On the validation of variable fidelity multi-physics simulations

The difficulties encountered in applying current normative approaches for validation to computational models of complex multi-physics engineering systems are identified and are associated with the untestable, and sometimes unprincipled, nature of these models. The behaviour of a structural panel on the surface of a hypersonic flight vehicle when subject to complex interactions between aerothermal, aeroelastic and material responses is employed as a key exemplar. A wide range of positions in the philosophy of science, that are applicable to validation, are discussed within the context of a schematic matrix, which allows models to be categorised according to whether they are testable and principled. In the absence of test data against which to assess the accuracy of predictions, it is proposed that a model's credibility should be established based on its epistemic values, theoretical ancestry and the credentials of the modelling techniques. This shift from an objectivist to a relativist approach requires the assignment of experts who acknowledge their biases while engaging intellectually and ethically with the model, the community of knowledge and stakeholders, in a hermeneutical approach.JRC.F.3-Chemicals Safety and Alternative Method

Calibration and evaluation of optical systems for full-field strain measurement

The design and testing of a reference material for the calibration of optical systems for strain measurement is described, together with the design and testing of a standardized test material that allows the evaluation and assessment of fitness for purpose of the most sophisticated optical system for strain measurement. A classification system for the steps in the measurement process is also proposed and allows the development of a unified approach to diagnostic testing of components or sub-systems in an optical system for strain measurement based on any optical technique. The results described arise from a European study known as SPOTS whose objectives were to begin to fill the gap caused by a lack of standards

Application of thermoelastic stress analysis for the experimental evaluation of the effective stress intensity factor

In recent years, the advent of staring array detectors has made Thermoelastic Stress Analysis (TSA) a technique with considerable potential for fatigue and fracture mechanics applications. The technique is noncontacting and provides full field stress maps from the surface of cyclically loaded components. In addition, the technique appears to have a great potential in the evaluation of the effective stress intensity factor range during fatigue since fracture mechanics parameters are derived directly from the temperature changes in the vicinity ofthe crack tip rather than from remote data. In the current work TSA is presented as a novel methodology formeasuring the effective stress intensity factor from the analysis of thermoelastic images. ?K values inferredusing TSA have been employed to estimate an equivalent opening/closing load at different R-ratios in a crackedaluminium 2024 CT specimen. Results have been compared with those obtained using the strain-offset technique showing a good level of agreement

A probabilistic metric for the validation of computational models

A new validation metric is proposed that combines the use of a threshold based on the uncertainty in the measurement data with a normalised relative error, and that is robust in the presence of large variations in the data. The outcome from the metric is the probability that a model's predictions are representative of the real world based on the specific conditions and confidence level pertaining to the experiment from which the measurements were acquired. Relative error metrics are traditionally designed for use with series of data values but orthogonal decomposition has been employed to reduce the dimensionality of data matrices to feature vectors so that the metric can be applied to fields of data. Three previously published case studies are employed to demonstrate the efficacy of this quantitative approach to the validation process in the discipline of structural analysis, for which historical data was available; however, the concept could be applied to a wide range of disciplines and sectors where modelling and simulation plays a pivotal role

Detecting and Monitoring Cracks in Aerospace Materials Using Post-Processing of TSA and AE Data

Thermoelastic stress analysis (TSA) is a non-contact technique for measuring the distribution of stress in the surface of a component subject to cyclic loading by using a sensitive infrared camera. The stress concentrations indicative of a crack can be located and tracked using an optical flow method, allowing the position of the crack-tip to be identified at a given time. Acoustic emission (AE) has been used to validate the TSA algorithm. AE events from cracking, located using the Delta-T Mapping method, were detected several seconds before the TSA algorithm first detected cracking; however, TSA provided significantly more accurate location information

Comparative Maps of Safety Features for Fission and Fusion Reactors

Abstract The differences between nuclear fission and fusion have been discussed widely in the literature. However, little has been done to investigate the key differences in safety designs and regulatory requirements between the nuclear reactor types. In this study, an innovative methodology was successfully developed to map nuclear safety features to the fundamental safety principles set out by the nuclear regulators. Three safety cases were assessed in the mapping study, a research fusion reactor (Joint European Torus), a research fission reactor (Tsing Hua Open-pool Reactor) and a commercial fission reactor (Hinkley Point C). The graphical representation allowed a comparative analysis of the safety features and fundamental principles which revealed differences between the hazard profiles of fission and fusion reactors and provided important insights for the creation of a similar map for a future commercial fusion device.</jats:p

Settling dynamics of nanoparticles in simple and biological media

The biological response of organisms exposed to nanoparticles is often studied in vitro using adherent monolayers of cultured cells. In order to derive accurate concentration-response relationships, it is important to determine the local concentration of nanoparticles to which the cells are actually exposed rather than the nominal concentration of nanoparticles in the cell culture medium. In this study, the sedimentation-diffusion process of different sized and charged gold nanoparticles has been investigated in vitro by evaluating their settling dynamics and by developing a theoretical model to predict the concentration depth profile of nanoparticles in solution over time. Experiments were carried out in water and in cell culture media at a range of controlled temperatures. The optical phenomenon of caustics was exploited to track nanoparticles in real time in a conventional optical microscope without any requirement for fluorescent labelling that potentially affects the dynamics of the nanoparticles. The results obtained demonstrate that size, temperature and the stability of the nanoparticles play a pivotal role in regulating the settling dynamics of nanoparticles. For gold nanoparticles larger than 60 nm in diameter, the initial nominal concentration did not accurately represent the concentration of nanoparticles local to the cells. Finally, the theoretical model proposed accurately described the settling dynamics of the nanoparticles and thus represents a promising tool to support the design of in vitro experiments and the study of concentration-response relationships