The Cut Beam Benchmark System: Developing Measurement Techniques for Nonlinear Damping and Stiffness in Frictional Interfaces

International audienceThis chapter deals with the damping caused by friction in joints. A new test bench is presented and justified by comparisons made with devices described in the literature. The purpose of this academic bench is to measure the damping induced by partial slip and friction in a planar joint. A new method for the so-called stopped-sine excitation was developed. It allows more precise monitoring of the evolution of the vibration frequency and damping of nonlinear modes, and it allows uncoupling normal static and dynamic tangential forces. This method is associated with piezoelectric exciters for greater efficiency when stopping excitation. A large number of experimental results are presented and discussed, which are used to characterize the damping induced by micro-sliding in the bonds

Boundary layer characteristics and turbulent exchange mechanisms in highly complex terrain

The Mesoscale Alpine Programme's Riviera project investigated the turbulence structure and related exchange processes in an Alpine valley by combining a detailed experimental campaign with high-resolution numerical modelling. The present contribution reviews published material on the Riviera Valley's boundary layer structure and discusses new material on the near-surface turbulence structure. The general conclusion of the project is that despite the large spatial variability of turbulence characteristics and the crucial influence of topography at all scales, the physical processes can accurately be understood and modelled. Nevertheless, many of the "text book characteristics" like the interaction between the valley and slope wind systems or the erosion of the nocturnal valley inversion need reconsideration, at least for small non-ideal valleys like the Riviera Valley. The project has identified new areas of research such as post-processing methods for turbulence variables in complex terrain and new approaches for the surface energy balance when advection is non-negligible. The exchange of moisture and heat between the valley atmosphere and the free troposphere is dominated by local "secondary" circulations due to the curvature of the valley axis. Because many curved valleys exist, and operational models still have rather poor resolution, parameterization of these processes may be required