[en] In order to predict more accurately the critical flow of fluidelastic instability, the motion equation of a cantilevered tube is established utilizing quasi-static fluid force coefficients of two-phase flow. After Galerkin discretization of the analytical model, the critical flow velocity of each void fraction is obtained by solving the characteristic equations. Moreover the response of cantilevered tube is solved using Runge-Kutta algorithm. Numerical results show that the critical velocity of instability increases with the increasing of the void fraction, and the numerical results agree with experimental results, which proving the analytical model utilizing quasi-static fluid force coefficients of two-phase flow is available for predicting the critical velocity of fluidelastic instability. (authors)

[en] Fluidelastic instability causes the large amplitude of the heat transfer tube, which results in its wear out. It is the key mechanism of the fluid-induced vibration of the team generator tube bundles subject to two-phase flow. In order to predict more accurately the critical flow of instability, the motion equation of single tube is firstly established utilizing the unsteady fluid force coefficients of two-phase flow which obtained by fitting experimental result data. After the nondimensionalize and Galerkin discretization of the analytical model, the critical flow velocity of each void fraction is calculated by solving the system of equations. Numerical results show that the numerical critical fluid force of instability agrees well with experimental results, which proving that the analytical model utilizing fitting parameters of unsteady fluid force of two-phase flow is available for the predicting of the critical velocity of instability. (authors)

[en] Highlights: • Streamwise FEI experiments were conducted on rotated triangular tube array. • One type of streamwise FEI called coupling instability is proposed. • The damping ratio of streamwise direction is greater than that of transverse direction. - Abstract: Streamwise fluidelastic instability of rotated triangular tube array subjected to air-water cross-flow is investigated in this paper. Critical velocity of fluidelastic instability was measured only from 0% to 30% void fraction because the tube bundles were destroyed at 30% void fraction. One type of streamwise fluidelastic instability called coupling instability was observed. As further study, damping ratio of two-phase and hydrodynamic mass of tube bundle both in transverse and streamwise directions were measured from 0% to 80% void fraction. The results suggest that, tube will destroy first in the direction with small stiffness if coupling instability occurs. The damping ratio in streamwise direction is greater than that of transverse direction at the same void fraction. With increasing of void fraction, the damping ratio increases first and then decreases. Fluidelastic instability constant K in transverse direction is 5.3, and the K in streamwise direction is 17.6 below 30% void fraction.

[en] In Nuclear physics, gamma detection techniques are the most common ones being used for spectroscopy. Scintillation detectors find their applications in a large number of fields. The most commonly used and famous scintillation detector was NaI(Tl) that has been in use since the last 50 years. Recently, several new detectors have also been introduced commercially and they include lanthanum-based detectors. This study focuses on the response function simulation of the LaBr3(Ce) detector crystal. This is accomplished by developing a model that calculates various key properties for the detector crystal. This is done by using the Monte Carlo N-Particle (MCNP) transport code. A complete model for the detector is developed to simulate the lab setup. The simulation is then used to obtain the energy distribution of pluses that are created in the detector. Several gamma sources are used to obtain the pulse height spectra to calculate our properties of interest. The effect of distance on the spectra is also simulated. For Cs137 (662KeV), the energy resolution comes out to be 3.447% and FWHM is 22.12 KeV. An increase in the incident gamma energy results in increased FWHM whereas energy resolution and detection efficiency show a decreasing trend. After simulations, the crystal was also studied experimentally. In this case, both the simulation and experimental coincided. This proves the validity of the model developed. (paper)