Numerical analysis for wake flow field of Ahmed model based on a nonlinear-LRN/DES turbulence model

Purpose This paper aims to propose a precise turbulence model for automobile aerodynamics simulation, which can predict flow separation and reattachment phenomena more accurately. Design/methodology/approach As the results of wake flow simulation with commonly used turbulence models are unsatisfactory, by introducing a nonlinear Reynolds stress term and combining the detached Eddy simulation (DES) model, this paper proposes a nonlinear-low-Reynolds number (LRN)/DES turbulence model. The turbulence model is verified in a backward-facing step case and applied in the flow field analysis of the Ahmed model. Several widely applied turbulence models are compared with the nonlinear-LRN/DES model and the experimental data of the above cases. Findings Compared with the experimental data and several turbulence models, the nonlinear-LRN/DES model gives better agreement with the experiment and can predict the automobile wake flow structures and aerodynamic characteristics more accurately. Research limitations/implications The nonlinear-LRN/DES model proposed in this paper suffers from separation delays when simulating the separation flows above the rear slant of the Ahmed body. Therefore, more factors need to be considered to further improve the accuracy of the model. Practical implications This paper proposes a turbulence model that can more accurately simulate the wake flow field structure of automobiles, which is valuable for improving the calculation accuracy of the aerodynamic characteristics of automobiles. Originality/value Based on the nonlinear eddy viscosity method and the scale resolved simulation, a nonlinear-LRN/DES turbulence model including the nonlinear Reynolds stress terms for separation and reattachment prediction, as well as the wake vortex structure prediction is first proposed.

Electroacupuncture inhibits the corneal ROS/TXNIP/NLRP3 signaling pathway in a rat model of dry eye syndrome

Background: Electroacupuncture (EA) treatment has been found to ameliorate clinical symptoms in patients with dry eye, but its mechanisms are still not entirely clear. Objective: To study the regulation of EA on ocular surface function and the corneal reactive oxygen species (ROS)/thioredoxin-interacting protein (TXNIP)/Nod-like receptor protein 3 (NLRP3) inflammatory signaling pathway in dry eye syndrome (DES) model rats. Methods: Male Sprague-Dawley (SD) rats were randomly divided into five groups: Normal, Model, Model + EA, Model + NAC (N-actetylcysteine) and Model + NS (normal saline). The DES model was developed by subcutaneous injection of scopolamine hydrobromide with exposure to an air draft in the latter four groups. After intervention, the Schirmer I test (SIT), tear film break-up time (BUT) and ROS content were measured, the histopathological changes of corneal tissues were observed, and the mRNA and protein expression levels of TXNIP, NLRP3, apoptosis-associated Speck-like protein containing CARD (ASC), caspase-1, interleukin (IL)-1β and IL-18 were detected. Results: Compared with the Model group, the SIT and BUT increased significantly in the Model + EA group after intervention (p < 0.05), and the corneal injury was improved. Corneal ROS content declined in both Model + EA and Model + NAC groups (p < 0.05), and mRNA expression of TXNIP, NLRP3, ASC and caspase-1 also decreased (p < 0.01). Corneal protein expression of TXNIP, NLRP3, IL-1β and IL-18 decreased significantly in the Model + EA group (p < 0.01). Conclusion: Inhibiting the ROS/TXNIP/NLRP3 signaling pathway may be the mechanism underlying the role of EA in improving corneal injury in DES model rats.

Simulation modularer Produktarchitekturen durch modellbasierte Konfiguration

Im Zuge der Globalisierung sehen sich produzierende Unternehmen mit einem kontinuierlich anwachsenden Wettbewerbsdruck konfrontiert. Aufgrund dessen sehen sich viele Marktakteure zu einer intensivierten Spezialisierung gezwungen, um auf kunden-individuelle Anforderungen eingehen zu können. Einen möglichen Lösungsansatz zur Bewältigung dieser Herausforderung bietet der Ansatz der Modularisierung. Hier wird allerdings nicht konkret ein Baukasten definiert, vielmehr werden verschiedene Alternativen generiert. Die Entscheidung, welcher Baukasten schlussendlich implementiert wird, fällt meist aufgrund einiger weniger Einflussfaktoren sowie maßgeblich durch Expertenentscheidungen. An dieser Stelle setzt der vorliegende Beitrag an. Um ein quantifizierbares und ganzheitliches Kriterium zur Unter-stützung der Auswahl modularer Baukastensysteme zu bieten, wird eine multifaktorielle Simulation eingesetzt. Einer der maßgeblichen Aspekte derer ist die beidseitige Inbezugnahme von sowohl Kunden- als auch Unternehmensperspektive. Dies wird v.a. durch die Verwendung eines dynamischen Produktkonfigurationssystems ermöglicht. Um die zugrundeliegenden, teils komplexen Produktarchitekturen datentechnisch konsistent und pflegbar zu halten, wird zusätzlich der Einsatz einer modellbasierten Datenstruktur aufgezeigt. Die Verwendung des Model-Based Systems-Engineering (MBSE) Ansatzes hilf dabei, die vielschichtigen Zusammenhänge des Modulbaukastens in einer konsistenten und maschinenlesbaren Form auszudrücken. Somit kann das Konfigurationssystem produktunabhängig auf die Ontologie der zugrundeliegenden Datenstruktur zugreifen. Für die Baukastensimulation wird dieses Konfigurationssystem rekursiv für mehrere Kundenanfragen und alternative Baukästen eingesetzt, um anschließend mittels eines geometrisch-mathematischen Algorithmus ein multi-dimensionales Entscheidungskriterium hinsichtlich der Baukasten-performance zu generieren.

Effect of different patient peak arrivals on an emergency department via discrete event simulation: a case study

Emergency department (ED) overcrowding is a well-recognized worldwide phenomenon which affects the quality of emergency care. A direct consequence of overcrowding is a long wait for visit and treatment of people who require primary care, possibly endangering the lives of critical patients. Healthcare management literature devoted to analyze ED operational policies is very wide, and many approaches have been proposed to address this important problem. However, less attention has been given to patient peak arrivals caused by the occurrence of some critical events which can strongly strain the operational efficiency of an ED. In this paper, we consider the particular case study of a medium-size ED located in a region of Central Italy recently hit by a severe earthquake, aiming at assessing the effects of such an occurrence on the ED operation. In particular, we propose a discrete event simulation (DES) model to analyze the patient flows through this ED, simulating unusual operational conditions due to a critical event, like a natural disaster, which causes a sudden spike in the number of patient arrivals. The availability of detailed data concerning the ED processes enabled building an accurate DES model and performing extensive scenario analyses. The model provides a valid decision support system for the ED managers in assessing specific emergency plans to be activated in case of mass casualty disasters.

Developing an Approach to Quantify Nurse Workload and Quality of Care Using Discrete Event Simulation

Intensive workload for nurses due to high demands directly impacts the quality of care and nurses’ health. To better manage workload, it is necessary to understand the drivers of workload. This multidisciplinary research provides an adaptable nurse-focused approach to discrete event simulation (DES) modelling that can quantify the effects of changing technical design and operational policies in terms of nurse workload and quality of care. In the first phase of this research, a demonstrator model was developed that explored the impact of nurse-patient ratios. As the number of patients per nurse (nurse-patient ratio) increased, nurse workload increased, and the quality of care deteriorated. In the second phase of this research, the DES model tested the interaction of patient acuity and nurse-patient ratios. As the levels of patient acuity and number of patients per nurse increased, nurse workload increased, and quality of care deteriorated – a result that was not surprising but an ability to quantify this proactively, was conceived. In the third phase of this research, the DES model was validated by means of an external field validation study by adapting the model to a real-world unit. The DES model showed excellent consistency between modelling and real-world outcomes (Intraclass iv Correlation Coefficient = 0.85 to 0.99; Spearman Rank-order Correlation Coefficient = 0.78). The fourth phase of this research used the validated simulation model to test the design implication of geographical patient bed assignment. As nurses were assigned to patient beds further away from the center of the unit or spread further apart, nurse workload increased as the nurse had to walk more leading to a deterioration in the quality of care. The DES modelling capability showed that both aspects of assignment were important for patient bed assignment. The fifth phase of this research combined Digital Human Modelling (DHM) and DES to produce a time-trace of biomechanical load and peak biomechanical load (‘activity’) for a full shift of nursing work. As the nurse was assigned to beds further away from the center of the unit, the cumulative biomechanical load decreased as the nurse spent more time walking yielding a reduced biomechanical load in comparison to the task group ‘activity’. As patient acuity is increased, a decrease in L4/L5 moment is observed as the task duration and frequency of most care task increase. Due to increased care demands, nurses must now spend more time delivering care. Since the care demands are much higher than the current capability of nurses, quality of care is deteriorated. As number of patients per nurse, increased a ‘ceiling’ effect on biomechanical load can be observed as nurses do not have the time to attend to this extra demand for care. The use of this adaptable DES modeling approach can assist decision makers by providing quantifiable information on the potential impact of these decisions on nurse workload and quality of care. Thereby, assisting decision makers to create technical design and operational policies for hospital units that do not compromise patient safety and health of nurses. Keywords: Behavioural operations research; Discrete Event Simulation; Nurse Workload; Quality of care; Healthcare Ergonomics; Human Factors Engineering; Nurses; Healthcare policy

Developing an Approach to Quantify Nurse Workload and Quality of Care Using Discrete Event Simulation

Intensive workload for nurses due to high demands directly impacts the quality of care and nurses’ health. To better manage workload, it is necessary to understand the drivers of workload. This multidisciplinary research provides an adaptable nurse-focused approach to discrete event simulation (DES) modelling that can quantify the effects of changing technical design and operational policies in terms of nurse workload and quality of care. In the first phase of this research, a demonstrator model was developed that explored the impact of nurse-patient ratios. As the number of patients per nurse (nurse-patient ratio) increased, nurse workload increased, and the quality of care deteriorated. In the second phase of this research, the DES model tested the interaction of patient acuity and nurse-patient ratios. As the levels of patient acuity and number of patients per nurse increased, nurse workload increased, and quality of care deteriorated – a result that was not surprising but an ability to quantify this proactively, was conceived. In the third phase of this research, the DES model was validated by means of an external field validation study by adapting the model to a real-world unit. The DES model showed excellent consistency between modelling and real-world outcomes (Intraclass iv Correlation Coefficient = 0.85 to 0.99; Spearman Rank-order Correlation Coefficient = 0.78). The fourth phase of this research used the validated simulation model to test the design implication of geographical patient bed assignment. As nurses were assigned to patient beds further away from the center of the unit or spread further apart, nurse workload increased as the nurse had to walk more leading to a deterioration in the quality of care. The DES modelling capability showed that both aspects of assignment were important for patient bed assignment. The fifth phase of this research combined Digital Human Modelling (DHM) and DES to produce a time-trace of biomechanical load and peak biomechanical load (‘activity’) for a full shift of nursing work. As the nurse was assigned to beds further away from the center of the unit, the cumulative biomechanical load decreased as the nurse spent more time walking yielding a reduced biomechanical load in comparison to the task group ‘activity’. As patient acuity is increased, a decrease in L4/L5 moment is observed as the task duration and frequency of most care task increase. Due to increased care demands, nurses must now spend more time delivering care. Since the care demands are much higher than the current capability of nurses, quality of care is deteriorated. As number of patients per nurse, increased a ‘ceiling’ effect on biomechanical load can be observed as nurses do not have the time to attend to this extra demand for care. The use of this adaptable DES modeling approach can assist decision makers by providing quantifiable information on the potential impact of these decisions on nurse workload and quality of care. Thereby, assisting decision makers to create technical design and operational policies for hospital units that do not compromise patient safety and health of nurses. Keywords: Behavioural operations research; Discrete Event Simulation; Nurse Workload; Quality of care; Healthcare Ergonomics; Human Factors Engineering; Nurses; Healthcare policy

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

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.

A CFD-Based Examination of Rotor-Rotor Separation Effects on Interactional Aerodynamics for eVTOL Aircraft

This study systematically investigates the aerodynamic interactions of a two-rotor system with a front rotor and an aft rotor aligned with the direction of flow. The rotors are 5.5 ft diameter fixed-pitch rotors operating at approximately 12 lb/ft2 disk loading, representative of large eVTOL aircraft. Fluid flow is simulated using the commercial Navier–Stokes solver, AcuSolve, with a detached eddy simulation (DES) model. Simulations were performed nominally at 40 kt edgewise flight for nine cases corresponding to three values of longitudinal hub–hub separation (2.5R, 3R, 3.5R) and three values of vertical offset (0, 0.25R, 0.5R). Aft rotor performance was compared to an isolated rotor operating in the same conditions in order to quantify the effects of rotor–rotor interaction. For the cases where the aft rotor is closest to the front rotor (2.5R longitudinal offset, zero vertical offset), the aft rotor produced 8.4% less thrust and required 13.4% higher torque than a rotor in isolation. When vertical rotor separation was increased, interactional aerodynamic effects decreased. For a 2.5R longitudinal offset, increasing the vertical offset to 0.5R decreased the lift deficit to 4.6% and the torque penalty to 6.8%. Increasing the longitudinal offset to 3.5R (while keeping the vertical offset at zero) also reduced interactional aerodynamic effects, but reductions in lift deficit and torque penalty were smaller than those observed with 0.5R vertical offset. Reducing disk loading was found to strengthen interactional aerodynamic effects, with an 11.5% thrust deficit at 6 lb/ft2 compared to 9.0% at 12 lb/ft2. An increase in flight speed also increased interactional aerodynamic penalties from 5.4% thrust deficit at 20 kt to 12.2% at 60 kt. The increased interactional aerodynamic penalties with the reduction in disk loading and increase in flight speed were both attributed to an increase in wake skew angle and the resulting decrease in separation between the aft rotor disk and front rotor wake.

A 2020 view of tension-based cortical morphogenesis

Mechanical tension along the length of axons, dendrites, and glial processes has been proposed as a major contributor to morphogenesis throughout the nervous system [D. C. Van Essen, Nature 385, 313–318 (1997)]. Tension-based morphogenesis (TBM) is a conceptually simple and general hypothesis based on physical forces that help shape all living things. Moreover, if each axon and dendrite strive to shorten while preserving connectivity, aggregate wiring length would remain low. TBM can explain key aspects of how the cerebral and cerebellar cortices remain thin, expand in surface area, and acquire their distinctive folds. This article reviews progress since 1997 relevant to TBM and other candidate morphogenetic mechanisms. At a cellular level, studies of diverse cell types in vitro and in vivo demonstrate that tension plays a major role in many developmental events. At a tissue level, I propose a differential expansion sandwich plus (DES+) revision to the original TBM model for cerebral cortical expansion and folding. It invokes tangential tension and “sulcal zipping” forces along the outer cortical margin as well as tension in the white matter core, together competing against radially biased tension in the cortical gray matter. Evidence for and against the DES+ model is discussed, and experiments are proposed to address key tenets of the DES+ model. For cerebellar cortex, a cerebellar multilayer sandwich (CMS) model is proposed that can account for many distinctive features, including its unique, accordion-like folding in the adult, and experiments are proposed to address its specific tenets.