[caption id="attachment_36046" align="alignright" width="300"]Bild_1_Montage_2 Pic 1: Selecting a city model region in the web-portal of the 3D city model of Frankfurt am Main for the simulation. The stars highlight different forms of building usage and simulation results are displayed in the web-portal in different colours[/caption] According to a study from the World Health Organization, some 54 per cent of the world’s population lived in cities in the year 2014, a trend which has been continuing to increase over time. When compared to the year 1960, for example, just 34 per cent lived in cities. The associated challenges are both complex and diverse. Recognising these requirements, the German federal government brought the Nationale Plattform Zukunftsstadt (NPZ) to life, which aims to address the development of sustainable solutions for modern problems. The initiative established a research agenda in 2014 with the contributions from Dr.-Ing. Günter Müller, founder of the company CADFEM GmbH. The NPZ is a part of the federal government’s high-tech strategy and has been designated as one of Germany’s top ten research priorities. In addition, the science Year 2015, an initiative of the Federal Ministry of Education and Research, was dedicated to the 'City of the Future' ('Zukunftsstadt'). CADFEM is also a member of the Fraunhofer Morgenstadt Initiative and is actively involved in developing the future strategies for an international and inter-disciplinary group of participants. Another platform concentrating on the development of modern, digital methods to tackle the most pressing challenges of the 21st century is the Leonhard Obermeyer Center (LOC) at the Technical University Munich. CADFEM has accompanied and shaped the LOC since its inception, as one of the Premium Members.

Collaboration: CADFEM and virtualcitySYSTEMS

[caption id="attachment_36069" align="alignright" width="146"]Picture 2 Picture 2: Simulation of turbulent air flows in the city region of Frankfurt am Main. The unsteady velocity field with wind speeds up to 16 metres per second is shown in sections at 10, 50, and 110 metres height[/caption] The future potential of this topic caught the attention of CADFEM, which began to focus on the ‘Digital City’ as one of its young business areas. Through close collaboration with virtualcitySYSTEMS, a subsidiary company of CADFEM International GmbH, new CAE-applications for urban areas based on digital 3D city models emerge. These CAE-applications aid in overcoming the challenges of progressive urbanisation while simultaneously addressing the consequences of global climate change. CADFEM intends to transfer the know-how and existing numerical solutions to the urban dimension and to handle the various constraints and requirements facing it. The basis for the application’s development are semantic 3D city models through virtualcitySYSTEMS. Underlying that is a data model, which handles urban complexities and makes them describable. This is a significant difference between sheer visualisation solutions, like those provided by Google or other vendors. The data model is defined in the open source standard CityGML, which increasingly establishes the management of urban 3D data worldwide while allowing it to be further expanded to a multitude of new themes or projects. The city model of Frankfurt am Main contains about 200,000 geometric objects, which are enriched for the purpose of building usage with additional attributes as shown in the main image (above). As a city is subjected to constant change, the models require routine updates. Given this complexity, it is clear that manual-derived models are no longer feasible and that those automated processes are an essential requirement for deriving reliable numerical models, too. Urban complexity further demands realistic numerical simulations to handle a variety of issues, such as the modelling of air flows, for instance (Picture 2, above right). CADFEM successfully entered the field of urban simulation through the research project DETORBA, which dealt with the propagation of detonation pressure waves in urban areas, including those arising from unexploded bombs left after World War II. Within the framework of this completed project, CADFEM created an automated workflow for this special application. The investigations of the Frankfurt city model illustrate that state police and security personnel can improve the necessary evacuation and safety measures, based on the data provided by the processed simulation results.

Basics technologies for many applications

[caption id="attachment_36074" align="alignright" width="278"]Picture 3: Integration of customised BIM building models for the city simulation in ANSYS Workbench Picture 3: Integration of customised BIM building models for the city simulation in ANSYS Workbench[/caption] Another area where urban simulations can be utilised is the modelling of turbulent wind flows (Picture 2, above right). Opportunities are continuously evolving for the efficient analysis of complex wind flows within the field of urban planning. Now engineers can not only determine wind loads for new buildings while taking those already existing into consideration, they can also identify necessary changes to improve current building constructions. This foundation makes it possible to answer additional questions during the urban planning process, such as improving city ventilation or enhancing individual comfort, for instance. The underlying workflow for the different applications is identical and builds on previously developed technologies. Through a web portal of the 3D city model that opens via a simple browser, a scenario can be defined and a part of a city model can be selected for simulation (see main image, above). Then, the data set is imported by an automated interface in ANSYS Workbench where the different applications are available. Additionally, detailed BIM building models (building information modelling) according to the International Finance Corporation standard can be amended in the city model (Picture 3). Correction and optimisation algorithms are used for geometric definition to ensure that the created numerical model and its meshing properly function. This is essential because the geometrical requirements are much higher for numerical models than for city models – an important finding from the work done so far. In combination with the latest options available for meshing the models, high quality CFD-models emerge, where a high degree of automation can be used. After carrying out the urban simulation, the results are again transferred to the web-portal of the city model and visualised there (see main image, above). Thus, the results can be discussed intensively with all involved planners and decision makers.

Improving urban flood protection

[caption id="attachment_36076" align="alignright" width="178"]Picture 4: Extract of a conventional 2D model of the Technical University Dresden with the river Elbe in the region of Dresden’s historical city centre showing flow depth during mean tide level (top) and during a flood with a peak level up to 8m (bottom) Picture 4: Extract of a conventional 2D model of the Technical University Dresden with the river Elbe in the region of Dresden’s historical city centre showing flow depth during mean tide level (top) and during a flood with a peak level up to 8m (bottom)[/caption] In early July 2015, a joint research project in the area of flood simulation was approved by the Institute of Hydraulic Engineering at the Technical University of Dresden, virtualcitySYSTEMS and CADFEM, which is funded by the German Environmental Foundation. The objective is to develop the simulation methods for improved flood-risk analysis in urban areas based on coupled hydrodynamic-numerical models and 3D city models. So far, 2D models are used for the flood simulation (Picture 3), which represent the city regions inaccurately. In co-operation with the involved cities Dresden and Magdeburg the accuracy of prediction can be improved by 3D models, allowing for better communication with those affected, as it is required by the European Flood Risk Management Directive. In the future, further application fields will be added and additional demonstrators will be brought to life; through these advancements, the functionality and user-friendliness of urban simulation will become all the more evident. Here, for example, the start-up accu:rate can be mentioned, which CADFEM gained as a new partner for the modelling of pedestrian flows in the planning of major events and evacuations. In addition, CADFEM is currently working on tailoring existing solutions to meet specific customer needs. Main image, Picture 1 and Picture 2 with kind support from the land surveying office of the city of Frankfurt am Main.

For further information, please contact Dr.-Ing. Stefan Trometer at CADFEM International: strometer@cadfem.de.