Time (s)

Fig。  9。 Gap forces on chord F1 and chord F2。

If no wind is applied, RPD goes up slowly。 This small RPD value is caused by the properties of the structure itself, such as stiffness and mass distribution of the whole structure。 When wind load is imposed on the hull, RPD value increases rapidly。 The larger the wind load is, the faster the RPD grows。 Difference between the total vertical reaction forces of pinions on chord  F1  and chord F2 increases with wind the load magnitude as well in the first stage。 After a certain time of jacking, gaps start to close。 Thus, more wind load-generated moment is resisted by the guides/wear plates。 As a result, RPD increment slows down。 For higher wind load, gaps are closed earlier and guide resistance forces are larger。 Obviously, due to the complicated gap status, the RPD increment is not in linear relation with the wind load magnitude。 In addition, it is also found that the duration for each stage is determined by the leg structure within the jacking region。 Although the horizontal wind load changes from 550 to 2200 kN, the duration for each stage does not change too  much。文献综述

5。4。Leg fixity effect

As described in the introduction, the leg fixity is very difficult to determine due to different geological condi- tions and various spudcan designs。 The legs can be as-

0 200       400       600       800     1,000    1,200    1,400    1,600 1,800

Fig。  10。 Member forces of some braces during jacking    opera- 80

1800 s was 104 mm, which was very close to the simu- lated result (111 mm)。 It means that the proposed nu- merical method is reasonable。 Since a lot of information (i。e。, reaction forces of pinions, RPD values, gap forces, member forces, leg reactions, and displacement of all nodes etc。) rather than RPD value alone can be achieved

0 200 400 600 800    1,000   1,200   1,400   1,600    1,800

Time (s)

Fig。  11。 RPDs of forward leg––under different wind  loads。

0 200      400      600      800    1,000   1,200   1,400   1,600   1,800

0 200      400      600      800    1,000   1,200   1,400   1,600   1,800

Time (s)Fig。 12。 Vertical reaction forces of pinions on forward leg–– under different wind loads。

Fig。 14。 Vertical reaction forces of pinions on forward leg–– with different leg fixity。

Fig。  13。 RPDs of forward leg––with different leg  fixity。

sumed as pinned, fixed or two legs pinned with star- board leg sliding as suggested by SNAME [14]。 To study the effect of leg-constraints, three simulations are per- formed on the jack-up unit under 1100 kN wind load。 RPDs and vertical reaction forces of pinions for the forward leg are compared in Figs。 13 and 14, respec- tively。

The behaviours of the jack-up unit depend signifi- cantly on leg fixity。 RPDs and vertical reaction forces of pinions for the jack-up unit with fixed and pinned legs are of the same trends。 With rotational DOF con- strained, the RPDs decrease more than 20% comparing to those of the structure with pinned legs。 Difference between the total vertical reaction forces of pinions on chord F1 and F2 becomes smaller。 However, if the starboard leg is released to slide along the seabed, the boundary conditions would not be symmetric anymore。 The RPDs go up much faster and extremely higher。 Moreover, gaps are closed much earlier。 Comparing to the three legs being pinned, the maximum RPD is 80% higher and the secondary RPD value is as high as 47。5 mm  instead  of  zero  value  as  in  the  other  two cases。来:自[优E尔L论W文W网www.youerw.com +QQ752018766-