No abstract

In this paper, a coupled FHN model with two different delays is investigated. The local stability and the existence of Hopf bifurcation for the system are analyzed. The effect of two different delays on dynamical behavior is discussed. Simulation results are presented to support theoretical analysis. Finally, main conclusions are included.

No abstract

Dynamic responses of four rigidly-connected square cylinders in a square configuration subjected to two-dimensional steady flow of a constant property Newtonian fluid were investigated numerically. The focus of the present study is to investigate the effects of the angle of attack α on the dynamic responses by varying α from 0 • to 15 • in intervals of 2.5 • at a fixed L = 4 (L is the non-dimensional center-to-center distance between two adjacent square cylinders, normalized by the side length of the square cylinder B). For each α, the reduced velocity (Vr) ranges from 1 to 40. The Reynolds number Re, mass ratio m * and structural damping ratio ζ maintain constants of 180, 10 and 0, respectively. Numerical results show that the angle of attack α has a significant influence on the dynamic response. When α ≤ 5 • , galloping occurs in addition to vortex-induced vibration (VIV), while it weakens for α = 7.5 • and 10 • , and finally disappears as α = 12.5 • and 15 • , leaving only VIV response. The effects of L on the responses of the four-square-cylinder oscillating system were also examined for Re = 180, Vr = 40, and α = 2.5 •. Numerical results show that L affects not only the response displacement but also the vortex shedding mode. Galloping with large response amplitude can happen at either large L = 4 or small L = 1.5 and 2. The response amplitude is relatively small as 2.5 ≤ L ≤ 3.5 due to the influence of the flow in the gap between the square cylinders. For the particular case of L = 3.5, a combined vortex shedding mode is identified, where the vortex shedding from the top row square cylinders behaves as that from an elongated single body while the vortex shedding from the bottom row cylinders presents a co-shedding mode.

The boundary layer flow induced by surface waves has been extensively investigated due to its significance in engineering applications such as sediment transport and hydrodynamic forces on subsea structures. Several forms of defect functions (referred to as DF hereafter) were developed in the past decades, e.g. Sleath (1970, 1982), Nielsen (1985, 2016) and etc., due to their good efficiency in the description of the velocity distribution in one dimensional wave boundary layer (WBL). In this work, two forms of DFs are proposed: (i) DF-I describes the velocity distributions and bottom shear stresses in phase space with 4 model parameters; (ii) DF-II describes the maximum WBL profile with 3 model parameters. A number of datasets to support the validation of the DFs were obtained through experimental and numerical tests. Two sets of experiments were conducted individually in a free-surface-wave flume located in Dalian University of Technology and an oscillating-flow flume located in the University of Western Australia. For the free surface wave tests, the velocity was measured.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/RK-z0Q8rTjk