Methodology validation

The validation of the conceptual design methodology is undertaken in this section by assessing the adequacy of its application through analysis of requirements and comparison with accepted scientific and industry frameworks and knowledge.

5.5.2.1 Design methodology requirements

Pahl et al. (2007) states that in order that a design methodology meet its needs and requirements it must possess various attributes. These attributes which have been detailed and discussed in Chapter 4 form the basis of requirements for this design methodology. In keeping with the matrix-based conceptual design methodology. Table 5 shows an assessment of this conceptual design methodology against the needs and requirements as outlined by Pahl et al. (2007). The assessment is therefore a statement

of compliance that this methodology fulfils the general requirements for a conceptual design methodology.

Table 5. Pahl et al. (2007) – Methodology needs and requirements

Pahl et al. (2007) Methodology needs and requirements

Conceptual design methodology compliance

1. Allow a problem-directed approach, in that it must be applicable to every type of design activity, no matter the specialist field it involves.

This conceptual design methodology is applicable to alternate fuel system and propulsion systems modifications on any small aircraft and related ground infrastructure as demonstrated by case studies shown in Appendices 1 and 3.

2. Foster inventiveness and understanding in searching for an optimum solution.

The conceptual design methodology promotes generation of ideas and concepts through application of morphological matrices to explore the design space for the best solution (refer Fig. 39 Step 2).

3. Be compatible with the concepts, methods and findings of other disciplines.

The conceptual design methodology has adopted and/or adapted accepted scientific principles, industry frameworks and processes as presented and discussed in this Chapter.

4. Not rely on finding solutions by chance. The conceptual design methodology has adopted an approach that explores the design space through a repeatable and structured process to generate viable solution concepts (refer Fig. 39 Step 2 ).

5. Facilitate the application of known solutions to related tasks.

The conceptual design methodology relies on industry accepted techniques and tools such as QFD, morphological matrices, Pugh’s matrices, change option MDMs, CPM, and DSMs techniques applicable to engineering and certification domains (refer Fig 39).

6. Be compatible with electronic data processing.

The conceptual design methodology is implemented in two spreadsheets supporting this thesis (Williams, 2018a, 2018b). This spreadsheet implementation can be developed as a dedicated software tool with the appropriate graphical user interfaces and functions to facilitate ease of use.

7. Be easily taught and learned. The conceptual design methodology is provided within a matrix-based framework and has adopted techniques and tools which have widespread usage within industry as described in this Chapter. This widespread usage facilitates ease of teaching and learning of the methodology within design teams by using a matrix-based approach shown in Fig. 39.

8. Reflect the findings of cognitive psychology and modern management science, that is reduce the workload, reduce design time, prevent human error, and help maintain an active interest.

The conceptual design methodology aligns with modern management science where it is intended to reduce workload, prevent errors and oversights through implementation of a matrix-based structure. It maintains interest of the design team through consultation with discipline specialists and subject matter experts throughout all design steps.

9. Ease the planning and management of teamwork in an integrated and inter-disciplinary product development process.

The conceptual design methodology promotes teamwork through consultation with team members and experts throughout the design lifecycle as noted in the case studies presented in Appendices 1 and 3.

Pahl et al. (2007) Methodology needs and requirements

Conceptual design methodology compliance

10. Provide guidance for leaders of product development teams.

The conceptual design methodology provides a matrix-based framework to which leaders of product teams can refer during each step of the design lifecycle (refer Fig 39).

5.5.2.2 Synthesis-evaluation-analyses process by Faulconbridge and Ryan (2014) Faulconbridge and Ryan (2014) suggest that Systems Engineering processes are developed on the basis of an iterative application of analysis, synthesis and evaluation.

The conceptual design methodology as presented in this thesis has adopted this synthesis-evaluation-analysis approach, which initially occurs at the systems level, followed by application to the subsystems level, and then at the various lower component levels. This synthesis, evaluation and analysis framework is shown at the top-level by Figure 38, with this thesis structured following these principal elements.

5.5.2.3 Mechanical systems conceptual design steps by Ullman (2010)

Ullman (2010) describes this conceptual design phase as being primarily concerned with the generation and evaluation of concepts with a functional modelling approach essential for developing concepts that will eventually lead to modified system that is fit for purpose. In this context the mechanical systems conceptual design steps described by Ullman (2010) are reflected in the conceptual design methodology as assessed in Table 6.

Table 6. Ullman (2010) – Mechanical systems conceptual design steps

Ullman (2010) Mechanical systems conceptual design steps

Conceptual design methodology compliance

1. Generation of concepts. This is achieved through application of morphological matrices used to generate system concepts applicable to the requirements (refer Fig. 39 Step 2).

2. Evaluation of concepts. This is achieved through application of the quantised

morphological matrices, CPM techniques, the engineering and certification DMMs, and concept evaluation against technical performance measures (refer Fig. 39 Steps 2 through 7).

3. Making concept decisions. This is achieved through application of the quantised morphological matrices, change options MDM, and PM techniques (refer Fig. 39 Steps 2, 3 and 4).

4. Documenting and communicating. This is achieved through development of the design methodology outputs as provided by the DSD, CBS, CPP and Project risk register/matrix (refer Fig. 39 Steps 8 and 9)

Ullman (2010) Mechanical systems conceptual design steps

Conceptual design methodology compliance

5. Redefining plans. This is achieved by the design methodology outputs as described above (refer Fig. 39 Step 8).

6. Approving concepts. The main output of the methodology is the DSD, which is the document that describes the modification technical, performance, operational and support characteristics for use in the next phase in the system design life-cycle.

5.5.2.4 Trade-off analysis by Faulconbridge and Ryan (2014)

Faulconbridge and Ryan (2014) state that a trade-off analysis is one of the tools available to undertake evaluations within a conceptual design framework. In this context, the steps of a trade-off analysis described by Faulconbridge and Ryan (2014) comprise several steps which are also incorporated in the conceptual design methodology as assessed in Table 7.

Table 7. Faulconbridge and Ryan (2014) – Trade-off analysis

Faulconbridge and Ryan (2014) Trade-off analysis

Conceptual design methodology compliance

1. Definition of requirements. The QFD matrix is used to define, record and analyse the modification requirements as a step within the conceptual design methodology (refer Fig. 39 Step 1).

2. Identification of alternative solutions. The quantified morphological matrices are used to generate system concepts applicable to the requirements (refer Fig. 39 Step 2).

3. Nomination of selection criteria such as metrics.

The QFD matrix along with the quantified morphological matrices are used to nominate selection criteria and metrics (refer Fig. 39 Steps 1 and 2).

4. Determination of criteria weighting. Criteria weightings are incorporated into the quantised

morphological matrices and Pugh matrices (refer Fig. 39 Steps 2 and 3).

5. Definition of scoring functions. Scoring functions are incorporated into the quantised morphological matrix through normalising scores and determination of a FoM for compatible solutions (refer Fig. 39 Step 2).

6. Evaluation of alternatives. Several techniques and tools are used including quantisation of the morphological matrices, CPM, engineering and certification DMMs, and concept evaluation against technical performance measures (refer Fig. 39 Steps 2 through 7).

Faulconbridge and Ryan (2014) Trade-off analysis

Conceptual design methodology compliance

7. Sensitivity studies Sensitivity studies are conducted within the design methodology and are based on metric uncertainties, key technical performance measures and derived parameters (refer Fig. 39 Step 8).

5.5.2.5 Feasibility analysis and trades studies by Blanchard and Fabrycki (1998) Blanchard and Fabrycki (1998) state that the accomplishment of a feasibility analysis or a trade study is a major step within conceptual design that involves three main steps. These three main steps are inherent in this conceptual design methodology as assessed in Table 8.

Table 8. Blanchard and Fabrycki (1998) – Feasibility analysis

Blanchard and Fabrycki (1998) Feasibility analysis

Conceptual design methodology compliance

1. Identification of possible design approaches.

Morphological matrices are used to generate and identify system concepts and design approaches applicable to the requirements (refer Fig. 39 Step 2).

2. Evaluation of these approaches based on performance, effectiveness, maintenance, logistic support, and cost economics.

Evaluation of design approaches are achieved by the application of quantised morphological matrices, CPM, engineering and certification DMMs, and concept evaluation against technical performance measures for both aircraft and ground infrastructure segments (refer Fig. 39 Steps 2 through 7).

3. A recommendation of the preferred course of action.

The design methodology outputs are provided by the DSD, CBS, CPP documents and the Project risk register/matrix.

Recommendations are provided in the DSD as the key document recording this design process.

5.5.2.6 Evaluation of solution variants by Pahl et al. (2007)

The evaluation of solution variants, as described by Pahl et al. (2007) involves several steps. These steps are inherent in this conceptual design methodology as assessed in Table 9.

Table 9. Pahl et al. (2007) – Evaluation of solution variants

Pahl et al. (2007) - Evaluation of solution variants

Conceptual design methodology compliance

1. Identification of evaluation criteria. The QFD matrix along with the quantified morphological matrices are used to identify evaluation criteria and metrics (refer Fig. 39 Steps 1 and 2).

2. Weighting of evaluation criteria. Evaluation criteria weightings are incorporated into the quantised morphological matrices and the PM (refer Fig. 39 Steps 2 and 3).

3. Compiling parameters. Several techniques and tools are used including quantisation of the morphological matrices, PM, and engineering and certification DMMs (refer Fig. 39 Steps 2 through 7).

4. Assessing values. Assessment of design value is achieved by the application of quantised morphological matrices, CPM, engineering and certification DMMs, and concept evaluation against technical performance measures for both aircraft and ground segments (refer Fig. 39 Steps 2 through 8).

5. Determining overall value. Determination of overall value is achieved by application of the of quantised morphological matrices where all metrics are incorporated (refer Fig. 39 Step 2).

6. Comparing concept variants. Several techniques and tools are used including quantisation of the morphological matrices, CPM, engineering and certification DMMs, and concept evaluation against technical performance measures (refer Fig. 39 Steps 2 through 8).

7. Estimating evaluation uncertainties. Sensitivity studies are conducted within the design methodology and are based on metric uncertainties, key technical performance measures and derived parameters (refer Fig. 39 Step 8).

8. Searching for weak spots. The design methodology requires design advice from discipline specialists and subject matter experts at selected steps in the process as described in Appendices 1 and 3. These design team inputs are particularly important in identifying impacts of change propagation on engineering design and certification activities.