Home Random Page


CATEGORIES:

BiologyChemistryConstructionCultureEcologyEconomyElectronicsFinanceGeographyHistoryInformaticsLawMathematicsMechanicsMedicineOtherPedagogyPhilosophyPhysicsPolicyPsychologySociologySportTourism






Model Preparation and Selection Method

I. CHAPTER ROADMAP

This chapter describes two paths toward models of products (Figure 13.1). Both paths begin and end at the preparation stage of modeling, followed by the distinction between mathematical and physical models.

 

II. INTRODUCTION: MODEL SELECTION BY PERFORMANCE SPECIFICATIONS

Before a product model is considered, a product development team must take stock of its current design status.

 

Model Preparation and Selection Method

Four steps initiate the creation of a product model for this purpose:

1. Map or relate the customer need weights to the product functions.

2. Identify the functions that relate most strongly to the customer needs.

3. Choose the metrics (engineering specifications, Chapter 7) that may be used to quantify the material, energy, or signal flows for these functions.

4. Identify target values for these metrics based on benchmarking results

(Chapter 7).

The first step provides a means of relating the customer need weights to the physics of the product. Recall when constructing product-function models, we ensure the functions themselves are a technical reflection of the customer needs. Step 2 then simplifies the modeling process by focusing on the primary function carriers of the product. Not all aspects of a product may be modeled mathematically. Practical limitations exist in the complexity of the model. It may require excessive computational resources, or take too much time to develop accurately, and there will be limitations of the model in predicting performance. By identifying the small subset of functions that relate most strongly to the customer needs, the scope of a model may be realistically reduced, while having the greatest potential for measuring real needs. Of course, as the product is developed, all functions of the product must be refined and tested fully. We just choose an initial subset to focus the development efforts on the most important and tractable issues. While all product functions affect the design, it is better not to be concerned with detailed secondary functions at this stage.

The third step of the process is implemented to choose a means of measuring the performance of a product. The choice of metrics must be tied to the flows of the primary product functions, since a transformation of flow models the physics of the product. Such choices may be made directly from benchmarking and engineering specifications (House of Quality, Chapter 7).

In preparing to model a product, the final step is to bound the metrics with target values. These target values provide goals for the final product performance, and may be chosen from benchmarking results. Choices of the target values are not trivial, nor should they be taken lightly. Targets will ultimately define the competitiveness of the product, its challenges for success, and its future marketing value. Chapter 7 discusses forecasting, the House of Quality, and other methods for choosing target values.



 

Product Application: Model Preparation and Selection

Figure 13.2 shows the mapping for the iced tea maker. Notice in the figure that the customer needs are associated with the functions that will address the needs. When more than one customer need relates to a function, the customer-need weights are summarized to assign importance to the function. Functions that are not directly associated with the high-weighted customer needs are assigned an importance of" 1" to identify them as supporting functions in the product. Such secondary functions are important to achieve the entire technical process carried out by the product. However, functions with higher importance weights are more useful for measuring the performance of a product model.

http://www.youtube.com/watch?v=at11iKgPG44

http://www.youtube.com/watch?v=FHRRGMp76d0

In the case of the iced tea maker, two functions are very highly rated: the "transmit heat" and "mix solid and liquid" sub functions (Figure 13.2). These functions are chosen through propagation of importance. If other customer needs are considered for modeling, then other functions can be chosen from the importance correlation mapping.

The next preparation step involves selecting metrics for the iced tea maker. From benchmarking, a list of measurements taken of each function reveals the metrics shown in Table 13.1. This information provides alternative metrics and avenues for modeling the iced tea maker. Let us focus on the first two customer needs, "stronger tea" and "use less ice:' which, as shown in the customer needs mapping, both relate directly to the main product functions of "transmit heat" and "mix solid and liquid." Using the metric list, we decide to base the strength of the tea on the amount of energy causing mixing (temperature of entering water) and the time the water is in contact with the tea. The time of contact is ultimately determined by measuring the geometry of the mixing chamber and the output flow of the mixture. These metric choices are supported and justified by background research into the steeping process for tea.

The second customer need, "use less ice," is primarily related to "cool exiting water" or "transmit heat." After observing the product operation and studying the measurements list, the two metrics "volume of medium" (volume of water in tank) and "final temperature" (temperature of tea entering storage pitcher) are chosen. Mathematical models are possible for these metrics based on the fluid mechanics and thermodynamics of the brewing process. These metrics are also identical to the metrics measured during benchmarking exercises for the domain of iced tea makers (Chapters 6 and 7).

The last stage of preparation involves the identification of target values for the chosen metrics. From background research and benchmarking results (Chapter 7), the target values may be determined (Figure 7.13). For iced tea makers, the target values include: "temperature of entering water" (slightly below boiling temperature of water), "time in contact" (5 minutes), "volume of water in tank" (3 cups and minimize to ensure tea saturation but reduce thermal mass), and "temperature of exiting tea" (minimize to reduce quantity of ice added to the brewed tea).

 


Date: 2016-01-14; view: 696


<== previous page | next page ==>
IV. A CONCEPT SELECTION PROCESS | III. MATHEMATICAL MODELING VERSUS PHYSICAL PROTOTYPING
doclecture.net - lectures - 2014-2024 year. Copyright infringement or personal data (0.008 sec.)