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291.
Internal Resonances for Heave, Roll and Pitch Modes of A Spar Platform Considering Wave and Vortex-Induced Loads in the Main Roll Resonance 总被引:1,自引:0,他引:1
We present a study of the nonlinear coupling internal resonance for the heave roll and pitch performance of a spar platform under the wave and vortex-induced loads when the ratio of the frequencies of heave, roll and pitch are approximately 2:1:1. In consideration of varying wet surface, the three DOFs nonlinear coupled equations are established for the spar platform under the effect of the first-order wave loads in the heave and pitch, and vortex-induced loads in the roll. By utilizing the method of multi-scales when the vortex-induced frequency is close to the natural roll frequency, the first-order perturbation solution is obtained analytically and further validated by the numerical integration. Sensitivity analysis is performed to understand the influence of the damping and the internal detuning parameter. Two cases with internal resonance are shown. The first case is that no saturation phenomenon exists under small vortex-induced loads. The first order perturbation solution illustrates that only the vortex-induced frequency motion in roll and the super-harmonic frequency motion in heave are excited. The second case is that the vortex-induced loads are large enough to excite the pitch and a saturation phenomenon in the heave mode follows. The results show that there is no steady response occurrence for some cases. For these cases chaos occurs and large amplitudes response can be induced by the vortex-induced excitation. 相似文献
292.
证明了流体力学边界层理论中著名的Blasius方程的一个新性质,它在二维平板流的研究中具有重要的作用,由此建立它的积分形式,并给出方程中的临界值βc的分析估计。 相似文献
293.
During the last decade, a number of models have been developed to consider the conflict in dynamic reservoir operation. Most of these models are discrete dynamic models which are developed based on game theory. In this study, a continuous model of dynamic game and its corresponding solutions are developed for reservoir operation. Two solution methods are used to solve the model of continuous dynamic game, namely the Ricatti equations and collocation methods. The Ricatti equations method is a closed form solution, requiring less computational efforts compared with discrete models. The collocation solution method applies Newton's method or a quasi-Newton method to find the problem solution. These approaches are able to generate operating policies for dynamic reservoir operation. The Zayandeh-Rud river basin in central Iran is used as a case study and the results are compared with alternative water allocation models. The results show that the proposed solution methods are quite capable of providing appropriate reservoir operating policies, while requiring rather short computational times due to continuous formulation of state and decision variables. Reliability indices are used to compare the overall performance of the proposed models. Based on the results from this study, the collocation method leads to improved values of the reliability indices for total reservoir system and utility satisfaction of water users, compared to the Ricatti equations method. This is attributed to the flexible structure of the collocation model. When compared to alternative water allocation models, lower values of reliability indices are achieved by the collocation method. 相似文献
294.
A two-dimensional lattice Boltzmann model (LBM) is presented for transient shallow water flows. The model is based on the shallow water equations coupled with the large eddy simulation model. In order to obtain accurate results efficiently, a multi-block lattice scheme is applied at the area where a local finer grid is needed for strong change in physical variables. The model is verified by applying to five cases with transient processes: (a) a tidal wave over steps; (b) a perturbation over a submerged hump; (c) partial dam break flow; (d) circular dam break flow; (e) interaction between a dam break surge and four square cylinders. The objectives of this study are to validate the two-dimensional LBM in transient flow simulation and provide the detailed transient processes in shallow water flows. 相似文献
295.
296.
297.
Ground-motion prediction equations for the intermediate depth Vrancea (Romania) earthquakes 总被引:2,自引:1,他引:1
Vladimir Sokolov Klaus-Peter Bonjer Friedemann Wenzel Bogdan Grecu Mircea Radulian 《Bulletin of Earthquake Engineering》2008,6(3):367-388
We present the regional ground-motion prediction equations for peak ground acceleration (PGA), peak ground velocity (PGV),
pseudo-spectral acceleration (PSA), and seismic intensity (MSK scale) for the Vrancea intermediate depth earthquakes (SE-Carpathians)
and territory of Romania. The prediction equations were constructed using the stochastic technique on the basis of the regional
Fourier amplitude spectrum (FAS) source scaling and attenuation models and the generalised site amplification functions. Values
of considered ground motion parameters are given as the functions of earthquake magnitude, depth and epicentral distance.
The developed ground-motion models were tested and calibrated using the available data from the large Vrancea earthquakes.
We suggest to use the presented equations for the rapid estimation of seismic effect after strong earthquakes (Shakemap generation)
and seismic hazard assessment, both deterministic and probabilistic approaches. 相似文献
298.
双相各向异性介质中偶数阶精度有限差分数值模拟 总被引:1,自引:1,他引:0
To improve the accuracy of the conventional finite-difference method, finitedifference numerical modeling methods of any even-order accuracy are recommended. We introduce any even-order accuracy difference schemes of any-order derivatives derived from Taylor series expansion. Then, a finite-difference numerical modeling method with any evenorder accuracy is utilized to simulate seismic wave propagation in two-phase anisotropic media. Results indicate that modeling accuracy improves with the increase of difference accuracy order number. It is essential to find the optimal order number, grid size, and time step to balance modeling precision and computational complexity. Four kinds of waves, static mode in the source point, SV wave cusps, reflection and transmission waves are observed in two-phase anisotropic media through modeling. 相似文献
299.
We have developed a least-squares minimization approach to determine the depth and the amplitude coefficient of a buried structure
from residual gravity anomaly profile. This approach is basically based on application of Werner deconvolution method to gravity
formulas due to spheres and cylinders, and solving a set of algebraic linear equations to estimate the two-model parameters.
The validity of this new method is demonstrated through studying and analyzing two synthetic gravity anomalies, using simulated
data generated from a known model with different random error components and a known statistical distribution. After being
theoretically proven, this approach was applied on two real field gravity anomalies from Cuba and Sweden. The agreement between
the results obtained by the proposed method and those obtained by other interpretation methods is good and comparable. Moreover,
the depth obtained by the proposed approach is found to be in very good agreement with that obtained from drilling information. 相似文献
300.
A weighted surface-depth gradient method for the numerical integration of the 2D shallow water equations with topography 总被引:1,自引:0,他引:1
A finite volume MUSCL scheme for the numerical integration of 2D shallow water equations is presented. In the framework of the SLIC scheme, the proposed weighted surface-depth gradient method (WSDGM) computes intercell water depths through a weighted average of DGM and SGM reconstructions, in which the weight function depends on the local Froude number. This combination makes the scheme capable of performing a robust tracking of wet/dry fronts and, together with an unsplit centered discretization of the bed slope source term, of maintaining the static condition on non-flat topographies (C-property). A correction of the numerical fluxes in the computational cells with water depth smaller than a fixed tolerance enables a drastic reduction of the mass error in the presence of wetting and drying fronts. The effectiveness and robustness of the proposed scheme are assessed by comparing numerical results with analytical and reference solutions of a set of test cases. Moreover, to show the capability of the numerical model on field-scale applications, the results of a dam-break scenario are presented. 相似文献