Analytical Solutions for Free-Hydrocarbon Recovery Using Skimmer and Dual-Pump wells

Accidental release of petroleum hydrocarbons to the subsurface may occur through spills around refineries, leaking pipelines, storage tanks, or other sources. If the spill is large, the hydrocarbon liquids may eventually reach a water table and spread laterally in a pancake-like lens. Hydrocarbons that exist as a separate phase are termed light nonaqueous phase liquids (LNAPLs). The portion of the LNAPL that is mobile, not entrapped as residual saturation, is termed "free product."
This paper presents new analytical solutions for the design of long-term free-product recovery from aquifers with skimmer, single- and dual-pump wells. The solutions are for steady-state flow, based on the assumption of vertical equilibrium, and include the effect of coning of LNAPL, air, and water on flow. The solutions are valid for soils of large hydraulic conductivity where the effect of capillary pressure on coning is small.
The results show how to estimate the maximum rate of inflow of LNAPL for skimmer wells, i.e., wells in which LNAPL is recovered with little or no water production. The paper also shows how to calculate the increase in LNAPL recovery when water is pumped by single- or dual-pump wells. A simple equation is given that can be used to adjust the water rate to avoid smearing of the LNAPL below the water table.     

Performance of a conceptual and physically based model in simulating the response of a semi‐urbanized watershed in San Antonio,Texas

The need for accurate hydrologic analysis and rainfall–runoff modelling tools has been rapidly increasing because of the growing complexity of operational hydrologic and hydraulic problems associated with population growth, rapid urbanization and expansion of agricultural activities. Given the recent advances in remote sensing of physiographic features and the availability of near real‐time precipitation products, rainfall–runoff models are expected to predict runoff more accurately. In this study, we compare the performance and implementation requirements of two rainfall–runoff models for a semi‐urbanized watershed. One is a semi‐distributed conceptual model, the Hydrologic Engineering Center‐Hydrologic Modelling System (HEC‐HMS). The other is a physically based, distributed‐parameter hydrologic model, the Gridded Surface Subsurface Hydrologic Analysis (GSSHA). Four flood events that took place on the Leon Creek watershed, a sub‐watershed of the San Antonio River basin in Texas, were used in this study. The two models were driven by the Multisensor Precipitation Estimator radar products. One event (in 2007) was used for HEC‐HMS and GSSHA calibrations. Two events (in 2004 and 2007) were used for further calibration of HEC‐HMS. Three events (in 2002, 2004 and 2010) were used for model validation. In general, the physically based, distributed‐parameter model performed better than the conceptual model and required less calibration. The two models were prepared with the same minimum required input data, and the effort required to build the two models did not differ substantially. Copyright © 2012 John Wiley & Sons, Ltd.     

Application of the honey-bees mating programming (HBMP) algorithm to sediment concentration modelling

Abstract

The honey-bees mating programming (HBMP) algorithm is introduced as a novel tool for predicting suspended sediment concentration for the Mad River catchment near Arcata, USA. The paper also applies gene expression programming (GEP) as a comparison and shows that these two approaches can the produce transparent, nonlinear relationships between the independent and dependent variables. Some modifications have been made to the HBMP algorithm to improve its capability and efficiency. The results achieved from this method and GEP are compared with two different sediment rating curves based on regression techniques. The findings show that the results from both the HBMP and GEP methods are promising and outperform the results obtained from the sediment rating curves.

Editor D. Koutsoyiannis; Associate editor L. See     

Effect of inertia nonlinearity on dynamic response of an asymmetric building equipped with tuned mass dampers

This study investigates the effect of nonlinear inertia on the dynamic response of an asymmetric building equipped with Tuned Mass Dampers (TMDs). In the field of structural engineering, many researchers have developed models to study the behavior of nonlinear TMDs, but the effect of nonlinear inertia has not received as much attention for asymmetric buildings. To consider nonlinear inertia, the equations of motion are derived in a local rotary coordinates system. The displacements and rotations of the modeled building and TMDs are defined by five-degree-of-freedom (5-DOFs). The equations of motion are derived by using the Lagrangian method. Also in the proposed nonlinear model, the equations of motion are different from a conventional linear model. In order to compare the response of the proposed nonlinear model and a conventional linear model, numerical examples are presented and the response of the modeled buildings are derived under harmonic and earthquake excitations. It is shown that if the nonlinear inertia is considered, the response of the modeled structures changes and the conventional linear approach cannot adequately model the dynamic behavior of the asymmetric buildings which are equipped with TMDs.     

Modification of MCM‐41 with Anionic Surfactant: A Convenient Design for Efficient Removal of Cationic Dyes from Wastewater

The potential of MCM‐41 for the removal of cationic dyes from water solution was evaluated using sodium dodecyl sulfate (SDS) for the surface modification of this mesoporous material. Admicelle structures formed on the surface of the calcined MCM‐41 are capable of removing organic pollutants and cationic species from water environment. The structural, textural, and surface chemical characteristics of the prepared SDS‐modified MCM‐41 (SDS‐MCM‐41) were studied. The adsorption capacity of SDS‐MCM‐41 was evaluated for methylene blue (MB) as a target cationic dye. Equilibrium adsorption isotherm data were manipulated employing nonlinear regression analysis. The Langmuir, Freundlich, and Sips isotherm models were examined. The adsorption data were well fitted to both Langmuir and Sips isotherm models. The maximum adsorption capacity of SDS‐MCM‐41 for MB, based on Langmuir and Sips models, were 290.8 and 297.3 mg g^?1, respectively. Ethanol was found to be an effective solvent for partial regeneration of the adsorbent.     

A numerical modeling of hydrodynamic characteristics of various planing hull forms

A numerical algorithm based on the boundary element method (BEM) is presented for predicting the hydrodynamic characteristics of the various planing hull forms. The boundary integral equation is derived using Green's theorem on the wetted body surface and the free surface. The ventilation function at the transom is estimated with Doctor's empirical formula. This function is defined as the transom zone free surface boundary condition. The combined boundary integral equation and modified free surface boundary condition are simultaneously solved to determine the dipole on the wetted hull surface and the source on the free surface. The method is applied to investigate three examples of planing hulls, which include flat-plates, as well as wedge-shaped and variable deadrise planing hulls. Their hydrodynamic characteristics are calculated for different speeds. Computational results are presented and compared with existing theories and experiments. On the whole, the agreement between the present method and the selected experimental and numerical data is satisfactory.     

Lessons learnt from a collaborative management programme in coastal Tanzania

The Tanga Coastal Zone Conservation and Development Programme, initiated in 1994, was among the first such projects to make livelihoods improvement a key objective, and to use a community-based approach. It developed an approach to coastal management planning that is broadly satisfactory to both communities and the government. Six fisheries management areas and two mangrove management areas were established. Institutional arrangements for the collaborative approach were strengthened and community leaders and local government officers were trained in a range of relevant skills. A coastal environmental education programme for primary schools involved several thousand schoolchildren, and a gender programme built the confidence of women. Implementation of the management measures was noticeably harder than planning, particularly elimination of destructive fishing methods. Fishers and coastal communities now however have a much greater involvement in, and understanding of, coastal management and consequently a greater sense of ownership.     

Computational hydrodynamic analysis of the propeller–rudder and the AZIPOD systems

A computational method has been developed to predict the hydrodynamic performance of the propeller–rudder systems (PRS) and azimuthing podded drive (AZIPOD) systems. The method employs a vortex-based lifting theory for the propeller and the potential surface panel method for the steering system. Three propeller models along with three steering systems (rudder and strut, flap and pod (SFP)) are implemented in the present calculations for the cases of uniform and non-uniform conditions. Computed velocity components show good agreement with the experimental measurements behind a propeller with or without the rudder. Calculated thrust, torque and lift also agree well with the experimental results. Computations are also performed for an AZIPOD system in order to obtain the pressure distributions on the SFP, and the hydrodynamic performance (thrust, torque and lift coefficients). The present method is useful for examining the performance of the PRS and AZIPOD systems in the hope of estimating the propulsion and the maneuverability characteristics of the marine vehicles more accurately.