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Noise radiated by aeroacoustical oscillation of low Mach number flow past a two-dimensional cavity has been investigated analytically and numerically using electro-acoustical analogy and a hybrid scheme combining CFD with an implementation of the porous Ffowcs Williams-Hawkings equation. The noise generation mechanism is illustrated and the interaction between flow and cavity as well as key factors of resonant frequency is discussed. The 2D compressible unsteady Reynolds averaged Navier-Stokes equations (URANS) are solved to obtain near field acoustic source and unsteady characteristics of cavity flow. A buffer domain is exerted along all external boundaries to suppress boundary wave reflection. Computed tonal frequency and amplitude of pressure oscillations demonstrate good agreement with previous computational simulations and experiments. The influences of the length and shape of the neck and porous inserts on the noise radiated to the far field are also investigated. The 3D far field numerical results show that at a certain incoming flow velocity and shear layer thickness the frequency of the dominant oscillation increases with the length of the neck and the magnitude in the downstream far field is 8dB greater than that in the upstream far field. The increasing chamfer decreases the resonance frequency and changes the effective streamwise opening length resulting in significant differences in acoustic pressure fluctuation. The porous inserts on the floor of the cavity reduce the mass flow flux through the cavity neck and accordingly suppress the amplitude of dominant oscillation. The preliminary simulations reveal promising methods for sound radiation control.

The parametric-excitation vibration characteristics are investigated considering the tension-ring’s effect and mode coupling of riser. The Floquet theory is used to study the parametric stability of deep-water risers as the top boundary condition is pinned or moving with or without damping. The effect of frequency and the amplitude of heave motion on the riser vibration response are studied considering the effect of mode coupling.

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For flow noise simulations, the nonreflecting boundary condition (NRBC) is significant to confine the computational domain to a small domain. Lattice Boltzmann method (LBM) has advantages for noise because of its low dissipation, but is limited to the uniform grid. In this paper, an absorbing boundary condition (ABC) based on perfectly matched layer (PML) technique is introduced to LBM. Then PML stability is analyzed and a new strategy is developed to achieve robustness. Invoking the decoupling time integration, the underlying equation for streaming is solved with the nodal discontinuous Galerkin method. Benchmark acoustic problems were used to demonstrate the PML absorption. Moreover, PML parameters, long time behavior and inhomogeneous pseudo mean flow are discussed. The methodology appears to work very well and would be hoped for practical flow noise computation.

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The aeroacoustical oscillation and acoustic field generated by subsonic flow grazing over open cavities has been investigated analytically and numerically. The tone generation mechanism is elucidated with an analytical model based on the coupling between shear layer instabilities and acoustic feedback loop. The near field turbulent flow is obtained using two-dimensional Large Eddy Simulation (LES). A special mesh is used to absorb propagating disturbances and prevent spurious numerical reflections. Comparisons with available experimental data demonstrate good agreement in both the frequency and amplitude of the aeroacoustical oscillation. The physical phenomenon of the noise generated by the feedback loop is discussed. The correlation analysis of primitive variables is also made to clarify the characteristics of wave propagation in space and time. The effects of free-stream Mach number and boundary layer thickness on pressure fluctuations within the cavity and the nature of the noise radiated to the far field are examined in detail. As free-stream Mach number increases velocity fluctuations and mass flux into the cavity increase, but the resonant Strouhal numbers slightly decrease. Both the resonant Strouhal numbers and sound pressure levels decrease with the increase of boundary layer thickness. Results indicate that the instability of the shear layer dominates both the frequency and amplitude of the aeroacoustical oscillation.

Background: Robot-assisted laparoscopic radical prostatectomy ( RALRP) has better effects than conventional laparoscopic radical prostatectomy (LRP). However, there were few research focus on the incidence and risk factors of postoperative delirium for patients with different procedures. Methods: Eighty-one cases of RLRP patients (group RALRP) and 71 cases of LRP patients (group LRP) under general anesthesia were collected from anesthesia information system from June 2013 to December 2019. Comparison of the time of preparation period before surgery(Tp), time of operation(To), time of anesthesia maintenance (Ta), time of anesthesia recovery(time from cessation of intravenous anesthetic to endotracheal extubation, Tr), time of endotracheal extubation(time from endotracheal extubation to discharge from post-anesthesia care unit, Te), dosage of anesthetic (propofol, sufentanil, remifentanil), PaCO2, plasma lactate level and airway pressure at different points (before pneumoperitoneum, post-pneumoperitoneum, after loosening pneumoperitoneum), the incidences of postoperative delirium and utilization of mannitol, IAP, dosage of vasoactive agents(ephedrine, methoxamine and atropine), fluid infusion volume, blood transfusion volume, blood loss, postoperative hospitalization time (Th) and overall cost. Results: The incidences of postoperative delirium and utilization of mannitol in group RALRP and LRP were (17.3% VS 32.4%, P=0.03;7.4% VS 21.1%, P=0.014), Tr was (31.52±9.89 VS 38.65±16.32 min; P=0.01,95%CI 2.72-11.54), IAP was (12.72±1.87 VS 13.37±1.12 mmHg; P=0.01, 95%CI 0.16-1.14), PaCO2 at post-pneumoperitoneum and after loosening pneumoperitoneum were (47.89±10.89 VS 38.65±16.32 mmHg; P <0.001, 95%CI 6.47-11.98; 40.77±5.34 VS 43.57±4.54 mmHg; P=0.001, 95%CI 1.17-4.37), the difference was statistically significant. Tp, To, Ta and overall cost of patients in the RLRP group were significantly longer than those in the LRP group (P <0.02). No statistical difference was found in other observation variables. The incidence of postoperative delirium was considered as the dependent variable for binary logistic regression analysis. The result showed the incidence of postoperative delirium increased 1.17 times (95%CI 1.06-1.17), 1.13 times (95%CI 1.03-1.24), and 1.66 times (95%CI 1.02-2.70) for each unit increase in Tr, post-pneumoperitoneum PaCO2 and IAP.Conclusion: Compared with group LRP, patients in group RALRP had lower IAP, lower incidence of postoperative delirium and shorter recovery time, but the overall cost was higher. IAP is the main factor affecting the incidence of postoperative delirium.