitude of the forces acting on the lift line at the boom tip. Later models used by CEL included those shown in Figures 3 and 4, with the latter being programmed for computer-based analysis. The criteria used in the design of the MCLS included minimizing internal friction and damping in the compensator unit and keeping the system's resonant period r^ significantly larger than the expected periods of the input X(t). These criteria tend to reduce system response, and thus to improve system performance. With the system designed so that the value of K is small, the dynamic line-tension variations are kept within the desired
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