Showing papers by "Hester Bijl published in 2011"
TL;DR: In this article, aero-acoustic resonance of cavities with a width much larger than their length or depth and partially covered, as often encountered in automotive door gaps, was investigated.
Abstract: The present investigation focuses on the aero-acoustic resonance of cavities with a width much larger than their length or depth and partially covered, as often encountered in automotive door gaps. The cavities are under influence of a low Mach number flow with a relatively thick boundary layer. Under certain conditions, these cavities can acoustically resonate with the flow. The upstream and downstream edge of the opening as well as the cover lip overhang location and boundary layer thickness are parametrically varied in an experimental campaign, and the effect of the parameters on the resonance amplitude is investigated. Slender rectangular cavity geometries with an opening length of 8 mm and spanwise width of 500 mm are used. The cavity flow-induced acoustic response is measured with pressure transducers at different spanwise locations inside the cavity. Hot-wire measurements are performed to quantify the boundary layer characteristics. Furthermore, high-speed time-resolved particle image velocimetry is used to capture the instantaneous velocity field around the opening geometries. When the boundary layer thickness is increased, the cavity resonance amplitude diminishes. The cover lip overhang location has a large influence on the resonance response, which can be attributed to changes in the cavity driven flow properties. Rounding of the upstream edge promotes resonance, whereas rounding of the downstream edge can diminish it. A possible explanation of the phenomenon is given on the basis of the PIV observations.
11 citations
05 Sep 2011
TL;DR: This work proposes to transform the optimization problem to the frequency domain, such that the cost of the optimization is now dominated by that of a single Fourier transform required to find the power spectrum of the observations, as a result of which the computational cost is now virtually independent of the number of optimization steps.
Abstract: We apply Ordinary Kriging to predict 75,000 terrain survey data from a randomly sampled subset of < 2500 observations. Since such a Kriging prediction requires a considerable amount of CPU time, we aim to reduce its computational cost. In a conventional approach, the cost of the Kriging analysis would be dominated by the optimization routine required to find the maximum likelihood, which provides an estimate of the correlation ranges. We propose to transform the optimization problem to the frequency domain, such that the cost of the optimization is now dominated by that of a single Fourier transform required to find the power spectrum of the observations, as a result of which the computational cost is now virtually independent of the number of optimization steps. For the present application, we find that the proposed approach is as accurate as the conventional approach for a sample size of 100 or more. The CPU time increases with the number of optimization steps for the conventional approach, while it is virtually constant for the proposed approach.
6 citations