An isogeometric numerical study of partially and fully implicit schemes for transient adjoint shape sensitivity analysis

In structural design optimization involving transient responses, time integration scheme plays a crucial role in sensitivity analysis because it affects the accuracy and stability of transient analysis. In this work, the influence of time integration scheme is studied numerically for the adjoint shape sensitivity analysis of two benchmark transient heat conduction problems within the framework of isogeometric analysis. It is found that (i) the explicit approach (beta = 0) and semi-implicit approach with beta < 0.5 impose a strict stability condition of the transient analysis; (ii) the implicit approach (beta = 1) and semi-implicit approach with beta > 0.5 are generally preferred for their unconditional stability; and (iii) Crank-Nicolson type approach (beta= 0.5) may induce a large error for large time-step sizes due to the oscillatory solutions. The numerical results also show that the time-step size does not have to be chosen to satisfy the critical conditions for all of the eigen-frequencies. It is recommended to use beta approximate to 0.75 for unconditional stability, such that the oscillation condition is much less critical than the Crank-Nicolson scheme, and the accuracy is higher than a fully implicit approach.