Notice that for the solenoidal portion of the rod, the vertical distance traveled by the dead weight is and is not . For the straight portion, however, the distance traveled by the dead weight remains .
Similarly, the energy spent by the external torque in twisting the rod is obtained as,
Notice that the total angle turned by the end moment is given as:
Then the total energy of the system and that of the external load and torque are written as
Minimizing the total energy with respect to yields
Minimizing the total energy with respect to yields
Similarly minimizing the total energy with respect to yields
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(24.17) |
Substitution of expression for in equation 24.14 into 24.15 and solution of equations 24.15 and 24.16, for and yields
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(24.18) |
Equation 24.15 to 24.18 present us six equations for eight unknowns: , , , , , , and . The ideas here is to fix the values for, say and , and calculate the values for six other unknowns.
The threshold values of different parameters at which the straight rod would turn to a helix is obtained by considering the stability of the above solutions. The solutions are stable when the eigen values of the Hessian matrix written as with and remain positive.
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