**4. Automotive vehicle gage panel**

254 Advanced Topics in Measurements

(a) (b)

(c)

 Fig. 13. Half of 3D model of optimal shape disk and real von Mises stresses distribution in it.

The proposed equipment allows using the standard wheel pair with removable measurement equipment as a tensometric wheel pair that considerably reduces material and time expenses required for preparing testing. By means of size and shape optimization, the total volume of the mounting disk of railway vehicle measurement system is reduced by ~64 % in comparison with the initial design. The method based on NURBS polygon points gives

the shape with at least 3% better objective (volume) than other used methods.

Fig. 12. Results of optimization of ellipsoidal disk. Shape of cross section is defined by (a) NURBS knot points, (b) NURBS polygon points, (c) points that are connected with

straight lines.

**3.5 Summary** 

In this section designing the mechanical part of an automotive vehicle gage panel is discussed. Automotive vehicle gage panels (GP) must meet many requirements - such functional characteristics as appropriate stress levels under loads, eigenfrequencies, stiffnesses, weight, accuracy etc. and last but not least they must have minimal environmental pollution during service lifetime. The 3D geometrical models of the gage panel are elaborated using SW. Static and dynamic responses of the gage panel are calculated using SW Simulation and impacts to environment are evaluated using SW Sustainability that include such indices as total energy consumed, carbon footprint, air acidification and water eutrophication. The stationary and transient behaviors of the gage panel under dynamic excitation as well as stress distribution under static loading are investigated. Due to the complexity of the gage panel FEM models, the appropriate metamodels are elaborated based on design of experiments. These metamodels are used for multiobjective optimization using a global search procedure. Partial objectives are aggregated in the complex objective function for optimization purposes. Dynamic behavior of the gage panel is then verified by solution of the full FEM models in case of random vibrations.

## **4.1 Specific requirements**

A constantly pressing problem is the development of safe and environmentally friendly engineering objects with high functional properties, attractive style and competitive price. We should try to take into account not only precisely measurable functional indices, but also such a difficult-to-formalize index as style of GP.

The Industrial Designer Society of America defines industrial design as the professional service of creating and developing concepts and specifications that optimize the function, value, and appearance of products and systems for the mutual benefit of both users and manufacturer. In fact, industrial designers focus their attention upon the form and user interaction of products. There are five critical goals (Ulrich & Eppinger, 2008): 1) Utility: The product`s human interfaces should be safe, easy to use, and intuitive. Each feature should be shaped so that it communicates its function to the user. 2) Appearance: Form, line, proportion, and color are used to integrate the product into a pleasing whole. 3) Easy maintenance: Product must also be designed to communicate how they are to be maintained and repaired. 4) Low costs: Form and features have a large impact on tooling and production costs, so these must be considered jointly by the team. 5) Communication: Product design should communicate the corporate design philosophy and mission through the visual qualities of the products. The practical concept selection methods (Ulrich & Eppinger, 2008) vary in their effectiveness and include the following: 1) External decision: Concepts are turned over to the customer, client, or some other external entity for selection. 2) Product champion: An influential member of the product development team chooses a concept based on personal preference. 3) Intuition: The concept is chosen by its feel. Explicit criteria or trade-offs are not used. The concept just seems better. 4) Multivoting: Each member of the team votes for several concepts. The concept with the most votes is selected. 5) Pros and cons: The team lists the strengths and weaknesses of each concept and makes a choice based upon group opinion. 6) Prototype and test: The organization builds and tests prototypes of each concept, making a selection based upon test data. 7) Decision matrices:

Shape Optimization of Mechanical Components for Measurement Systems 257

Generally the strength of the GP design is checked on special vibrostands. The GP is subjected to different dynamic loads. Vibrostability and vibration strength of the GP are checked on excitations in the frequency domain from 10 to 250 Hz. One of the main natural experiments is a test of shock resistance of the GP design under acceleration level *a* = 10*g*. Such experiments require significant material and time expenses and for optimization purposes the computer based design check must be used. The 3D geometrical model (Fig. 14) of the GP is created using SW and it consists of 18 parts: 6 deformable bodies and 12 rigid bodies that take into account the inertial characteristics of the internal devices. The deformable parts are made from the ABC 2020 plastic, but for the internal device bodies are assumed as alloy steel. The initial volume of the GP assembly is *v*0 = 764674 cm³ and mass *m*0 = 1.02 kg. The 3D model of the GP assembly is used for FEM analysis by SW Simulation to evaluate different responses of the GP. The FE mesh (Fig. 15) is generated with curvature based mesh (max elements size = 9 mm, min element size = 1.8 mm, element size growth ratio = 1.5), that ensures accurate discretization of the complex shape bodies of the GP. The FE mesh consists of ~ 210,000 nodes, ~147,000

In the initial design of the GP von Mises stresses from impact loading are shown on Fig. 15. We can see that maximal stresses are concentrated on the bracket's cross-section and it reaches 4 MPa. Other parts of the GP design are stressed considerably less. This implies that

Fig. 15. Meshed 3D model and von Mises stresses distribution in initial design of GP.

The numerical solver FFEPlus of SW is used for calculations.

Frequency analysis is implemented to find natural frequencies of the GP model and evaluate possible resonance in the case of external excitation. The same FE mesh for model as considered before is used. The contacts between assembly's parts are defined as bonded.

The obtained results show that the fundamental frequency of the GP is sufficiently high *f*1 = 170.47 Hz. The obtained mode shapes for the GP natural frequencies (*f*2 = 201.35 Hz, *f*3 = 264

**4.3 Strength calculation of GP design** 

elements, ~640,000 DOF.

the bracket design should be improved.

**4.4 Frequency analysis of GP** 

Hz, *f*4 = 331.85 Hz) are shown on Fig. 16.

The team rates each concept against pre specified selection criteria, which may be weighted. The concept selection method is built around the use of decision matrices for evaluating each concept with respect to a set of selection criteria. At the same time such formalized methods are elaborated as method of imprecision (Zimmermann, 2001) with noncompensating aggregation and compensating aggregation as well as fuzzy design method with different level interval algorithms.

The GP styles of different cars significantly differ and should be evaluated in context of the specific vehicle. At the same time style determines an arrangement of particular components (distances between gage axes etc.). In Fig. 14 we can see initial styles and the 3D model of the GP designed for new vehicles (Company Amoplant, 2011).

Fig. 14. Frontal view of GP of the initial styles and 3D geometrical model of GP.
