tailieunhanh - Finite Element Analysis - Thermomechanics of Solids Part 12

Tham khảo tài liệu 'finite element analysis - thermomechanics of solids part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | tọ Rotating and Unrestrained Elastic Bodies FINITE ELEMENTS IN ROTATION We first consider rotation about a fixed axis. The coordinate system is embedded in the fixed point and rotates. The undeformed position vector X in the rotated system is related to its counterpart X in the unrotated system by X Q t X. The counterpart for the deformed position is x Q t x. The displacement also satisfies u Q t u. The rotation is represented by the axial vector m satisfying m X Q t QT t . Recall that Q t QT t is antisymmetric . The time derivatives in rotating coordinates satisfy du dt _ du mx u dt d 2u dt2 _d2u 2mx u fflXfflx u ax u dt2 d where a dt and dt imply differentiation with the coordinate system instantaneously fixed. The rightmost four terms in are called the translational Coriolis centrifugal and angular accelerations respectively. Applied to the Principle of Virtual Work the inertial term becomes iSu Tpd u X dV. Assuming that u ọT X y t f b Tp dV YT M ậ G dY G A Y dt2 1 dt 2 M bT Jp p pTd V0 G2 bT ip pQ2 pTdV G1 bTJ p pQ pTdV I A I T JpcpAcpTd V I . The matrix M is the conventional positive-definite and symmetric mass matrix the Coriolis matrix G1 is antisymmetric the centrifugal matrix G2 is negative-definite and the angular acceleration matrix A is antisymmetric. Also Q QQT A Q. 167 2003 by CRC CRC Press LLC 168 Finite Element of Analysis Thermomechanics of Solids FIGURE Elastic rod on rotating rigid shaft. There is also a rigid-body force term d 2 J Su pd-ĩX dV -ÕỴTfrot frot h J pp Q2 A X dV. The governing equation is now M d G1 dY K g2 A y f - frot. sit sib Consider a rod attached to a thin shaft rotating steadily at angular velocity m see Figure with f0 0. If r is the undeformed position along the shaft the governing equation is EA -m2 r u . dr2 Assuming a one-element model with u r t ru L t L we obtain E- p AL 1u L t O2AA rdr L 3 Jo L pm2 AL2 3 Clearly u L t becomes unbounded if m becomes equal to the .

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