Your Failure is My Opportunity - Eff ects of Elimination in Contests

In this paper, we consider a sequence of multi-prize all-pay auctions, where the contestants who exert the lowest e fforts in a round are eliminated. We analyze if and how the behavior of contestants is influenced by the possibility that strong rivals are eliminated along the way. The conditions under which behavior is not influenced are rather restrictive. For cases where these conditions are not met, we derive equilibria in a two-period model. We compare our equilibrium predictions to those of a static model and a two-stage contest where the sequential structure is not announced in the first round

Wind turbine noise code benchmark: A comparison and verification exercise

In a number of institutions and companies, researchers and engineers are developing numerical models and frameworks that are used to predict the aerodynamic noise emissions from wind turbine rotors. The simulation codes range from empirically tuned engineering models to high-fidelity computational ones. Their common feature is the fact that they all specifically model the main aerodynamic noise mechanisms occurring at the rotating blades (namely, the turbulent boundary layer): trailing-edge and turbulent inflow noise. Nevertheless, different modelling techniques and implementations may generate different results, even when assessed on the same rotor design and operating conditions, whicmodels. Trailing-edge noise is put at the forefront of the present study, as it is recognized to be the main source of audible noise from modern wind turbines. The present benchmark aims at comparing the results from different modelling approaches and drawing some conclusions from these comparisons. This effort, denoted as Wind Turbine Noise Code benchmark, was initiated in 2019 as a joint activity between the IEA Wind Task 39 (Quiet Wind Turbine Technology) and Task 29 (Detailed Aerodynamics of Wind Turbines, now Task 47). In addition to the investigation of the noise emissions themselves, the rotor aerodynamic characteristics are investigated, as they are the source of the noise generation mechanisms discussed herein. A number of test cases are defined, and the aerodynamic and aeroacoustic predictions from the various models are compared. A fair agreement between the aerodynamic predictions is observed. There exist some discrepancies between the different noise prediction methods, but it is difficult to conclude if one methodology is better than another in order to design a wind turbine with noise as a constraint

Actuator Concepts for Active Gust Alleviation on Transport Aircraft at Transonic Speeds

This paper investigates different concepts for active gust alleviation (GLA) on a generic transport aircraft configuration at transonic speed by means of viscous and inviscid CFD simulations. Four types of dynamic actuator concepts are presented including a fuselage flap, a wing tip flap, a trailing edge flap and a leading edge flap. The wing tip flap is investigated on a forward swept wing configuration being specifically designed for this purpose. The overall aerodynamic effect of the fuselage flap on the lift distribution is relatively small and has significant Phase angles relative to the flap motion. The wing tip flap instead, seems to be a promising approach to alleviate gusts, affecting the lift distribution on the complete wing. The dynamic trailing edge flap and leading edge flap are investigated on a representative 2.5D setup to derive the most effective actuator setup. The 2.5D simulations confirm the potential of the trailing edge flap allowing a compensation of about 95% of gust induced lift increase at moderate incidence angles, while the effect of the droop nose –in the way implemented so far– is much lower. Despite the rather small potential of the leading edge flap regarding lift force preservation, the time history of the pitching moment reveals its favourable effect on eliminating about 50% of the nose up moment induced by the upward deflected flap without significantly affecting the lift Response