Mechanical Engineering - Research Publications

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 855
  • Item
    No Preview Available
    Effect of storage conditions on the characteristics of cryogenic hydrogen jet dispersion
    Saini, D ; Talei, M ; Yang, Y ; Sandberg, RD ; Berry, JD (Elsevier BV, 2024-05-20)
  • Item
    No Preview Available
  • Item
    Thumbnail Image
    Identifying regions of importance in wall-bounded turbulence through explainable deep learning.
    Cremades, A ; Hoyas, S ; Deshpande, R ; Quintero, P ; Lellep, M ; Lee, WJ ; Monty, JP ; Hutchins, N ; Linkmann, M ; Marusic, I ; Vinuesa, R (Springer Science and Business Media LLC, 2024-05-13)
    Despite its great scientific and technological importance, wall-bounded turbulence is an unresolved problem in classical physics that requires new perspectives to be tackled. One of the key strategies has been to study interactions among the energy-containing coherent structures in the flow. Such interactions are explored in this study using an explainable deep-learning method. The instantaneous velocity field obtained from a turbulent channel flow simulation is used to predict the velocity field in time through a U-net architecture. Based on the predicted flow, we assess the importance of each structure for this prediction using the game-theoretic algorithm of SHapley Additive exPlanations (SHAP). This work provides results in agreement with previous observations in the literature and extends them by revealing that the most important structures in the flow are not necessarily the ones with the highest contribution to the Reynolds shear stress. We also apply the method to an experimental database, where we can identify structures based on their importance score. This framework has the potential to shed light on numerous fundamental phenomena of wall-bounded turbulence, including novel strategies for flow control.
  • Item
    No Preview Available
    Data-driven turbulence modelling of inherently unsteady flow in stratified water storage tanks
    Xu, X ; Haghiri, A ; Sandberg, RD ; Oda, T ; Tanimoto, K (PERGAMON-ELSEVIER SCIENCE LTD, 2024-02)
  • Item
    No Preview Available
    Direct Numerical Simulation of Transitional and Turbulent Flows Over Multi-Scale Surface Roughness-Part II: The Effect of Roughness on the Performance of a High-Pressure Turbine Blade
    Nardini, M ; Jelly, TO ; Kozul, M ; Sandberg, RD ; Vitt, P ; Sluyter, G (ASME, 2024-03-01)
    Abstract Turbine blades generally present surface roughness introduced in the manufacturing process or caused by in-service degradation, which can have a significant impact on aero-thermal performance. A better understanding of the fundamental physical mechanisms arising from the interaction between the roughness and the turbine flow at engine-relevant conditions can provide insights for the design of blades with improved efficiency and longer operational life. To this end, a high-fidelity numerical framework combining a well-validated solver for direct numerical simulation and a second-order accurate immersed boundary method is employed to predict roughness-induced aero-thermal effects on an LS89 high-pressure turbine (HPT) blade at engine-relevant conditions. Different amplitudes and distributions of surface roughness are investigated and a reference smooth-blade simulation under the same flow conditions is conducted for comparison. Roughness of increasing amplitude progressively shifts the blade suction side boundary layer transition upstream, producing larger values of the turbulent kinetic energy and higher total wake losses. The on-surface data-capturing capabilities of the numerical framework provide direct measurements of the heat flux and the skin friction coefficient, hence offering quantitative information between the surface topology and engineering-relevant performance parameters. This work may provide a benchmark for future numerical studies of turbomachinery flows with roughness.
  • Item
    No Preview Available
    A Geometry-Based Distributed Connectivity Maintenance Algorithm for Discrete-time Multi-Agent Systems with Visual Sensing Constraints
    Li, X ; Fu, J ; Liu, M ; Xu, Y ; Tan, Y ; Xin, Y ; Pu, Y ; Oetomo, D (WORLD SCIENTIFIC PUBL CO PTE LTD, 2024-03)
    This paper presents a novel approach to address the challenge of maintaining connectivity within a multi-agent system (MAS) when utilizing directional visual sensors. These sensors have become essential tools for enhancing communication and connectivity in MAS, but their geometric constraints pose unique challenges when designing controllers. Our approach, grounded in geometric principles, leverages a mathematical model of directional visual sensors and employs a gradient-descent optimization method to determine the position and orientation constraints for each sensor based on its geometric configuration. This methodology ensures network connectivity, provided that initial geometric constraints are met. Experimental results validate the efficacy of our approach, highlighting its practical applicability for a range of tasks within MAS.
  • Item
    No Preview Available
    Computational Fluid Dynamics of Stent-Mounted Neural Interfaces in an Idealized Cerebral Venous Sinus.
    Qi, W ; Ooi, A ; Grayden, DB ; John, SE (IEEE, 2023-07)
    Hemodynamic changes in stented blood vessels play a critical role in stent-associated complications. The majority of work on the hemodynamics of stented blood vessels has focused on coronary arteries but not cerebral venous sinuses. With the emergence of endovascular electrophysiology, there is a growing interest in stenting cerebral blood vessels. We investigated the hemodynamic impact of a stent-mounted neural interface inside the cerebral venous sinus. The stent was virtually implanted into an idealized superior sagittal sinus (SSS) model. Local venous blood flow was simulated. Results showed that blood flow was altered by the stent, generating recirculation and low wall shear stress (WSS) around the device. However, the effect of the electrodes on blood flow was not prominent due to their small size. This is an early exploration of the hemodynamics of a stent-mounted neural interface. Future work will shed light on the key factors that influence blood flow and stenting outcomes.Clinical Relevance-The study investigates blood flow through a stent-based electrode array inside the cerebral venous sinus. The hemodynamic impact of the stent can provide insight into neointimal growth and thrombus formation.
  • Item
    No Preview Available
    NAPA-VQ: Neighborhood Aware Prototype Augmentation with Vector Quantization for Continual Learning
    Malepathirana, T ; Senanayake, D ; Halgamuge, S (IEEE, 2023-01-01)
  • Item
    No Preview Available
    Focused Contrastive Loss for Classification With Pre-Trained Language Models
    He, J ; Li, Y ; Zhai, Z ; Fang, B ; Thorne, C ; Druckenbrodt, C ; Akhondi, S ; Verspoor, K (Institute of Electrical and Electronics Engineers (IEEE), 2023-01-01)
  • Item
    No Preview Available
    Direct Numerical Simulation of Transitional and Turbulent Flows Over Multi-Scale Surface Roughness-Part I: Methodology and Challenges
    Nardini, M ; Kozul, M ; Jelly, TO ; Sandberg, RD (ASME, 2024-03-01)
    Abstract High-fidelity simulation of transitional and turbulent flows over multi-scale surface roughness presents several challenges. For instance, the complex and irregular geometrical nature of surface roughness makes it impractical to employ conforming structured grids, commonly adopted in large-scale numerical simulations due to their high computational efficiency. One possible solution to overcome this problem is offered by immersed boundary methods, which allow wall boundary conditions to be enforced on grids that do not conform to the geometry of the solid boundary. To this end, a three-dimensional, second-order accurate boundary data immersion method (BDIM) is adopted. A novel mapping algorithm that can be applied to general three-dimensional surfaces is presented, together with a newly developed data-capturing methodology to extract and analyze on-surface flow quantities of interest. A rigorous procedure to compute gradient quantities such as the wall shear stress and the heat flux on complex non-conforming geometries is also introduced. The new framework is validated by performing a direct numerical simulation (DNS) of fully developed turbulent channel flow over sinusoidal egg-carton roughness in a minimal-span domain. For this canonical case, the averaged streamwise velocity profiles are compared against results from the literature obtained with a body-fitted grid. General guidelines on the BDIM resolution requirements for multi-scale roughness simulation are given. Momentum and energy balance methods are used to validate the calculation of the overall skin friction and heat transfer at the wall. The BDIM is then employed to investigate the effect of irregular homogeneous surface roughness on the performance of an LS-89 high-pressure turbine blade at engine-relevant conditions using DNS. This is the first application of the BDIM to realize multi-scale roughness for transitional flow in transonic conditions in the context of high-pressure turbines. The methodology adopted to generate the desired roughness distribution and to apply it to the reference blade geometry is introduced. The results are compared to the case of an equivalent smooth blade.