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Phase-average technique based on wavelet multi-resolution analysis and continuous wavelet transform are used to reveal the phase-averaged features of square cylinder wake measured by high-speed PIV. The one-dimensional orthogonal wavelet analysis is first applied to decompose the measured velocity fields into large-, intermediate- and small-scale structures. Then the phase information referenced with large- and intermediate-scale flow structures are clearly identified based on Morlet wavelet transform. Finally, the data ensembles are phase-sorted to give phase-averaged representations of measured flow field. The instantaneous multi-scale structures suggest that large-scale vortices are weakened and begin to transfer into intermediate-vortices at the downstream of separation region. The intermediate-scale vortex observed at the upper boundary of shear layer is considered to be associated with the secondary vortex movement. The phase-averaged intermediate-scale structures tend to convey downstream along streamwise direction, with the rotation sense varying from the first half period to the last half period. The peaks of phase-averaged large-scale Reynolds stress tend to move back and forth in the near-wake region. These findings suggest that the proposed phase-average technique is effective in revealing multi-scale fluid dynamics of wake flow structures. [ABSTRACT FROM AUTHOR]

This study focuses on the multi-scale turbulent structures of triangle cylinder wake flow measured by high-speed particle image velocimetry (PIV). The measured turbulent structures were spatially extracted into large-, intermediate-, relatively small-, and small-scale components using two-dimensional orthogonal wavelet analysis. Then the features of multi-scale turbulent structures were analyzed in terms of two-point auto correlation, power spectra, turbulent kinetic energy and Reynolds shear stress. It is found that the large-scale structure attributed to coherent motions in the wake flow makes largest contribution to the total fluctuating energy and maximum Reynolds shear stress, accounting for 84% and 92% respectively. The intermediate scale structures, which are unidentifiable by PIV measurement, are found to shed into the separated shear layer due to Kelvin-Helmholtz instability, and the central frequency of intermediate scale vortex is approximately twice of Kármán vortex shedding frequency. Besides, two symmetric regions of intensive velocity fluctuations having relatively small-scale are observed near the cylinder surface and the boundary of separation region, and they are not dominant. [ABSTRACT FROM AUTHOR]

The three-dimensional (3D) turbulent structure was simulated by large eddy simulation (LES), and then the numerical result was validated by PIV experiment. In order to give a detailed description of dune wake flow, the instantaneous velocity, vorticity, and pressure were decomposed into the large-, intermediate- and relatively small-scale components by 3D wavelet multi-resolution technique. To get a further understanding of coherent structure, the decomposed wavelet components were employed to calculate Q-criterion. It was found that the rollers and horse-shoe structures in the separation bubble were mainly contributed from large-scale structures and it made the most significance to the vorticity concentration. The observations of intermediate-scale horse-shoe structures indicated that the coherent structure was the combined effect of large- and intermediate-scale structures. Besides, from the visualization of 3D streamlines and pressure iso-surfaces, the separation bubble and pressure distribution are found to be dominated by large-scale structure. [ABSTRACT FROM AUTHOR]

Dynamic characteristic of ball screw feed system in a milling machine is studied numerically in this work. In order to avoid the difficulty in determining the stiffness of rolling joints theoretically, a dynamic modeling method for analyzing the feed system is discussed, and a stiffness calculation method of the rolling joints is proposed based on the Hertz contact theory. Taking a 3-axis computer numerical control (CNC) milling machine set ermined as a research object, the stiffness of its fixed joint between the column and the body together with the stiffness parameters of the rolling joints is evaluated according to the Takashi Yoshimura method. Then, a finite element (FE) model is established for the machine tool. The correctness of the FE model and the stiffness calculation method of the rolling joints are validated by theoretical and experimental modal analysis results of the machine tool’s workbench. Under the two modeling methods of joints incorporating the stiffness parameters and rigid connection, a theoretical modal analysis is conducted for the CNC milling machine. The natural frequencies and modal shapes reveal that the joints’ dynamic characteristic has an important influence on the dynamic performance of a whole machine tool, especially for the case with natural frequency and higher modes. [ABSTRACT FROM AUTHOR]

Wavelet multiresolution analysis has been applied to digital images of ethanol sprays injected into air at atmospheric pressure and at room temperature. The imaging was performed with laser-sheet imaging using the 308 nm light from a XeCl excimer laser. Image capturing was performed with a CCD camera. The importance of different scales in the turbulent structure of the sprays was easily recognized using wavelet multiresolution analysis. It was observed that the intermediate and small scale levels contained information of such important phenomena as the spray break-up. This was not easily recognized in the original images, due to averaging over all scales. [ABSTRACT FROM AUTHOR]

The flow feature of the jet issuing from the circular pipe with the rotating inclined section has been investigated by the methods of flow visualization and image processing. It has been found that the jet diffusion is affected by the inclined angle and the rotating speed. The coherent structure of the jet has also been studied by using wavelet multiresolution analysis. The multiscale turbulent structures were visualized and the core and edge of the vortex were identified at different broad scales. [ABSTRACT FROM AUTHOR]

This paper describes an application of the wavelet transform in in-line solder paste inspection. In the development of a three-dimensional (3D) automatic inspection device of solder paste, it is necessary to detect the characteristic positions in images. In this paper, on the basis of the property of local wavelet transform modulus maximum (WTMM) and the deference filter, a practical algorithm is proposed for the detection of the characteristic positions. The proposed algorithm is applied to more than 20 actual images obtained from the 3D automatic inspection device. The detected errors are smaller than the maximum permissible error of 5 pixels. Also, the proposed algorithm is verified in-line. The experimental results show that the quality of solder paste can be successfully judged in-line. The proposed algorithm is superior to other possible techniques reported so far because of its implementation in assembly lines. [ABSTRACT FROM AUTHOR]

The opening of a gated community to expand the micro-road network in an urban traffic system is an importance research topic related to urban congestion. To satisfy the demands of opening an early choosing case, this paper proposes a comprehensive selection framework on qualified communities and their appropriate opening times by describing the traffic state at the boundary road network accurately. The traffic entropy model and fuzzy c-means (FCM) method are used in this paper. In the framework, a new opening evaluation entropy model is built using basic theory of the thermodynamic traffic entropy method. The traffic state entropy values of the boundary road network and entropy production are calculated to determinate the opening time. In addition, a specific fuzzy range evaluation standard at a preset gated community is drawn with an FCM algorithm to verify the opening determination. A case study based on the traffic information in a simulated gated community in Shanghai is evaluated and proves that the findings of opening evaluation are in accordance with the actual situation. It is found that the micro-inter-road network of a gated community should be opened as the entropy value reaches 2.5. As the travel time is less than 20 s, the correlation between the opening entropy value and the journey delay time exhibits a good linear correlation, which indicates smooth traffic flow. [ABSTRACT FROM AUTHOR]

Highlights • The three-dimensional dune wake are investigated by PIV. • The large-scale structure is responsible for the formation of separation region. • The intermediate-scale structure is more active near the separation region. • The intermediate-scale structure makes more contribution to Reynolds stresses. • The small-scale vortical structures decay quickly at the downstream. Abstract The three-dimensional wake structures behind a barchan dune model are investigated by the high-speed particle image velocimetry (PIV) at the Reynolds number of 5530. The measured velocity fields are first evaluated by time-averaged flow patterns and power spectra analysis. Then the one-dimensional orthogonal wavelet analysis is applied to reveal multi-scale turbulent structures and their corresponding second order statistics in the dune wake. The instantaneous multi-scale structures suggest that the large-scale structure is responsible for the formation of separation region. The intermediate-scale structure tends to be more active at the boundary of separation region, which may be due to the secondary vortex movement caused by the interactions between the wake and main flow. The appearance of small-scale vortices at the downstream of separation region indicates the breakdown process of large-scale vortices. The Reynolds stress and kinetic energy distribution suggest that the large-scale structures dominate the generation of turbulence in the dune wake. The lower kinetic energy contained in intermediate- and small- scale structures is considered to be related to smaller-scale interactions that reflect energy cascading phenomenon. The Reynolds shear stresses distributions suggest that the intermediate-scale structures also make significance in the separated boundary layer. As for small-scale structure, it is worthy to note that a region of high Reynolds shear stresses with an opposite sign is observed around the dune crest. The cross-correlation function of multi-scale structures suggest the quasi-periodicity of large-scale structure. The intermediate-scale structures also show a certain periodicity, however, such structures tend to be more unstable and the strength of them reduces as they travel downstream. When decreasing to small-scale, the vortical structures decays quickly at the downstream with larger convective velocity. This may indicate the breakdown process of large-scale vortices and the quick dissipation of small-scale vortices. [ABSTRACT FROM AUTHOR]

A preface for the 2006 issue of the "International Journal of Wavelets, Multiresolution and Information Processing" is presented.

• Front inclined hole is used for passive flow control of a wall-mounted cube wake. • Jet injected from hole suppress separation flow above free-end significantly. • Flow structures and statistic characteristics in near-wake are influenced. • Wake vortical shedding becomes more regular and is accelerated near the free-end. • POD analysis indicates that alternating spanwise vortices are suppressed. To control the wake flow around a wall-mounted cube, passive control is performed by drilling a front inclined hole (FIH) from the front surface to the free end of the cube. To study the control features and mechanism, controlled and uncontrolled cubes are experimentally investigated. A circulation water tunnel is used to perform PIV measurements, where the Reynolds number is Re D = 11550 based on the cube side length of D = 70 mm, and the thickness of the boundary layer on the tunnel bottom is δ/D = 0.25. To study the effect of the hole position, three FIHs with inlet heights of 20, 35, or 50 mm are investigated. The time-averaged flow fields show that the velocity of the FIH jet increases with the FIH inlet height. Comparing with the flow structures around standard cube, it is found that the reverse zone and shear layer above free-end are obviously suppressed due to the FIH jet. In addition, the scale of the reverse zone and arch-type vortex in the near-wake is reduced by the FIH jets. Because the FIH jets disrupt the development of wake vortices, the Reynolds shear stress and turbulent kinetic energy in the near-wake decrease. The control effect is most apparent for the cube with an FIH at a spanwise height of 50 mm (the FIH50 cube). In this case the effect of the free-end downwash flow on the wake is weaker, and the shedding frequency of the wake vortices near the free-end increases. Proper orthogonal decomposition analysis indicates that the FIH50 suppresses the alternately arranged flow features and enhances the symmetrically arranged features. [ABSTRACT FROM AUTHOR]