Measurements of Fire Whirls From a Single Flame in a Vertical Square Channel With Symmetrical Corner Gaps

1999 ◽  
Author(s):  
Kohyu Satoh ◽  
K. T. Yang
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Infrared Camera ◽  
Temperature Fields ◽  
Small Scale ◽  
Simulation Studies ◽  
Square Channel ◽  
Physical Measurements ◽  
Urban Fires ◽  
Important Basis

Abstract One of the most destructive forces in large urban fires is the occurrence of fire whirls. Despite the relatively recent experimental and numerical simulation studies on the global behaviors of small-scale whirling fires, much of the whirling fire phenomena still remain unknown. The purpose of this experimental study is to examine closely the detailed structures of the velocity and temperature fields in a stable whirling flame generated in a vertical square channel with symmetrical corner gaps by both physical measurements using conventional means and by quantitative observations using both a high-speed motion camera and a thermographic infrared camera. The results showed a rather complex non-uniform velocity and temperature field in the lower half of the whirling flame and could provide an important basis to validate the fire field models for the study of real large-scale fire whirls.

High-Speed Noncontact Profiling of Pavement Surface Texture and Its Significance

1986 ◽  
Vol 108 (3) ◽  
pp. 455-461
Author(s):  
J. C. Wambold ◽  
J. J. Henry
Keyword(s):  
Surface Texture ◽  
High Speed ◽  
Large Scale ◽  
Vision System ◽  
Small Scale ◽  
Skid Resistance ◽  
Texture Measurement ◽  
Pavement Surface ◽  
Texture Characteristics ◽  
Regression Techniques

It is generally agreed that the friction between a tire and a wet pavement (skid resistance) is controlled by the surface texture characteristics. Therefore, by measuring the relevant parameters describing texture, or by measuring a physical process dependent on texture, regression techniques can be used to relate skid resistance to the chosen texture parameter or process. Two scales of texture are of particular importance: microtexture (small-scale asperities) and macrotexture (large-scale asperities). This paper describes work performed to: (1) review candidate macrotexture and microtexture measurement methods that can be made at highway speeds (at or about 64 km/h [40 mph]), which are presently used or have potential for use in pavement texture measurement; (2) design and build a prototype of the most promising method; and (3) evaluate the effects of pavement surface texture on skid resistance. A prototype noncontact vision system that makes texture measurements at highway speeds was developed, and several improvements were made to upgrade the system to provide an improved prototype. Both hardware and software enhancements have yielded a texture measurement system that can obtain pavement macrotexture data in a fast, efficient, and reliable way.

scholarly journals Failure Mechanism of Rock Bridge Based on Acoustic Emission Technique

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Guoqing Chen ◽  
Yan Zhang ◽  
Runqiu Huang ◽  
Fan Guo ◽  
Guofeng Zhang
Keyword(s):  
Acoustic Emission ◽  
Failure Mechanism ◽  
High Speed ◽  
Large Scale ◽  
Small Scale ◽  
Failure Behavior ◽  
Long Distance ◽  
Rock Bridge ◽  
Rocky Slope ◽  
Landslide Model

Acoustic emission (AE) technique is widely used in various fields as a reliable nondestructive examination technology. Two experimental tests were carried out in a rock mechanics laboratory, which include (1) small scale direct shear tests of rock bridge with different lengths and (2) large scale landslide model with locked section. The relationship of AE event count and record time was analyzed during the tests. The AE source location technology and comparative analysis with its actual failure model were done. It can be found that whether it is small scale test or large scale landslide model test, AE technique accurately located the AE source point, which reflected the failure generation and expansion of internal cracks in rock samples. Large scale landslide model with locked section test showed that rock bridge in rocky slope has typical brittle failure behavior. The two tests based on AE technique well revealed the rock failure mechanism in rocky slope and clarified the cause of high speed and long distance sliding of rocky slope.

Unsteady Structure Measurement of Cloud Cavitation on a Foil Section Using Conditional Sampling Technique

1989 ◽  
Vol 111 (2) ◽  
pp. 204-210 ◽  
Author(s):  
A. Kubota ◽  
H. Kato ◽  
H. Yamaguchi ◽  
M. Maeda
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Laser Doppler Anemometry ◽  
Low Frequency ◽  
Sampling Technique ◽  
Experimental Result ◽  
Small Scale ◽  
Conditional Sampling ◽  
Cloud Cavitation ◽  
Structure Of Flow

The structure of flow around unsteady cloud cavitation on a stationary two-dimensional hydrofoil was investigated experimentally using a conditional sampling technique. The unsteady flow velocity around the cloud cavitation was measured by a Laser Doppler Anemometry (LDA) and matched with the unsteady cavitation appearance photographed by a high-speed camera. This matching procedure was performed using data from pressure fluctuation measurements on the foil surface. The velocities were divided into two components using a digital filter, i.e., large-scale (low-frequency) and small-scale (high frequency) ones. The large-scale component corresponds with the large-scale unsteady cloud cavitation motion. In this manner, the unsteady structure of the cloud cavitation was successfully measured. The experimental result showed that the cloud cavitation observed at the present experiment had a vorticity extremum at its center and a cluster containing many small cavitation bubbles. The convection velocity of the cavitation cloud was much lower than the uniform velocity. The small-scale velocity fluctuation was not distributed uniformly in the cavitation cloud, but was concentrated near its boundary.

scholarly journals Optimization Problem of Pricing and Seat Allocation Based on Bilevel Multifollower Programming in High-Speed Railway

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Lianbo Deng ◽  
Jing Xu ◽  
Ningxin Zeng ◽  
Xinlei Hu
Keyword(s):  
Optimization Model ◽  
Dynamic Pricing ◽  
High Speed ◽  
Large Scale ◽  
Solution Method ◽  
Programming Model ◽  
Divide And Conquer ◽  
Small Scale ◽  
High Speed Railway ◽  
Seat Allocation

This paper studies the multistage pricing and seat allocation problems for multiple train services in a high-speed railway (HSR) with multiple origins and destinations (ODs). Taking the maximum total revenue of all trains as the objective function, a joint optimization model of multistage pricing and seat allocation is established. The actual operation constraints, including train seat capacity constraints, price time constraints in each period, and price space constraints among products, are fully considered. We reformulate the optimization model as a bilevel multifollower programming model in which the upper-level model solves the seat allocation problem for all trains serving multiple ODs in the whole booking horizon and the lower optimizes the pricing decisions for each train serving each OD in different decision periods. The upper and lower are a large-scale static seat allocation programming and many small-scale multistage dynamic pricing programming which can be solved independently, respectively. The solving difficulty can be significantly reduced by decomposing. Then, we design an effective solution method based on divide-and-conquer strategy. A real instance of the China’s Wuhan-Guangzhou high-speed railway is employed to validate the advantages of the proposed model and the solution method.

scholarly journals High Accurate Crack Reconstruction Based on an Improved Discontinuous Digital Image Correlation: Subset Restore and Adaptation Method

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Wenzhi Tang ◽  
Hanbin Xiao ◽  
Chentong Chen
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Large Scale ◽  
High Accuracy ◽  
Image Correlation ◽  
Small Scale ◽  
Adaptation Algorithm ◽  
Subset Size ◽  
Nondestructive Technique

Digital image correlation (DIC) is an efficient nondestructive technique for measuring surface displacement in engineering. However, standard DIC is restricted to continuous deformation, and the existing discontinuous DIC (DDIC) techniques are only able to measure small-scale cracks. In this report, a novel subset restore model and a corresponding subset size adaptation algorithm are presented to overcome this limitation for crack-state and displacement field reconstruction for large-scale cracks. The technique introduces a new subset restore method for splicing the segmented subset by tracing the motion trajectory caused by pure discontinuities. The proposed model facilitates the calculation of the rotation angle and the pivot of the subset movement. The subset size adaptation algorithm is designed based on an evaluation of the intensity gradient and correlation coefficient to allow the model to achieve high accuracy. Validation of the approach was performed using two typical crack models, by deforming a numerically synthesized Gaussian speckle image according to the deformation data from finite element analysis (FEA) results and photographing a laboratory tensile test with a high-speed CCD camera, respectively. The results validate the efficacy and high accuracy of the proposed approach compared to standard DIC in the reconstruction of the displacement fields in both continuous and discontinuous regions. The accuracy of resultant displacement reconstruction achieves approximately 0.015 pixels and 0.05 pixels in continuous region and crack vicinity, respectively.

scholarly journals Instabilities in Pressure Confined Beams and Morphology of Extended Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 229-230
Author(s):  
A. Ferrari ◽  
S. Massaglia ◽  
E. Trussoni ◽  
L. Zaninetti
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Small Scale ◽  
Relativistic Electrons ◽  
Confined Fluid ◽  
Extended Radio ◽  
Cascade Processes ◽  
Intrinsic Correlation

Several authors have suggested that radio jet morphologies resolved in extragalactic sources are the effects of large-scale Kelvin-Helmholtz instabilities in high-speed, pressure-confined fluid beams ejected from parent active galactic nuclei (Ferrari et al. 1978, 1979, 1981; Hardee 1979;Benford et al. 1980). In particular results from studies for cylindrical geometries indicate how to connect the “wiggles” (observed in 3C449, NGC 6251, M87 and Cen A) with helical perturbations and the “knots” (observed in NGC 315, M87, Cen Aetc.) with pinching modes. Correspondingly small scale MHD perturbations, generated by the same instability or nonlinear cascade processes, are efficient in accelerating relativistic electrons via stochastic scatterings (Lacombe 1977; Ferrari et al. 1979). This picture may satisfy both the requirements for in situ re-acceleration and the intrinsic correlation between morphology and emission.

Scale interactions in a mixing layer – the role of the large-scale gradients

2016 ◽  
Vol 791 ◽  
pp. 154-173 ◽  
Author(s):  
D. Fiscaletti ◽  
A. Attili ◽  
F. Bisetti ◽  
G. E. Elsinga
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Large Scale ◽  
Mixing Layer ◽  
Physical Space ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Small Scales ◽  
Low Pass ◽  
Scale Characteristics

The interaction between the large and the small scales of turbulence is investigated in a mixing layer, at a Reynolds number based on the Taylor microscale ($Re_{{\it\lambda}}$) of $250$, via direct numerical simulations. The analysis is performed in physical space, and the local vorticity root-mean-square (r.m.s.) is taken as a measure of the small-scale activity. It is found that positive large-scale velocity fluctuations correspond to large vorticity r.m.s. on the low-speed side of the mixing layer, whereas, they correspond to low vorticity r.m.s. on the high-speed side. The relationship between large and small scales thus depends on position if the vorticity r.m.s. is correlated with the large-scale velocity fluctuations. On the contrary, the correlation coefficient is nearly constant throughout the mixing layer and close to unity if the vorticity r.m.s. is correlated with the large-scale velocity gradients. Therefore, the small-scale activity appears closely related to large-scale gradients, while the correlation between the small-scale activity and the large-scale velocity fluctuations is shown to reflect a property of the large scales. Furthermore, the vorticity from unfiltered (small scales) and from low pass filtered (large scales) velocity fields tend to be aligned when examined within vortical tubes. These results provide evidence for the so-called ‘scale invariance’ (Meneveau & Katz, Annu. Rev. Fluid Mech., vol. 32, 2000, pp. 1–32), and suggest that some of the large-scale characteristics are not lost at the small scales, at least at the Reynolds number achieved in the present simulation.

Analysis of Crank Angle-Resolved Vortex Characteristics Under High Swirl Condition in a Spark-Ignition Direct-Injection Engine

2017 ◽  
Author(s):  
Fengnian Zhao ◽  
Penghui Ge ◽  
Hanyang Zhuang ◽  
David L. S. Hung
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
High Speed ◽  
Large Scale ◽  
Early Stage ◽  
Direct Injection ◽  
Spark Ignition ◽  
Small Scale ◽  
Vortex Center ◽  
Intake Stroke

In-cylinder air flow structure makes significant impacts on fuel spray dispersion, fuel mixture formation, and flame propagation in spark ignition direct injection (SIDI) engines. While flow vortices can be observed during the early stage of intake stroke, it is very difficult to clearly identify their transient characteristics because these vortices are of multiple length scales with very different swirl motion strength. In this study, a high-speed time-resolved 2D particle image velocimetry (PIV) is applied to record the flow structure of in-cylinder flow field along a swirl plane at 30 mm below the injector tip. First, a discretized method using flow field velocity vectors is presented to identify the location, strength, and rotating direction of vortices at different crank angles. The transients of vortex formation and dissipation processes are revealed by tracing the location and motion of the vortex center during the intake and compression strokes. In addition, an analysis method known as the wind-rose diagram, which is implemented for meteorological application, has been adopted to show the velocity direction distributions of 100 consecutive cycles. Results show that there exists more than one vortex center during early intake stroke and their fluctuations between each cycle can be clearly visualized. In summary, this approach provides an effective way to identify the vortex structure and to track the motion of vortex center for both large-scale and small-scale vortices.

Amplitude and frequency modulation of the small scales in a jet

2015 ◽  
Vol 772 ◽  
pp. 756-783 ◽  
Author(s):  
D. Fiscaletti ◽  
B. Ganapathisubramani ◽  
G. E. Elsinga
Keyword(s):  
Amplitude Modulation ◽  
Frequency Modulation ◽  
High Speed ◽  
Large Scale ◽  
Spectral Band ◽  
Physical Space ◽  
Small Scale ◽  
Length Scale ◽  
Air Jet ◽  
Amplitude And Frequency Modulation

The present study is an experimental investigation of the relationship between the large- and small-scale motions in the far field of an air jet at high Reynolds number. In the first part of our investigation, the analysis is based on time series of hot-wire anemometry (HWA), which are converted into space series after applying the Taylor hypothesis. By using a spectral filter, two signals are constructed, one representative of the large-scale motions ($2{\it\lambda}_{T}-L$, where ${\it\lambda}_{T}$ is the Taylor length scale, and $L$ is the integral length scale) and the other representative of the small-scale motions ($1.5{-}5{\it\eta}$, where ${\it\eta}$ is the Kolmogorov length scale). The small-scale signal is found to be modulated both in amplitude and in frequency by the energy-containing scales in an analogous way, both at the centreline and around the centreline. In particular, for positive fluctuations of the large-scale signal, the small-scale signal is locally stronger in amplitude (amplitude modulation), and it locally exhibits a higher number of local maxima and minima (frequency modulation). The extent of this modulation is quantified based on the strength of the large-scale fluctuations. The response of the small-scale motions to amplitude modulation can be considered instantaneous, being on the order of one Kolmogorov time scale. In the second part of our investigation we use long-range ${\it\mu}$PIV to study the behaviour of the small-scale motions in relation to their position in either high-speed or low-speed regions of the flow. The spatially resolved velocity vector fields allow us to quantify amplitude modulation directly in physical space. From this direct estimation in physical space, amplitude modulation is only 25 % of the value measured from HWA. The remaining 75 % comes from the fixed spectral band filter used to obtain the large- and small-scale signals, which does not consider the local convection velocity. A very similar overestimation of amplitude modulation when quantified in the time-frame is also obtained analytically. Furthermore, the size of the structures of intense vorticity does not change significantly in relation to the large-scale velocity fluctuation, meaning that there is no significant spatial frequency modulation. The remaining amplitude modulation in space can be explained as a statistical coupling between the strength of the structures of vorticity and their preferential location inside large-scale high-velocity regions. Finally, the implications that the present findings have on amplitude and frequency modulation in turbulent boundary layers (TBLs) are discussed.

scholarly journals Fast Recursive Low-rank Tensor Learning for Regression

2017 ◽  
Author(s):  
Ming Hou ◽  
Brahim Chaib-draa
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Real Life ◽  
Low Rank ◽  
Small Scale ◽  
Low Rank Approximation ◽  
Rank Tensor ◽  
Fast Processing ◽  
Small Set ◽  
Time Required

In this work, we develop a fast sequential low-rank tensor regression framework, namely recursive higher-order partial least squares (RHOPLS). It addresses the great challenges posed by the limited storage space and fast processing time required by dynamic environments when dealing with large-scale high-speed general tensor sequences. Smartly integrating a low-rank modification strategy of Tucker into a PLS-based framework, we efficiently update the regression coefficients by effectively merging the new data into the previous low-rank approximation of the model at a small-scale factor (feature) level instead of the large raw data (observation) level. Unlike batch models, which require accessing the entire data, RHOPLS conducts a blockwise recursive calculation scheme and thus only a small set of factors is needed to be stored. Our approach is orders of magnitude faster than all other methods while maintaining a highly comparable predictability with the cutting-edge batch methods, as verified on challenging real-life tasks.

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