Software for Evaluating Pumping Tests on Real Wells

As the climate is changing, greater exploitation of groundwater reserves is becoming evident; however, this would have been apparent even without climate change. Therefore, increasing emphasis is given to maintaining well functionality. Wells are susceptible to aging, which reduces their efficiency. Today, there exist several solutions for determining the size of additional resistance (the skin effect), which indicates a well’s current state and that of its close surroundings. The implementation of most of these solutions is often time-consuming. To improve our tools, a goal has been set to accelerate and facilitate the method of determining the size of additional resistance. In this study, we present new software that accelerates this process. It applies an innovative method based upon a partial differential equation describing the radially symmetric flow to a real well, which occurs under an unsteady regime, using the Laplace transform. Stehfest algorithm 368 is used to invert the Laplace transform. Such software can be used to evaluate an additional-resistance well, even when a straight section evaluated using the Cooper–Jacob method is not achieved in the semilogarithmic plot of drawdown vs. log time during the pumping test. This solution is demonstrated in the comprehensive evaluation of 10 wells and 3 synthetic pumping tests.

Numerical Computations of Vortex Formation Length in Flow Past an Elliptical Cylinder

We examine two dimensional properties of vortex shedding past elliptical cylinders through numerical simulations. Specifically, we investigate the vortex formation length in the Reynolds number regime 10 to 100 for elliptical bodies of aspect ratio in the range 0.4 to 1.4. Our computations reveal that in the steady flow regime, the change in the vortex length follows a linear profile with respect to the Reynolds number, while in the unsteady regime, the time averaged vortex length decreases in an exponential manner with increasing Reynolds number. The transition in profile is used to identify the critical Reynolds number which marks the bifurcation of the Karman vortex from steady symmetric to the unsteady, asymmetric configuration. Additionally, relationships between the vortex length and aspect ratio are also explored. The work presented here is an example of a module that can be used in a project based learning course on computational fluid dynamics.

Квантовое сжатие поля одноатомного лазера в условиях переменной константы связи

In this work we investigate unsteady regime of generation of squeezed light in a single-atom laser. Dependences of the parameter of quantum squeezing and light intensity on modulation frequency of the coupling constant between an atom and field were calculated numerically for this. We showed that at the modulation frequency equal to double coupling constant parametric resonance occurs. This regime leads to more effective quantum squeezing than regime under steady generation with the same parameters of the pumping and the relaxation.

Combined effects of the velocity and the aspect ratios on the bifurcation phenomena in a two-sided lid-driven cavity flow

Purpose This paper aims to analyze the effect of aspect ratio A and aspect velocity ratio a on the bifurcation occurrence phenomena in lid-driven cavity by using finite volume method (FVM) and multigrid acceleration. This study has been performed for certain pertinent parameters; a wide range of the Reynolds number values has been adopted, and aspect ratios ranging from 0.25 to 1 and various velocity ratios from 0.25 to 0.825 have been considered in this investigation. Results show that the transition to the unsteady regime follows the classical scheme of Hopf bifurcation, giving rise to a perfectly periodic state. Flow periodicity has been verified through time history plots for the velocity component and phase-space trajectories as a function of Reynolds number. Velocity profile for special case of a square cavity (A = 1) was found to be in good agreement between current numerical results and published ones. Flow characteristics inside the cavity have been presented and discussed in terms of streamlines and vorticity contours at a fixed Reynolds number (Re = 5,000) for various aspect ratios (a = 0). Design/methodology/approach The numerical method is based on the FVM and multigrid acceleration. Findings Computations have been investigated for several Reynolds numbers and aspect ratios A (0.25, 0.5, 0.75, 0.825 and 1). Besides, various velocity ratios (a = 0.25, 0.5, 0.75 and 0.825) at fixed aspect ratios (A = 0.25, 0.5 and 0.75) were considered. It is observed that the transition to the unsteady regime follows the classical scheme of Hopf bifurcation, giving rise to a perfectly periodic state. Flow periodicity is verified through time history plots for velocity components and phase-space trajectories. Originality/value The bifurcations between steady and unsteady states are investigated.

Study of Heat Transfer Processes in Modelled Core of Nuclear Reactor with Helium Coolant

The paper considers prospects of multi-purpose use of high-temperature gas (helium) nuclear reactors. The processes of hydrodynamics and heat exchange in the modelled core of the hightemperature nuclear reactor with spherical fuel elements were studied. The influence of geometrical and mode parameters on the temperature distribution was analyzed. The paper presents results of calculating unsteady regime with reduction of in consumption of coolant flow in the core.

The Dependence of QPF on the Choice of Microphysical Parameterization for Lake-Effect Snowstorms

Several lake-effect-snow forecasts are compared to assess how the choice of microphysical parameterization affects quantitative precipitation forecasting (QPF). Eight different schemes, with different numbers of moments and categories of hydrometeors, are considered. Half of the schemes are in the steady regime (so named because the precipitation rates are nearly constant with time), and the remaining experiments are in the unsteady regime, which has a high temporal variation in precipitation. The steady-regime members have broader precipitation shields and 24-h accumulations that range from 43 to 50 mm. In the unsteady regime, the precipitation shields are narrower, leading to higher accumulations (ranging from 55 to 94 mm). These differences are the result of lower terminal velocities υt in the steady regime, which allows for relofting or suspension of hydrometeors (assuming the vertical velocity is sufficiently large) and, hence, a longer in-cloud residence time and stronger downstream transport. In the six-category experiments, low υt values in the steady regime occur in conjunction with a lower production of graupel, which is primarily due to less accretion of rain by snow. In the five-category experiments, differences are due to the way υt is functionally dependent on environmental temperature and the degree of riming, with the steady regime having a more conservative relation. The steady regime compares better to available observations, although both have notable forecast errors.

Numerical Study of the Flow in the Wake of an Impulsively Started Rotating and Translating Circular Cylinder

In the present work, a detailed investigation in the wake region of the flow for the case of a two dimensional, laminar, incompressible flow past a rotating and translating circular cylinder has been carried out by applying a second order time accurate finite difference method using primitive variable formulation for different values of α ranging between 0 and 8 for Re = 200, where α is a nondimensional peripheral velocity of the cylinder. It has been observed that lift coefficient increases monotonically with α. But the effect of rotational speed on the steadiness of the flow is found significantly critical. Within the present range of α it is found that there have been back and forth regimes of unsteadiness in the flow. The flow remains unsteady for α ≤ 1.95, becomes steady for 1.95 ≤ α ≤ 4.33 and is unsteady again for 4.33 ≤ α ≤ 4.73. For α > 4.73 the flow is again steady. It is found that while the first steady regime of flow is characterised by two oppositely rotating static vortices, the second steady regime is characterised by only one rotating static vortex wrapping around the cylinder. It is also found that the nature of two unsteady regimes are not same. Detailed investigation reveals that in the first mode of vortex shedding, vortices are shed alternatively from both top and bottom surfaces, while in the second mode, the shedding occurs only from the bottom surface. Investigation also explains the cause behind increase of lift, decrease of drag with respect to α. From FFT analysis it can be concluded that lift curves corresponding to the first unsteady regime are simple sinusoidal waves, while those corresponding to the second unsteady regime are combinations of different harmonics. On the other hand, simple sinusoidal nature of the drag variation is found only when α is zero. By tracking the vortex shedding process closely, it is observed that during the process of formation, a small anticlockwise vortex is formed inside a large anticlockwise wrapping vortex around the cylinder to result into a higher pressure stagnation region just below the cylinder which in turn, effects maximum lift and detaches the small vortex from the lower surface of the cylinder resulting into vortex shedding from the bottom surface.

The pulsatile propagation of a finger of air within a fluid-occluded cylindrical tube

We computationally investigate the unsteady pulsatile propagation of a finger of air through a liquid-filled cylindrical rigid tube. The flow field is governed by the unsteady capillary number CaQ(t)=μQ*(t*)/πR2γ, where R is the tube radius, Q* is the dimensional flow rate, t* is the dimensional time, μ is the viscosity, and γ is the surface tension. Pulsatility is imposed by CaQ(t) consisting of both mean (CaM) and oscillatory (CaΩ components such that CaQ(t)=CaM+CaΩ sin(Ωt). Dimensionless frequency and amplitude parameters are defined, respectively, as Ω=μωR/γ and A=2CaΩ/Ω, with Ω epresenting the frequency of oscillation. The system is accurately described by steady-state behaviour if CaΩ<CaM; however, when CaΩ>CaM, reverse flow exists during a portion of the cycle, leading to an unsteady regime. In this unsteady regime, converging and diverging surface stagnation points translate dynamically along the interface throughout the cycle and may temporarily separate to create internal stagnation points at high Ω. For CaΩ<10CaM, the bubble tip pressure drop ΔPtip may be estimated accurately from the pressure measured downstream of the bubble tip when corrections for the downstream viscous component of the pressure drop are applied. The normal stress gradient at the tube wall ∂τn/∂z is examined in detail, because this has been shown to be the primary factor responsible for mechanical damage to epithelial cells during pulmonary airway reopening (Bilek, Dee & Gaver III 2003; Kay et al. 2004). In the unsteady regime, local film-thinning produces high ∂τn/∂z at low CaΩ; however, film thickening at moderate Ca protects the tube wall from large ∂τn/∂z. This stress field is highly dynamic and exhibits intriguing spatial and temporal characteristics that may be used to reduce ventilator-induced lung injury.