29,108 research outputs found
Setting intelligent city tiling strategies for urban shading simulations
Assessing accurately the solar potential of all building surfaces in cities, including shading and multiple reflections between buildings, is essential for urban energy modelling. However, since the number of surface interactions and radiation exchanges increase exponentially with the scale of the district, innovative computational strategies are needed, some of which will be introduced in the present work. They should hold the best compromise between result accuracy and computational efficiency, i.e. computational time and memory requirements.
In this study, different approaches that may be used for the computation of urban solar irradiance in large areas are presented. Two concrete urban case studies of different densities have been used to compare and evaluate three different methods: the Perez Sky model, the Simplified Radiosity Algorithm and a new scene tiling method implemented in our urban simulation platform SimStadt, used for feasible estimations on a large scale. To quantify the influence of shading, the new concept of Urban Shading Ratio has been introduced and used for this evaluation process. In high density urban areas, this index may reach 60% for facades and 25% for roofs. Tiles of 500 m width and 200 m overlap are a minimum requirement in this case to compute solar irradiance with an acceptable accuracy. In medium density areas, tiles of 300 m width and 100 m overlap meet perfectly the accuracy requirements. In addition, the solar potential for various solar energy thresholds as well as the monthly variation of the Urban Shading Ratio have been quantified for both case studies, distinguishing between roofs and facades of different orientations
Simulation of ultrasonic lamb wave generation, propagation and detection for an air coupled robotic scanner
A computer simulator, to facilitate the design and assessment of a reconfigurable, air-coupled ultrasonic scanner is described and evaluated. The specific scanning system comprises a team of remote sensing agents, in the form of miniature robotic platforms that can reposition non-contact Lamb wave transducers over a plate type of structure, for the purpose of non-destructive evaluation (NDE). The overall objective is to implement reconfigurable array scanning, where transmission and reception are facilitated by different sensing agents which can be organised in a variety of pulse-echo and pitch-catch configurations, with guided waves used to generate data in the form of 2-D and 3-D images. The ability to reconfigure the scanner adaptively requires an understanding of the ultrasonic wave generation, its propagation and interaction with potential defects and boundaries. Transducer behaviour has been simulated using a linear systems approximation, with wave propagation in the structure modelled using the local interaction simulation approach (LISA). Integration of the linear systems and LISA approaches are validated for use in Lamb wave scanning by comparison with both analytic techniques and more computationally intensive commercial finite element/difference codes. Starting with fundamental dispersion data, the paper goes on to describe the simulation of wave propagation and the subsequent interaction with artificial defects and plate boundaries, before presenting a theoretical image obtained from a team of sensing agents based on the current generation of sensors and instrumentation
TRAPHIC - Radiative Transfer for Smoothed Particle Hydrodynamics Simulations
We present TRAPHIC, a novel radiative transfer scheme for Smoothed Particle
Hydrodynamics (SPH) simulations. TRAPHIC is designed for use in simulations
exhibiting a wide dynamic range in physical length scales and containing a
large number of light sources. It is adaptive both in space and in angle and
can be employed for application on distributed memory machines. The commonly
encountered computationally expensive scaling with the number of light sources
in the simulation is avoided by introducing a source merging procedure. The
(time-dependent) radiative transfer equation is solved by tracing individual
photon packets in an explicitly photon-conserving manner directly on the
unstructured grid traced out by the set of SPH particles. To accomplish
directed transport of radiation despite the irregular spatial distribution of
the SPH particles, photons are guided inside cones. We present and test a
parallel numerical implementation of TRAPHIC in the SPH code GADGET-2,
specified for the transport of mono-chromatic hydrogen-ionizing radiation. The
results of the tests are in excellent agreement with both analytic solutions
and results obtained with other state-of-the-art radiative transfer codes.Comment: 31 pages, 20 figures. Accepted for publication in MNRAS. Revised
version includes many clarifications and a new time-dependent radiative
transfer calculation (fig. 19
5G 3GPP-like Channel Models for Outdoor Urban Microcellular and Macrocellular Environments
For the development of new 5G systems to operate in bands up to 100 GHz,
there is a need for accurate radio propagation models at these bands that
currently are not addressed by existing channel models developed for bands
below 6 GHz. This document presents a preliminary overview of 5G channel models
for bands up to 100 GHz. These have been derived based on extensive measurement
and ray tracing results across a multitude of frequencies from 6 GHz to 100
GHz, and this document describes an initial 3D channel model which includes: 1)
typical deployment scenarios for urban microcells (UMi) and urban macrocells
(UMa), and 2) a baseline model for incorporating path loss, shadow fading, line
of sight probability, penetration and blockage models for the typical
scenarios. Various processing methodologies such as clustering and antenna
decoupling algorithms are also presented.Comment: To be published in 2016 IEEE 83rd Vehicular Technology Conference
Spring (VTC 2016-Spring), Nanjing, China, May 201
Exploring performance and power properties of modern multicore chips via simple machine models
Modern multicore chips show complex behavior with respect to performance and
power. Starting with the Intel Sandy Bridge processor, it has become possible
to directly measure the power dissipation of a CPU chip and correlate this data
with the performance properties of the running code. Going beyond a simple
bottleneck analysis, we employ the recently published Execution-Cache-Memory
(ECM) model to describe the single- and multi-core performance of streaming
kernels. The model refines the well-known roofline model, since it can predict
the scaling and the saturation behavior of bandwidth-limited loop kernels on a
multicore chip. The saturation point is especially relevant for considerations
of energy consumption. From power dissipation measurements of benchmark
programs with vastly different requirements to the hardware, we derive a
simple, phenomenological power model for the Sandy Bridge processor. Together
with the ECM model, we are able to explain many peculiarities in the
performance and power behavior of multicore processors, and derive guidelines
for energy-efficient execution of parallel programs. Finally, we show that the
ECM and power models can be successfully used to describe the scaling and power
behavior of a lattice-Boltzmann flow solver code.Comment: 23 pages, 10 figures. Typos corrected, DOI adde
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