The dynamics of cross-flow tubes were studied in consideration of initial axial load and distributed impacting constraints, modeled as cubic and trilinear spring constraints. The tubes were modeled as Euler–Bernoulli beams and supported at both ends, including the simply supported tube and clamped-clamped tube. The analytical model involves a time-delayed displacement term induced by the cross flow based on the quasi-steady theory. For simplicity, a single flexible supported beam in a rigid square array of cylinders was studied by using the damping-controlled mechanism. The mean extension of the tube was considered, and thus, it added another nonlinear term in the equation of motion. Results show that the tube loses stability by buckling and fluttering at various initial pressure loads and cross-flow velocities. An increase was observed for critical velocities and initial pressure loads. Chaotic oscillations were observed for the trilinear spring model. The distribution of the impacting forces was also calculated. Some of the fresh results obtained in the impact system are expected to be helpful in understanding and controlling the dynamic responses of fluid-conveying pipes.
In this paper, a N-rich B–N polymorph named as B20N24 is proposed through first-principles calculations. The stability of the B20N24 polymorph at ambient conditions is confirmed using the phonon dispersion spectra and the Born stability criteria. Electronic properties calculations show that B20N24 exhibits a semiconducting feature, with a 0.87 eV direct band gap derived from HSE06 functions, which is much lower than many other B–N polymorphs. Specifically, owing to its cage-like framework, B20N24 may be used in hydrogen storage at a capacity of ~6.8 wt.%. The B20N24 polymorph enriches the B–N system theoretically, and this polymorph is promising for use in electronic devices and hydrogen storage.
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