Blog: Basics of Design by Analysis v. Design by Rule

FEA of Vessel

Introduction – Design by Analysis v. Design by Rule

Engineering design is a critical process that involves creating reliable structures, systems, and products. To ensure the safety and functionality of these designs, engineers employ various methodologies, two of which are Design by Analysis and Design by Rule.

Design By Rule

Design by Rule (DBR) is a simplified and empirical approach to engineering design. It relies on established codes, standards, and guidelines that dictate design specifications for various types of structures, components, or systems. These rules are typically based on extensive testing, historical data, and expert knowledge, ensuring a level of safety and reliability.

DBR provides a straightforward and efficient way to design structures, as engineers can directly apply predetermined formulas, tables, and graphs to determine the required dimensions, material properties, and load capacities. This approach is commonly employed in industries where designs are well-understood and repetitive, such as building construction, bridge design, and pressure vessel manufacturing.

The main advantage of DBR is its simplicity and ease of implementation. Engineers can quickly generate designs without the need for extensive analysis or specialized software. It also promotes standardization and ensures compliance with established safety regulations and industry best practices. DBR is particularly beneficial for smaller projects with limited budgets or time constraints, as it offers a cost-effective and time-efficient design process. However, DBR has inherent limitations. It relies on conservative assumptions and standardized values, which may lead to overdesign or underutilization of materials. This can result in increased costs or inefficiencies.

Additionally, DBR may not adequately address unique or non-standard design requirements, limiting its applicability in complex or innovative projects. The lack of flexibility and adaptability can hinder innovation in engineering design.


Design by Analysis

Design by Analysis (DBA) is an engineering approach that relies on complex mathematical models and analysis to evaluate the behavior and performance of a design under different conditions. It is a comprehensive and rigorous process that involves Finite Element Analysis and Computational Fluid Dynamics.
FEA Model of Vessel
FEA Model of a Vessel.

DBA allows engineers to not only investigate the stress distributions, and dynamic responses and structural integrity of a particular design – but also refine and optimize designs. By considering various factors such as material properties, loading conditions, and environmental effects, engineers can ensure that their designs meet specific safety and performance criteria. Design by Analysis is commonly used in industries such as aerospace, automotive, and power, where safety and reliability are critical.

One of the main advantages of DBA is its ability to account for complex interactions and non-linear behavior that cannot be easily captured by simple design rules. It allows engineers to push the boundaries of design, optimizing performance (e.g. thickness, geometry, weight, cost) while maintaining safety.

Additionally, DBA offers a systematic and quantitative approach, providing engineers with detailed insights into the identifying potential weaknesses and subsequent failure modes.

However, DBA also has limitations. The analysis process can be computationally intensive and time-consuming, requiring specialized software, expertise, and computational resources. Moreover, DBA heavily relies on assumptions and simplifications, which may introduce uncertainties and errors in the analysis. Engineers must carefully validate and verify their models to ensure their accuracy and reliability.

Conclusion

In summary, DBA provides detailed insights, flexibility, and optimization capabilities but requires more resources and expertise. On the other hand, DBR offers simplicity, efficiency, compliance, and standardization but may not adequately address unique or non-standard design requirements. The choice between DBA and DBR depends on the specific project requirements, complexity, available resources, and desired level of optimization and accuracy.

References

“Shigley’s Mechanical Engineering Design” Richard G. Budynas and J. Keith Nisbett, The McGraw-Hill Companies, Inc., New York, NY, 2011
“Pressure Vessel Design Manual” by Dennis R. Moss and Michael M. Basic, Elsevier Science, 2012
“Piping Handbook” Mohinder L. Nayyar, 7th Ed., McGraw Hill, 1999
“Structural Analysis” R.C. Hibbeler, 8th Ed., Pearson College, 2011

 


Read the Blog on Basics of Pressure Vessel Design.
O’Donnell Consulting performs Design & Analysis of Equipment – including Pressure Vessels for Clients in Various Industries.

(412) 835-5007

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