Christian Bendicks

Improved 3-D Particle Tracking Velocimetry with Colored Particles

The present work introduces an extension to three-dimensional Particle Tracking Velocimetry (3-D PTV) in order to investigate small-scale flow patterns. Instead of using monochrome particles the novelty over the prior state of the art is the use of differently dyed tracer particles and the identification of particle color classes directly on Bayer raw images. Especially in the case of a three camera setup it will be shown that the number of ambiguities is dramatically decreased when searching for homologous points in different images. This refers particularly to the determination of spatial parti- cle positions and possibly to the linking of positions into trajectories. The approach allows the handling of tracer parti- cles in high numbers and is therefore perfectly suited for gas flow investigations. Although the idea is simple, difficult- ties may arise particularly in determining the color class of individual particle when its projection on a Bayer sensor is too small. Hence, it is not recommended to extract features from RGB images for color class recognition due to infor- mation loss during the Bayer demosaicing process. This article demonstrates how to classify the color of small sized tracers directly on Bayer raw images.

Multiparametervisualisierung zur Exploration dynamischer Bilddaten

Wir beschreiben Methoden zur Exploration dynamischer CT- und MR-Daten. Dabei konzentrieren wir uns auf die Interaktion mit Parameterbildern, speziell auf die gleichzeitige Darstellung mehrerer Parameter. Zu diesem Zweck wurden erstmalig kolorierte Hohenfelder und Farbikonen fur die integrierte Visualisierung mehrerer Parameter basierend auf dynamischen Daten eingesetzt. Justierbare synchronisierte Linsen nutzen die Symmetrie in axialen Schichten des Gehirns. Sie erweitern das Konzept herkommlicher ROIs und erlauben die integrierte Darstellung von originalem Schichtbild und zugehorigem Parameterbild.

Tracking of a Handheld Ultrasonic Sensor for Corrosion Control on Pipe Segment Surfaces

The article describes a combination of optical 3-d measurement technique and ultrasonic testing for areawide acquisition of wall thickness on piping segments. It serves the purpose to match automatically ultrasonic measurements to their 3-d positions at the examined pipe segment. The sensor, which is normally occluded by hand, is equipped with a cap with a number of attached LEDs. A model based approach is presented to track these LEDs and to visualise the measured wall thickness at a three-dimensional surface. Therefore the model of the cap is fitted to the segmented image data, so that the 3-d position of the ultrasonic sensor can be derived from computed model orientation. Our approach works robustly and can build the basis for further applications in real industrial environments.

Use of Coloured Tracers in Gas Flow Experiments for a Lagrangian Flow Analysis with Increased Tracer Density

In this article a 3-d particle tracking velocimetry system (PTV system) is presented which enables the investigation of relatively fast gaseous (air) flows and tiny turbulences in a small scaled wind tunnel. To satisfy the demand of a high spatial and temporal resolution, a sufficiently high tracer particle concentration has to be applied to the gas. Solving the correspondence problem among different cameras becomes extremely difficult due to ambiguities: Each tracer has to be found in all pictures of the different views during many successive time steps. Here, the correspondence problem is facilitated by the use of coloured particles and the application of suitable classifiers for particle classification.

Coloured Tracer Particles Employed for 3-D Particle Tracking Velocimetry (PTV) in Gas Flows

This work describes an improved method for Particle Tracking Velocimetry in three dimensions (3-DPTV), applicable for gaseous flows and based on coloured tracer particles. This method allows a considerable increase of the tracer number density, while maintaining a constant rate of 3-D correspondence ambiguities from the different cameras. It is therefore perfectly suited for gas flows, where a high tracer density is requested to follow small-scale flow features. Furthermore, coloured tracer particles enable a longer next-step searching distance for the lagrangian reconstruction of trajectories. First, theoretical and numerical considerations are presented to check the ability of the employed coloured tracer particles to follow the considered flow. Then, 3-D PTV results obtained by the method described here are shown and appear to be very promising for later investigations of gas flows involving vortical structures and recirculation zones down to small scales, around 1 mm.

Optical Sensor Tracking and 3D-Reconstruction of Hydrogen-Induced Cracking

This paper presents an approach, which combines a stereo-camera unit and ultrasonic sensors to reconstruct hydrogen-induced crack HIC three-dimensional locations. The sensor probes are tracked in the images and their 3D position is triangulated. The combination with the ultrasonic measurement leads to a determination of the crack position in the material. To detect varying crack characteristics, different probes have to be used. Their measurements are combined in a common coordinate system. To evaluate the method, a milled reference block was examined and the results are compared to the ground-truth of the block model.

Multiple Camera Approach for SLAM Based Ultrasonic Tank Roof Inspection

This paper presents an approach of an autonomous measuring system for the wall thickness of tank roofs. It consists of a mobile robot, a multi-camera system and an ultrasonic sensor. A simultaneous localization and mapping with six degrees of freedom (SLAM-6D) is performed. The developed algorithms are optimized to work in man-made environments. Because of the great amount of line features in such environments, feature extraction is based on line segment detection. We propose a simple method for matching line segments in multiple images of three cameras. The correspondences are used to calculate 3D lines, which are used for localization. The accuracy of the system is evaluated by measurements on a prepared scene with unique markers.

3-D Particle Tracking Velocimetry (PTV) in gas flows using coloured tracer particles

Although relatively often used for liquid flows, Particle Tracking Velocimetry (PTV) is still considered as a major challenge in gaseous flows. One of the main objections is the higher tracer density necessary for gaseous measurements [1, 2], resulting from higher characteristic speeds and smaller spaceand time-scales of the important flow structures. Nevertheless, the widely recognized interest of Lagrange-based measurements (such as PTV) for the investigation of turbulence and vortical structures in real flows [3] is a sufficient reason to face all these challenges. The solution proposed in this work is to employ coloured particles and use the associated separation into different colour classes. Considering separately each resulting colour class, the apparent particle density is decreased without restrictions in the measurement accuracy.