Analysis of the Shear-Thinning Viscosity Behavior of the Johnson–Segalman Viscoelastic Fluids

This paper presents a numerical comparison of viscoelastic shear-thinning fluid flow using a generalized Oldroyd-B model and Johnson–Segalman model under various settings. Results for the standard shear-thinning generalization of Oldroyd-B model are used as a reference for comparison with those obtained for the same flow cases using Johnson–Segalman model that has specific adjustment of convected derivative to assure shear-thinning behavior. The modeling strategy is first briefly described, pointing out the main differences between the generalized Oldroyd-B model (using the Cross model for shear-thinning viscosity) and the Johnson–Segalman model operating in shear-thinning regime. Then, both models are used for blood flow simulation in an idealized stenosed axisymmetric vessel under different flow rates for various model parameters. The simulations are performed using an in-house numerical code based on finite-volume discretization. The obtained results are mutually compared and discussed in detail, focusing on the qualitative assessment of the most distinct flow field differences. It is shown that despite all models sharing the same asymptotic viscosities, the behavior of the Johnson–Segalman model can be (depending on flow regime) quite different from the predictions of the generalized Oldroyd-B model.

A study on the temperature profile of bifurcation tunnel fire under natural ventilation

This study simulated a series of bifurcation tunnel fire scenarios using the numerical code to investigate the temperature profile of bifurcation tunnel fire under natural ventilation. The bifurcation tunnel fire scenarios considered three bifurcation angles (30°, 45°, and 60°) and six heat release rates (HRRs) (5, 10, 15, 20, 25, and 30 MW). According to the simulation results, the temperature profile with various HRRs and bifurcation angles was described. Furthermore, the effects of bifurcation angles and HRRs on the maximum temperature under the bifurcation tunnel ceiling and the temperature decay along the longitudinal direction of the branch were investigated. According to the theoretical analysis, two prediction models were proposed. These models can predict a bifurcation tunnel fire’s maximum temperature and longitudinal temperature decay in the branch. The results of this study could be valuable for modelling a bifurcation tunnel fire and benefit the fire engineering design of bifurcation tunnels.

Experimental and Modeling Study of Kinetics for Hydrate Decomposition Induced by Depressurization in a Porous Medium

The hydrate decomposition kinetics is a key factor for the gas production from hydrate-saturated porous media. Meanwhile, it is also related to other factors. Among them, the permeability and hydrate dissociation surface area on hydrate dissociation kinetics have been studied experimentally and numerically in this work. First, the permeability to water was experimentally determined at different hydrate saturations (0%, 10%, 17%, 21%, 34%, 40.5%, and 48.75%) in hydrate-bearing porous media. By the comparison of permeability results from the experimental measurements and theoretical calculations with the empirical permeability models, it was found that, for the lower hydrate saturations (less than 40%), the experimental results of water permeability are closer to the predicted values of the grain-coating permeability model, whereas, for the hydrate saturation above 40%, the tendencies of hydrate accumulation in porous media are quite consistent with the pore-filling hydrate habits. A developed two-dimensional core-scale numerical code, which incorporates the models for permeability and hydrate dissociation surface area along with the hydrate accumulation habits in porous media, was used to investigate the kinetics of hydrate dissociation by depressurization, and a “shrinking-core” hydrate dissociation driven by the radial heat transfer was found in the numerical simulations of hydrate dissociation induced by depressurization in core-scale porous media. The numerical results indicate that the gas production from hydrates in porous media has a strong dependence on the permeability and hydrate dissociation surface area. Meanwhile, the simulation shows that the controlling factor for the dissociation kinetics of hydrate switches from permeability to hydrate dissociation surface area depending on the hydrate saturation and hydrate accumulation habits in porous media.

Numerical Simulation of Two-Phase Water-Oil Flow in a Horizontal Pipe Using the Smoothed Particle Hydrodynamics Method

In this work, the numerical code DualPhysics, based on the Lagrangian particle and mesh free method Smoothed Particle Hydrodynamics, has been employed to solve the slightly compressible isothermal two-phase water-oil flow. The continuity and momentum equations are solved, and we used the modified Tait equation of state to determine the pressure. To validate the numerical code, we solved the modified Couette flow of two fluids. As a practical case, we solved the isothermal and two-dimensional two-phase water-oil flow. The mixing of the fluids occurs after passing through a 45 degree Y junction placed at the entrance of the horizontal pipeline. Results showed the potential for using the numerical code, although some modifications and alterations are still necessary to solve practical problems.

Assessment of threat arising by closed - volume explosions of fuel - air mixtures

The method of estimation of maximal parameters of combustion of gaseous mixtures in closed space is presented. Estimation of chemical composition of combustion products is based on simplified rules of decomposition of reactive medium. Exemplary calculations of temperature, pressure, heat of combustion of hydrocarbon/air mixtures are presented. The accuracy of presented method was validated by comparison with calculations performed by thermodynamic numerical code that include wide list of chemical substances present in combustion products. The obtained results confirm applicability of the proposed method to predict closed space combustion parameters of gaseous mixtures. Semi-empirical methods of estimation of flammability limits are briefly referred

Aciniccell carcinoma of the salivary glands: clinical and histopathological study of 12 cases

Objective:Acinic cell carcinoma (CCA) is the third malignant epithelial tumor of the salivary glands in adults; low-grade tumor of malignancy, composed of neoplastic cells with serous acinar differentiation. The objective of this work was to analyze 12 cases of CCA according to their location, clinical characteristics, histological and immunohistochemical pattern and cell types, following the latest classification of the World Health Organization. Methods: The study included 12 cases of CCA from the files of salivary tumor biopsies of our work team, corresponding to the period 1997-2020. A numerical code was used to identify the samples, preserving the identity of the patients. Histological sections of the paraffin-embedded biopsies were evaluated with H/E, PAS and Toluidine blue and immunostained with the monoclonal antibodies pancytokeratin AE1 / AE3, Ki67, MUC-1 and mammaglobin. Results: The most frequent histologic pattern was the solid type as a single pattern or integrated with other patterns of lesser development, with almost exclusive location in the parotid gland and more frequent in women. Cells like normal acinar serocytes predominated in the solid growth pattern. The most frequent cell type in the microcystic patternwas the nonspecific glandular cell together with a lower proportion of acinar and intercalated duct-like cells. The papillary-cystic pattern was lined by nonspecific glandular cells. No clear cells found. With Ki67 a low cell proliferation was demonstrated in all the cases studied. Cell labeling for MUC-1 was grade 1 positive (less than 10% immunoreactive cells) and negative for mammaglobin.Conclusions: Patient follow-up is a priority because CCA tends to recur and metastasize and its behavior can become aggressive. We must deepen the study of its proliferative capacity as a treatment and prognosis tool, especially with immunohistochemistry and standardized molecular biology methods.

THE FLOODING AFTER DAMAGE OF A WARSHIP WITH COMPLEX INTERNAL COMPARTMENTS – EXPERIMENTS ON A FULLY CONSTRAINED MODEL IN CALM WATER AND REGULAR BEAM SEAS

In order to provide data to assist in developing and validating a numerical code to simulate the flooding immediately following damage scale model experiments were conducted on a fully constrained model to investigate the progressive flooding through a complex series of internal compartments within a generic destroyer type hull form. A 3.268 metre long model of a generic destroyer hull form with a simplified, typical internal arrangement was constructed to cover the configuration of greatest interest. A very rapid damage opening scenario was simulated by rupturing a taut membrane covering an opening. The model was instrumented to measure the levels of water and the air pressures in various compartments. In addition, video footage was obtained of the flooding process from both internally and externally of the model. Previous work presented by Macfarlane et al. (2010) showed the results for the unconstrained model. This paper reports on the outcomes from the experimental program where the model was fully constrained in all six degrees of freedom. Firstly, tests were conducted in calm water with damage opening extents ranging from 50% to 100%. When the damage opening was only 50% the rate of rise of water in each of the compartments was only marginally slower than for the 100% damage extent case. Secondly, the test results in calm water were compared against results from tests in regular beam seas. A ‘set-up’ of water inside each of the compartments on the 2nd Deck was found during the wave tests. The result of this is that the mean equilibrium water level in each compartment in the regular beam sea cases is noticeably higher than the equivalent calm water case, particularly for the two compartments on the port side, away from the damage. Finally, analysis of the data from further calm water and beam sea tests suggests that a similar result also occurs when the model is fixed at various non-zero heel angles.

Numerical Dimensioning of a Pre-Cooler for sCO2 Power Cycles to Utilize Industrial Waste Heat

The annual waste heat available from industry in the European Union is more than 2700 PJ. Consequently, the utilization of the unexploited thermal energy will decisively contribute to a reduced overall power consumption and lower greenhouse gas emissions. In the present investigation, a cycle layout, based on supercritical carbon dioxide (sCO2), was applied for a certain waste heat source, a gas compressor station. The boundary conditions determined by the cycle were used by the numerical code ANSYS CFX to design a pre-cooler. Subsequently, this printed circuit heat exchanger was examined for sCO2 mass fluxes between 100 kg/m²s and 900 kg/m²s. The heat transfer and pressure drop increase as the flow channel diameter is reduced. As the pressure drop of the coolant channel is more sensitive to the diameter, a larger coolant channel diameter is selected to maintain a reasonably low pressure drop. The optimum pre-cooler design consists of a 0.5 mm and 0.8 mm channel diameter for the sCO2 and coolant channel. Based on these results, internal fins were applied and optimized, to improve the heat transfer performance. An internal fin height of 4 mm was found to achieve the optimum thermal-flow performance for the pre-cooler.

Opening the reheating box in multifield inflation

The robustness of multi-field inflation to the physics of reheating is investigated. In order to carry out this study, reheating is described in detail by means of a formalism which tracks the evolution of scalar fields and perfect fluids in interaction (the inflatons and their decay products). This framework is then used to establish the general equations of motion of the background and perturbative quantities controlling the evolution of the system during reheating. Next, these equations are solved exactly by means of a new numerical code. Moreover, new analytical techniques, allowing us to interpret and approximate these solutions, are developed. As an illustration of a physical prediction that could be affected by the micro-physics of reheating, the amplitude of non-adiabatic perturbations in double inflation is considered. It is found that ignoring the fine-structure of reheating, as usually done in the standard approach, can lead to differences as big as ∼ 50%, while our semi-analytic estimates can reduce this error to ∼ 10%. We conclude that, in multi-field inflation, tracking the perturbations through the details of the reheating process is important and, to achieve good precision, requires the use of numerical calculations.

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

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.