Before the introduction of the 3D glyph-based visualization, engineers at AVL-List GmbH used static diagrams to evaluate and analyze timing drive simulation results. Experienced engineers can certainly infer useful information from diagrams. However, they still face difficulties un-derstanding position and orientation of bodies as well as directions in 3D space. It is especially difficult to judge and compare relative positions and distances. Characteristics of temporal be-havior, such as frequency of vibration are also intuitively visualized using animation. Engineers using the application listed the following advantages to their previous workflow:
• Contours that are in contact and the actual contact point positions are clearly identified. This is especially important if the model is somehow incorrect, for example the contour of a sprocket is not continuous or it does not match the contour of the toothed belt. Discovering a very loose
6.4. EVALUATION 91
Figure 6.22: Distortion of the crankshaft un-der load. Deformation is magnified by two or-ders of magnitude. The arrows indicate the constraint forces at the nodes of the reduced crankshaft mesh.
Figure 6.23: Arrows depicting displacement on a cross-section of the crankshaft. The dis-placement data available at all nodes are re-sampled to a grid of lower resolution to reduce visual clutter.
toothed belt that skips the teeth of a pulley (see Figure 6.10) is also very easy. Errors in modeling and initial conditions became a lot easier to detect. Finding these types of problems used to be complicated because the irrational simulation results (e.g., extreme forces) were the only indication.
• Directions of forces are made clear. This is important when the engineer expects a force to act in one direction, but simulation proves that it acts in some other direction. In fact showing the direction and magnitude of vector attributes at the same time is something they could not do before without 3D visualization.
• Motion of tensioners can be seen clearly. This has also been very difficult to understand by studying diagrams.
• Animation shows all chain links at a given time step creating an overall impression of how the chain moves. To the contrary, individual charts were created previously for each chain link and the overall motion was difficult to infer from them.
• It is easier to spot periodic behavior at a given point in space.
• Distribution of forces between chain links is seen. Areas of extreme tension are quickly found.
Less experienced engineers and professionals working in neighboring fields (manufacturing, namely) can also profit from the more accessible presentation of the simulation results. Con-vincing movies for presentations can be generated with little effort, which is also valuable for marketing purposes. Many user groups ranging from inexperienced, young engineers through experienced professionals to marketing department can benefit from interactive 3D visualization.
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6.5 Chapter Conclusions
Tasks like exploring the dependency between simulation control parameters and results, or opti-mization require the simultaneous analysis of many simulation runs. 3D depictions of different simulation runs can be shown in windows arranged side by side, but in practice this only allows the comparison of a few (two to four) cases. The interactive 3D visualization system is not suitable for the analysis and comparison of many simulation runs and it is not meant for that purpose. To the contrary, it is meant as a tool for the detailed analysis of one or a few simula-tions with complete 3D spatial context. Those few simulation runs that are analyzed in depth in 3D can be identified using the more abstract approaches described in the previous chapters.
The 3D view could be integrated into the coordinated multiple views framework introduced in Chapter 3, and show data pertaining to the brushed simulation cases when there are only a few.
We admit, however, that this integration has not been implemented yet.
Chapter 7
Demonstration
“Reality is frequently inaccurate.”
— Douglas Adams (1952–2001)1 The science of visual analytics is very applicable in engineering applications. Simulation and measurement data sets are complex, optimization goals are often conflicting, the trends and dependencies in the data can be indirect. Engineers and designers must make defensible and responsible decisions because design mistakes can have very expensive consequences if short-comings are discovered during production. The time-to-market for new designs needs to be short, so designers work under time pressure. They also need to communicate their findings to collaborating teams.
In this chapter we present two case studies that document the visual exploration and analysis of real-world simulation data sets from automotive engineering. Section 7.1 contains the analysis of Diesel fuel injection system simulation data. In Section 7.2, an optimization of a timing chain drive is presented. Both case studies were performed working in cooperation with engineers at AVL-List GmbH (www.avl.com), the largest privately owned company for the development of powertrain systems with internal combustion engines. The case studies demonstrate that the approach described in the previous chapters is indeed applicable and useful in the analysis of real life engineering problems. All simulation data in this chapter are courtesy of AVL-List GmbH.
7.1 Interactive Visual Analysis of a Fuel Injection System
There are many (often conflicting) goals of Diesel engine design including the need for high power and good fuel efficiency, meeting emission regulations, reducing noise levels, and im-proving driveability (smooth and reliable delivery of power at various engine speeds). The fuel injection system is the key Diesel engine component to achieve those goals. The following properties are considered important in the fuel injection procedure:
• high injection pressure for good atomization and combustion,
1English writer, humourist, and dramatist, best known as the author ofThe Hitchhiker’s Guide to the Galaxy.
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Figure 7.1: Main components of a common rail injector system. Image courtesy of AVL-List GmbH.
• flexible timing of the injection,
• short pre-injection before the main burst to reduce combustion noise,
• accurate control of injected fuel quantity,
• ability to inject small amounts of fuel to achieve economical operation and good emission properties.
Currently, the two most popular injection systems for Diesel engines are the electronic unit injector type [46, 82] and the common rail injection systems [29]. Matkovi´c et al. [161] have demonstrated the interactive visual analysis of an electronic unit injector. In this section, we an-alyze a common rail injection system. Common rail injection has been identified as an attractive injection system for Diesel car engines. It is offered by all major car manufacturers today.
7.1.1 Diesel Common Rail Injection Systems
Common rail injection systems can be controlled in a very flexible way. Injection pressure and quantity can be controlled with a high degree of flexibility, multiple fuel injections are possible within one injection cycle, and the time and duration of the injections can be controlled precisely by the engine control unit based on the engine speed and load. These properties are instrumental in meeting current and future very stringent emission regulations. Therefore, common rail injec-tion systems are seen as a very popular opinjec-tion by many manufacturers. In this case study we use the simulation results of a conventional series common rail Diesel fuel injection system [29].
The injector is the central part of an injection system that injects a desired fuel quantity into the cylinder. Figure 7.1 shows a typical injector with main components. The common rail