scholarly journals A Validation/Uncertainty Quantification Analysis for a 1.5 MW Oxy-Coal Fired Furnace: Sensitivity Analysis

2018 ◽  
Vol 3 (1) ◽  
Author(s):  
Oscar H. Díaz-Ibarra ◽  
Jennifer Spinti ◽  
Andrew Fry ◽  
Benjamin Isaac ◽  
Jeremy N. Thornock ◽  
...  
Keyword(s):  
Heat Flux ◽  
Sensitivity Analysis ◽  
Uncertainty Quantification ◽  
Complex Geometry ◽  
Heat Removal ◽  
Operating Conditions ◽  
Model Parameters ◽  
Reacting Flow ◽  
Simulation Data ◽  
The Impact

A validation/uncertainty quantification (VUQ) study was performed on the 1.5 MWth L1500 furnace, an oxy-coal fired facility located at the Industrial Combustion and Gasification Research Facility at the University of Utah. A six-step VUQ framework is used for studying the impact of model parameter uncertainty on heat flux, the quantity of interest (QOI) for the project. This paper focuses on the first two steps of the framework. The first step is the selection of model outputs in the experimental and simulation data that are related to the heat flux: incident heat flux, heat removal by cooling tubes, and wall temperatures. We describe the experimental facility, the operating conditions, and the data collection process. To obtain the simulation data, we utilized two tools, star-ccm+ and Arches. The star-ccm+ simulations captured flow through the complex geometry of the swirl burner while the Arches simulations captured multiphase reacting flow in the L1500. We employed a filtered handoff plane to couple the two simulations. In step two, we developed an input/uncertainty (I/U) map and assigned a priority to 11 model parameters based on prior knowledge. We included parameters from both a char oxidation model and an ash deposition model in this study. We reduced the active parameter space from 11 to 5 based on priority. To further reduce the number of parameters that must be considered in the remaining steps of the framework, we performed a sensitivity analysis on the five parameters and used the results to reduce the parameter set to two.

scholarly journals Design and execution of a Verification, Validation, and Uncertainty Quantification plan for a numerical model of left ventricular flow after LVAD implantation

2021 ◽  
Author(s):  
Alfonso Santiago ◽  
Constantine Butakoff ◽  
Beatriz Eguzkitza ◽  
Richard A Gray ◽  
Karen May-Newman ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Numerical Model ◽  
Uncertainty Quantification ◽  
Aortic Root ◽  
Solution Procedure ◽  
Left Ventricular ◽  
Operating Conditions ◽  
Numerical Code ◽  
Performance Curve ◽  
The Impact

Background: left ventricular assist devices (LVADs) are implantable pumps that act as a life support therapy for patients with severe heart failure. Despite improving the survival rate, LVAD therapy can carry major complications. Particularly, the flow distortion introduced by the LVAD in the left ventricle (LV) may induce thrombus formation. While previous works have used numerical models to study the impact of multiple variables in the intra-LV stagnation regions, a comprehensive validation analysis has never been executed. The main goal of this work is to present a model of the LV-LVAD system and to design and follow a verification, validation and uncertainty quantification (VVUQ) plan based on the ASME V&V40 and V&V20 standards to ensure credible predictions. Methods: The experiment used to validate the simulation is the SDSU cardiac simulator, a bench mock-up of the cardiovascular system that allows mimicking multiple operation conditions for the heart-LVAD system. The numerical model is based on Alya, the BSC's in-house platform for numerical modelling. Alya solves the Navier-Stokes equation with an Arbitrarian Lagrangian-Eulerian (ALE) formulation in a deformable ventricle and includes pressure-driven valves, a 0D Windkessel model for the arterial output and a LVAD boundary condition modeled through a dynamic pressure-flow performance curve. The designed VVUQ plan involves: (a) a risk analysis and the associated credibility goals; (b) a verification stage to ensure correctness in the numerical solution procedure; (c) a sensitivity analysis to quantify the impact of the inputs on the four quantities of interest (QoIs) (average aortic root flow, maximum aortic root flow, average LVAD flow, and maximum LVAD flow); (d) an uncertainty quantification using six validation experiments that include extreme operating conditions. Results: Numerical code verification tests ensured correctness of the solution procedure and numerical calculation verification showed small numerical errors. The total Sobol indices obtained during the sensitivity analysis demonstrated that the ejection fraction, the heart rate, and the pump performance curve coefficients are the most impactful inputs for the analysed QoIs. The Minkowski norm is used as validation metric for the uncertainty quantification. It shows that the midpoint cases have more accurate results when compared to the extreme cases. The total computational cost of the simulations was above 100 [core-years] executed in around three weeks time span in Marenostrum IV supercomputer. Conclusions: This work details a novel numerical model for the LV-LVAD system, that is supported by the design and execution of a VVUQ plan created following recognised international standards. We present a methodology demonstrating that stringent VVUQ according to ASME standards is feasible but computationally expensive.

scholarly journals Modeling Bacterial Regrowth and Trihalomethane Formation in Water Distribution Systems

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 463
Author(s):  
Gopinathan R. Abhijith ◽  
Leonid Kadinski ◽  
Avi Ostfeld
Keyword(s):  
Distribution Systems ◽  
Water Distribution ◽  
Mechanistic Model ◽  
Water Distribution Systems ◽  
Sensitivity Study ◽  
Operating Conditions ◽  
Growth Rate Constant ◽  
Model Parameters ◽  
Bacterial Regrowth ◽  
The Impact

The formation of bacterial regrowth and disinfection by-products is ubiquitous in chlorinated water distribution systems (WDSs) operated with organic loads. A generic, easy-to-use mechanistic model describing the fundamental processes governing the interrelationship between chlorine, total organic carbon (TOC), and bacteria to analyze the spatiotemporal water quality variations in WDSs was developed using EPANET-MSX. The representation of multispecies reactions was simplified to minimize the interdependent model parameters. The physicochemical/biological processes that cannot be experimentally determined were neglected. The effects of source water characteristics and water residence time on controlling bacterial regrowth and Trihalomethane (THM) formation in two well-tested systems under chlorinated and non-chlorinated conditions were analyzed by applying the model. The results established that a 100% increase in the free chlorine concentration and a 50% reduction in the TOC at the source effectuated a 5.87 log scale decrement in the bacteriological activity at the expense of a 60% increase in THM formation. The sensitivity study showed the impact of the operating conditions and the network characteristics in determining parameter sensitivities to model outputs. The maximum specific growth rate constant for bulk phase bacteria was found to be the most sensitive parameter to the predicted bacterial regrowth.

Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

2020 ◽  
Author(s):  
Γεώργιος Πατεράκης
Keyword(s):  
Experimental Investigation ◽  
Turbulent Flow ◽  
Bluff Body ◽  
Operating Conditions ◽  
Reacting Flow ◽  
Wide Range ◽  
Flow Features ◽  
Air Mixing ◽  
The Impact ◽  
Stratified Flames

The current work describes an experimental investigation of isothermal and turbulent reacting flow field characteristics downstream of axisymmetric bluff body stabilizers under a variety of inlet mixture conditions. Fully premixed and stratified flames established downstream of this double cavity premixer/burner configuration were measured and assessed under lean and ultra-lean operating conditions. The aim of this thesis was to further comprehend the impact of stratifying the inlet fuelair mixture on the reacting wake characteristics for a range of practical stabilizers under a variety of inlet fuel-air settings. In the first part of this thesis, the isothermal mean and turbulent flow features downstream of a variety of axisymmetric baffles was initially examined. The effect of different shapes, (cone or disk), blockage ratios, (0.23 and 0.48), and rim thicknesses of these baffles was assessed. The variations of the recirculation zones, back flow velocity magnitude, annular jet ejection angles, wake development, entrainment efficiency, as well as several turbulent flow features were obtained, evaluated and appraised. Next, a comparative examination of the counterpart turbulent cold fuel-air mixing performance and characteristics of stratified against fully-premixed operation was performed for a wide range of baffle geometries and inlet mixture conditions. Scalar mixing and entrainment properties were investigated at the exit plane, at the bluff body annular shear layer, at the reattachment region and along the developing wake were investigated. These isothermal studies provided the necessary background information for clarifying the combustion properties and interpreting the trends in the counterpart turbulent reacting fields. Subsequently, for selected bluff bodies, flame structures and behavior for operation with a variety of reacting conditions were demonstrated. The effect of inlet fuel-air mixture settings, fuel type and bluff body geometry on wake development, flame shape, anchoring and structure, temperatures and combustion efficiencies, over lean and close to blow-off conditions, was presented and analyzed. For the obtained measurements infrared radiation, particle image velocimetry, laser doppler velocimetry, chemiluminescence imaging set-ups, together with Fouriertransform infrared spectroscopy, thermocouples and global emission analyzer instrumentation was employed. This helped to delineate a number of factors that affectcold flow fuel-air mixing, flame anchoring topologies, wake structure development and overall burner performance. The presented data will also significantly assist the validation of computational methodologies for combusting flows and the development of turbulence-chemistry interaction models.

scholarly journals Parameter Dependencies of a Biomechanical Cervical Spine FSU - The Process of Finding Optimal Model Parameters by Sensitivity Analysis

2021 ◽  
Author(s):  
Sabine Bauer ◽  
Ivanna Kramer
Keyword(s):  
Sensitivity Analysis ◽  
Intervertebral Discs ◽  
Model Parameters ◽  
Biomechanical Behavior ◽  
Functional Spinal Unit ◽  
Spine Model ◽  
Biomechanical Parameters ◽  
Multi Body ◽  
The Impact

The knowledge about the impact of structure-specific parameters on the biomechanical behavior of a computer model has an essential meaning for the realistic modeling and system improving. Especially the biomechanical parameters of the intervertebral discs, the ligamentous structures and the facet joints are seen in the literature as significant components of a spine model, which define the quality of the model. Therefore, it is important to understand how the variations of input parameters for these components affect the entire model and its individual structures. Sensitivity analysis can be used to gain the required knowledge about the correlation of the input and output variables in a complex spinal model. The present study analyses the influence of the biomechanical parameters of the intervertebral disc using different sensitivity analysis methods to optimize the spine model parameters. The analysis is performed with a multi-body simulation model of the cervical functional spinal unit C6-C7.

Nonintrusive Global Sensitivity Analysis for Linear Systems With Process Noise

2019 ◽  
Vol 14 (2) ◽  
Author(s):  
Souransu Nandi ◽  
Tarunraj Singh
Keyword(s):  
Sensitivity Analysis ◽  
Linear Systems ◽  
Global Sensitivity Analysis ◽  
Benchmark Problems ◽  
Model Parameters ◽  
Parameter Uncertainties ◽  
Sobol Indices ◽  
Global Sensitivity ◽  
Time Invariant ◽  
The Impact

The focus of this paper is on the global sensitivity analysis (GSA) of linear systems with time-invariant model parameter uncertainties and driven by stochastic inputs. The Sobol' indices of the evolving mean and variance estimates of states are used to assess the impact of the time-invariant uncertain model parameters and the statistics of the stochastic input on the uncertainty of the output. Numerical results on two benchmark problems help illustrate that it is conceivable that parameters, which are not so significant in contributing to the uncertainty of the mean, can be extremely significant in contributing to the uncertainty of the variances. The paper uses a polynomial chaos (PC) approach to synthesize a surrogate probabilistic model of the stochastic system after using Lagrange interpolation polynomials (LIPs) as PC bases. The Sobol' indices are then directly evaluated from the PC coefficients. Although this concept is not new, a novel interpretation of stochastic collocation-based PC and intrusive PC is presented where they are shown to represent identical probabilistic models when the system under consideration is linear. This result now permits treating linear models as black boxes to develop intrusive PC surrogates.

Nanoparticle aggregation kinematics on the quadratic convective magnetohydrodynamic flow of nanomaterial past an inclined flat plate with sensitivity analysis

2021 ◽  
pp. 095440892110562
Author(s):  
AS Sabu ◽  
Joby Mackolil ◽  
B Mahanthesh ◽  
Alphonsa Mathew
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Sensitivity Analysis ◽  
Heat Transfer Coefficient ◽  
Heat Source ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Inclined Plate ◽  
The Impact ◽  
The Heat Transfer Coefficient

The study focuses on the aggregation kinematics in the quadratic convective magneto-hydrodynamics of ethylene glycol-titania ([Formula: see text]) nanofluid flowing through an inclined flat plate. The modified Krieger-Dougherty and Maxwell-Bruggeman models are used for the effective viscosity and thermal conductivity to account for the aggregation aspect. The effects of an exponential space-dependent heat source and thermal radiation are incorporated. The impact of pertinent parameters on the heat transfer coefficient is explored by using the Response Surface Methodology and Sensitivity Analysis. The effects of several parameters on the skin friction and heat transfer coefficient at the plate are displayed via surface graphs. The velocity and thermal profiles are compared for two physical scenarios: flow over a vertical plate and flow over an inclined plate. The nonlinear problem is solved using the Runge–Kutta-based shooting technique. It was found that the velocity profile significantly decreased as the inclination of the plate increased on the other hand the temperature profile improved. The heat transfer coefficient decreased due to the increase in the Hartmann number. The exponential heat source has a decreasing effect on the heat flux and the angle of inclination is more sensitive to the heat transfer coefficient than other variables. Further, when radiation is incremented, the sensitivity of the heat flux toward the inclination angle augments at the rate 0.5094% and the sensitivity toward the exponential heat source augments at the rate 0.0925%. In addition, 41.1388% decrement in wall shear stress is observed when the plate inclination is incremented from [Formula: see text] to [Formula: see text].

scholarly journals A physically-based parsimonious hydrological model for flash floods in Mediterranean catchments

2011 ◽  
Vol 11 (9) ◽  
pp. 2567-2582 ◽  
Author(s):  
H. Roux ◽  
D. Labat ◽  
P.-A. Garambois ◽  
M.-M. Maubourguet ◽  
J. Chorda ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Soil Properties ◽  
Overland Flow ◽  
Hydrological Model ◽  
Extreme Event ◽  
Model Parameters ◽  
Peak Time ◽  
Efficiency Coefficient ◽  
Soil Saturation ◽  
The Impact

Abstract. A spatially distributed hydrological model, dedicated to flood simulation, is developed on the basis of physical process representation (infiltration, overland flow, channel routing). Estimation of model parameters requires data concerning topography, soil properties, vegetation and land use. Four parameters are calibrated for the entire catchment using one flood event. Model sensitivity to individual parameters is assessed using Monte-Carlo simulations. Results of this sensitivity analysis with a criterion based on the Nash efficiency coefficient and the error of peak time and runoff are used to calibrate the model. This procedure is tested on the Gardon d'Anduze catchment, located in the Mediterranean zone of southern France. A first validation is conducted using three flood events with different hydrometeorological characteristics. This sensitivity analysis along with validation tests illustrates the predictive capability of the model and points out the possible improvements on the model's structure and parameterization for flash flood forecasting, especially in ungauged basins. Concerning the model structure, results show that water transfer through the subsurface zone also contributes to the hydrograph response to an extreme event, especially during the recession period. Maps of soil saturation emphasize the impact of rainfall and soil properties variability on these dynamics. Adding a subsurface flow component in the simulation also greatly impacts the spatial distribution of soil saturation and shows the importance of the drainage network. Measures of such distributed variables would help discriminating between different possible model structures.

Sensitivity analysis of an integrated numerical flow model output to key parameters used in common qualitative vulnerability assessment methods

2020 ◽  
Author(s):  
Joanna Doummar ◽  
Assaad H. Kassem
Keyword(s):  
Sensitivity Analysis ◽  
Vulnerability Assessment ◽  
Groundwater Vulnerability ◽  
Assessment Methods ◽  
Qualitative Assessment ◽  
Model Parameters ◽  
Karst Aquifers ◽  
Model Output ◽  
Local Sensitivity ◽  
The Impact

<p>Qualitative vulnerability assessment methods applied in karst aquifers rely on key factors in the hydrological compartments usually assigned different weights according to their estimated impact on groundwater vulnerability. Based on an integrated numerical groundwater model on a snow-governed karst catchment area (Assal Spring- Lebanon), the aim of this work is to quantify the importance of the most influential parameters on recharge and spring discharge and outline potential parameters that are not accounted for in standard methods, when in fact they do play a role in the intrinsic vulnerability of a system. The assessment of the model sensitivity and the ranking of parameters are conducted using an automatic calibration tool for local sensitivity analysis in addition to a variance-based local sensitivity assessment of model output time series (recharge and discharge)  for two consecutive years (2016-2017) to various model parameters. The impact of each parameter was normalized to estimate standardized weights for each of the process based key-controlling parameters. Parameters to which model was sensitive were factors related to soil, 2) fast infiltration (bypass function) typical of karst aquifers, 3) climatic parameters (melting temperature and degree day coefficient) and 4) aquifer hydraulic properties that play a major role in groundwater vulnerability inducing a temporal effect and varied recession. Other less important parameters play different roles according to different assigned weights proportional to their ranking. Additionally, the effect of slope/geomorphology (e.g., dolines) was further investigated.  In general, this study shows that the weighting coefficients assigned to key vulnerability factors in the qualitative assessment methods can be reevaluated based on this process-based approach.</p><p> </p><p> </p><p> </p>

Experimental Characterization of Single and Multiple Droplet Impingement on Surfaces Subject to Constant Heat Flux Conditions

2010 ◽  
Author(s):  
Guillermo Soriano ◽  
Jorge L. Alvarado ◽  
Yen Po Lin
Keyword(s):  
Heat Flux ◽  
Heat Removal ◽  
Spray Cooling ◽  
Constant Heat Flux ◽  
Droplet Impact ◽  
Fluid Temperature ◽  
Impact Zone ◽  
Constant Heat ◽  
Droplet Impingement ◽  
The Impact

Spray cooling is one of the most promising technologies in applications which require large heat removal capacity in very small areas. Previous experimental studies have suggested that one of the main mechanisms of heat removal in spray cooling is forced convection with strong mixing due to droplet impingement. These mechanisms have not been completely understood mainly due to the large number of physical variables, and the inability to modulate and control variables such as droplet frequency and size. Our approach consists of minimizing the number of experimental variables by controlling variables such as droplet direction, velocity and diameter. An experimental study of single and multiple droplet impingements using HFE 7100 as the cooling fluid under constant heat flux conditions is presented. A monosized droplet train is produced using a piezoelectric droplet generator with the ability to adjust droplet frequency, diameter and velocity. In this study, heaters consisting of a layer of Indium Tin Oxide (ITO) as heating element, and silicon substrates are used. Film morphology was characterized using a Laser Induced Fluorescence (LIF) technique with a focus on the droplet impact zone by measuring variables such as film thickness and diameter of the impact zone. Infrared thermography was used to measure surface temperature at the liquid-solid interface. The IR thermography technique was also used to characterize temperature gradients at the droplet impact zone. The results and effects of droplet frequency, fluid flow rate, and fluid temperature on heat flux are also presented.

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