Adaptation of NEMO-LIM3 model for multigrid high resolution Arctic simulation

High-resolution regional hindcasting of ocean and sea ice plays an important role in the assessment of shipping and operational risks in the Arctic Ocean. The ice-ocean model NEMO-LIM3 was modified to improve its simulation quality for appropriate spatio-temporal resolutions. A multigrid model setup with connected coarse- (14 km) and fine-resolution (5 km) model configurations was devised. These two configurations were implemented and run separately. The resulting computational cost was lower when compared to that of the built-in AGRIF nesting system. Ice and tracer boundary-condition schemes were modified to achieve the correct interaction between coarse- and fine grids through a long ice-covered open boundary. An ice-restoring scheme was implemented to reduce spin-up time. The NEMO-LIM3 configuration described in this article provides more flexible and customisable tools for high-resolution regional Arctic simulations

Turbulent flow and heat transfer in eccentric annulus

Published versio

Surrogate-Assisted Evolutionary Generative Design Of Breakwaters Using Deep Convolutional Networks

In the paper, a multi-objective evolutionary surrogate-assisted approach for the fast and effective generative design of coastal breakwaters is proposed. To approximate the computationally expensive objective functions, the deep convolutional neural network is used as a surrogate model. This model allows optimizing a configuration of breakwaters with a different number of structures and segments. In addition to the surrogate, an assistant model was developed to estimate the confidence of predictions. The proposed approach was tested on the synthetic water area, the SWAN model was used to calculate the wave heights. The experimental results confirm that the proposed approach allows obtaining more effective (less expensive with better protective properties) solutions than non-surrogate approaches for the same time

Revealing sub-{\mu}m inhomogeneities and {\mu}m-scale texture in H2O ice at Megabar pressures via sound velocity measurements by time-domain Brillouin scattering

Time-domain Brillouin scattering technique, also known as picosecond ultrasonic interferometry, which provides opportunity to monitor propagation of nanometers to sub-micrometers length coherent acoustic pulses in the samples of sub-micrometers to tens of micrometers dimensions, was applied to depth-profiling of polycrystalline aggregate of ice compressed in a diamond anvil cell to Megabar pressures. The technique allowed examination of characteristic dimensions of elastic inhomogeneities and texturing of polycrystalline ice in the direction normal to the diamond anvil surfaces with sub-micrometer spatial resolution via time-resolved measurements of variations in the propagation velocity of the acoustic pulse traveling in the compressed sample. The achieved two-dimensional imaging of the polycrystalline ice aggregate in-depth and in one of the lateral directions indicates the feasibility of three-dimensional imaging and quantitative characterization of acoustical, optical and acousto-optical properties of transparent polycrystalline aggregates in diamond anvil cell with tens of nanometers in-depth resolution and lateral spatial resolution controlled by pump laser pulses focusing.Comment: 32 pages, 5 figure

Effects of thermal expansion on moderately intense turbulence in premixed flames

This study aims at analytically and numerically exploring the influence of combustion-induced thermal expansion on turbulence in premixed flames. In the theoretical part, contributions of solenoidal and potential velocity fluctuations to the unclosed component of the advection term in the Reynolds-averaged Navier-Stokes equations are compared, and a new criterion for assessing the importance of the thermal expansion effects is introduced. The criterion highlights a ratio of the dilatation in the laminar flame to the large-scale gradient of root mean square (rms) velocity in the turbulent flame brush. To support the theoretical study, direct numerical simulation (DNS) data obtained earlier from two complex-chemistry, lean H2-air flames are analyzed. In line with the new criterion, even at sufficiently high Karlovitz numbers, the results show significant influence of combustion-induced potential velocity fluctuations on the second moments of the turbulent velocity upstream of and within the flame brush. In particular, the DNS data demonstrate that (i) potential and solenoidal rms velocities are comparable in the unburnt gas close to the leading edge of the flame brush and (ii) potential and solenoidal rms velocities conditioned to unburnt gas are comparable within the entire flame brush. Moreover, combustion-induced thermal expansion affects not only the potential velocity but even the solenoidal one. The latter effects manifest themselves in a negative correlation between solenoidal velocity fluctuations and dilatation or in the counter-gradient behavior of the solenoidal scalar flux. Finally, a turbulence-in-premixed-flame diagram is sketched to discuss the influence of combustion-induced thermal expansion on various ranges of turbulence spectrum

Solenoidal and potential velocity fields in weakly turbulent premixed flames

Direct Numerical Simulation data obtained earlier from two statistically 1D, planar, fully-developed, weakly turbulent, single-step-chemistry, premixed flames characterized by two significantly different (7.53 and 2.50) density ratios {\sigma} are analyzed to explore the influence of combustion-induced thermal expansion on the turbulence and the backward influence of such flow perturbations on the reaction-zone surface. For this purpose, the simulated velocity fields are decomposed into solenoidal and potential velocity subfields. The approach is justified by the fact that results obtained adopting (i) a widely used orthogonal Helmholtz-Hodge decomposition and (ii) a recently introduced natural decomposition are close in the largest part of the computational domain (including the entire mean flame brushes) except for narrow zones near the inlet and outlet boundaries. The results show that combustion-induced thermal expansion can significantly change turbulent flow of unburned mixture upstream of a premixed flame by generating potential velocity fluctuations. Within the flame brush, the potential and solenoidal velocity fields are negatively (positively) correlated in unburned reactants (burned products, respectively) provided that {\sigma}=7.53. Moreover, correlation between strain rates generated by the solenoidal and potential velocity fields and conditioned to the reaction zone is positive (negative) in the leading (trailing, respectively) halves of the mean flame brushes. Furthermore, the potential strain rate correlates negatively with the curvature of the reaction zone, whereas the solenoidal strain rate and the curvature are negatively (positively) correlated in the leading (trailing, respectively) halves of the mean flame brushes.Comment: The work is accepted for oral presentation at the 38th Symposium (International) on Combustion. arXiv admin note: substantial text overlap with arXiv:2007.0833

Conditioned structure functions in turbulent hydrogen/air flames

Direct numerical simulation data obtained from two turbulent, lean hydrogen-air flames propagating in a box\ua0are analyzed to explore the influence of combustion-induced thermal expansion on turbulence in unburned gas.\ua0For this purpose, Helmholtz-Hodge decomposition is applied to the computed velocity fields. Subsequently, the\ua0second-order structure functions conditioned to unburned reactants are sampled from divergence-free solenoidal\ua0velocity field or irrotational potential velocity field, yielded by the decomposition. Results show that thermal\ua0expansion significantly affects the conditioned potential structure functions not only inside the mean flame brushes,\ua0but also upstream of them. Upstream of the flames, first, transverse structure functions for transverse potential\ua0velocities grow with distance r between sampling points more slowly when compared to the counterpart structure\ua0functions sampled from the entire or solenoidal velocity field. Second, the former growth rate depends\ua0substantially on the distance from the flame-brush leading edge, even at small r. Third, potential root-mean-\ua0square (rms) velocities increase with decreasing distance from the flame-brush leading edge and are comparable\ua0with solenoidal rms velocities near the leading edge. Fourth, although the conditioned axial and transverse\ua0potential rms velocities are always close to one another, thus, implying isotropy of the potential velocity field in\ua0unburned reactants; the potential structure functions exhibit a high degree of anisotropy. Fifthl thermal expansion\ua0effects are substantial even for the solenoidal structure functions and even upstream of a highly turbulent flame.\ua0These findings call for development of advanced models of turbulence in flames, which allow for the discussed\ua0thermal expansion effects