Spatial Distribution of Viscoelastic Relaxation Following a Subduction Earthquake

<p>Viscoelastic relaxation is generally considered as the dominant process of the long-term post-seismic deformation, while viscoelastic characteristic relaxation time represents the time scale of deformation caused by viscoelastic relaxation effect after the earthquake. The subduction earthquakes which occurred at the boundary of the ocean and continental plates often release greater stress, and the stress relaxation of mantle materials is more significant due to the response to viscoelasticity. Satellite gravity mission GRACE (gravity recovery and climate experience) is able to observe the corresponding co-seismic and post-seismic gravity changes. Therefore, in this study, we use the monthly gravity field model data of GRACE RL06 to study the post-seismic gravity changes of 2011 Tohoku earthquake and 2004 Sumatra earthquake. After removing the influence of sea level changes, GIA changes and GLDAS on the seasonal precipitation changes in the land area, as well as the sea water correction, we get the post-seismic deformation only related to the deformation of the solid earth. Then we use the attenuation function to fit each grid value and obtain the spatial distribution of viscoelastic characteristic relaxation time after rejecting the afterslip from the total post-seismic deformation. Thus，we can capture  the viscous structure in the subduction area.</p>

Experimental Research on Dynamic Stability of Asphalt Mixture Based on Time-Temperature Equivalence Principle

Asphalt mixture is a kind of a viscoelastic material with viscoelastic characteristic of time-temperature equivalence. This paper, from the engineering practical consideration, and the perspective of time-temperature equivalence principle, based on the Rutting Test of Asphalt Mixture,has obtained equivalence relations of the effect of wheel speed and temperature on asphalt mixture rut index by different wheel speed and different temperatures rutting test, so as to provide the data support for the research of anti-rutting mechanism of asphalt pavement.

Near-critical swirling flow of a viscoelastic fluid in a circular pipe

The interaction between flow inertia and elasticity in high-Reynolds-number, axisymmetric and near-critical swirling flows of an incompressible and viscoelastic fluid in an open finite-length straight circular pipe is studied at the limit of low elasticity. The stresses of the viscoelastic fluid are described by the generalized Giesekus constitutive model. This model helps to focus the analysis on low fluid elastic effects with shear thinning of the viscosity. The application of the Giesekus model to columnar streamwise vortices is first investigated. Then, a nonlinear small-disturbance analysis is developed from the governing equations of motion. It reveals the complicated interactions between flow inertia, swirl and fluid rheology. An effective Reynolds number that links between steady states of swirling flows of a viscoelastic fluid and those of a Newtonian fluid is revealed. The effects of the fluid viscosity, relaxation time, retardation time and mobility parameter on the flow development in the pipe and on the critical swirl for the appearance of vortex breakdown are explored. It is found that in vortex flows with either an axial jet or an axial wake profile, increasing the shear thinning by decreasing the ratio of the viscoelastic characteristic times from one (with fixed values of the Weissenberg number and the mobility parameter) increases the critical swirl ratio for breakdown. Increasing the fluid elasticity by increasing the Weissenberg number from zero (with a fixed ratio of the viscoelastic characteristic times and a fixed value of the mobility parameter) or increasing the fluid mobility parameter from zero (with fixed values of the Weissenberg number and the ratio of viscoelastic times) causes a similar effect. The results may explain the trend of changes in the appearance of breakdown zones as a function of swirl level that were observed in the experiments by Stokes et al. (J. Fluid Mech., vol. 429, 2001, pp. 67–115), where Boger fluids were used. This work extends for the first time the theory of vortex breakdown to include effects of non-Newtonian fluids.

The Residual Bolt Force and the Sealing Performance of Flanged Connections With Expanded PTFE Gaskets (Based on Test Results for One Year)

It is known that bolt forces reduce significantly after tightening bolted flanged connections in which expanded PTFE gaskets are used. Bolts are often post-tightened in practice after initial tightening to compensate for the reduction of bolt forces. The viscoelastic characteristic of expanded PTFE gaskets is thought to be the main cause for the phenomenon. Some gasket users are not confident whether the bolt forces remain above a minimum required gasket load until next maintenance. However, the long term characteristics of the residual bolt forces and the sealing performance of flanged connections have not been clarified yet. In this study, using flanged connections with expanded PTFE gaskets, the reduction of bolt forces and the change in the sealing performance were measured at room temperature for one year. Based on the test results, the residual bolt force and the sealing performance were studied. It was clarified that bolt forces converges to a certain level at early stage within almost 1000 hours. After that, the bolt forces were significantly affected by the ambient temperature change. This is because the thermal expansion of PTFE material is high and also the thermal characteristic of PTFE material has a temperature dependency. It was confirmed that although the bolt force reduced significantly at early stage, it is maintained in long-term. The sealing performance was improved due to the increased compression of gasket.

Effects of Post-Tightening on the Residual Bolt Force and the Sealing Performance of Flanged Connections With PTFE Gaskets (Long Term Effects at Room Temperature)

It is known that bolt forces reduce significantly after tightening bolted flanged connections in which expanded PTFE gaskets are used. Bolts are often post-tightened in practice after a while to compensate for the reduction of bolt forces. The viscoelastic characteristic of expanded PTFE gaskets is the main cause for the phenomenon. However, the long term effects of the post-tightening on the residual bolt forces and the sealing performance of flanged connections have not been clarified yet. In this study, two sets of flanged connections (2 inch in nominal size), in which PTFE gaskets were used, were prepared and tightened. One of the flanges was post-tightened after a designated time. The reduction of bolt forces and the change in the sealing performance were measured for about two months. The results were compared with those of flanges without post-tightening. Based on the test results, the effectiveness of post-tightening was discussed from the viewpoint of the residual bolt force and the sealing performance. It has been clarified that the effectiveness of post-tightening depends on gasket material and that post-tightening is effective for expanded PTFE gaskets.

TRANSIENT RESPONSE OF VISCOELASTIC MOVING BELTS USING BLOCK-BY-BLOCK METHOD

The linear, viscoelastic, integral constitutive law is employed to model the viscoelastic characteristic of belt materials. By assuming the translating eigenfunctions instead of stationary eigenfunctions to be the spatial solutions, the governing equation is reduced to differential-integral equations in time, which are then solved by the block-by-block method. The transient amplitudes of parametrically excited viscoelastic moving belts with uniform and non-uniform travelling speed are obtained. The effects of viscoelastic parameters and perturbed axial velocity on the system response are also investigated.