Description of laminar-turbulent transition of an airfoil boundary layer measured by differential image thermography using directed percolation theory

Transition from laminar to turbulent flow is still a challenging problem. Recent studies indicate a good agreement when describing this phase transition with the directed percolation theory. This study presents a new experimental approach by means of differential image thermography (DIT) enabling to investigate this transition on the suction side of a heated airfoil. The results extend the applicability of the directed percolation theory to describe the transition on curves surfaces. The experimental effort allows for the first time an agreement between all three universal exponents of the (1+1)D directed percolation for such airfoil application. Furthermore, this study proves that the theory holds for a wide range of flows, as shown by the various conditions tested. Such a large parameter space was not covered in any examination so far. The findings underline the significance of percolation models in fluid mechanics and show that this theory can be used as a high precision tool for the problem of transition to turbulence.

The Hybrid-Agile Design of Experiments Methodology

A DOE (Design of Experiments) is the laying out of a detailed experimental plan in advance of doing the experiment. Optimal DOEs maximize the amount of information that can be obtained for a given amount of experimental effort. The traditional DOE methodology is waterfall-type methodology implying a sequential and linear life-cycle process. The success of the experiment and usefulness of the results are highly dependent on the initial experimental setup and assumptions, and does not allow to go back and change something that was not well-documented or thought upon in the design stage. The fast-changing software development industry have made it understandable that the traditional waterfall methodology for developing systems, which follows similar patters to the traditional DOE, lacks the agility required for developing robust systems. These limitations have triggered the development of agile: a type of incremental model of software development based on principles that focuses more on flexible responses to change, instead of in-depth planning at the design stage. This paper proposes the hybrid-agile DOE methodology – a methodology that incorporates agile principles in traditional waterfall DOE methodologies – to design effective experimental layouts that allow for improvement during the experimental trial process. The methodology is applied to the natural ageing of adhesives tapes for building applications. This methodology can overcome traditional DOE, by adding agility in the whole process, especially in cases where the investigated products lack prior information and are characterised by large variability.

Residual stress in laser-based directed energy deposition of aluminum alloy 2024: simulation and validation

Simulations of laser-based directed energy deposition of metals have received increasing interest aimed at reducing the experimental effort to select the proper processing condition for the repair or overhaul of actual components. One of the main issues to be addressed is the evaluation of the residual stress, which may lead to part failure under nominal loading. In this frame and specifically relating to aluminum alloys, few works have been developed and validated. This lack of knowledge is addressed in this paper: namely, the proper approach to simulate the activation of the deposited metal is discussed in case of single deposition and is shifted to a case of multiple depositions over a substrate. The validation of the predicted residual stress is made by comparison with the actual stress resulting from X-ray diffraction.

Simulation of the Mechanical Behaviour of Metal Gyroids for Bone Tissue Application

Additive manufacturing is a valid solution to build complex geometries, including lightweight structures. Among these, gyroids offer a viable concept for bone tissue application, although many preliminary trials would be required to validate the design before actual implantation. In this frame, this study is aimed at presenting the background and the steps to build a numerical simulation to extract the mechanical behaviour of the structure, thus reducing the experimental effort. The results of the simulation are compared to the actual outcome resulting from quasi-static compressive tests and the effectiveness of the model is measured with reference to similar studies presented in the literature about other lightweight structures.

Evaluation of S-N curves including failure probabilities using short-time procedures

In recent years, different short-time procedures have been developed that significantly reduce the experimental effort required to generate S-N curves and thus S-N databases. Methods like StressLife, StrainLife, and SteBLife are some of those which have shown enormous potential in this respect. In this contribution, the practicability of the SteBLife method is shown. Two S-N curve evaluation strategies based on temperature and magnetic field measurements are presented. These take statistical evaluation into account, describing a material’s scatter in terms of fatigue life. In order to demonstrate the versatility of the approach and to underline the advantages in terms of effort saved when compared to conventional procedures, the process on how to get the required information obtained is shown for three unalloyed and low-alloyed steels under different heat treatment conditions.

Digital Twin Application for Model-Based DoE to Rapidly Identify Ideal Process Conditions for Space-Time Yield Optimization

The fast exploration of a design space and identification of the best process conditions facilitating the highest space-time yield are of great interest for manufacturers. To obtain this information, depending on the design space, a large number of practical experiments must be performed, analyzed, and evaluated. To reduce this experimental effort and increase the process understanding, we evaluated a model-based design of experiments to rapidly identify the optimum process conditions in a design space maximizing space-time yield. From a small initial dataset, hybrid models were implemented and used as digital bioprocess twins, thus obtaining the recommended optimal experiment. In cases where these optimum conditions were not covered by existing data, the experiment was carried out and added to the initial data set, re-training the hybrid model. The procedure was repeated until the model gained certainty about the best process conditions, i.e., no new recommendations. To evaluate this workflow, we utilized different initial data sets and assessed their respective performances. The fastest approach for optimizing the space-time yield in a three-dimensional design space was found with five initial experiments. The digital twin gained certainty after four recommendations, leading to a significantly reduced experimental effort compared to other state-of-the-art approaches. This highlights the benefits of in silico design space exploration for accelerating knowledge-based bioprocess development, and reducing the number of hands-on experiments, time, energy, and raw materials.

Development of a Multi-Shaker-Control to Investigate the Influence of the Interblade Phase Angle on Frictionally Damped Turbine Blades

Constructive damper concepts are developed and integrated in turbomachinery to reduce vibration amplitudes generated by dynamic loads. The potential damping effectiveness of friction-based damper concepts is strongly dependent on the relative motion between adjacent blades, besides other factors such as normal force. In cyclic symmetric structures the phase difference is determined by the excited nodal diameter, which leads to different damper movements and efficiencies for given mode shapes. Several studies on the investigation of the damper performance of different underplatform damper geometries have been carried out on non-rotating test stands consisting usually of two blades in order to reduce the experimental effort before setting up rotational tests. Based on the existing modes of the two blades and the application of commonly just one shaker, the investigations are limited to the in-phase and out-of-phase modes. In this paper an experimental approach is developed to reduce the gap of transferability between non-rotating and rotational tests to analyze the effects of a variable interblade phase angle on the damping effect of underplatform dampers. For this purpose, a cascaded control system using two shakers is being developed to control the force amplitudes and the phase difference between the response of the two blades. The control algorithm is designed in a model-based way by using a two degrees of freedom oscillator with friction contact and is subsequently integrated in the non-rotating test stand.

How university diversity rationales inform student preferences and outcomes

It is currently commonplace for institutions of higher education to proclaim to embrace diversity and inclusion. Though there are numerous rationales available for doing so, US Supreme Court decisions have consistently favored rationales which assert that diversity provides compelling educational benefits and is thus instrumentally useful. Our research is a quantitative/experimental effort to examine how such instrumental rationales comport with the preferences of White and Black Americans, specifically contrasting them with previously dominant moral rationales that embrace diversity as a matter of intrinsic values (e.g., justice). Furthermore, we investigate the prevalence of instrumental diversity rationales in the American higher education landscape and the degree to which they correspond with educational outcomes. Across six experiments, we showed that instrumental rationales correspond to the preferences of White (but not Black) Americans, and both parents and admissions staff expect Black students to fare worse at universities that endorse them. We coded university websites and surveyed admissions staff to determine that, nevertheless, instrumental diversity rationales are more prevalent than moral ones are and that they are indeed associated with increasing White–Black graduation disparities, particularly among universities with low levels of moral rationale use. These findings indicate that the most common rationale for supporting diversity in American higher education accords with the preferences of, and better relative outcomes for, White Americans over low-status racial minorities. The rationales behind universities’ embrace of diversity have nonlegal consequences that should be considered in institutional decision making.

Computer-assisted catalyst development via automated modelling of conformationally complex molecules: application to diphosphinoamine ligands

Simulation of conformationally complicated molecules requires multiple levels of theory to obtain accurate thermodynamics, requiring significant researcher time to implement. We automate this workflow using all open-source code (XTBDFT) and apply it toward a practical challenge: diphosphinoamine (PNP) ligands used for ethylene tetramerization catalysis may isomerize (with deleterious effects) to iminobisphosphines (PPNs), and a computational method to evaluate PNP ligand candidates would save significant experimental effort. We use XTBDFT to calculate the thermodynamic stability of a wide range of conformationally complex PNP ligands against isomeriation to PPN (ΔGPPN), and establish a strong correlation between ΔGPPN and catalyst performance. Finally, we apply our method to screen novel PNP candidates, saving significant time by ruling out candidates with non-trivial synthetic routes and poor expected catalytic performance.