A collection of conclusions from each participant, which addresses 

 both general and specific conclusions from the seminar, is included in 

 this report. Many of the items listed below are developed in these 

 summary reports. 



CONCLUSIONS FROM SEMINAR DISCUSSIONS 



Th CEL Mooring Dynamics Seminar fully satisfied its objectives 

 (i.e., to define the present state-of-the-art in mooring analysis and 

 simulation, to identify the problem areas and uncertainties associated 

 with available mooring models, and to recommend guidelines for the 

 development of mooring models to suit Navy needs). The Seminar discus- 

 sions also initiated a development effort that may lead to significant 

 advances in the analyses of nonlinear dynamic systems. Some of the 

 major contributions within each objective are outlined below. 



Present Mooring Analysis Capabilities 



As illustrated in Figure 1, there are several models available for 

 mooring analysis. Each analysis technique is useful because of trade-offs 

 in accuracy versus computational costs, which allow the mooring analyzer 

 to choose the model that best suits his particular needs. For example, 

 the fully nonlinear time-domain model, although the most accurate, is 

 certainly not necessary for all applications. Alternatively, applying a 

 large factor of safety and omitting the dynamic analysis, although it is 

 very inexpensive, is likewise not appropriate in all cases. 



The majority of available mooring analysis models known to CEL 

 assume a ship-dominated system, with the mooring lines treated as massless 

 springs. System response is determined in either the time or frequency 

 domain. Mooring line tensions are determined in a subsequent quasi-static 

 analysis with the ship displacement imposed on the cable. The most 

 accurate mooring models have no major restrictions or assumptions, and 

 are based on a time-domain representation of vessel and cable response. 



It was generally agreed that DSSM is a very cost-effective mooring 

 model. As demonstrated in Figure 1, DSSM uses a fully nonlinear static 

 analysis model (finite element) and a fully coupled, but linearized, 

 frequency-domain dynamic model. The only major improvement possible 

 would be to add a nonlinear time-domain model, that would add at least 

 an order of magnitude to the computation costs. Since the degree of 

 nonlinearity (i.e., effect of the slowly varying drift force) for moorings 

 involving Navy (intermediate-sized) ships is unknown, the need for a 

 nonlinear dynamic solution is unknown. It was recognized that the 

 accuracy of the linearized dynamic solution in DSSM might be adequate 

 for Navy applications, and that major model improvements might not be 

 necessary. Further details regarding the evaluation of DSSM are included 

 after the next section. 



Problem Areas and Uncertainties 



Identification of the problems associated with state-of-the-art 

 mooring simulation will be discussed without reference to any particular 

 applications or computational cost limitations. Evaluation of these 

 items is left to the reader. Some of the most significant problems are 

 discussed below: 



4 



