Complicated Flow Conditions Research Articles

An Intelligent Monitoring System for the Force Characteristics of Floating Bollards in a Ship Lock

Due to the large scale of navigation ships, the fast speed of entering the lock, and the irregular mooring and the complicated flow conditions in the lock chamber, it is common for the floating bollards of the lock to suffer structural damage or even failure due to the overloaded mooring force. However, the traditional cable load measurement method cannot offer real-time feedback on force characteristics of floating bollards, making it difficult to accurately judge its service status. To this end, according to the floating bollard structure type and load condition of a representative ship lock project in China, this paper determines the theoretical model parameters of a floating bollard load response based on three-dimensional finite element numerical simulation test data and constructs a modified load response model of floating bollards. On this basis, an intelligent floating bollard monitoring system based on big data, internet, and cloud services is developed to intelligently perceive real-time floating bollard force characteristics and monitor the long-term service status. Relying on a representative ship lock in China, a field test of the floating bollard intelligent monitoring system is carried out. The relative error between the calculated values via the model (i.e., system exhibition results) based on the numerical results and the field-measured values is within 15%. This result verified the accuracy and effect of the monitoring system. This research supports the establishment of the digital perception monitoring platform for ship lock facilities and improves the automation level of ship lock operation and management as well as overall risk prevention and control capabilities.

Aerodynamic Optimization of Transonic Rotor Using Radial Basis Function Based Deformation and Data-Driven Differential Evolution Optimizer

The complicated flow conditions and massive design parameters bring two main difficulties to the aerodynamic optimization of axial compressors: expensive evaluations and numerous optimization variables. To address these challenges, this paper establishes a novel fast aerodynamic optimization platform for axial compressors, consisting of a radial basic function (RBF)-based blade parameterization method, a data-driven differential evolution optimizer, and a computational fluid dynamic (CFD) solver. As a versatile interpolation method, RBF is used as the shape parameterization and deformation technique to reduce optimization variables. Aiming to acquire competitive solutions in limited steps, a data-driven evolution optimizer is developed, named the pre-screen surrogate model assistant differential evolution (pre-SADE) optimizer. Different from most surrogate model-assisted evolutionary algorithms, surrogate models in pre-SADE are used to screen the samples, rather than directly estimate them, in each generation to reduce expensive evaluations. The polynomial regression model, Kriging model, and RBF model are integrated in the surrogate model to improve the accuracy. To further save optimization time, the optimizer also integrates parallel task management programs. The aerodynamic optimization of a transonic rotor (NASA Rotor 37) is performed as the validation of the platform. A differential evolution (DE) optimizer and another surrogate model-assisted algorithm, committee-based active learning for surrogate model assisted particle swarm optimization (CAL-SAPSO), are introduced for the comparison runs. After optimization, the adiabatic efficiency, total pressure ratio, and surge margin are, respectively, increased by 1.47%, 1.0%, and 0.79% compared to the initial rotor. In the same limited steps, pre-SADE gets a 0.57% and 0.51% higher rotor adiabatic efficiency than DE and CAL-SAPSO, respectively. With the help of parallel techniques, pre-SADE and DE save half the optimization time compared to CAL-SAPSO. The results verify the effectiveness and the rapidity of the fast aerodynamic optimization platform.

Compound-eye imaging imitation-based whole-field flow measurement

Large-scale particle image velocimetry (LSPIV) has been increasingly applied in whole-field flow measurement for its non-contact operation mode. However, due to the complicated flow conditions and optical disturbances on the water-air interface, commonly-used imaging technologies are degenerated by the low visibility and image distortion. There are also increased challenges for control point calibration. This paper proposes an imaging measurement method that imitates the imaging computation mechanism in compound eyes. The method is independent of ground control points and can achieve flow measurement with natural patterns, which can solve the problem caused by the lack of visible tracers. Field evaluation results demonstrate that this is the first method to achieve real-world whole-field flow measurement in challenging conditions. Specifically, the velocimetry error is less than 5%, while ranging from 5% to 15% for other LSPIV systems. The method meets current hydrological standards and acquires flow data in wild rivers, performance that is realized with difficulty by other methods.

Influence of Balance Hole Diameter on Leakage Flow of the Balance Chamber in a Centrifugal Pump

The balancing holes in centrifugal pumps with seals mounted in both suction and discharge sides are one of the approaches used by pump manufacturers to reduce the axial thrust. The balance hole diameter directly affects the axial force of the centrifugal pump. The flow characteristics in the balance chamber are closely related to the balance hole diameter. However, research is not very clear on the internal flow of the balanced chamber, due to the small axial and radial sizes and the complicated flow conditions in the chamber. In this paper, we analyzed the influence of the balance hole diameter on the liquid leakage rate, flow velocity, and vortex motion in the balance chamber. The results indicated that when the balance hole diameter was lower than the design value, the volume flow rate of leakage flow was proportional to the diameter. The liquid flow rate and vortex distribution rules in the balance chamber were mainly associated with the coeffect of radial leakage flow in the rear sealing ring interval and the axial balance hole leakage flow. The research has revealed the mechanisms of leakage flow of the balance chamber in the centrifugal pump and that this is of great significance for accurate calculation and balancing of the axial force.

A Minimized Valveless Electromagnetic Micropump for Microfluidic Actuation on Organ Chips

In recent years, organ chips have become an ideal alternative for physiological and pathological studies as well as drug screening. To more realistically simulate the in vivo physiological environment, micropumps are often needed as power sources to achieve dynamic culture in organ chips. In this study, we present a valveless electromagnetic micropump that can be used in organ chips. Fluid flow is actuated by the vibration of a PDMS membrane through a varying magnetic field. This micropump uses a nozzle/diffuser structure instead of valves, which simplifies the structure. By reducing the volume of the coil and magnet, the size of the electromagnetic micropump is minimized so that it can be integrated on a microfluidic chip. The micropump and the chip can be portably packaged by using a small signal generation module and a dry battery to supply the coil with a square wave, reducing the dependence on external devices. In addition, multiple electromagnetic micropumps can be integrated on a single chip. These micropumps can be connected in series or in parallel, which can achieve complicated flow conditions and can simulate physiological fluid flow more realistically in different types of organ chips. The flow rate was measured to characterize the actuating performance of the micropump. We established the dynamic coculture of a liver and breast cancer model on the chip, with medium actuated by the electromagnetic micropump. Cell viability, albumin and IL-6 were analyzed. The results indicated that dynamic coculture, which was actuated by the electromagnetic micropump, was beneficial for cell growth and function compared with the static control group.

Experimental study: bridge pier protection against local scour using guide panels

The most important cause of failure in hydraulic structures is local scour. Local scour around a bridge pier is generally the result of the actions of a complex vortices system that appears due to the modification of flow patterns caused by obstructions associated with the bridge pier. Experimental studies have always been considered to be a powerful tool for understanding and analysing the performance of these complicated flow conditions, and for examining the effect of countermeasures which otherwise could not be subjected to theoretical analysis. This study was thus conducted to determine the efficiency of the proposed method of reducing the depth of scour under laboratory conditions. This was done by conducting scour studies for a pier protected by a guide panels of various heights under different hydraulic conditions suffering from clear water scour. The results showed that as the height of panels decreased, the scour depth also decreased, with a maximum reduction of scour depth equal to 93%, with negligible side effects on the guide panels’ scour. Dimensional analysis was used, and based on the laboratory results, an empirical formula was derived using IBM SPSS v.24 with a coefficient of determination R2 = 0.967; this indicates considerable convergence between predicated and observed data.

Complete spatial concentration distribution for Taylor dispersion in packed tube flow

Understanding solute transport process is of fundamental significance for industrial and natural processes such as mixing and separation. Since detailed information for the transverse concentration distribution is required for associated applications, compared with the sole consideration of the cross-sectional mean concentration in previous studies, the present paper analytically explores the complete spatial concentration distribution in packed tube flow by the proposed two-scale perturbation analysis (Z. Wu, G.Q. Chen, Journal of Fluid Mechanics, 740 (2014) 196–213.). With modification on the zeroth-order concentration up to the first-order, the deduced analytical solution gives a good prediction for the longitudinal distribution of mean concentration as well as the transverse distribution, according to comparisons with new results of numerical simulation. Importantly we show in the paper that instead of being uniformly distributed in the cross-section as expected in traditional view, the transverse concentration is highly non-uniform when Taylor dispersion model is applicable. Representing the complicated flow conditions for packed tube flow, the unique dimensionless parameter as a damping factor affects the complete spatial concentration distribution in two ways: cause the contraction of the solute concentration cloud, and the flattening of the concentration contours.

A unified and preserved Dirichlet boundary treatment for the cell-centered finite volume discrete Boltzmann method

A new boundary treatment is proposed for the finite volume discrete Boltzmann method (FVDBM) that can be used for accurate simulations of curved boundaries and complicated flow conditions. First, a brief review of different boundary treatments for the general Boltzmann simulations is made in order to primarily explain what type of boundary treatment will be developed in this paper for the cell-centered FVDBM. After that, the new boundary treatment along with the cell-centered FVDBM model is developed in detail. Next, the proposed boundary treatment is applied to a series of numerical tests with a detailed discussion of its qualitative and quantitative properties. From the results, it can be concluded that the new boundary treatment is at least first-order accurate for a variety of Dirichlet boundary conditions (BCs). It can handle both the velocity and density Dirichlet BCs in a unified way and further realize some BCs that the conventional lattice Boltzmann model fails to simulate. In addition, such a boundary treatment can incorporate different lattice models without changing its framework, and it can preserve the Dirichlet BCs up to machine accuracy in different situations.

Numerical Simulation on the Shock Wave/Boundary Layer Interaction with Heating/Cooling Effect

The complicated flow conditions inner or outer of the high speed vehicle would make the shock wave boundary layer (SWBLI) much different from its standard state on an adiabatic wall. The heating and cooling effects on the SWBLI achieved by changing the wall temperature, are evaluated by the numerical simulations. It is found that the wall temperatures have significant influence on the flow patterns of SWBLI. The scale of shock induced boundary layer separation increases obviously with the rise of the wall temperature, and the separation would shrink dramatically with the decrease of the wall temperature. This could be partially explained by the variation of the momentum thickness and displacement thickness of the incoming turbulent boundary layer under different wall temperature.

Shear-induced demixing in polymeric membrane dopes

One of the critical challenges in producing hollow fiber membranes is controlling fiber microstructure. The dope solutions involved possess (by design) an inherent thermodynamic sensitivity to phase separation, and are therefore susceptible to shear-induced microstructural changes when they are subjected to the complicated flow conditions that accompany spinning. This study demonstrates that shear-induced demixing is relevant in polymeric membrane dopes, and that it can affect macrovoid formation. Furthermore, we find that surprisingly subtle changes in shear history can affect demixing. Our investigation consisted of a two-tier approach. First, we used shear-small-angle light scattering (shear-SALS) to observe the microstructural evolution in liquid dope solutions before, during, and after shear flow. By varying the speed at which samples were syringe-loaded into the rheometer, we found that the pattern (and hence, the microstructure) observed after demixing varied based on shear history. In the second set of experiments, dopes with varying shear histories were extruded into a non-solvent bath to form solid fibers. Despite the fact that the fibers were all extruded under identical conditions, scanning electron microscopy (SEM) showed that the number of macrovoids observed varied widely between fibers. A comparison of the shear-SALS and extrusion results showed that shear-demixing is strongly linked to macrovoid formation. Our findings suggest that low-shear, upstream flow conditions (e.g., in supply tubing) could be just as important for fiber microstructure as the high-shear flow within the actual spinneret.

Characteristics of liquid and tracer dispersion in trickle-bed reactors: Effect on CFD modeling and experimental analyses

The characteristics of mechanical dispersion of tracer and liquid are analyzed using CFD modeling and experimental results from the literature. The most significant differences are underlined and their impact is discussed further. When compared to uniform liquid distribution, the more complicated flow conditions in liquid source measurements are considered to have a significant effect on result analysis and should be paid more attention to. Modeling of mechanical dispersion of liquid using CFD is discussed. Finally, liquid source dispersion cases are simulated and the results are compared to the experimental liquid as well as tracer dispersion results.

Surgically Implantable Magnetic Resonance Angiography Coils Improve Resolution to Allow Visualization of Blood Flow Dynamics

Magnetic resonance angiography (MRA) is clinically useful but of limited applicability to small animal models due to poor signal resolution, with typical voxel sizes of 1 mm(3) that are insufficient to analyze vessels of diameter <1 mm. We determined whether surgically implantable, extravascular MRA coils increase signal resolution adequately to examine blood flow dynamics A custom MRA coil was surgically implanted near the carotid artery of a New Zealand White rabbit. A stenosis was created in the carotid artery to induce complicated, non-laminar flow. Phase contrast images were obtained on multiple axial planes with 3T MRA and through-plane velocity profiles were calculated under laminar and complicated flow conditions. These velocity profiles were fit to a laminar flow model using ordinary least squares in order to quantify the degree of flow complication (Matlab). Flow was also measured with a Doppler flow probe; vessel diameters and flow velocities were compared with duplex ultrasound Carotid artery blood flow was 24.7 +/- 2.6 ml/min prior to stenosis creation and reduced to 12.0 +/- 1.7 ml/min following injury (n=3). An MRA voxel size of 0.1 x 0.1 x 5 mm was achieved. The control carotid artery diameter was 1.9 +/- 0.1 mm, and cross-sectional images containing 318 +/- 22 voxels were acquired (n=26). Velocity profiles resembled laminar flow proximal to the stenosis, and then became more complicated just proximal and distal to the stenosis. Laminar flow conditions returned downstream of the stenosis Implantable, extra-vascular coils enable small MRA voxel sizes to reproducibly calculate complex velocity profiles under both laminar and complicated flow in a small animal model. This technique may be applied to study blood flow dynamics of vessel remodeling and atherogenesis.

Analytical treatment of source terms for complex channel geometry

Starting from the classical conservative form of the shallow water equations, the source term of the momentum balance equation was modified to increase computational stability. This was achieved by replacing the term representing the local bed slope by an alternative expression of the pressure effect due to cross-section irregularities in non-prismatic channels. The resulting mathematical model turns out to be particularly suitable for complex channel and natural river geometries, and also improves the computational stability for complicated flow conditions. The explicit finite difference MacCormack scheme was adopted for numerical implementation. The model was thoroughly tested using a set of numerical test cases involving various channel geometries and a wide range of flow conditions. The same simulations were compared also with the classical model and with other schemes. Finally, a real flood event on the Italian river Reno was simulated, to confirm the model suitability for natural channels.

Surgically implantable magnetic resonance angiography coils improve resolution to allow visualization of blood flow dynamics

Fitzgerald, Tamara N. MD, PhD; Muto, Akihito MD, PhD; Fancher, Tiffany T. MD; Brown, Peter B.; Martin, Karen A. RT(R); Muhs, Bart E. MD, PhD; Rothman, Douglas L. PhD; Constable, Todd R. PhD; Sampath, Smita PhD; Dardik, Alan MD, PhD, FACS Author Information

Wave forces on a single and on a group of cylinders in response to two wave spectra of same significant wave height

Spectral analysis is used to determine the wave force characteristics on structures exposed to random waves. Considerable work has been carried out to determine the magnitude of random wave forces acting on a single cylinder, but little information is available in the case of a group of cylinders in random waves. Such situations arise when structures comprise multiple tubular members which are in close proximity, and wave forces cannot be calculated precisely by analytical methods due to complicated flow conditions past the group. Experimental studies are also required for proper understanding and analysis. An experimental scheme was carried out to study the wave force characteristics on a single cylinder and on a group of cylinders in response to two different wave spectra with the same significant wave height, and the results are compared.

Stoplog Closure—Model Prototype Correlation

Hydraulic model tests give accurate solutions to problems involving complicated flow conditions but designers should adopt designs which avoid unpredictable situations. To achieve one stage of diversion at Kainji Dam, Nigeria, for a River Niger flow of about 2,000 m³/s (71,000 cfs), reinforced concrete stoplogs were placed into guide slots by a specially built handling beam. The system was developed by extensive model tests prior to construction. Records kept during prototype operations enabled correlation to be made with the model tests which indicated good agreement apart from one event of severe overloading. Prototype conditions were subsequently reconstructed in the model but the phenomenon could not be reproduced. It was found that a late change in the type of seals between stoplogs could have contributed to the problem. Some speculation on possible mechanical and hydraulic explanations are given.