Numerous Visualization Techniques Research Articles

Evaluation of depth perception in crowded volumes

Depth perception in volumetric visualization plays a crucial role in the understanding and interpretation of volumetric data. Numerous visualization techniques, many of which rely on physically based optical effects, promise to improve depth perception but often do so without considering camera movement or the content of the volume. As a result, the findings from previous studies may not be directly applicable to crowded volumes, where a large number of contained structures disrupts spatial perception. Crowded volumes therefore require special analysis and visualization tools with sparsification capabilities. Interactivity is an integral part of visualizing and exploring crowded volumes, but has received little attention in previous studies. To address this gap, we conducted a study to assess the impact of different rendering techniques on depth perception in crowded volumes, with a particular focus on the effects of camera movement. The results show that depth perception considering camera motion depends much more on the content of the volume than on the chosen visualization technique. Furthermore, we found that conventional non-photorealistic rendering techniques, which have often performed poorly in previous studies, showed comparable performance to modern photorealistic techniques in our study. The source code for the visualization system, survey, and analysis, as well as the data set used in the study and the participants’ responses, have been made publicly available.

A numerical visualization technique based on the hydraulic analogy

The principles of experimental visualization are widely used in developing numerical visualization techniques. Numerous techniques have been created by the simulation of experimental techniques, such as dye, smoke, surface oil, and optical techniques. In this research, a numerical visualization technique is proposed by the computational modeling of the visualization process of hydraulic analogy. First, the principle and implementation of the current technique are introduced and defined, respectively. Then, flow datasets of double Mach reflection and Rayleigh–Taylor instability are used for examining the display effects of the current technique. The effects of physical parameters and specific heat ratio on the current technique are investigated. In addition, the current technique is compared with six other techniques. The comparison indicates that the current technique not only can accurately display shock waves and slip lines, but also has an advantage in stereoscopically and cleanly visualizing vortices. Furthermore, the relationship between the current technique and numerical Schlieren and Shadowgraph is discussed. The current technique is further improved for the presentation of the information of colors and illumination. Finally, the limits of the current technique are highlighted.

(Invited) Segmented Cells: A Tool for Studying Fuel Cell Operation Heterogeneities, MEA Degradation Mechanisms, and Possible Mitigation Strategies

The operating conditions in a PEMFC are by nature heterogeneous because the concentration in oxygen and hydrogen diminishes along the channels while gases enrich in water. Furthermore, depending on the quality of the cooling circuit, the temperature may not be uniform over the MEA surface. Although modeling can put forward some local variations in current density, gas concentration, and liquid water content in PEMFC [1-2], the diversity and complexity of the physical phenomena taking place in MEA makes experimental investigations indispensable. Numerous visualization techniques have been used, from optical photography [3, 4] and Magnetic Resonance Imaging [5] to neutron [6] and synchrotron X-ray imaging [7]. However, visualization techniques mostly provide qualitative information, so that quantitative information about local operation inside an elementary cell is generally obtained using segmented cells. Many groups have developed their own tools [8] but fundamentally, a segmented cell is an ordinary single cell with one of the electrodes divided into smaller electrodes, where current density, impedance or even potential and active surface area can be measured independently of the other segments. Segmented cells are increasingly used for in situinvestigation of PEM fuel cell operation, to design flow fields, or to optimize the performances [9]. In some cases, segmented cells can be used in parallel with a visualization technique, for instance to study the impact of channel flooding on the local current density [4]. Using segmented cells recently enabled understanding the origin of local degradations in PEMFC, in occasions put forward by post-mortem analyses [10]. One of the most spectacular phenomena they contributed to unveil is the reverse currents occurring during cell start-up or shut-down under open circuit conditions. Their main mechanisms were initially presented by Reiser et al. [11] but to the best of our knowledge, Siroma et al. [12] and Maranzana et al. [13] were the first to succeed in measuring internal currents in PEMFC. From our point of view, there are currently two main perspectives in the use of segmented cells. The first one is to explore degradation mechanisms in other situations than start-up and shut-down events, for instance when a fuel cell is operated in dead-end mode [14]: in this case, excessive accumulation of liquid water and possibly nitrogen and oxygen in the anode compartment can result in significant rise of the anode potentials. More generally, segmented cells could be used to analyze the local operation of a cell during any kind of transient or steady-state operation. The main challenge in these cases consists in finding reliable markers of the degradation of the electrolyte membrane: up to now, instrumented cells were mostly used to monitor the degradation of the electrodes. The second perspective concerns the temperature heterogeneity over the MEA surface and through its thickness. Contrary to local variations in gas concentration, the impact of temperature heterogeneities is far from being well understood although MEA components degradation phenomena, reaction mechanisms/kinetics, and mass-transport phenomena are all dependent on that parameter. These issues and the main dificulties in designing and operating segmented cells will be discussed in the presentation.

O corpo transparente: visualização médica e cultura popular no século XX

In today's societies, successful new medical imaging technologies have focused unprecedented attention on the inside of the human body. These techniques have jumped the walls of the biomedical field per se, penetrating the fields of culture and law. The article traces a genealogy of twentieth-century medical techniques used to visualize the human body and brain, from X-rays to the more sophisticated CTs, MRIs, and PET scans. It explores the changes that these ever more numerous visualization techniques have occasioned in our corporality and examines how these technologies have been received in the courtroom and in popular culture, especially in literature, movies, and magazines.

241 円筒容器内で回転する角柱周りの流れの研究(S41-1 移動境界・連成(1),S41 移動境界・連成・振動と騒音問題)

It is known that flow structures similar to the famous Taylor vortex can be observed between an outer stationary cylinder and an inner rotating square cylinder, and one of their characteristic features is recognized to be the generation of waves at the boundary of each vortex cell and their propagation toward the outer cylinder wall. The main objective of this study is to investigate the generation process of the waves by using experimental and numerical visualization techniques. It was identified that, in addition to the characteristic vortex and wave structures, remarkable flow appears at the corner of the top (or equivalently the bottom) wall and the edge of the inner cylinder.

Numerical visualization and residence time determination of turbulent reacting duct flow with mass bleed and a backstep on one wall

A numerical experiment was performed to study turbulent reacting duct flows with a backstep and mass bleed on one wall. The time-dependent two-dimensional compressible conservation equations were solved with a subgrid-scale turbulence model. The combustion process considered was a one-step, irreversible, and infinitely fast chemical reaction. The numerical code used the finite-volume technique, which involved alternating in time the second-order, explicit MacCormack's and modified Godunov's schemes. Computed mean-velocity profiles are compared with existing experimental data, and good agreement is attained. Various numerical visualization techniques are implemented to reveal the evolution of large-scale vortical structures, temperature and species contour maps, and paths of fuel and air particles. The numerical time lines experimental allows the particle residence time in the flame-holding recirculation zone to be determined directly by the Lagrangian method through residence time probability density function for the first time. Moreover, a compact exponential expression for the particle number decay rate is provided to correlate the numerical data. A comparison of the Eulerian method previously used by all the researchers to indirectly find the residence time with the present Lagrangian method is further performed. An insight into the size of the detecting area and its relation to the uncertainty associated with the residence time determination using the Eulerian method are then provided.

Three-dimensional numerical simulation of periodic natural convection in a differentially heated cubical enclosure

A high-resolution, finite-difference numerical study is carried out of three-dimensional unsteady periodic natural convection of air in a cubical enclosure at the Rayleigh number of 8.5×106. The enclosure is subjected to differential heating at the two vertical side walls. The other vertical walls are insulated. A linear temperature profile is specified at the thermally-conducting horizontal walls. Flow details in the three-dimensional field are captured by elaborate post-processing of the computational results, for which the state-of-the-art numerical visualization techniques are utilized. The three-dimensionality of the mean flow fields is observed to be confined into narrow regions near the end walls. The time-dependent solutions clearly indicate the periodic nature of the flow. The oscillation frequency is in close agreement with the previous experimental measurements reported in the literature.