Model reduction for nonlinear aerodynamics and aeroelasticity using a Discrete Empirical Interpolation Method

A novel surrogate model is proposed in lieu of Computational Fluid Dynamics (CFD) solvers, for fast nonlinear aerodynamic and aeroelastic modeling. A nonlinear function is identified on selected interpolation points by
a discrete empirical interpolation method (DEIM). The flow field is then reconstructed using a least square approximation of the flow modes extracted
by proper orthogonal decomposition (POD). The aeroelastic reduce order
model (ROM) is completed by introducing a nonlinear mapping function
between displacements and the DEIM points. The proposed model is investigated to predict the aerodynamic forces due to forced motions using
a N ACA 0012 airfoil undergoing a prescribed pitching oscillation. To investigate aeroelastic problems at transonic conditions, a pitch/plunge airfoil
and a cropped delta wing aeroelastic models are built using linear structural models. The presence of shock-waves triggers the appearance of limit
cycle oscillations (LCO), which the model is able to predict. For all cases
tested, the new ROM shows the ability to replicate the nonlinear aerodynamic forces, structural displacements and reconstruct the complete flow
field with sufficient accuracy at a fraction of the cost of full order CFD
model.

Feasibility, normative heuristics and the proper place of historical responsibility – a reply to Ohndorf et al.

In this comment, we pick up three points raised by Ohndorf et al. (2015) in their reply to our ethical assessment of the German Advisory Council’s Budget Approach (WBGUBA). First, we discuss and clarify the relationship between ethics and political feasibility, highlighting that the way Ohndorf et el. use feasibility creates an unwarranted status quo bias. Second, we explain the proper place historical responsibility should have within the WBGUBA, stressing the fact that the reasons why we choose one policy proposal over another matter. Third, we analyze the limited extent to which a normative heuristic should motivate an ethically ambitious policy proposal like the WBGUBA.