TAILIEUCHUNG - Theory Design Air Cushion Craft Episode 10

Tham khảo tài liệu 'theory design air cushion craft episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 346 Model experiments and scaling laws due to its fixed characteristic. Normally the fan system in a skirt test box is not changed for each test For this reason the skirt test box is more suitable for experiments to optimize static shaping of skirts and will create large errors needing correction in the case of skirt dynamic response characteristic testing unless the fan and air speed system are also specially modelled. Skirt weight per unit area Skirt weight is directly related to its static geometry and surface area since it is essentially a membrane so scaling between model and full scale has to satisfy - Ấ where Wss is the weight per unit area of skirt including the connections of full-scale craft N m2 and PFsm the weight per unit area of skirt including connections of models N m . The problems concerned with the elastic aerodynamics of skirts have to be considered during the investigation of the dynamic shaping of skirts however this does not greatly affect the skirt shaping and can therefore be neglected. Strouhal number sr Strouhal s number is closely related to the elastic aerodynamic characteristics of the skirt fingers. It characterizes the ratio of inertia force due to the air pressure and the elastic modulus of skirt materials and can be expressed as s I ElPt VJa or co iN E pa co Ua where vis the velocity of air flow m s a the velocity of sound in skirts or other structural materials m s co the vibration frequency of skirts 1 s and any linear length. In the case where the skirt material of the full-scale craft has the same characteristics as those of the model then the model skirts Sr is not scaled correctly compared to the full-scale craft. Thus it may be noted that in the calculation of skirt shaping described in Chapter 7 the skirt bag membrane tension and stresses of both the model and craft are not similar even though the skirt geometric scaling with the same specific weight can be satisfied. The tension in the skirt bag membrane is .

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