Free-flow Conditions Research Articles

Discharge coefficients for ogee spillways

Abstract Discharge over an ogee weir is related to the length of the weir, upstream total head above the weir crest and the discharge coefficient. The discharge coefficient is influenced by several factors; in this study, some parameters that influence discharge coefficients of ogee weirs are investigated. These factors include: the weir upstream slope, apron elevation, and downstream submergence. In this regard, ogee weir physical models were fabricated. These models comprise: an ogee weir with a vertical upstream face, ogee weirs with inclined upstream faces (18, 33, and 45 degrees), ogee weirs with downstream apron thicknesses of 3, 5, 7, and 10 cm in free flow and an ogee weir with a vertical upstream slope under submerged-flow conditions. Results show that for all ogee weirs, the discharge coefficient (C) increases with increasing P/He, and then remains constant (P is the spillway height and He is the head above the weir crest). The value of the discharge coefficient decreases from 2.25 in free-flow conditions to 2.15 with submerged-flow conditions. For a constant head over the ogee weirs (He), the discharge coefficient decreases with increasing downstream apron elevation and submergence. The relative discharge coefficient shows a constant trend initially, with increasing hd/He, then later shows a decreasing tendency (hd is the difference between the downstream head and the ogee spillway crest). The threshold value for submergence ratio (hd/He) is 0.75 in the ogee weir in this study. With increasing submergence ratio from 0.75 to 1, the relative discharge coefficient (Cs/C0) decreases from 0.88 to 0.24.

Determination of the General Formula to Estimate the Discharge Quantity of Composite Structure for Free Flow

River and open channel flow measurement is regarded as an important element in improving water system management. An experimental analysis in a laboratory flume has been executed to obtain formulas which can be used to predict the discharge quantity which crosses over the sharp crested weir and under the gate in the composite structure which is a tool of flow measurement. These formulas are applied for the free flow condition. Different configurations of composite structure have been used. These configurations have regular and irregular shapes. The derivation of the discharge quantity equation is based on the dimensional analysis which is employed to analyze the factors that control the operation of the composite structure. The family of formulas consists of eight formulas that are divided into two groups. The first group consists of four formulas which are derived based on the variable that dominates the hydraulic behavior of the composite structure, while the second group consists of four formulas based on the same variables of the first group but taking into consideration the effect of weir and gate shape by adopting the hydraulic radius of weir and gate. Based on the evaluation process, all formulas can be used perfectly well to predict the discharge quantity, regardless of the shape of weir and gate. On the other hand, based on the validation process, the formula that considered the effects of shape geometry, flow and fluid properties has given the best prediction of the discharge quantity.

Optimisation of H-Darrieus VAWT Solidity for Energy Extraction in Cooling Tower Exhaust Systems

The technologies surrounding renewable energy have been receiving surmountable attention to producing clean energy and reducing the dependency on depleting fossil fuel sources. In this context, research investigations on vertical axis wind turbines (VAWT) in free stream flow condition has been extensively conducted to improve the energy extraction efficiency from the wind. VAWTs are particularly advantageous in locations not suitable for conventional horizontal axis wind turbines (HAWT). However, the applications of VAWTs are still limited due to their lower performances compared to their counterparts. Furthermore, the wind energy extraction problem is more prominent in urban areas with unpredictable and inadequate wind speed conditions. The present study focuses on an alternative way to harness wind energy from unnatural sources such as cooling tower exhaust systems with the reliable and consistent exhaust air. A three-dimensional numerical study has been conducted to investigate the performance of a 3-bladed H-Darrieus wind turbine (HDWT) using S-1046 airfoils of four different solidities under accelerated wind conditions of a cooling tower. The HDWT model is positioned at the cooling tower outlet, where it rotates using sliding mesh to measure the power output. Shear stress transport (SST) k- turbulence model solver was used to solve the implicit unsteady Reynolds-Averaged Navier-Stokes equations. It is observed that the higher solidity HDWT reached peak power coefficient at a lower tip speed ratio (TSR). In contrast, lower solidity HDWT achieved peak power coefficient at higher TSR. The higher solidity 0.375 and 0.450 produced a maximum power coefficient of 0.233 at TSR of 2.0.

Rancang Bangun Smoke Generator pada Kecepatan Angin Rendah dengan Wind Tunnel Rangkaian Terbuka

Flow Visualization is the process of making the physical flow of a fluid visible. The air fluid used is transparent, so the flow pattern must be shown by several special methods. There are three methods for visualizing flow: surface flow visualization, particle tracking method, and optical method. Turbulence is one of the most important subjects related to testing the test section in a wind tunnel, at different wind speeds turbulence levels and other flow quality parameters must be kept as close as possible to free flow conditions. The flow visualization test is carried out using a slow motion camera at speeds of 1 m/s, 2 m/s, 3 m/s, 4 m/s and 5m/s which will form a fluid flow in the form of lines of smoke coming out of the nozzle holes inside. Test section. From the research results, the authors can conclude that the flow obtained forms a laminar flow and good suction power from various wind speed variables.

Experimental study of discharge formulas for rectangular sharp-crested weirs under free flow condition

Laboratory experiments were carried out to investigate the discharge characteristics of rectangular sharp-crested weirs under free flow condition. The performances of available discharge formulas have been evaluated by using the experimental data sets of present and previous studies. Error statistics of our experimental data indicate that the recent stage-discharge relationships show satisfactory performances. Discharge formula in terms of weir Reynolds number proposed by Vatankhah gives the highest accuracy among the existing slit weir equations, with E±4=100.00% (i.e. percent error less than or equal to ±4) and a mean absolute error |E|m=0.88%. The full-range discharge equation presented by Bijankhan and Mahdavi Mazdeh shows the highest accuracy among the relationships in terms of weir contraction ratio, with E±4=100.00%, |E|m=0.91% for slit weirs and, E±4=94.64%, |E|m=1.60% for partially contracted weirs, respectively. The weir velocity formulae suggested by Gharahjeh et al. exhibit the relatively better performance, with E±4=98.41%, |E|m=1.34% for slit weirs and, E±4=91.07%, |E|m=1.91% for contracted weirs, respectively. Statistical results of this study confirm the weir velocity approach presented by Aydin et al. and show that, the weir velocity is a predominant quantity for rectangular sharp-crested weirs, unique characteristics of the weir velocity curves make it more suitable for expressing the discharges. Moreover, it is important to point out that the performance of weir velocity formulae can be further improved.

Towards human-like speed control in autonomous vehicles: A mountainous freeway case

A driving strategy for autonomous vehicles (AVs) that is consistent with human behavior while demonstrating superior performance seems to have a good chance to be accepted by early AV users and be successful in the long run. Most of the past research focused on motion strategies affected by the presence of other vehicles. On the other hand, AV not constrained by other vehicles must select a safe and comfortable speed that is perceived as such by its occupants. This line of research is not well covered by the published work. The baseline speed, which is the speed AVs will follow without interaction with other vehicles, implemented via cruise control (CC) in modern vehicles is a constant speed consistent with speed limits and design speeds. A more advanced strategy of road-limiting speed control (RC) responds to influencing geometric features ahead of the AV’s current position. Neither of the two strategies considers AV occupants’ preferences. The current void in research is particularly obvious for free-flow conditions where baseline speeds must be implemented for extended periods of travel. Although the existing strategies have not been yet evaluated on roadways with demanding alignments and operating in free-flow conditions, the principles on which they are based provide a basis for skepticism if they can be acceptable to AV occupants. This study used the Tongji University driving simulator to evaluate the CC and RC strategies and their potential limitations in free-flow conditions on a mountainous freeway with complex alignments. Human speed-selection behavior was observed among a group of participating drivers. The clustering analysis of the data revealed three distinct driving styles: slow, fast, and consistent. The resulted analytical models provided human-focused road-dependent baseline speed profiles– a key element of the proposed human-like speed control (HC) strategy. The comparison of the existing speed-control strategies CC and RC with the proposed HC confirmed the limitations of the two existing ones if applied to roads with complex alignments. Considerable discrepancies were revealed between the baseline speeds produced with the existing and the proposed ones.

Longitudinal River Monitoring and Modelling Substantiate the Impact of Weirs on Nitrogen Dynamics

The fluvial nitrogen dynamics at locations around weirs are still rarely studied in detail. Eulerian data, often used by conventional river monitoring and modelling approaches, lags the spatial resolution for an unambiguous representation. With the aim to address this knowledge gap, the present study applies a coupled 1D hydrodynamic–water quality model to a 26.9 km stretch of an upland river. Tailored simulations were performed for river sections with water retention and free-flow conditions to quantify the weirs’ influences on nitrogen dynamics. The water quality data were sampled with Eulerian and Lagrangian strategies. Despite the limitations in terms of required spatial discretization and simulation time, refined model calibrations with high spatiotemporal resolution corroborated the high ammonification rates (0.015 d−1) on river sections without weirs and high nitrification rates (0.17 d−1 ammonium to nitrate, 0.78 d−1 nitrate to nitrite) on river sections with weirs. Additionally, using estimations of denitrification based on typical values for riverbed sediment as a reference, we could demonstrate that in our case study, weirs can improve denitrification substantially. The produced backwater lengths can induce a means of additional nitrogen removal of 0.2-ton d−1 (10.9%) during warm and low-flow periods.

Real-time dynamic optimized band detection method for hypersonic glide vehicle

The glide phase is the main time window of detection for a hypersonic glide vehicle (HGV). During a long flight, both skin temperature and background change dynamically, neither of which can be regarded as constant. The traditional fixed band detection can’t adapt to the dynamic changes of target and background infrared radiation characteristics, which not only reduces the tracking and detection efficiency, but also compresses the subsequent countermeasures reaction time. Therefore, based on the real-time infrared characteristics of target and background, this paper presents a real-time dynamic optimized band detection method for the HGV under entire trajectory. Firstly, considering the influence of free-flow conditions, target velocity, angle of attack (AOA), and geometry, we established the heat flux calculation model with a modified reference enthalpy method. Then, the transient temperature of the skin at different trajectory points is obtained by calculating the wall heat flux from convection and thermal radiation. Finally, the detection efficiency of the HGV in different wavebands is simulated by combining different types of backgrounds. Considering the signal-to-noise ratio (SNR) and signal-to-clutter ratio (SCR), a new detection index, comprehensive signal-to-noise ratio (CSNR), is proposed to analyze the optimal band. Research results show that the undetectable time after band optimization can be reduced from 250 s to 70 s compared to the fixed band with CSNRth=10 as the threshold. At 250 s, the detection efficiency of optimized band is 18 times that of fixed band. The band optimization method presented in this work provides a theoretical reference for the defense of hypersonic weapons.

Effect of Ramp Slope on the Efficiency of Symmetrical Hump Weirs in Free Flow Condition

Effect of Ramp Slope on the Efficiency of Symmetrical Hump Weirs in Free Flow Condition

Simultaneous identification of sensor faults and origin-destination matrix estimation

Efficient estimation of the origin-destination (OD) matrix is a crucial requirement for traffic monitoring and control. The OD matrix estimation problem has received significant attention over the past decades and various approaches using traffic counts from fixed location sensors have been developed and tested. A significant challenge when using information obtained from traffic sensors, is that such sensors are subject to considerable disruptions due to system errors, that affect the quality and reliability of the information provided. This paper presents a novel approach for OD matrix estimation in the presence of faulty sensors. For the purposes of this work we assume that the network under study operates under free-flow conditions and utilise a variation of the cell transmission model to capture the traffic flow dynamics in a pre-specified time window. The problem is formulated in an optimisation framework and solved by taking into account the presence of faulty measurements. We test and validate the proposed methodology on a sample network and investigate the advantage of OD matrix estimation in the presence of faulty measurements compared to OD matrix estimation when faulty sensors are not considered.

A systematic approach for microscopic models based on cellular automata for road traffic

The transportation infrastructure is one of the most important resources for a country's economic and social well-being. The effectiveness of a country's street network will decide whether it develops further or stagnates. With the increasing number of vehicles on the road and the effects of urbanization, traffic roads are being subjected to a variety of requests and uses for which they were not designed, sized, or predicted. Because of the critical relevance of traffic roads, research must begin to lessen the effects of traffic jams in the streets, determine the appropriate number of traffic lanes, and integrate real-time traffic information into GPS systems. The goal of modeling a traffic-road system is to either build new traffic systems or gain a better knowledge of existing traffic systems so that they can be optimized. The accuracy, performance, stochastic and dynamic behavior of the model produced will be evaluated using a simulation of a genuine traffic system. This paper provides microscopic models based on cellular automation to replicate the behavior of various automobiles on a set of urban streets in Cluj Napoca city downtown. This model includes streets with multiple traffic lanes, various types of vehicles such as automobiles, buses, and trams, intersections with multiple possible upcoming streets controlled by traffic lights, bus stops inside and outside the traffic lane, tram stops inside the traffic lane, pedestrian crosswalks, and parking areas alongside and transversely with the right traffic lane of a street. TCA (Traffic Cellular Automata) is a proposed model that produces adequate findings in urban traffic theory. The results were obtained in both free-flow and traffic-jam conditions.

РАСЧЕТЫ УСТАНОВИВШЕЙСЯ СВОБОДНОЙ ФИЛЬТРАЦИИ ИЗ НЕОБЛИЦОВАННЫХ КАНАЛОВ

Purpose: to obtain calculated dependencies for determining free and banked seepage from irrigation canals. Materials and methods: during the research, methods of the theory of filtration from unlined and lined canals of irrigation and drainage systems were used. Results. Free seepage from the canals with steady flow shows significant water losses, reaching 30 % of discharge. As a result, the canal efficiency decreases, thus contributing to the flooding of the canal areas, the subsequent soil salinization, waterlogging and their gradual withdrawal from agriculture. Free steady seepage from canals will be observed in the absence of impermeable water-resistant depth layers or when the groundwater level occurs at a depth of more than 20–25 m from the earth's surface. In this regard, to determine the seepage discharge with free seepage, the calculated dependences of N. N. Pavlovsky, V. V. Vedernikov, A. N. Kostyakov, S. F. Averyanov and Yu. M. Kosichenko are recommended. In the case when banked-up seepage occurs during steady motion, the method of filtration resistance and the formulas of S. F. Averyanov, N. N. Verigin, A. Ya. Oleinik, taking into account the unsteady seepage process, with differential equation of unsteady flow motion of the Fourier type may be used. Conclusions. The solutions obtained of seepage problems under steady motion made it possible to find calculated dependencies and calculation methods for free and banked-up seepage from irrigation canals. A classification of seepage losses from irrigation canals for free flow conditions has been developed.

Energy dissipation of flow over the type-B Piano Key Weir

Piano Key Weir (PKW) is an evolution with an efficient implementation over conventional labyrinth weir, especially at low heads. It is used as the crest of spillways and specific flow regulation applications for overflow control structures. The effects of a PKW on the downstream flood regime have not yet been thoroughly studied; only a few studies have focused so far on the downstream characteristics of the PKWs. The consideration of energy-dissipation is the main component of downstream elements for all hydraulic structures. Therefore, there is a need to log and assess details on the energy dissipation of the PKWs. This paper presents the results of the experimental study to investigate the energy dissipation at the base of type-B PKW under free-flow conditions in a rectangular channel. According to the current study's findings, the type-B PKWs show a higher energy dissipation efficiency at low heads than other nonlinear or ordinary weirs, but dissipation efficiency decreases as the discharge or head over the weir increases. The energy dissipation was found to decrease with the increasing magnification ratio and relative width ratio; however, the energy dissipation was found to increase with increasing cycle number (for a constant-width channel). In addition, the sensitivity of the weir, i.e., using the steps at the outlet key instead of the slopping floor, increases the efficiency of energy dissipation for low head discharges about 6.43% while decreasing by 2.05% for higher head discharges.

Determination of Discharge Coefficient for both Semicircular and Triangular Labyrinth Weirs

A Labyrinth weir is a type of nonlinear weir folded in plan-view, with the ability to pass a large flow at low heads due to an increase in the effective length of the weir crest for a given channel width. The discharge coefficients (Cd) were experimentally determined for both semicircular and triangular labyrinth weirs of varying sidewall angles (α) under free-flow conditions using eight physical models. Dimensional analyses are conducted using the Buckingham π theorem to find the dependent and non-dependent variables. A nonlinear empirical equation was developed using (Statistical Package for the Social Sciences 22) software. The findings show that the discharge coefficient decreases with the increase of headwater to (Ht/P) for both types of labyrinth weir with different plan forms. It is found that the efficiency of the semicircular and triangular labyrinth is higher than linear weir for (Ht/P ≤ 0.45) and decreases with increasing the value of (Ht/P) due to interference of flow between the layers in downstream. The obtained results revealed that the discharge coefficient (Cd) values obtained empirically using multivariable power regression and 5th degree polynomial equations considerably agree with the experimental data, for both of the semicircular and triangular labyrinth weirs. Furthermore, the correlation coefficient R2was (0.9951) and (0.9637) using 5th degree polynomial equation, and their values were (0.9643) and (0.9274) using multivariable power regression equation for both semicircular and triangular labyrinth weir models, respectively. The results in the present study compared quite well with the predicted results of the proposed equations obtained by other investigators.

Swimming behaviour of silver carp (Hypophthalmichthys molitrix) in response to turbulent flow induced by a D-cylinder.

Turbulence is a complex hydraulic phenomenon which commonly occurs in natural streams and fishways. Riverine fish are subjected to heterogeneous flow velocities and turbulence, which may affect their movements and ability to pass the fishways. However, studies focusing on fish response to turbulent flows are lacking for many species. Here we investigate the effects of the turbulence created by a vertical half-cylinder of various diameters (1.9, 2.5, 3.2 and 5.0cm) on the swimming ability and behaviour of silver carp, Hypophthalmichthys molitrix. The large D-cylinders (3.0 and 5.0cm) create specific vorticity and reduced velocities areas in their vicinity, which favours flow refuging behaviours (FRBs) and thus increased relative critical swimming speeds (Urcrit , BL/s) of silver carp, by comparison to free-flow conditions and cylinders of smaller diameter (1.9 and 2.5cm). The flow speed at which silver carp maximized FRBs such as Karman gaiting downstream of the cylinder, holding position in the bow wake or entraining on the side ranged from 40 to 70 cm s-1 , depending on fish body size. When holding station near a cylinder under optimal flow speeds, the distance between the fish and the cylinder is related to the size of the fish, but also to the size of the cylinder and the produced vortices. The optimal holding region in the drag wake of the cylinder ranged from 28 to 40 cm downstream of the centre of the cylinder, depending on the size of the fish. Smaller fish, however, tend to use the reduced velocities areas located in the bow wake of the large cylinders. We hypothesize that fish will display FRBs, including maintaining a Karman gait in turbulent flow, when the ratio of the cylinder diameter to their body length is between 1:3 and 1:4. They also match their tail beat frequency to the vortex shedding frequency of the cylinder. Our results provide a better understanding of how silver carp respond to turbulent flows around physical structures, with implications for the design of nature-like fishways or exclusion devices in both its native and invasive ranges.

Discharge coefficient prediction of canal radial gate using neurocomputing models: an investigation of free and submerged flow scenarios

In the current study, three machine learning (ML) models, i.e. Gaussian process regression (GPR), generalized regression neural network (GRNN), and multigene genetic programming (MGGP), were developed for predicting the discharge coefficient (Cd ) of a radial gate under two different flow conditions, i.e. free and submerged. The modeling development of the flow and geometry input variables for the Cd was determined based on statistical correlations. We also performed a sensitivity analysis of the input variables for the Cd . The modeling results indicated that the developed ML models attained acceptable predictable performance; however, the prediction accuracy of the models was better under the free flow condition. In quantitative terms, the minimum root mean square error (RMSE) value was 0.010 using the GPR model and 0.019 using the MGGP model for the submerged and free flow conditions, respectively. The sensitivity analysis evidenced that the ratio of the gate opening height to the depth of water in the upstream (W:Y o) was the influential variable for the Cd under the free flow condition, whereas the ratio of the depth of water in the upstream to the depth of water in downstream (Y o:YT ) was the influential variable for the Cd under the submerged flow condition.

Investigating the control of exercise hyperpnoea: A synergy of contributions.

Investigating the control of exercise hyperpnoea: A synergy of contributions.

Hydrogeological simulation of head changes of a south Benin artesian aquifer

Artesian basins include groundwater that may rise above the land surface with free-flow conditions which make it possible to exploit groundwater without pumping. The change to non-artesian conditions may have large implications for local people using artesian wells for drinking and other purposes. We applied a 3D physically based model to assess future head developments in the Turonian-Coniacian artesian (T.C.) aquifer of southern Benin under different artesian outflows and climate scenarios. A sensitivity analysis of the hydraulic and storage properties of the subsurface layers was performed to determine the importance of each property. Results revealed that artesian basins are structured into peripheral and central zones behaving differently to external stresses. Head amplitudes in the peripheral zones which are adjacent to recharge zones are higher and decrease towards the central artesian zones due to the influence of the confined aquifer's hydraulic diffusivity and the leakance of the confining layer. Based on the regional climate model (RACMO) that better reproduces the historical rainfall in the study area, lower recharge is predicted for the period until 2030 and will lead to head drops by 1 m at the peripheral artesian zone. However, such head drops will likely recover during the period 2030–2050 for which higher recharge is predicted. If the current artesian outflows double by 2050 this would cause heads to reduce by only a few centimeters both in the central and at the periphery of the artesian zone. Among all the subsurface layers properties, the hydraulic conductivity of the confined T.C. aquifer is most influencing the simulated heads across the artesian zone and its specific storage is revealed as the least influencing one.

Dynamical efficiency for multimodal time-varying transportation networks

Spatial systems that experience congestion can be modeled as weighted networks whose weights dynamically change over time with the redistribution of flows. This is particularly true for urban transportation networks. The aim of this work is to find appropriate network measures that are able to detect critical zones for traffic congestion and bottlenecks in a transportation system. We propose for both single and multi-layered networks a path-based measure, called dynamical efficiency, which computes the travel time differences under congested and free-flow conditions. The dynamical efficiency quantifies the reachability of a location embedded in the whole urban traffic condition, in lieu of a myopic description based on the average speed of single road segments. In this way, we are able to detect the formation of congestion seeds and visualize their evolution in time as well-defined clusters. Moreover, the extension to multilayer networks allows us to introduce a novel measure of centrality, which estimates the expected usage of inter-modal junctions between two different transportation means. Finally, we define the so-called dilemma factor in terms of number of alternatives that an interconnected transportation system offers to the travelers in exchange for a small increase in travel time. We find macroscopic relations between the percentage of extra-time, number of alternatives and level of congestion, useful to quantify the richness of trip choices that a city offers. As an illustrative example, we show how our methods work to study the real network of a megacity with probe traffic data.

Interactions between autonomous vehicles and pedestrians at unsignalized mid-block crosswalks considering occlusions by opposing vehicles

Visibility can be identified as one of the critical determinants for the safety performance of autonomous vehicles (AVs) on unsignalized mid-block crosswalks (UMC), which may be significantly influenced by build-up environment and surrounding vehicles. This study investigates the safety performance when AVs interact with pedestrians approaching from far-side sidewalks to UMCs considering the visual occlusion of opposing vehicles. A mathematical model is proposed for judging the visibilities of objects from observers’ location under the impact of visual obstacles and is embedded into an agent-based pedestrian-vehicle interaction framework. Two yielding decision modules is assumed for AVs: The normal decision module implements the pedestrian priority rule simply based on the current detectable information, whereas the memory aid decision module extends AVs’ detection abilities by incorporating the memory data. Through simulation experiments, it is found that the percentages of short post encroachment time (%SPET) between AVs and far-side pedestrians reach peaks when the pedestrian flow rate is 300–400 ped/h. When opposing vehicles are in stationary queue conditions, %SPETs are only sensitive to the net distance between the last opposing vehicles in the queue and crosswalks (Dqueue). As the Dqueue decreases to lower than 15 m, %SPETs start to increase drastically. However, when opposing vehicles are in free flow conditions, %SPETs are influenced by multiple factors such as pedestrians’ crossing decisions, sizes and flow rates of opposing vehicles. Furthermore, only when opposing vehicles are in free flow conditions, memory aid AVs can significantly eliminate the impacts of opposite vehicles. Finally, several countermeasures are developed to enhance the visibility and safety at UMCs based on the findings of this study.