Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Tham khảo tài liệu 'ship hydrostatics and stability 2010 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Intact stability regulations II 225 distance a. As the volume of water above the still-water line must equal that below the same line we can write 2 z - 0 10.3 JO We can separate the above integral into two integrals that we calculate separately. The first integral is 2 27 zdx r cos 9 R r cos 0 d9 Jo Jo 10-4 7rr2 The second integral is 27T I adx o x q ĨTĩaR 10.5 Jo Equating Eqs. 10.4 and 10.5 we obtain r2 a 10.6 Z-ft We mention here without proving two interesting hydrodynamical properties of the trochoidal wave. 1. Motion decay with depth The radius of orbits decays exponentially with depth. For a given depth h the amplitude of the orbital motion is rh re h R 10.7 The amplitude on the sea bottom should be zero. In our model this only happens at an infinite depth therefore the trochoidal wave model is correct only in infinite depth seas. However let us calculate the radius of the orbit at a depth equal to half a wave length r-A 2 r exp í 2R 0.0043r that is practically zero. 2. Virtual gravity A water particle moving along a circular orbit is subjected to two forces its weight mg a centrifugal force mrw2 where w is the angular velocity of the particle. It can be shown that w2 g R. 226 Ship Hydrostatics and stability In the trough the two forces add up to m9 Í1 r while on a wave crest the result is I1 - r Thus a floating body experiences the action of a virtual gravity acceleration whose value varies between g l r R and g l g R . One wave height-to-length ratio frequently employed in Naval Architecture is 1 20. With this value the apparent gravity varies between 0-843 9 and 1.157g. The variation of apparent gravity and consequently of buoyancy in waves is known as the Smith effeciafter the name of the researcher who described it first in 1883. The reduction of virtual gravity on wave crest was considered another cause of loss of stability in waves. To quote Attwood and Pengelly I960 This is the explanation of the well-known phenomenon of the tenderness of sailing .
