Flow Reconstruction Research Articles

Proper Orthogonal Decomposition and Statistical Analysis of 2D Confined Impinging Jets Chaotic Flow

AbstractProper orthogonal decomposition (POD) is shown to be a statistical operation that identifies the main characteristics of chaotic flows and separates them into a few modes. The dynamic chaotic flow is obtained from two‐dimensional (2D) computational fluid dynamics simulations, for different Reynolds numbers, of a confined impinging jets mixer. POD enables reconstruction of the dynamic flow from a few modes that are related to coherent flow structures. The POD flow reconstruction enables a large compression of the flow data set. The decomposition of the flow field into orthogonal modes related to coherent structures provides direct insight into the mixing dynamics and scales which are not accessible from flow dynamics statistic quantities, which were introduced in the context of turbulence and are here applied to chaotic flow.

Mean and Unsteady Flow Reconstruction Using Data-Assimilation and Resolvent Analysis

A methodology is presented that exploits both data-assimilation techniques and resolvent analysis for reconstructing turbulent flows, containing organized structures, with an efficient set of measurements. The mean (time-averaged) flow is obtained using variational data-assimilation that minimizes the discrepancy between a limited set of flow measurements, generally from an experiment, and a numerical simulation of the Navier–Stokes equations. The fluctuations are educed from resolvent analysis and time-resolved data at a single point in the flow. Resolvent analysis also guides where measurements of the mean and fluctuating quantities are needed for efficient reconstruction of a simple example case study: flow around a circular cylinder at a Reynolds number of . For this flow, resolvent analysis reveals that the leading singular value, most amplified modes, and the mean profile for scale with the shedding frequency and length of the recirculation bubble. A relationship between these two parameters reinforces the notion that a wave maker, for which the length scales with the recirculation bubble, determines the frequency and region where an instability mechanism is active. The procedure offers a way to choose sensor locations that capture the main coherent structures of a flow and a method for computing mean pressure by using correctly weighted resolvent modes.

Inter-amphibian predation in the Early Cretaceous of China

For most fossil taxa, dietary inference relies primarily on indirect evidence from jaw morphology and the dentition. In rare cases, however, preserved gut contents provide direct evidence of feeding strategy and species interaction. This is important in the reconstruction of food webs and energy flow through ancient ecosystems. The Early Cretaceous Chinese Jehol Biota has yielded several such examples, with lizards, birds, small dinosaurs, and mammals as both predator and prey. Here we describe an Early Cretaceous fossil frog specimen, genus Genibatrachus, that contains an adult salamander within its body cavity. The salamander is attributed to the hynobiid-like genus Nuominerpeton. The salamander skeleton is complete and articulated, suggesting it was caught and swallowed shortly before the frog itself died and was buried.

Does Biliodigestive Anastomosis Have Any Effect on the Reversal of Hepatopulmonary Syndrome in a Biliary Cirrhosis Experimental Model?

Biliary cirrhosis is associated with hepatopulmonary syndrome (HPS), which is related to increased posttransplant morbidity and mortality. This study aims to analyze the pathophysiology of biliary cirrhosis and the onset of HPS. Twenty-one-day-old Wistar rats were subjected to common bile duct ligation and were allocated to two groups: group A (killed 2, 3, 4, 5, or 6weeks after biliary obstruction) and group B (subjected to biliodigestive anastomosis 2, 3, 4, 5, or 6weeks after the first procedure and killed 3weeks later). At the killing, arterial blood was collected for the analyses, and samples from the liver and lungs were collected for histologic and molecular analyses. The gasometric parameters as well as the expression levels of ET-1, eNOS, and NOS genes in the lung tissue were evaluated. From a total of 42 blood samples, 15 showed hypoxemia (pO2 < 85mmHg) and 17 showed an increased oxygen gradient [p (A-a) O2 > 18mmHg]. The liver histology revealed increased ductular proliferation after common bile duct ligation, and reconstruction of bile flow promoted decreased ductular proliferation 5 and 6weeks post-common bile duct ligation. Pulmonary alterations consisted of decreased parenchymal airspace and increased medial wall thickness. Biliary desobstruction promoted transitory improvements 5weeks after biliary obstruction (increased parenchymal airspace and decreased MWT-p = 0.003 and p = 0.004, respectively) as well as increased endothelin expression levels (p = 0.009). The present model showed lung tissue alterations promoted by biliary obstruction. The biliodigestive anastomosis had no clear direct effects on these alterations.

Super-resolution reconstruction of turbulent flows with machine learning

We use machine learning to perform super-resolution analysis of grossly under-resolved turbulent flow field data to reconstruct the high-resolution flow field. Two machine learning models are developed, namely, the convolutional neural network (CNN) and the hybrid downsampled skip-connection/multi-scale (DSC/MS) models. These machine learning models are applied to a two-dimensional cylinder wake as a preliminary test and show remarkable ability to reconstruct laminar flow from low-resolution flow field data. We further assess the performance of these models for two-dimensional homogeneous turbulence. The CNN and DSC/MS models are found to reconstruct turbulent flows from extremely coarse flow field images with remarkable accuracy. For the turbulent flow problem, the machine-leaning-based super-resolution analysis can greatly enhance the spatial resolution with as little as 50 training snapshot data, holding great potential to reveal subgrid-scale physics of complex turbulent flows. With the growing availability of flow field data from high-fidelity simulations and experiments, the present approach motivates the development of effective super-resolution models for a variety of fluid flows.

Impact of heat and mass transfer in porous catalytic monolith: CFD modeling of exothermic reaction

Impact of mass and heat transfer on exothermic reaction performance in porous catalytic monolith with triangular channels is investigated by CFD modeling. Detailed analysis of spatial distributions of process characteristics for methane oxidation shows that in the initial part of catalyst volume there is the active subsurface layer. The domain of sharp gradients of the reaction rate is revealed that includes the parts of external surface and thin subsurface layers near the monolith inlet, which results in sharp rearrangement of 3D-field of temperature and reagent concentrations. It is shown that the formation of such conditions is strongly influenced by complex gaseous flow reconstruction with gas penetration into the catalyst volume, significant heat release, and heat transfer between channel wall and gas flow. Though the region with high reaction rate is rather short this could be of high importance for reactor design and selection of optimal operation conditions.

Revascularization treatment for complex proximal posterior inferior cerebellar artery aneurysms

Objective To evaluate the clinical effect of revascularization on the treatment of complex proximal posterior inferior cerebellar artery (PICA) aneurysms. Methods A retrospective analysis was conducted on 10 cases (accounting for 5.1% of 10/198 cases of PICA aneurysm admitted during the same period) of complex proximal PICA aneurysms (10 aneurysms) who were admitted to Neurosurgical Department of Tianjin Huanhu Hospital from June 2008 to January 2018. According to the morphological characteristics and collateral circulation of aneurysms, various ways of revascularization were undergone. Eight cases underwent occipital artery (OA)-PICA anastomosis + aneurysm trapping; vertebral artery (VA) occlusion + OA-PICA anastomosis was performed in 1 case; aneurysm depression and PICA in situ anastomosis was performed in 1 case. The patency of anastomotic vessels and postoperative complications were observed after operation and the patients' outcomes were evaluated with modified Rankin scale (mRS). Results Ten cases successfully underwent the blood flow reconstruction. Intraoperative fluorescein angiography revealed the patency of anastomotic vessels. Two cases developed hoarseness post operation and fully recovered to normal after treatment. One patient developed dyspnea and pulmonary infection 3 days post operation and fully recovered to normal after treatment. Ten cases were followed up effectively. The follow-up period was 3-118 months after operation. No recurrent or ruptured aneurysms were found in the follow-up period. One patient died of cerebral hemorrhage because of hypertension after 12 months. Ventriculoperitoneal drainage was performed in 1 case of hydrocephalus. Nine cases of anastomotic vessels were patent and 1 case showed occlusion. All aneurysms disappeared. The score of mRS was 0 in 8 cases, 1 in 1 and 6 in 1. Conclusions Depending on the morphological characteristics and collateral circulation, different revascularization techniques are selected. Revascularization is an effective method for the treatment of complex proximal PICA aneurysms in terms of relief of space-occupying effect and removal of aneurysms. Key words: Intracranial aneurysm; Neurosurgical procedures; Prognosis; Posterior inferior cerebellar artery; Revascularization

MIGRATION FLOWS IN THE SOUTH OF WEST SIBERIAN PLANE DURING THE LATE BRONZE AGE TO IRON AGE TRANSITION

The article is dedicated to anniversary of a brilliant scientist, an outstanding scythologist S. A. Skoryy. I suppose this essay, devoted to the Early Scythian period in the south of West Siberian Plain, will be interesting for our hero of the day. The atricle present the reconstruction of migration flows during the Late Bronze to Iron Age transition in the south of West Siberian plane based on archaeological data from Chicha 1 and Bolshoy Log settlements. The main vectors of migration flows, revealed and described in this article, indicate a strong penetration of different archaeological cultures to the Ob-Irtysh forest steppe. The bearers of Suzgun, Atlym, Berlik and other cultures that occupied nearby territories for more than two centuries have adapted to aboriginal late Irmen population. The Ob-Irtysh area was an attractive place for living. The abundant pastures with a stable herbage yields and the wealth of fish and game equally attracted both herdsmen and fishermen-hunters. Apparently, during this time the migration flows changed their directions and didn’t get in each other’s way. The mosaic of cultural formations peacefully shared Ob-Irtysh area was developed in the south of West Siberian plane during Bronze to Iron Age transition. This has been possible because of the different orientation of paleoeconomy of these societies. Besides, it must be noted that the bearers of aboriginal late Irmen culture were quite tolerant. They involved newcomers in their influence arena and even lived with them on the one living space area, e. g. on settlements. This evidence of this behavior was discovered on Chicha 1 and Bolshoy Log sites for instance.

Properties of a Variational Model for Video Inpainting

We consider a variational model analyzed in March and Riey (Inverse Probl Imag 11(6): 997–1025, 2017) for simultaneous video inpainting and motion estimation. The model has applications in the field of recovery of missing data in archive film materials. A gray-value video content is reconstructed in a spatiotemporal region where the video data is lost. A variational method for motion compensated video inpainting is used, which is based on the simultaneous estimation of apparent motion in the video data. Apparent motion is mathematically described by a vector field of velocity, denoted optical flow, which is estimated through gray-value variations of the video data. The functional to be minimized is defined on a space of vector valued functions of bounded variation and the relaxation method of the Calculus of Variations is used. We introduce in the functional analyzed in March and Riey(Inverse Probl Imag 11(6): 997–1025, 2017) a suitable positive weight, and we show that diagonal minimizing sequences of the functional converge, up to subsequences as the weight tends to infinity, to minimizers of an appropriate limit functional. Such a limit functional is the relaxed version of a functional, modified with suitable improvements, proposed by Lauze and Nielsen (2004) and which permits an accurate joint reconstruction both of the optical flow and of the video content.

Volumetric reconstruction of acoustic energy flows in a reverberation room.

This study examines the spatial and directional properties of net energy flows in a reverberation chamber. Based on measurements with a spherical array, a method is proposed to estimate the flows of acoustic energy in the volume surrounding the array. The proposed method is used to examine the steady state, early decay, and late decay of the sound field in a reverberation room (both empty and with an absorber on the floor). The results show that the approach is successful in characterizing the spatio-spectral and spatio-temporal properties of power flows in reverberant sound fields, constituting a valuable analysis tool.

Networked sensor data error estimation

Nowadays, the effectiveness of any smart transportation management or control strategy would heavily depend on reliable traffic data collected by sensors. Two problems regarding sensor data quality have received attention: first, the problem of identifying malfunctioning sensors; second, reconstruction of traffic flow. Most existing studies concerned about identifying completely malfunctioning sensors whose data should be discarded. In this paper, we focus on the problem of error detection and data recovery of partially malfunctioning sensors that could provide valuable information. By integrating a sensor measurement error model and a transportation network model, we propose a Generalized Method of Moments (GMM) based estimation approach to determine the parameters of systematic and random errors of traffic sensors in a road network. The proposed method allows flexible data aggregation that ameliorates identification and accuracy. The estimates regarding both systematic and random errors are utilized to conduct hypothesis test on sensor health and to estimate true traffic flows with observed counts. The results of three network examples with different scales demonstrate the applicability of the proposed method in a large variety of scenarios.

Proper orthogonal decomposition and dynamic mode decomposition of jet in channel crossflow

The paper is devoted to the application of the model order reduction to the results of direct numerical simulation of a low momentum laminar jet discharged into a laminar channel crossflow through a circular orifice (Reynolds number Re=3333, jet-to-crossflow velocity ratio is R=1/6, mesh 13 million nodes, (Wu et al., 2017a)). Main attention is paid to the post-processor analysis of the computational results via model order reduction techniques: the Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) which can drastically reduce the amount of data needed. Up to 400 snapshots, obtained by direct numerical simulation, are used to extract the structures. We study the sensitivity of both algorithms to the sampling frequency and time span. For the first time different DMD ranking approaches are analysed in the application to a low-dimensional flow reconstruction. It is shown that the DMD approach with the ranking with respect to the amplitudes averaged over time is the most efficient technique for the problem in study. A comparative analysis is also carried out for both POD and DMD. It is shown the energy is more evenly distributed in the DMD. In turn, the POD is quite optimal in reconstructing the flow while the DMD requires more modes to capture the same amount of energy. However, DMD modes automatically reveal the frequency information and corresponding spatial structures in the entire field as well as interactions between different parts of the flow domain.

Fast 3D flow reconstructions from 2D cross-plane observations

A computationally efficient flow reconstruction technique is proposed, exploiting homogeneity in a given direction, to recreate three-dimensional instantaneous turbulent velocity fields from snapshots of two dimension planar fields. This methodology, termed as ’snapshot optimisation’ or SO, can help to provide 3D data sets for studies which are currently restricted by the limitations of experimental measurement techniques. The SO method aims at optimising the error between an inlet plane with a homogeneous direction and snapshots, obtained over a sufficient period of time, on the observation plane. The observations are carried out on a plane perpendicular to the inlet plane with a shared edge normal to the homogeneity direction. The method is applicable to all flows which display a direction of homogeneity such as cylinder wake flows, channel flow, mixing layer, and jet (axisymmetric). The ability of the method is assessed with two synthetic data sets, and three experimental PIV data sets. A good reconstruction of the large-scale structures is observed for all cases. The small-scale reconstruction ability is partially limited especially for higher dimensional observation systems. POD-based SO method and averaging SO variations of the method are shown to reduce discontinuities created due to temporal mismatch in the homogenous direction providing a smooth velocity reconstruction. The volumetric reconstruction is seen to capture large-scale structures for synthetic and experimental case studies. The algorithm run time is found to be in the order of a minute providing results comparable with the reference. Such a reconstruction methodology can provide important information for data assimilation in the form of initial condition, background condition, and 3D observations.

Location of turning ratio and flow sensors for flow reconstruction in large traffic networks

In this work we examine the problem of minimizing the number of sensors needed to completely recover the vehicular flow in a steady state traffic network. We consider two possible sensor technologies: one that allows the measurement of turning ratios at a given intersection and the other that directly measures the flow in a road. We formulate an optimization problem that finds the optimal location of both types of sensors, such that a minimum number is required. To solve this problem, we propose a method that relies on the structure of the underlying graph, which has a quasi-linear computational complexity, resulting in less computing time when compared to other works in the literature. We evaluate our results using dynamical traffic simulations in synthetic networks.

3-D Flow Reconstruction Using Divergence-Free Interpolation of Multiple 2-D Contrast-Enhanced Ultrasound Particle Imaging Velocimetry Measurements

Quantification of 3-D intravascular flow is valuable for studying arterial wall diseases but currently there is a lack of effective clinical tools for this purpose. Divergence-free interpolation (DFI) using radial basis function (RBF) is an emerging approach for full-field flow reconstruction using experimental sparse flow field samples. Previous DFI reconstructs full-field flow from scattered 3-D velocity input obtained using phase-contrast magnetic resonance imaging with low temporal resolution. In this study, a new DFI algorithm is proposed to reconstruct full-field flow from scattered 2-D in-plane velocity vectors obtained using ultrafast contrast-enhanced ultrasound (>1000 fps) and particle imaging velocimetry. The full 3-D flow field is represented by a sum of weighted divergence-free RBFs in space. Because the acquired velocity vectors are only in 2-D and hence the problem is ill-conditioned, a regularized solution of the RBF weighting is achieved through singular value decomposition (SVD) and the L-curve method. The effectiveness of the algorithm is determined via numerical experiments for Poiseuille flow and helical flow with added noise, and it is found that an accuracy as high as 95.6% can be achieved for Poiseuille flow (with 5% input noise). Experimental feasibility is also determined by reconstructing full-field 3-D flow from experimental 2-D ultrasound image velocimetry measurements in a carotid bifurcation phantom. The method is typically faster for a range of problems compared with computational fluid dynamics, and has been found to be effective for the three flow cases.

Spectral Decomposition and Reconstruction of Unsteady Flow in a Multi-blade Fan

Spectral Decomposition and Reconstruction of Unsteady Flow in a Multi-blade Fan

Reconstruction of Magma Flow in Permo–Triassic Intrusions of the Angara–Taseeva Syneclise (Siberian Platform) Based on Magnetic Susceptibility Anisotropy Data

Abstract —Based on detailed studies of the anisotropy of magnetic susceptibility (AMS), the directions of magmatic-melt propagation have been reconstructed in large dolerite sills of the Angara–Taseeva syneclise. Half the sites studied showed a magnetic fabric of “normal” type, i.e., the minimum K3 axis of the AMS ellipsoid is orthogonal to the contact, and the other two axes lie in the plane of the intrusive body. Interpreting the orientation of the maximum K1 axis as the direction of the melt flow at such sites, we compiled a scheme of the main magma flow directions. The obtained results are generally consistent with the hypothesis of magma-feeding zone in the central, most downwarped part of the Angara–Taseeva depression. The distribution of the maximum axes of the AMS ellipsoid is different in sills and points to the existence of local intrusion centers. Intrusions with an AMS ellipsoid of “reverse” type are predominant on the periphery of the depression. The sites with a “normal” magnetic fabric do not demonstrate any prevailing direction of magma propagation, because there is no general direction of the melt flow in the peripheral subsurface zones of large intrusions.

Particle Flow reconstruction in the CMS Level-1 Trigger For The HL-LHC

With the planned addition of the tracking information in the Level-1 trigger in CMS for the High-Luminosity Large Hadron Collider (HL-LHC), the algorithms for the Level-1 trigger can be completely reconceptualized. Following the example for offline reconstruction in CMS to use complementary subsystem information and mitigate pileup, we explore the feasibility of using Particle Flow-like and pileup-per-particle identification techniques at the hardware trigger level. We present the challenges of adapting these algorithm to the timing and resource constraints of the Level-1 trigger, the first prototype implementations, and the expected performance on physics object reconstruction.

Mud Flow Reconstruction by Means of Physical Erosion Modeling, High-Resolution Radar-Based Precipitation Data, and UAV Monitoring

Storm events and accompanying heavy rain endanger the silty soils of the fertile and intensively-used agricultural landscape of the Saxon loess province in the European loess belt. In late spring 2016, persistent weather conditions with repeated and numerous storm events triggered flash floods, landslides, and mud flows, and caused severe devastation to infrastructure and settlements throughout Germany. In Saxony, the rail service between Germany and the Czech Republic was disrupted twice because of two mud flows within eight days. This interdisciplinary study aims to reconstruct the two mud flows by means of high-resolution physical erosion modeling, high-resolution, radar-based precipitation data, and Unmanned Aerial Vehicle monitoring. Therefore, high-resolution, radar-based precipitation data products are used to assess the two storm events which triggered the mud flows in this unmonitored area. Subsequently, these data are used as meteorological input for the soil erosion model EROSION 3D to reconstruct and predict mud flows in the form of erosion risk maps. Finally, the model results are qualitatively validated by orthophotos generated from images from Unmanned Aerial Vehicle monitoring and Structure from Motion Photogrammetry. High-resolution, radar-based precipitation data reveal heavy to extreme storm events for both days. Erosion risk maps show erosion und deposition patterns and source areas as in reality, depending on the radar-based precipitation product. Consequently, reconstruction of the mud flows by these interdisciplinary methods is possible. Therefore, the development of an early warning system for soil erosion in agricultural landscapes by means of E 3D and high-resolution, radar-based precipitation forecasting data is certainly conceivable.

Preservation of Anterior Choroidal Artery Blood Flow During Trapping of the Internal Carotid Artery for a Ruptured Blood Blister-Like Aneurysm with High-Flow Bypass

The ideal surgery for a blood blister-like aneurysm (BBA) in the internal carotid artery (ICA) involves complete termination of blood flow into the BBA by trapping of the ICA at sites both proximal and distal to the BBA. In the present report, we describe a clipping method with ICA trapping for prevention of anterior choroidal artery ischemia, a major problem in ICA trapping with reconstruction surgery using external carotid artery-middle cerebral artery high-flow bypass (HFB). The data from patients with a ruptured BBA treated by the combination of ICA trapping and blood flow reconstruction from 2008 to 2018 were retrospectively evaluated. Fifteen patients had been treated with the combination surgery. Clip placement for ICA trapping depended on the relationship between the distal neck of the BBA and the posterior communicating artery. In the case of the BBA distal neck located at the same level or distal to the posterior communicating artery, oblique placement of a distal clip to the ICA was mandatory to maintain blood flow of the anterior choroidal artery. No patients developed recurrence of the BBA after trapping. The outcomes were assessed using the modified Rankin scale score, with a score of 0 or 1 in 12 of the 15 patients (80%). A complete shutdown of blood flow to the BBA by ICA trapping is essential for the permanent prevention of BBA recurrence. In cases of a BBA distal neck located distal to the posterior communicating artery, the oblique clipping technique applied to the ICA is useful to prevent ischemic complications of the anterior choroidal artery.