CFD Investigation of Gear Pump Mixing Using Deforming/Agglomerating Mesh

2006 ◽  
Vol 129 (4) ◽  
pp. 476-484 ◽  
Author(s):  
Wayne Strasser
Keyword(s):  
Large Scale ◽  
Accurate Solution ◽  
Progression Rate ◽  
Gear Pump ◽  
Feed Stream ◽  
Time Step ◽  
Pump Speed ◽  
Lower Viscosity ◽  
Fluid Properties ◽  
Process Fluid

A moving-deforming grid study was carried out using a commercial computational fluid dynamics (CFD) solver, FLUENT® 6.2.16. The goal was to quantify the level of mixing of a lower-viscosity additive (at a mass concentration below 10%) into a higher-viscosity process fluid for a large-scale metering gear pump configuration typical in plastics manufacturing. Second-order upwinding and bounded central differencing schemes were used to reduce numerical diffusion. A maximum solver progression rate of 0.0003 revolutions per time step was required for an accurate solution. Fluid properties, additive feed arrangement, pump scale, and pump speed were systematically studied for their effects on mixing. For each additive feed arrangement studied, the additive was fed in individual stream(s) into the pump-intake. Pump intake additive variability, in terms of coefficient of spatial variation (COV), was >300% for all cases. The model indicated that the pump discharge additive COV ranged from 45% for a single centerline additive feed stream to 5.5% for multiple additive feed streams. It was found that viscous heating and thermal/shear-thinning characteristics in the process fluid slightly improved mixing, reducing the outlet COV to 3.2% for the multiple feed-stream case. The outlet COV fell to 2.0% for a half-scale arrangement with similar physics. Lastly, it was found that if the smaller unit’s speed were halved, the outlet COV was reduced to 1.5%.

CFD Investigation of Gear Pump Mixing

2005 ◽  
Author(s):  
Wayne Strasser
Keyword(s):  
Large Scale ◽  
Accurate Solution ◽  
Viscous Heating ◽  
Progression Rate ◽  
Gear Pump ◽  
Feed Stream ◽  
Pump Speed ◽  
Lower Viscosity ◽  
Fluid Properties ◽  
Process Fluid

A moving-deforming grid study was carried out using a commercial CFD solver, Fluent® 6.2.16, in order to quantify the level of mixing of a lower viscosity additive (at a mass concentration below 10%) into a higher viscosity process fluid for a large-scale metering gear pump configuration typical in plastics manufacturing. Second order upwinding and bounded central differencing schemes were used to reduce numerical diffusion. A maximum solver progression rate of 0.0003 revolutions per timestep was required for an accurate solution. Fluid properties, additive feed arrangement, pump scale, and pump speed were systematically studied for their effects on mixing. For each additive feed arrangement studied, the additive was fed in individual stream(s) into the pump intake. Pump intake additive variability, in terms of coefficient of variation (COV), was > 300% for all cases. The model indicated that the pump discharge additive COV ranged from 32% for a single centerline additive feed stream to 3.9% for multiple additive feed streams. It was found that viscous heating and thermal/shear-thinning characteristics in the process fluid slightly improved mixing, reducing the outlet COV to 2.3% for the multiple feed stream case. The outlet COV fell to 1.4% for a half-scale arrangement with similar physics. Lastly, it was found that if the smaller unit’s speed were halved, the outlet COV was reduced to 1.1%.

scholarly journals Multitemporal Classification of River Floodplain Vegetation Using Time Series of UAV Images

2018 ◽  
Vol 10 (7) ◽  
pp. 1144 ◽  
Author(s):  
Wimala van Iersel ◽  
Menno Straatsma ◽  
Hans Middelkoop ◽  
Elisabeth Addink
Keyword(s):  
Land Cover ◽  
Large Scale ◽  
Accurate Solution ◽  
Vegetation Types ◽  
Time Step ◽  
Floodplain Vegetation ◽  
Herbaceous Vegetation ◽  
Single Time ◽  
Uav Images

The functions of river floodplains often conflict spatially, for example, water conveyance during peak discharge and diverse riparian ecology. Such functions are often associated with floodplain vegetation. Frequent monitoring of floodplain land cover is necessary to capture the dynamics of this vegetation. However, low classification accuracies are found with existing methods, especially for relatively similar vegetation types, such as grassland and herbaceous vegetation. Unmanned aerial vehicle (UAV) imagery has great potential to improve the classification of these vegetation types owing to its high spatial resolution and flexibility in image acquisition timing. This study aimed to evaluate the increase in classification accuracy obtained using multitemporal UAV images versus single time step data on floodplain land cover classification and to assess the effect of varying the number and timing of imagery acquisition moments. We obtained a dataset of multitemporal UAV imagery and field reference observations and applied object-based Random Forest classification (RF) to data of different time step combinations. High overall accuracies (OA) exceeding 90% were found for the RF of floodplain land cover, with six vegetation classes and four non-vegetation classes. Using two or more time steps compared with a single time step increased the OA from 96.9% to 99.3%. The user’s accuracies of the classes with large similarity, such as natural grassland and herbaceous vegetation, also exceeded 90%. The combination of imagery from June and September resulted in the highest OA (98%) for two time steps. Our method is a practical and highly accurate solution for monitoring areas of a few square kilometres. For large-scale monitoring of floodplains, the same method can be used, but with data from airborne platforms covering larger extents.

scholarly journals Evolution of the Distribution of Upper-Tropospheric Humidity over the Indian Ocean: Connection with Large-Scale Advection and Local Cloudiness

2017 ◽  
Vol 56 (7) ◽  
pp. 2035-2052 ◽  
Author(s):  
Thomas Garot ◽  
Hélène Brogniez ◽  
Renaud Fallourd ◽  
Nicolas Viltard
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Transport Model ◽  
Intraseasonal Variability ◽  
Back Trajectory ◽  
Time Step ◽  
Air Masses ◽  
Upper Troposphere ◽  
Upper Tropospheric Humidity ◽  
The Indian Ocean

AbstractThe spatial and temporal distribution of upper-tropospheric humidity (UTH) observed by the Sounder for Atmospheric Profiling of Humidity in the Intertropics by Radiometry (SAPHIR)/Megha-Tropiques radiometer is analyzed over two subregions of the Indian Ocean during October–December over 2011–14. The properties of the distribution of UTH were studied with regard to the phase of the Madden–Julian oscillation (active or suppressed) and large-scale advection versus local production of moisture. To address these topics, first, a Lagrangian back-trajectory transport model was used to assess the role of the large-scale transport of air masses in the intraseasonal variability of UTH. Second, the temporal evolution of the distribution of UTH is analyzed using the computation of the higher moments of its probability distribution function (PDF) defined for each time step over the domain. The results highlight significant differences in the PDF of UTH depending on the phase of the MJO. The modeled trajectories ending in the considered domain originate from an area that strongly varies depending on the phases of the MJO: during the active phases, the air masses are spatially constrained within the tropical Indian Ocean domain, whereas a distinct upper-tropospheric (200–150 hPa) westerly flow guides the intraseasonal variability of UTH during the suppressed phases. Statistical relationships between the cloud fractions and the UTH PDF moments of are found to be very similar regardless of the convective activity. However, the occurrence of thin cirrus clouds is associated with a drying of the upper troposphere (enhanced during suppressed phases), whereas the occurrence of thick cirrus anvil clouds appears to be significantly related to a moistening of the upper troposphere.

scholarly journals Assessing the large-scale impacts of environmental change using a coupled hydrology and soil erosion model

2018 ◽  
Vol 6 (3) ◽  
pp. 687-703 ◽  
Author(s):  
Joris P. C. Eekhout ◽  
Wilco Terink ◽  
Joris de Vente
Keyword(s):  
Soil Erosion ◽  
Environmental Change ◽  
Sediment Yield ◽  
Large Scale ◽  
Catchment Scale ◽  
Time Step ◽  
Vegetation Development ◽  
Erosion Model ◽  
Complete Representation ◽  
Large Catchment

Abstract. Assessing the impacts of environmental change on soil erosion and sediment yield at the large catchment scale remains one of the main challenges in soil erosion modelling studies. Here, we present a process-based soil erosion model, based on the integration of the Morgan–Morgan–Finney erosion model in a daily based hydrological model. The model overcomes many of the limitations of previous large-scale soil erosion models, as it includes a more complete representation of crucial processes like surface runoff generation, dynamic vegetation development, and sediment deposition, and runs at the catchment scale with a daily time step. This makes the model especially suited for the evaluation of the impacts of environmental change on soil erosion and sediment yield at regional scales and over decadal periods. The model was successfully applied in a large catchment in southeastern Spain. We demonstrate the model's capacity to perform impact assessments of environmental change scenarios, specifically simulating the scenario impacts of intra- and inter-annual variations in climate, land management, and vegetation development on soil erosion and sediment yield.

scholarly journals CFD Simulation and Experimental Study on Coupled Motion Response of Ship with Tank in Beam Waves

2022 ◽  
Vol 10 (1) ◽  
pp. 113
Author(s):  
Tao He ◽  
Dakui Feng ◽  
Liwei Liu ◽  
Xianzhou Wang ◽  
Hua Jiang
Keyword(s):  
Working Conditions ◽  
Large Scale ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Body Motion ◽  
Time Step ◽  
Coupled Motion ◽  
Motion Response ◽  
Time Step Size ◽  
Tank Sloshing

Tank sloshing is widely present in many engineering fields, especially in the field of marine. Due to the trend of large-scale liquid cargo ships, it is of great significance to study the coupled motion response of ships with tanks in beam waves. In this study, the CFD (Computational Fluid Dynamics) method and experiments are used to study the response of a ship with/without a tank in beam waves. All the computations are performed by an in-house CFD solver, which is used to solve RANS (Reynold Average Navier-Stokes) equations coupled with six degrees-of-freedom solid-body motion equations. The Level Set Method is used to solve the free surface. Verification work on the grid number and time step size has been conducted. The simulation results agree with the experimental results well, which shows that the numerical method is accurate enough. In this paper, several different working conditions are set up, and the effects of the liquid height in the tank, the size of the tank and the wavelength ratio of the incident wave on the ship’s motion are studied. The results show the effect of tank sloshing on the ship’s motion in different working conditions.

scholarly journals A Natural History Comparison of SOD1-Mutant Patients with Amyotrophic Lateral Sclerosis between Chinese and German Populations

2021 ◽  
Author(s):  
Lu Tang ◽  
Johannes Dorst ◽  
Lu Chen ◽  
Xiaolu Liu ◽  
Yan Ma ◽  
...  
Keyword(s):  
Amyotrophic Lateral Sclerosis ◽  
Large Scale ◽  
Age Of Onset ◽  
Diagnostic Delay ◽  
Chinese Patients ◽  
Common Mutation ◽  
Progression Rate ◽  
Causative Gene ◽  
Sod1 Mutant ◽  
Lateral Sclerosis

Abstract Background: The gene coding the Cu/Zn superoxide dismutase ( SOD1 ) was the first-identified causative gene of amyotrophic lateral sclerosis (ALS), and the second most common genetic cause for ALS worldwide. The promising therapeutic approaches targeting SOD1 mutations are on the road. The purpose of the present study was to compare the mutational and clinical features of Chinese and German patients with ALS carrying mutations in SOD1 gene, which will facilitate the strategy and design of SOD1 -targeted trials.Methods: Demographic and clinical characteristics were collected from two longitudinal cohorts in China and Germany. Chinese and German patients carrying SOD1 mutations were compared with regard to mutational distribution, age of onset, site of onset, body mass index (BMI) at diagnosis, diagnostic delay, progression rate, and survival.Results: A total of 66 Chinese and 84 German patients with 69 distinct SOD1 mutations were identified. The most common mutation in both populations was p.His47Arg. It was found in 8 Chinese and 2 German patients and consistently showed a slow progression of disease in both countries. Across all mutations, Chinese patients showed a younger age of onset (43.9 vs 49.9 years, p=0.002), a higher proportion of young-onset cases (62.5% vs 30.7%, p<0.001) and a lower BMI at diagnosis (22.8 vs 26.0, p<0.001) compared to German patients. Although riluzole intake was less frequent in Chinese patients (28.3% vs 81.3%, p<0.001), no difference in survival between populations was observed (p=0.90). Across both cohorts, female patients had a longer diagnostic delay (15.0 vs 11.0 months, p=0.01) and a prolonged survival (248.0 vs 60.0 months, p=0.005) compared to male patients.Conclusions: Our data demonstrate the distinct mutational and clinical spectrums of SOD1 -mutant patients in Asian and European populations. Clinical phenotypes seem to be primarily influenced by mutation-specific, albeit not excluding ethnicity-specific factors. Further large-scale transethnical studies are needed to clarify determinants and modifiers of SOD1 phenotypes.

scholarly journals The Treatment of Shortwave Radiation and Open Water in Large-Scale Models of Sea-Ice Decay

1990 ◽  
Vol 14 ◽  
pp. 242-246
Author(s):  
Donald K. Perovich ◽  
Gary A. Maykut
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Open Water ◽  
Shortwave Radiation ◽  
Areal Extent ◽  
Time Step ◽  
Climate Simulations ◽  
Scale Models ◽  
Ice Concentration ◽  
Ice Pack

Sea ice covering the polar oceans is only a thin veneer whose areal extent can undergo large and rapid variations in response to relatively small changes in thermal forcing. Positive feedback between variations in ice extent and global albedo has the potential to amplify small changes in climate. Particularly difficult to model is the summer decay and retreat of the ice pack which is strongly influenced by shortwave radiation entering the upper ocean through leads (Iw). Most models assume that all of this energy is expended in lateral melting at floe edges. In reality, only a portion of Iw contributes directly to lateral melting, with the remainder going to bottom ablation and warming of the water. This partitioning of Iw affects not only the magnitude, but also the character of the predicted ice decay, reducing the change in ice concentration and enhancing the thinning of the ice and the storage of heat in the water. In this paper we present an analytical model which includes many of these processes and is stable regardless of time step, making it suitable for use in climate simulations.

scholarly journals Comparison of generalized non-data-driven lake and reservoir routing models for global-scale hydrologic forecasting of reservoir outflow at diurnal time steps

2020 ◽  
Vol 24 (5) ◽  
pp. 2711-2729 ◽  
Author(s):  
Joseph L. Gutenson ◽  
Ahmad A. Tavakoly ◽  
Mark D. Wahl ◽  
Michael L. Follum
Keyword(s):  
Large Scale ◽  
Spatial Scales ◽  
Model Performance ◽  
Global Scale ◽  
Army Corps ◽  
Time Step ◽  
Large Spatial Scale ◽  
Reservoir Routing ◽  
Routing Methods ◽  
Improved Model

Abstract. Large-scale hydrologic forecasts should account for attenuation through lakes and reservoirs when flow regulation is present. Globally generalized methods for approximating outflow are required but must contend with operational complexity and a dearth of information on dam characteristics at global spatial scales. There is currently no consensus on the best approach for approximating reservoir release rates in large spatial scale hydrologic forecasting, particularly at diurnal time steps. This research compares two parsimonious reservoir routing methods at daily steps: Döll et al. (2003) and Hanasaki et al. (2006). These reservoir routing methods have been previously implemented in large-scale hydrologic modeling applications and have been typically evaluated seasonally. These routing methods are compared across 60 reservoirs operated by the U.S. Army Corps of Engineers. The authors vary empirical coefficients for both reservoir routing methods as part of a sensitivity analysis. The method proposed by Döll et al. (2003) outperformed that presented by Hanasaki et al. (2006) at a daily time step and improved model skill over most run-of-the-river conditions. The temporal resolution of the model influences model performances. The optimal model coefficients varied across the reservoirs in this study and model performance fluctuates between wet years and dry years, and for different configurations such as dams in series. Overall, the method proposed by Döll et al. (2003) could enhance large-scale hydrologic forecasting, but can be subject to instability under certain conditions.

Comparison of DDES and URANS for Unsteady Tip Leakage Flow in an Axial Compressor Rotor

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Yangwei Liu ◽  
Luyang Zhong ◽  
Lipeng Lu
Keyword(s):  
Reynolds Stress ◽  
Large Scale ◽  
Turbulence Modeling ◽  
Axial Compressor ◽  
Small Time ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
Time Step ◽  
Tip Leakage ◽  
Eddy Simulation

Tip leakage vortex (TLV) has a large impact on compressor performance and should be accurately predicted by computational fluid dynamics (CFD) methods. New approaches of turbulence modeling, such as delayed detached eddy simulation (DDES), have been proposed, the computational resources of which can be reduced much more than for large eddy simulation (LES). In this paper, the numerical simulations of the rotor in a low-speed large-scale axial compressor based on DDES and unsteady Reynolds-averaged Navier–Stokes (URANS) are performed, thus improving our understanding of the TLV dynamic mechanisms and discrepancy of these two methods. We compared the influence of different time steps in the URANS simulation. The widely used large time-step makes the unsteadiness extremely weak. The small time-step shows a better result close to DDES. The time-step scale is related to the URANS unsteadiness and should be carefully selected. In the time-averaged flow, the TLV in DDES dissipates faster, which has a more similar structure to the experiment. Then, the time-averaged and instantaneous results are compared to divide the TLV into three parts. URANS cannot give the loss of stability and evolution details of TLV. The fluctuation velocity spectra show that the amplitude of high frequencies becomes obvious downstream from the TLV, where it becomes unstable. Last, the anisotropy of the Reynolds stress of these two methods is analyzed through the Lumley triangle to see the distinction between the methods and obtain the Reynolds stress. The results indicate that the TLV latter part in DDES is anisotropic, while in URANS it is isotropic.

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