Time Average Method Research Articles

Modelling Lassa virus dynamics in West African Mastomys natalensis and the impact of human activities.

Lassa fever is a West African rodent-borne viral haemorrhagic fever that kills thousands of people a year, with 100 000 to 300 000 people a year probably infected by Lassa virus (LASV). The main reservoir of LASV is the Natal multimammate mouse, Mastomys natalensis. There is reported asynchrony between peak infection in the rodent population and peak Lassa fever risk among people, probably owing to differing seasonal contact rates. Here, we developed a susceptible-infected-recovered ([Formula: see text])-based model of LASV dynamics in its rodent host, M. natalensis, with a persistently infected class and seasonal birthing to test the impact of changes to seasonal birthing in the future owing to climate and land use change. Our simulations suggest shifting rodent birthing timing and synchrony will alter the peak of viral prevalence, changing risk to people, with viral dynamics mainly stable in adults and varying in the young, but with more infected individuals. We calculate the time-average basic reproductive number, [Formula: see text], for this infectious disease system with periodic changes to population sizes owing to birthing using a time-average method and with a sensitivity analysis show four key parameters: carrying capacity, adult mortality, the transmission parameter among adults and additional disease-induced mortality impact the maintenance of LASV in M. natalensis most, with carrying capacity and adult mortality potentially changeable owing to human activities and interventions.

A time-averaged method to analyze slender rods moving in tubes

The motion of slender rods in narrow tubes involves the coupling of axial movements and transverse vibrations, in which the transverse vibration exhibits high frequency and chaotic characteristics. These characteristics render the computational cost of the time integration to the motions of rods and tubes expensive. To solve this problem, this paper proposes a novel time-averaged method, which contains two innovations: 1) By time averaging the traditional dynamic equations, the time-averaged dynamic equations describing the rod-tube system are established based on the time-averaged concept used in turbulence problems; 2) Two time-averaged contact models are developed, by fitting the time-averaged sample set using the polishing function and the machine learning, respectively, to construct the relationship between the time-averaged contact gaps and the time-averaged contact forces. The time-averaged method can use a large time step, which is far larger than that required for the time integration of traditional methods, thus reducing the computational cost. Inclined and rolling experiments of the rod-tube system, as well as numerical experiments of the control rod drop in a nuclear reactor, are conducted to validate the accuracy of the time-averaged method. Comparative analyses are carried out between the time-averaged method and six continuous contact models, demonstrating the high computational efficiency of the proposed method. Moreover, the experimental results can provide benchmark data for algorithm verification for scholars studying dynamic contact algorithms.

Statistical data treatment for residence time distribution studies in pharmaceutical manufacturing

Residence time distribution (RTD) method has been widely used in the pharmaceutical manufacturing for understanding powder dynamics within unit operations and continuous integrated manufacturing lines. The dynamics thus captured is then used to develop predictive models for unit operations and important RTD-based applications ensuring product quality assurance. Despite thorough efforts in tracer selection, data acquisition, and calibration model development to obtain tracer concentration profiles for RTD studies, there can exist significant noise in these profiles. This noise can make it challenging to identify the underlying signal and get a representative RTD of the system under study. Such concerns have previously indicated the importance of noise handling for RTD measurements in literature. However, the literature does not provide sufficient information on noise handling or data treatment strategies for RTD studies. To this end, we investigate the impact of varying levels of noise using different tracers on measurement of RTD profile and its applications. We quantify the impact of different denoising methods (time and frequency averaging methods). Through this investigation, we see that Savitsky Golay filtering turns out to a good method for denoising RTD profiles despite varying noise levels. The investigation is performed such that the key features of the RTD profile (which are important for RTD based applications) are preserved. Subsequently, we also investigate the impact of denoising on RTD-based applications such as out-of-specification (OOS) analysis and RTD modeling. The results show that the degree of noise levels considered in this work do not significantly impact the RTD-based applications.

Effects of film cooling injection inclination angle on cooling performance in rotating detonation combustors

Film cooling is a promising thermal management solution for rotating detonation combustors (RDCs) maturing toward long-duration engineering implementation. Aimed at elucidating the interaction between air coolant and rotating detonation waves (RDWs) and assessing the cooling performance, three-dimensional numerical simulations are conducted on an RDC utilizing four different film cooling injection inclination angles and compared to a case without coolant injection. Increasing injection angles from 30° to 90° results in a broader detachment region and deeper penetration, negatively influencing the cooling performance. A time-averaged method is adopted to evaluate the overall cooling performance, including axial temperature profiles, film protection coverage, RDC film effectiveness, and pattern factor. The results show that the cylindrical cooling hole with a 30° injection angle outperforms others due to enhanced wall attachment of the coolant and reduced interaction with the mainstream hot gas. Consequently, a low injection angle within the manufacturing limits is recommended for practical applications. Furthermore, this study uncovers several phenomena unique to RDCs when introducing film cooling, absent in conventional gas turbines, such as temperature discrepancy between the inner and outer walls, elevated upstream temperature caused by coolant injection, and non-uniform cooling effectiveness between the two sides of the cooling holes. Finally, the interplay between film cooling and RDW is illustrated through temperature and pressure gradient contours.

Optimisation of stable flight posture of ski jumping based on computational fluid dynamics simulation technology

ABSTRACT The stable flight posture that affects sports performance during flight is usually formed by the multiple angles of the athlete—ski posture. At present, research on the flight phase is mainly based on the single-factor impact analysis based on computational fluid dynamics simulation technology, but studies on the multi-factor coupling relationship of two or more factors is less. This study aims to determine the best optimal-level combination based on the simulation model of this work through comprehensive evaluation from the optimisation perspective of multi-factor coupling. Here, a refined model of the athlete—ski system with the characteristics of ski jumping was established. Reynolds time-averaged method was used for the simulation. A three-factor and five-level simulation test was conducted on the relative inclination between skis, the angle between the body and the ski and the ski V-angle through orthogonal experiment design. Our results show that the optimal-level combination of the relative inclination between skis of 120°, the angle between the body and the ski of 20°, and the ski V-angle of 30° is relatively best in terms of aerodynamic characteristics. Simulation results were similar to the results of the winter field data from video analysis, and the results were effective.

Detached eddy simulation of the heat release characteristics of H2-O2 reacting flow in supercritical water

The mild H2-O2 reaction is critical for coal-gasification-based polygeneration of power and heat in supercritical water. Time-averaged methods turbulence studies cannot accurately predict the flow, reaction, and heat release during the start-up of the H2-O2 reaction, which was crucial for the start-up and safe operation of supercritical water environment oxidation reactors (SCOR). In contrast, ordinary time-accurate method studies require a tremendous computational effort. Detached eddy simulation (DES), a hybrid model, could balance numerical simulation's computational accuracy and speed. Consequently, this paper has conducted a DES investigation on the start-up process of H2-O2 reaction in SCW with detailed kinetics. Through this article, the spatio-temporal distribution and reaction structure of the H2-O2 reaction start-up process had been unveiled. The process could be divided into the transition and the steady stage, with H2 mass fraction (XH2) and inlet temperature significantly affecting the H2-O2 reaction start-up process. Moreover, the stability of the H2-O2 reaction start-up process was heavily influenced by the XH2. This numerical study could guide the design, scale-up and optimization of SCOR.

Instability analysis of vibrated thermo-convection in Casson nanofluid suspension

This work is motivated by the importance of vertical vibration in nanofluids suspension, because of its wide applications in heat exchangers from one fluid to another, controlling the mixing in microvolumes, pharmaceutical industry, and engineering. The current study analyzes the effects of high-frequency vertical vibration on a horizontal Casson nanofluid layer heated from below saturated between rigid-rigid, rigid-free, and free-free boundary conditions. Field equations are derived by using time-average method, which describes the vibrational thermo-convection. These field equations are solved by utilizing linear stability analysis and Galerkin technique to obtain the thermal stability curve. By using this curve, the impacts of vertical vibration and physical governing factors on temperature profile are discussed. High-frequency vertical vibration is observed to have a stabilizing effect on Casson nanofluid suspension, thereby reducing thermo-convective heat transfer from one fluid to another. Stability threshold of vibrated suspension is increased approximately as [Formula: see text] and [Formula: see text] when [Formula: see text] and [Formula: see text], respectively. The significance of Brownian motion and thermophoretic force on convective heat transfer with vertical vibration is discussed. The resisting nature of Casson nanofluid on vibrational convective heat transfer is also tabulated.

Dynamic Regulation Process of the Variable-Geometry Power Turbine

In this paper, the dynamic regulating process of a variable-geometry power turbine is investigated through wind-tunnel experiments. Particle image velocimetry is used to obtain the dynamic evolution of the flowfield in the cascade passage, including two adjustment processes of increasing and decreasing the throat area. During the test, snapshots of the clockwise/counterclockwise rotation of a blade in the range of to are processed with a piecewise time-averaged method. The results indicate that the macroscopic change in the flowfield structure mainly appears in the wake region and the high-velocity region. In this process, the velocity and flow angle change monotonously with the blade rotation. The change rate of velocity is determined by both the blade position and the dimensionless outlet location . The overall change rate of velocity when the blade approaches the design position is higher than that at other positions, and the airflow near the suction surface is more sensitive to the adjustment of the cascade geometry compared with that near the pressure surface. As for the flow angle, the specific value is mainly determined by the blade position, and the variation law is related to the blade rotation speed.

Study on Pressure Pulsation and Force Characteristics of Kaplan Turbine

With the continuous increase in the size and power generation of turbines, the operational characteristics of turbines under off-design conditions are gradually receiving attention. In this paper, the Reynolds time-averaged method (RANS) is applied to the unsteady calculation of three different flow rate of a large Kaplan turbine under three heads: high head, rated head and low head. The focus is on the internal flow pattern of the turbine and the hydraulic excitation characteristics under low flow conditions. The unsteady characteristics of pressure pulsation, axial force of runner, radial force of runner and hydraulic torques along blade shank (τb) for six blades are analyzed. The results show that the pressure pulsation in the vaneless space is larger under low flow conditions, and frequencies of 0.33–1 fn ( fn is the rotating frequency of the runner) can be observed at monitoring points at different heights in the vaneless space. The analysis of the flow field under low flow conditions reveals the presence of larger scale vortices in the vaneless space. The position and intensity of vortices fluctuate periodically and cause larger amplitude pressure fluctuations. The frequency of 0.33–1 fn can also be observed for axial force, radial force, and τb for six blades due to the influence of vortices in the vaneless space. The low-frequency pulsations of pressure, force and τb are much greater under the low head and high head condition than that under rated head condition. The amplitude of pulsation of various parameters is the smallest under the low flow and rated head compared to that under the low flow conditions of other heads. The flow passage under low head is more influenced by the flow rate. Low-frequency pulsations occur under both the low flow and medium flow conditions. The asymmetry of the flow in the vaneless space causes unbalanced force and hydraulic instability of the runner, which seriously threatens the safe and stable operation of the turbine.

The properties of wind and jet from a super-Eddington accretion flow around a supermassive black hole

ABSTRACT Wind and jet are important medium of active galactic nucleus (AGN) feedback thus it is crucial to obtain their properties for the feedback study. In this paper we investigate the properties of wind and jet launched from a magnetized super-Eddington accretion flow around a supermassive black hole. For this aim, we have performed radiation magnetohydrodynamical simulation of a magnetically arrested super-Eddington accretion flows. We then have analysed the simulation data by the ‘virtual particle trajectory’ approach and obtained the mass flux, poloidal, and toroidal velocities, and mass-flux-weighted momentum and energy fluxes of wind and jet. The mass flux is found to be two to six times higher than that obtained based on the time-averaged streamline method widely used in literature. The momentum flux of wind is found to be larger than that of jet, while the total energy flux of jet is at most three times larger than that of wind. These results are similar to the case of hot accretion flows and imply that winds likely play a more important role than jet in AGN feedback. The acceleration mechanism of wind and jet is analysed and found to be dominated by Lorentz force rather than radiation force.

A non-stochastic control with admissible probabilities for SDDEs, application to linear reactors

We will develop a time-averaging method to compute an approximate control for a stochastic differential equation. The obtained control is nonstochastic, easy to compute, and has an absolute advantage in exactness with admissible probabilities compared to direct approximate control. The results are applied to a linear reactor under small white noise and are verified through numerical simulations.

Numerical investigation of the translational motion of bubbles: The comparison of capabilities of the time-resolved and the time-averaged methods.

In the present study, the accuracies of two different numerical approaches used to model the translational motion of acoustic cavitational bubble in a standing acoustic field are compared. The less accurate but less computational demanding approach is to decouple the equation of translational motion from the radial oscillation, and solve it by calculating the time-averaged forces exerted on the bubble for one acoustic cycle. The second approach is to solve the coupled ordinary differential equations directly, which provides more accurate results with higher computational effort. The investigations are carried out in the parameter space of the driving frequency, pressure amplitude and equilibrium radius. Results showed that both models are capable to reveal stable equilibrium positions; however, in the case of oscillatory solutions, the difference in terms of translational frequency may be more than three fold, and the amplitude of translational motion obtained by the time-averaged method is roughly 1.5 times higher compared to the time-resolved solution at particular sets of parameters. This observation implies that where the transient behaviour is important, the time-resolved approach is the proper choice for reliable results.

STABILITY ANALYSIS OF BIOCONVECTIVE HEAT TRANSFER IN A SUSPENSION OF GYROTACTIC MICROORGANISMS UNDER VERTICAL VIBRATION

Vertical vibration is an important technique to reduce or increase the bioconvective heat transfer. It has great applications in biotechnology, biomedicine, enhancing oil recovery, mixing in microvolumes, analysis of whole body vibration (WBV), and industry. The present study aims to investigate the influence of vertical vibration on the initiation of thermo-bioconvection in a suspension of randomly swimming gyrotactic microorganisms in a shallow thermally stratified horizontal fluid layer. The time-averaged method, linear stability analysis, and single-term Galerkin technique with different boundary layers are employed on the set of field equations. A secular equation is obtained in terms of vibrational and bioconvectional parameters for rigid-rigid and rigid-free boundary conditions. The analysis reported that vertical vibration destabilizes the suspension due to randomly swimming of gyrotactic microorganisms, i.e., enhancing the rate of bioconvective heat transfer. The authors also found that pertinent controlling parameters influence the size of the cell of vibrational thermo-bioconvection. It is observed that the diffusion and average volume of randomly swimming microorganisms affect the bioconvective heat transfer of the vibrational system inversely.

Establishment of a Reynolds average simulation method and study of a drag reduction mechanism for viscoelastic fluid turbulence

Reynolds average simulation governing equations are derived for viscoelastic fluid turbulence using the Reynolds time-averaged method combined with the Navier–Stokes equations, the viscoelastic fluid finitely extensible nonlinear elastic-Peterlin constitutive equation, the viscoelastic fluid molecular conformation tensor transport equation, and the k−ε−v′2¯−f turbulence model. To identify the relevant viscoelastic terms, user-defined functions and the programing language C are used to write a simulation subroutine for the Reynolds average of viscoelastic fluid turbulence; this subroutine is embedded into computational fluid dynamics software to establish a simulation method for Reynolds average of viscoelastic fluid turbulence. Then, the flow field structure of viscoelastic fluid turbulence is analyzed. Using energy transport theory, expressions for the contribution of viscous, elastic, and Reynolds shear stress to the turbulent friction factor of viscoelastic fluid in a horizontal tube are established, and the turbulent drag reduction mechanism of the viscoelastic fluid is revealed. The simulated values for pressure drop, Fanning friction factor, and the drag reduction rate of viscoelastic fluid in tests are in good agreement with experimental values, and the average relative error is less than 12.37%. In addition, elastic shear stress is produced after the dissolution of drag reduction agents in water, which increases the turbulent friction factor; however, Reynolds shear stress is greatly reduced, and viscous shear stress is weakened by inhibiting the turbulence fluctuation, so the turbulent friction factor decreases; more importantly, the increase in the friction factor of the former is much smaller than that of the latter.

Spin Josephson effects of spin–orbit-coupled Bose–Einstein condensates in a non-Hermitian double well

In this paper, we investigate the spin and tunneling dynamics of a spin–orbit-coupled noninteracting Bose–Einstein condensate in a periodically driven non-Hermitian double-well potential. Under high-frequency driving, we obtain the effective time-averaged Hamiltonian by using the standard time-averaging method, and analytically calculate the Floquet quasienergies, revealing that the parity-time ()-breaking phase transition appears even for arbitrarily small non-Hermitian parameters when the spin–orbit coupling strength takes half-integer value, irrespective of the values of other parameters used. When the system is -symmetric with balanced gain and loss, we find numerically and analytically that in the broken -symmetric regions, there will exist the net spin current together with a vanishing atomic current, if we drop the contribution of the exponential growth of the norm to the current behaviors. When the system is non--symmetric, though the quasienergies are partial complex, a stable net spin current can be generated by controlling the periodic driving field, which is accompanied by a spatial localization of the condensate in the well with gain. The results deepen the understanding of non-Hermitian physics and could be useful for engineering a variety of devices for spintronics.

Replica-averaging: An algorithm to study mechano-reactive processes for polymers under flow conditions

A new method based on quasi-independent parallel simulation approach, replica-averaging, has been developed to study the influence of flow on mechanical force-mediated polymer processes, such as denaturation and breaking of bonds. This method considerably mitigates the unphysical prediction of force-mediated events inherent in Brownian dynamics (BD) polymer chain simulations that employ instantaneous force profile-based criteria to identify the occurrence of such events. This inaccuracy in predicting force-mediated event kinetics is due to high fluctuations of the instantaneous force profile around the average force. Replica-averaging reduces such high fluctuation effects by computing a force profile that faithfully represents the average force profile of the polymer chain conformation, which is then used to predict reactive events. For transient conformation conditions, the replica-averaged method more accurately predicts the mechano-reactive kinetics than the time-averaged method typically employed to reduce the unphysical prediction of force-mediated events in BD simulations. Furthermore, the influence of the proposed replica-averaging method parameters on the accuracy of predicting the true average force profile along the polymer is discussed.

Parameter-tuning stochastic resonance as a tool to enhance wavelength modulation spectroscopy using a dense overlapped spot pattern multi-pass cell.

The parameter-tuning stochastic resonance (SR) method can convert part of the noise energy into the signal energy to suppress the noise and amplify the signal, comparing with traditional weak periodic signal detection methods (e.g., time average method, filtering method, and correlation analysis method). In this work, the numerical calculation is conducted to find the optimal resonance parameters for applying the SR method to the wavelength modulation spectroscopy (WMS). Under the stochastic resonance state, the peak value of 2f signal (a constant concentration of CH4∼20 ppm) is effectively amplified to ∼0.0863 V, which is 3.8 times as much as the peak value of 4000-time average signal (∼0.0231 V). Although the standard deviation also increases from ∼0.0015 V(1σ) to ∼0.003 V(1σ), the SNR can be improved by 1.83 times (from ∼25.9 to ∼15.8) correspondingly. A linear spectral response of SR 2f signal peak value to raw 2f signal peak value is obtained. It suggests that the SR method is effective for enhancing photoelectric signal under strong noise background.

Method of color holographic display with speckle noise suppression.

In this paper, a method of color holographic display with speckle noise suppression is proposed. Firstly, the intensity information of the object is extracted according to the red, green and blue (RGB) channels. The band-limited phase is calculated and used as the initial phase for each color channel. Secondly, the double-step Fresnel diffraction algorithm is used to calculate the computer-generated holograms (CGHs), and a filter plane that dynamically adjusts the position of the filter in the optical path is designed. Then, a divergent spherical phase factor is added to the CGHs. Finally, the time average method is used to further reduce the speckle noise. When the CGHs of the RGB channels are loaded on the digital micromirror device and illuminated by the RGB lights emitting in a temporal sequence, the color reconstructed images with speckle noise suppression can be displayed. The validity of the proposed method is verified.

Supervised learning with probability interpretation in airfoil transition judgment

Transition prediction has always been a frontier issue in the field of aerodynamics. A supervised learning model with probability interpretation for transition judgment based on experimental data was developed in this paper. It solved the shortcomings of the point detection method in the experiment, that which was often only one transition point could be obtained, and comparison of multi-point data was necessary. First, the Variable-Interval Time Average (VITA) method was used to transform the fluctuating pressure signal measured on the airfoil surface into a sequence of states which was described by Markov chain model. Second, a feature vector consisting of one-step transition matrix and its stationary distribution was extracted. Then, the Hidden Markov Model (HMM) was used to pre-classify the feature vectors marked using the traditional Root Mean Square (RMS) criteria. Finally, a classification model with probability interpretation was established, and the cross-validation method was used for model validation. The research results show that the developed model is effective and reliable, and it has strong Reynolds number generalization ability. The developed model was theoretically analyzed in depth, and the effect of parameters on the model was studied in detail. Compared with the traditional RMS criterion, a reasonable transition zone can be obtained using the developed classification model. In addition, the developed model does not require comparison of multi-point data. The developed supervised learning model provides new ideas for the transition detection in flight experiments and other experiments.

Impacts of low atmospheric pressure on distribution of indoor hot air jet in plateau area

The existing design parameters of hot-air heating for local buildings do not consider the distinctive low-pressure that can be experienced in the plateau regions, resulting in significant inefficiency. In this study, a numerical model based on the Reynolds time-averaged method coupled with the RNG k–ε turbulence model was established by considering the air thermal properties influenced by pressure. Four atmospheric conditions of 101.325 kPa, 84.547 kPa, 70.093 kPa and 57.708 kPa were selected to simulate the velocity and temperature fields of the horizontal and vertical hot-air jets. The influence of low pressure on the flow characteristics of hot-air jets was analyzed subsequently. The results suggest the jet flow patterns are essentially similar under various pressures. The horizontal hot-air jets bent upward more significantly and the diffusion range of the vertical jets was reduced under low pressure. The jet velocity decayed faster at low pressure, and the axial velocity of a vertical jet at 57.708 kPa was 0.26 m/s lower than that at 101.325 kPa. The temperature gradient of the room with a hot-air jet was increased with decreasing pressure, which was 5.0 K/m at 57.708 kPa. This study should be helpful to the detailed design and efficient operation of hot-air heating in buildings in the plateau regions.