W. de Leeuw

A probe for local flow field visualization

A probe for the interactive visualization of flow fields is presented. The probe can be used to visualize many characteristics of the flow in detail for a small region in the data set. The velocity and the local change of velocity (the velocity gradient tensor) are visualized by a set of geometric primitives. To this end, the velocity gradient tensor is transformed to a local coordinate frame, and decomposed into components parallel with and perpendicular to the flow. These components are visualized as geometric objects with an intuitively meaningful interpretation. An implementation is presented which shows that this probe is a useful tool for flow visualization.A probe for the interactive visualization of flow fields is presented. The probe can be used to visualize many characteristics of the flow in detail for a small region in the data set. The velocity and the local change of velocity (the velocity gradient tensor) are visualized by a set of geometric primitives. To this end, the velocity gradient tensor is transformed to a local coordinate frame, and decomposed into components parallel with and perpendicular to the flow. These components are visualized as geometric objects with an intuitively meaningful interpretation. An implementation is presented which shows that this probe is a useful tool for flow visualization. >

Enhanced spot noise for vector field visualization

Spot noise is a technique for texture synthesis, which is very useful for vector field visualization. This paper describes improvements and extensions of the basic principle of spot noise. First, better visualization of highly curved vector fields with spot noise is achieved, by adapting the shape of the spots to the local velocity field. Second, filtering of spots is proposed to eliminate undesired low frequency components from the spot noise texture. Third, methods are described to utilize graphics hardware to generate the texture, and to produce variable viewpoint animations of spot noise on surfaces. Fourth, the synthesis of spot noise on grids with highly irregular cell sizes is described.Spot noise is a technique for texture synthesis, which is very useful for vector field visualization. This paper describes improvements and extensions of the basic principle of spot noise. First, better visualization of highly curved vector fields with spot noise is achieved, by adapting the shape of the spots to the local velocity field. Second, filtering of spots is proposed to eliminate undesired low frequency components from the spot noise texture. Third, methods are described to utilize graphics hardware to generate the texture, and to produce variable viewpoint animations of spot noise on surfaces. Fourth, the synthesis of spot noise on grids with highly irregular cell sizes is described.

Collapsing flow topology using area metrics

Visualization of topological information of a vector field can provide useful information on the structure of the field. However, in turbulent flows standard critical point visualization will result in a cluttered image which is difficult to interpret. This paper presents a technique for collapsing topologies. The governing idea is to classify the importance of the critical points in the topology. By only displaying the more important critical points, a simplified depiction of the topology can be provided. Flow consistency is maintained when collapsing the topology, resulting in a visualization which is consistent with the original topology. We apply the collapsing topology technique to a turbulent flow field.

Three ways to show 3D fluid flow

Visualizing 3D fluid flow fields presents a challenge to scientific visualization, mainly because no natural visual representation of 3D vector fields exists. We can readily recognize geometric objects, color, and texture: unfortunately for computational fluid dynamics (CFD) researchers, vector fields are harder to grasp. Thus, we must construct simplified representations that human observers can understand. Simplification means focusing on relevant aspects of the flow. This offers many options, making a wide variety of flow visualization techniques both feasible and desirable. This article presents an overview of three different visualization techniques developed in the Netherlands. The three useful techniques for visualizing 3D flows are: implicit stream surfaces, turbulent particle animation, and a flow probe.<<ETX>>

Standardization of on-line VHF PD measurements on turbo generators

Based on field experiences on a number of different turbo-generators in the Netherlands, several fundamental and applied aspects of on-line very high frequency (VHF) partial discharge (PD) diagnostics are discussed. In particular the systematic results presented in this paper contribute to: 1. the characteristics of different on-line detection using suitable VHF sensors, 2. the methods to suppress disturbances and to distinguish between different types of discharges and 3. the interpretation of measured results to obtain knowledge about the insulation condition.

Comparing LIC and spot noise

Spot noise and line integral convolution (LIC) are two texture synthesis techniques for vector field visualization. The two techniques are compared. Continuous directional convolution is used as a common basis for comparing the techniques. It is shown that the techniques are based on the same mathematical concept. Comparisons of the visual appearance of the output and performance of the algorithms are made.

Visualization of time dependent confocal microscopy data

The microscopic analysis of time dependent 3D live cells provides considerable challenges to visualization. Effective visualization can provide insight into the structure and functioning of living cells. The paper presents a case study in which a number of visualization techniques were applied to analyze a specific problem in cell biology: the condensation and de-condensation of chromosomes during cell division. The spatial complexity of the data required sophisticated presentation techniques. The interactive virtual reality enabled visualization system, proteus, specially equipped for time dependent 3D data sets is described. An important feature of proteus is that it is extendible to cope with application-specific demands.

BM3D: motion estimation in time dependent volume data

This paper describes BM3D: a method for the analysis of motion in time dependent volume data. From a sequence of volume data sets a sequence of vector data sets representing the movement of the data is computed. A block matching technique is used for the reconstruction of data movement. The derived vector field can be used for the visualization of time dependent volume data. The method is illustrated in two applications.This paper describes BM3D: a method for the analysis of motion in time dependent volume data. From a sequence of volume data sets a sequence of vector data sets representing the movement of the data is computed. A block matching technique is used for the reconstruction of data movement. The derived vector field can be used for the visualization of time dependent volume data. The method is illustrated in two applications.

The importance of generator operating conditions on PD data evaluation

This paper summarizes the results of a preliminary study on the influence of generator operating conditions on its partial discharge (PD) activity. This study covers results from the field measurements as well as from laboratory investigations. The turbo generator discussed in this paper showed an extra PD source at high temperature. This extra PD source was activated at high temperatures and vanished at lower temperatures. The activation and the de-activation process had a clear hysteresis character. Both the measurements on the turbo generator and in the laboratory showed that there is certain dependence between the internal PD and the actual temperature of the stator coil. Due to the fact that in practice the moment at which a periodic measurement is performed does not always represent the PD activity of a generator under all its operating conditions, it is of practical interest to investigate the dependences between the power, temperature and the actual PD activity. A full investigation into the relation between generator operating conditions and its PD activity is justified.

Virtual reality in biological microscopic imaging

Confocal microscopes have recently allowed biologists and biomedical researchers to obtain time dependent 3D data sets of biological. objects, such as cells and tissues. Scientific visualization can provide visual presentations of structural characteristics of these data sets. This paper addresses the role of virtual reality in gaining insight in these presentations. The understanding of structural characteristics of time dependent 3D confocal biological data requires spatial judgments. Perceiving these characteristics is enhanced by using virtual reality technology. The advantage of virtual reality is particularly apparent in the exploration phase of the analysis when the behavior of the underlying biological processes is not a priori known.