Three-dimensional Duct Research Articles

Media Modulation Based Molecular Communication

In conventional molecular communication (MC) systems, the signaling molecules used for information transmission are stored, released, and then replenished by a transmitter (TX). However, the replenishment of signaling molecules at the TX is challenging in practice. Furthermore, in most envisioned MC applications, e.g., in the medical field, it is not desirable to insert the TX into the MC system, as this might impair natural biological processes. In this paper, we propose the concept of media modulation based MC where the TX is placed outside the channel and utilizes signaling molecules already present inside the system. The signaling molecules can assume different states which can be switched by external stimuli. Hence, in media modulation based MC, the TX modulates information into the state of the signaling molecules. In particular, we exploit the group of photochromic molecules, which undergo light-induced reversible state transitions, for media modulation. We study the usage of these molecules for information transmission in a three-dimensional duct system, which contains an eraser, a TX, and a receiver for erasing, writing, and reading of information via external light, respectively. We develop a statistical model for the received signal which accounts for the distribution of the signaling molecules in the system, the initial states of the signaling molecules, the reliability of the state control mechanism, the randomness of irrepressible, spontaneous state switching, and the randomness of molecule propagation. We adopt a maximum likelihood detector and show that it can be reduced to a threshold based detector. Furthermore, we derive analytical expressions for the optimal threshold value and the resulting bit error rate (BER), respectively. Both the statistical model and BER results are verified by computer simulations. Our results reveal that media modulation enables reliable information transmission, validating it as a promising alternative to MC based on molecule emitting TXs.

周期的かく乱を伴う３次元ダクト内バックステップ下流の熱流動特性

The flow and heat transfer characteristics were investigated by numerically simulating backstep flow in a three-dimensional duct with periodic disturbance to the inlet velocity at moderate Reynolds numbers (Re = 625, 700, and 1000). The periodic disturbance was applied to the approximate equation for a well-developed flow by varying the relative amplitude and forcing frequency. The results show that the reattachment position moves upstream as the disturbance increases. Furthermore, as the Reynolds number increased, the amount of change in the reattachment position due to the disturbance became smaller. This change in the reattachment position was more dependent on the forcing frequency than on the relative amplitude, because the meander spacing of the mainstream narrowed as the forcing frequency increased. The spatiotemporally averaged Nusselt number at each Reynolds number increased by 27.2% when a disturbance was applied, compared to the case where no disturbance was applied. This is due to the fact that the higher the disturbance, the more active the heat exchange becomes not only in the flow direction but also in the height direction, resulting in a higher rate of rise. As with the reattachment position, the amount of change became smaller as the Reynolds number increased. These results suggest that the use of the disturbance can be expected to enhance heat transfer at the lower wall.

Numerical investigation on separated turbulent flow in a three-dimensional U-turn duct with spanwise diverging

The flow in a U-turn duct with a 180-degree curved section is a typical model of various applications such as the bend and return channel in multi-stage radial turbo-machines. The flow exhibits complex patterns including the separation on the inner wall, highly sheared flow in the curved and downstream sections, and recovery of deficit flow to uniform flow. Most of current researches focus on the simplified models of two-dimensional plane duct or three-dimensional duct with constant cross-section, while in realistic circumstances the duct can be varying in the shape and area of the cross-section to meet the design requirement. In this work, we performed a numerical investigation on the turbulent flow in a U-turn duct with spanwise diverging at Reynolds number Re = 106. The effect of diverging, as represented by the height of the duct, on the formation of secondary flow, flow separation and recovery is explored, and the three-dimensionality of the separated flow is quantitatively assessed. Numerical results reveal that with stronger spanwise diverging, the flow separates earlier from the inner wall and the size of the separated vortex is larger; the primary characteristics of the secondary flow also change significantly. The three-dimensional separated flow substantially affects the flow in the downstream straight duct that both streamwise and radial velocities exhibit fluctuating patterns as a result of the spatially non-uniform separation. The characteristics of boundary layer flow on all solid walls are also analyzed and discussed regarding the pressure field and local shearing.

Stabilization Effect of Frictions for Transonic Shocks in Steady Compressible Euler Flows Passing Three-Dimensional Ducts

Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets. For the three-dimensional steady non-isentropic compressible Euler system with frictions, we constructe a family of transonic shock solutions in rectilinear ducts with square cross-sections. In this article, we are devoted to proving rigorously that a large class of these transonic shock solutions are stable, under multidimensional small perturbations of the upcoming supersonic flows and back pressures at the exits of ducts in suitable function spaces. This manifests that frictions have a stabilization effect on transonic shocks in ducts, in consideration of previous works which shown that transonic shocks in purely steady Euler flows are not stable in such ducts. Except its implications to applications, because frictions lead to a stronger coupling between the elliptic and hyperbolic parts of the three-dimensional steady subsonic Euler system, we develop the framework established in previous works to study more complex and interesting Venttsel problems of nonlocal elliptic equations.

Low-Frequency Acoustic Propagation Through Crossing Internal Waves in Shallow Water

Crossing internal wave trains are commonly observed in continental shelf shallow water. In this paper, we study the effects of crossing internal wave structures on three-dimensional acoustic ducts with both theoretical and numerical approaches. We show that, depending on the crossing angle, acoustic energy, which is trapped laterally between internal waves of one train, can be either scattered, cross-ducted or reflected by the internal waves in the crossing train. We describe the governing physics of these effects and illustrate them for selected internal wave scenarios using full-field numerical simulations.

Numerical simulation of Ice Slurry Flow with Heat Transfer in a Three-Dimensional Duct by the Thermal Immersed Boundary－Lattice Boltzmann Method

Numerical simulation of Ice Slurry Flow with Heat Transfer in a Three-Dimensional Duct by the Thermal Immersed Boundary－Lattice Boltzmann Method

Large-eddy simulation of the flow in Z-Shape duct

A numerical study is conducted of the transient flow in a z-shape three-dimensional duct using large-eddy simulation (LES) with dynamic eddy viscosity subgrid-scale (SGS) model with a fully structured grid system. The numerical results of the velocity profiles are quantitatively validated against experimental data for z-shape ducts with various lateral separation distance configurations. The framework of the current LES model has been studied and discussed and the performance of LES in predicting the flow in z-shape ducts as a function of separation distances was evaluated. LES predictions of the mean flow velocity profiles are in good agreement (within the experimental uncertainty) with experimental data for the investigated wide range of l/d configurations. This is attributed to the well-resolved large-scale flow structures. Some slight over-predictions and under-predictions were found at certain separation distances. These numerical errors are due to the limited modeling approach to predict small eddies structures with the current SGS model. The main key features of the flow after the first elbow are also identified as separation and re-attachment regions. Some discrepancies are identified for lateral separation distances at sections x/d = 3 and x/d = 5 inside the flow transition regions. These discrepancies are believed to be inherited from the upstream flow numerical errors that arise in the non-uniform flow mixing regions. The potential remedy includes applying finer mesh resolution and/or higher order spatial discretization to accurately resolve the local velocity gradients and the complex flow structures.

Peristaltic propulsion of Jeffrey nano-liquid and heat transfer through a symmetrical duct with moving walls in a porous medium

In this article, a computational study has been performed on the peristaltic propulsion of nanofluid flow through a porous rectangular duct. A non-Newtonian fluid model, i.e. Jeffrey model is considered to examine the behavior of nanoparticles. A Cartesian coordinate system is adopted for the three-dimensional duct. Furthermore, the three-dimensional rectangular duct contains porous wavy walls. An approximation of long wavelength and small Reynolds number have been applied to formulate the governing equations of momentum, energy, continuity, and concentration equation. These resulting coupled partial differential equations are further solved using Homotopy perturbation method and Genetic algorithm with a combination of Nelder Mead method. The purpose of the Genetic algorithm and Nelder Mead method is to reduce the residual error. For this purpose, numerical comparison of residual error is presented with a Homotopy perturbation method.

Vibroacoustic characteristics and sound attenuation analyses of a duct–membrane system coupled with strip masses

In this paper, the vibroacoustic characteristics and noise reduction behavior of a duct–membrane system with attached strip masses are investigated analytically. Fully coupled structural–acoustic interactions between membrane–mass dynamics and duct sound propagation are constructed using the energy formulation and Rayleigh–Ritz procedure. Results from the current model are compared to those calculated by finite element analysis to verify the accuracy and effectiveness of the proposed model. Effective dynamic density and average vibrational velocity of the membrane are explicitly demonstrated at the peak/valley frequencies of transmission loss. The transmission loss peak frequency for such a model can be tuned by the variation of mass position and its weight, in which the first peak is mainly dependent on the mass properties, while the second one is more sensitive to the mass position. An extension to noise reduction analysis of a three-dimensional duct–membrane coupling system is also conducted. Significant enhancement of duct silencing performance has been obtained for the first time by making use of strip mass attachment.

Diffusive instabilities and spatial patterning from the coupling of reaction–diffusion processes with Stokes flow in complex domains

We study spatial and spatio-temporal pattern formation emergent from reaction–diffusion–advection systems formed by considering reaction–diffusion systems coupled to prescribed fluid flows. While there have been a number of studies on the planar dynamics of such systems and the resulting instabilities and spatio-temporal patterning in the plane, less has been done on complicated flows in complex domains. We consider a general approach for the study of bounded domains in order to model two- and three-dimensional geometries which are more likely to be of relevance for modelling dynamics within fluid vessels used in experiments. Considering a variety of problem geometries with finite cross-sections, such as two-dimensional channels, three-dimensional ducts and three-dimensional pipes, we demonstrate the role cross-section geometry plays in pattern formation under such systems. We find that the generic instability is that of an oscillatory or wave Turing instability, resulting in patterns which change in time, often being advected with the fluid flow. As in previous works, we observe a change in patterns formed when progressing from zero to weak to strong advection for uniform advection across the domain, with particularly strong advection destroying patterns. One novel finding is that heterogeneous fluid flow can induce qualitatively different patterns across the domain. For instance, Poiseuille flow with maximal advection in the centre of a vessel and zero advection at the boundary of a vessel is shown to exhibit patterns in the centre of the vessel which are different from patterns near the boundary, with differences attributed to the differential local advection within each region of the vessel. Additionally, we observe sheared patterns, which appear due to gradients in the fluid velocity, and cannot be obtained via any kind of uniform flow. Finally we also explore flow in more complex domains, including wavy-walled channels, continuous stirred-tank reactors, U-shaped pipes and a toroidal domain, in order to demonstrate behaviours when the flow is both heterogeneous and bidirectional, as well as to demonstrate that our results still apply for complex finite domains. Our analysis suggests that such non-trivial advection results in moving patterns which are more complex than observed in simpler reaction–diffusion–advection, and may be more characteristic of realistic flow regimes in biological media.

Internal heat transfer coefficient estimation in three-dimensional ducts through the reciprocity functional approach – An analytical approach and validation with experimental data

In the current paper it is presented and tested an innovative method for estimating internal heat transfer coefficients in ducts adopting only thermal measurements acquired on the external wall surface. This approach is based on the reciprocity functional analysis, which is a powerful non-intrusive inverse problem technique. The adoption of this technique is promising since it avoids intrusive measurements, it is fully non-iterative and the computational time and cost are very limited. In this paper, it is presented an extension of the classical reciprocity functional methodology in the sense that a fully analytical expression, obtained by the integral transform technique, is developed for estimating the internal heat transfer coefficient in a three-dimensional problem. Such methodology, avoiding the solution of linear systems, reduces the computational costs that are massive when the traditional approaches are applied to three dimensional problems. The proposed procedure is first validated adopting synthetic temperature data and then tested using real temperature measurements acquired by an infrared camera. The results highlight that the methodology is able to recover the unknown functions in a very short computational time with a good accuracy.

The Subgrid-Scale Approach for Modeling Impingement Cooling Flow in the Combustor Pedestal Tile

The widely used gas turbine combustor double-walled cooling scheme relies on very small pedestals. In a combustor it is impractical for computational fluid dynamics (CFD) to resolve each pedestal individually as that would require a very large amount of grid points and consequent excessive computation time. These pedestals can be omitted from the mesh and their effects captured on the fluid via a pedestal subgrid-scale (SGS) model. The aim is to apply the SGS approach, which takes into account the effects on pressure, velocity, turbulence, and heat transfer, in an unstructured CFD code. The flow inside a two-dimensional (2D) plain duct is simulated to validate the pedestal SGS model, and the results for pressure, velocity, and heat transfer are in good agreement with the measured data. The conjugate heat transfer inside a three-dimensional (3D) duct is also studied to calibrate the heat source term of the SGS model due to the pedestals. The resolved flow in the combustor pedestal tile geometry is numerically investigated using Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) in order to first assess the viability of the RANS and LES to predict the impinging flow and second to provide more validation data for the development of the SGS pedestal correlations. It is found that the complexity of such a flow, with high levels of curvature, impingement, and heat transfer, poses a challenge to the standard RANS models. The LES provides more details of the impinging flow features. The pedestal model is then applied to the complete tile to replace the pedestals. The results are close to both the fully resolved CFD and the measurements. To improve the flow features in the impingement zone, the first two rows were resolved with the mesh and combined with the SGS modeling for the rest of the tile; this gave optimum results of pressure, velocity, and turbulence kinetic energy (TKE) distribution inside the pedestal cooling tile.

Global uniqueness of steady subsonic Euler flows in three-dimensional ducts

ABSTRACTWe show for certain boundary conditions, under suitable assumptions on the velocity field, the steady compressible Euler flows in three-dimensional straight ducts must be irrotational, and hence, prove global uniqueness of uniform subsonic flows in these ducts. The proof depends on careful analysis of transport equations of vorticity and theory of second-order elliptic equations in bounded or unbounded domains.

Three-Dimensional Study of Multiple-Jet Cross Flow Cooling System with Single Array of Heat Sources

ABSTRACTThe objective of this study is to predict fluid flow and thermal characteristics associated with forced convection cooling of an array of heat sources mounted in a three-dimensional duct by impinging jets in the presence of cross flow. The equations governing fluid flow and heat transfer are solved using Streamline Upwind / Petrov - Galerkin based finite element method. The role of three dimensional flow structures, horseshoe vortex and counter rotating vortex pair in overall heat transfer distribution is examined. A parametric study is performed to analyze the performance of jets in cross flow for various Reynolds numbers (Re = 100, 250, 500) and velocity ratios (VR = 1.0, 5.0, 10.0). It is observed that with the increase in velocity ratio, the enhancement of heat transfer from heat sources occurs due to increase in the dominance of jet flow accompanied by an unfavorable reduction in heat transfer owing to the increase in size of horseshoe vortex. From numerical studies, it can be concluded that VR = 5.0 exhibits higher overall surface averaged Nusselt number (51.7% over VR = 1.0 and 44.1% over VR = 10.0 for Re = 500) compared to other velocity ratios considered in this study.

Study on multi-density contrast agent fillers of duct casting based on CT three-dimensional reconstruction.

The three-dimensional visualization model of human body duct is based on virtual anatomical structure reconstruction with duct angiography, which realizes virtual model transferred from two-dimensional, planar and static images into three-dimensional, stereoscopic and dynamic ones repectively. In recent years, the multi-duct segmentation and division of the same specimen (or organ) is the focus of attention shared by surgeons and clinical anatomists. On the basis of 4.22 g/cm3 body bone density, this study has screened out metal oxide contract agent with different density for infusion and modeling, as well as compared and analyzed the effects of three-dimensional image of CT virtual bronchoscopy (CTVB), three-dimensional image of CT maximum intensity projection and three-dimensional model. This experiment result showed synchronously infusing multi-duct of same specimen (or organ) with contrast agent in different densities could reconstruct three-dimensional models of all ducts once only and adjust threshold to develop single or multiple ducts. It was easier to segment and observe the duct structure, anastomosis, directions and crossing in different parts, which was beyond comparison with three-dimensional image of CTVB. Although the existing three-dimensional duct reconstruction techniques still cannot be applied in living bodies temporarily, this study focused on a creative design of ducts segmentation in different density, which proposed a new experimental idea for developing multi-duct three-dimensional model in living body in the future. It will play a significant role in disease diagnosis and individual design in surgical treatment program. Therefore, this study observes the three-dimensional status of human duct with the application of contrast agent fillers in different density, combined with three-dimensional reconstruction technology. It provides an innovative idea and method for constructing three-dimensional model of digital multi-duct specimen, and the ultimate goal is to develop the digitized virtual human and precise medical treatment better and faster.

Prediction of the moments in advection-diffusion lattice Boltzmann method. I. Truncation dispersion, skewness, and kurtosis.

The effect of the heterogeneity in the soil structure or the nonuniformity of the velocity field on the modeled resident time distribution (RTD) and breakthrough curves is quantified by their moments. While the first moment provides the effective velocity, the second moment is related to the longitudinal dispersion coefficient (k_{T}) in the developed Taylor regime; the third and fourth moments are characterized by their normalized values skewness (Sk) and kurtosis (Ku), respectively. The purpose of this investigation is to examine the role of the truncation corrections of the numerical scheme in k_{T}, Sk, and Ku because of their interference with the second moment, in the form of the numerical dispersion, and in the higher-order moments, by their definition. Our symbolic procedure is based on the recently proposed extended method of moments (EMM). Originally, the EMM restores any-order physical moments of the RTD or averaged distributions assuming that the solute concentration obeys the advection-diffusion equation in multidimensional steady-state velocity field, in streamwise-periodic heterogeneous structure. In our work, the EMM is generalized to the fourth-order-accurate apparent mass-conservation equation in two- and three-dimensional duct flows. The method looks for the solution of the transport equation as the product of a long harmonic wave and a spatially periodic oscillating component; the moments of the given numerical scheme are derived from a chain of the steady-state fourth-order equations at a single cell. This mathematical technique is exemplified for the truncation terms of the two-relaxation-time lattice Boltzmann scheme, using plug and parabolic flow in straight channel and cylindrical capillary with the d2Q9 and d3Q15 discrete velocity sets as simple but illustrative examples. The derived symbolic dependencies can be readily extended for advection by another, Newtonian or non-Newtonian, flow profile in any-shape open-tabular conduits. It is established that the truncation errors in the three transport coefficients k_{T}, Sk, and Ku decay with the second-order accuracy. While the physical values of the three transport coefficients are set by Péclet number, their truncation corrections additionally depend on the two adjustable relaxation rates and the two adjustable equilibrium weight families which independently determine the convective and diffusion discretization stencils. We identify flow- and dimension-independent optimal strategies for adjustable parameters and confront them to stability requirements. Through specific choices of two relaxation rates and weights, we expect our results be directly applicable to forward-time central differences and leap-frog central-convective Du Fort-Frankel-diffusion schemes. In straight channel, a quasi-exact validation of the truncation predictions through the numerical moments becomes possible thanks to the specular-forward no-flux boundary rule. In the staircase description of a cylindrical capillary, we account for the spurious boundary-layer diffusion and dispersion because of the tangential constraint of the bounce-back no-flux boundary rule.

Influence of the heated blocks on the natural convection in 3D cylindrical and divergent annular duct

In this paper, a numerical investigation of natural convection in three-dimensional cylindrical and divergent annular duct is studied. In the inner cylinder of thin thickness, are mounted a cylindrical blocks which subjected to a volumetric heat generation. The governing equations of mass, momentum and energy equation for both the fluid and the solid are solved by the finite volume method using the commercially available CFD software Fluent. The effect of the number of heated blocks (N = 1, 2, 3 and 5) and the inclination angle of the divergent (φ = 0°, 15°, 23° and 45°) have been studied. The temperature and velocity contours fields, stream lines also the local Nusselt number have been presented here for Ra = 2.105 and N = 3 while temperature and velocity profiles in the span-wise direction of the flow were plotted for Ra = 1.105 (φ = 0°, 15°, 23° and 45°) and (N = 1, 2, 3 and 5) also the local and average Nusselt number for those geometries.

Entrance and Temperature-Dependent Property Effects on Laminar Duct Flows of Liquids

The results of a numerical investigation on the effects of the temperature dependence of viscosity and thermal conductivity in simultaneously developing laminar flows of liquids in straight ducts of constant cross sections are used to obtain new correlations for the axial distributions of the peripherally averaged local Nusselt number. Three different cross-sectional geometries are considered, corresponding to both axisymmetric (circular and concentric annular) and three-dimensional (square) ducts. Uniform heat flux boundary conditions are specified at the heated walls. Viscosity is assumed to vary with temperature according to an exponential relation, while a linear dependence of thermal conductivity on temperature is assumed. The other fluid properties are held constant. A superposition method is applied to obtain the values of the peripherally averaged local Nusselt number by separately considering the effects of temperature-dependent viscosity and those of temperature-dependent thermal conductivity.

PanIN-associated pericyte, glial, and islet remodeling in mice revealed by 3D pancreatic duct lesion histology.

Pericytes and glial cells are accessory cells of neurovascular networks, which have been reported to participate in scar formation after tissue injury. However, it remains unclear whether similar reactive cellular responses occur in pancreatic intraepithelial neoplasia (PanIN). In this study we developed three-dimensional (3D) duct lesion histology to investigate PanIN and the associated pericyte, glial, and islet remodeling. Transparent mouse pancreata with a Kras(G12D) mutation were used to develop 3D duct lesion histology. Deep-tissue, tile-scanning microscopy was performed to generate panoramic views of the diseased pancreas for global examination of early stage and advanced duct lesion formation. Fluorescence signals of ductal and neurovascular networks were simultaneously detected to reveal associated remodeling. Significantly, in Kras(G12D)-mutant mice, when the low-grade PanINs emerge, duct lesions appear as epithelial buds with perilesional pericyte and glial activation. When PanINs occur in large scale (induced by cerulein injections to the mutant mice), the 3D image data identifies 1) aggregation of PanINs in clusters in space; 2) overexpression of the pericyte marker NG2 in the PanIN microenvironment; and 3) epithelial in-growth to islets, forming the PanIN-islet complexes. Particularly, the PanIN-islet complexes associate with proliferating epithelial and stromal cells and receive substantial neurovascular supplies, making them landmarks in the atrophic lobe. Overall, perilesional pericyte and glial activation and formation of the PanIN-islet complex underline cellular heterogeneity in the duct lesion microenvironment. The results also illustrate the advantage of using 3D histology to reveal previously unknown details of neurovascular and endocrine links to the disease.

Computational optimization of catalyst distributions at the nano-scale

Catalysis is a key phenomenon in a great number of energy processes, including feedstock conversion, tar cracking, emission abatement and optimizations of energy use. Within heterogeneous, catalytic nano-scale systems, the chemical reactions typically proceed at very high rates at a gas–solid interface. However, the statistical uncertainties characteristic of molecular processes pose efficiency problems for computational optimizations of such nano-scale systems. The present work investigates the performance of a Direct Simulation Monte Carlo (DSMC) code with a stochastic optimization heuristic for evaluations of an optimal catalyst distribution. The DSMC code treats molecular motion with homogeneous and heterogeneous chemical reactions in wall-bounded systems and algorithms have been devised that allow optimization of the distribution of a catalytically active material within a three-dimensional duct (e.g. a pore). The objective function is the outlet concentration of computational molecules that have interacted with the catalytically active surface, and the optimization method used is simulated annealing. The application of a stochastic optimization heuristic is shown to be more efficient within the present DSMC framework than using a macroscopic overlay method. Furthermore, it is shown that the performance of the developed method is superior to that of a gradient search method for the current class of problems. Finally, the advantages and disadvantages of different types of objective functions are discussed.