In recent years, simulation has become increasingly important to industrial decision-making. As a result, expectations for simulation credibility have risen significantly. To achieve this goal, appropriate Verification, Validation & Uncertainty Quantification (VVUQ) processes are essential, with validation playing a central role. However, successful implementation of validation faces several challenges. One of the primary issues is the availability of dedicated high-quality experiments that serve as validation referents, in line with recommendations of existing standards. Therefore, a broader range of validation referents needs to be considered in practice, leading to a wide spectrum of validation approaches with varying levels of rigour and credibility. Consequently, assessing the rigour of validation becomes increasingly important.

In light of these challenges, this book focuses specifically on the validation of physics-based simulation models. Our aim is to provide guidance for industry practitioners, helping them overcome these obstacles and enhance the credibility of their simulation results.

The book has been written by a team of four authors, all from different engineering simulation backgrounds, aiming at covering a broad scope of engineering simulation domains. Its content intentionally avoids focusing on any specific discipline within engineering simulation or any particular industrial application.

There is a justifiable debate over the use and definition of the word “validation” in the context of engineering simulation. NAFEMS has adopted the definition of ISO 9000, as per ISO 9001:2015, “Quality management systems, Requirements”, which is the basis of the NAFEMS “Engineering Simulation Quality Management Standard” (ESQMS). Other organizations, notably the American Society of Mechanical Engineers (ASME) and their ASME VVUQ standards, require validation to be based on empirical evidence, i.e. physical experiments. The ISO/NAFEMS definition embeds the more stringent ASME definition as a subset, but allows for a wider range of validation referents, so that the same processes can be applied on applications with varying criticality and credibility requirements.

There are two key contributions of this book. First of all, it formally introduces the concept of a “spectrum of validation methods”. The methods span the range from the strict definition of validation used in the ASME VVUQ standards, through to weaker validation approaches, including those supported by expert review. The introduction of the spectrum of validation methods is purposely high level and may need appropriate tailoring for application to specific industry applications. This tailoring is well outside of the scope of this book. The second main contribution of the book lies in the formal definition of validation rigour attributes that significantly impact the credibility of simulations. It is recommended to incorporate these rigour attributes during the specification and planning of validation activities. Furthermore, this contribution is expected to stimulate additional work, particularly in defining a validation rigour scale.