Multi-point Simultaneous Measurements Research Articles

The Impact of Cutting with a Shearer on the Conditions of Longwall Ventilation

In coal mines that are exploiting methane-saturated seams, high-level emission of methane is often the basic limitation for modern and high-efficiency longwall complexes. This paper presents selected observations and tests carried out in the Cw-4 longwall in seam 364/2 of the Budryk mine, which belongs to JSW SA. To observe the methane levels in the Cw-4 longwall, additional sensors were installed at the end section of the longwall from the side of the gobs, and the air velocity and methane concentration were registered in a multi-point system that were built in the selected longwall cross-section. The air parameters were recorded in the monitoring system. The use of multi-point simultaneous measurements of the local velocities and concentrations of methane in the longwall cross-section allowed for the precise determination of the air and methane volume flow using the velocity field method. This allowed us to perform a comparative analysis of the obtained records of the air parameters using special software to determine the distribution of the parameters in the cross-section of the excavation. An important element of the study was the simultaneous registration of the methane concentration in the longwall, information on the operating times, the direction of shearer operation, and the type of work being done (i.e., mining/cleaning).

Visualization system for bridge deformations under live load based on multipoint simultaneous measurements of displacement and rotational response using MEMS sensors

Abstract Displacement-induced fatigue accounts for most of the fatigue damage in steel bridges. In order to implement appropriate countermeasures against displacement-induced fatigue, it is important to understand bridge deformations under live load that cause stress concentration, and eventually lead to fatigue damage. Furthermore, knowledge of the positions of live load can shed light on the cause of bridge deformation. In the present study, a visualization system for bridge deformations is proposed. In the system, multipoint simultaneous measurements of displacement and rotational response are made by microelectromechanical systems (MEMS) sensors placed on an actual in-service bridge. The measured responses are input into a pre-made FEM model as the boundary conditions. MEMS sensors are suitable for multipoint simultaneous measurements of an in-service steel bridge, because they do not require a fixed reference point and can be attached by magnets on the painted surface of the bridge. Furthermore, the proposed system provided the positions of live load using the acceleration responses measured at the vertical stiffener on both longitudinal edges of the main girder. Implementation of the proposed system in an actual in-service bridge revealed the relationship between the bridge deformations that leads to the stress concentration and the positions of traveling vehicles.

Fibre Bragg Grating-Based Cascaded Acoustic Sensors for Potential Marine Structural Condition Monitoring

This paper explores the potential of using multiple fibre Bragg grating-based sensors for acoustic emission (AE) detection, thus offering an effective alternative to conventional piezoelectric (PZT) sensors, especially where they have shown limitations in use, such as in the marine sector. A cascaded fibre optic acoustic sensor system, using optical filter signal demodulation has been developed and its performance extensively evaluated. To undertake this under standardized conditions, the optical sensor system was evaluated using a glass plate to detect the acoustic signal, followed by an evaluation using a metal plate to identify the location of acoustic sources, when subjected to sonotrode excitation, mimicking acoustic detection in cavitation detection. Under these circumstances, very good agreement has been reached between the outputs of the optical acoustic sensors and of the colocated PZT acoustic sensors. This work confirms the utility of these sensors—they can detect not only weak AE signals, but also enable multipoint simultaneous measurement, showing their potential for condition monitoring applications, especially in the marine sector.

Investigation of End-Milling Process Based on Monitoring Method with Wireless Telegraphic Multifunctional Tool Holder and Infrared Thermography

Infrared thermographic technology has attracted the attention of various industrial fields. We therefore focus on it as a novel tool temperature monitoring method to improve the end-milling conditions of difficult-to-cut materials. However, it is difficult to measure tool temperature under coolant conditions because coolant prevents the monitoring of end-mill tool surfaces. Thus, we developed a novel temperature monitoring method by applying a pore electric discharge machining process to place a thermocouple sensor in the end-mill tool and by using a wireless telegraphic multifunctional tool holder to directly measure the internal temperature of the end-mill tool under rotation. We evaluated internal temperature distribution under various end-milling conditions on the basis of multipoint simultaneous measurements and discussed the influence of forced convection heat transfer on the internal temperature of the tool under various rotating conditions. In addition, we used a finite element method to analyze unsteady heat conduction on the basis of temperature measurement by high-speed video infrared thermography and compared the results with those of the wireless telegraphic multifunctional tool holder to demonstrate its validity and usefulness.

Experimental investigation of open sea atmospheric optical turbulence

In this article, a high-quality fiber optical turbulence sensing array is arranged on the ocean-going instrumentation ship-Yuan Wang for 37 day continuous measurement. It is the first time that the spatial multipoint simultaneous measurement of maritime atmospheric optical turbulence has been realized. According to the measurement, the essential characteristics and quantitative data of the atmospheric optical turbulence on the open sea are obtained. Then the Greenwood spatial correlation function model is used for evaluating the outer scale of optical turbulence by a nonlinear fitting algorithm. Finally, the optical turbulence spectrum is divided into two sections, and the power spectrum scaling exponent is given by a section algorithm. Results show that the intensity of maritime atmospheric optical turbulence is a little smaller than that in the near ground layer and has no obvious diurnal variation characteristic. The value of outer scale is small and in a range of 0.2-0.3 m. It is easily found that the probability that the turbulence spectrum scaling exponent conforms to -5/3 is about 25% near the surface of open sea, which is smaller than that in the near ground layer.

Device Fabrication for Creating Multiscale Miniature Neuronal Networks and Spatiotemporal Pattern Analysis of Spontaneous Electrical Activities

SUMMARYTo investigate the dynamics of neuronal networks, a device which is capable of multipoint simultaneous measurement and multiscale miniature neuronal network construction was fabricated. The results of culturing rat embryo hippocampal neurons showed that the device is biocompatible and can be successfully used in long‐term culture. Analysis of the electrical data obtained with the device suggested that, in miniature neuronal networks consisting of about 2000 neurons, there occurred spatiotemporal activity patterns of neurons, which were considered to be very important to the process of storing and transforming information of a brain.

Characteristics of Two-Dimensional Turbulent Jet in Flapping Motion

The characteristics of a two-dimensional turbulent jet in the flapping motion are investigated by simultaneously measuring the velocity and pressure. The simultaneous measurements are performed by using a combined probe that consists of an X-type hot-wire probe and a static pressure tube. The measurement data are analyzed by using a conditional sampling technique and the ensemble-averaging technique, on the basis of an intermittency function. This function is used to determine whether the jet is in the flapping motion or not. The measurement results of two hot-wire probes set in the self-preserving region of the jet are analyzed by performing a wavelet transform. The experimental results show that the ensemble-averaged velocity field during the flapping motion shows a good agreement with the measurement result obtained by Sakai, et al. (2006) through multi-point simultaneous measurement of velocity. Further, the ensemble-averaged static pressure field during the flapping motion indicates the pressure of a vortex coherent structure, interpreted as a combination of flapping and puffing motions in the self-preserving region of the jet. In addition, the estimation of the turbulent energy budget shows that the turbulent energy production and its transportation from the inner region to the outer region of the jet by the diffusion are enhanced during the flapping motion. In particular, this enhancement of the turbulent energy transportation is caused by the combination of the increasing of the turbulent diffusion to the outer region of the jet and the decreasing of the pressure diffusion to the inner region of the jet.

Spatio-temporal turbulent structures of thermal boundary layer subjected to non-equilibrium adverse pressure gradient

We have experimentally investigated a non-equilibrium turbulent boundary layer subjected to an adverse pressure gradient developing on a uniformly heated flat wall. The spatio-temporal structures educed from a multi-point simultaneous measurement are reasonably interpolated based on the “proper orthogonal decomposition (POD)”. In the near-wall region, elongated hot regions stay dull and less active, whereas, large-scale cold regions having strong energy frequently intrude into the near-wall region. The energy-containing events in the near-wall region are discussed based on the results of wavelet analysis.

Spatial Structure of Internal Gravity Waves and Occurrence of Counter-Gradient Heat Flux

The spatial structure of internal gravity waves and counter-gradient heat flux were investigated in a strongly stably-stratified mixing layer. Multi-point simultaneous measurement was made on its temperature and velocity fields by a rake of 7 cold-and hot-wire system. Streamwise change in temperature spectrum showed that the internal gravity waves developed in the mixing layer and suddenly collapsed in the downstream region. Vertical correlation between the temperature fluctuations became stronger as the internal gravity waves grew downstream. Coherence and phase difference between the temperature fluctuations showed that the collapse of the grownup internal gravity waves started from around the wave front. Nonlinear interaction between the resonant components and their higher harmonics generated negative heat flux by converting large potential energy contained in the waves to turbulent kinetic energy in the turbulence producing process.

On the Development of Coherent Structure in a Plane Jet: Part 4, The Multipoint Simultaneous Measurement of Two-Component Velocities and the Simple Coherent Structure Model

To clarify the large-scale coherent structure in a turbulent plane jet, the simultaneous measurement of the main streamwise and the cross-streamwise velocity at 9 points in the self-preserving region of a turbulent plane jet has been performed using an array of X-type hot-wire probes. From the time variation of the main streamwise fluctuating velocity field, it is found that there exists a pair of fluid lumps with the positive and negative fluctuating velocity on opposite sides of the jet centerline. On the other hand, the instantaneous cross-streamwise fluctuating velocity shows the same sign over the cross section; i.e., a vertically striped pattern is formed. On the basis of the result of the Karhunen-Loève (KL) expansion, a new interpretation of the coherent structure model in the self-preserving region of a turbulent plane jet has been given from the combination of “flapping” and “puffing”.

An Experimental Study on the Development of Coherent Structure in a Plane Jet (3rd Report, Multi-point Simultaneous Measurement of Main Streamwise Velocity and the Reconstruction of Velocity Field by the KL Expansion)

An Experimental Study on the Development of Coherent Structure in a Plane Jet (3rd Report, Multi-point Simultaneous Measurement of Main Streamwise Velocity and the Reconstruction of Velocity Field by the KL Expansion)

An Experimental Study on the Development of Coherent Structure in a Plane Jet (4th Report, Multi-point Simultaneous Measurement of Two Velocity Components and the Large-scale Structure Model by the KL Expansion)

In order to clarify the large-scale coherent structure in a turbulent plane jet, the simultaneous measurement of the main streamwise and the cross-streamwise velocity at 9 points in the self-preserving region of a turbulent plane jet has been preformed by an array of X-type hot wire probes. From the time variation of the main streamwise fluctuating velocity field, it is found that there exist a pair of fluid lumps with the positive and negative fluctuating velocity on opposite sides of the jet centerline. On the other hand, the instantaneous cross-streamwise fluctuating velocity shows the same sign over the cross-section, i.e., the vertically-striped pattern is formed. As the result of the KL expansion, it is found hat the first u and v modes present a character of the “flapping”, and the second and third modes show the one of the “puffing”. From the combination of the “flapping” and the “puffing”, a new coherent structure model in the self-preserving region of a turbulent plane jet has been developed.

807 2次元噴流の速度2成分多点同時測定による構造抽出と変動静圧場の特性に関する研究(OS2-2,OS2 乱流・混相流・超臨界流動現象の実験とシミュレーション,学術講演)

807 2次元噴流の速度2成分多点同時測定による構造抽出と変動静圧場の特性に関する研究(OS2-2,OS2 乱流・混相流・超臨界流動現象の実験とシミュレーション,学術講演)

1206 2 次元乱流噴流速度場の多点同時計測と時空間構造解析

1206 2 次元乱流噴流速度場の多点同時計測と時空間構造解析

Effects of adverse pressure gradient on quasi-coherent structures in turbulent boundary layer

Statistical and kinematic characteristics of turbulent boundary layer flows subjected to adverse pressure gradients are found to differ significantly from those of zero-pressure-gradient ordinary boundary layers. The turbulent energy and shear stress transport vu2 and vuv occurs in the direction toward the wall from the regions away from the wall, as the pressure gradient parameter P+ increases. This event is completely opposite to that in zero-pressure-gradient cases. The instantaneous waveforms of third-order moments are markedly altered in the near-wall region. The quadrant splitting and trajectory analyses reveal that obvious changes do occur in large-amplitude sweep motions (Q4) and outward interactions (Q1). On the other hand, the contributions from other coherent motions, especially the ejection motions (Q2), significantly decrease and their durations become longer, i.e., these motions are dull and less active. Moreover, multi-point simultaneous measurements with five X-probes are made to depict the kinematic pictures of the effects of the adverse pressure gradient on the eddy structures.

Quasi-Coherent Structures in Adverse-Pressure-Gradient Turbulent Boundary Layer.

Statistical characteristics of turbulent boundary layer flows subjected to adverse pressure gradients are known to differ significantly from those of zero-pressure -gradient ordinary boundary layers. In this study, the dynamical characteristics of the quasi-coherent structures in adverse pressure gradient flow are investigated experimetally. As the pressure gradient paramenter P+ increases, the turbulent energy and shear stress transport <νu2> - and <υuυ> -, in the direction toward the wall from the region away from the wall, become significant in contrast to those in zero-pressure-gradient cases. The quadrant splitting and trajectory analyses reveal the obvious changes do occur in large-amplitude sweep motions(Q4)and outward interactions(Q1). On the other hand, the contribution from other coherent motions, especially the ejection motions(Q2), significantly decrease and their durations become longer, i.e., these motions are dull and less active. Moreover, multi-point simultaneous measurements with five X-probes are made to depict the kinematic pictures of the effects of the adverse pressure gradient on the eddy structures.

Reconstruction of a quasi-instantaneous image of coherent structures from hotwire signals obtained by a multi-point simultaneous measurement system

The turbulent velocity components (u, v) at 11 points in a reciprocating oscillatory turbulent flow have been measured simultaneously by a set of eleven X-type hotwire probes located in a plane perpendicular to the mean flow. Using a conditional sampling technique and a new method of data analysis for the inverse estimation of flow fields called the "virtual plate/load and MASCON model", a quasi-instantaneous three-dimensional image of coherent structures of turbulence was first reconstructed directly from the experimental velocity data. The quasi-instantaneous image was expressed in terms of the velocity components u, v, w and the vorticity components ωx ωy, ωz and we found that the large-scale coherent structure was composed of a pair of counter-rotating fluid motions with asymmetry which was quite different from that of the ensemble-averaged one. Flow patterns induced by the large-scale structure have been clarified by perspective representations visualized by computer simulations that produce timelines and streaklines of fluid particle traces. Results showed that the new experimental method was applicable for investigating the three-dimensional feature of coherent structures including asymmetry.

An experimental investigation of vortex motions near surfaces

Laminar vortex rings approaching a solid planar surface and a free surface have been investigated experimentally over the range of Reynolds numbers based on the circulation, ReΓ, from 900 to 2350. The emphasis is on the process of vortex stretching, induction of boundary layer on the surface, formation of secondary vortices, and rebounding of the primary vortex ring. Detailed measurements were made using laser-induced photochemical anemometry (LIPA), a nonintrusive visualization technique which enables multipoint simultaneous measurement of the unsteady velocity field. Results show that enstrophy, rather than circulation, clearly signifies three stages of the behavior of the primary vortex ring—free-traveling stage, vortex stretching stage, and vortex rebounding stage. Although the flow phenomena are very similar when a vortex ring approaches a solid surface or a slightly contaminated free surface, the difference between the induced boundary layers under two surface conditions is obvious in terms of the circulation and the enstrophy. In addition, the surface deformation and subsequent surface waves resulting from the impacting vortex ring on the contaminated free surface are also discussed. The present study provides a basis for validation and comparison with numerical simulations.