TAILIEUCHUNG - PARTICLE-LADEN FLOW - ERCOFTAC SERIES Phần 9

Tham khảo tài liệu 'particle-laden flow - ercoftac series phần 9', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 338 . Wells Fig. 5. The laboratory experiment used to determine the influence of Coriolis forces upon sedimentation patterns. forms a weak turbidity current that is deflected to the right and is seen as the black sediment at the base of the images. The observed radius L of the sedimentation patterns are plotted in figure 7 and show an inverse dependence upon rotation rate f. In analogy to the radius of the bulge of the buoyant river plume we assume that the radius of sedimentation on the rotating turbidity current is that which has Ro 1. The Rossby number is defined as Ro U fL. The initial speed of collapse of the turbidity currents is U ựg h so that the Rossby number is one when L ỵ g o h f. Based upon the low measured values of entrainment for flows where Fr 1 in figure 4 we will assume there is little entrainment to change the volume or g . If we then use conservation of volume of the turbidity current so that V hL2n 4 the radius L of the quarter circle is related to the reduced gravity the initial volume and the Coriolis parameter by L - 4 n 1 4 g0V f 1 4. 6 This radius is similar to the scaling of non-sedimenting rotating experiments by Hogg et al. 2001 . In figure 7 there is good agreement between the scaling 6 and the observed reduction in L with increasing f. Influence of Coriolis forces on turbidity currents 339 Fig. 6. Eight images of the sedimentation patterns resulting from the release of a black silicon carbide turbidity current in a rotating tank of area 1m2. The two dashed circles in each picture define the minimum and maximum estimates of the radius L. 4 Applications to the 1929 Grand Banks earthquake The 1929 earthquake off the Canadian coast of Nova Scotia triggered a turbidity current which spread a thick layer of sediment over 280 000 km2 of the sea floor Piper et al. 1987 . Heezen Ewing 1952 calculated the speed of the turbidity current based on the times that the trans-Atlantic telegraph service was interrupted and found that speeds .

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