Channel Simulation Research Articles

Lattice Boltzmann simulation of fluid flow and heat transfer in a micro channel with heat sources located on the walls

This study investigated a numerical study of fluid flow and heat transfer in micro channel with four heat sources that located on upper and lower walls. Four heat sources are located in the upper and lower walls symmetrically respect to centerline. Lattice Boltzmann method is used to solve related equations of flow and temperature of fluids, this method is included two steps such as collision and streaming steps. Reynolds number is varied from 0.1 to 10 and Knudsen number is changed from 0 to 0.1 for air. The slip velocity and temperature jump boundary condition are used for micro channel simulation with Knudsen numbers related to slip velocity flow. Bounce-back boundary conditions were applied on all solid boundaries, which means that incoming boundary populations are equal to out-going populations after the collision. A comparison with other study is done and a good result is gained. The results show that the Knudsen number has important role in heat transfer and the highest mean temperature at outlet occurs at highest Knudsen number and heat transfer convection is more significant for first heat source comparing second heat source.

Indoor and Outdoor Physical Channel Modeling and Efficient Positioning for Reconfigurable Intelligent Surfaces in mmWave Bands

Reconfigurable intelligent surface (RIS)-assisted communication appears as one of the potential enablers for sixth generation (6G) wireless networks by providing a new degree of freedom in the system design to telecom operators. Particularly, RIS-empowered millimeter wave (mmWave) communication systems can be a remedy to provide broadband and ubiquitous connectivity. This paper aims to fill an important gap in the open literature by providing a physical, accurate, open-source, and widely applicable RIS channel model for mmWave frequencies. Our model is not only applicable in various indoor and outdoor environments but also includes the physical characteristics of wireless propagation in the presence of RISs by considering 5G radio channel conditions. Various deployment scenarios are presented for RISs and useful insights are provided for system designers from the perspective of potential RIS use-cases and their efficient positioning. The scenarios in which the use of an RIS makes a big difference or might not have a big impact on the communication system performance, are revealed. The open-source and comprehensive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SimRIS Channel Simulator</i> is also introduced in this paper.

On the Spectral Efficiency for Distributed Massive MIMO Systems

Distributed MIMO (D-MIMO) systems are expected to play a key role in deployments for future mobile communications. Together with massive MIMO technology, D-MIMO aims to maximize the spectral efficiency and data rate in mobile networks. This paper proposes a deep study on the spectral efficiency of D-MIMO systems for essential channel parameters, such as the channel power balance or the correlation between propagation channels. For that purpose, several propagation channels were acquired in both anechoic and reverberation chambers and were emulated using channel simulators. In addition, several frequency bands were studied, both the sub–6 GHz band and mmWave band. The results of this study revealed the high influence of channel correlation and power balance on the physical channel performance. Low-correlated and high-power balance propagation channels show better performances than high correlated and power unbalance channels in terms of spectral efficiency. Given these results, it will be fundamental to take into account the spectral efficiency of D-MIMO systems when designing criteria to establish multi-connectivity in future mobile network deployments.

Boundary layers in turbulent vertical convection at high Prandtl number

Many environmental flows arise due to natural convection at a vertical surface, from flows in buildings to dissolving ice faces at marine-terminating glaciers. We use three-dimensional direct numerical simulations of a vertical channel with differentially heated walls to investigate such convective, turbulent boundary layers. Through the implementation of a multiple-resolution technique, we are able to perform simulations at a wide range of Prandtl numbers ${Pr}$ . This allows us to distinguish the parameter dependences of the horizontal heat flux and the boundary layer widths in terms of the Rayleigh number $\mbox {{Ra}}$ and Prandtl number ${Pr}$ . For the considered parameter range $1\leq {Pr} \leq 100$ , $10^{6} \leq \mbox {{Ra}} \leq 10^{9}$ , we find the flow to be consistent with a ‘buoyancy-controlled’ regime where the heat flux is independent of the wall separation. For given ${Pr}$ , the heat flux is found to scale linearly with the friction velocity $V_\ast$ . Finally, we discuss the implications of our results for the parameterisation of heat and salt fluxes at vertical ice–ocean interfaces.

Interface Tracking Investigation of the Sliding Bubbles Effects on Heat Transfer in the Laminar Regime

Helium gases are utilized to remove fission products from the molten salt fast reactor (MSFR) core during operation. Helium gases and other volatile fission products may be introduced into the intermediate heat exchanger channels. The effect of these gases on heat transfer is essential for the MSFR to operate properly, especially in laminar flow regimes. The computational fluid dynamics code PSI-BOIL was selected to examine this problem because of its interface tracking capability. A periodic square duct simulation created the flow regime, resulting in a sliding bubble regime. Following that, we examined the impact of heat transfer using an extended nonperiodic channel simulation with a succession of corner bubble arrays. Due to the combined effects of low thermal diffusivity and laminar flow characteristics, it is shown that the length of heat transfer augmentation may extend to at least five bubble diameters downstream of the bubble placement. Finally, we examined the impact of interphasic heat transfer between an inert gas and a liquid. The bulk of the heat transfer amplification effect was due to the motion of the bubbles rather than interphasic heat transfer.

Practical distributed quantum information processing with LOCCNet

Distributed quantum information processing is essential for building quantum networks and enabling more extensive quantum computations. In this regime, several spatially separated parties share a multipartite quantum system, and the most natural set of operations is Local Operations and Classical Communication (LOCC). As a pivotal part in quantum information theory and practice, LOCC has led to many vital protocols such as quantum teleportation. However, designing practical LOCC protocols is challenging due to LOCC’s intractable structure and limitations set by near-term quantum devices. Here we introduce LOCCNet, a machine learning framework facilitating protocol design and optimization for distributed quantum information processing tasks. As applications, we explore various quantum information tasks such as entanglement distillation, quantum state discrimination, and quantum channel simulation. We discover protocols with evident improvements, in particular, for entanglement distillation with quantum states of interest in quantum information. Our approach opens up new opportunities for exploring entanglement and its applications with machine learning, which will potentially sharpen our understanding of the power and limitations of LOCC. An implementation of LOCCNet is available in Paddle Quantum, a quantum machine learning Python package based on PaddlePaddle deep learning platform.

Measurements and Characterization for Millimeter-Wave Massive MIMO Channel in High-Speed Railway Station Environment at 28 GHz

The millimeter-wave (mmWave) and massive multiple-input multiple-output (MIMO) wireless communication technologies provide vital means to resolve many technical challenges of the fifth-generation (5G) or beyond 5G (B5G) network. Analyzing the measured datasets extracted from the channel measurements can provide insight into the characteristics of radio channels in different scenarios. Therefore, mmWave massive MIMO channel measurements, simulation, and modeling are carried out in the high-speed railway waiting hall environments at 28 GHz. The multipath components (MPCs) parameters are estimated for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios based on the space-alternating generalized expectation-maximization (SAGE) algorithm. Delay spread (DS), azimuth angle of arrival (AAoA), and elevation angle of arrival (EAoA) are analyzed. And they are processed by using the K-mean algorithm. In addition, propagation characteristics are simulated based on the improved ray tracing method of shooting and bouncing ray tracing/image (SBR/IM). The correctness of the improved ray tracing method is verified by comparing the measured results with the simulated results. The large-scale path loss (PL) is characterized based on close-in (CI) free-space reference distance model and the floating-intercept (FI) path loss model. Furthermore, statistical distributions for root-mean-square delay spread (RMS DS) are investigated. The Gaussian distribution best fits the measured data of RMS delay spread. Finally, multipath clustering is identified using the multipath component distance (MCD). The analysis of these results from mmWave massive MIMO channel measurements and simulation may be instructive for the deployment of the 5G or B5G wireless communications systems at 28 GHz.

Wideband hybrid precoding techniques for THz massive MIMO in 6G indoor network deployment

Terahertz (THz) communication is becoming an up-and-coming technology for the future 6G networks as it offers an ultra-wide bandwidth. Appropriate channel models and precoding techniques are indispensable to support the desired coverage and to resolve the severe path loss in THz signals. Initially, in this work, the Sub-THz channel (140 GHz) response is investigated by using NYUSIM Channel Simulator for 6G indoor office scenario.The major highlight will be on radio propagation mechanisms, which impact the network performnace in the form of path-loss, received power, time delays, azimuth AoD, Azimuth AoA, Elevation AoD, Elevation AoA and RMS delay in LOS environments. Recent hybrid precoding techniques depending upon frequency-independent phase-shifters not able to cope up with the beam split effect in THz massive MIMO systems, where the directional beams will split into various physical directions at various sub-carrier frequencies. The beam split effect will result in a serious array gain loss across the entire bandwidth, which has not been well investigated in THz massive MIMO systems. Therefore, to address this challenge, delay-phase precoding is proposed in this work. We then extensively investigate its diverse number of time delayers, varying number of antenna elements, and comparison with frequency—mmWave and Sub-THz have been discussed. Finally, the proposed delay-phase precoding techniques outperforms the other existing narrowband and wideband precoding techniques. Therefore,it is an effective technique to implement the future 6G indoor communication network deployment.

Experimental measurements on the effect of vehicle movement direction on received signal power in V2V communication

Vehicle-to-Vehicle (V2V) communication has been a popular topic in recent years. V2V communication channel measurements in different environments and scenarios have been performed to reveal the effect of different parameters such as vehicles, buildings, or trees. However, vehicle movement direction is generally neglected when the measurement data are analyzed. In this study, V2V channel measurements were carried out in open roads similar to a highway but with less traffic. The measurement data are divided into two groups: the vehicles approaching each other and moving away from each other. The effect of vehicle movement direction on the received signal power is indicated by comparing the received signal power values of these two groups. The results show that the received signal power differs depending on vehicle movement direction. However, according to our findings, it is not clear which movement direction causes more path loss. The authors suggest that vehicle movement direction should be taken into account in analyzing, modeling, and simulations of V2V communication channel.

Generation of Overspill Pyroclastic Density Currents in Sinuous Channels

AbstractDue to their mobility, high velocities, and common occurrence, small‐volume pyroclastic density currents (PDCs) represent a major hazard around volcanoes. Small‐volume events are particularly sensitive to topography and channelization into drainage basins. Understanding the flow transition initiated by avulsion or overspill from valley confined PDC to unconfined PDC is necessary to mitigate their damage. We present three‐dimensional multiphase models of channelized PDCs and link the generation of overspill currents to channel geometry (width, depth, and curvature). Our simulation geometries span the range of natural channels commonly found in stratovolcanic landforms. Channels help inhibit ambient air entrainment into the underflow and can maintain and deliver material with minimal cooling during transport. We show that the main avulsion mechanism can include significant portions of the insulated underflow layer from the channel leading to a dangerously hot overspilled current. In all sinuous channel simulations, the underflow of the current becomes superelevated when it encounters bends and is able to overwhelm channel walls. The amount of mass overspilled is a function of channel curvature. Superelevation of the current increases with channel curvature and decreasing channel width but is underestimated using traditional estimates of superelevation due to the lack of the free surface in these flows. We also identify the occurrence of buoyant plume and secondary overspill events due to cross stream flow within the channel which would produce complex deposits associated with overspill events.

Incoherent ultrarelativistic channeling particle scattering by electrons

The problem of high-energy charged particle motion in the field of atomic strings and planes of oriented crystals, widely applied to control large accelerator beams and generate intense gamma radiation, is addressed. Following the previously developed theory of channeled particles incoherent scattering by crystal atom nuclei, we consider here the same by crystal atom electrons. The theory developed takes into consideration all the effects of momentum transfer between fast particles and electrons of atoms in a crystal in the range from the nuclear radius up to the many inter-atomic distances. The theory also includes the temperature-dependent Debye – Waller factor, as well as both the atomic form factors and scattering function, evaluated with the detail consideration of atomic structure. All the modifications of electron scattering in crystals are reduced to the value of the effective minimum momentum transfer, which by an order of value exceeds that one, related with the Bethe – Bloch mean atomic energy. Substituting this quantity to the expression for the mean square of the scattering angle of a classically moving particle makes it possible to compare the scattering by electrons and nuclei, while its joint use with the Rutherford cross section allows for the correct simulations of the planar channeling of positively charged particles in the thickest crystals, supposed to be used for the beam extraction from high energy accelerators, measurement of electromagnetic characteristics of short-living particles and development of intense narrow-band X-ray and gamma radiation sources based on crystal undulators.

Discrete-Particle Model to Optimize Operational Conditions of Proton-Exchange Membrane Fuel-Cell Gas Channels.

Operation of proton-exchange membrane fuel cells is highly deteriorated by mass transfer loss, which is a result of spatial and temporal interaction between airflow, water flow, channel geometry, and its wettability. Prediction of two-phase flow dynamics in gas channels is essential for the optimization of the design and operating of fuel cells. We propose a mechanistic discrete particle model (DPM) to delineate dynamic water distribution in fuel cell gas channels and optimize the operating conditions. Similar to the experimental observations, the model predicts seven types of flow regimes from isolated, side wall, corner, slug, film, and plug flow droplets for industrial temporal and spatial scales. Consequently, two-phase flow regime maps are proposed. The results suggest that an increase in water accumulation in the channel is related to the increase in the water cluster density emerging from the gas diffusion layer rather than the increased water flow rate through constant water pathways. From a modeling perspective, the DPM replicated well volume-of-fluid channel simulation results in terms of saturation, water coverage ratio, and interface locations with an estimated 5 orders of magnitude increase in calculation speed.

Molecular dynamics simulation of TMEM16A channel: Linking structure with gating

TMEM16A, the calcium-activated chloride channel, is broadly expressed and plays pivotal roles in diverse physiological processes. To understand the structural and functional relationships of TMEM16A, it is necessary to fully clarify the structural basis of the gating of the TMEM16A channel. Herein, we performed the protein electrostatic analysis and molecular dynamics simulation on the TMEM16A in the presence and absence of Ca2+. Data showed that the separation of TM4 and TM6 causes pore expansion, and Q646 may be a key residue for the formation of π-helix in the middle segment of TM6. Moreover, E705 was found to form a group of H-bond interactions with D554/K588/K645 below the hydrophobic gate to stabilize the closed conformation of the pore in the Ca2+-free state. Interestingly, in the Ca2+ bound state, the E705 side chain swings 100o to serve as Ca2+-binding coordination and released K645. K645 is closer to the hydrophobic gate in the calcium-bound state, which facilitates the provision of electrostatic forces for chloride ions as the ions pass through the hydrophobic gate. Our findings provide the structural-based insights to understanding the mechanisms of gating of TMEM16A.

Turbulent drag reduction over liquid-infused textured surfaces: effect of the interface dynamics

Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformation. The flow conditions consider a viscosity ratio , several values of the micro-ridge pitch and two different Weber numbers, We = 0 and We = 50. The performance is analyzed in terms of drag reduction (DR) with respect to an equivalent smooth channel, and the results compared with those available for super-hydrophobic surfaces (SHS). It is found that, due to the relatively high viscosity of the liquid locked in the substrate, the drag reduction offered by LIS is substantially lower than the corresponding SHS. When reported in terms of the streamwise slip length normalized in wall units, the amount of DR obtained by LIS in the ideal case of flat interface collapses on the SHS data. The interface dynamics has a detrimental effect on the performance, that becomes particularly severe when the pitch increases. The degradation of DR is well parametrized by the log-law shift of the velocity profile, that is found to be proportional to the difference between the virtual origin of the mean flow and that experienced by the overlying turbulence.

Predictions of flame acceleration, transition to detonation, and detonation propagation using the Chemical-Diffusive Model

This paper presents numerical simulations of the evolution of premixed flames in channels with obstacles using the Chemical-Diffusive Model (CDM) coupled to a compressible Navier-Stokes solver. The CDM is a parametric model for chemical reaction and diffusive transport, and it is calibrated to reproduce a set of properties of one-dimensional laminar flame and the Zel’dovich-Neumann-Döring (ZND) detonation. In this work, we use two different CDMs, one calibrated using the theoretical half-reaction distance of the ZND detonation and the other calibrated with the experimental detonation cell size, to simulate a stoichiometric hydrogen-air mixture and investigate flame acceleration, deflagration-to-detonation transition (DDT), and detonation propagation in obstacle-laden channels. As the channel geometry varies, both CDMs predict propagation of fast flames in the choking, quasi-detonation, and CJ-detonation regimes. When the channel width is much greater or smaller than the minimal scale requirement for the onset of DDT, both CDMs predict similar choked fast flames and CJ detonations. In cases where the channel widths are close to the critical conditions, deflagration waves are more likely to undergo DDT if the CDM is calibrated for the half-reaction distance, which produces smaller computed detonation cells than experiments. In numerical simulations of channels with the same geometries as prior experiments, using the cell size-constrained CDM improves predictions of DDT.

Cloud‐Radiation Interactions and Their Contributions to Convective Self‐Aggregation

AbstractThis study investigates the direct radiative‐convective processes that drive and maintain aggregation within convection‐permitting elongated channel (and smaller square) simulations of the UK Met Office Unified Model. Our simulations are configured using three fixed sea surface temperatures (SSTs) following the Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) protocol. By defining cloud types based on the profile of condensed water, we study the importance of radiative interactions with each cloud type to aggregation. We eliminate the SST dependence of the vertically integrated frozen moist static energy (FMSE) variance budget framework by normalizing FMSE between hypothetical upper and lower limits based on SST. The elongated channel simulations reach similar degrees of aggregation across SSTs, despite shortwave and longwave interactions with FMSE contributing less to aggregation as SST increases. High‐cloud longwave interactions are the main drivers and maintainers of aggregation. Their influence decreases with SST as high clouds become less abundant. This SST dependence is consistent with changes in grid spacing and the critical humidity threshold for condensation (RHcrit). However, the domain‐mean longwave‐FMSE feedback would likely decrease as grid spacing and RHcrit are reduced by lowering the condensed water path and cloud top height of high‐cloud, and altering the distribution of different cloud types. Shortwave interactions with water vapor are key maintainers of aggregation and are dependent on SST and the degree of aggregation itself. The analysis method used provides a new framework to compare the effects of radiative‐convective processes on self‐aggregation across different SSTs and model configurations to help improve our understanding of self‐aggregation.

Numerical simulation and optimization of centrifugal compressor return channels: methods and results

The authors actively use their engineering Universal Modelling Method for gas-dynamic design of centrifugal compressors for industrial partners. Currently, there are two approaches to improving the Method: improving the preliminary design and increasing the accuracy of gas-dynamic characteristics calculation. Computational Fluid Dynamics (CFD) methods give good results for the flow path stator part. Recently, massive CFD calculations of the vaneless diffusers (VLD) characteristics were generalized by a system of algebraic equations, which replaced the previous more complex mathematical model in the Method. Then, based on CFD optimization of a large series of return channels (RCh), corrections were made to the preliminary design of this element of the flow path.This paper presents the results of the joint CFD optimization of a vaneless diffuser and a return channel. Stator elements have many geometric parameters. For a stage with the flow rate coefficient of 0.0597 and the loading factor of 0.60, only the VLD relative radial length D 4/D 2, the number and the inlet angle of the return channel vanes were optimized. Engineering calculations and design experience predicted an optimal value of D 4/D2 within the interval 1.9 - 2.0. CFD optimization demonstrated almost linear reduction of the total head loss towards the end of the investigated range D 4/D2 = 2.3. After careful optimization of the U-bend, the optimization of D 4/D2 was repeated. The influence of on the loss coefficient has decreased, but the value of D 4/D 2 = 2.3 is still far from optimum. It significantly exceeds technically acceptable radial size. The result obtained influenced the design plan of future calculation experiments with a large series of stator elements of the stages in a practically significant range of design parameters.

Multiscale Modeling of Meandering Fluvial Reservoir Architecture Based on Multiple-Point Geostatistics: A Case Study of the Minghuazhen Formation, Yangerzhuang Oilfield, Bohai Bay Basin, China

Meandering river reservoirs are essential targets for hydrocarbon exploration, although their characterization can be complex due to their multiscale heterogeneity. Multipoint geostatistics (MPS) has advantages in establishing reservoir architectural models. Training image (TI) stationarity is the main factor limiting the uptake of MPS modeling algorithms in subsurface modeling. A modeling workflow was designed to reproduce the distribution of heterogeneities at different scales in the Miocene Minghuazhen Formation of the Yangerzhuang Oilfield in the Bohai Bay Basin. Two TIs are established for different scales of architecture. An initial unconditional model generated with a process-based simulation method is used as the megascale TI. The mesoscale TI of the lateral accretion layers is characterized by an uneven spatial distribution of mudstone in length, thickness, frequency, and spacing. Models of different scales are combined by the probability cube obtained by lateral accretion azimuthal data as an auxiliary variable. Moreover, the permeability function sets are more suitable than the porosity model for collaboratively simulating the permeability model. Model verification suggests this workflow can accurately realize the multiscale stochastic simulation of channels, point bars, and lateral accretion layers of meandering fluvial reservoirs. The produced model conforms geologically realistically and enables the prediction of interwell permeability variation to enhance oil recovery.

Verification of an Intelligent Ray Launching Algorithm in Indoor Environments in the Ka‐Band

AbstractThis paper presents the verification of indoor propagation channel simulations based on an intelligent ray launching algorithm (IRLA) in the Ka‐band of the millimeter‐wave (mmWave) spectrum in various indoor environments, including a classroom, an office, and a corridor, by radio channel measurements. Power delay profiles (PDPs), path loss, and root‐mean‐square (RMS) delay spreads were obtained from both the simulation results and the measurement results. Moreover, parameters of two site‐general path loss models, the close‐in free space reference distance path loss model and the floating‐intercept path loss model, were estimated based on the measured and simulated path loss. The comparison between the simulation results and the measurement results indicates that the IRLA‐based simulation can accurately describe the main characteristics of the indoor propagation channel in the Ka‐band.

An experimental research on the net output power and current density distribution of PEM fuel cells with trapezoid baffled flow fields

The net output power and current density distribution uniformity of proton exchange membrane (PEM) fuel cells are particularly important evaluation criteria in the flow field design. In recent years, the flow field with baffles has become research hotspots, and the trapezoid baffled flow field has been proved to increase the performance of fuel cells. However, most of the research studies only stay at the level of single flow channel simulation and little experimental data on the flow field of the entire bipolar plate. In this study, the performance, pressure drop, and current density distribution of PEM fuel cells with different baffled flow field plates are tested experimentally. The results indicate that adding baffles in the conventional parallel flow field can significantly improve the output performance and current density distribution uniformity of the fuel cell, and the improvement effect is better with the increase in baffle height. However, increasing the baffle height will inevitably raise the pressure drop of the flow field. To solve this problem, the flow field with a half baffle arrangement is innovatively designed. The proposed half-baffled flow field can keep the uniformity of current density distribution and reduce the pressure drop at the same time. This method provides a new inspiration for the design of the flow field.