Optimum Boundary Research Articles

Chemical Activation of Sludge from Drinking Water Treatment Plant for Adsorption of Methylene Blue Dye

The objective of this study is to explore the preparation and application of sludge produced in plants of drinking water treatment, to remove methylene blue (MB) dye from polluted water. Adsorbate (methylene blue) is prepared in the lab. as a stock solution. To create new adsorbents, chemical activation of the used sludge has been carried out. The activation is performed by HCl and H2O2 and a mixture of HCl and H2O2. The experiments were carried out under different boundary conditions, like the initial concentration of dye, dosage of adsorbent, solution pH, contact time, and temperature of the adsorption, to determine the optimum boundary conditions for operation. All of the experiments in this study were carried out in a batch system. The results show that sludge activation by a mixture of 2:1 HCl/ H2O2 was selected as the best chemically activated adsorbent (removal of 99.9%). For the best MB adsorption results, the following criteria must be met: 50 ppm initial dye concentration, 90 min of contact time, pH 7, and a dosage of 0.25 g of the adsorbent. Adsorbents suit the Langmuir and Freundlich models well, according to applications of the Freundlich Isotherm and Langmuir models.

Optimum boundaries for maximum load-carrying capacity in water-lubricated composite journal bearings incorporating turbulences and inertial effects based on elastohydrodynamic analysis

Abstract The application of polymer-based composite materials as bearing liner materials in eco-friendly water lubrication has received considerable attention owing to their superior tribological behaviors, corrosion resistance, and high damping characteristics, and their design flexibility can improve the bearing performances in response to the distribution of lubricant film pressure based on the regulation of elastic constants. However, the low viscosity and high density of water essentially cause thin-filmed lubrication accompanied by a low load-carrying capacity. Particularly, a high rotational speed enhancing the wedge effect induces turbulence and considerable inertial effect. Moreover, substantial elastic deformation of the composite bearing liners alters the formation of the lubricant film. In this study, we analyze a water-lubricated composite journal bearing system incorporating the turbulence, inertial effect, and elastic deformation of the bearing liner. Reynolds equation was modified considering the turbulence and inertial effect. The elastic deformation of the composite bearing liner was determined by solving the constitutive equation. The Reynolds equation and the constitutive equation were solved via the finite difference method and finite element method, respectively. In addition, the analytical relation for the elastic deformation was derived that suitably eliminated the requirement of solving the constitutive equation. With the introduction of the primary parameters, Sommerfeld number, Reynolds number, and deformation coefficient, the relation of the normalized minimum film thickness with respect to the parameters was modeled based on the Gaussian regression model. Accordingly, we proposed the new optimal maximum load-carrying capacity boundaries that narrowed down the operating region compared to conventional boundaries.

Effect of isolated footing on fly ash subgrade reinforced with PET bottles: An experimental and analytical study

The continuous and significant excavation of subsurface soil and rock for structural backfilling, impacts the environment negatively. The present study attempts on the exploitation of non-biodegradable and hard-to-dispose waste materials (in different capacities) such as fly ash (FA), rock quarry dust (RQD), and refurbished Polyethylene Terephthalate (PET) bottles were used as an alternative for structural backfill and reinforcement. For model testing, two phase novel methodology was proposed (Unreinforced and reinforced FA system). A total of 29 systems were examined, encompassing a broad range of boundary conditions like FA subgrade system, unreinforced FA system (FA + RQD) with varying RQD layer thickness “H”, and reinforced FA system (FA + RQD with PET bottle mattress as an interface between the FA subgrade and the RQD layer). The parameters pertaining to the reinforcement (width “b”) are varied with respect to the constant value of “H”. Loading was applied on isolated footings for both phases. The model testing demonstrates that the performance of footings resting on RQD laid over stabilized FA subgrade with PET bottle mattress as an interface outperforms other systems significantly. Optimum values for boundary conditions were obtained in case of both the systems. It is observed that in case of reinforced FA system with optimum boundary conditions, the bearing capacity was increased by 10 % and the RQD layer’s thickness was reduced by 47 % as compared to optimum values of an unreinforced FA system. Further, the optimized values of the phases were validated by using PLAXIS 3D software.

Effect of Native Oxide on Stress in Silicon Nanowires: Implications for Nanoelectromechanical Systems

Understanding the origins of intrinsic stress in Si nanowires (NWs) is crucial for their successful utilization as transducer building blocks in next-generation, miniaturized sensors based on nanoelectromechanical systems (NEMS). With their small size leading to ultrahigh-resonance frequencies and extreme surface-to-volume ratios, silicon NWs raise new opportunities regarding sensitivity, precision, and speed in both physical and biochemical sensing. With silicon optoelectromechanical properties strongly dependent on the level of NW intrinsic stress, various studies have been devoted to the measurement of such stresses generated, for example, as a result of harsh fabrication processes. However, due to enormous NW surface area, even the native oxide that is conventionally considered as a benign surface condition can cause significant stresses. To address this issue, a combination of nanomechanical characterization and atomistic simulation approaches is developed. Relying only on low-temperature processes, the fabrication approach yields monolithic NWs with optimum boundary conditions, where NWs and support architecture are etched within the same silicon crystal. Resulting NWs are characterized by transmission electron microscopy and micro-Raman spectroscopy. The interpretation of results is carried out through molecular dynamics simulations with ReaxFF potential facilitating the incorporation of humidity and temperature, thereby providing a close replica of the actual oxidation environment─in contrast to previous dry oxidation or self-limiting thermal oxidation studies. As a result, consensus on significant intrinsic tensile stresses on the order of 100 MPa to 1 GPa was achieved as a function of NW critical dimension and aspect ratio. The understanding developed herein regarding the role of native oxide played in the generation of NW intrinsic stresses is important for the design and development of silicon-based NEMS.

Influences of granule properties on the performance of autotrophic nitrogen removal granular reactor: A model-based evaluation

This work studied the impacts of key granule properties on the granular reactor performing partial nitritation/anammox from the modeling perspective. The results could guide not only future reliable modeling but also practical startup/operation of the reactor. To achieve high total nitrogen (TN) removal whilst avoiding significant N2O production, inoculated granules should be big and anammox-enriched. The optimum boundary layer thickness for maximum TN removal increased with the decreasing diffusivity of soluble components in the granule structure. Even though a thick boundary layer could protect anammox bacteria from elevated dissolved oxygen (DO) (e.g., 0.5 g-O2/m3) and obtain high TN removal (>90.0%) and low N2O production (<1.8%), even complete removal of the boundary layer would fail to provide sufficient substrate for anammox and therefore couldn’t increase TN removal to 90.0% and decrease N2O production to <2.4% at insufficient DO (e.g., 0.3 g-O2/m3 in the presence of lifted influent NH4+ concentration).

Concurrent shape optimization for macro- and micro-structure of 3D multiscale porous structure

In this study, we present a 3D shape optimization method for designing micro- and macro-structures concurrently. We assume the macrostructure consists of several arbitrary subdomains, which have different periodic microstructures. The macro- and microstructures are bridged by the homogenized elastic tensors, which are calculated by applying the homogenization method to the unit cells of the microstructures. Defining the boundary shapes of the macro-, microstructures and the interface shapes between the subdomains as design variable, the compliance of the macrostructure is minimized. The volume of the macrostructure considering the whole holes in the microstructures is used as the constraint. The homogenization equations for the microstructures and the equilibrium equation for the macrostructure are also used as the constraint. This design problem is formulated as a distributed-parameter optimization problem, and the shape sensitivity functions are theoretically derived. The optimum boundaries of the macro- and microstructures are determined by the H1 gradient method. The proposed method is applied to a numerical example to confirm the effectiveness of the proposed method.

Stratification Methods for an Auxiliary Variable Model-Based Allocation under a Superpopulation Model

In this paper, the problem of optimum stratification of heteroscedastic populations in stratified sampling is considered for a known allocation under Simple Random Sampling With and Without Replacement (SRSWR & SRSWOR) design. The known allocation used in the problem is one of the model-based allocations proposed by Gupt [1,2] under a superpopulation model considered by Hanurav [3], Rao [4], and Gupt and Rao [5] which was modified by the author (Gupt [1,2]) to a more general form. The problem of finding optimum boundary points of stratification (OBPS) in stratifying populations considered here is based on an auxiliary variable which is highly correlated with the study variable. Equations giving the OBPS have been derived by minimizing the variance of estimator of the population mean. Since the equations giving OBPS are implicit and difficult for solving, some methods of finding approximately optimum boundary points of stratification (AOBPS) have also been obtained as the solutions of the equations giving OBPS. While deriving equations giving OBPS and methods of finding AOBPS, basic statistical definitions, tools of calculus, analytic functions and tools of algebra are used. While examining the efficiencies of the proposed methods of stratification, they are tested in a few generated populations and a live population. All the proposed methods of stratification are found to be efficient and suitable for practical applications. In this study, although the proposed methods are obtained under a heteroscedastic superpopulation model for level of heteroscedasticity one, the methods have shown robustness in empirical investigation in varied levels of heteroscedastic populations. The stratification methods proposed here are new as they are derived for an allocation, under the superpopulation model, which has never been used earlier by any researcher in the field of construction of strata in stratified sampling. The proposed methods may be a fascinating piece of work for researchers amidst the vigorously progressing theoretical research in the area of stratified sampling. Besides, by virtue of exhibiting high efficiencies in the performance of the methods, the work may provide a practically feasible solution in the planning of socio-economic survey.

دراسة تجريبية لتأثير مولد الدوامة على الطبقة الحدودية للوحة مسطحة

This paper is dealing with an experimental study to show the influence of the geometric characteristics of the vortex generators VG son the thickness of the boundary layer (∂) and drag coefficients (CD) of the flat plate. Vortex generators work effectively on medium and high angles of attack, since they are "hidden" under the boundary layer and practically ineffective at low angles. The height of VGs relative to the thickness of the boundary layer enables us to study the efficacy of VGs in delaying boundary layer separation. The distance between two VGs also has an effect on the boundary layer if we take into account the interference between two pairs of VGs. The effect of the changing in (h- the height of vortex generator, d- the average distance between tow vortex generators) on the thickness of the flat plate boundary layer and the drag coefficients has been studied for triangular vortex generator. The measurements of the vortex generator have been changed to determine the optimum boundary layer thickness and the change in drag coefficients. An experiment was done at an average free stream velocity, (U∞,) of 28 m/s. The experiment was conducted in the wind tunnel UTAD-2 University (NAU) Kiev, Ukraine.

Effect of substrate surface roughness on the wear of molybdenum disulphate coated rolling contact bearings

Abstract The objective of the present experimental work is to investigate the influence of subsurface roughness on the friction and wear performance of high-temperature ball bearing. Bearings, which are used in high-temperature applications, are affected by several operating conditions. Some factors under high-temperature conditions such as short grease life, thin-film thickness at low speed, and insufficient internal clearance can drastically reduce bearing service life due to an increase in surface friction. For this reason, rolling contact bearings are coated with molybdenum disulfide. Before the molybdenum disulfide (MoS2) coating, phosphatization is applied to the bearings. Because the phosphate layer is micro-porous, it assures that molybdenum disulfide is entrapped in the interstitials between the phosphates. Also, phosphate coating provides a much larger surface area for the lubricant to attach to. In this study, several process steps, sandblasting, manganese phosphate coating, molybdenum disulfide coating, friction moment testing, wear testing, wear depth measurement, SEM, and XRD analyses were carried out. Wear tests and friction moment tests were applied to the rings of bearings of varied raceway roughness. This process ultimately provides molybdenum disulfide coated bearings optimum raceway roughness parameters for good wear resistance and optimum boundary lubrication.

Boundary Element Modeling for Simulation and Optimization of Three-Temperature Anisotropic Micropolar Magneto-thermoviscoelastic Problems in Porous Smart Structures Using NURBS and Genetic Algorithm

The main objective of the present paper is to propose a new boundary element modeling technique for simulation and optimization of three-temperature micropolar magneto-thermoviscoelastic problems in anisotropic porous smart structures, where we implemented the genetic algorithm (GA), as a method of optimization based on the free form deformation (FFD) methodology to improve the performance of our proposed technique. Two numerical examples are presented herein, in order to prove that the proposed technique is able to optimize the shape of the domains with minimum computational effort. A nonuniform rational B-spline curve (NURBS) has been introduced to define the optimum boundary where it decreases the number of control points and offers a new degree of versatility in the design of various different shapes. The profiles of the items considered shall be represented by the FFD methodology. The location vectors of the FFD control points are known to be the genes, and then the chromosomes for the profiles are determined by the gene sequence. The population is made up of several chromosomes individuals, where the fitness functions of individuals are assessed using BEM. The numerical results are depicted graphical forms to show the effects of viscosity and magnetic fields on the three temperatures, displacement components, microrotation components, pore pressure, electric potential, and thermal stress components. The validity, accuracy, and computational efficiency of the proposed BEM technique were demonstrated by comparing our BEM-obtained results with the corresponding results of normal mode analysis method (NMAM), finite difference method (FDM), and finite element method (FEM).

Biohydrogen production using horizontal and vertical continuous stirred tank reactor- a numerical optimization

This paper illustrates the method to predict the production of biohydrogen and biogas from the horizontal and vertical continuous mixed tank reactor using a numerical approach. Utilization of computational fluid dynamics on the estimation of bioreactor performance is very crucial owing to the uncertainty in the numerical results. Since there has been little work on CFD to determine the influence of hydraulic retention time, impeller speeds, vortex growth, and pH on biohydrogen yield rate the effort had been made. A series of simulations are done with optimal boundary conditions to ensure maximum hydrogen and biogas production rate. Two types of reactors HCSTR and VCSTR are operated at different impeller speed from 40 rpm to 120 rpm. Further, the rate of HRT and organic loading are varied. As the rpm of the impeller increase the rate of hydrogen and biomass production increases not later than 80 rpm. Meanwhile, the optimal range of HRT and pH are 4–8 h and 6.0–8.0. Running the impeller at optimized rate with derived conditions leads to high hydrogen and biogas production of 6 LH2/Ld and 30 L/d. The obtained results are validated with the experimental findings to compare the uncertainty formed due to the numerical simulations. The optimum boundary condition obtained from the study is expected to provide the essential knowledge in establishing the full-scaled reactors.

The use of release analysis to show the selectivity of reagents towards differently sized feeds of the same coal

ABSTRACT Release analysis is used to characterize the cleaning ability of coal fines. It defines the limit of separation at any target level of ash. Since flotation depends upon many factors like feed size and its composition, surface properties, and type of reagents, it is important to characterize the optimum boundary of separation. Release analysis following the BS7503 procedure was used to characterize a − 0.5 mm composite feed and three sized feeds, i.e., −0.5 + 0.25, −0.25 + 0.1, and −0.1 mm using different reagent combinations. Coal response reflected by release curves and corresponding batch flotation results for various reagent combinations was found to be different for all three feeds. No single combination of collector and frother could deliver the maximum separation over the entire clean coal ash range for all three feeds. Significant yields ranging from 35% to 86% could be obtained at the 13% to 17% ash level for the medium volatile metallurgical coal investigated. Release curves and subsequent batch flotation results were found to be sensitive to feed size, feed size distribution, and reagent combination types with their corresponding dosage indicating that the clean coal ash requirement would dictate the application of reagents. The investigation results further show that release analysis results can be reproduced by batch flotation.

A numerical study on optimum shape of steel slit dampers

Steel slit dampers are among the passive energy dissipating devices that have been proposed to improve seismic performance of steel structures. Several experimental and numerical studies have also been carried out to investigate capacity of the dampers in energy dissipation. In this article, a numerical model is developed to obtain optimum boundary shape of the dampers. To achieve this, isogeometric analysis method is utilized as a powerful tool in precise modeling of complex geometries for the purpose of non-linear analysis of the dampers. A conventional steel slit damper shape is modeled by non-uniform rational B-splines, and then, the shape is optimized with the aim of maximizing the structural energy dissipation under a volume constraint. To verify the model, measurements of an experimental test in literature are compared with the model results. A mathematical-based approach is employed for the optimization process and analytical shape sensitivity analysis is performed. As a result of optimization process, a new steel slit damper is suggested and its performance is evaluated via comparing with other shapes suggested in the literature.

Optimum Boundary Inductance Control Concerning Limited PF for a DCM Boost PFC Converter

The discontinuous conduction mode boost power factor correction converter features zero-current turn- on for the switch, no reverse recovery in diode, and constant frequency operation. With traditional constant duty ratio control, the power transfer in each switching cycle exhibits great difference during a half-line cycle. Consequently, the peak and root mean square values of the inductor current are large, the same goes for the switch and diode. This increases not only the current stress of the power components but also the conduction and switching turn- off loss, and lowers the efficiency of the converter. Introducing third and fifth harmonics into the input current and varying the duty cycle correspondingly can reduce the aforementioned power transfer difference, and provide huge space for the increment of boundary inductance as well. An optimum boundary inductance control concerning limited power factor (PF) is proposed in this paper. For the maximum boundary inductance of the converter within wide input voltage range, the optimum harmonics amounts are analyzed and figured out. The proposed method brings about efficiency improvement, output voltage ripple reduction, and PF increase as well, especially at high input voltages. A prototype has been built and the experimental results are presented to show the validity of the scheme.

Visualization of density variations produced by alternating-current dielectric-barrier-discharge plasma actuators using the background-oriented schlieren method

Gas density perturbations generated by an alternating-current dielectric-barrier-discharge plasma actuator (ac-DBDPA) are quantitatively visualised using the background-oriented schlieren (BOS) method. A method of setting the optimum boundary condition for solving the Poisson equation in the BOS method is studied, and an integration method for the boundary condition in the vicinity of the plasma where the density change is steep is proposed. The BOS method is applied in two cases with different voltage amplitudes, and the variation in the absolute value of the density is discussed with the discharge properties. The results show a decrease in density in the synthetic jet induced by the ac-DBDPA and a spatiotemporal variation indicating a step-wise gas-heating phenomenon due to plasma discharge.

Numerical Investigation into the Product’s Weight loss and Display Shelf life inside the Serve-over Cabinet

One of the most important aspects of chilled food deterioration in delicatessen cabinets economically is associated with drying, rather than spoilage mechanism, especially for unwrapped products. Investigating the effects of the bacterial spoilage and moisture migration for chilled-unwrapped food product such as sandwiches, which have short display shelf life, and knowing the optimum boundary conditions that provide longer displays shelf life can significantly contribute to reduction of wastage of this type of product during its display, and operate refrigeration systems in the most efficient manner. Recent years have seen an increase in customer demand for fresh convenience food, which has resulted in a major increase in the volume of sales of unwrapped products. Surface drying has been identified as the main reason for commercial loss from unwrapped chilled food in display cabinets. Surface drying increases weight loss and leads to colour changes that are undesirable. A 2D Computational Fluid Dynamic model was constructed for the serve-over display cabinet that includes the weight loss from products inside the cabinet. The model was used to investigate the effect of the environmental boundary conditions on the drying rate and display shelf life. Validation was carried out by comparison of measured results of the product temperature, drying rate and display shelf life of the product inside the cabinet, to those predicted by the simulations. The results show that improving the operating boundary conditions inside the display cabinet can improve the food quality, reduce the drying rate of the food product and increase the display shelf life.

Using greater flamingo tracking and count data in delineating marine protected areas in the coastal zone of Abu Dhabi, United Arab Emirates: Conservation planning in an economically important area

Systematic conservation planning is essential in the justification and design of protected areas, especially in an era where every piece of land or water is at a high premium. We used satellite tracking data and regular monitoring of Greater flamingos into the spatial prioritization planning tool Marxan to identify the most important zones for the conservation of the greater flamingo and many other species of waterbirds and marine habitats in one of the economically important areas in the coastal zone of Abu Dhabi. Locations from 10 satellite tracked flamingos and monthly count data since 2009 in the Bul Syayeef area showed a predominant use of a relatively small area which when integrated in Marxan provided optimum boundary with minimum cost. Marxan identified 1, 5, 10 and 15 ha planning units and provided the best solution with 15 ha. The reduced total area of 145 km2 is nearly 40% of the originally proposed area for protection, is more pragmatic and easy to establish, given the high importance of the area for economic development. Using approximately the same boundary, the proposed area was declared a Ramsar site in September 2016 and was subsequently declared a protected area through a government decree in November 2017.

Plasmons in Ballistic Nanostructures With Stubs: Transmission Line Approach

The plasma wave instabilities in ballistic Field Effect Transistors (FETs) have a promise of developing sensitive THz detectors and efficient THz sources. One of the difficulties in achieving efficient resonant plasmonic detection and generation is assuring proper boundary conditions at the contacts and at the heterointerfaces and tuning the plasma velocity. We propose using the tunable narrow channel regions of an increased width, which we call "stubs" for optimizing the boundary conditions and for controlling the plasma velocity. We developed a compact model for THz plasmonic devices using the transmission line (TL) analogy. The mathematics of the problem is similar to the mathematics of a TL with a stub. We applied this model to demonstrate that the stubs could effectively control the boundary conditions and/or the conditions at interfaces. We derived and solved the dispersion equation for the device with the stubs and showed that periodic or aperiodic systems of stubs allow for slowing down the plasma waves in a controllable manner in a wide range. Our results show that the stub designs provide a way to achieve the optimum boundary conditions and could also be used for multi finger structures - stub plasmonic crystals - yielding better performance of THz electronic detectors, modulators, mixers, frequency multipliers and sources.

Optimization of bioclogging in vermifilters: A statistical approach

In the present research, an experiment was conducted with the objective of optimization of the role of earthworms in alleviating the bioclogging of a horizontal subsurface flow vermifilter (HSSFVF), caused due to the application of organics rich brewery wastewater. In this experiment, for the optimization of bioclogging of the vermifilters, the Box-Behnken Design (BBD) and response surface methodology (RSM) were involved. Hydraulic loading rate (HLR), influent COD and earthworm density (EWD) are the variables against which the bioclogging of the HSSFVF has been optimized. EWD of 9475 earthworms/m3, HLR of 1.84 m3/m2-d and influent COD of 3701 mg/L have been observed as the optimized values for the minimum bioclogging in the vermifiltration of brewery wastewater. At this optimum boundary conditions, the reduction in hydraulic conductivity was obtained as 1.49%, against the predicted value of 1.67% based upon the BBD model. The verification of the model against real brewery wastewater yielded insignificant error and thus very strongly portrays the suitability of the derived BBD model. The study indicates that the bioclogging from the vermifilters can be minimized, if the variables are optimized using the response surface methodology.

Optimal stratification in stratified designs using weibull-distributed auxiliary information

Sampling has evolved into a universally accepted approach for gathering information and data mining as it is widely accepted that a reasonably modest-sized sample can sufficiently characterize a much larger population. In stratified sampling designs, the whole population is divided into homogeneous strata in order to achieve higher precision in the estimation. This paper proposes an efficient method of constructing optimum stratum boundaries (OSB) and determining optimum sample size (OSS) for the survey variable. The survey variable may not be available in practice since the variable of interest is unavailable prior to conducting the survey. Thus, the method is based on the auxiliary variable which is usually readily available from past surveys. To illustrate the application as an example using a real data, the auxiliary variable considered for this problem follows Weibull distribution. The stratification problem is formulated as a Mathematical Programming Problem (MPP) that seeks minimization of the variance of the estimated population parameter under Neyman allocation. The solution procedure employs the dynamic programming technique, which results in substantial gains in the precision of the estimates of the population characteristics.