A CLOSED SYSTEM OF EQUATIONS FOR DENSE TWO-PHASE FLOW AND EXPRESSIONS OF SHEARING STRESS OF DISPERSED PHA’E AT A WALL

Inthis paper, each of the two phases in dense two-phase flow is considered as continuous medium and the fundamental equations for two-phase flow arc described in Eulerian form. The generalized constitutive relation of the Bingham fluid is applied to the dispersed phase with the analysis oj physical mechanism of dense two-phase flow. The shearing stress of dispersed phase at a wall is used to give a boundary condition. Then a mathematical model for dense two-phase flow is obtained. In addition, the expressions of shearing stress of dispersed phase at a wall is derived according to the fundamental model of the friclional collision between dispersed-plutse particles and the wall.

Qianshi Hutong Once a Wall Street,Now a Narrow Haven

QIANSHI Hutong is located near the Dashilan’er commercial street,just on the west side of Zhubaoshi Street.With its narrowest point preserved at 40 cm,it is the most constricted alley in Beijing’s city limits.It was,once upon a time,China’s Wall Street. "Qianshi" literally means "money market." The hutong’s history can be traced back to the Qing Dynasty(1644-1911), when it was Beijing’s official area for currency trading.Home to 26 governmentauthorized mints that produced coins for all the city’s banks,large business firms,

Physical Modeling and Parametric Study on Two-Degree-of-Freedom VIV of A Cylinder near Rigid Wall

Unlike most previous studies on the transverse vortex-induced vibration（VlV） of a cylinder mainly under the wallfree condition （Williamson ＆ Govardhan, 2004）, this paper experimentally investigates the vortex-induced vibration of a cylinder with two degrees of freedom near a rigid wall exposed to steady flow. The amplitude and frequency responses of the cylinder are discussed. The lee wake flow patterns of the cylinder undergoin^g VIV were visualized by employing the hydrogen bubble technique. The effects of the gap-to-diameter ratio （eo/D） and the mass ratio on the vibration amplitude and frequency are analyzed. Comparisons of VIV response of the cylinder are made between one degree （only transverse） and two degrees of freedom （streamwise and transverse） and those between the present study and previous ones. The experimental observation indicates that there are two types of streamwise vibration, i.e. the first streamwise vibration （FSV） with small amplitude and the second streamwise vibration （SSV） which coexists with transverse vibration. The vortex shedding pattern for the FSV is approximately syrmnetric and that for the SSV is ahernate. The first streamwise vibration tends to disappear with the decrease of eo/D. For the case of large gap-to-dianeter ratios （ e.g. eo/D = 0. 54 ～ 1.58）, the maximum amplitudes of the second streamwise vibration and transverse one increase with the increasing gap- to-diameter ratio. But for the case of small gap-to-diameter ratios （e. g. eo/D= 0. 16, 0.23）, the vibration amplitude of the cylinder increases slowly at the initial stage （i.e. at small reduced velocity Vr）, and across the maximum amplitude it decreases quickly at the last stage （i.e. at large Vr）. Within the range of the examined small mass ratio （m 〈 4）, both streamwise and transverse vibration amplitude of the cylinder decrease with the increase of mass ratio for the fixed value of Vr- The vibration range （ in terms of Vr） tends to widen with the decrease of the mass ratio. In the second streamwise vibration region, the vibration frequency of the cylinder with a small mass ratio （ e.g. mx = 1.44） undergoes a jump at a certain Vr＋ The maximum amplitudes of the transverse vibration for two-degree-of-freedom case is larger than that for one-degree-of-freedom case, but the transverse vibration frequency of the cylinder with two degrees of freedom is lower than that with one degree of freedom（transverse）.

An ultrasound simulation method for carotid arteries with a wall structure of three membranes

Ultrasound simulation for carotid arteries is helpful to the performance assessments of vessel wall detection and signal processing methods by using ultrasound techniques. An ul- trasound simulation method of carotid artery wall with a three-membrane structure is proposed in present study. According to the ultrasound speckle distributions varying with the shapes and densities of scatterer distributions, as well as the statistic results of the clinical images, the parameters of distributions, densities and intensities of scatterers for different kinds of tissues in the carotid artery phantoms are determined. Each region is acoustically characterized using FIELD II software to produce the radio frequency echo signals, from which ultrasound images are derived. The results based on 30 simulations show that the echo distributions of the intimae, mediae, adventitias and blood are consistent with the clinical ones. Moreover, compared with the results from the central frequency of 8 MHz, the mean measurements for thicknesses of the intima, media and adventitia membranes, as well as the lumen diameter from the simulation images based on 12 MHz are the same as the preset ones, and the maximum relative errors are the 4.01%, 1.25%, 0.04% and 0.15%, respectively. The simulation under this condition is more realistic.