Longitudinal Wind Speed Research Articles

Experimental Investigation of the Influence of Longitudinal Tilt Angles on the Thermal Performance of a Small-Scale Linear Fresnel Reflector

This paper analyses the influence of the longitudinal tilt angle of the secondary system of a low-concentration photovoltaic system based on a small-scale linear Fresnel reflector. Several evaluation indicators, such as useful heat gain, thermal efficiency, incident solar irradiance gain on the photovoltaic cells, and total useful energy gain, were evaluated for five wind speed conditions and six locations in the Northern Hemisphere. The tests were performed with two small-scale linear Fresnel reflector configurations: the classical large-scale linear Fresnel reflector configuration (base configuration) and the optimal longitudinal tilt angle configuration (longitudinal tilt configuration). An experimental platform based on an open-loop wind tunnel was designed and built for this purpose. As far as useful heat production, the longitudinal tilt configuration performs worse as the longitudinal tilt angle and wind speed increase. A useful heat gain 33.91% lower than the base configuration is obtained with a wind speed of 10.03 (m/s) at the 36.86 (°) latitude location. Thermal efficiency decreases with increasing wind speed and longitudinal tilt angle. The thermal efficiency is between 0.3 and 0.2 with wind speeds of 4.99 (m/s) and 10.03 (m/s). The longitudinal tilt configuration shows the best increase in total useful energy gain in the absence of wind (up to 53% at a latitude of 36.86 (°)). This increase is 25% at this same location with a wind speed of 10.03 (m/s). It can be concluded that the effect of the longitudinal tilt of the secondary system has a positive effect. To highlight the importance of this work, the results obtained in the configuration comparison were used to compare a nonconcentrating photovoltaic system and a low-concentration photovoltaic system. The incident solar irradiance on the photovoltaic cells is much higher with nonconcentrating photovoltaic technology. This solar irradiance gain is over 60% for the base configuration and 45% for the longitudinal tilt configuration. The total useful energy gain is 70% in the absence of wind and at the 36.86 (°) latitude location in favour of the low-concentration photovoltaic system. The nonconcentrating photovoltaic system performs better with a wind speed of 10.03 (m/s).

Reconstructing turbulent wind-fields using inverse-distance-weighting interpolation and measurements from a pulsed mounted-hub lidar

This study evaluates a numerical multi-beam pulsed lidar mounted on the hub of the NREL 5MW reference wind turbine using the HAWC2 v13.1 numerical sensor for synthetic lidar measurement generation. While initially designed for single-beam operations, it facilitates multi-beam configuration simulations. We conducted an analysis of full-rotor longitudinal wind speed reconstruction by combining inverse-distance-weighting with synthetic sensor data from HAWC2. Utilizing a Mann-generated turbulence box for wind input at U = 11.4 m/s, we examined three lidar configurations for efficacy. The hub-mounted lidar proved efficient in capturing the incoming flow towards the turbine, showing a 60% improvement in overall reconstruction accuracy across the plane compared to the baseline, where hublidar measurements are simple average across the rotor plane. The rotor average wind speed showed a 30% enhancement compared to the baseline. Crucially, the lidar configuration, which impacted the spatial distribution across the rotor plane, emerged as a pivotal factor for effective reconstruction. Proper configuration assessment is essential, especially given the implications of rotational sampling and its impact under various wind conditions, for optimal performance. The proposed method, combining inverse-distance weighting with hub-lidar data for high spatial resolution measurements across the rotor plane, shows significant potential for real-time windflow estimation and lidar-assisted control applications.

Thermal runaway propagation characteristics of lithium-ion battery modules in a restricted channel with different longitudinal wind velocities

Thermal runaway (TR) and its propagation (TRP) in lithium-ion batteries (LIBs) present safety challenges, especially in confined spaces where wind speed's impact on TRP remains poorly understood. This study investigates the influence of longitudinal wind speed on TRP in LIBs within restricted channels. Results reveal a decreased incidence of TR with higher wind speeds. At 0 m/s, all cells in the two types of modules sequentially trigger TR, while speeds above 4 m/s prevent TR in any cells. TR onset temperature decreases, and onset time increases with wind speed. In the four-cell module, as wind speed rises from 0 m/s to 3 m/s, the TR onset for cell #1 increases from approximately 355 s to about 786 s. Dimensionless maximum remaining heat and dimensionless TR rate display a negative linear relationship with dimensionless wind speed. Dimensionless maximum remaining heat and TR rate exhibit a negative linear relationship with dimensionless wind speed. Additionally, the dimensionless TRP rate follows a power function with dimensionless wind speed. Energy flow distribution at different wind speeds is calculated, showing effective heat dissipation by longitudinal wind, delaying or preventing TRP. This research advances TRP theory and proposes a novel approach to mitigate TRP in LIBs.

Wind Speed Spectrum of a Moving Vehicle under Turbulent Crosswinds

Wind loads have become one of the key influencing factors for the running safety of vehicles and comfort of passengers. The investigation of the wind speed spectrum characteristics of a moving vehicle under turbulent crosswinds is of great importance. Expressions of the wind speed spectrum of a moving vehicle were obtained from the von Kármán spectrum, based on Taylor’s frozen flow hypothesis. The influencing factors, including the ratio of the vehicle speed to the wind speed and wind yaw angles, were analyzed. The change rules of the wind speed spectrum peak and its corresponding frequency were also studied. The results show that the wind speed spectrum peak values of the moving vehicle were larger than those of the static vehicle. The wind speed spectrum peak values corresponding to the moving vehicle were first increased and then decreased, as the wind yaw angles increased. Some of the frequencies corresponding to the longitudinal wind speed spectrum values of the moving vehicle were smaller than those of the static vehicle. Therefore, the energy had been transferred to the lower frequency. For the moving vehicle, the frequency values corresponding to the longitudinal wind speed spectrum peak were first increased and then decreased, as the ratio of the vehicle speed to the wind speed and the wind yaw angle increased.

Trend analysis and inter-annual variability in wind speed in South Africa

Reliable forecasts of long-term longitudinal wind speed patterns may help predict air circulation changes. They are also essential for the planning and financing of wind projects for Independent Power Producers (IPPs). Long-term wind speed trends and variations in historical mean wind speed data were examined using Mann Kendall’s test and calculating inter-annual variability (IAV). The Wind Atlas for South Africa (WASA) provides high resolution quality wind data for research and applications locally. WASA has 19 meteorological stations in South Africa. The WASA project began in 2009 with the aim of mapping South Africa's wind resource, allowing stakeholders in the wind energy sector and industry to explore and prepare for utility-scale wind power generation. For the past ten years, WASA has been measuring and providing data.The results showed an increasing trend at WM01 and a decreasing trend at WM08. There was no clear trend at other wind masts. Satellite data was used to validate results and no trends were observed at most of the stations. IAV values for this study ranged between 1.088% and 3.353% which is relatively low compared to the commonly found IAV values of 5-6%, implying that mean annual wind speed variation at these stations is low. To confirm a clear trend in wind speed, it is recommended that further work be done with long term periods and substantiate our finding with the use of historical simulation and climate change scenarios.

A Study on the Evacuation of an Extra-Long Highway Tunnel Fire—A Case Study of Chengkai Tunnel

The smoke from tunnel fires spreads over long distances and is difficult to vent. Smoke accumulation leads to high temperatures, low visibility, and high concentrations of toxic gases, which greatly hinders the evacuation of people inside the tunnel. In this paper, a representative extra-long highway tunnel—Chengkai Tunnel—is selected as the engineering background, and a tunnel model is built using FDS and Pathfinder software to simulate the fire scenario and evacuation scenario under different longitudinal wind speeds. The concept of safe evacuation reliability is proposed to describe the relationship between the ASET (available safe egress time) and the RSET (required safe egress time). The simulation results show that with the increase in longitudinal wind speed, the ASET upstream of fire source increases first and then remains unchanged, while ASET downstream of fire source increases first and then decreases. The ASET upstream of the fire source is affected by visibility, while the ASET downstream of the fire source is affected by visibility when the wind speed is low, and is affected by temperature as the wind speed increases. The bottleneck effect is an important reason for the long evacuation time of people. The blockage time is a power function of the evacuation movement time, and increasing the width of the cross passage can improve the evacuation efficiency of the tunnel. The increase in the number of evacuees will reduce the reliability of the safe evacuation of personnel. Among all simulated scenarios, a longitudinal wind speed of 2.5 m/s has the highest safe evacuation reliability, with 0.79, 0.92, and 0.99 for scenarios R1, R2, and R3, respectively. Excessive wind speed reduces the safe evacuation reliability downstream of the fire source.

Flame spread over cables in a utility tunnel: Effect of longitudinal wind and inclination angle

Tables in utility tunnels pose a major fire hazard. This work aims to provide a comprehensive understanding of the effects of cable inclination angle and longitudinal wind (U∞) on the flame spread behaviors of cables in a utility tunnel. Flame inclination angle (β) increases with the increase of cable inclination angle and longitudinal wind speed, while the amplification decreases as the longitudinal wind speed increases. Both flame length (xf) and pyrolysis length (xp) increase linearly with sinθ when U∞ is smaller than 0.65 m/s and they also increase with the increase of longitudinal wind speed. The increasing inclination angle and longitudinal wind speed contribute to the increasing flame spread rates. The flame spread rate accelerates significantly when the longitudinal wind speed and inclination angle are 0.65 m/s and 12° respectively. In addition, a model based on heat transfer analysis was established to predict the flame propagation rate under different cable inclination angles, and the experimental results were in good agreement with the predicted results. The results of the study contribute to cable fire risk assessment, which is beneficial for cable fire prevention and control in utility tunnels.

Gaussian mixture model for extreme wind turbulence estimation

Abstract. Uncertainty quantification is necessary in wind turbine design due to the random nature of the environmental inputs, through which the uncertainty of structural loads and response under specific situations can be quantified. Specifically, wind turbulence (described by the standard deviation of the longitudinal wind speed over a 10 min time duration) has a significant impact on the extreme and fatigue design envelope of the wind turbine. The wind parameters (mean and standard deviation of longitudinal wind speed over 10 min time duration) are not independent stochastic variables, and structural reliability analysis or uncertainty quantification therefore requires these wind parameters to be correlated stochastic parameters. An accurate probabilistic model should be established to model the correlation among wind parameters. Compared to univariate distributions, theoretical multivariate distributions are limited and not flexible enough to model the wind parameters from different sites or direction sectors. Copula-based models are often used for correlation description, but existing parametric copulas may not model the correlation among wind parameters well, due to limitations of the copula structures. The Gaussian mixture model is widely applied for density estimation and clustering in many domains, but limited studies have been conducted in wind energy and few have used it for density estimation of wind parameters. In this paper, the Gaussian mixture model is used to model the joint distribution of mean and standard deviation of longitudinal wind speed over 10 min time duration, which is calculated from 15 years of wind measurement time series data. As a comparison, the Nataf transformation (Gaussian copula) and Gumbel copula are compared with the Gaussian mixture model in terms of the estimated marginal distributions and conditional distributions. The Gaussian mixture model is then adopted to estimate the extreme wind turbulence (wind parameters for extreme load), which could be taken as an input to design loads used in the ultimate design limit state of turbine structures. The wind parameter contour associated with a 50-year return period computed from the Gaussian mixture model is compared with what is used in the design of wind turbines as given in IEC 61400-1. The Gaussian mixture model is able to model the joint distribution of wind parameters well, where the estimated tail distributions of both the marginal distributions and conditional distribution have good accuracy, and it is a good candidate for extreme turbulence estimation.

Experimental study on temperature decay and smoke control in tunnel fires with combination of multi-point smoke exhaust and longitudinal ventilation

This paper investigates the longitudinal temperature distribution characteristics beneath the ceiling and smoke control of the tunnel with combination of multi-point smoke exhaust and longitudinal ventilation. Experiments are carried out in a model tunnel with dimensions of 60 m × 1.3 m × 0.67 m. The longitudinal wind speed is set to 0–0.5 m/s, the exhaust air volume to 0.34–1.09 m³/s and the fire heat release rates (HRR) are 30.7 kW and 61.4 kW. The results show that the tunnel fire with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel) causes the offset of flame, and the maximum temperature point beneath the tunnel ceiling appears in the upstream direction from the fire source. The large smoke exhaust air volume will cause smoke layering plug-holing at the smoke exhaust vents, and the temperature of the vents where plug-holing occurs is lower. Longitudinal ventilation combined with the top multi-point smoke exhaust system has a better smoke control effect, but the longitudinal wind speed cannot be greater than 0.5 m/s. The temperature decay beneath the tunnel ceiling is in accordance with the exponential attenuation law in a tunnel with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel), and the longitudinal temperature decay rate of the side close to the exhaust fan is smaller than that of the other side.

Pseudo-2D modelling of heat redistribution through H2 thermal dissociation/recombination: consequences for ultra-hot Jupiters

ABSTRACT Thermal dissociation and recombination of molecular hydrogen, H2, in the atmospheres of ultra-hot Jupiters (UHJs) has been shown to play an important role in global heat redistribution. This, in turn, significantly impacts their planetary emission, yet only limited investigations on the atmospheric effects have so far been conducted. Here, we investigate the heat redistribution caused by this dissociation/recombination reaction, alongside feedback mechanisms between the atmospheric chemistry and radiative transfer, for a planetary and stellar configuration typical of UHJs. To do this, we have developed a time-dependent pseudo-2D model, including a treatment of time-independent equilibrium chemical effects. As a result of the reaction heat redistribution, we find temperature changes of up to ∼400 K in the atmosphere. When TiO and VO are additionally considered as opacity sources, these changes in temperature increase to over ∼800 K in some areas. This heat redistribution is found to significantly shift the region of peak atmospheric temperature, or hotspot, towards the evening terminator in both cases. The impact of varying the longitudinal wind speed on the reaction heat redistribution is also investigated. When excluding TiO/VO, increased wind speeds are shown to increase the impact of the reaction heat redistribution up to a threshold wind speed. When including TiO/VO there is no apparent wind speed threshold, due to thermal stabilization by these species. We also construct pseudo-2D phase curves from our model, and highlight both significant spectral flux damping and increased phase offset caused by the reaction heat redistribution.

Experimental study on the tunnel temperature distribution under the coupling effect of train blocking and fire inside the carriage

The understanding of temperature distribution in a railway tunnel caused by train fire can help to optimize the design of ventilation and rescue systems. In this study, a series of experimental tests were conducted in a 1/11 reduced-scale tunnel to investigate the effect of train blocking and internal fire of the carriage on the maximum temperature distribution. Different fire scenarios were discussed, including blocking length and opening modes of doors and windows under typical longitudinal wind speeds. In order to quantify the high-temperature load in the tunnel, a dimensionless model of the maximum temperature rise under different fire scenes was proposed. The results showed that the maximum temperature under the blocking condition was relatively higher than the non-blocking condition, and the maximum temperature increases with the blocking length at the same measuring point. Besides, the position of the openings, the number of openings, as well as the space of openings all would affect the heat spread, but these factors might have less influence on the maximum temperature in comparison with heat release rate and longitudinal wind speed. These results can assist an optimal ventilation design for train fire in a railway tunnel.

Full-scale experimental study on water mist fire suppression in a railway tunnel rescue station: Temperature distribution characteristics

Rescue stations are essential for emergency evacuation in super-long railway tunnels. However, the deficiency of related studies aiming at improving the fire suppression performance of water mist system in fire scenarios limits its application significantly. In this work, 20 sets of full-scale water mist fire suppression experiments were conducted to examine the impacts of water mist system on smoke temperature characteristics, including water mist activation time (denoted by t), working pressure (P), k-factor (K) and longitudinal wind speed. Results show that when t = 3 min, P = 12 MPa, and K = 0.5, the best performance of temperature control could be achieved. Although there are violent temperature fluctuations in the train side, the smoke temperature could be easily restrained. Moreover, it is found that longitudinal ventilation is helpful to improve the visibility at platform and reduce smoke temperature. When P = 12 MPa, the coupling effect of water mist and longitudinal ventilation on cooling smoke is better. In addition, the non-dimensional maximum temperature rise is found to show a great cubical dependency on vertical height, and decreases along with a larger longitudinal distance for all cases. Also, under longitudinal ventilation, the non-dimensional maximum temperature rises are lower than that without longitudinal ventilation in the coverage area of water mist. Results of this work can provide a significant reference for the design of water mist system in railway tunnel rescue stations.

The Smoke Spread Rule under Different Longitudinal Wind Speed in the Case of Fire in a Blocked Tunnel

In recent years the development of the field of underground transportation is entering a new era. At the same time the loss caused by the tunnel fire is also incalculable. In the case of fire, its complex interior, less entrances and exits, and long evacuation routes bring great difficulties to the evacuation of people, often causing significant casualties and property losses. In this paper, FDS will be used to study the smoke spreading law of the tunnel with train blockage in terms of no mechanical ventilation and different ventilation speeds in different fire source locations. The results show that the critical wind speed of the tunnel with train blockage is lower than that of the tunnel without train blockage.

Study on the Smoke Spread Law of a Subway Tunnel Fire under the Synergistic Action of Shaft Smoke Exhaust and Longitudinal Ventilation

Urban rail transit improves the urban spatial structure, solves the problem of urban traffic congestion, so its safety problem can not be ignored. Fire is one of the major factors threatening the safety of urban rail transit. Taking the tunnel between wengjiao road and Maqing road of Xiamen Rail Transit Line 2 as an example, the paper uses FDS software to simulate the mechanical smoke exhaust of the shaft under different wind speed conditions of the main tunnel, and deeply analyzes the smoke and temperature distribution under the fire conditions of the tunnel with the shaft. The results show that when the longitudinal wind speed v=1.7m/s and the shaft uses mechanical exhaust, there is no smoke upstream of the fire source, all the smoke is discharged through the shaft, and the height of the flue gas layer is significantly smaller than the thickness of the flue gas layer without longitudinal ventilation. The combination of longitudinal wind and mechanical smoke exhaust is more conducive to the safe evacuation of people.

Experimental and Numerical Investigation of Wind Characteristics over Mountainous Valley Bridge Site Considering Improved Boundary Transition Sections

To study wind characteristics over mountainous terrain, the Xiangjiang Bridge site was employed in this paper. The improved boundary transition sections (BTS) were adopted to reduce the influence of “artificial cliffs” of the terrain model on the wind characteristics at the bridge site over the mountainous terrain. Numerical simulation and experimental investigations on wind characteristics over mountainous terrain with/without BTS were conducted for different cases, respectively. The research results show that the cross-bridge wind speed ratios and wind attack angles at the main deck level vary greatly along the bridge axis, which can be roughly divided into three parts, namely the mountain (I, III) and central canyon areas (II). The cross-bridge wind speed ratios at the main deck level with BTS is generally larger than that without BTS in the central canyon area (II) for most cases, while the opposite trend can be found in wind attack angles. The longitudinal wind speed ratios of the terrain model with BTS at L/4, L/2, and 3L/4 of the bridge length are larger than that of the terrain model without BTS for most cases. In general, the maximum relative error between numerical results and experimental results is about 30% for most cases.

A Simple Method to Improve Smoke Exhaust Effectiveness of a Shallow-buried Urban Tunnel Fire with Natural Ventilation

ABSTRACT In order to improve the natural ventilation performance of a shallow-buried urban tunnel under the influence of external wind blowing above the shaft, a new method with installing a jet fan downstream of the shaft was proposed and a set of simulations were conducted to validate its effectiveness. The detailed smoke spread characteristics, such as mass flow rate, temperature, and velocity vector, were analyzed together with varying the ambient wind speed above the shaft, the longitudinal wind speed in the tunnel, and the velocity of the jet fan. Results show that under the coupled push effect of the longitudinal wind upstream of the fire and the airflow of jet fan downstream of the shaft, the block effect of the strong ambient wind on the vertical flow of smoke through the shaft can be overcome completely. In the tunnel, almost all the fire-induced smoke is confined between the fire and the shaft, and smoke can only be exhausted from the shaft. The findings can be a reference for tunnel ventilation design.

Large Eddy Simulation of effectiveness of solid screen on improving natural ventilation performance in urban tunnels

To improve natural ventilation performance in urban tunnels, a method of adding solid screens below shafts, was proposed to accumulate fire-induced smoke and weaken negative influence of plug-holing. A series of simulations were carried out to analyze the reliability of this method based on Large Eddy Simulation. Thermal and spreading characteristics of smoke were studied in detail, with systematically varying the angle of solid screen and the longitudinal wind speed in the tunnel. Results show that without wind in the tunnel, all smoke is blocked from spreading downstream after adding the solid screen, thus the smoke layer thickness downstream of the fire increases, and the plug-holing is prevented. The stack effect is enhanced due to the thicker and higher-temperature smoke layer. With wind in the tunnel, the smoke spreads across the solid screen and continues spreading downstream, but the solid screen with different angles can still increase the effective mass flow rate of exhausted smoke greatly. The solid screen with an acute angle performs better than that with an obtuse angle in exhausting smoke. Meanwhile, the practical engineering application of solid screens in tunnels with natural ventilation was demonstrated in detail.

Wind Characteristics Investigation on The Roofs of Three Adjacent High-Rise Buildings in a Coastal Area during Typhoon Meranti

This paper presents the study of the pulsating characteristics of three adjacent high-rise buildings A, B, and C under typhoon ‘Moranti’ (2016) based on the measurement of the actual top wind speed. The studied pulsating characteristics included mean wind speed and direction, turbulence intensity, gust factor, turbulence integral scale, wind speed spectrum and correlation. The relationships between each pulsating parameter and the relationship between the pulsating parameter and gust duration have been investigated. Results show that the mean wind speed and wind direction of three buildings are close. When U ≥ 10 m/s in three different sites at the same time, the turbulence intensity variation of three buildings is consistent and decreases when mean wind speed increases. Once only two locations are acquired simultaneously and the wind angle between 35° and 45°, the mean values of the along-wind and cross-wind turbulence of building A and building C are close. The along-wind turbulence of the three buildings is greater than the predicted Chinese codes for various terrains. The turbulence intensity and gust factors obtained through the analysis of the samples with the mean wind speed U ≥ 10 m/s are reasonable. The turbulence integral scales of buildings A and C are equal to the predicted values of ASCE-7 and AIJ-2004, whereas the turbulent integral scale of building B is evidently small. The gust factors of three buildings increase when the turbulence intensity increases; these two characteristics have a linear relationship. At the same time interval, building B has the maximum along-wind turbulence intensity and gust factors during the low wind speed period and building C achieves the minimum values. Building A acquires the maximum and building C obtains the minimum values in the high wind speed period. The turbulence intensity and gust factors of building B show a certain pulsation. Results show that turbulence intensity and gust factors are mainly affected by the short-term fluctuation of wind. The longitudinal wind speed spectrum of three buildings conforms well to the von Karman model. The correlation of along-wind speed depends on the wind speed, whereas the correlation of cross-wind direction is independent of wind speeds. The measured data and statistical parameters provide useful information for the wind resistance design of high-rise buildings in typhoon-prone areas.

Longitudinal wind speed time series generation to wind turbine controllers tuning

Although there are a wide variety of applications that require wind speed time series (WSTS), this paper emphases on WSTS to be used into wind turbine controllers tuning. These simulations involve several WSTS to perform a proper assessment. These WSTS must assure realistic wind speed variations such as wind gusts and include some rare events such as extreme wind situations. The architecture proposed to generate this WSTS is based on autoregressive models with certain post-processing. The methodology used is entirely described by precise notation as well as it is parametrized by means of data gathered from a weather station. Two main different simulations are performed and assessment; the first simulation is fed by weather data with high wind speed and great variability. The second simulation, on the opposite, use calm wind speed as a data source.Article History: Received 1st June 2018; Received in revised form Sept 6th 2018; Accepted October 10th 2018; Available onlineHow to Cite This Article: González, A.G. and Guede, J.M.L. (2018) Longitudinal Wind Speed Time Series Generated With Autoregressive Methods For Wind Turbine Control. International Journal of Renewable Energy Development, 7(3), 199-204.https://doi.org/10.14710/ijred.7.3.199-204

Effects of fire location on the capacity of smoke exhaust from natural ventilation shafts in urban tunnels

SummaryInvestigation of natural ventilation using shafts in tunnels has been receiving more attentions; however, analyses on how fire position influences the natural ventilation performance have rarely been addressed. This study investigated the influence of different fire positions between two shafts on natural ventilation effectiveness in a tunnel by large eddy simulation. The smoke movement characteristics were studied in detail, with systematically varying the fire position between two shafts and the longitudinal wind speed in the tunnel. The typical smoke characteristic parameters, such as temperature distribution, mass flow rate and CO concentration were emphatically investigated. Some special phenomena, such as plug‐holing and smoke bifurcation, were also discussed.