Extremely large-amplitude oscillation of soft pipes conveying fluid under gravity

In this work,the nonlinear behaviors of soft cantilevered pipes containing internal fluid flow are studied based on a geometrically exact model,with particular focus on the mechanism of large-amplitude oscillations of the pipe under gravity.Four key parameters,including the flow velocity,the mass ratio,the gravity parameter,and the inclination angle between the pipe length and the gravity direction,are considered to affect the static and dynamic behaviors of the soft pipe.The stability analyses show that,provided that the inclination angle is not equal to π,the soft pipe is stable at a low flow velocity and becomes unstable via flutter once the flow velocity is beyond a critical value.As the inclination angle is equal to π,the pipe experiences,in turn,buckling instability,regaining stability,and flutter instability with the increase in the flow velocity.Interestingly,the stability of the pipe can be either enhanced or weakened by varying the gravity parameter,mainly dependent on the value of the inclination angle.In the nonlinear dynamic analysis,it is demonstrated that the post-flutter amplitude of the soft pipe can be extremely large in the form of limit-cycle oscillations.Besides,the oscillating shapes for various inclination angles are provided to display interesting dynamical behaviors of the inclined soft pipe conveying fluid.

Characteristics of gravity signal and loading effect in China

The complex geographical environment in China makes its gravity signals miscellaneous.This work gives a comprehensive representation and explanation in secular trend of gravity change in different regions,the key features of which include positive trend in inner Tibet Plateau and South China and negative trend in North China plain and high mountain Asia（HMA）.We also present the patterns of amplitudes and phases of annual and semiannual change.The mechanism underlying the semiannual period is explicitly discussed.The displacement in three directions expressed in terms of geo-potential spherical coefficients and load Love numbers are given.A case study applied with these equations is presented.The results show that Global Positioning System（GPS） observations can be used to compare with Gravity Recovery and Climate Experiment（GRACE） derived displacement and the vertical direction has a signal-noise-ratio of about one order of magnitude larger than the horizontal directions.

Maximum Momentum,Minimal Length and Quantum Gravity Effects of Compact Star Cores

Based on the generalized uncertainty principle with maximum momentum arid minimal length, we discuss the equation of state of ideal ultra-relativistic Fermi gases at zero temperature. Maximum momentum avoids the problem that the Fermi degenerate pressure blows up since the increase of the Fermi energy is not limited. Applying this equation of state to the Tolman-Oppenheimer Volkoff （TOV） equation, the quantum gravitational effects on the cores of compact stars are discussed. In the center of compact stars, we obtain the singularity-free solution of the metric component, gtt ～-（1 ＋ 0.2185×r^2）. By numerically solving the TOV equation, we find that quantum gravity plays an important role in the region r～10^4α0（△x）min. Current observed masses of neutron stars indicate that the dimensionless parameter α0 cannot exceed 10^19.

Effect of gravity gradient in weak equivalence principle test

A high accuracy test of the weak equivalence principle（WEP） is of great scientific significance no matter whether its result is positive. We analyze the gravity gradient effect which is a main systematic error source in the test of WEP.The result shows that the uncompensated gravity gradient effect from the coupling term of the dominated gravity gradient multipole moment component q_（21） and the relative multipole field component Q_（21） contributes to an uncertainty of 1×10^（-11） on the E otv os parameter. We make a Q_（21） compensation to reduce the effect by about 20 times, and the limit of the test precision due to this coupling is improved to a level of a part in 10^（13）.

A study of influence of gravity on bulk behaviour of particulate solid

This paper examines the influence of gravity on the bulk responses of a granular solid. The loading scenarios in this study include confined compression, rod penetration into a granular medium and discharging through an orifice. Similar loading and flow conditions are likely to be encountered in the stress and deformation regimes that regoliths are subjected to in extraterrestrial exploration activities including in situ resource utilisation processes. Both spherical and non-spherical particles were studied using the discrete element method （DEM）. Whilst DEM is increasingly used to model granular solids, careful validations of the simulation outcomes are rather rare. Thus in addition to exploring the effect of gravity, this paper also compares DEM simulations with experiments under terrestrial condition to verify whether DEM can produce satisfactory predictions. The terrestrial experiments were conducted with great care and simulated closely using DEM. The key mechanical and geometrical properties for the particles were measured in laboratory tests for use in the DEM simulations. A series of DEM computations were then performed under reduced gravity to simulate these experiments under extraterrestrial environment. It was found that gravity has no noticeable effect on the force transmission in the confined compression case; the loading gradient in the rod penetration is linearly proportional to the gravity; the mass flow rate in silo discharge is proportional to square root of the gravity and the angle of repose increases with reducing gravity. These findings are in agreement with expectation and existing scientific evidence.

EFFECTS OF WIND SHEAR ON ATMOSPHERIC GRAVITY WAVE SPECTRUM

The effects of constant wind shear on atmospheric gravity wave spectrum are examined.At first a three- dimensional equilibrium spectral model of gravity waves is established in which wind shear rate β is implicit. Based on this model,the expressions for one-dimensional frequency spectrum of atmospheric gravity waves are derived in which β is explicit.Numerical results show that (1) if we assume that mean wind U(z)=βz (z represents the altitude) and the internal gravity wave spectrum at the altitude of U=0 (that is,z=0) is VanZandt one,then the effect of Doppler shifting due to mean wind may be ignored;(2) when Richardson number J(J=N^2/β~2,N is Brunt-V(?)is(?)l(?) frequency,and is equal to 10^(-2)s^(-1) in this paper) satisfies J≥10.0,the effects ofwind shear arealso ignored;(3)for f^2(?)ω~2(?)N^2 (f is the inertia frequency,and f=10^(-4)s^(-1) in this paper,and co is the observed frequency),the wind shear only affects the spectral amplitude,and does not alter the spectral shape;and (4) as wind shear becomes strong,a part of wave potential energy turns into wave kinetic one,and a part of the vertical kinetic energy further turns into the horizontal one.

A modeling study of different kinds of sessile droplets on the horizontal surface with surface wettability and gravity effects considered

Droplet phase change is important for energy storage and saving technology.The initial profile of the droplet is extremely important for its vaporization or solidification on a horizontal surface.To understand the effect of liquid physical properties on droplet profile,a theoretical model was developed in this study,based on the Young-Laplace equation with gravity effect specially considered.After the model was experimentally validated by comparing the geometric shape of water droplets,it was further used for predicting droplet shapes of other materials,and thus analyzing the influence of different physical properties,such as temperature,pressure,surface wettability,etc.Results show that the results of this model agree well with the experimental data.The maximum and average deviations are less than 4.5%and 1.5%,respectively.For all kinds of droplets on the fixed surfaces,when the temperature increases,the droplet contact radius increases and height decreases.The droplets of nitro-gen and carbon dioxide are more sensitive to temperature than ethanol and ethylene glycol droplets.For 20𝜇L droplets on the surface of contact angle 150°,when the temperature changes from 273.15 K to 293.15 K,the droplet contact radiuses increase by 30.6%for carbon dioxide,1.2%for ethanol and 0.67%for ethylene glycol,and the droplet heights decrease by 42.9%,2.5%,1.1%,respectively.Results of this study are meaningful for predicting the phase change process of droplets on the horizontal surface by controlling their initial profiles.

Numerical Study of Wetting Transitions on Biomimetic Surfaces Using a Lattice Boltzmann Approach with Large Density Ratio

The hydrophobicity of natural surfaces has drawn much attention of scientific communities in recent years. By mimicking natural surfaces, the manufactured biomimetic hydrophobic surfaces have been widely applied to green technologies such as self-cleaning surfaces. Although the theories for wetting and hydrophobicity have been developed, the mechanism of wetting transitions between heterogeneous wetting state and homogeneous wetting state is still not fully clarified. As understanding of wetting transitions is crucial for manufacturing a biomimetic superhydrophobic surface, more fundamental discussions in this area should be carried out. In the present work, the wetting transitions are numerically studied using a phase field lattice Boltzmann approach with large density ratio, which should be helpful in understanding the mechanism of wetting transitions. The dynamic wetting transition processes between Cassie-Baxter state and Wenzel state are presented, and the energy barrier and the gravity effect on transition are discussed. It is found that the two wetting transition processes are irreversible for specific inherent contact angles and have different transition routes, the energy barrier exists on an ideally patterned surface and the gravity can be crucial to overcome the energy barrier and trigger the transition.