For the visualization of velocity distributions of flow simulations, various methods have been established. These include the presentation of information by means of small arrows, color-coded stream and path lines and Schlieren. All these methods have their pros and cons. Above all, without the knowledge of the observed data they are difficult to interpret. For this reason, the software STRING XE "STRING:software" was developed in a cooperation between the delta h engineering company ltd. and the Fraunhofer Institute for Technical and Industrial Mathematics (ITWM) in . STRING provides intuitive access to the results of flow simulations. The program allows you to visualize steady state and transient flows in two spatial dimensions as a video. The relevant direction and velocity information are displayed by the moving flow streamlets. A short line segment of a streamline is called streamlet. The moving direction of a streamlet is the direction of the flow and the length correlates with the velocity.
Example of Visualization
The software allows the import of flow data from SPRING and storing the calculated images for a single video. These images can also be provided with a transparent background, so you can show in a subsequent step, any additional data in the video. To facilitate this, a world file is stored together with the single picture that allows the georeferencing of the video in any geographic information system (GIS). The generation of a video requires from SPRING information of geometry and of the velocities of flow within this area. For the initial distribution of the streamlets a proven method is used, which is applied within the Finite Pointset Method (FPM) and has long been developed on ITWM. The equations of motion of the streamlets are solved using an adaptive Runge-Kutta method of higher order. The error tolerance is adjustable. For interpolating the velocities from the data calculated in SPRING the method of Moving Least Squares is used. It also takes into account special cases related to complicated geometries.
Within the animation it can happen, that very dense accumulations of streamlets are formed in depressions of the flow area or that the streamlets flow away from all sources. In these areas no assessment of the prevailing flow is possible. To avoid this, a management of the local distribution of the streamlets is necessary.
The ITWM uses years of experience in the area of the FPM to solve such problems. Various algorithms from this environment were implemented in STRING.
The program STRING is controllable by a graphical user interface and the output of each image of the video can be adjusted freely. Parameters are for example given by the resolution and the running time of the finished video. But the appearance of each streamlet can be customized in great detail.
In this way, clear impressions of the flow direction, course, speed and temporal evolution of the water flow can be obtained. In combination with SPRING 5, STRING unfolds its full potential.
Results of the intermediate points of time of the transient flow calculation