Direct numerical simulation of turbulent flow over a rough surface based on a surface scan

Typical engineering rough surfaces show only limited resemblance to the artificially constructed rough surfaces that have been the basis of most previous fundamental research on turbulent flow over rough walls. In this article flow past an irregular rough surface is investigated, based on a scan of a rough graphite surface that serves as a typical example for an irregular rough surface found in engineering applications. The scanned map of surface height versus lateral coordinates is filtered in Fourier space to remove features on very small scales and to create a smoothly varying periodic representation of the surface. The surface is used as a no-slip boundary in direct numerical simulations of turbulent channel flow. For the resolution of the irregular boundary an iterative embedded boundary method is employed. The effects of the surface filtering on the turbulent flow are investigated by studying a series of surfaces with decreasing level of filtering. Mean flow, Reynolds stress and dispersive stress profiles show good agreement once a sufficiently large number of Fourier modes are retained. However, significant differences are observed if only the largest surface features are resolved. Strongly filtered surfaces give rise to a higher mean-flow velocity and to a higher variation of the streamwise velocity in the roughness layer compared with weakly filtered surfaces. In contrast, for the weakly filtered surfaces the mean flow is reversed over most of the lower part of the roughness sublayer and higher levels of dispersive shear stress are found

Simple free-surface detection in two and three-dimensional SPH solver

A simple free-surface particle detection method for two and three-dimensional SPH simulation has been implemented. The method uses sphere representation for the SPH particle. The fluid domain is covered by overlapping spheres. A sphere whose surface is not fully covered considered as boundary. To test particle boundary status, we used a sum of normalized relative position vectors from neighbouring particles to the test particle. By checking the existence of un- covered sphere surface by this vector sum, boundary status of the test particle can be determined. This boundary detection method can be easily embedded in the SPH solver algorithm.Comment: 10 pages, 11 figures, Selected Paper from the International Symposium on Computational Science 201

Computer-Aided Test Flow in Core-Based Design

This paper copes with the test-pattern generation and fault coverage determination in the core based design. The basic core-test strategy that one has to apply in the core-based design is stated in this work. A Computer-Aided Test (CAT) flow is proposed resulting in accurate fault coverage of embedded cores. The CAT now is applied to a few cores within the Philips Core Test Pilot IC projec

A Hierachical Infrastrucutre for SOC Test Management

HD2BIST - a complete hierarchical framework for BIST scheduling, data-patterns delivery, and diagnosis of complex systems - maximizes and simplifies the reuse of built-in test architectures. HD2BIST optimizes the flexibility for chip designers in planning an overall SoC test strategy by defining a test access method that provides direct virtual access to each core of the system

DFT and BIST of a multichip module for high-energy physics experiments

Engineers at Politecnico di Torino designed a multichip module for high-energy physics experiments conducted on the Large Hadron Collider. An array of these MCMs handles multichannel data acquisition and signal processing. Testing the MCM from board to die level required a combination of DFT strategie

3D view of transient horizontal magnetic fields in the photosphere

We infer the 3D magnetic structure of a transient horizontal magnetic field (THMF) during its evolution through the photosphere using SIRGAUS inversion code. The SIRGAUS code is a modified version of SIR (Stokes Inversion based on Response function), and allows for retrieval of information on the magnetic and thermodynamic parameters of the flux tube embedded in the atmosphere from the observed Stokes profiles. Spectro-polarimetric observations of the quiet Sun at the disk center were performed with the Solar Optical Telescope (SOT) on board Hinode with Fe I 630.2 nm lines. Using repetitive scans with a cadence of 130 s, we first detect the horizontal field that appears inside a granule, near its edge. On the second scan, vertical fields with positive and negative polarities appear at both ends of the horizontal field. Then, the horizontal field disappears leaving the bipolar vertical magnetic fields. The results from the inversion of the Stokes spectra clearly point to the existence of a flux tube with magnetic field strength of $\sim400$ G rising through the line forming layer of the Fe I 630.2 nm lines. The flux tube is located at around $\log\tau_{500} \sim0$ at $\Delta t$=0 s and around $\log\tau_{500} \sim-1.7$ at $\Delta t$=130 s. At $\Delta t$=260 s the horizontal part is already above the line forming region of the analyzed lines. The observed Doppler velocity is maximally 3 km s$^{-1}$, consistent with the upward motion of the structure as retrieved from the SIRGAUS code. The vertical size of the tube is smaller than the thickness of the line forming layer. The THMF has a clear $\Omega$-shaped-loop structure with the apex located near the edge of a granular cell. The magnetic flux carried by this THMF is estimated to be $3.1\times10^{17}$ Mx.Comment: 35 pages, 9 figures, Accepted for publication in Ap

Morphing surfaces for the control of boundary layer transition

A structure configured to modify its surface morphology between a smooth state and a rough state in response to an applied stress. In demonstrated examples, a soft (PDMS) substrate is produced, and is pre-strained. A relatively stiff overlayer of a metal, such as chromium and gold, is applied to the substrate. When the pre-strained substrate is allowed to relax, the free surface of the stiff overlayer is forced to become distorted, yielding a free surface having a roughness of less than 1 millimeter. Repeated application and removal of the applied stress has been shown to yield reproducible changes in the morphology of the free surface. An application of such morphing free surface is to control a boundary layer transition of an aerodynamic fluid flowing over the surface