Digital Twin Cities: Multi-Disciplinary Modeling and High-Performance Simulation of Cities

The digital twin concept has virtually exploded in recent years, asevidenced by the exponentially growing number of scientific articlesmaking use of the concept.The concept originates from the manufacturing industry where the useof CAD models enables the creation of exact digital replicas ofcomponents and products. The earliest use of the term dates back to2003 and is often credited to Grieves and Vickers, but earlier references tothe concept can be found; certainly, the understanding that mathematicaland, more recently, digital models of physical systems are of enormousimportance to both science and engineering dates back centuries.The concept has since spread from the manufacturing industry to otherdisciplines, such as agriculture, electricity, vessels, manufacturing,construction, cities, healthcare, aerospace, waste, water, transport,and automotive.In this short note, we present an overview of the use of digital twinsin the built environment; that is, digital twins of cities andbuildings. In this context, the term digital twin is closely linked tothe concept of smart cities (or smart buildings). Therelation between a digital city twin and a smart city is that thedigital twin is the enabling technology for making a city smart. Evenif a digital twin is not a sufficient condition for making a citysmart, it is a necessary condition

DTCC Builder: A mesh generator for automatic, efficient, and robust mesh generation for large-scale city modeling and simulation

Digital Twin Cities Centre (DTCC) Builder is a mesh generator for automatic, efficient, and robust mesh generation for large-scale city modeling and simulation. Using standard and widely available raw data sources in the form of point clouds and cadastral data, DTCC Builder generates high-quality 3D surface and volume meshes, suitable for both visualization and simulation. In particular, DTCC Builder is capable of generating large-scale, conforming tetrahedral volume meshes of cities suitable for finite element (FEM) simulation

Combining Open Source and Commercial Tools in Digital Twin for Cities Generation

Evidently, Smart Cities are on the rise and there is an increasing need for digital twins of these complex environments and their corresponding 3D models. The creation and maintenance of such twins is a time consuming task, since cities are living evolving organisms. In this paper we are presenting work done within the Digital Twin Cities Centre (DTCC) in Sweden in the field of automated 3D city model generation. We showcase a novel method of combining open source and commercial software for creating digital twins of any urban context in a procedural way from raw input data and using Unreal Engine as a visualization front-end. We combine two different workflows, one based on the commercial software suite Feature Manipulation Engine and in parallel we utilize the open source code developed within the Centre, dubbed DTCC Builder. The assets created can be used in urban planning, multiphysics continuum mechanics simulations and for visualization and illustration on a 3D scale. By using, in a complementary way, established commercial software and state of the art open source C++ code we manage to utilize the quality of life features the first provides, while assigning the demanding tasks of comforming mesh generation to the former. The longer term goal is (nearly) real-time mesh digital twinning of any city and user interaction with the 3D assets provided. Copyright (C) 2022 The Authors

CFD Simulation and 3D Visualization on Cultural Heritage sites: The Castle of Mytilene

This paper presents a CFD and 3D Visualization pipeline to simulate wind flow over a heritage site and then visualize the results. As case study, a coarse 3D geometry model of the Fortress of Mytilene, Lesvos island, Greece and its surrounding was generated from open access Digital Elevation Models. The CFD simulation of the air flow on the wider heritage site area was performed using the steady-state version of the in-house flow solver IBOFlow (Immersed Boundary Octree Flow Solver) developed at Fraunhofer-Chalmers Research Centre. All the simulations were completed considering the mean wind direction and wind speed during the last 22 years from actual weather data retrieved from Open Weather Map. The visualization results were achieved through Unreal Engine, using built-in visualization tools and a tailored-made plugin to visualize the air flow over the monument and on the monument’s wall. As discussed in the conclusion section, the overall process proposed in this paper can be implemented for an initial assessment of the effect of environmental parameters over any heritage site and moreover, it may form the basis for valuable assistive tool for conservators and engineers

Roof Segmentation Towards Digital Twin Generation in LoD2+Using Deep Learning

There is an increasing need for digital twins of cities and their base maps, 3D city models. Creating and updating these twins is not an easy task, so automating and streamlining the process is a field of active research. A significant part of the urban geometry is residential buildings and their roofs. Modeling of roofs for urban buildings can be divided into three main areas - building detection, roof recognition and building reconstruction. The building and roofs are segmented with the help of machine learning and image processing. Afterwards the extracted information is used to generate parametric models for the roofs using methods from computational geometry. The goal is to create correct virtual models of roofs belonging to many different types of buildings. In this study, a supervised deep learning approach is proposed for the segmentation of roof edges from a single orthophoto. The predicted features include the linear elements of roofs. The experiments show that, despite the small amount of training data, even in the presence of noise, the proposed method performs well on semantic segmentation of roofs with different shapes and complexities. The quality of the extracted roof elements for the test area is about 56% and 71% for mean intersection over union (IOU) and Dice metric scores, respectively. Copyright (C) 2022 The Authors

Towards spatial integration of qualitative data for urban transformation – challenges with automated geovisualization of perception of urban places

Urban planning needs to face and integrate ecological, social, and economic aspects of city living. So far, attempts to integrate different urban simulation models into one technical platform have focused on quantitative data. The aim of this paper is to present the preparation for an automated method to spatially integrate and visualize interview-based qualitative data on the perception of urban places into a virtual platform. The Gothenburg suburb of Hammarkullen is used as a case study. Two CAQDAS software, NVivo and Atlas.ti, were tested. In bothsoftware, locations and urban qualities were coded and clustered. Visualization strategies such as information tree structures, geo-coded quotations, spatial word clouds, linked to 2D maps and 3D environments were developed. Results identify the challenges to overcome and show limitations of the software in terms of creating graphs and relationships as well as automated geocoding of data to maps. The project offers a step towards the integration of qualitative (social)data into digital environments that can be scaled up. By that, it contributes with a new dimension of analysis of urban environments which is necessary for sustainable transformation of cities

Visualisation of traffic noise exposure and health impact in a 3D urban environment

It is becoming increasingly common to work with urban planning using 3D visualisation tools. In the project DemoVirPEN a research team with participation from different research fields cooperated to create a demonstration concept for visualising traffic noise and the associated health impact in a 3D graphics environment. The project included participation from the following fields; 3D modelling and mapping, traffic noise calculation, auralisation, urban planning and architecture and health impact of noise exposure. The final product of the project is summarised in a film clip that illustrates the main results by visualising and auralising traffic in different configurations from different perspectives. A few key points are visualising short time frames (single vehicle passage) versus yearly average (noise map), and impact of changes such as removing or modifying traffic flows and buildings

An urban planning tool demonstrator with auralisation and visualisation of the sound environment

The paper presents findings from a recent project about the development of a demonstrator of an urban planning tool that includes auralised sounds as well as visualisations of sound propagation and facade noise levels linked to health impact. In urban development projects, the sound environment is one of the key elements, but often enters late in the planning process. As a result, even if the noise regulations are fulfilled, the potentially good sound environment may suffer unnecessary quality reductions. In addition, the standard ways of presenting and analysing the situations, using noise levels and noise maps, has potential for improvement, especially considering the transdisciplinary approaches to planning that are increasing in use. The tool aims to simplify the usage also at early stage planning, including scenario analysis, as well as to facilitate the urban planners\u27 understanding of the sound environment and its effects. The paper presents results from the development of the demonstrator, reflecting on auralisation as well as on multiple aspects of visualisation including grid noise maps, health-related facade noise levels and choice of colour scales

A novel multiphase DNS method for the resolution of Brownian motion in a weakly rarefied gas using a continuum framework

In this paper, we formulate an Immersed boundary based direct numerical simulation (DNS) technique for resolving the particle-fluid coupling between a nano-particle and a (weakly) rarefied gas. Such a method resolves the mobility of these solid particles by incorporating the hydrodynamics of the fluid more rigorously within the conventional Langevin description of the system. We analyse the consequences of resolving the subsequent Brownian motion of spherical soot-like hydrocarbon (HC) nano-particles in an unbounded domain using such a framework. The proposed method is able to capture the transition from a particle-inertia dominated (highly correlated) ballistic regime (t^2) to a non-correlated diffusive one (2Dt as given by the Stokes-Einstein relation) and further accurately estimate the resulting diffusivity of the nano-particle. This method can be used within any multiphase DNS framework to reproduce the meandering motion of soot-like Brownian particles under similar conditions

Modeling and Simulating Cities with Digital Twins

The digital twin concept has virtually exploded in recent years, but within the built environment the traditional term has long been ‘3D city model’. However, the digital twin concept is increasingly gaining acceptance as a useful concept that extends beyond 3D city models for not only modelling but also simulating cities. So what are digital twins, how are they being used, and what challenges are involved