Book review: Practical Ship and Offshore Structure Aerodynamics

Abstract

Werner Blendermann is known for his publications on wind loads on ships and offshore structures. The book summarizes his expertise in that field, concentrating on all kinds of practical applications. After a short introduction to fluid dynamic terms and basic formulae he describes the wind itself: Its dependence on the vertical coordinate (corresponding to the turbulent boundary layer over a rough surface), on geographic location and season, and its velocity spectrum ranging from periods of 10−3 h (gusts, ≈ 3 s) to 10 3 h (≈ a month). Maximum measured wind speed (1 minute average, 10 m above ground) in a tornado was 509 km/h; in a cyclone, i.e. on a larger geographical range, 300 km/h. Blendermann distinguishes between a microscale (turbulence, velocity spectrum and distribution, gust factors), a mesoscale (wind climate) and a macroscale (long-term statistics). The next chapter gives, at first, drag coefficients of 2 and 3 -dimensional simple shapes. The circular cylinder in two-dimensional flow is a body of much practical interest, but also a particularly difficult object: drag coefficients change between 1 .2 for low Reynolds numbers and as low as 0 .2 (smooth surface, low turbulence of the incident flow) just after transition to a turbulent boundary layer at Re ≈ 5 ·10 5 , and nobody seems to know its drag coefficient beyond Re ≈ 10 7 . Interference effects, transverse forces, flow-induced vibrations of elastic objects and squall loads (including added-mass effects) are also dealt with. Wind loads on the above-water parts of ships and offshore structures are extensively covered by giving coefficients of the longitudinal and lateral force and the heel and yaw moment as functions of wind angle. Diagrams giving data for 21 wind-tunnel ship models are presented. CFD is also suitable, but meshing the space around a ship’s deck and superstructures is quite laborious and thus seldom done. Approximate formulae for these functions are given, both according to the author’s and another published method. Results for various specialties are also presented: wind-tunnel models mounted above a ground plate (with and without a cavity in the model’s bottom), heeled models, overtaking ships, tankers moored alongside, effect of wind shields. Regarding the effect of increasing wind velocity with height, for the longitudinal wind force one should use the wind velocity at the average height of the structure, not at the centroid height; and between both heights for other forces and moments. Indirect wind effects on required propulsion power are caused by the transverse wind force, which causes a drift velocity changing both the above-water and below-water longitudinal pressure force; and by the wind yaw moment, which must be canceled by the rudder, causing additional drag. A chapter on the probability distribution of wind loads is following. It treats gust loads and long-term