Effect of Slip Boundary Condition and Non-Newtonian Rheology of Lubricants on the Dynamic Characteristics of Finite Hydrodynamic Journal Bearing

In the present study, the influence of various slip zone locations on the dynamic stability of finite hydrodynamic journal bearing lubricated with non-Newtonian and Newtonian lubricants has been investigated. Linearized equation of motion with free vibration of rigid rotor has been used to find the optimum location of the slip region with maximum stability margin limit. It has been observed that bearing with interface of slip and no-slip region near the upstream side of minimum film-thickness location is effective in improving the direct and cross stiffness coefficient, critical mass parameter, and critical whirling speed. The magnitude of dynamic performance parameters with slip effect is highly dependent on the rheology of lubricant. Shear-thinning lubricants combined with slip boundary condition shows higher dynamic stability as compared to the Newtonian lubricants under the conventional boundary condition. For all considered rheology of lubricants, the dynamic stability of bearing with slip effect is improving by increasing the eccentricity ratio.

Potential of megathrust earthquakes along the southern Ryukyu Trench inferred from GNSS data

The southern part of the Ryukyu subduction zone has recorded tsunami events with a recurrence interval of several hundred years. Although their source is controversial, one model suggests that the last 1771 Yaeyama tsunami was caused by a shallow megathrust earthquake with a magnitude of 8. However, the current knowledge on interplate coupling based on recent geodetic data is limited. Here, a time series of Global Navigation Satellite System data from January 2010 to February 2021 was analyzed, including newly installed stations by Kyoto and Kyushu Universities, to obtain the distance changes between stations and vertical secular velocities. The distance changes ranged from 2.4 mm/year in contraction and to 4.7 mm/year in extension, and the vertical velocities exhibited no clear uplift or subsidence, with − 2.4 to 1.1 mm/year. The back slip inversion results indicated a slip deficit of 17–47 mm/year to the south of the Yaeyama Islands. The large slip deficit area is complementarily intervened between the shallower source area of low-frequency earthquakes and the deeper slow slip region, suggesting the spatial heterogeneity of frictional properties along the plate interface. If the large slip deficit area accumulates stress in the same rate since the last 1771 earthquake, it could result in a megathrust event with a moment magnitude greater than 7.5. Because the limited onshore data cannot resolve the slip deficit on the shallow plate interface, seafloor geodetic observations are essential to clarify the detailed spatial distribution of the slip deficit and discuss its earthquake and tsunami potential. Graphical Abstract

Fretting Wear of Rubber Sealing Ring Caused by Fluid Pressure Fluctuation

In the process of gas charging and discharging of gas cylinder, the fluid pressure fluctuates causing fretting wear of rubber sealing ring, which affects the sealing performance. The model of O-ring that installed at the mouth of the gas cylinder was established to study the fretting wear in the static seal. Effects of fluid pressure, compression ratio, friction coefficient and temperature on the fretting wear of the O-ring were considered. The results show that the fretting wear of O-ring can be divided into non-contact region, slip region and sticky region. In the static seal, the compression ratio and friction coefficient are the main factors affecting the fretting wear. The sealing performance is greatly influenced on the compression ratio and it is less affected by the temperature. The junction of slip region and sticky region has the greatest probability of seal failure.

Potential of Megathrust Earthquakes Along the Southern Ryukyu Trench Inferred from GNSS Data

The southern part of the Ryukyu subduction zone has recorded tsunami events with a recurrence interval of several hundred years. Although their source is controversial, one model suggested that the last 1771 Yaeyama tsunami was caused by a shallow megathrust earthquake with a magnitude of 8. However, the current knowledge on interplate coupling based on recent geodetic data is limited. This study analyzed a time series of Global Navigation Satellite System data from January 2010 to February 2021, including newly installed stations by Kyoto and Kyushu Universities to obtain the distance changes between stations and vertical secular velocities. The distance changes ranged 2.4 mm/yr in contraction and 4.7 mm/yr in extension, and the vertical velocities exhibited no clear uplift or subsidence of -2.4 to 1.1 mm/yr. The back slip inversion results indicated the slip deficit of 16–54 mm/yr in the south of the Yaeyama Islands. The large slip deficit area is complementarily intervened between the shallower source area of low-frequency earthquakes and the deeper slow slip region, suggesting the spatial heterogeneity of frictional properties along the plate interface. If the large slip deficit area accumulates stress in the same rate since the last 1771 earthquake, it could result in a megathrust event of at least greater than a moment magnitude of 7.7. Because the limited onshore data cannot resolve the slip deficit on the shallow plate interface, seafloor geodetic observations are essential to clarify the detailed spatial distribution of slip deficit and discuss its earthquake and tsunami potential.

Slow Slip Events Following the 2002 Mw 7.1 Hualien Offshore Earthquake Afterslip

The recurrence intervals of slow slip events may increase gradually after a large earthquake during the afterslip. Stress perturbations during coseismic and postseismic periods may result in such an increase of intervals. However, the increasing recurrence intervals of slow slip events are rarely observed during an afterslip. The evolution process along with the afterslip remains unclear. We report an observation of slow slip events following the 2002 Mw 7.1 Hualien offshore earthquake afterslip in the southernmost Ryukyu subduction zone. Slow slip events in 2005, 2009, and 2015 are adjacent to the Mw 7.1 earthquake hypocenter. An increasing slow-slip interval of 3.1, 4.2, and 6.2 years has been observed after the earthquake. We calculated coseismic and postseismic slips from the Mw 7.1 earthquake and then estimated the Coulomb stress changes in the slow slip region. The Mw 7.1 earthquake has contributed positive Coulomb stresses to both the 2005 slow-slip region and 2009/2015 repeating slow-slip region. The coseismic and postseismic Coulomb stress change on the 2005 slow-slip region is approximately 0.05 MPa and 0.035 MPa, respectively. However, both Coulomb stress changes on the 2009/2015 repeating slow-slip region are not over 0.03 MPa. The ongoing afterslip following the Mw 7.1 earthquake last for at least five years, evolving with a decaying stress rate with time. The long-term stress perturbations may be able to trigger the 2005 slow slip event during the afterslip. The 2009 slow slip event seems to be influenced by the afterslip as well. Postseismic stress evolution and frictional and stressed conditions of the slow-slip region can be a reason to affect the evolution process of slow slip events intervals.

Transpressional Deformation Of Bukit C, Guar Sanai: Lithostratigraphic Implication

The upper part of the Setul Formation and the lower part of the Kubang Pasu Formation are well exposed in Guar Sanai, Perlis due to the earth quarry activities. However, compared to the Hill A and Hill B, the outcrops in Hill C clearly illustrates the influence of structure on the lithostratigraphy of the area. The boundary between the Setul Formation and the Kubang Pasu Formation is marked by the thrust fault generally trending north-south to northeast-southwest and mylonite. The thrust belt associated with folding and uplift clearly developed in the zone between parallel lateral faults (trending north-south and southeast-northwest) and is interpreted to accommodate slip along the transpression zone. The sinistral faults are then deformed by transpression movement of dextral faults (trending east-southwest and east-west) which amplified the earlier structures. The combination of lateral and thrust movements formed flower structure that associated with folding and uplift, commonly found in transpressional zone of the strike-slip region. Deformation has caused the older Setul Formation being uplifted to almost equivalent position to the younger Kubang Pasu Formation and led to the displacement of original bed position and repetition of similar sequences. The formation of folding and reverse faulting associated with left lateral strike-slip fault are interpreted to cause by movement of major fault in the northwest Peninsular Malaysia, known as the Bok Bak Fault.

Rupture kinematics of 2020 January 24 Mw 6.7 Doğanyol-Sivrice, Turkey earthquake on the East Anatolian Fault Zone imaged by space geodesy

SUMMARY Here, we present the results of a kinematic slip model of the 2020 Mw 6.7 Doğanyol-Sivrice, Turkey Earthquake, the most important event in the last 50 yr on the East Anatolian Fault Zone. Our slip model is constrained by two Sentinel-1 interferograms and by 5 three-component high-rate GNSS (Global Navigation Satellite System) recordings close to the earthquake source. We find that most of the slip occurs predominantly in three regions, two of them at between 2 and 10 km depth and a deeper slip region extending down to 20 km depth. We also relocate the first two weeks of aftershocks and find a distribution of events that agrees with these slip features. The HR-GNSS recordings suggest a predominantly unilateral rupture with the effects of a directivity pulse clearly seen in the waveforms and in the measure peak ground velocities. The slip model supports rupture propagation from northeast to southwest at a relatively slow speed of 2.2 km s−1 and a total source duration of ∼20 s. In the absence of near-source seismic stations, space geodetic data provide the best constraint on the spatial distribution of slip and on its time evolution.

Comparison of non-Hertzian modeling approaches for wheel–rail rolling contact mechanics in the switch panel of a railway turnout

Due to the complicated wheel–rail contact relation of railway turnouts, it is necessary to select a reasonable rolling contact model to simulate the vehicle–turnout dynamics and wheel–rail damages. This paper mainly aims to evaluate the calculation accuracy and efficiency of different non-Hertzian modeling approaches in solving normal and tangential wheel–rail contact problems of railway turnouts. Four different non-Hertzian approaches, namely CONTACT, Kik–Piotrowski, Ayasse–Chollet, and Sichani methods are compared and analyzed. The above four models are built considering the relative motion of stock/switch rails. A wheel profile called LMA contacting with stock/switch rails (head width 35 mm) of CN60-1100-1:18 turnouts is selected as the object of analysis. The normal contact problems are evaluated by the wheel–rail contact areas, shapes, and normal contact pressures. The assessment of tangential contact problems is based on the creep curves, tangential contact stresses, and distribution of the stick/slip region. In addition, a contrast analysis is performed on the calculation efficiencies of the four approaches. It is found that the normal and tangential contact results calculated based on the Sichani method coincide well with those obtained according to CONTACT, and the calculation efficiency is about 262 times that of CONTACT. The conclusions can provide some guidance to the selection of wheel–rail rolling contact approach in the simulation of vehicle–turnout dynamics and wheel–rail damages.