Influence Of Velocity Fluctuations Research Articles

Dynamics modeling and stress response solution for liquid-filled pipe system considering both fluid velocity and pressure fluctuations

Dynamics modeling and stress response solution of the liquid-filled pipe system (LFPS) are necessary to predict the reliability of the pipe. However, the existing methods still need further research to solve the stress response of pipe system, and the influence of fluid velocity and pressure (FVAP) fluctuations on the vibration response is not considered. Based on this, a dynamics modeling method named FEM-TMM is proposed to solve the natural characteristics and stress response of the LFPS based on the combination of the finite element method (FEM) and transfer matrix method (TMM), which can consider the fluctuations of FVAP. The incompatible solid (Solid-NC) and virtual beam (VBeam) elements are constructed to establish the finite element models of the solid and fluid domains respectively, and the coupling elements are introduced to couple the solid and fluid domains. TMM is used to solve the FVAP fluctuations of the LFPS under external excitation, and the steady-state resonant frequency and vibration mode are obtained based on the iteration method. The virtual force iteration and stress smoothing methods are adopted to solve the stress response of the LFPS, then the dynamics modeling method FEM-TMM is obtained, and the rationality of the modeling method is verified by experiments. Finally, the analysis results show that the influence of velocity fluctuation on resonance frequency and stress response can be ignored. The critical pressures of resonant frequencies are less than or equal to those of resonant frequencies without considering pressure fluctuation. There are multiple stress barriers and valleys in the different-order stress responses of the LFPS, and the pressure fluctuation will change the distribution laws and maximum peak values of the stress barriers.

Influence of velocity fluctuations on the Kelvin‐Helmholtz instability and its associated mass transport

AbstractKelvin‐Helmholtz instability (KHI) and associated magnetic reconnection and diffusion processes provide plasma transport from solar wind into the magnetosphere. The efficiency of this transport depends on the magnetosheath and magnetospheric plasma and field properties at the vicinity of the magnetopause. Our recent statistical study using data from the Time History of Events and Macroscale Interactions during Substorms spacecraft indicates that the amplitude of the magnetosheath velocity fluctuations perpendicular to the magnetopause can be substantial. We have performed a series of local macroscale 2.5‐dimensional magnetohydrodynamic simulations of the KHI during strongly northward interplanetary magnetic field and with the initial plasma parameters typical to the dayside magnetopause by perturbing the initial equilibrium with time‐dependent perpendicular velocity field fluctuations. The effect of the single‐mode and multimode seed spectrums at different frequencies and amplitudes is studied. The plasma transport in Kelvin‐Helmholtz vortices is quantified. The results show that when large‐amplitude, low‐frequency seed velocity fluctuations exist in the magnetosheath, the resulting KH waves grow faster, get larger in size, and can transport more plasma through magnetic boundary, resulting in diffusion coefficient of the order 109 m2/s. The relevance of these findings to the solar wind‐magnetosphere coupling is discussed.

Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part I. Theoretical basis and simulations

A method for determination of single solute adsorption isotherms based on the analysis of the nonlinear frequency response (FR) of a chromatographic column is developed theoretically. In order to demonstrate this method, the FR of a chromatographic column is simulated for the periodical inlet concentration changes (sine waveform) around several steady-state concentrations. The frequency response functions (FRFs) up to the third order are calculated from the inlet and outlet concentration changes, which are analysed using the fast Fourier transform. Afterwards the coefficients of an adsorption isotherm are estimated from the low-frequency asymptotes of the FRFs and their derivatives. The obtained coefficients compare well with those used for simulations. Also discussed are some aspects that might affect the accuracy of the suggested method when it is applied to the analysis of experimental data, e.g. influence of velocity fluctuations, noise and size of the analysed data set.

Flutter of a plate-like member in horizontal fluctuating flow

Flutter derivatives of bridge deck sections are normally obtained under laminar flow conditions. The paper considers the theoretical stability of a thin plate in a fluctuating flow. The theory of stability of dynamic systems with periodic coefficients is applied to a derived equation of motion. Because of the assumptions made in the stability analysis, the procedure should only be viewed as a preliminary approach. The author gives details of proposed future research. Typical values are used in a worked example. The solution of a system of equations is shown to be stable where no eigenvalues are equal to one-half the fundamental frequency of the equation coefficients. The influence of velocity fluctuations upon the real part of the characteristic exponents corresponding to flow was found to be insignificant. (TRRL)