Bài tập thủy lực bằng tiếng anh

Một hình ảnh của Allen cơn bão được xem qua vệ tinh: Mặc dù có chuyển động đáng kể và cấu trúc cho một cơn bão, sự biến đổi áp suất theo chiều thẳng đứng là xấp xỉ bằng mối quan hệ áp lực sâu cho một chất lỏng tĩnh. 1Visible và hồng ngoại hình ảnh cặp từ một vệ tinh NOAA bằng cách sử dụng một kỹ thuật được phát triển tại xã giao NASA/GSPC
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Bài tập thủy lực bằng tiếng anh 7708d_c02_40-99 8/31/01 12:33 PM Page 40 mac106 mac 106:1st_Shift:7708d: An image of hurricane Allen viewed via satellite: Although there is considerable motion and structure to a hurricane, the pressure variation in the vertical direction is approximated by the pressure-depth relationship for a static fluid. 1Visible and infrared image pair from a NOAA satellite using a technique developed at NASA/GSPC.2 1Photograph courtesy of A. F. Hasler [Ref. 7].2 7708d_c02_40-99 8/31/01 12:33 PM Page 41 mac106 mac 106:1st_Shift:7708d: 2 Fluid Statics In this chapter we will consider an important class of problems in which the fluid is either at rest or moving in such a manner that there is no relative motion between adjacent parti- cles. In both instances there will be no shearing stresses in the fluid, and the only forces that develop on the surfaces of the particles will be due to the pressure. Thus, our principal con- cern is to investigate pressure and its variation throughout a fluid and the effect of pressure on submerged surfaces. The absence of shearing stresses greatly simplifies the analysis and, as we will see, allows us to obtain relatively simple solutions to many important practical problems. 2.1 Pressure at a Point As we briefly discussed in Chapter 1, the term pressure is used to indicate the normal force per unit area at a given point acting on a given plane within the fluid mass of interest. A question that immediately arises is how the pressure at a point varies with the orientation of the plane passing through the point. To answer this question, consider the free-body diagram, illustrated in Fig. 2.1, that was obtained by removing a small triangular wedge of fluid from some arbitrary location within a fluid mass. Since we are considering the situation in which there are no shearing stresses, the only external forces acting on the wedge are due to the There are no shear- pressure and the weight. For simplicity the forces in the x direction are not shown, and the ing stresses present z axis is taken as the vertical axis so the weight acts in the negative z direction. Although we in a fluid at rest. are primarily interested in fluids at rest, to make the analysis as general as possible, we will allow the fluid element to have accelerated motion. The assumption of zero shearing stresses will still be valid so long as the fluid element moves as a rigid body; that is, there is no rel- ative motion between adjacent elements. 41 7708d_c02_042 8/2/01 1:10 PM Page 42 42 I Chapter 2 / Fluid Statics z ps δ x δ s θ δs py δ x δ z y δz δx θ I FIGURE 2.1 δy Forces on an arbi- ...