Discharge Velocity Research Articles

Thermal Pollution Mitigation and Energy Harnessing of the Condensation Process of an Olive Oil Extraction Refinery: A Case Study

This paper presents a model to assess strategies for bettering a hexane condensation system from an olive oil extraction refinery in Portugal’s mountainous north. The water used as a cooling fluid is discharged with a higher temperature than the mountain river, provoking the deterioration of the aquatic flora and fauna, leading to high environmental impact. The model allowed the comparison of solutions for different temperatures of discharge for summer and winter and possible heat recovery back to the factory. The current condensation system power is 1.838 MW and consists of a four-walled pond of 115.3 m3 that cools down the submerged hexane pipes. Nudging in the pond’s structure leads to the introduction of internal channels to increase the turbulence, thus increasing the hexane–water heat exchange rate. Heat recovery of 19.38 kW is possible for the water coming from the pond in the drying bagasse process inside the factory, before discharge into the river. However, the model demonstrates that the decrease in temperature after the heat recovery process falls short of avoiding thermal pollution, leading to complementary actions such as shading the channel or changing the discharge velocity or angle to mitigate the thermal pollution locally.

ANALISIS MUTU AIR AKIBAT AKTIVITAS PENAMBANG PASIR DENGAN METODE STORET DI SUNGAI SP PADANG OKI

Sand mining in the village of Sp Padang is carried out in an open pit mining model through several processes, for example the washing process which is carried out to separate sand from other components.When the sludge in the form of mud and fine sand enters the river, this part causes the quality of river water around the sand mining location to decline. The purpose of this research was to determine the condition of water quality due to sand mining in the river Sp.Padang.The type of data collected is primary data. The research was conducted at 3 stations on the river Sp.Padang.The physico-chemical parameters of river water are used, namely: turbidity, temperature, pH, TSS, DO, BOD, COD, water discharge and current velocity. The data obtained from the laboratory were then analyzed, then comparisons were made with the Storet method.Sampling for water quality replaces the surrounding area with direct measurements and measurements made in the laboratory.The use of the Storet method refers to PP No. 82 of 2001. The principle of Storet is to integrate river water quality data with river water standards and then adjust it according to its use, by classifying water quality into four classes. The results of the data analysis of the quality of river water in Sp.Padang as a result of the sand mining activities are categorized as good class B (lightly polluted) with a score of -6. Sand mining activity affects the water quality of the Sirah River in Padang Island, OKI Regency.Key words : OKI, sand miners, storet method, water quality

Trying to choose the less bad route: Individual migratory behaviour of Atlantic salmon smolts (Salmo salar L.) approaching a bifurcation between a hydropower station and a navigation canal

Contrary to small- and medium-sized rivers, little attention has been paid to the downstream migration of Atlantic salmon smolts in large-sized rivers and the size-related impact of hydropower stations. From 2014 to 2016, we investigated the downstream migration of n = 72 acoustic-tagged smolts in the Meuse river at a bifurcation zone between a hydropower station equipped with three Kaplan turbines and a navigation canal. A hydrodynamic model that solves the depth-integrated shallow water equations on a Cartesian grid using a finite volume technique was used to infer the influence of water discharge and flow velocity on the smolts' behaviour upstream of the hydroelectric complex. Of the migrating smolts, 41.5% performed back and forth movements before approaching the complex for the first time, sometimes over long distances and at a slow pace, leading to significant delays (3–298 h). Beyond about 250 m3 s−1, the water flow direction changes towards the hydropower station with a gradual acceleration. A median water discharge of 161 m3 s−1 and associated median flow velocity of 0.14 m s−1 tended to favour a more direct and downstream movement towards the hydropower station. On the other hand, the navigation canal was mainly approached at low water discharge (median 132 m3 s−1), due to a higher flow velocity (median 0.11 m s−1) at the entrance. Of the released smolts, only 38.6% passed through the complex, of which 36.4% migrated by the navigation canal and 63.6% by the hydropower station, with a median research time of 04:44. Among all the released individuals, the escapement rate at the end of the study site was 2.9% by the canal and 8.3% by the Meuse river. This site, which offers two non-optimal, unattractive and unsafe migration routes, turns out to be problematic for successful downstream smolt migration.

Experimental and theoretical modeling of a quarter-circular gate flow

Gates are important hydraulic structures and used for flow measurement, water delivery, and water level regulation in open channels and irrigation networks. In this study, the quarter-circular gate is introduced and investigated. The cross section of this gate consists of a quarter circular arc and the lip angle of the gate equals to zero. Discharge coefficient, variation of downstream flow depth, and velocity distribution at opening section of gate were experimentally measured. Using potential flow theory supported by dimensional analysis, equations for discharge coefficient and velocity distribution at gate opening section of quarter-circular gate were derived and then validated using experimental data. The mean percentage error (MPE) of obtained equation for discharge coefficient of quarter-circular gate was calculated as 2.24%, indicating the high precision of the proposed theory. Based on obtained results, downstream flow depth of quarter-circular gate is uniform. Also, velocity distribution at gate opening section is nearly uniform. Discharge coefficient of quarter-circular gate was averagely obtained 55% larger than that of sluice gate. It was also obtained larger than that of radial gate. Elimination of contraction section at downstream of gate opening, which is the main source for energy loss and therefore discharge capacity reduction, is the main reason for larger discharge coefficient of quarter-circular gate.

Obtaining flow curve for viscoplastic fluids through inclined open-channel apparatus

Non-Newtonian fluids are commonly seen in industrial processes, such as those of the oil and mining industry, and in natural flows, like dam ruptures, landslides or mud flows. The hydrodynamic modeling of such processes/phenomena is directly linked to the rheological properties of the flowing fluid, usually characterized through rheometers. The high cost of rheometers and possible inaccessibility for certain applications demand for research of alternative rheometric methods. In order to assess the problem, the present work discusses a detailed experimental methodology to evaluate if the steady and uniform flow in an inclined channel is able to produce the flow curve for the test fluid carbopol 996 gel and work as an alternative rheometer. In order to estimate the shear rates and shear stresses, we measured the normal depth (ultrasonic technique), specific discharge (manual gravimetric method) and free surface velocity (manually and with laser barrier sensors). Based on the theoretical solutions, a simplified fitting procedure was adopted to make possible the assessment of shear rate and shear stress through the experimental data. The obtained flow curves were then compared with the reference flow curve, determined by a commercial R/S rheometer. Results showed that the experimental methods were able to provide the flow curves within acceptable uncertainty and the defined methodology detailed in the work can estimate satisfactorily the flow curve of non-Newtonian fluids. Finally, we highlighted that the wide channel hypothesis is the strongest condition to be guaranteed in order to obtain precise flow curves through the methodology present in this work.

Research on the efficient self-adaptive servo-control strategy in micro-EDM milling

As an important fabricating technology, micro-EDM is always confined by the rather low efficiency in practical applications. To solve this problem, a self-adaptive servo-control strategy is proposed in this study. Firstly, a self-determination technique is developed to define the threshold voltages of different discharge conditions. Then, the least square method is applied to predict the discharge condition of the next sampling period. After that, a detailed servo-control strategy considering both discharge condition and velocity is put forward to adjust the feed speed to match up with the actual material removal rate. Finally, a comparative experiment is undertaken to verify the effects of the proposed self-adaptive strategy. The results demonstrated that the material removal rate and ratio of spark pulse to the whole discharge pulses are significantly improved in comparison with the traditional constant speed strategy. The surface texture and tool wear generated by the two strategies are also compared. The results indicated that the proposed self-adaptive strategy enhances the efficiency without bringing extra disadvantages to the surface precision or tool wear. Moreover, retraction of the electrode is significantly decreased and the feed speed can steadily keep close to the material removal rate under the proposed strategy. Thus, the dynamic performance of the machine tool was better and the microelectrode was prevented from crashing into the workpiece. The idea of the proposed strategy can also be applied to other micro-EDM techniques such as drilling and die sinking.

Impact of a wall downstream of an air curtain nozzle on air curtain separation efficiency

Air curtains (ACs) employ plane turbulent jets to separate two environments in terms of heat and mass transfer, while still allowing unrestricted access through the opening between these environments. Most previous studies focused on ACs discharged from nozzles located just above the opening. However, in some cases ACs have to be installed close to the ceiling at a substantial distance from the top of the opening. The AC blown downwards along the vertical wall then first resembles a wall jet and after reaching the top of the opening starts resembling a free jet. The present study analyzes the behavior and performance of an AC with upstream wall above the opening. 2D steady RANS CFD simulations are performed based on grid-sensitivity analyses and validation with experimental data for a wall jet and a free jet. The total opening height is 4 m and vertical walls of 0.5 m, 1 m and 2 m, partly closing this opening, are considered. AC performance is evaluated both with the separation efficiency η (based on infiltration) and the adapted separation efficiency η* (based on infiltration and exfiltration). It is shown that the presence of the wall reduces jet decay. The longer the wall, the larger the jet momentum over the opening height. This reduces infiltration and increases η, but it increases exfiltration and therefore decreases η*. In practice, the jet discharge velocity (jet momentum) will have to be adjusted to keep high η*.

Flashover discharges dynamic with continuous and discontinuous pollution layer under lightning impulse stress

The paper is aimed at the study of the dynamic of discharges propagating at the surface of flat PVC insulator (i) with uniform continuous pollution layer and (ii) with uniform discontinuous pollution layer of different conductivities, under lightning impulse voltage for both polarities. It is shown that the morphology of discharges, the current and the voltage as well as the discharge velocity depend on the polarity of voltage, the configuration and the conductivity of the pollution layer; and the behavior of discharges is similar to that of discharges in long air gaps.

Tide-Induced Variability and Mechanisms of Surface Suspended Sediment in the Zhoushan Archipelago along the Southeastern Coast of China Based on GOCI Data

The variations and dynamics of suspended sediment in the coastal waters around the Zhoushan Archipelago are complex due to strong tidal dynamics. This study aims to delineate the tide-induced variability of surface suspended sediment and reveal its mechanisms in the Zhoushan Archipelago based on Geostationary Ocean Color Imager (GOCI) data. Suspended sediment concentration (SSC) estimations through the ultraviolet wavelength atmospheric correction (UV-AC) algorithm and a tuned empirical inversion algorithm using extensive in situ measurements are presented. GOCI-processed remote sensing reflectance (Rrs) is validated using field data and is cross-validated with Landsat 8 Operational Land Imager (L8/OLI) measurements, respectively. The estimated SSC is validated with independent datasets. The validations reveal that GOCI-processed Rrs is reasonable and that the GOCI-retrieved SSC is accurate and can be used to quantify SSC distributions and variations in the Zhoushan Archipelago. The variations of the SSC in the study area are closely related to the temporal variations of the tidal level. High SSCs often occur in the middle of ebb or flood tides due to large tidal discharge and high tidal velocity. Significant hourly variations of the SSC are mainly controlled by tidal forces. Dynamic mechanism analysis indicates that during neap and middle tides, the local high SSC is mainly attributed to the sediment resuspension process driven by tidal currents; in addition, during the spring tide, the variations of the SSC are simultaneously modulated by sediment resuspension and horizontal advection processes.

Correction factor for measuring mean overland flow velocities on stony surfaces under rainfall using dye tracer

Dye tracing is a common and simple method for measuring surface velocity of overland flow. However, a correction factor is needed to convert the velocity of the dye front to mean velocity. Selecting the appropriate correction factor for particular conditions is complex and its behavior has not been well studied in sheet flow under rainfall on actively eroding surfaces. A series of simulated rainfalls were conducted on a 2 m by 6 m plot with gravelly sandy loam soil. The plot was progressively eroded to examine a wide range of hydraulic conditions. A total of 178 velocities (maximum and mean) were measured using electrolyte and dye tracers over three travel distances (1.65, 3.5, and 5.8 m), and three slope gradients (5%, 12% and 20%). Discharge, sediment yield, random roughness, rock cover, and a range of hydraulic variables were also determined. Mean flow velocity was derived from the centroid of the electrolyte breakthrough curve. Our findings suggest that the velocity correction factor is a dynamic, site specific property. A linear model was proposed to estimate the correction factor based on readily available predictor variables, those being travel distance, unit discharge, and maximum velocity. The results will benefit further investigations of overland flow hydraulics on semiarid rangelands by providing more comprehensive correction factors to determine mean velocity.

Morphometric analysis and flash floods hazards assessment for Wadi Al Aawag drainage Basins, southwest Sinai, Egypt

Assessment of surface runoff in arid regions is extremely important. Water means life; hence, the best management of flash floods promote groundwater recharge, prevents flood hazards and soil drift that is required for developing purposes. The main objective of the present work is to evaluate the morphometric parameters and flash flood hazards that frequently occurred in Wadi Al Aawag Drainage Basin. The study is based on applying the Arc GIS 10.5 program to draw drainage basins and to compute their morphometric attributes. The hydraulic model (HEC-HMS) in the WMS program was used to compute the peak flow hydrograph of floods for different sub-basin. The calculations of water quantities and peak flow were based on the SCS unit hydrograph approach. Results indicate that all the studied sub-basins have low Rb (1.99–3.7), this tends to give more possibilities to flash floods. The studied sub-basins have high densities ranges between 1.21 (Maier) and 1.62 km/Km2 (Ghewitat), this reflects high relief, impermeable subsurface material, and low contribution for groundwater, especially in the area covered by basement rocks (upstream portions). The decrease in time of concentration of Gebah is associated with an increase in the relief (1900 m) and relief ratio (83.3 m/km), which represent the land has a steep slope. Maier and Habran sub-basin, gives the maximum runoff volume, peak discharge, runoff depth, and runoff velocity during the storms of March 2014 and March 2020. These sub-basins have high CN value, the biggest area, long stream length, and high stream numbers. The study ended with a set of recommendations that mitigate the flash flood risks.

БАЛЛИСТИКА СТРУЙ ИЗ УНИВЕРСАЛЬНЫХ НАСАДКОВ СТВОЛЬНОЙ ПОЖАРНОЙ ТЕХНИКИ

Purpose. The article analyzes assessment methods of existing fire extinguishing agent (FEA) jet ballistics. FEA discharge velocity from the nozzle effect on FEA drops in the air motion and trajectory has been investigated. Applying a new method for calculating FEA jets ballistics has been grounded. With the help of mathematical modeling, calculations have been carried out for FEA flow rate indicators depending on the pressure and flow rate for a universal nozzle, which forms different jet discharge angles from solid to spray. A model has been developed that describes FEA jet ballistics for both universal and conical or conoid fire nozzles. Methods. A logical method based on forces influence on a water drop in a medium has been used, as well as an empirical method, i.e. experiment. Findings. To confirm the developed jet ballistics theory, a series of field tests has been carried out. A fire monitor with a universal nozzle has been used as a test unit under the following conditions: equivalent diameter 29 mm; pressure in front of the nozzle 0.6 MPa; flow rate at the outlet 35 m/s (calculated by numerical simulation); nozzle inclination angle in relation to horizon 30°; nozzle cutting height from the horizon 1 m. The discrepancy in the indices of calculated and experimental jet range did not exceed 3 %. An insignificant effect of medium density change on jet range capability has been revealed, that is, under the same initial conditions, but at different ambient temperatures, fire extinguishing agent jet range capability will differ. This should be taken into account when using fire extinguishing installations based on monitors in different climatic regions. Research application field. The research results will simplify nozzle fire equipment development and design process, algorithm construction for robotic fire extinguishing installations operation based on fire monitors. Conclusions. The developed method for calculating jet ballistics is fully correlated with in-situ indicators. Jet ballistics is highly effected by fire extinguishing agents nozzle discharge velocity and medium density in which the fire extinguishing agent is flowing. In the future, it is required to conduct a number of scientific studies to determine extinguishing agent discharge velocity from various nozzles dependences on pressure and consumption.

Seasonal and Daily Variation of Hydrodynamic Conditions in the Amazon River Mouth: Influence of Discharge and Tide on Flow Velocity

Less, D.F.S.; Ward, N.D.; Richey, J.E., and Da Cunha, A.C., 2021. Seasonal and daily variation of hydrodynamic conditions in the Amazon River Mouth: Influence of discharge and tide on flow velocity. Journal of Coastal Research, 37(6), 1181–1192. Coconut Creek (Florida), ISSN 0749-0208. Hydrodynamics characteristics control various biogeochemical processes related to the phenomena of transport of particulate materials, biogeochemical components, and greenhouse emissions; however, the hydrodynamic conditions in the North Channel of the Amazon River Mouth is relatively little understood. The seasonal and tidal variability of hydrodynamic characteristics in the North Channel of the Amazon River Mouth were investigated using an acoustic measurement technique. The measurements of discharge (Q), water velocity (U), and water level (h) were performed during a semidiurnal tidal cycle in a 12 km wide transect during four hydrological seasons. The hydrodynamics are mainly controlled by the river discharge, being directly related to the rain pattern with a well-defined time lapse for the Amazon Basin. The amplitude of the tides, the mean discharge, and the velocity of the natural flow presented during high discharge season were 3 m, 12,423 m3 s–1 and 1.18 m s–1, respectively. The analyses of tidal effects showed a phase opposition between the water level, river discharge, and water velocity; the water velocity was ∼42% higher during the ebb tide with a duration ∼1 hour and 30 minutes longer than the flood phase. The U and h are inversely proportional (R = –0.72, p < 0.01); significant variations in velocity throughout the tidal cycle are associated with the highest values observed at ebb tide, when the velocity and level of the water are significantly influenced by both diurnal and seasonal components. Thus, the results can contribute to the evaluations of more detailed potential interactions of the advective processes, such as mixing and dilution of passive agents of the natural flow, which are very poorly recorded in the existing literature.

Study on discharge velocity of tailings mortar in dam break based on FLOW-3D

Tailings pond is used to store the tailings discharged from the mine after separation and mining. As a potential hazard source with high potential energy, the tailings mortar with high potential energy after dam break is transformed into high-speed dynamic energy sand flow to impact the downstream area through energy conversion. In this paper, through the establishment of a three-dimensional model of a tailings pond, the FLOW-3D software is used for numerical simulation, and the influence of correlation coefficient on the discharge speed of tailings mortar after dam break is analyzed, and the relevant migration law is obtained. The test in this paper can provide a reference for the corresponding disaster and protection engineering research.

Influence of rotor speed, discharge pressure, and clearance size on the unsteady flow dynamics and heat interaction of roots blower

The geometry of the 2-lobe rotors of a roots blower is proposed by the combination of three arcs and is parameterized by two independent variables. By considering a standard combination of these variables, attempts are made to grasp the unsteady interior flow phenomena and thermal interaction in the blower as well as to comprehend the effect of main influencing factors on the performance of the blower using a transient finite volume-based dynamic-mesh-rearrangement method. A grid-independent test is conducted, and the adopted methodology is validated. At first, an endeavor is made to realize the transient internal flow field and heat interaction within the roots blower. Then, individual efforts are made to apprehend the effect of rotor speed, discharge pressure, and clearance size (provided in between the rotors or in between the rotors and casing) on the said transient flow dynamics and heat interaction. Time variation of the discharge velocity, mass flowrate, and discharge temperature are found to be fluctuating in nature. Pressure, velocity, and temperature distributions in the blower, as well as the leakages, backflow, vortices in the blower, etc., at different moments, are found to be strongly dependent on the rotor speed, discharge pressure, clearance size between the rotors or between the rotor and housing. The nature and amplitude of the time variation of exhaust velocity, discharge mass flowrate, outlet-temperature, and the blower performance are also found to be very much sensitive to the chosen rotor speed, discharge pressure, and clearance size.

Transboundary River Hydrodynamic Conditions Assessment in Sustainable Development Context. A Case Study of Danube River: Chilia Branch - Bystroe Channel Area

Located in the Danube Delta Biosphere Reserve, the Chilia branch serves as country boundary between Romania and Ukraine. The former state started in 2004 a project intended to increase the navigability capacity of Bystroe Channel, the environmental impact of the works carried out being discordantly considered by the Romanian and Ukrainian authorities. The Inquiry Commission established under the Espoo Convention, of which both countries are part of, delivered its final opinion that the project was likely to have a significant adverse transboundary impact on the hydrodynamic local conditions and habitat loss for fish and birdlife. Statistical analysis was operated on daily and monthly averaged water discharge values and the results were graphically displayed as hydrographs and probability curves and distribution. Addressing the in situ data measurements deficit for the Chilia branch - Bystroe Channel Area, measurement campaigns have been carried out in order to monitor the alterations of the hydrodynamic parameters. Using the specialized Acoustic Doppler Current Profilers technique, there have been recorded water flow parameters (water discharge and water current velocity vectors) and the data used for analysis and 2D and 3D representation of the hydrodynamic conditions.

Assessing the hydrological effects of land-use changes on a catchment using the Markov chain and WetSpa models

ABSTRACT Predicting the effects of land-use (LU) changes and hydrological processes on a rapidly urbanized catchment using the Markov chain and WetSpa models is the main objective of this research. Hourly hydrometeorological data for 2001–2016, land use maps, a digital elevation model (DEM) and soil texture were used as inputs into the models. The simulation results verified some negative impacts of LU changes, such as increases in peak discharge and flow velocity from 2001 to 2032 by 57.1% and 39.4%, respectively. Additionally, the time of concentration decreased from 6 h in 2001 to 5 h in 2016 and to 4 h in 2032. Surface runoff recorded the highest increases by 48.4% and 83.9%, respectively, in 2016 and 2032, compared to 2001. We concluded that the combination of both models is an appropriate tool for predicting the possible effects of LU changes on different hydrological features, which provide vital information for land managers.

Field methods of a near-bed suspended sediment experiment in the Yangtze River, China

Using experimental data of near-bed suspended sediment concentrations at five typical hydrometric stations of the Three Gorges Reservoir at the early reserving stage, the differences were investigated between the common method and improved method during flood seasons and non-flood seasons. The impact of taking measurements below 0.2 times the water depth on the results was discussed. The results show that the average discharges and velocities at each station calculated by the common method were slightly larger than those calculated by the improved method. Regarding the suspended sediment concentration at each station, the errors in the reservoir and downstream channels in dynamic equilibrium state were small, and the largest errors occurred where the river bed was strongly scoured in the downstream reach below the large dam. There was no significant relationship between water discharge and flow velocity, and the missed measurement phenomenon also occurred. The sediment discharge error was affected by the suspended sediment concentration, implying that errors usually occurred in channels with serious erosion during flood seasons. The correction coefficients (R2) of sediment discharge at each station were given during the experiment, which showed that the sediment discharges at the hydrometric stations where a large amount of sediment transport occurred near the river bottom, needed to be modified. Furthermore, the test methods proposed in this study were applied to calculate the sediment discharges of three rivers, and the results indicate that this method can narrow the gap between bathymetric comparisons and sediment load measurements.

Convective heat transfer enhancement of ionic wind under variable air pressures

Presently, limited studies are available in understanding the ionic wind's behaviour under restricted or extreme environmental conditions. Thus, this study aims to investigate ionic wind characteristics and its convective heat transfer enhancement under the influence of varying air pressures. Here, an ionic wind generated from a cone to mesh configuration was used. Results showed that the discharge current (which translates to power consumption) and velocity of the ionic wind behaved in opposing manners at pressures above and below atmospheric pressure. Increasing the pressure above the atmospheric pressure led to a decrease in velocity for both positive and negative ionic wind, while the wind velocity was relatively constant at air pressures below atmospheric pressure. On the other hand, the power consumption was also seen to be consistent for positive ionic wind, while the negative ionic wind showed a power consumption decline with increasing air pressure. The highest power consumption was observed for the negative ionic wind at the lowest air pressure. Further investigations on the convective heat transfer showed a maximum achievable enhancement of 17% over natural convection for both positive and negative ionic wind. The optimum performance, which is defined as the heat transfer enhancement ratio over power consumption of the ionic wind, was found to be at just beneath the atmospheric pressure at 0.9 bar for both positive and negative ionic wind, with the positive ionic wind superseding the efficiency of negative ionic wind by 17%.

Optical study on needle lift and its effects on reacting diesel sprays of a single hole solenoid injector

Precise control of needle lift provides one possibility to control the diesel spray and combustion process actively. However, most studies of needle lift focus on internal flow or near nozzle spray. Little work has been performed on its effects on reacting spray. In this work, one way to change the needle lift profile of a solenoid injector has been developed and the relationship between needle lift and reacting spray has been investigated. The needle movement was detected with an optical nozzle. In addition, the visualization of reacting sprays of the same injector equipped with a single hole nozzle was conducted in a combustion chamber. Some simulations were also performed to assist the analysis. The results show that the needle lift profile can be regulated by changing the thickness of an adjusting pad. It seems the different needle lift profiles do not bring in significant influences on reacting spray characteristics. The CFD results indicate that it is mainly caused by the similar internal flow characteristics which do not show strong variation when needle lift is higher than 0.1 mm. However, the discharge coefficient and velocity coefficient decrease sharply when needle lift is smaller than 0.05 mm because of the ?throttle? effect.