力学专业外文翻译

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1、 1 中文 2500 字 附 录：外文翻译 5.1Introduction Cylindrical shells are used innuclear,fossil and petrochemical industries. They are also used in heat exchangers of the shell and tube type.Generally.These vessels are easy to fabricate and install and economical to maintain. The design procedures in pressure ve

2、ssel codes for cylindrical shells are mostly based on linear elastic assumption,occasionally allowing for limited inelastic behavior over a localized region.The shell thickness is the major design parameter and is usually controlledby internal pressure and sometimes by external pressure which can pr

3、oduce buckling.Applied loads are also important in controlling thickness and so are the disconti-nuity and thermal stresses.The basic thicknesses of cylindrical shells are Based on simplied stress analysis and allowable stress for the material of construction.There are some variations of the basic e

4、quations in various design codes.Some of the equations are based on thick-wall Lame equations.In this chapter such equations will be discussed.Also we shall discuss the case of cylindrical shells under external pressure where there is a propensity of buckling or collapse. 5.2 Thin-shell equations A

5、shell is a curved plate-type structure.We shall limit our discussion to Shells of revolutions.Referring to Figure5.1 this is denoted by anangle ,The meridional radius r1 and the conical radius r2,from the center line.The horizontal radius when the axis is vertical is r. If the shell thickness is t,w

6、ith z being the coordinate across the thickness,following the convention of Flugge, We have the following stress resultants: 2211 )(ttdzr zrN (5.1) 2222 )(ttdzr zrN (5.2) 2222 )(ttdzr zrN (5.3) 2 Figure 5.1 Thin shell of revolution. 2211 )(ttdzr zrN (5.4) These stress resultants are assumed to be du

7、e only to an internal pressure, p,acting in the direction of r. For membrane shells where the Effects of bending can be ignored,all the moments are zero and further development leads to NN The following equations result from considering force equilibrium along with the additional requirement of rota

8、tional symmetry: 0c o s)( 1 NrdrNd (5.6) NrrprN122 (5.7) Noting that sin2rr ,we have,by solving Eqs.(5.6)and(5.7), 22prN (5.8) )2(2122 rrprN (5.9) The above two equations are the results for a general shell of revolution. Two specic cases result: 3 1. For a spherical shellof radius R, r1= r2 =R,whic

9、h gives 2pRNN (5.10) 2. For a cylindrical pressure vessel of radius R,we have r1 = ； r2 = R,which gives 2pRN (5.11) pRN (5.12) This gives the hoop stress tpRtNhoop (5.13) and the longitudinal stress tpRtNlong 2 (5.14) These results will be shown to be identical to the results that follow. Let us con

10、sider a long thin cylindrical shell of radius R and thickness t, subject to an internal pressure p.By thin shell we mean the ones having the ratio R/t typically greater than about10.If the ends of the cylindrical shell are closed,there will be stresses in the hoop as well as the axial (longitudinal)

11、 directions. A section of such a shell is shown in Figure5.2. The hoop(circumfer-ential)stress, hoopand the longitudinal stress, long are indicated in the gure.The shell is assumed to be long and thin resulting in hoopandlongto be uniform through the thickness.Therefore in this case hoopandlong are also referred to as membrane stress(there are no bending stresses associated with this type of loading). Considering equilibrium across the cut section,we have, tLRpL hoop2)2(