Research on wind buffeting noise characteristics of a vehicle based on ILRN and DES-ILRN methods

In view of the unsatisfactory calculation accuracy of common turbulence models, two improved models, called improved low-Reynolds number (ILRN) k− ε and Detached EddySimulation (DES)-ILRN are proposed. Basing on the low-Reynolds number (LRN k− ε) turbulence model in this paper, revised concepts include the introduction of turbulence time scale, eddy viscosity coefficient limitation concept and separation perception model. Otherwise, the DES model is improved by introducing the ILRN model. The accuracy of the two models is validated through wind tunnel test. Then, the wind buffeting noise from rear windows is received by ILRN and DES-ILRN turbulence models, and the obtained results are compared with the road test. The accuracy of ILRN and DES-ILRN turbulence models in calculating wind buffeting noise of a real vehicle is validated by experiment. ILRN and DES-ILRN models are applied to research the wind buffeting noise, and good calculation results are obtained. They are promising methods to solve wind buffeting noise problems.

Seasonal variation of the main tidal constituents in the Bohai Bay

The seasonal variability of the M2 tidal amplitude has been observed widely, especially in the coastal regions, but the seasonal variations in several major tidal constituents have not been investigated sufficiently. In this study, the seasonal variations in the major tidal constituents, including M2, S2, K1, and O1, in the Bohai Bay, China, are studied by analysing one-year observations of the sea level at two stations, E1 and E2. At E2, the frequencies of the M2 tidal amplitude and phase are annual, with large values in summer and small values in winter, while the frequencies of the S2 and K1 tidal amplitudes are semi-annual. Furthermore, the O1 tidal amplitude increases constantly from winter to autumn. The maxima of the phases appear twice in one year for the S2, K1, and O1 tides, which take place nearly in winter and summer. The seasonally varying trends at E1 estimated by the enhanced harmonic analysis are similar to those at E2, except for the O1 tidal amplitude. The results of the numerical experiments indicate that the seasonality of the stratification and the corresponding vertical eddy viscosity coefficient induce seasonal variations in the phases and amplitudes for all the major tidal constituents, respectively.

Inversion Study of Vertical Eddy Viscosity Coefficient Based on an Internal Tidal Model with the Adjoint Method

Based on an isopycnic-coordinate internal tidal model with the adjoint method, the inversion of spatially varying vertical eddy viscosity coefficient (VEVC) is studied in two groups of numerical experiments. In Group One, the influences of independent point schemes (IPSs) exerting on parameter inversion are discussed. Results demonstrate that the VEVCs can be inverted successfully with IPSs and the model has the best performance with the optimal IPSs. Using the optimal IPSs obtained in Group One, the inversions of VEVCs on two different Gaussian bottom topographies are carried out in Group Two. In addition, performances of two optimization methods of which one is the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) method and the other is a simplified gradient descent method (GDM-S) are also investigated. Results of the experiments indicate that this adjoint model is capable to invert the VEVC with spatially distribution, no matter which optimization method is taken. The L-BFGS method has a better performance in terms of the convergence rate and the inversion results. In general, the L-BFGS method is a more effective and efficient optimization method than the GDM-S.