Fractal characteristics of cracking solids are studied using acoustic emission (AE). The plastic zone size (PZS) for model I fracture has been further redefined according to fractal theory. The relationships between the stress ratio and dimensionless PZS with the fractal dimension are investigated. The results show that the increase in the fractal dimension, the dimensionless PZS constant, will substantially decrease the stress ratio. The semiempirical relationship between fractal AE count and the stress intensity factor (SIF) is studied. The results show that the fractal AE count varied with SIF in the same manner as the Paris law for crack propagation in fatigue. The exponent is a function of the fractal dimension D f . Results by proposed method are compared with the experimental results, and fairly good agreements are observed.
The Morison equation is widely used to estimate the loads by surface waves on cylinders. The formulation and coefficients determination method of the original work by Morison et al. are revisited, it is found that there exist some issues yet to be explained, e.g., the larger uncertainties in drag coefficient and the underestimated maximum moments. Numerical simulation with a similar configuration is used to reproduce these issues and the results help discover the reason and mechanism for these phenomena. The analysis shows that the larger uncertainties in drag coefficient are caused by the introduction of linear wave theory, which is used to derive the velocity and acceleration at cylinder location as direct measurements are not available. The results also show that the underestimation of maximum moments is induced by the wave run-up process, which is neglected in the Morison equation. The scale of wave run-up is approximately the length of cylinder diameter. The results indicate although most recent studies are focusing on the high-frequency loads on cylinders by nonlinear waves, there still exist some issues to be resolved in the linear wave regime. Further studies are required to parameterize the additional loads by wave run-up to strengthen the robustness of the Morison equation.
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