The Development of a New IFOG-Based 3C Rotational Seismometer

For many years, seismological research mainly focuses on translational ground motions due to the lack of appropriate sensors. However, because of the development of devices based on Sagnac effect, measuring rotational waves directly comes available. In this work, a portable three-component broadband rotational seismometer named RotSensor3C based on open loop interferometric fiber optic gyroscope (IFOG) is designed and demonstrated. Laboratory tests and results are illustrated in detail. The self-noise ranging from 0.005 Hz to 125 Hz is about 1.2×10−7rads−1/Hz, and with the harmonics compensation the scale factor variation over ±250∘/s is lower than 10 ppm (parts per million). The misalignment matrix method is adopted to revise the output rotation rate. In a special near field experiment using the explosive source, the back-azimuths and phase velocity are estimated by the recorded acceleration and rotation rate. All the results prove the practicability of this new rotational sensor.

Wave-like solutions in Cosserat micropolar elasticity

<p>The Cosserat model generalises an elastic material taking into account the possible microstructure of the elements of the material continuum. In particular, within the Cosserat model the structured material point is rigid and can only experience microrotations, which is also known as micropolar elasticity. The propagation of elastic waves in such a medium is studied and we find two classes of waves, transversal rotational waves and longitudinal rotational waves, both of which are solutions of the nonlinear partial differential equations. For certain parameter choices, the transversal wave velocity can be greater than the longitudinal wave velocity.  We couple the rotational waves to linear elastic waves to study the behaviour of the coupled system and find wave-like solutions with differing wave speeds. In addition we also consider the so-called Cosserat coupling term. In this setting we seek soliton type solutions assuming small elastic displacements, however, we allow the material points to experience full rotations which are not assumed to be small.</p>

Localized structures on librational and rotational travelling waves in the sine-Gordon equation

We derive exact solutions to the sine-Gordon equation describing localized structures on the background of librational and rotational travelling waves. In the case of librational waves, the exact solution represents a localized spike in space-time coordinates (a rogue wave) that decays to the periodic background algebraically fast. In the case of rotational waves, the exact solution represents a kink propagating on the periodic background and decaying algebraically in the transverse direction to its propagation. These solutions model the universal patterns in the dynamics of fluxon condensates in the semi-classical limit. The different dynamics are related to modulational instability of the librational waves and modulational stability of the rotational waves.

Rotational waves in fragmented and blocky geomaterials

<p>An important mechanism of oscillation and wave propagation in fragmented and blocky geomaterials such as rock masses and the Earth’s crust is the movement and rotation of the fragments/blocks as rigid bodies with deformation mainly residing at the interfaces. There are cases when the gouge in the interfaces is very weak and soft such that the resistance to parting the fragments is provided by the ambient compression which prevents the fragments/blocks from parting but allows their mutual rotation.</p><p> </p><p>In order to investigate this type of block movement we performed a series of vibration tests on blocky beams of different heights under horizontal vibrations of the base. The fragmented/blocky geomaterial was modelled using osteomorphic blocks. The osteomorphic blocks have a special shape that ensures topological interlocking. The assembly is an engineered material with internal architecture which captures the fragmented and blocky nature of geomaterials [1]. The observations using the DIC technique confirm that the blocks undergo relative rotational movement. The associated rotational waves travel within the assembly transferring the energy within the blocks. This is an extension of our previous analysis that established the formation of stationary points in fragmented bodies [2]. There is energy exchange between the assembly and the loading device. The energy calculations show that the energy fluctuates around a constant value. The spectrum of block oscillations exhibits the main peak corresponding to the driving frequency as well as secondary peaks that correspond to the multiples of the driving frequency. This is in line with our previous results on bilinear oscillators [3]. The results contribute to the understanding of wave propagation in blocky/fragmented rock mass and the Earth’s crust.</p><p> </p><ol><li>Pasternak, E., A.V. Dyskin and Y. Estrin, 2006. Deformations in transform faults with rotating crustal blocks. PAGEOPH, 163, 2011-2030.</li> <li>Dyskin, A.V., E. Pasternak and I. Shufrin, 2014. Structure of resonances and formation of stationary points in symmetrical chains of bilinear oscillators. Journal of Sound and Vibration 333, 6590–6606.</li> <li>Dyskin, A.V., E. Pasternak and E. Pelinovsky, 2012. Periodic motions and resonances of impact oscillators. Journal of Sound and Vibration 331(12) 2856-2873. ISBN/ISSN 0022-460X, 04/06/2012.</li> </ol><p> </p><p><strong>Acknowledgements</strong>. The authors acknowledge support from the Australian Research Council through project DP190103260. The authors acknowledge the UWA workshop in developing and manufacturing the experimental setup. In the experiments some setup fixtures previously developed by M. Khudyakov were used. AVD acknowledges the support from the School of Civil and Transportation, Faculty of Engineering, Beijing University of Civil Engineering and Architecture.</p>

Flow Instabilities of Coupled Rotation and Thermal-Solutal Capillary Convection of Binary Mixture in Czochralski Configuration

In order to understand the flow instabilities of coupled rotation and thermal-solutal capillary convection of binary mixture in a Czochralski configuration subjected to simultaneous radial thermal and solutal gradients, a series of three-dimensional direct numerical simulation have been conducted. The capillary ratio of the silicon-germanium mixture is −0.2. The rotation Reynolds numbers of crystal and crucible, Res and Rec range from 0 to 3506 and 0 to 1403, respectively. Results show that the basic flow is axisymmetric and steady. It has rich flow structures in the meridian plane, depending on the competitions among the driving forces. With the increase of thermocapillary and rotation Reynolds numbers, the basic flow will transit to three dimensional oscillatory flow. For different combination of rotation rate and thermocapillary Reynolds number, the oscillatory flow can be displayed as spoke patterns which is steady in time but oscillate in space, spoke patterns propagate in azimuthal direction, rotational waves or coexistence of spokes and rotational waves. The crucible rotation has an inhibitory effect on the flow instability, inducing the monotonically increase of critical value for flow transitions, however, for crystal rotation, the critical thermocapillary Reynolds number increases at first and then decreases. When the rotation rate is large, two flow transitions are captured.