Discrete Phase Research Articles

Robust Beamforming Design for an IRS-Aided NOMA Communication System With CSI Uncertainty

Intelligent reflecting surface (IRS) is a promising technology that provides high throughput in future communication systems and is compatible with various communication techniques, such as non-orthogonal multiple-access (NOMA). This paper studies the downlink transmission of IRS-assisted NOMA communication, considering the practical case of imperfect channel state information (CSI). Aiming to maximize the system sum rate, a robust IRS-aided NOMA design is proposed to jointly find the optimal beamforming vector for the access point and the passive reflection matrix for the IRS. This robust design is realised using the penalty dual decomposition (PDD) scheme, and it is shown that the results have a close performance to their upper bound obtained from the corresponding perfect CSI scenario. The presented method is compatible with both continuous and discrete phase shift elements of the IRS. Our findings show that the proposed algorithms, for both continuous and discrete IRS, have low computational complexity compared to other schemes in the literature. Furthermore, we conduct a performance comparison between the IRS-aided NOMA and the IRS-aided orthogonal multiple access (OMA). This comparison shows that robust beamforming techniques are crucial for the system to reap the advantages of IRS-aided NOMA communication in the presence of CSI uncertainty.

Numerical prediction of cavitation nuisance on hydrofoils: Combined analysis of cavity dynamics and the aggressiveness of collapsing cavitating structures

The unsteady cavitating flow past a three-dimensional twisted hydrofoil is numerically investigated by a large eddy simulation to obtain in-depth insight into the bubble dynamics near the cavitation erosion region. Macroscopic cavity evolution is captured by a multiphase flow computing frame, while the bubble oscillations in the cavitating flow are computed by solving the Gilmore bubble dynamic model, in which the driving force for the bubble movement is exported through the application of a discrete phase model. The cavitation erosion potential is then computed by a robust indicator developed based on the energy balance hypothesis. The relevance between the dynamics and the destructive essence of a cavitation bubble and the erosion intensity is thoroughly analyzed. The results show that the unsteadiness involved in the turbulent cloud cavitation is well reproduced, and the main cavitation erosion risk in the middle region of the hydrofoil is also accurately predicted comparing with the painting test results. A localized high-pressure region is identified near the rear part of the attached cavity where the mainstream encounters the primary reentrant jet flows. The peak bubble internal pressure can reach 487 MPa near the middle plane of the hydrofoil, during the stage when the surrounding liquid pressure is continuously increased. The bubbles with the smallest radius, ranging from 23.1 to 26.3 μm after compressing from their initial sizes (R0 = 100–700 μm) in the near wall region, are associated with the extremely high internal pressure, and they are responsible for the cavitation erosion damage on the hydrofoil surface.

Optimal Passive Beamforming for Reconfigurable Intelligent Surface-Assisted Communications With Discrete Phase Shifts

Optimal Passive Beamforming for Reconfigurable Intelligent Surface-Assisted Communications With Discrete Phase Shifts

Numerical investigation on design parameters of orifice plate for positioning of workpiece in cavitation zone for cavitation machining

ABSTRACT The recent development of non-traditional machining techniques, such as cavitation machining (CM), has been gaining traction amongst researchers due to its sustainable nature. The present research focuses on the use of computational fluid dynamics (CFD) model to predict the location of workpiece in the fluid domain and bubble distribution during CM process. For efficient CM, the correct positioning of a workpiece in cavitation zone is essential, as the implosion of the cavity bubble leads to formation of micro-jet and shock waves for a few milli-to-microseconds generating high temperature and pressure on workpiece. The aim is to harness cavitation phenomena in material processing, particularly by using orifice plates as a common tool to induce hydrodynamic cavitation. To generalise the investigation, the flow simulation through orifice plate with different aspect ratios (l/d) are carried out. For the bubble distribution and their diameters, the Lagrangian discrete phase model (DPM) is used in the downstream side of the flow domain. Using this information, bubble dynamics have also been investigated using the Keller–Miksis (KM) model to compute the implosion time and intensity in the zone. The presented exploration determines the orifice dimensions to optimize implosion intensity, ensuring precise workpiece placement in real-time CM.

CFD Analysis for Valve-Holding Camber Permanent Inhaler Spacer (AerospaAcer) with Different Valves

During the COVID-19 pandemic, data statistics showed that patients with respiratory problems become infected. One of the therapy techniques for the respiratory condition was the use of a metered-dose inhaler and spacer. The objective of this paper is to determine the flow parameters of three types of valves which is duckbill valve, cross slit valve and umbrella valve in inhaler spacer to compare fluid flow between valve Previous researchers chose the duckbill valve to control fluid flow in inhaler spacer. The flow characteristics are unaffected by the materials used in the new disposable inhaler spacers, such as paper and polylactic acid (PLA). Several design valves reduced the skewness below 0.94 by suppressing the fillet and chamfer. ANSYS Workbench Fluent 19.2 is used to calculate flow parameters such as turbulence kinetic energy (TKE), turbulence eddy dissipation (TED), velocity, particle velocity magnitude, streamline, and vector velocity. The setup input data is based on the previous researcher's specified parameters such as viscosity model, drug characteristics (salbutamol and propellant), discrete phase model (DPM) equal to 80, boundary condition model, and SIMPLE technique. For the three types of valves, the nozzle injection used a 0.50-millimetre dimension. The simulation work is cross-checked against the results of prior simulations. Within each iteration, the transient flow employed a time step size of 0.01 for 200 steps. The results show that computational analysis can distinguish between models of varying complexity. The TED, TKE, and velocity graphs showed the approximate value between the model geometries. Overall, the study was successful in achieving the desired velocity magnitude in terms of visual and graph representations of the various valve.

Hydrothermal performance and entropy production rate of rGO-CO3O4/H2O hybrid nanofluid in corrugated-converging pipes

The ever-growing interest in developing more effective and compact heat exchangers necessitates the investigation of combined passive solutions. Despite the diverse related literature, there are no studies on corrugated-converging pipes. This work examines the effect of Reynold's number (5.0×103≤Re≤5.0×104), diameter ratio (1≤DR≤2), and concentration of nanoparticle (0≤VR≤0.2%), on the Poiseuille number (fRe), average Nusselt number (Nu), performance evaluation criterion (PEC), and EPR of rGO−CO3O4/ H2O hybrid nanofluid (NF) flowing in corrugated-converging pipes of different orientations (inwardly and outwardly) and smooth converging pipes in turbulent flow regime. The k−ω and discrete phase models were used to simulate the turbulent hybrid NF flow by Ansys Fluent. The results revealed that the Nu in the corrugated converging pipe is higher than that of a smooth pipe, but this is accompanied by a higher pressure drop (dP). The argumentation of Nu is attributed to flow acceleration, thinning of the thermal boundary layer (TBL), and an increase in the rate of mixing as a result of the relative increase in turbulence introduced by the presence of corrugation. In addition, it was noted that the modified pipes have lower EPR due to temperature gradient (TEPR) compared with straight pipe. However, the opposite is the case for EPR due to fluid flow (VEPR). The lower TEPR and higher VEPR are attributed to a relative increase in flow turbulence. Quantitatively, the normalized values (referencing smooth pipe) of Nu, (fRe), TEPR, and VEPR at Re=5×103 in inwardly and outwardly corrugated converging pipes and smooth converging pipes of DR = 2 are {2.24, 8.15×101, 4.13×10−1, and 8.62×101}, {1.94, 4.45×101, 4.78×10−1, and 4.15×101} and {1.03, 3.1×101,9.20×10−1, and 3.17×101}, respectively. PEC increases with increasing VR. For instance, across the range of VR considered (0 % ≤ VR ≤ 0.2 %), the values of PEC increase by 20.69 %. Consequently, it can be presented as a promising heat transfer enhancement technique in terms of energy saving. Consequently, corrugated-converging pipes can be presented as a promising heat transfer enhancement technique in terms of energy saving.

Numerical simulation of gas-solid flow in a cyclone separator with additional inlet

In this study, an additional inlet was added to the gas-solid cyclone separator to enhance the separation efficiency. Four different heights were tested, including 0.95D, 1.4D, 1.5D, and 1.95D (D is the diameter of the cylindrical section). The investigation involved two inlet flow conditions: increasing and dividing the inlet flow rate. The finite volume method and Reynolds stress turbulence model were used to solve the averaged Navier–Stokes equations, whereas the Eulerian–Lagrangian approach and discrete phase model (DPM) were applied to track particles with a uniform diameter of 0.5–1.8 microns as the discrete phase. Owing to the low Stokes number and small and low-volume-fraction particles, a one-way coupling method was employed between air and the particles. The addition of an additional inlet reduced the static pressure in the center and downstream areas and increased the reverse flow velocity at the end of the cyclone. The installation of an additional inlet at 0.95D had the most positive effect on the separation efficiency, with an increase of 28.8% in the increasing flow rate case and 19.6% in the dividing flow rate case compared with the cyclone without an additional inlet. Furthermore, the increase in the separation efficiency of the submicron particles was greater than that of the larger particles in both flow distribution cases.

Active multi-focus vortex beam terahertz encoding metasurface based on Dirac semimetals.

An electromagnetic wavefront can be flexibly manipulated by discrete phase coding on the coding unit. In this paper, we designed two coding metasurfaces with 1-bit and 3-bit based on active tuning of Dirac semimetals by controlling the Fermi level (E F) with an external polarization voltage. The size and structure of the metasurface remain unchanged with this strategy. Both designs were found to be dynamically tunable. The 1-bit coding metasurface enables beam conversion, single-focus switching, and switching between single-focus and multi-focus. On the other hand, the 3-bit coding metasurface enables the switching between vortex beams and single-beam mirror reflections. These proposed structures have potential applications in terahertz (THz) communications and terahertz-focused imaging, opening up new possibilities for the dynamic modulation of THz waves.

Tomographic Universality of the Discrete Wigner Function

We observe that the discrete Wigner functions (DWFs) of n-partite systems with odd local dimensions are tomographically universal, as reflected in the delta function form of the DWF for any stabilizer. However, in the n-qubit case, this property does not hold due to the non-factorization of the mapping kernel, the explicit form of which depends on a particular partition of the discrete phase space. Nonetheless, it turns out that the DWF for some specific stabilizers, not included in the set used for the construction of the Wigner map, takes on the form of a delta function. This implies that the possibility of classical simulations of Pauli measurements in a given stabilizer state for qubit systems is closely tied to the experimental setup.

A novel transparent cabin used in the classroom during the coronavirus pandemic: a CFD analysis

A coronavirus family is a diverse group of many viruses. Coronavirus disease 19 (COVID-19) spreads when an infected person breathes out droplets and very small particles that contain the virus. These droplets and particles can be breathed in by other people or land on their eyes, noses, or mouths. In this paper, the airflow distribution and the movement of coronavirus particles during normal breathing and sneezing in classrooms have been studied using a CFD model developed in ANSYS® 2022R2. The objective is to find ways to control the spread of the virus that enable us to practice academic activity and deal normally with the pandemic and the spread of the disease. Experiments were done with more than one turbulence model to know which was closest to the experiments as well as to determine the best number of meshes in the classroom. The effect of turbulent dispersion on particles is resolved using a discrete random walk model for the discrete phase and the RANS model for the continuous phase in a coupled Eulerian–Lagrangian method. Furthermore, that is done in two scenarios: the first is to find the best ventilation configuration by investigating the following parameters: the effect of air change per hour, the height of the air inlets and outlets, and the infected student's position. The second is to control the spread of the coronavirus in the classroom in the event of sneezing from an infected student by placing cabins and an air filter with optimal design installed at the top around each student. It was found that optimal ventilation is achieved when fresh air enters from the side walls of the classroom at a distance of 1 m from the floor and the air exits from the ceiling in the form of two rows, and the rate change of air per hour (ACH) is 4, which leads to energy savings. In addition, a novel transparent cabin is designed for the student to sit in while in the classroom, consisting of a high-efficiency particulate air filter (HEPA) that collects any contamination and recirculates it from the top of the cabin back into the classroom with different fan speeds. Through this study, this cabin with a filter was successfully able to prevent any sneeze particles inside from reaching the rest of the students in the classroom.

Study of the performance of an adiabatic cooling pad in an air cooler system

Adiabatic cooling pads are mostly used as a previous step for cooling systems, they cause the raise of the cooling system global efficiency. In this study, several types of pads have been analysed regarding on its compactness and thickness. The problem is addressed from an experimental, analytical and numerical point of view.. The validation of the temperature drop and cooling efficiency of the cooling pad numerical model is the main objective of this paper, and, in order to get this goal, Discrete Phase Model (DPM) of ANSYS Fluent software is used to calculate how water droplets, injected over the pad to cool the air, evaporate and how the continuous phase affect them. The results of this paper, focused to be a part of a complete cooling system analysis carried out by the research group, show the performance of an adiabatic cooling pad varying its width and compactness.

Fieldnotes as never really ‘raw’ data: Analysing the social life of public space on London's South Bank

AbstractUnlike for other forms of qualitative data, examples of how fieldnotes are analysed are rarely provided in the literature. Using fieldnotes from my ethnographic study of the production of public space on London's South Bank as a starting point, this paper considers why this might be the case. In particular, the paper argues that for fieldnote‐based research, analysis is a feature of note‐taking, rather than a discrete phase of activity conducted using our fieldnotes once they have been collected. In this vein, the paper encourages researchers to be aware of the analytical in their fieldnotes, and to be open to the ways that analysis inside the notebook can help us identify salient objects of enquiry in our work.

Mechanism evaluations of conventional and suspended HVOF thermal spraying based on EDC and EDM combustion models

Suspended high-velocity oxygen fuel (SHVOF) thermal spraying technology can spray solid particles with nano or sub-micron scale, and effectively prepare high quality coatings by wrapping solid particles into suspension with solvent. The HVOF and SHVOF processes are numerically simulated in this study. The gas phase and discrete phase were simulated by the bidirectional coupling Euler-Lagrange method. The state equation of ideal gas and realizable k-ε turbulence model were used to simulate gas phase flow. The effect of eddy dissipation model (EDM) and eddy dissipation concept (EDC) model on turbulent combustion reaction was discussed. Due to that EDM model simplifies the Arrhenius rate of different reactions, there are errors in the prediction of spraying combustion process. To solve the problem, the chemical kinetic mechanism of multi-component combustion reaction for the propylene, ethanol and oxygen was introduced in EDC model for the first time in this study. This method has not yet been used in the modeling of thermal spraying. The suspended droplets are a mixture of ethanol and WC-12Co powder. Results show that the atomization and evaporation of suspension significantly disturb the flow field and reduce the internal pressure and temperature of spray gun. Compared with the EDM model, the EDC model can well predict the peak temperature in the combustion chamber, the prediction of particle temperature and velocity is higher, and the temperature and velocity decay are slower during flight. Compared with the median particle size d50 in actual, two combustion models can effectively predict the median particle size after drying, which is the premise of accurately predicting the flight characteristics of particles.

Effects of axial misalignment welding defects on the erosive wear of natural gas piping

When considering solid particles in the pipe and axial misalignment weld defects in natural gas transmission systems, changes in the flow field due to structural differences can lead to various erosion characteristics in the bends. To investigate the erosion process within the bend, the computational fluid dynamics (CFD) - discrete phase model (DPM) method to develop a bend model with axial misalignment weld seam defects was employed. The erosion distributions of a bend with an axial misalignment weld were investigated under various transport parameters, bend orientation, axial misalignment height, and particle incidence angle. The results indicated that the erosion rate of the outermost elbow increases with the increase of the height of the axial misalignment weld on the outside of the bend pipe. When the axial misalignment height ranges from 1 mm to more than 5 mm, the difference in the maximum erosion rate escalates from 7 % to approximately 30 %. When the length of the inlet straight pipe is shorter, an increased incident angle intensifies the erosion effect and vice versa. This research can provide a reference for field construction work involving defective natural gas pipe bends.

Deeper Flow Behavior Explanation of Temperature Effects on the Fluid Dynamic inside a Tundish

The continuous casting tundish is non-isothermal due to heat losses and temperature variation from the inlet stream, which generate relevant convection forces. This condition is commonly avoided through qualitative fluid dynamic analysis only. This work searches to establish the conditions for which non-isothermal simulations are mandatory or for which isothermal simulations are enough to accurately describe the fluid dynamics inside the tundish by quantifying the buoyant and inertial forces. The mathematical model, simulated by CFD software, considers the Navier-Stokes equations, the realizable k-ε model for solving the turbulence, and the Lagrangian discrete phase to track the inclusion trajectories. The results show that temperature does not significantly impact the volume fraction percentages or the mean residence time results; nevertheless, bigger velocity magnitudes under non-isothermal conditions than in isothermal conditions and noticeable changes in the fluid dynamics between isothermal and non-isothermal cases in all the zones where buoyancy forces dominate over inertial forces were observed. Because of the results, it is concluded that isothermal simulations can accurately describe the flow behavior in tundishes when the flow control devices control the fluid dynamics, but simulations without control devices or with a weak fluid dynamic dependence on the control devices require non-isothermal simulations.

Fuel-clad interactions: Uranium nitride and uranium dioxide with FeCrAl and Ti-modified stainless steel

This study elucidates on the compatibility of fuel and clad materials for potential use in lead cooled fast reactors. Diffusion couples were performed on representative, unirradiated fuel forms (UN and UO2) with potential cladding materials, a Ti-modified stainless steel (D9) and a FeCrAl alloy (Kanthal APMT). Temperatures of 800–1200°C, with durations up to 100 h, were investigated. Chemical interaction between all combinations of the fuel and cladding candidates was found to be minimal, with no diffusion gradients observed or extensive interface phases formed. When interaction occurred, it was in the production of a minor discrete phase. At the highest temperatures, D9 with UN resulted in the formation of a Ti-C-N phase. D9 with UO2 resulted in the formation of a Ti-C-O phase. FeCrAl with UN resulted in the formation of an Al-N phase. FeCrAl with UO2 results in the formation of an Al-O phase. Despite the observed mechanical bonding between fuel and cladding material, no evidence of any chemical interaction with the uranium in the fuel material was found. At the higher temperatures investigated (>1000°C) there was evidence of clad softening resulting in transfer of material to the fuel surface.

Research on snow prevention in the bogie region based on active blowing method

To reduce excessive snow accumulation on bogie surfaces during high-speed train operations in cold regions, two active blowing schemes are designed in this study based on the shape of the bogie cavity and the relative position of the brake caliper. The unsteady Reynolds-averaged Navier–Stokes algorithm coupled with a discrete phase model was used to calculate the airflow and snow flow under the train. Moreover, the algorithm is employed to explore the impact of active blowing on the flow field characteristics and snow accumulation in the bogie region. Results show that active blowing changes the upward airflow in the bogie region, causing air at the bottom of the train to flow outwards, carrying off numerous snow particles from the bogie region. Active blowing accelerates the surface friction velocity on the bogie, increases the shear force on snow particles, and effectively reduces the snow accumulation on the bogie surface. The foregoing observation indicates that active blowing has considerable potential for snow accumulation prevention.

Modeling of Motion of Inclusions in Argon‐Stirred Steel Ladles

A 3D discrete phase model (DPM)‐ and volume of fluid–coupled model is developed to investigate the multiphase flow in a 260 ton argon‐stirred ladle. The flow field and interfacial behavior in the argon‐stirred ladle are accurately predicted. Then, the Lagrangian DPM is used to trace the motion of inclusions in the liquid steel. Residence time maps, which provided the residence time required for inclusions travelling from the bulk liquid steel to the steel–slag interface, are proposed and plotted as functions of inclusion diameter and percentage of inclusions. For inclusions smaller than 10 μm, the average residence time is size‐independent but decreases from 175 to 93 s with an increment in the gas flow rate from 50 to 400 NL min−1. With increasing the inclusion size, the average residence time is dependent on both gas flow rate and inclusion diameter. When the inclusion diameter increases to 1000 μm, the average residence time is almost independent of the gas flow rate. The current model overestimates the inclusion removal rate. However, this overestimation indicates that only appropriately considering the behavior of inclusions at the steel–slag interface can accurately predict the removal of inclusions in argon‐stirred ladles.

Computational analysis of radon progeny deposition patterns in the human respiratory system

In the last year, the use of computational fluid dynamics (CFD) techniques has gained prominence as a powerful tool for modeling biological phenomena and influencing the design of biomedical devices. In this study, we utilized a computational fluid dynamics (CFD) model to simulate airflow and the deposition of aerosol particles within the human respiratory tract. To achieve this, we meticulously constructed a 3D model of the human tracheobronchial airways using SolidWorks software. Our computational analyses encompassed a range of breathing conditions, ranging from 15 to 60 (L/min). Through the application of discrete phase modeling (DPM), we investigate the behavior of two-phase flow dynamics. Our focus lies in the examination of aerosol particles, with diameters ranging from 1 to 10 (μm), in order to evaluate the influence of aerosol particle size on deposition rates. Our findings encompass velocity contour maps, deposition rates of aerosol particles, and insights into the process of aerosol particle entrapment at various locations within the respiratory tract. Our study reveals a direct correlation between higher inhalation rates and larger aerosol particle sizes, resulting in increased deposition rates. Additionally, we observe a heightened deposition of aerosol-particles at bronchi region. These computational results hold significant value in estimating the distribution of doses resulting from radon progeny exposure in distinct anatomical regions of the respiratory tract.

Parametric Investigation of Pelton Turbine Injector under Hydro-abrasive Erosion Conditions

In high-head Pelton turbines, the injector faces severe erosion due to suspended sediment leading to a reduction in turbine efficiency and higher maintenance costs. Here, the effects of design parameters such as the bend angle of the nozzle pipe, nozzle angle, and needle angle along with an operating parameter stroke ratio on hydro-abrasive erosion of Pelton turbine injector are numerically investigated. The Volume of Fluid (VOF) model was implemented for capturing the interphase between air and water; whereas, the SST k-ω model is used for modelling the turbulence effect. For tracking the discrete phase, a Eulerian-Lagrangian based Discrete Phase Model (DPM) is considered. The bend angles led to flow circulations in the nozzle pipe causing the non-uniform distribution of sediment concentration and uneven erosion patterns. Irrespective of the bend angle, the erosion hotspot in the needle is observed toward the bend side. Further, for larger sediment particles, higher bend angles lead to more erosion rate in both the nozzle and needle and must be avoided to prevent excessive damage. As the needle angle increases from 40° to 60° for a constant nozzle angle, the nozzle erosion rate increases by 70% and the needle erosion rate decreases by 99%. Hence, an injector design can be optimized in hydro-abrasive erosion conditions by selecting a needle angle between 40° and 60°. Further, the operation of the injector at too high and low a stroke ratio results in excessive erosion of the nozzle and needle, respectively. In this study, a stroke ratio of 0.45 is found to be the most suitable for hydro-abrasive erosion conditions. Moreover, the asymmetricity in the erosion pattern of the needle increases with needle angle and stroke ratio resulting in jet quality degradation, one major reason for efficiency reduction in Pelton turbines.