Resolved CFD-DEM simulation of blood flow with a reduced-order RBC model

Mathematical modeling of the blood flow with a resolved description of biological cells mechanics such as red blood cell (RBC) has been a challenge in the past decades as it involves physical complexities and demands high computational costs. In the present study, we propose an approach for efficient simulation of blood flow with several suspended RBCs. In this approach, we employ our previously proposed reduced-order model for deformable particles (Nair et al. in Comput Part Mech 7:593–601, 2020) to mimic the mechanical behavior of an individual RBC as a cluster of overlapping spheres interconnected by flexible mathematical bonds. This discrete element method-based model is then coupled with a fluid flow solver using the immersed boundary method with continuous forcing in the context of computational fluid dynamics-discrete element method (CFD-DEM) coupling. The present computational method is tested with a couple of validation cases in which the single RBC dynamics, as well as the blood flow with several RBCs, were tested in comparison with existing literature date. First, the RBC deformation index in shear flow at different shear rates is studied with a good accuracy. Then, the blood flow in micro-tubes of different diameters and hematocrits was simulated. The key characteristics of blood flow such as cell-free layer (CFL) thickness, Fahraeus effect and the relative apparent viscosity are used as the validation metrics. The proposed approach can predict the formation of the migration of RBC toward the tube center-line and the CFL thickness in good agreement with previous measurement and simulations. Furthermore, the model is employed to study the CFL enhancement for plasma separation based on channel constriction. The simulation results compute the CFL thickness downstream of the channel constriction in good agreement with the experiments in a wide range of flow rates and constriction lengths. The original contribution of this study lies in proposing an efficient resolved CFD-DEM simulation method for blood flows with many RBCs which can be employed for numerical investigation of bio-microfluidic applications.

Monitoring ice break-up on the Mackenzie River using MODIS data

The aim of this study was to develop an approach for estimating ice break-up dates on the Mackenzie River (MR) using more than a decade of MODIS Level 3 500 m snow products (MOD/MYD10A1), complemented with 250 m Level 1B radiance products (MOD/MYD02QKM) from the Terra and Aqua satellite platforms. The analysis showed break-up began on average between days of year (DOYs) 115 and 125 and ended between DOYs 145 and 155 over 13 ice seasons (2001–2013), resulting in an average melt duration of ca. 30–40 days. Thermal processes were more important in driving ice break-up south of the MR confluence with the Liard River, while dynamically driven break-up was more important north of the Liard. A comparison of the timing of ice disappearance with snow disappearance from surrounding land areas of the MR with MODIS Level 3 snow products showed varying relationships along the river. Ice-off and snow-off timing were in sync north of the MR–Liard River confluence and over sections of the MR before it enters the Mackenzie Delta, but ice disappeared much later than snow on land in regions where thermal ice break-up processes dominated. MODIS observations revealed that channel morphology is a more important control of ice break-up patterns than previously believed with ice runs on the MR strongly influenced by channel morphology (islands and bars, confluences and channel constriction). Ice velocity estimates from feature tracking were able to be made in 2008 and 2010 and yielded 3–4-day average ice velocities of 1.21 and 1.84 m s−1 respectively, which is in agreement with estimates from previous studies. These preliminary results confirm the utility of daily MODIS data for monitoring ice break-up processes along the Mackenzie River. The addition of optical and synthetic aperture radar data from recent and upcoming satellite missions (e.g. Sentinel-1/2/3 and RADARSAT Constellation) would improve the monitoring of ice break-up in narrower sections of the MR.

Monitoring ice break-up on the Mackenzie River using MODIS data

This study involves the analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) Level 3 500 m snow products (MOD/MYD10A1), complemented with 250 m Level 1B data (MOD/MYD02QKM), to monitor ice cover during the break-up period on the Mackenzie River, Canada. Results from the analysis of data for 13 ice seasons (2001–2013) show that first day ice-off dates are observed between days of year (DOY) 115–125 and end DOY 145–155, resulting in average melt durations of about 30–40 days. Floating ice transported northbound could therefore generate multiple periods of ice-on and ice-off observations at the same geographic location. During the ice break-up period, ice melt was initiated by in situ (thermodynamic) melt over the drainage basin especially between 61–61.8° N (75–300 km). However, ice break-up process north of 61.8° N was more dynamically driven. Furthermore, years with earlier initiation of the ice break-up period correlated with above normal air temperatures and precipitation, whereas later ice break-up period was correlated with below normal precipitation and air temperatures. MODIS observations revealed that ice runs were largely influenced by channel morphology (islands and bars, confluences and channel constriction). It is concluded that the numerous MODIS daily overpasses possible with the Terra and Aqua polar orbiting satellites, provide a powerful means for monitoring ice break-up processes at multiple geographical locations simultaneously along the Mackenzie River.

Modeling inundation of seasonally flooded wetlands at McCarran Ranch on Truckee River, USA

This paper among the first presents the application and validation of a hydrodynamic model (Adaptive Hydraulics model, AdH) of the McCarran ranch. We use the AdH model with topographic data by combining the DEM data from USGS seamless server and the ESRI tin data from United States Army Corps of Engineers (USACE) to predict floodplain inundation for a river reach of ~10 km located at lower Truckee River in Nevada state. We tested the mesh independence, sensitivity of input parameters and time steps, and then compared the modeling results to the existing gauged data (both the discharge and water stage heights). Results show that the accuracy of prediction from AdH model can decline slightly at higher discharge and water levels. The modeling results are much sensitive to the roughness coefficient of main channel, suggesting the model calibration should give priority to the main channel roughness. The simulation results suggest that large flood events could lead to a significantly higher proportion of total flow that routed through the floodplains. During peak discharge, a river channel constriction diverted as much as 65% of the river's 512.3 m3s−1 discharge into the floodplain. During the overbank flow, the transboundary flux ratio is about 5–45% of the total river discharge. Results also showed that both the relation of inundation area and volume between the discharge exhibit an apparent looped curve form.