Mixed FE-SP method for nonlinear structure-water interactions with freak waves

This paper develops a mixed finite element – smoothing particle method for violent water-structure interactions involving freak waves and separation between structure and water. The structure undergoes a large rigid motion of 6 DOF with a small elastic deformation, so that its elastic displacement relative to the rigid motion can be represented in a mode summation based on FE analysis. The water is assumed inviscid - incompressible and its motion governed by nonlinear N-S equation. On the coupling interface where no FS separation happens, the equilibrium and consistence conditions are required. The numerical iteration process is suggested to solve the nonlinear FSI equations, and validation examples are shown a good agreement with available experiment results

Effect of thermal cycling frequency on the durability of Yb-Gd-Y-based thermal barrier coatings

The effects of thermal cycling frequency and buffer layer on the crack generation and thermal fatigue behaviors of Yb–Gd–Y-stabilized zirconia (YGYZ)-based thermal barrier coatings (TBCs) were investigated through thermally graded mechanical fatigue (TGMF) test. TGMF tests with low- (period of 10 min) and high-frequency (period of 2 min) cycling were performed at 1100 °C with a 60 MPa tensile load. Different cycling frequencies in TGMF test generate two kinds of crack propagation modes. The sample with low-frequency cycling condition shows penetration cracks in the YGYZ top coat, and multiple narrow vertical cracks are generated in high-frequency cycling. To enhance the thermomechanical properties, different buffer layers were introduced into the TBC systems, which were deposited with the regular (RP) or high-purity 8 wt% yttria stabilized zirconia (HP-YSZ) feedstock. The purity of the feedstock powder used for preparing the buffer layer affected the fracture behavior, showing a better thermal durability for the TBCs with the HP-YSZ in both frequency test conditions. A finite element model is developed, which takes creep effect into account due to thermal cycling. The model shows the high stresses at the interfaces between different layers due to differential thermal expansion. The failure mechanisms of YGYZ-based TBCs in TGMF test are also proposed. The vertical cracks are preferentially created, and then the vertical and horizontal cracks will be propagated when the vertical cracks are impeded by pores and micro-cracks

Pulsars as candidates of LHAASO sources J2226+6057, J1908+0621 and J1825-1326

The LHAASO Collaboration has observed ultrahigh-energy photons up to $1.4$PeV from $12$ $\gamma$-ray Galactic sources. In particular, the $\gamma$-ray spectra of the sources J2226+6057, J1908+0621, J1825-1326 have been published. We investigate the possibility of suggested origin pulsars near the sources as the PeVatrons. The pulsar is described by a rotating magnetic dipole. Assuming protons are uniform distributed out of the light cylinders, we obtain the Lorentz distribution of proton energy spectrum. It is found that the protons around pulsar could be accelerated to PeV at short times. The hadronic $\gamma$-ray spectra of the suggested origin pulsars are in good agreement with the LHAASO observed $\gamma$-ray spectra of the sources J2226+6057, J1908+0621, J1825-1326.Comment: This paper has been accepcted by MNRA