The investigation of the complete equations of motion would require 

 a complete knowledge of the coefficients representing hydrodynamic forces 

 and moments. Since the in-situ plants under study may have irregular or 

 unconventional forms, model tests should be undertaken to more accurately 

 establish hydrodynamic characteristics for validating the final design. 



In-Situ Plant Emplacement and Recovery. The emplacement and 

 recovery of an in-situ power plant is costly and risky. For this reason, these 

 operations are extremely important and deserve detailed analysis and careful 

 planning. 



Emplacement and recovery concepts considered for analysis were free 

 descent and ascent, forced descent and ascent, guided descent and ascent, and 

 combinations of these concepts. 



The concept of free descent and ascent is based on a free, powerless 

 descent using negative buoyancy. The prime disadvantage of this concept is 

 that the bottom positioning during free descent is somewhat random. 

 Figure 5 illustrates how buoyancy, net downward force, and descent velocity 

 may be expected to vary with velocity. 



A free descent begins with the in-situ plant on the surface and rigged 

 for free descent (stabilizers rigged, proper trim, etc.). A set of tanks may be 

 flooded to cancel a small amount of reserve surface buoyancy. The plant then 

 will take on negative buoyancy and sink. As the plant sinks, two parameters 

 change: seawater density increases with pressure and external pressure causes 

 the pressure hull to contract, thereby reducing total displacement. The net 

 effect causes the plant to become slightly more buoyant with a proportionate 

 decrease in net downward force, which causes the plant to gradually slow 

 down. With proper negative buoyancy, the plant should begin its descent at 

 about 3 to 4 fps and approach the bottom at 1 to 2 fps. A hanging weight 

 suspended 100 to 200 feet below the plant will make the initial contact with 

 the bottom and the plant will immediately decelerate to a stop. The plant 

 could be positioned at the bottom by mechanical means such as a power 

 winch. If the plant is to be positioned on the bottom, a foundation analysis 

 will be required. Temperature variations encountered during descent and 

 while the plant is positioned at the bottom will affect the plant's buoyancy. 

 These variations must be factored into the final in-situ plant pressure hull 

 design. Water absorption and fouling should also be considered for an extended 

 deployment time. The plant may be surfaced by free ascent. Prior to ascent, 

 the stabilizers must be rigged at the bottom, the trim adjusted, and the plant 

 must then be released completely from hanging weights. As the plant ascends 

 it is opposed by drag and gravitational forces and will reach its terminal 

 velocity when the net buoyancy forces, and therefore the velocity, decrease. 

 A terminal velocity of 3 to 4 fps is expected. Once on the surface, the surface 

 tanks can be blown for reserve buoyancy to keep the plant stable. 



28 



