On different numerical inverse Laplace methods for solute transport problems

Numerical simulation of vortex-induced vibration of a full-scale flexible riser at supercritical Reynolds number in uniform and linear shear flow

Hydrodynamic dispersion, the combined effects of chemical diffusion and differences in solute path length and flow velocity, is an important factor controlling contaminant migration in the subsurface environment. However, few comprehensive three‐dimensional datasets exist for critically evaluating the impact of travel distance and site heterogeneity on solute dispersion, and the conservative nature of several commonly used groundwater tracers is still in question. Therefore, we conducted a series of field‐scale experiments using tritiated water ( 3 H 1 HO), bromide (Br − ), and two fluorobenzoates (2,4 Di‐FBA, 2,6 Di‐FBA) as tracers in the water‐table aquifer on the USDOE's Savannah River Site (SRS), located on the upper Atlantic Coastal Plain. For each experiment, tracer‐free groundwater was injected for approximately 24 h (56.7 L min −1 ) to establish a steady‐state forced radial gradient before the introduction of a tracer pulse. After the tracer pulse, which lasted from 256 to 560 min, the forced gradient was maintained throughout the experiment using nonlabeled groundwater. Tracer migration was monitored using six multilevel monitoring wells, radially spaced at approximate distances of 2.0, 3.0, and 4.5 m from the central injection well. Each sampling well was further divided into three discrete sampling depths that were pumped continuously (∼0.1 L min −1 ) throughout the course of the experiments. Longitudinal dispersivity (α L ) and travel times for 3 H 1 HO breakthrough were estimated by fitting the field data to analytical approximations of the advection–dispersion equation (ADE) for uniform and radial flow conditions. Dispersivity varied greatly between wells located at similar transport distances and even between zones within a given well, which we attributed to variability in the hydraulic conductivity at the study site. The radial flow equation generally described tritium breakthrough better than the uniform flow solution, as indicated by the coefficient of determination, r 2 , yielding lower α L while accounting for breakthrough tailing inherent to radial flow conditions. Complex multiple‐peak breakthrough patterns were observed within certain sampling zones, indicative of multiple major flow paths and the superposition of resulting breakthrough curves. A strong correlation was found between α L and arrival times observed from one experiment to the next, indicative of the general reproducibility of the tracer results. Temporal moment analysis was used to evaluate tracer migration rate as an indicator of variations in hydraulic conductivity and flow velocity, as well as mass recovery and retardation for the ionic solutes compared with tritiated water. Retardation factors for Br − ranged from 0.99 to 1.67 with no clear trend with respect to transport distance; however, Br − mass recovery decreased with distance, suggesting that the retardation values are biased in terms of early arrival because of limited detection and an insufficient monitoring duration. Anion retardation was attributed to sorption by iron oxides. Similar results were observed for the FBA tracers. The assumption of conservative behavior for the anionic tracers would generally result in higher α L values and lower estimated flow velocities.

Moonpools are holes in the middle of a ship's hull and through its deck. In this study, the flow mechanisms in moonpools in calm water were investigated. Star-CCM+ software was used to calculate the flow within a two-dimensional (2D) moonpool under uniform flow conditions. A 2D moonpool numerical calculation model was constructed, and the convergence analysis results and experimental data were used to verify the accuracy of the calculated results. Flow field and free surface fluctuations are the main factors that cause the drag force of the moonpool. The drag force increases with the flow velocity, and the drag coefficient presents different trends at different stages. With an increase in the Froude number, Fr, the 2D moonpool enters the frequency lock-in state of the piston and sloshing natural frequency. Additionally, increasing the moonpool length results in a nonlinear change in the flow state.

Staggered circular cylinders immersed in a uniform planar shear flow

A comparison of two methods for the numerical inversion of laplace transforms

Formation damage study with a horizontal wellbore model

Numerical modelling of sediment–bacteria interaction processes in surface waters

수공구조물 설계 또는 하상의 유동 특징을 나타내기 위해선 마찰속도 산정이 필수적이다. 하지만 기존의 개수로 내의 마찰속도 공식인 Log 방법이나 Power방법은 벽면 근처에서 경계층 조건 혹은 다양한 수리적 특성이 지속적으로 변화하기 때문에 마찰속도의 산정에 어려움이 있다. 따라서 본 연구에서는 매개변수를 최소화하고 오차를 줄일 수 있는 새로운 마찰속도 공식을 제안하였다. 제안한 공식에 대한 신뢰성과 정확성을 검증하기 위하여 엔트로피매개변수M을 각각의 수로마다 산정을 하여 Dr.Song이 산정한 3가지 방법(Clauser 방법, <TEX>$\sqrt{gRI}$</TEX> 방법, 레이놀즈 응력법)으로 산정한 마찰속도와 비교하였다. 그 결과 가속부등류 조건의 경우 <TEX>$R^2=0.9621$</TEX> 감속부등류 조건의 경우 <TEX>$R^2=0.9274$</TEX> 등류흐름 조건의 경우 <TEX>$R^2=0.8865$</TEX>로 매우 높은 정확성으로 등류조건뿐만 아니라 부등류 조건에서도 거의 일치하였다. In order to demonstrate the flow properties of the river bed and the design of hydraulic structures, the estimation of friction velocity is essentially required. However, existing friction velocity equations such as Log method and Power law have trouble to estimate the friction velocity because a boundary condition and various hydraulic properties are changed constantly in near the wall. In the present study, therefore, a new friction velocity equation that can minimize the parameters and reduce an error was suggested. To verify accuracy and reliability for the proposed equation, Clauser method, <TEX>$\sqrt{gRI}$</TEX> method, reynolds stress method by Dr. Song were compared with the proposed method by estimated entropy parameter M for each channel. Consequently, the results show that uniform flow condition as well as non-uniform flow condition with highly accuracy nearly matched in case of accelerating non-uniform condition of <TEX>$R^2=0.9621$</TEX>, Decelerating Non Uniform condition of <TEX>$R^2=0.9274$</TEX>, Uniform condition of <TEX>$R^2=0.8865$</TEX>.

Waterjet propulsion has many advantages when operating at high-speed conditions. As a special way of navigation, it is mostly used in high-speed ships and shallow draft ships. In this paper, a mixed-flow waterjet pump was taken as the research object. For the two cases of non-uniform inflow and uniform inflow, a modified RANS/LES method was adopted for unsteady calculation of the whole channel, aiming at investigating the influence mechanism of the non-uniform inflow on the energy performance and pressure pulsation characteristics of the waterjet pump. The hydrodynamic characteristics of the waterjet pump were comprehensively analyzed such as head, efficiency, axial-force, internal flow and pressure pulsation. It is found that the non-uniform inflow will reduce the external characteristics of the waterjet pump and lead to the huge fluctuation of energy performance with time. Low-speed swirls occur locally in the intake duct for non-uniform inflow, in which condition the vorticity is much higher than that for uniform inflow. In terms of the low-speed area, [Formula: see text] and [Formula: see text], the values under non-uniform inflow condition are generally larger than those under uniform flow condition when in the impeller and guide vane zone. The dominant frequencies of pressure pulsation are, respectively, [Formula: see text], 7[Formula: see text] and 4[Formula: see text] in the intake duct, impeller and diffuser, which are almost consitent for the two cases. However, the frequency features are more diverse, and the amplitudes corresponding to the same frequencies are more intense for non-uniform inflow.

Interest in flow resistance and discharge calculation in channels and pipes has a long history dating back to the early hydraulic engineering achievements in Europe and the Ancient Near East. However it was only comparatively recently that a scientific basis for flow calculation was laid with the development of uniform flow equations such as those attributed to Chezy and Manning for channels and to Darcy and Weisbach for pipeflow. Such equations have been very widely used even where uniform flow conditions do not apply, and they have been incorporated into more complex expressions used to analyse varied and unsteady flow regimes

Anomalous (or non-Fickian) transport is ubiquitous in the context of tracer migration in geological formations. We quantitatively identify the origin of anomalous transport in a representative model of a heterogeneous porous medium under uniform (in the mean) flow conditions; we focus on anomalous transport which arises in the complex flow patterns of lognormally distributed hydraulic conductivity (K) fields, with several decades of K values. Transport in the domains is determined by a particle tracking technique and characterized by breakthrough curves (BTCs). The BTC averaged over multiple realizations demonstrates anomalous transport in all cases, which is accounted for entirely by a power law distribution approximate to t-1- of local transition times. The latter is contained in the probability density function (t) of transition times, embedded in the framework of a continuous time random walk (CTRW). A unique feature of our analysis is the derivation of (t) as a function of parameters quantifying the heterogeneity of the domain. In this context, we first establish the dominance of preferential pathways across each domain, and characterize the statistics of these pathways by forming a particle-visitation weighted histogram, Hw(K), of the hydraulic conductivity. By converting the ln(K) dependence of Hw(K) into time, we demonstrate the equivalence of Hw(K) and (t), and delineate the region of Hw(K) that forms the power law of (t). This thus defines the origin of anomalous transport. Analysis of the preferential pathways clearly demonstrates the limitations of critical path analysis and percolation theory as a basis for determining the origin of anomalous transport. Furthermore, we derive an expression defining the power law exponent in terms of the Hw(K) parameters. The equivalence between Hw(K) and (t) is a remarkable result, particularly given the nature of the K heterogeneity, the complexity of the flow field within each realization, and the statistics of the particle transitions.

An aerodynamic distortion grill is employed to create non-uniform flow from arbitrary uniform upstream flow conditions. Such grills find widespread use in aerodynamic testing applications to generate non-uniform flow conditions. In this paper, the numerical results of the distortion created by one such aerodynamic distortion grill are reported. The computational results were validated against the experimentally observed distortion indices. Further, parametric numerical studies were done by varying the inlet turbulence intensity and by scaling up the geometry of the flow system.

Interaction between the free surface and the bed material in flow over rock chutes under macroroughness conditions leads to a high air entrainment into the flow. The note reports on an experimental study about air diffusion features in the flow over a long rock chute. Air concentration profiles and water depths over a uniform bed material were measured. An empirical equation for the average air concentration in macroroughness condition for steep slopes is proposed. A new Darcy-Weisbach equivalent friction factor for long chutes as a function of the slope and the relative equivalent depth has also been found.

Fouling and fouling mitigation on heated metal surfaces

In this work, a numerical simulation using Computation Fluid Dynamics technique was used to investigate the flow properties and turbulence characteristics through flow of one-line cylinder in an open channel with uniform flow conditions. A two-dimensional turbulence model was applied using ANSYS. Flow properties were investigated against varying cylinder diameters that forms a one-line cylinder physical model and varying flow rates. Three cylinders diameters D were used (5.0 cm, 2.5 cm and 1.25 cm) and located at 12.5 cm apart along the flume centreline. Spatial distributions of mean-stream-wise velocity, pressure, turbulent kinetic energy, and eddy viscosity were estimated. Results showed symmetrical distribution of flow velocity, turbulence eddy, and turbulent kinetic energy along the one-line cylinder for the largest cylinder diameter. Vortex shedding patterns were well predicted by the numerical simulation behind the cylinders. Different configurations of vortices distribution behind the cylinders were recorded for the diameters of 1.25 cm and 2.5 cm. The flow pattern difference between the largest diameter (5 cm) and the small diameters (2.5 cm and 1.25 cm) was leaded to the strong overlap for the vortices in the wake for the lined cylinders with the large diameter in comparison to the other diameters. Consequently, this study is investigated the different diameter sizes of a one-line cylinder with the same spacing between them on the flow pattern along the channel.