125 research outputs found
Assessment of Neural Network Augmented Reynolds Averaged Navier Stokes Turbulence Model in Extrapolation Modes
A machine-learned (ML) model is developed to enhance the accuracy of
turbulence transport equations of Reynolds Averaged Navier Stokes (RANS) solver
and applied for periodic hill test case, which involves complex flow regimes,
such as attached boundary layer, shear-layer, and separation and reattachment.
The accuracy of the model is investigated in extrapolation modes, i.e., the
test case has much larger separation bubble and higher turbulence than the
training cases. A parametric study is also performed to understand the effect
of network hyperparameters on training and model accuracy and to quantify the
uncertainty in model accuracy due to the non-deterministic nature of the neural
network training. The study revealed that, for any network, less than optimal
mini-batch size results in overfitting, and larger than optimal batch size
reduces accuracy. Data clustering is found to be an efficient approach to
prevent the machine-learned model from over-training on more prevalent flow
regimes, and results in a model with similar accuracy using almost one-third of
the training dataset. Feature importance analysis reveals that turbulence
production is correlated with shear strain in the free-shear region, with shear
strain and wall-distance and local velocity-based Reynolds number in the
boundary layer regime, and with streamwise velocity gradient in the
accelerating flow regime. The flow direction is found to be key in identifying
flow separation and reattachment regime. Machine-learned models perform poorly
in extrapolation mode, wherein the prediction shows less than 10% correlation
with Direct Numerical Simulation (DNS). A priori tests reveal that model
predictability improves significantly as the hill dataset is partially added
during training in a partial extrapolation model, e.g., with the addition of
only 5% of the hill data increases correlation with DNS to 80%.Comment: 50 pages, 18 figure
Nonlinear vibration of beams and rectangular plates
Der Einfluss von Vorspannungen auf die freien und erzwungenen nichtlinearen Schwingungen von Balken und rechteckigen Platten wird mittels einer einfachen Erweiterung der Lösungen fĂŒr FĂ€lle ohne Vorspannung untersucht. Es wird eine einzige Koordinatenfunktion benĂŒtzt; es werden einfach aufgelegte und eingespannte FĂ€lle betrachtet; und die Diskussion wird auch auf den ĂŒberkritischen Bereich ausgedehnt.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43314/1/33_2005_Article_BF01602658.pd
Electroosmotic flow of biorheological micropolar fluids through microfluidic channels
An analysis is presented in this work to assess the influence of micropolar nature of fluids in fully developed flow induced by electrokinetically driven peristaltic pumping through a parallel plate microchannel. The walls of the channel are assumed as sinusoidal wavy to analyze the peristaltic flow nature. We consider that the wavelength of the wall motion is much larger as compared to the channel width to validate the lubrication theory. To simplify the Poisson Boltzmann equation, we also use the Debye-HĂŒckel linearization (i.e. wall zeta potential †25mV). We consider governing equation for micropolar fluid in absence of body force and couple effects however external electric field is employed. The solutions for axial velocity, spin velocity, flow rate, pressure rise and stream functions subjected to given physical boundary conditions are computed. The effects of pertinent parameters like Debye length and Helmholtz-Smoluchowski velocity which characterize the EDL phenomenon and external electric field, coupling number and micropolar parameter which characterize the micropolar fluid behavior, on peristaltic pumping are discussed through the illustrations. The results show that peristaltic pumping may alter by applying external electric fields. This model can be used to design and engineer the peristalsis-lab-on-chip and micro peristaltic syringe pumps for biomedical applications
Nonlinear Stochastic Partial Differential Equations of hyperbolic type driven by LĂ©vy-type noises
An assessment of simple material behaviour models for predicting the mechanical ratchetting of a stepped beam
Circumferentially Cracked Bimaterial Hollow Cylinder Under Mechanical and Transient Thermal Loading
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