Recent development of satellite technique has given us many pictures of sandydeserts. We can see a number of forms of sandy surface in the pictures. These forms must have much information of desert environments such as wind direction and wind speed.
In this paper, I try to review classical and recent works on the development of aeolian dunes and sand transport. In § 2 the classical theories of the generation of sand ripples are introduced. In § 3 several formulas of sand transport are discussed in relation to the so-called 'saltation'. The characteristics of the vertical structure of winds associated with 'saltation' is also reviewed in § 4. In § 5 many kinds of aeolian dunes in sandy deserts are introduced and the discussion is extended to the factors determining these dune types. In § 6 a recent numerical model of development and migration of a dune is presented. In the final section, future studies of the sand sea are discussed.

View full abstract

The steady viscous shear flows past a circular cylinder are studied to Oseen's approximations and by numerical analysis to the Navier-Stokes equations, and those results for some properties are compared for the range of Reynolds numbers, Re, Re≤1 and a shear parameter, ε, ε≤1.0.
The expansion formulae for the stream function Ψ and the vorticity ζ are obtained up to the terms of orders O (Re⁴), and ones for the drag and the moment are obtained up to the terms of order O (Re³) and one for the lift is obtained up to the term of order O (1).
Numerical calculations are performed by using the initial values of the flow fields and the outer boundary ones at infinity obtained with the our previous analytical solutions, and pressure distributions are devised to be single-valued throughout the field of flow.
The flow patterns, the moment and the pressure distributions on a circular cylinder as predicted by analytical solutions coincide almost with those as predicted by numerical solutions in the range of Re< 0.3 and ε < 0.5, but the expressions of lift from both solutions are different.
Especially, it is noted that the direction of the lift is in contrary ones.

View full abstract

Measurements of the base pressure of rectangular cylinders with different depth-to-height ratios, d/h=0.4-0.6 are presented. A cylinder with d/h=0.5 shows characteristic fluctuations in base pressure, with alternately high and low values, almost equal to those for d/h=0.4 and 0.6, respectively. This is caused by a sudden change in the flow pattern around a cylinder, associated with the vortex formation. Namely, the flow around rectangular cylinders initially changes gradually with increasing d/h, but, when d/h reaches a transitional range around d/h =0.5, there is an abrupt change in the flow pattern.

View full abstract