TAILIEUCHUNG - Theory Design Air Cushion Craft 2009 Part 4

Tham khảo tài liệu 'theory design air cushion craft 2009 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 106 Steady drag forces Fig. Sketch of wetted surface of SES. Sf Si0 Sout0 out where Á4ut can be obtained from Fig. which has been obtained by statistical analysis of photographs on model no. 4 by MARIC. It is found that there are two hollows on the curve of the outer wetted surface area the first is due to the hump speed which leads to a large amount of air leakage amidships and the second is caused by small trim angle at higher craft speed. Method used in Japan 28 Reference 28 introduces the measurement of the inner outer wetted surface area of a plate-like sidewall of an SES with cushion length beam ratio 4Aổc of about 2 on the cushion and represented as follows Fig. Sf Sf Sro - sfx eFr 4 ic 4 s where Sf is the area of the wetted surface of sidewalls m2 Sfoo the area of the wetted surface of sidewalls at high speed m2 and fs the correction coefficient for the area of the wetted surface which can be related to Frh as shown in Fig. and which is obtained by model test results. In the case of craft at very high speed higher than twice hump speed the water surface is almost flat at the inner outer wave surface and also equal to each other. With respect to the rectangular transverse section of the sidewalls the wetted area can be written as 5f00 4 z2 - zeq 2 7 s 4 Sf0 is the wetted surface area of the sidewalls of craft hovering statically m Sidewall water friction drag 107 Frt v-JgTc Fig. Correction coefficient of outer wetted surface area of SES with flexible bow stern seals. fc Fig. Sketch of SES running attitude at Fr 0 a and Fr 00 b . Sro - 4 2 - Aj 2 zc 2 4 4 Tj 2 hc 2 Bs 4 where Bs is the width of the sidewalls with rectangular transverse section m 4 the length of sidewalls m hc the depth of cushion air water depression hovering static m hị the vertical distance between the lower tip of skirts and inner water surface . hx h2 Tị as shown in Fig. hovering static m h2 the vertical distance between the lower

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