scholarly journals Novel CFD modeling approaches to assessing urine flow in prostatic urethra after transurethral surgery

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bin Zhang ◽  
Shuang Liu ◽  
Yinxia Liu ◽  
Bo Wu ◽  
Xuhui Zhang ◽  
...  
Keyword(s):  
Flow Behavior ◽  
Urine Flow ◽  
Prostatic Urethra ◽  
Dynamics Simulation ◽  
Cfd Modeling ◽  
Transverse Diameter ◽  
Cfd Models ◽  
Post Surgery ◽  
Through Flow ◽  
Urethral Orifice

AbstractAssessment of the pressure and velocity of urine flow for different diameter ratios of prostatic urethra (RPU) after transurethral surgery using computational fluid dynamics (CFD). A standardized and idealized two-dimensional CFD model after transurethral surgery (CATS-1st) was developed for post-surgery mid-voiding. Using CATS-1st, 210 examples were amplified according to an array of size [3][5][14], which contained three groups of longitudinal diameters of prostatic urethra (LD-PU). Each of these groups contained five subgroups of transverse diameters of the bladder neck (TD-BN), each with 14 examples of transverse diameters of PU (TD-PU). The pressure and velocity of urine flow were monitored through flow dynamics simulation, and the relationship among RPU-1 (TD-PU/TD-BN), RPU-2 (RPU-1/LD-PU), the transverse diameter of the vortex, and the midpoint velocity of the external urethral orifice (MV-EUO) was determined. A total of 210 CATS examples, including CATS-1st examples, were analyzed. High (bladder and PU) and medium/low (the rest of the urethra) pressure zones, and low (bladder), medium (PU), and high (the rest of the urethra) velocity zones were determined. The rapid changes in the velocity were concentrated in and around the PU. Laminar flow was present in all the examples. The vortices appeared and then gradually shrank with reducing RPU on both the sides of PU in 182 examples. In the vortex examples, minimum RPU-1 and RPU-2 reached close to the values of 0.79 and 0.02, respectively. MV-EUO increased gradually with decreasing RPU. In comparison to the vortex examples, the non-vortex examples exhibited a significantly higher (p < 0.01) MV-EUO. The developed CFD models (CATS) presented an effective simulation of urine flow behavior within the PU after transurethral surgery for benign prostatic hyperplasia (BPH). These models could prove to be useful for morphological repair in PU after transurethral surgery.

Benchmark for Numerical Models of Stented Coronary Bifurcation Flow

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
P. García Carrascal ◽  
J. García García ◽  
J. Sierra Pallares ◽  
F. Castro Ruiz ◽  
F. J. Manuel Martín
Keyword(s):  
Blood Flow ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Velocity Fields ◽  
Cfd Modeling ◽  
Coronary Bifurcation ◽  
Stent Restenosis ◽  
Cfd Models ◽  
In Stent Restenosis

In-stent restenosis ails many patients who have undergone stenting. When the stented artery is a bifurcation, the intervention is particularly critical because of the complex stent geometry involved in these structures. Computational fluid dynamics (CFD) has been shown to be an effective approach when modeling blood flow behavior and understanding the mechanisms that underlie in-stent restenosis. However, these CFD models require validation through experimental data in order to be reliable. It is with this purpose in mind that we performed particle image velocimetry (PIV) measurements of velocity fields within flows through a simplified coronary bifurcation. Although the flow in this simplified bifurcation differs from the actual blood flow, it emulates the main fluid dynamic mechanisms found in hemodynamic flow. Experimental measurements were performed for several stenting techniques in both steady and unsteady flow conditions. The test conditions were strictly controlled, and uncertainty was accurately predicted. The results obtained in this research represent readily accessible, easy to emulate, detailed velocity fields and geometry, and they have been successfully used to validate our numerical model. These data can be used as a benchmark for further development of numerical CFD modeling in terms of comparison of the main flow pattern characteristics.

scholarly journals Performance Prediction of a Hard-Chine Planing Hull by Employing Different CFD Models

2021 ◽  
Vol 9 (5) ◽  
pp. 481
Author(s):  
Azim Hosseini ◽  
Sasan Tavakoli ◽  
Abbas Dashtimanesh ◽  
Prasanta K. Sahoo ◽  
Mihkel Kõrgesaar
Keyword(s):  
Water Flow ◽  
Performance Prediction ◽  
Cfd Modeling ◽  
Computational Time ◽  
Resistance Force ◽  
Stagnation Line ◽  
Mesh Structure ◽  
Cfd Models ◽  
High Speeds ◽  
Des Model

This paper presents CFD (Computational Fluid Dynamics) simulations of the performance of a planing hull in a calm-water condition, aiming to evaluate similarities and differences between results of different CFD models. The key differences between these models are the ways they use to compute the turbulent flow and simulate the motion of the vessel. The planing motion of a vessel on water leads to a strong turbulent fluid flow motion, and the movement of the vessel from its initial position can be relatively significant, which makes the simulation of the problem challenging. Two different frameworks including k-ε and DES (Detached Eddy Simulation) methods are employed to model the turbulence behavior of the fluid motion of the air–water flow around the boat. Vertical motions of the rigid solid body in the fluid domain, which eventually converge to steady linear and angular displacements, are numerically modeled by using two approaches, including morphing and overset techniques. All simulations are performed with a similar mesh structure which allows us to evaluate the differences between results of the applied mesh motions in terms of computation of turbulent air–water flow around the vessel. Through quantitative comparisons, the morphing technique has been seen to result in smaller errors in the prediction of the running trim angle at high speeds. Numerical observations suggest that a DES model can modify the accuracy of the morphing mesh simulations in the prediction of the trim angle, especially at high-speeds. The DES model has been seen to increase the accuracy of the model in the computation of the resistance of the vessel in a high-speed operation, as well. This better level of accuracy in the prediction of resistance is a result of the calculation of the turbulent eddies emerging in the water flow in the downstream zone, which are not captured when a k-ε framework is employed. The morphing approach itself can also increase the accuracy of the resistance prediction. The overset method, however, overpredicts the resistance force. This overprediction is caused by the larger vorticity, computed in the direction of the waves, generated under the bow of the vessel. Furthermore, the overset technique is observed to result in larger hydrodynamic pressure on the stagnation line, which is linked to the greater trim angle, predicted by this approach. The DES model is seen to result in extra-damping of the second and third crests of transom waves as it calculates the stronger eddies in the wake of the boat. Overall, a combination of the morphing and DES models is recommended to be used for CFD modeling of a planing hull at high-speeds. This combined CFD model might be relatively slower in terms of computational time, but it provides a greater level of accuracy in the performance prediction, and can predict the energy damping, developed in the surrounding water. Finally, the results of the present paper demonstrate that a better level of accuracy in the performance prediction of the vessel might also be achieved when an overset mesh motion is used. This can be attained in future by modifying the mesh structure in such a way that vorticity is not overpredicted and the generated eddies, emerging when a DES model is employed, are captured properly.

scholarly journals Research on the viscosity of stabilized emulsions in different pipe diameters using pressure drop and phase inversion

2021 ◽  
Author(s):  
Jose Plasencia ◽  
Nathanael Inkson ◽  
Ole Jørgen Nydal
Keyword(s):  
Pressure Drop ◽  
Salt Water ◽  
Flow Behavior ◽  
Turbulent Viscosity ◽  
Relative Viscosity ◽  
Cfd Modeling ◽  
Water Fraction ◽  
Water Fractions ◽  
Oil Emulsions ◽  
Mixture Velocity

AbstractThis paper reports experimental research on the flow behavior of oil-water surfactant stabilized emulsions in different pipe diameters along with theoretical and computational fluid dynamics (CFD) modeling of the relative viscosity and inversion properties. The pipe flow of emulsions was studied in turbulent and laminar conditions in four pipe diameters (16, 32, 60, and 90 mm) at different mixture velocities and increasing water fractions. Salt water (3.5% NaCl w/v, pH = 7.3) and a mineral oil premixed with a lipophilic surfactant (Exxsol D80 + 0.25% v/v of Span 80) were used as the test fluids. The formation of water-in-oil emulsions was observed from low water fractions up to the inversion point. After inversion, unstable water-in-oil in water multiple emulsions were observed under different flow regimes. These regimes depend on the mixture velocity and the local water fraction of the water-in-oil emulsion. The eddy turbulent viscosity calculated using an elliptic-blending k-ε model and the relative viscosity in combination act to explain the enhanced pressure drop observed in the experiments. The inversion process occurred at a constant water fraction (90%) and was triggered by an increase of mixture velocity. No drag reduction effect was detected for the water-in-oil emulsions obtained before inversion.

A Joint-Industry Effort to Develop and Verify CFD Modeling Practice for Vortex-Induced Motion of a Deep-Draft Semi-Submersible

2021 ◽  
Author(s):  
Hyunchul Jang ◽  
Dae-Hyun Kim ◽  
Madhusuden Agrawal ◽  
Sebastien Loubeyre ◽  
Dongwhan Lee ◽  
...  
Keyword(s):  
Test Data ◽  
Model Test ◽  
Working Group ◽  
Cfd Modeling ◽  
Physical Model Test ◽  
Mooring Lines ◽  
Cfd Models ◽  
Induced Motion ◽  
Modeling Practice ◽  
Decay Tests

Abstract Platform Vortex Induced Motion (VIM) is an important cause of fatigue damage on risers and mooring lines connected to deep-draft semi-submersible floating platforms. The VIM design criteria have been typically obtained from towing tank model testing. Recently, computational fluid dynamics (CFD) analysis has been used to assess the VIM response and to augment the understanding of physical model test results. A joint industry effort has been conducted for developing and verifying a CFD modeling practice for the semi-submersible VIM through a working group of the Reproducible Offshore CFD JIP. The objectives of the working group are to write a CFD modeling practice document based on existing practices validated for model test data, and to verify the written practice by blind calculations with five CFD practitioners acting as verifiers. This paper presents the working group’s verification process, consisting of two stages. In the initial verification stage, the verifiers independently performed free-decay tests for 3-DOF motions (surge, sway, yaw) to check if the mechanical system in the CFD model is the same as in the benchmark test. Additionally, VIM simulations were conducted at two current headings with a reduced velocity within the lock-in range, where large sway motion responses are expected,. In the final verification stage, the verifiers performed a complete set of test cases with small revisions of their CFD models based on the results from the initial verification. The VIM responses from these blind calculations are presented, showing close agreement with the model test data.

Optimization Method of the Multistage Axial Compressors Using CFD Simulation

2021 ◽  
pp. 2141006
Author(s):  
Grigorii Popov ◽  
Igor Egorov ◽  
Evgenii Goriachkin ◽  
Oleg Baturin ◽  
Daria Kolmakova ◽  
...  
Keyword(s):  
Cfd Simulation ◽  
Optimization Problems ◽  
Search Algorithm ◽  
Pressure Ratio ◽  
Optimization Method ◽  
Cfd Modeling ◽  
Turbine Engines ◽  
Stability Margins ◽  
Axial Compressors ◽  
Cfd Models

The current level of numerical methods of gas dynamics makes it possible to optimize compressors using 3D CFD models. However, the methods and means are not sufficiently developed for their wide application. This paper describes a new method for the optimization of multistage axial compressors based on 3D CFD modeling and summarizes the experience of its application. The developed method is a complex system of interconnected components (an effective mathematical model, a parameterizer, and an optimum search algorithm). The use of the method makes it possible to improve or provide the necessary values of the main gas-dynamic parameters of the compressor by changing the shape of the blades and their relative position. The method was tested in solving optimization problems for multistage axial compressors of gas turbine engines (the number of stages from 3 to 15). As a result, an increase in efficiency, pressure ratio, and stability margins was achieved. The presented work is a summary of a long-years investigation of the research team and aims at creating a complete picture of the obtained results for the reader. A brief description of the results of industrial compresses optimization contained in the paper is given as an illustration of the effectiveness of the developed methods.

Simulation of Spouted Bed Using a Eulerian Multiphase Model

2005 ◽  
Vol 498-499 ◽  
pp. 270-277 ◽  
Author(s):  
Claudio Roberto Duarte ◽  
Valéria V. Murata ◽  
Marcos A.S. Barrozo
Keyword(s):  
Control Volume ◽  
Flow Behavior ◽  
Cfd Modeling ◽  
Gas Flows ◽  
Present Calculation ◽  
Multiphase Model ◽  
Spouted Bed ◽  
Particle Coating ◽  
Spouted Beds ◽  
Good Agreement

Spouted bed systems have emerged as very efficient fluid-particle contactors and find many applications in the chemical and biochemical industry. Some important applications of spouted beds include coal combustion, biochemical reactions, drying of solids, drying of solutions and suspensions, granulation, blending, grinding, and particle coating. An extensive overview can be found in Mathur and Epstein[1]. The pattern of solid and gas flows in a spouted bed was numerically simulated using a CFD modeling technique. The Eulerian-Eulerian multifluid modeling approach was applied to predict gas-solid flow behavior. A commercially available, control-volume-based code FLUENT 6.1 was chosen to carry out the computer simulations. In order to reduce computational times and required system resources, the 2D axisymmetric segregated solver was chosen. The typical flow pattern of the spouted bed was obtained in the present calculation. The simulated velocity and voidage profiles presented a good agreement qualitative and quantitative with the experimental results obtained by He et al. [4].

Renal function in the chronically cannulated fetal llama: comparison with studies in the ovine fetus

1995 ◽  
Vol 7 (5) ◽  
pp. 1311 ◽  
Author(s):  
EM Wintour ◽  
R Riquelme ◽  
C Gaete ◽  
C Rabasa ◽  
E Sanhueza ◽  
...  
Keyword(s):  
Amniotic Fluid ◽  
Flow Rate ◽  
Urine Flow ◽  
Urine Flow Rate ◽  
Fetal Kidney ◽  
Fetal Plasma ◽  
Post Surgery ◽  
Fetal Urine ◽  
Ovine Fetus ◽  
Ovine Fetal

Samples of maternal and fetal plasma, fetal urine, and amniotic fluid were collected from 8 chronically cannulated pregnant llamas, in the last third of gestation. The samples were obtained for up to 18 days post-surgery. Osmolality, sodium (Na), potassium (K), chloride (Cl), and urea were measured on 40 samples collected on days 1, 2, 3, 4-5, 6-7, 8-9, and 10-19. The osmolalities of maternal and fetal plasma, fetal urine and amniotic fluid, averaged over these 7 time periods, were, respectively, 312 +/- 2, 311 +/- 1, 484 +/- 14, and 317 +/- 1 mosmol kg-1. Values are given as mean +/- s.e. The major differences from fetal fluid values in the ovine fetus (from previously published values) were the higher osmolality and urea concentration of llama fetal urine. Urine flow rate measured in 6 fetuses, 4.5-6.5 kg body weight, was 5.8 +/- 0.4 mliter h-1; urea clearance rate was 55.5 +/- 11.8 mliter h-1. Glomerular filtration rate (GFR), measured with 51Cr-EDTA in 5 fetuses on 1-4 occasions, was 111.4 +/- 23.3 mliter h-1. Fractional reabsorptions (FR) of Na, K and Cl were 97.9 +/- 1, 75.9 +/- 13.5 and 97.7 +/- 0.4% respectively. The GFR (25 mliter kg-1 h-1) and urine flow rate (1 mL kg-1 h-1) were less than half and about one-tenth the respective values in ovine fetuses. As Na reabsorption is the major oxygen-consuming activity of the kidney, the llama fetal kidney requires only half the oxygen needed by the ovine fetal kidney to reabsorb the filtered sodium load. The reason for the formation of hypertonic, rather than hypotonic, urine in the fetal llama may be due to both greater morphological maturity of the kidney and the excretion of as yet unidentified osmotically active organic substances.

Improvements on a Newton-Krylov Based Solver for CFD Models Using Finite Rate NOx Chemistry

2004 ◽  
Author(s):  
Qing Tang ◽  
Martin Denison ◽  
Mike Maguire ◽  
Mike Bockelie ◽  
Jyh-Yuan Chen
Keyword(s):  
Electric Utility ◽  
Iteration Scheme ◽  
Cfd Modeling ◽  
Finite Rate ◽  
Modeling Tool ◽  
Krylov Method ◽  
Cfd Models ◽  
Reduced Mechanism ◽  
Computational Fluid Dynamics Cfd ◽  
Matrix Free

In this paper, we describe our progress on improving the performance of a newly developed Computational Fluid Dynamics (CFD) modeling tool, which uses reduced chemical kinetics mechanisms to model the finite rate chemistry effects and solves the resulting system of stiff partial differential equations with a matrix-free Newton-Krylov method. A multi-grid based preconditioner and a Newton iteration scheme have been implemented in the Newton-Krylov solver and the reduced mechanism module, respectively, to replace the original Picard based preconditioner and the point iteration scheme for steady state species evaluation. Preliminary tests of the improved modeling tool have been conducted using simple hotbox and a full-scale, coal fired electric utility boiler, and shown very promising results in terms of the accuracy, robustness, and efficiency of the new tool.

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