Presence Of Dead Zones Research Articles

Survey on Optical Wireless Communication with Intelligent Reflecting Surfaces

Optical Wireless Communication (OWC) technology has gained significant attention in recent years due to its potential for providing high-data-rate wireless connections through the large license-free bandwidth available. A key challenge in OWC systems, similar to high-frequency Radiofrequency (RF) systems, is the presence of dead zones caused by obstacles like buildings, trees, and moving individuals, which can degrade signal quality or disrupt data transmission. Traditionally, relays have been used to mitigate these issues. Intelligent Reflecting Surfaces (IRSs) have recently emerged as a promising solution, enhancing system performance and flexibility by providing reconfigurable communication channels. This paper presents an overview of the application of IRSs in OWC systems. Specifically, we categorize IRSs into two main types: mirror array-based IRSs and metasurface-based IRSs. Furthermore, we delve into modeling approaches of mirror array-based IRSs in OWC and analyze recent advances in IRS control, which are classified into system power or gain optimization-oriented, system link reliability optimization-oriented, system data rate optimization-oriented, system security optimization-oriented, and system energy optimization-oriented approaches. Moreover, we present the principles of metasurface-based IRSs from a physical mechanism perspective, highlighting their application in OWC systems through the distinct roles of light signal refraction and reflection. Finally, we discuss the key challenges and potential future directions for integrating IRS with OWC systems, providing insights for further research in this promising field.

A question of personalities: evolution of viscous and wind-driven protoplanetary discs in the presence of dead zones

A question of personalities: evolution of viscous and wind-driven protoplanetary discs in the presence of dead zones

EHB Gear-Drive Symmetric Dead-Zone Finite-Time Adaptive Control

Intelligent driving vehicles require more accurate and stable braking control. Electrohydraulic braking (EHB) systems can better adapt to the development of autonomous driving technology. The gear transmission system plays a crucial role in EHB deceleration and torque increase mechanisms. However, its dead-zone nonlinearity poses challenges for EHB control. To address the position-control problem in the EHB gear transmission system, we propose a finite-time adaptive control method for the symmetrical dead zone. This approach combines adaptive control theory with finite-time control theory and designs parameter-updating laws for the unknown parameters in the system. Boundary estimates are introduced into the parameter-update laws and control laws to compensate for unknown disturbances. By adjusting the relevant parameters, the convergence rate can be improved, ensuring that errors converge within a specified range within a limited time. After modifying the parameter-updating laws and control laws, all closed-loop signals remain bounded. Finally, we validate the proposed control strategy through simulation and hardware-in-the-loop (HIL) testing. The results demonstrate that the control strategy developed in this study achieves high tracking accuracy and stability even in the presence of dead zones, unknown parameters, and unknown interferences in the EHB gear-drive servo system.

Hydrodynamics of an integrated fish and periphyton recirculating aquaculture system

Marine aquaculture helps to mitigate a number of environmental problems, such as overfishing, loss of biodiversity, and eutrophication. Periphyton-based biofilters are a promising technology for marine aquaculture water treatment because periphyton repurposes nutrients as fish feed and produces dissolved oxygen (DO). Integration of periphyton biofilters into recirculating aquaculture systems (RAS) also preserves water and prevents pollutant discharges. In this study, we examined the effect of system hydrodynamics on two pilot-scale (2500 L) RAS with integrated periphyton biofilters, which were used to grow Ariopsis felis (hardhead catfish). Periphyton was harvested weekly from hanging nets. Conservative tracer tests conducted at varying fluid velocities indicated the presence of dead zones along tank edges. Growth of periphyton biomass was found to be primarily dependent on the nutrient mass loading rate. Improved mass transport and uptake of aqueous nutrients by periphyton occurred at higher fluid velocities. DO production by periphyton photosynthesis also increased with increasing fluid velocities. Mass balances on C, N, and DO were carried out to elucidate the nutrient transformation pathways and quantities. DO analysis revealed that periphyton provided 1.31 ± 0.20 mg DO/(L*m2*day) during daytime hours. This was nearly enough to support microbial and fish respiration without the use of a blower. Periphyton and filamentous algae, Oscillatoriaceae, removed 32 ± 4 % of the input nitrogen and 61 ± 3 % of input carbon from the feed that was not taken up by the cultured fish. The overall water quality goals for the catfish were either met or exceeded through application of periphyton biofilters in the RAS.

ИССЛЕДОВАНИЯ ВЛИЯНИЯ СКОРОСТИ ПЕРЕМЕШИВАНИЯ ОТХОДОВ АГРОПРОМЫШЛЕННОГО КОМПЛЕКСА НА КОЛИЧЕСТВО ПРОИЗВОДИМОГО БИОГАЗА

At the enterprises of the agro-industrial complex there is a large amount of waste, most of which is not recycled. This leads to a number of environmental problems, such as soil acidification and the greenhouse effect caused by methane emissions into the atmosphere. Meanwhile, waste from the agro-industrial complex (AIC) is an excellent raw material for the production of biogas, an environmentally friendly fuel that agribusiness enterprises can use for their own generation of heat and electricity, thus reducing the volume of energy purchases from generating companies. In addition to heat and electricity, biogas technologies make it possible to obtain high-quality fertilizers, which agricultural enterprises can later use, for example, for growing greenhouse cropsIn this paper, we studied the effect of the waste mixing rate in a bioreactor on the amount of biogas produced. The studies were carried out at the following mixing speeds: 40, 70 and 100 rpm. The research results showed that at a speed of 70 rpm, the most efficient mixing of the biomass in the reactor is observed. At a stirrer speed of 40 rpm, the presence of dead zones was observed in the reactor, which indicates a low efficiency of biomass mixing. In addition, at a stirrer speed of 70 rpm, the maximum daily production of biogas is observed, namely 1100 l. At a stirrer speed of 100 rpm, a noticeable reduction in the amount of biogas produced was observed due to the high mixing intensity. In general, in the studied time period (17 days), at mixing speeds of 40, 70 and 100 rpm, 9800, 10400 and 8000 liters of gas are produced, respectively. Thus, the highest performance of the bioreactor is achieved at a biomass stirring speed of 70 rpm.

Evaluation of mixing performance and validation of CFD simulations in baffled anaerobic digesters using radiotracer technique

The anaerobic digesters find usage in treating the huge amount of waste such as trash, garbage, human waste and animal waste. The sustained performance of an anaerobic digester depends on the flow pattern and mixing behaviour in the digester. A cylindrical digester tank with vertical baffles can provide flow behaviour approaching that of a plug flow reactor. However, the presence of dead zones and recirculating regions cause non-ideal flow in the digester. In this work, the mixing behaviour in two scaled-down models of baffled digester tanks is characterized by measurement of residence time distribution (RTD) using a radioactive tracer. While the first design has three vertical baffles, the second design include horizontal static flaps on the baffles. The flow behaviour in the digester is also simulated using computational fluid dynamics (CFD) and RTD is obtained computationally. The comparison of RTD curves obtained from CFD simulations with those obtained from radiotracer experiments show good agreement between them. There appear to be only minor difference in the flow behaviour and the RTD curves in the two digester designs. Using the RTD curve data, two commonly used RTD models, tank-in-series and dispersion models, have been fitted and both models are able to predict the RTD in the digester qualitatively.

SPECIFICS OF CALCULATING AREAS OF CITY BLOCKS BY UTILIZING THE PHOTOGRAMMETRIC (PHOTOTHEODOLITE) METHOD

The definition of the territory of urban development by various methods, including such as geodetic, photogrammetric and cartographic, is considered. It is found that the use of geodetic methods with direct coordination of contour points of the figure on the ground allows to obtain the most accurate and reliable result. The advantages and disadvantages of using photogrammetric method of research located in a closed area, where you can not always see the entire contour of the area. It is noted that when processing aerial photographs, regardless of what they were obtained, there are questions of correct decoding. In the process of decoding is finding the right area, which is associated with the correct location of the contour surrounding the area. It is proved that photogrammetric methods for determining the area remain priority methods that helps to proper allocation of time and funding through the use of such an approach. Problems of using quasi-aerial photographs taken from a height of about 2 km are described. The main obstacles that arise when processing aerial photographs are analyzed, namely - correct decoding, which depends on the openness of the territory in which the city district is located, that is the presence of dead zones. Recommendations are given to eliminate problems that occur in dead zones where 3D measurements are virtually impossible, for example, in this case, you can use either multiple measurements or a comparative method with other methods of determining areas.

Energy efficient design of high depth raceway pond using computational fluid dynamics

Abstract Open Raceway Ponds (RWP) are at present the most used large-scale reactors for microalgae culture. RWPs are extensively applied technology for algae mass cultivation although the scientific design of these ponds remains a major hurdle in this field. An erroneous design result in the presence of dead zones where the fluid flow is sluggish and non-uniform velocity throughout the pond actualized negative impact on algae growth, further these designs are energy inefficient. A dominant component of energy loss is the energy required to circulate the fluid around the raceway, particularly at the 180° bends. This paper investigates effects of various ratio of channel length to width (L/W) and position of side entry axial flow impeller (distance from the bottom of the tank) on the hydrodynamics in RWP. To curtail the dead zone, power consumption, shear stress and enhance surface renewal, the different designs of RWPs with flow deflectors and different types of central baffles were investigated by using Computational Fluid Dynamics (CFD). The CFD model was validated through Particle Image Velocimetry (PIV) tests. A feasible move headed for energy optimization and thus reduction in operational cost can be established through a better understanding of the mixing phenomena by CFD simulations.

Investigation of hydrodynamic non-idealities in a pilot-scale pond bioreactor

Pond-type reactors are widely used in biological wastewater treatment in view of their simplicity and low cost of construction. The knowledge of an approximate hydrodynamic behavior can contribute to the rational design of such operation. Thus, the aim of this work is to investigate, in a pilot scale pond bioreactor, the non-ideality through residence time distribution (RTD) technique and validation of a model for the homogeneous phase material balance. Experimental runs were carried out using the pulse injection technique of methylene blue tracer at constant water flow rate. The pilot-scale reactor constructed with a typical geometry design of those employed in animal waste treatment in southern Brazil. Residence time of 3, 6, and 9 days and a height/width ratio geometry parameter (H/D) of 0.25 and 0.18 were adopted. For each run normalized RTD functions and their moments (average residence time, variance and asymmetry) were evaluated. Variance analysis shows equivalent hydrodynamic behavior in the parameter range employed. To describe the non-idealities, we theorized several dimensionless RTD function models using a series of CSTRs (classified as conventional, bypass and recycle).The models were adjusted to the experimental data by non-linear regression and evaluated by the successive calculation method using the moments of RTD. The best model found is the representation of the pond reactor as two CSTRs in series with different volumes (first reactor with 91.5% of useful volume) and presence of dead zones (useful volume 84.9% of real volume).

Residual chlorine behavior in a distribution network of a small water supply system

Abstract This study presents the behavior of residual chlorine using computer modeling for a small water supply system located in La Sirena, Cali, Colombia. The study included field work to calibrate and validate the model together with lab determinations. Results show that the kinetics of first and second order together with the kinetics of mixed order can adequately describe the behavior of residual chlorine in this type of network. The research showed the variables that influence the behavior of residual chlorine in the network are: the quality of the input water, chlorine dosing, the effect of storage that increases the water age, and the presence of dead zones in the tanks. The study revealed that 95% of the reaction occurs in the storage tanks due to the small variation in the water level and the negligible reactions at the pipe walls. This study proved that the residual chlorine modeling in this small network in particular is a valuable tool for monitoring the water quality in the distribution network, which is useful to comply with water quality guidelines.

Estimating the impact of natural and technogenic factors on the incidence of malignant neoplasms in Altai krai

Air pollution by industry and motor vehicles, the use of coal ash for the construction of residential and nonresidential buildings, and the presence of dead zones in the residential sector are the main factors of carcinogenic risk to human health. Natural factors (such as topography and prevailing wind directions) can weaken or strengthen technogenic factors. Based on the estimate of pollutant concentrations in the snow cover of Barnaul, we reveal residential areas that are located at the crossroads of atmospheric transport of carcinogenic substances and characterized by concentrations considerably exceeding the maximum allowable concentration. These areas are characterized by the integral accumulation of carcinogenic substances concurrently from multiple sources; for almost any wind rose, the impact of one of the pollution sources is observed throughout the year. The assessment of the carcinogenic risk for a territory depends much on the correlation between local topography and the height of apartments above ground level. Using cancer register data for Barnaul, we reveal an increased level of the incidence of malignant neoplasms in people living in high-rise buildings located in areas with a sharp change in topography (such as ledges, hills, and lowlands). This may occur due to stagnant zones and wind shadows; under certain correlation between topography and the height and shape of buildings, carcinogenic substances accumulate maximally.

Experimental investigating the effect of bed geometry on solids mixing in fluidized beds

ABSTRACTEffect of fluidized bed geometry on solids mixing was investigated. Experiments were carried out in cylindrical and square fluidized beds. White and black particles with 850 µm average diameter were used in the experiments in which black particles were considered as tracer. In order to determine the concentration of tracers in each sample, the method of image processing was applied. Based on the final value of the mixing index, it was concluded that complete random mixing can be achieved in both beds. The results indicated that mixing is faster and mixing time is shorter in the cylindrical bed than in the square bed. This trend was attributed to the fact that the movement of solids in the cylindrical bed is faster compared to the squared bed due to the presence of dead zones in the square bed which reduce the cross-section area available for passage of bubbles. A one-dimensional dispersion model was used to predict the solids axial dispersion coefficient. It was shown that the axial dispersion coefficient in the case of cylindrical bed is greater than that in the square bed and that the axial dispersion coefficient increases by increasing the superficial gas velocity in both beds.

EVALUATION OF ECOLOGICAL SITUATION IN CASE OF ACCIDENTS ON TOWNSHIP ROADS

Purpose. The paper examines the question of creation a mathematical apparatus for estimation the ecological situation in case of accidents on township roads (explosions). First of all the development of numerical model to calculate the level of air pollution in the emission of toxic chemical, taking into account meteorological parameters of the environment. Identifying areas where the maximum allowable concentration of this pollutant (in this case, ammonia) is exceeded and favorable areas for the population.Methodology. The developed method of numerical calculation of the air pollution concentration in case of toxic chemical (ammonia) was used, which is based on the coordinated decision of the hydrodynamic task and task of the pollutants transfer in the atmosphere. Hydrodynamic solution is based on the method of discrete vortices with the different geometry of buildings and their relative position, and solution of the task about transfer the pollutant is based on convection-diffusion equation of pollutant transfer using implicit difference schemes.Findings. Several computational experiments were made on the base of the developed numerical model.As a result of the calculations the vortex structures were obtained, which are formed in the flow around buildings; the velocity field of the wind flow around buildings and picture of the streamlines in the flow were come out; the concentration of the toxic chemical (ammonia) in research domain was calculated; the comparative analysis with the maximum permissible concentration (MPC) for this pollutant were made; the regularities of changing the ammonia concentration from different sides of the building were determined. Originality. A numerical model that allows visually reconstructing and analyzing the flow pattern, the presence of dead zones, areas of reverse flow at different geometry of buildings and their relative position that influences the distribution of pollutant in the atmosphere was calculated.Practical value. The obtained results will allow evaluating the level toxic shock to persons in case of accidents (explosions) on township roads with taking into account the influence of the buildings geometry on the hydrodynamic flow structure and dispersion of pollution.

Modeling and Predicting Gas-Solid Fluidized Bed Dynamics to Capture Nonuniform Inlet Conditions

The hydrodynamics of fluidized beds involving gas-solids interactions are very complex, and modeling such a system using computational fluid dynamics (CFD) modeling is even more challenging for mixtures composed of nonuniform particle characteristics such as diameter or density. Another issue is the presence of dead-zones, regions of particles that do not fluidize and accumulate at the bottom of the bed, affecting uniform fluidization of the material. The dead zones typically form between the gas jets and depend on the spacing of the distributor holes and gas velocity. Conventionally, in Eulerian–Eulerian modeling for gas-solid mixtures, the solid phase is assumed to behave like a fluid, and the presence of dead zones are not typically captured in a CFD simulation. Instead, the entire bed mass present in an experiment is usually modeled in the simulations assuming complete fluidization of the bed mass. A different modeling approach was presented that accounts for only the fluidizing mass by adjusting the initial mass present in the bed using the measured pressure drop and minimum fluidization velocity from the experiments. In order to demonstrate the fidelity of the new modeling approach, three different bed materials were examined that can be classified as Geldart B particles. Glass beads and ceramic beads of the same mean particle diameter were used, as well as larger-sized ceramic particles. Binary mixture models were also validated for two types of bed mixtures consisting of glass-ceramic and ceramic-ceramic compositions. It was found that adjusting the amount of fluidizing mass in the modeling of fluidized beds best predicted the fluidization dynamics of an experiment for both single phase and binary mixture fluidized beds.

Models of methane behaviour in auxiliary ventilation of underground coal mining

Abstract Studies have been conducted in a roadway excavated in a coalbed of a deep underground coal mine located in Northern Spain (Hullera Vasco Leonesa SA), by both airflow velocity and methane concentration measurements. Modelling of ventilation and methane behaviour of that roadway by Computational Fluid Dynamics (CFD), through software Ansys CFX 10.0, is presented. A good correlation was found between the experimental data and the results predicted by CFD. Then a comparison of the results obtained by conventional methods with the results obtained by CFD 4D modelling, for the auxiliary ventilation in a dead-end roadway, was made. Although conventional methods give satisfactory results when considering methane dilution, this research proves that there may be some roadway zones in which methane concentration is higher than regulation values. This is owing to the airflow and methane behaviour in the roadway with the presence of dead zones, and the fact that only a part of the airflow provided by the fan reaches the working face. CFD modelling allows us to know in which zones of the roadway it may be necessary to reinforce forcing ventilation by additional systems, such as a forcing system with exhaust overlap, jet fans, spray fan systems or compressed air injectors.

Source identification in river pollution problems: A geostatistical approach

The geostatistical method, formulated in the groundwater field, has been applied to identify contaminant sources in river pollution problems. The problem consists of recovering a contaminant source at a known location from a finite number of concentration measurements. It is an ill‐posed problem, whose solution is nonunique and cannot be determined through standard techniques. The presence of dead zones has been considered because of their relevant influence on transport processes. The possibility of linear decay reactions in the main stream and in the dead zones has also been included. Applications to field data show that the method is efficient in recovering the release history of an arbitrarily distributed source as well as multiple independent point sources, given a finite number of observed concentrations at one or several downstream points. The influence of the degree of dispersion on the observations is stressed. Finally, the effects of measurement errors and of the number of measurement points have been investigated.

Macroscopic fluid flow conditions in spiral-wound membrane elements

Reverse osmosis (RO) finds increasing applications as separation technique in chemical and environmental engineering where desalination, selective separations in the agro-industrial processes or wastewater purification are well-established examples. To fully evaluate the potential of RO and facilitate scale-up procedures, the modelling of the process is an important tool and literature models analyze the separation efficiency in terms of mass transfer with material balances, pressure drop through the module and mass transfer coefficients as dominant parameters. Important underlying factors are the geometry of the module and the hydrodynamic flow regime since mass transfer and pressure drop are a function of these factors, as witnessed by several publications. Since the concentrate-side (which is also the feed side) of the membrane plays the key-role, measurements should focus on the concentrate-channel of the spiral-wound membrane element. The determination of the channel flow regime and hydrodynamics of spiral-wound RO-channels can be carried out through the measurement of the residence time distribution (RTD). The present paper describes our experimental investigations on RTD through the application of a step change in tracer concentrations and relates the RTD-response curves to the regime of flow through the concentrate channels. This tracer-technique is common in characterizing flow regimes in chemical reactors. Its application to RO flow channels is innovative and results obtained stress its applicability to this specific geometrical layout. Results indeed demonstrate that the experimental average residence time of the concentrate channel is smaller than the theoretically calculated residence time, with differences between both values gradually decreasing with increasing liquid flow rate. This observation corresponds with findings for traditional packed bed applications where the presence of dead volumes reduces the real average residence time. The presence of dead zones in the spiral-wound membrane element is therefore evident. Since in our experimental procedure, residence time distributions are measured both between the tracer injection point and respectively the inlet and outlet of the spiral-wound element, the nett RTD-contribution of the membrane element itself can only be determined by eliminating the influence of the inlet flow equalization zone. This is performed by applying the convolution principle. Experimental and calculated RTD-curves for values of the Péclet-number of approximately 20 are in very good agreement. In analogy with fixed bed applications, the interpretation of the findings corresponds to a laminar flow profile with a limited dispersion. The definition of this flow profile in the concentrate channel is important in the use of transport models to characterize the membrane performance, as will be shown in a further paper.