108 research outputs found
Dataset for the study of various error measures steering adaptive model order reduction algorithms in vibroacoustic applications
No full textThe dataset is associated with the university dissertation titled "Surrogate modeling of high-dimensional vibroacoustic problems using parametric model order reduction" by Harikrishnan K. Sreekumar. To evaluate the accuracy of a reduced order model in the context of model order reduction in the frequency domain, a range of error measures are available. The error measures are extensively used in adaptive algorithms to build reduced order models of optimal dimensions with the least effort. The author performs a detailed study on some of the popular error measures using simple plate examples that are discussed in the thesis. This current dataset publication contains essential artifacts (computational notebook, model data and primary results) that enable reproducibility of the outcome presented in the dissertation
Microstructural Instabilities in Nickel-based Single Crystal Superalloys
No full textSingle crystal superalloys, mostly Nickel-based, have been, so far, the material of choice for high-temperature applications, such as gas turbine blades. Single crystalline turbine blades are usually cast in the direction, providing the best combination of properties. While misorientations up to 15��� are within accepted tolerance, the elastic/viscoplastic response of the bi-phased ��/��0 microstructure in superalloys is highly sensitive towards the crystalline orientation. Further, multiaxial stress states create microstructural gradients and alter the performance of the material. As the microstructure stability dictates the blade���s structural integrity, it is necessary to understand the microstructural state as a function of the crystallographic orientation and multiaxial stress state to quantify the creep performance.
The lifetime of Ni-based single crystal superalloys is connected to the integrity of the strengthening phase, �� 0 . During high-temperature thermomechanical loading, the cuboidal shaped �� 0 phase coalesces, directionally coarsens(rafting), and is finally topologically inverted, viz. surrounds the �� phase and acts as the matrix. The topological inversion comes along with an increase in the plastic strain rate known as the tertiary creep. X-ray tomography experiment has recently revealed that the tertiary creep initiates before the expected increase in the volume fraction of pores. Thus, the initiation of the tertiary creep stage might also be due to the destabilization of the ��/��0 interfacial dislocation network leading to the massive shearing of �� 0 rafts concomitantly resulting in topological inversion. Simultaneously, the strain-hardening and the void growth in these viscoplastic single crystals lead to the ductile fracture. Hence, for a fundamental understanding of the microstructural instability and to improve lifetime predictions, it is necessary to consider the interplay of orientation-specific microstructural evolutions, the destabilization of the interfacial network, and subsequent shearing of �� 0 particles, as well as dislocation, creep and void growth to fully explain what triggers the increase of the plastic strain rate in the tertiary creep stage leading to failure.
This dissertation aims to elucidate the microstructural instabilities in Ni-based single crystal superalloys through a multi-scale microstructure-sensitive thermo-mechanically coupled damage model in a finite-element crystal plasticity framework through the integration of high-temperature multiaxial creep experiments, advanced characterization techniques, and high fidelity computational tools. To that end, a phase-field model was extended to account for microstructural destabilization and damage. For the first time, topological inversion during creep was predicted using a phase-field model. Further, macroscale finite-element calculations were carried out using the realistic 3D microstructures derived from the phase-field model. A viscoplastic description of 3D rafting predicted the channel evolution irrespective of the loading conditions and crystallographic orientation. Results from this work will elucidate the effects of microstructural degradation, crystallography, and multiaxial stresses towards rupture in Ni-based single crystal superalloy subjected to high-temperature/low stress creep conditions
Recommended from our members
Composite solution to the neutron lifetime anomaly
No full textMeasurements of the lifetime of neutrons trapped in a bottle have been consistently shorter than the lifetime measured in neutron beam experiments. With trapping potentials as low as 50 neV and neutron detectors located only at the top of the bottle, this discrepancy could be the result of the soft scattering of dark matter with neutrons. However, it is challenging to obtain the observed loss rate in conventional models of dark matter scattering. We show that this phenomenology is possible in composite models of dark matter where the soft scattering is from dark matter that has been captured and accumulated in the Earth. This solution can be tested by placing more neutron detectors around the trap, providing better angular coverage. The phenomenology of soft scattering by trapped composite dark matter is generic and suggests new experimental directions that could be pursued to detect this large class of models
Interplay of asexual and sexual reproduction in bifunctional insects
No full textReproduction is a fundamental biological process, with organisms reproducing sexually, asexually, and, in some cases, utilizing both modes of reproduction within the same population. Does the ability to reproduce through a combination of asexual and sexual modes offer an evolutionary advantage over relying on either mode alone? Here, we introduce an empirically driven theoretical model to examine the dynamics and interplay between sexual and asexual reproduction in stick insect populations. We analyse it using a novel phase transition approach and corroborate it using published experimental data. We find that the presence of males can either increase or decrease the overall population size. However, maintaining an optimal ratio of parthenogenetic to sexual reproduction is crucial for male resilience, effectively delaying male extinction. Conversely, extreme levels of parthenogenetic reproduction—whether too high or too low—can lead to male extinction, emphasizing the need for a balanced number of virgin females to ensure the persistence of males. Our model also explains male absence in Carausius morosus and persistence in Extatosoma tiaratum. Our findings provide valuable insights into the interplay of reproductive strategies and contribute to broader discussions on the transitions between sexual and asexual reproduction
On the motion of hairpin filaments in the atmospheric boundary layer
No full textAbstract: A recent work of Harikrishnan et al. [arXiv:2110.02253 (2021)] has revealed an abundance of hairpin-like vortex structures, oriented in a similar direction, in the turbulent patches of a stably stratified Ekman flow. The Ekman flow over a smooth wall is a simplified configuration of the Atmospheric Boundary Layer (ABL) where effects of both stratification and rotation are present. In this study, hairpin-like structures are investigated by treating them as slender vortex filaments, i.e., a vortex filament whose diameter is small when compared to its radius of curvature . The corrected thin-tube model of Klein and Knio [J. Fluid Mech. (1995)] is used to compute the motion of these filaments with the ABL as a background flow. The influence of the mean background flow on the filaments is studied for two stably stratified cases and a neutrally stratified case. Our results suggest that the orientation of the hairpin filament in the spanwise direction is linked to its initial starting height under stable stratification whereas no such dependency can be observed with the neutrally stratified background flow. An improved feature tracking scheme based on spatial overlap for tracking -criterion vortex structures on the Direct Numerical Simulation (DNS) data is also developed. It overcomes the limitation of using a constant threshold in time by dynamically adjusting the thresholds to accommodate the growth or deterioration of a feature. A comparison between the feature tracking and the filament simulation reveals qualitatively similar temporal developments. Finally, an extension of the asymptotic analysis of Callegari and Ting [J. App. Math (1978)] is carried out to include the effect of gravity. The results show that, in the regime considered here, a contribution from the gravity term occurs only when the tail of an infinitely long filament is tilted at an angle relative to the wall. (c) 2023 Author(s)
Investigating the extension of service life of box-beam bridge girders: And it's impact on circularity
No full textThe main motivation within this thesis is to explore the possibility of increasing the service life of box-beam bridge girders to aid the ambition of the Dutch government to become a circular economy. The construction industry still follows a more or less linear economy system. Many bridges in the Netherlands are approaching the end of their service lives, and efforts are being made to extend the lives of these bridges. This is but a temporary solution, and these bridges will require replacement within 20-30 years. This provides an opportunity to incorporate circularity within new and upcoming structures from the design phase onward rather than only as an end-of-life practice. Therefore this thesis explores the possibilities of incorporating the strategy of lifespan extension, in the form of a cover increase against chloride-induced corrosion. The exact increase was calculated through the use of a relevant service life design model (DuraCrete) and compared with the Eurocodes. The reliability of the model was checked using a Monte Carlo simulation. Subsequently, the circular aspects of future adaptability were also investigated considering a fictitious scenario of increased traffic load. Hence, it was concluded that a marginal increase in concrete volume and prestressing steel per beam would allow for a more durable and adaptable beam for the future. Civil Engineering | Structural Engineering | Concrete Structure
Feasibility of incorporating the concept of demountable (modular) construction to an existing integral bridge design
No full textAdopt the concept of demountable and rebuildable brides to an existing idea of an integral bridge. An understanding of the different forces and moments that the bridge will have to take up and how the critical connections (deck-abutment) can be realized. Applying the understanding of how integral and demountable bridges behave and try to integrate the characteristics of both to achieve rebuildable/demountable construction. In this additional thesis, the first steps to make an integral bridge demountable is looked at in detail. The concepts of vertical prestressing with unbonded bars are explored to achieve the demountable abutment, and abutment- deck connection. The different forces that arise due to this method of prestressing have been accounted for to ensure the basic safety of this design is met.Civil Engineering | Structural Engineerin
- …
