Maximum Allowable Pump Research Articles

An ensemble-based approach for pumping optimization in an island aquifer considering parameter, observation and climate uncertainty

Abstract. In coastal zones, a major objective of groundwater management is often to determine sustainable pumping rates which avoid well salinization. Understanding how model and climate uncertainties affect optimal management solutions is essential for providing groundwater managers with information about salinization risk and is facilitated by the use of optimization under uncertainty (OUU) methods. However, guidelines are missing for the widespread implementation of OUU in real-world coastal aquifers and for the incorporation of climate uncertainty into OUU approaches. An ensemble-based OUU approach was developed considering parameter, observation and climate uncertainty and was implemented in a real-world island aquifer in the Magdalen Islands (Quebec, Canada). A sharp-interface seawater intrusion model was developed using MODFLOW-SWI2 and a prior parameter ensemble was generated containing multiple equally plausible realizations. Ensemble-based history matching was conducted using an iterative ensemble smoother which yielded a posterior parameter ensemble conveying both parameter and observation uncertainty. Sea level and recharge ensembles were generated for the year 2050 and were then used to generate a predictive parameter ensemble conveying parameter, observation and climate uncertainty. Multi-objective OUU was then conducted, aiming to both maximize pumping rates and minimize the probability of well salinization. As a result, the optimal trade-off between pumping and the probability of salinization was quantified considering parameter, historical observation and future climate uncertainty simultaneously. The multi-objective, ensemble-based OUU led to optimal pumping rates that were very different from a previous deterministic OUU and close to the current and projected water demand for risk-averse stances. Incorporating climate uncertainty into the OUU was also critical since it reduced the maximum allowable pumping rates for users with a risk-averse stance. The workflow used tools adapted to very high-dimensional, nonlinear models and optimization problems to facilitate its implementation in a wide range of real-world settings.

Performance analysis of an SDM-WDM multicore optical fiber link

Analytical evaluation of inter-channel and inter-core coupling induced crosstalk including Amplified Spontaneous Emission (ASE) noise in a single mode 7-core homogeneous multi-core optical fiber (MCF) based Space Division Multiplexed Wavelength Division Multiplexing (SDM-WDM) communication system with distributed Raman amplifier is presented. The Stimulated Raman Scattering (SRS) induced crosstalk impairment including ASE noise and inter-core and inter-channel coupling induced crosstalk at the output of any core with excitation into other core of the MCF is investigated. Signal to Crosstalk plus Noise Ratio (SCNR) is determined at the output of photo detector of the excited core. Finally, Bit Error Rate (BER) performance results are evaluated for different system parameters, viz. WDM channel number, channel spacing, propagation distance, pump power etc. It is noticed that BER deteriorates with SRS induced crosstalk and ASE noise, which is worsened further by the effect of inter-core crosstalk (IC-XT). The maximum acceptable propagation distance for a desired value of BER and other system parameters considering inter-channel crosstalk (Ich-XT), IC-XT including SRS induced crosstalk and ASE noise is also evaluated analytically. For example, to maintain a particular BER (10E-9, say) we need to increase the input signal power from 2.5dBm to 5.5dBm while increasing the WDM channels from 12 to 16 considering only the SRS and ASE noise. On the other hand, we need to increase the input signal power from 5.5dBm to 9.0dBm to increase the WDM channels from 12 to 16 when the IC-XT is added up with the SRS and ASE noise. The maximum allowable pump power considering the collective impact of Ich-XT and IC-XT including SRS and ASE noise is determined for a given value of BER (10E-9). Power penalty versus WDM channel spacing at a given BER value (10E-10), link distance and pump power at different WDM channels is also evaluated and presented.

Analytical solutions for seawater intrusion and the maximum pumping rate of a well in unconfined coastal aquifers bounded by L-shaped coastlines

Determining the maximum pumping rate (i.e., the maximum allowable pumping rate that does not cause seawater intrusion into the well under the steady-state condition) of a well is the key for sustainable management of coastal aquifers, as overexploitation of coastal aquifers could lead to the widespread occurrence of aquifer salinization (i.e., seawater intrusion). In this study, we develop steady-state analytical solutions to describe seawater intrusion and the maximum pumping rate of a well located in unconfined coastal aquifers bounded by L-shaped coastlines. Rectangular coastal aquifers bounded by two orthogonal constant-head boundaries (i.e., two coastlines) and two orthogonal no-flow inland boundaries are assumed in conceptual models, where replenishment of aquifers is via surface recharge. Analytical solutions are derived by the potential theory and the conformal mapping method, and validated by variable-density flow numerical simulations. It is found that analytical solutions based on the sharp-interface approximation overestimate seawater intrusion and underestimate the maximum pumping rate. An acceptable, conservative maximum pumping rate is obtained by using the correction factor proposed by Lu and Werner (2013). Moreover, the sensitivity of the well location on the maximum pumping rate is investigated, showing that an optimal well location exists. Analytical solutions developed in the current study provide a convenient tool for assessing pumping effects in coastal aquifers bounded by L-shaped coastlines, servicing to various management objectives.

Experimental and modeling investigation of pumping from a fresh groundwater lens in an idealized strip island

Groundwater lens floating on the seawater in surficial coastal aquifers is an important freshwater supply for small island inhabitants. This study addresses an unanswered, simple but important question for groundwater resources management in small islands: how much freshwater can be sustainably withdrawn from a groundwater lens in small islands. We derive an approximate analytical solution to describe the freshwater-seawater sharp interface profile in an idealized strip island subject to a pumping well located at the domain center to determine the critical or maximum allowable pumping rate that prevents saltwater upconing. A simple formula of the critical pumping rate is provided as a function of hydrogeologic parameters, including the recharge rate, densities, hydraulic conductivity and well penetrating depth. It shows that the critical pumping rate increases linearly with the recharge rate and decreases linearly with the hydraulic conductivity and the squared well penetrating depth. Laboratory visualization experiments and numerical simulations were conducted to validate the derived analytical solution. Results indicate that the maximum pumping rate can be as high as 50% of the total recharge for a single well located at the top of the domain center. Our solutions and results provide useful insights for sustainable groundwater management in small islands and can potentially render significant social and economic impact for inhabitants on small islands.

A high-efficient solution for electro-hydraulic actuators with energy regeneration capability

This paper proposes a cost-effective, robustly practical solution for a high-efficient electro-hydraulic actuator (EHA) for linear drives. The solution addresses the challenges of high costs and limited efficiency that limit the application of EHA for the electrification of many off-road vehicles. Based on a variable-speed electric motor and a low-cost technology for a fixed-displacement pump, the proposed solution is suitable for a compact implementation and it is capable of energy regeneration under overrunning load conditions. Two different architectures—an open circuit and a closed circuit one—are considered to determine the most practical and efficient configuration as well as the control features. Both architectures minimize throttling losses associated with the conventional regulation of hydraulic actuators. Actuator velocities below the minimum and beyond the maximum allowable pump flow rate are achieved in both architectures using a proportional valve that bypasses the pump flow. The paper describes the design methodology as well as the simulation and experimental activities performed to verify the control strategies as well as energy efficiency. Considering an EHA system of about 20 kW, a complete efficiency map of the system is determined for all the possible four quadrants of operation thus including both resistive and overrunning loads, where energy recuperation is implemented. Simulation and experimental results show that the energy efficiency of the hydraulic systems can reach 84.7% in resistive phases. In assistive phases, the hydraulic system can recover up to 81.8% of the actuator energy. The comparison between open-circuit and closed-circuit structures shows the advantages of the former in terms of energy efficiency. The proposed solution is suitable for electrified hydraulic actuation systems, in both industrial and mobile applications. With the advantages of the low cost of the hydraulic unit and high energy efficiency, it is particularly suitable for mobile applications such as construction machines, that are recently experiencing a significant electrification trend.

Interface Flow With Vertically Varying Hydraulic Conductivity

AbstractWe present an approach for solving problems of saltwater intrusion in aquifers with an hydraulic conductivity that varies in the vertical direction. The approach is based on the concept of a comprehensive potential, whose gradient exactly represents the vertically integrated discharge, which is, by definition, a two‐dimensional vector. We apply the approach to an island in Sweden and use it to estimate maximum allowable pumping rates of wells that recover part of the infiltration on the island.

A new approach to evaluate temperature distribution and stress fracture within solid state lasers

This work presents a new approach to determine the maximum allowable pump power that causes fractures in solid-state lasers. By considering temperature-dependent-thermal conductivity, heat equation was solved and an analytical thermal model of laser diode double end-pumped cylindrical laser rod was deduced. Taking into account two unequal pump radii focused on each rod faces, the temperature distribution and thermal stresses components were calculated at the two end faces of the rod under top-hat pump profile. The results showed that at the maximum total pump power of 200 W (80 W on the right side and 120 W on the left side) the rod is subject to fracture.

Slow light generation using SBS in a liquid-core photonic crystal fiber

Based on stimulated Brillouin scattering (SBS), the slow light effect in photonic crystal fibre (PCF), which is filled with highly nonlinear liquid-carbon disuphide in the core region, is investigated. Maximum allowable pump power for undistorted output pulse, minimum value of pump power required to initiate the SBS effect, Brillouin gain and time-tonic delay experienced by the pulse in the designed liquid-core photonic crystal fibre, are all calculated numerically. We have found that the maximum time-delay up to ∼134.4 ns at 1.064 μm can be obtained using 1 m long liquid-core PCF pumped with only 65.8 mW, which is lower than the value reported in the literature for achieving such a high delay time. The results indicate that liquid-core PCF is capable of generating tunable time-delay that is adjusted by the pump power and structural parameters of the proposed liquid-core PCF.

Design of As2Se3 based chalcogenide ridge waveguide for generation of slow light

A theoretical investigation of the design of a ridge waveguide in highly nonlinear As2Se3 chalcogenide glass has been carried out for the generation of stimulated Brillouin scattering (SBS) based slow light. The effective-mode-area and confinement loss of the waveguide structure has been obtained for single-mode operation and their variation with the geometrical parameters. Maximum allowable pump power and the time delay experienced by the pulse propagating in the ridge waveguide operating at a wavelength of 1.56μm have been calculated. A maximum delay of ∼249ns has been achieved for a 10cm long ridge waveguide at a pump power of 390mW. It is observed that time delay can be tuned with input pump power and length of the proposed ridge waveguide. Such tunable features of the slow light can have potential applications in realization of an all-optical network.

Design and analysis of single-mode tellurite photonic crystal fibers for stimulated Brillouin scattering based slow-light generation.

We theoretically examine two designs of single-mode (i) Er-doped tellurite and (ii) undoped tellurite photonic crystal fiber (PCF) for generation of slow light with tunable features based on stimulated Brillouin scattering. We obtained (i) Brillouin gain up to 91 dB and time delay of ∼145 ns at maximum allowable pump power of ∼775 mW in a 2 m Er-doped tellurite PCF and (ii) Brillouin gain up to ∼88 dB and time delay of ∼154 ns at maximum allowable pump power ∼21 mW in a 100 m undoped tellurite photonic crystal fiber. Simulated results clearly indicate that the doped tellurite PCF with Er enhances the maximum allowable pump power and comparable time delay can be obtained even with reduced photonic crystal fiber length. We believe that the carried out examination and simulation have potential impact on design and development of slow-light-based photonic devices applicable in telecommunication systems, enhancement of optical forces, and quantum computing.

Analysis and Design of Single-Mode As2Se3-Chalcogenide Photonic Crystal Fiber for Generation of Slow Light With Tunable Features

Theoretical investigation leading to design of a single-mode As2Se3-chalcogenide photonic crystal fiber is reported for generation of a tunable slow light. Maximum allowable pump power for undistorted output pulse, Brillouin gain, and time-delay experienced by the pulse propagating in designed photonic crystal fibers are simulated. We have found that Brillouin gain upto ∼88 dB/m and time delay up to ∼137 ns can be obtained from 1-m-long photonic crystal fiber pumped with 100 mW. Simulated results indicate that the time delay experienced by the pulse can be tuned with the pump power and structural parameters of As2Se3 -chalcogenide photonic crystal fiber.

Optimization of pumping policy using coupled finite element-particle swarm optimization modelling

An optimal pumping policy during groundwater extraction ensures the sustainability of groundwater resources. In this paper, a coupled finite element-particle swarm simulation–optimization model is implemented to assess the optimal pumping policy in a confined heterogeneous anisotropic synthetic aquifer. Pumping wells are set up in the aquifer to meet a specified water demand. The objective is to find the optimum number and pumping discharges of these wells such that their collective drawdown is minimized while meeting the demand at a reasonable cost. Constraints on the maximum allowable pumping discharge and the location of the wells are also imposed. After analysing the aquifer behaviour in the presence of 8, 9 and 10 pumping wells, the optimal number of wells is selected. The coupled FEM-PSO model also predicts the spatial distribution of the wells that incur the minimum cost for installation and pumping to a specified storage location. Adequate tuning of the PSO parameters involving population size, inertia weight, acceleration constants and number of iterations is performed to arrive at their optimal values.

Slow light generation in single-mode tellurite fibers

Theoretical investigations of stimulated brillouin scattering-based tunable slow light in (i) Er-doped tellurite and (ii) undoped tellurite fibers are reported. Maximum allowable pump power for undistorted output pulse, Brillouin gain, time-delay, figure-of-merit, and time-delay slop efficiency of both the fibers has been obtained. We have found that (i) Brillouin gain up to ~91 dB and time delay of 140 ns can be achieved using 1100 mW pump power in 2 m Er-doped fiber and (ii) Brillouin gain up to ~86 dB and time delay of ~227 ns using 23 mW pump power in 100 m undoped tellurite fiber can be achieved. Simulated results indicate that the time delay in fibers can be tuned with the pump power to obtain tunable slow light features in these fibers. We feel that detailed theoretical investigations and simulations carried out in the study have potential impact in the design and development of slow light-based photonic devices.

Groundwater pumping in head-controlled coastal systems: The role of lateral boundaries in quantifying the interface toe location and maximum pumping rate

Summary The current study explores quantitatively the impact of lateral impermeable boundaries on groundwater pumping in head-controlled coastal systems, based on the potential theory and the image-well superposition method. We compare the interface toe location and maximum pumping rate among three scenarios that assume (S1) an infinite domain width and a finite domain length, (S2) a finite domain width and length, and (SS) an infinite domain width and length. Focusing exclusively on boundary effects, the upstream freshwater discharge is assumed the same for all scenarios, regardless of the variation in domain size. It is found that the impact from both inland and lateral boundaries could play a significant role on the interface toe location and maximum pumping rate (defined as the maximum allowable pumping rate that will not lead to pumping saltwater), depending on sizes of domain length and width. Since the impacts of inland fixed-head boundary and lateral impermeable boundaries are contrary on the maximum interface toe location (defined as the farthest inland point of the interface toe under pumping condition) and maximum pumping rate, they can be offset under certain critical conditions such that the results of the two quantitative indictors (i.e. the maximum interface toe location and maximum pumping rate) in S2 are close to those in SS. In particular, a linear equation is derived to reflect the relationship between the domain width and length under such critical conditions and expressed as L * = 0.87 W * + 0.62 ( W * > 1 or L * > 1.5), in which W * and L * are the domain width and length normalized by the distance between the coastline and pumping well. When L * > 0.87 W * + 0.62, the impact from lateral overcomes that from inland, producing a larger maximum interface toe location and a lower maximum pumping rate than those in SS. When L * W * + 0.62, by contrast, the impact from inland exceeds that from lateral and hence, resulting in a smaller maximum interface toe location and a higher maximum pumping rate. It is expected that the results developed in the current study could support the design of numerical models and 3D laboratory experiments as well as the assessment of domain size impact on pumping in head-controlled coastal groundwater systems.

Groundwater Availability as Constrained by Hydrogeology and Environmental Flows

Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes-St. Lawrence River Basin Water Resources Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications.

Estimation of Salt Water Upconing Using a Steady‐State Solution for Partial Completion of a Pumped Well

A new steady-state analytical solution to the two-dimensional radial-flow equation was developed for drawdown (head) conditions in an aquifer with constant transmissivity, no-flow conditions at the top and bottom, constant head conditions at a known radial distance, and a partially completed pumping well. The solution was evaluated for accuracy by comparison to numerical simulations using MODFLOW. The solution was then used to estimate the rise of the salt water-fresh water interface (upconing) that occurs under a pumping well, and to calculate the critical pumping rate at which the interface becomes unstable, allowing salt water to enter the pumping well. The analysis of salt water-fresh water interface rise assumed no significant effect on upconing by recharge; this assumption was tested and supported using results from a new steady-state analytical solution developed for recharge under two-dimensional radial-flow conditions. The upconing analysis results were evaluated for accuracy by comparison to those from numerical simulations using SEAWAT for salt water-fresh water interface positions under mild pumping conditions. The results from the equation were also compared with those of a published numerical sharp-interface model applied to a case on Cape Cod, Massachusetts. This comparison indicates that estimating the interface rise and maximum allowable pumping rate using the analytical method will likely be less conservative than the maximum allowable pumping rate and maximum stable interface rise from a numerical sharp-interface model.

Determination of groundwater availability in shallow arid region aquifers utilizing GIS technology: a case study in Hada Al-Sham, Western Saudi Arabia

A simple, physically based method is developed in this paper to assist in the allocation of areas with high groundwater potential and for the determination of maximum allowed pumping rate to ensure proper groundwater management. This method utilizes the aquifer physical properties as well as GIS technology to accomplish this purpose. The design of this method was considered to be applicable in areas with little data, such as in most arid regions. This technique was applied to a catchment in an arid environment where qualitative as well as quantitative analyses of the results were undertaken. Locations of available groundwater and rates of maximum allowable pumping were compared with observations and experiments in the field and a good agreement was found. It was concluded that the best groundwater location was in the alluvial area, which represents only 16% of the total aquifer, which is a typical case in arid region catchments. The rate of maximum pumping was estimated to be 65 m3/h. However, to benefit 55% of the area, the maximum pumping rate should only be 40 m3/h with an average rate throughout the area (55%) of about 24 m3/h.

In-Situ Rheological Characterization of Drilling Mud

Summary The rheological model of Herschel and Bulkley reported in 1926 can be applied to determine the characteristic parameters of a drilling fluid. In this paper, an in-situ characterization approach is proposed. During flow tests at fixed drilling depths inside the well the pump rates and the relative stand pipe pressures (SPP's) are recorded. This allows one to determine in-situ the Herschel and Bulkley rheological parameters and the behavior of the drilling mud circulating in the well. The results are compared to those obtained in the laboratory using a Fann VG 35 viscometer for the same drilling mud. It is found that the rheological triad from the viscometer data does not always coincide with the rheological triad from the in-situ drilling test. Thus, the calculated SPP using viscometer readings could lead to misleading errors for an actual process. This method could be useful not only to calculate and predict the SPP, but also to evaluate with accuracy the annular pressure drop in order to obtain the maximum allowable pump rates without fracturing the formations. We discuss the sensitivity of the results in relation to the equivalent viscosity of the drilling fluids considered to some of the main practical drilling parameters, such as the flow velocity and pressure spatial distribution along the wellbore profile and, with reference to the mud structure, sensitivity to pressure and temperature. Considering the drilling well essentially as a viscometer (WAV) enables one to investigate the performance of the drilling hydraulic circuit and also the effects of the true effective viscosity (here called equivalent viscosity) and of the rheological behavior of the muds in all types of wells, and overall in deep wells with great accuracy.

New Disclosures in Predicting Stand Pipe Pressures While Drilling

For the purpose of the present paper the analytical formulations of Herschel and Bulkley rheological model including the most relevant expressions of pressure drops, valid both for circular and annular sections, are applied in order to determine the three characteristic parameters of a known drilling fluid, having yield pseudoplastic behaviour, and flowing in the drilling hydraulic circuit, starting from field circulation tests. As it is well known, a typical standard drilling hydraulic circuit consists of the surface circuit (stand pipe, rotary hose, swivel and kelly, the circular section (inside the drill string with variable diameters), the bit and the annular section (the gap between the borehole wall or casing and the drill string). In this circuit the drilling mud enters the drill pipe, comes out from the bit, flows up through the annulus up to the surface, where (after a short time for cleaning) it is put back in the circuit. The parameters to be inspected are the yield point t0, the consistency index k, the flow behaviour index n. By means of at least 3 flow tests at a certain drilling depth, with the bit off bottom, the pump rates and the corresponding stand pipe pressures are recorded. The obtained N couple of values of stand pipe pressure and pump rate, the geometry of the hydraulic circuit and the fluid density are the input data for a numerical procedure to determine the three parameters of the considered drilling fluid. In this way, using this numerical process, a nonlinear system of N equations (with N≥3) having 3 unknowns (the three parameters of the fluid: n, k and t0) is solved determining the Herschel and Bulkley rheological parameters. This procedure inspects the most probable solution for each tentative value of the flow behaviour index np, considering the infinite couples of t0 and k satisfying the input value of the stand pipe pressure. Through the computation of the mean square deviation for each of the tentative values of np , the solution term of the nonlinear system of N equations can be obtained. The computed results are compared to the ones obtained using the readings on the same drilling mud performed on Fann VG 35 viscometer. Not always the rheological term outcoming from the viscometer data exactly fits the equivalent rheological term found by considering the drilling well as a viscometer. Computed SPP data using the equivalent rheological term and the rheological parameters from viscometer readings, using diferent rheological models such a s Bingham, Ostwald and de Waele and Herschel and Bulkley, are compared to field stand pipe pressure data. It can be seen that the overall average error between measured and computed SPP (using the Herschel and Bulkley equivalent term) has drastically reduced to very small values, while the com- puted SPP using viscometer readings with most of the rheological models today used could lead to large errors, thus misleading an accurate evaluation of the SPP on the rig floor site. This procedure shows to be useful even to carefully evaluate the annular pressure drop and the corresponding ECD, in order to have the maximum allowable pump rates without fracturing the crossed formations. Additionally, it could be used to monitor the SPP behaviour for potential problems in the hydraulic circuit, such a s wash out events, plugged nozzles, and also in the case of gas kicks in the well. If applied to different dril- ling depths, the method can usefully inspect the influence of pressure and temperature exis- ting in the well upon the rheology of the mud. This particular characterization is going to be inspected in the forthcoming research stages, which have already been designed to date.

The Tanggu geothermal reservoir (Tianjin, China)

The Tanggu geothermal system is an extensive, highly permeable, horizontal sandstone reservoir, situated within the North China Sedimentary Basin. Twenty-three successful production wells, yielding water with an average temperature of about 70°C, have been drilled into this reservoir since 1987, distributed over an area of some 330 km 2. The hot water is mostly used for space heating. In 1995 the annual production exceeded 5 million tons. Hot water extraction has caused the water level to drop to a depth of 80 m in the production wells, and it continues to decline at a rate of 3–4m per year. This has raised the question as to whether the reservoir may be overexploited. The main objective of a reservoir evaluation carried out in 1996 was to estimate the long-term production potential of the Tanggu reservoir. Two simple models were developed for this purpose. The potential is determined by specifying a maximum allowable pump setting depth of 150m. On this basis the potential of the Tanggu reservoir is estimated to be about 10 million tons per year, for the next ten years. A comprehensive reservoir management program must be implemented in Tanggu. The first priority of such a program should be to improve the energy efficiency of space heating in the district, which should result in about 50% reduction in hot water consumption. Another management option is reinjection, which would counteract the water level draw-down.