Virtual Reality for Architectural Acoustics

Over the last decades, powerful prediction models have been developed in architectural acoustics, which are used for the calculation of sound propagation in indoor and/or outdoor scenarios. Sound insulation is predicted rather precisely by using direct and flanking transmission models of sound and vibration propagation. These prediction tools are already in use in architectural design and consulting. For the extension towards virtual reality (VR) systems, it is required to accelerate the prediction and simulation tools significantly and to allow an adaptive and interactive data processing during the simulation and 3D audio stimulus presentation. This article gives an overview on the current state-of-the-art of acoustic VR and discusses all relevant components in terms of accuracy, implementation and computational effort. With the progress in processing power, it is already possible to apply such VR concepts for architectural acoustics and to start perceptual studies in integrated architectural design processes.

Electrical and mechanical activity of the intestine

Mattia Bertschi

The intestine is today still an organ whose mechanisms of functions are not fully understood. The diffculty in its understanding comes from the fact that it is regulated by a complex network of signals of different natures. Granting that a multitude of experimental techniques have brought precious information on the electrophysiological processes associated to the intrisic activity of the intestin, there is still shadow covering over the boundary of knowledge. With a view to sharpening the study of the complex spatio-temporal dynamics of the intrinsic electrical and mechanical activity of the intestine, three different numerical models of intestinal tissue were developed. Of particular interest are the networks of coupled oscillators, exhibiting a mass behavior with marked analogy to the intestinal tissue. The conception of these models were conducted by the handling of effective numerical methods and evaluation of numerical instability and errors. A simplified geometrical model of human colon was also developed, so as to allow a realistic visualization of the simulated results. Experimental measures in vitro and in vivo of an animal model, namely the pig, endorsed us the recordings of intrinsic electrical and mechanical activity of different intestinal segments. The recordings of the mechanical activity were obtained by three different tools: visual inspection, manometry, and Magnet Tracking. The first method implies the use of image processing for the evaluation of intestinal movement. The second one provides local pressure measurements. Only the third method enables noninvasive measurements along the digestive tube. In order to automate the extraction of valuable information contained in the signals recorded by the last method, an approch was proposed based on morphological filtering. These three methods of measure were also used in a parallel study to evaluate the electrical stimulation of the colon, with a goal to find an alternative solution to clasical treatments of chronic constipation. We showed that it is possible to induce local contraction in the cecum with electrical stimulation generated by an implantable device. Computer models guarantee at any time the realization of reproducible simulations of technically dicult, and even impossible, experiments. They compel, nonetheless, a simplification of the physiological reality. So as to validate the computer models, the result of simulations must be treated by particular methods. Electrograms and signals representing the mass movement were computed and faced to observations and real measurements. Simulated electrograms revealed a similarity to those recorded on animal intestines. Numerous resemblances are likewise observable between simulated signals of mass movement and the recordings of Magnet Tracking.

EPFL2005

Flow and bathymetry in sharp open-channel bends: Experiments and predictions

Koen Blanckaert, Serban George Constantinescu

This paper focuses on experiments and simulations conducted in very sharp open-channel bends with flat and equilibrium bathymetry, corresponding to the initial and final phases of the erosion and deposition processes, respectively. The study of flow in curved open bends is relevant for flow in natural river configurations, as most river reaches are not straight. The configuration considered in the present work was designed as a test case in which the role of the cross-sectional flow is more severe than in meandering natural river reaches ( radius of curvature of the channel is close to the channel width) and, thus, can serve for validation of numerical models used to predict flow and sediment transport in river engineering applications. This paper presents detailed new experimental data on the equilibrium bathymetry as well as depth-averaged distributions, vertical profiles, and cross-sectional patterns of the streamwise velocity, the cross-stream circulation, streamwise vorticity, and the turbulent kinetic energy at the initial and final stages of the erosion and deposition processes. The numerical simulations are performed using a three-dimensional nonhydrostatic RANS model for flow, sediment transport, and bathymetry, which employs fine meshes, accounts for the effect of small bed forms, and avoids the use of the law of the wall. The model predicts, rather accurately, the distribution of the streamwise velocity, the cross-stream circulation, and the turbulent kinetic energy in the simulations conducted with a fixed ( flat and deformed bed corresponding to equilibrium conditions) prescribed bathymetry. In the case of a simulation conducted with loose bed, the model predicts satisfactorily the main features of the bathymetry at equilibrium conditions, despite the fact that including the interaction between the flow and the bathymetry increases the overall uncertainty in the model predictions. Results indicate that both improvements in the level of turbulence modeling and in the modeling of the sediment transport would allow further improvement in the predictive capabilities of morphodynamic models.

2008

A model-based data-interpretation framework for improving wind predictions around buildings

Ian Smith, Didier Vernay

Although Computational Fluid Dynamics (CFD) simulations are often used to assess wind conditions around buildings, the accuracy of such simulations is often unknown. This paper proposes a data-interpretation framework that uses multiple simulations in combination with measurement data to improve the accuracy of wind predictions. Multiple simulations are generated through varying sets of parameter values. Sets of parameter values are falsified and thus not used for predictions if differences between measurement data and simulation predictions, for any measurement location, are larger than an estimate of uncertainty bounds. The bounds are defined by combining measurement and modeling uncertainties at sensor locations. The framework accounts for time-dependent and spatially-distributed modeling uncertainties that are present in CFD simulations of wind. The framework is applied to the case study of the CREATE Tower located at the National University of Singapore. Values for time-dependent inlet conditions, as well as values for the roughness of surrounding buildings, are identified with measurements carried out around the CREATE Tower. Results show that, on average, ranges of horizontal wind-speed predictions at an unmeasured location have been decreased by 65% when measurement data are used. (C) 2015 Elsevier Ltd. All rights reserved.