Ground Rotation Research Articles

A data-driven control method for ground locomotion on sloped terrain of a hybrid aerial-ground robot

In this work, we present a data-driven solution for the attitude control of DoubleBee on slopes. DoubleBee is a novel hybrid aerial-ground robot with two rotors and two active wheels. Inspired by the physcics modeling of the system, we add a channel-separated attention head to a deep ReLU neural network to predict disturbances from ground effects, motor torques and rotation axis shift. The proposed neural network is Lipschitz continuous, has fewer parameters and performs better for disturbance estimation than the baseline deep ReLU neural network. Then, we design a sliding mode controller using these predictions and establish its input-to-state stability and error bounds. Experiments show improvements of the proposed neural network in training speed and robustness over a baseline ReLU network, and a 40% reduction in tracking error compared to a baseline PID controller.

Fiber-optic gyroscope for rotational seismic ground motion monitoring of the Campi Flegrei volcanic area

The real-time monitoring of densely populated areas with high seismic and volcanic risk is of crucial importance for the safety of people and infrastructures. When an earthquake occurs, the Earth surface experiences both translational and rotational motions. The latter are usually not monitored, but their measurement and characterization are essential for a full description of the ground motion. Here we present preliminary observational data of a high-sensitivity rotational sensor based on a 2-km-long fiber-optic Sagnac gyroscope, presently under construction in the middle of the Campi Flegrei Volcanic Area (Pozzuoli, Italy). We have evaluated its performance by analyzing data continuously recorded during an acquisition campaign of five months. The experimental setup was composed of a digital nine-component seismic station equipped with both a rotational sensor and conventional seismic sensors (seismometers, accelerometers, and tiltmeters). During this experiment we detected seismic noise and ground rotations wavefield induced by small to medium local earthquakes (M D <3). The prototype gyroscope shows a very promising sensitivity in the range of 5×10−7−8×10−9rad/s/Hz over the frequency bandwidth 5 mHz–50 Hz. Future upgrades and perspectives are discussed.

Improved pseudostatic analysis of pile response to seismic ground movement: Multiple characteristic ground displacement profiles

Piles may be subjected to significant kinematic loading from ground movement under earthquakes. Pseudostatic analysis, which is based on the Winker beam model, traditionally adopts a single ground displacement profile, known as the characteristic ground displacement profile, for assessments of pile response under this loading condition. This study conducts dynamic analyses with different soil, pile-head-fixity, and seismic conditions and generates displacement, moment, and shear force response envelopes to evaluate the appropriateness of the characteristic displacement profiles of four common methods. These methods give inconsistent predictions because the maximum responses at different depths in the pile response envelopes occur at different points in time. To address this issue, we propose using multiple characteristic ground displacement profiles, which are determined by the maximum ground relative deformation or rotation. These multiple profiles, when used in pseudostatic analyses, give consistent predictions with dynamic pile response envelopes in most scenarios, thus overcoming the limitations of conventional single-profile methods.

Antisymmetric stretching vibration of sulfur dioxide and carbon disulfide modified by optical cavity

For sulfur dioxide (SO2) and carbon disulfide (CS2) molecules in the optical cavity, we study the collective asymmetric Rabi splitting of vibrational strong coupling (VSC) and vibrational ultrastrong coupling (V-USC) between the antisymmetric stretching vibration mode of SO2/CS2 and the optical cavity mode using molecular dynamics simulations. We also study the modification effects of the optical cavity on their ground state bond lengths and rotation behavior. Through the simulation results, we find that although the asymmetric Rabi splitting phenomenon can both occur for SO2 and CS2 molecules, the promotion (or inhibition) effects on their upper polarons (UPs) are different with the increase of the coupling strength. In addition, we find that the relationship between polaron frequencies of SO2 molecules and cavity mode frequencies is consistent with that of CS2 molecules when the cavity mode frequency is highly positively detuned. However, the lower polaron(LP) of SO2 almost disappears and the LP's characteristic of CS2 is dominated by the cavity mode when the cavity mode frequency is highly negatively detuned. Finally, we find that there are obvious hole effects on the ground state rotation behavior of the two molecules. By comparing the different modification effects of the cavity on ground polar molecules (SO2 molecules) and ground non-polar molecules (CS2 molecules), we can not only further understand the differences between the vibrational modes of SO2 and CS2 molecules, but also provide important evidence that we may be able to change the chemical properties of SO2 and CS2 molecules by using VSC-V-USC in a reversible way. In addition, the cavity mode is used to regulate their UP and LP, which opens up a new way to control the physical and chemical properties of SO2 and CS2 molecules. Meanwhile, it also provides reliable information for vibration-polariton science, and provides comparable results for more complex experiments of light—matter coupling in the future.

Investigation on axial-lateral-torsion nonlinear coupling vibration model and stick-slip characteristics of drilling string in ultra-HPHT curved wells

In view of the vibration failure of drilling string system in ultra-high temperature and high pressure (ultra-HPHT) curved wells, an axial-lateral-torsion coupling (ALTC) nonlinear vibration model of drilling string system was established using energy method and Hamiltonian principle, in which, the influence of wellbore trajectory change, wellbore constraint, interaction between bit and rock and ultra-HPHT of wellbore on elastic modulus and viscosity of drilling fluid were taken into account. The finite element method (FEM) is used to realize the numerical solution of the nonlinear vibration model. The correctness and validity of the ALTC nonlinear vibration model was verified by comparing the measured data of four ultra-HPHT wells with the theoretical calculation results of the proposed model.Based on this, according to the parameters of M directional well in Ledong ultra-HPHT block, South China Sea, the influences of ground rotation speed, drilling string length, weight on bit (WOB), torsional impact tools and drill collar length on stick slip vibration characteristics were investigated, and the method of increasing drilling speed in ultra-HPHT curved wells was put forward. The results obtained demonstrate that, firstly, when other requirements were met, the rotary speed should be increased as much as possible, which can effectively improve the drilling efficiency. Secondly, with the increase of drilling depth on-site, the drilling efficiency will be reduced, the whirl phenomenon of drill string system will be intensified, and the service life of bottom hole assembly (BHA) will be reduced. Thirdly, the optimized parameters of WOB and the torsional impact tool depended on the well structure, downhole tool size, etc. and can be determined using the proposed analysis method. The research results provide a theoretically sound guidance for designing and practically sound approach for effectively improving rate of penetration (ROP) and the service life of drilling string in ultra-HPHT curved wells.

Seismic Wave Propagation Through Layered Reduced Micropolar Medium

AbstractThe ground motions recorded in the near‐field regions of earthquakes reveal that, along with translational motions the rotational motions can severely damage structures. To capture these ground rotations more realistically, the present study makes a novel attempt to model the Earth medium as a horizontally layered reduced micropolar half‐space. Layers in this medium are characterized by five material constants: Lame's constant (), Eringen's shear modulus (), density (), rotational moment of inertia (), and an additional material constant (). Cylindrical coordinate system is used to analytically derive the Green's functions and obtain the response of the layered Earth medium subjected to a point earthquake force. The analytically obtained surface translations and rotations involve integrations over the wavenumber and frequency parameters and hence, are evaluated numerically. These solutions converge to corresponding classical elastic medium when the micropolar medium parameters obey the relations and , where is the maximum frequency considered in the simulation. Thereafter, ground motions are simulated for several combinations of earthquake magnitudes and epicenter distances by modeling the Earth medium as an eight layered reduced micropolar half‐space. Further, ground motions for the 2012 Wutai earthquake were simulated using the proposed model and compared with the response of classical elastic medium. The comparisons indicate that the surface rotations are significantly higher in the case of reduced micropolar medium. The proposed formulation can be extended to simulate ground motions for finite‐fault seismic sources.

Monitoring Local Earthquakes in Central Italy Using 4C Single Station Data.

In this study, performed on a set of twenty-two earthquakes that occurred in central Italy between 2019 and 2020, we will explore the possibility to locate the hypocenter of local events by using a ring laser gyroscope observing the vertical ground rotation and a standard broadband seismometer. A picking algorithm exploiting the four components (4C) polarization properties of the wavefield is used to identify the first shear onset transversely polarized (SH). The wavefield direction is estimated by correlation between the vertical rotation rate and the transverse acceleration. The picked times for Pg and Sg onsets are compared to the ones obtained after manual revision on the GIGS station seismometer. The results are compared with the location provided by the national monitoring service of the INGV.

A multi-orientation low-frequency rotational accelerometer.

We present a low frequency rotational accelerometer coined ALFRA with a few nrad/Hz readout sensitivity above 20 mHz and 0.1 nrad/Hz above 50 mHz. The ALFRA is a beam-balance style rotation sensor, which pivots about a cross flexure designed to allow mounting with any orientation, the axis of the pivot determining which rotational component is measured. The high sensitivity is achieved through the use of a walk-off sensor readout used in a feedback loop with an electromagnetic coil to keep the beam dynamically locked. The ALFRA is relatively compact for a ground rotation sensor, measuring at 780 × 240 × 55mm3.

Simulation of near-fault ground strains and rotations from actual strike-slip earthquakes: case studies of the 2004Mw 6.0 Parkfield, the 1979Mw 6.5 Imperial Valley and the 1999Mw 7.5 Izmit earthquakes

SUMMARYPrevious studies have demonstrated that finite-fault simulations of actual or hypothetical earthquakes using deterministic, physics-based simulation techniques constitute an effective tool for characterizing near-fault ground strains and rotations in the low-frequency range. The characteristics of these motions are further investigated in this study by performing forward ground-motion simulations of three well-documented strike-slip earthquakes (i.e. 2004 Mw 6.0 Parkfield, 1979 Mw 6.5 Imperial Valley and 1999 Mw 7.5 Izmit) using models of the seismic source and crustal structure available in the literature. Time histories of ground strains and rotations are numerically generated at near-fault stations and at a dense grid of observation points extending over the causative fault. This is achieved by finite differencing translational motions simulated at very closely spaced stations using a kinematic modelling approach. The simulation results show that the three strike-slip earthquakes produce large-amplitude pulse-like shear strain and torsion in the forward direction of rupture propagation. The time histories of specific components of displacement gradient, strain and rotation at near-fault stations can be estimated from those of ground velocities using a phase velocity, whereas peak ground torsions in the near-fault region can be reasonably estimated from peak horizontal ground velocities using a scaling factor. However, both the phase velocity and the scaling factor exhibit significant variability in the near-fault region of the considered earthquakes. The concept of isochrones is also utilized to associate fault rupture characteristics with near-fault ground strains and rotations. The results indicate that the seismic energy radiated from the high-isochrone-velocity region of the fault—which encompasses areas of large slip locally driven by high stress drop—arrives at a near-fault station in a short time interval that coincides with the time window of the large-amplitude pulse-like shear strain and torsion.

Towards windproofing LIGO: reducing the effect of wind-driven floor tilt by using rotation sensors in active seismic isolation

Modern gravitational-wave observatories require robust low-frequency active seismic isolation in order to keep the interferometer at its ideal operating conditions. Seismometers are used to measure both the motion of the ground and isolated platform. These devices are susceptible to contamination from ground tilt at frequencies below 0.1 Hz, particularly arising from wind-pressure acting on building walls. Consequently, during LIGO’s first observing run both observatories suffered significant downtime when wind-speeds were above 7 m s−1. We describe the use of ground rotation sensors at the LIGO Hanford Observatory to correct nearby ground seismometers to produce tilt-free ground translation signals. The use of these signals for sensor correction control improved low-frequency seismic isolation and allowed the observatory to operate under wind speeds as high as 15–20 m s−1.

Prediction of rotational ground motion for mining-induced seismicity – Case study from Upper Silesian Coal Basin, Poland

For decades, coal mining in the Upper Silesian Coal Basin (USCB) in Poland has been inducing annually more than 150 seismic events with local magnitude M > 2. Two sets of sensors were installed in the USCB in Poland to measure angular velocities and translational accelerations from seismic events induced by underground coal mining. In the period from December 2015 to November 2016, 503 seismic events were recorded with local magnitude M between 1.1 and 3.5. Analysis of measurement data for induced seismicity confirmed a strong linear correlation between peak ground acceleration of shear S-waves, PGA and peak ground motion of angular velocity, PRV. The observed correlation can be a result of previously observed coupling between the angular instantaneous velocity vector and the respective displacement vector at the ground surface. Three types of empirical equations for induced seismicity in Upper Silesia in Poland were developed to predict the peak rotational ground motion of the vertical (torsion), horizontal (rocking), and instantaneous 3D-xyz components. The prediction values of horizontal peak angular velocity ground motion indicate that for strong mining-induced seismic events in the USCB with a magnitude of M = 3.5, we can expect that the mean values of PRVH will reach 7.5 mrad/s in the epicentral area (r = 500 m) and with magnitude M = 4 respectively will reach 19.7 mrad/s. Such values of ground rotation may substantially contribute to the overall seismic response of civil infrastructure, particularly for tall buildings. The study of angular velocity ground motion is important not only from the cognitive point of view, but also from practical significance for assessing the seismic impact on very high buildings, chimneys and stability of slopes.

Six Degree-of-Freedom Broadband Ground-Motion Observations with Portable Sensors: Validation, Local Earthquakes, and Signal Processing

ABSTRACTThe additional observation of three components of rotational ground motions has benefits for tilt-seismometer coupling (e.g., ocean-bottom seismometry and volcano seismology), local site characterization, wavefield separation, source inversion, glacial and planetary seismology, as well as the monitoring of structural health. Field applications have been mostly hampered by the lack of portable sensors with appropriate broadband operation range and weak-motion sensitivity. Here, we present field observations of the first commercial portable broadband rotation sensor specifically designed for seismology. The sensor is a three-component fiber-optic gyro strictly sensitive to ground rotation only. The sensor field performance and records are validated by comparing it with both array-derived rotation measurements and a navigation-type gyro. We present observations of the 2018 Mw 5.4 Hualien earthquake and the 2016 central Italy earthquake sequence. Processing collocated rotation and classical translation records shows the potential in retrieving wave propagation direction and local structural velocity from point measurements comparable to small-scale arrays of seismic stations. We consider the availability of a portable, broadband, high sensitivity, and low self-noise rotation sensor to be a milestone in seismic instrumentation. Complete and accurate ground-motion observations (assuming a rigid base plate) are possible in the near, local, or regional field, opening up a wide range of seismological applications.

A Parametric Investigation of Near‐Fault Ground Strains and Rotations Using Finite‐Fault Simulations

AbstractAlthough previous studies have performed finite‐fault simulations of actual or hypothetical earthquakes to generate time histories of near‐fault ground strains and rotations, no systematic attempt has been made to assess the sensitivity of these motions to variations in seismic source parameters (e.g., fault type, magnitude, rupture velocity, slip velocity, hypocenter location, burial depth). Such a parametric investigation is presented in this article by generating time histories of ground strains and rotations at near‐fault stations and at a dense grid of observation points extending over the causative fault for a suite of hypothetical strike‐slip and dip‐slip earthquakes. The simulation results show that strike‐slip earthquakes produce large shear strain and torsion, whereas dip‐slip earthquakes generate large axial strain and rocking. The time histories of specific components of displacement gradient, strain, and rotation at near‐fault stations may be estimated from those of ground velocities using a simple scaling relation, whereas peak rotational motions in the near‐fault region may be reasonably estimated from peak translational motions using a properly selected scaling factor. The parametric analysis results show that near‐fault ground strains and rotations exhibit strong sensitivity to variations in rupture velocity, slip velocity, and burial depth, whereas a change in hypocenter location significantly alters the spatial distributions of peak ground strains (PGSs) and rotations (PGRs). The presence of a low‐velocity surface layer increases the amplitude and duration of ground strains and rotations, whereas their static offsets are also amplified. Distinct attenuation characteristics are observed for PGSs and PGRs depending on the component of interest, the earthquake magnitude, and the rupture distance. Finally, the spatial distributions of PGSs and PGRs obtained from a stochastically generated variable slip distribution are overall similar to those obtained from a tapered uniform slip distribution, whereas the spatial distributions of the respective static offsets differ significantly.

Physics-Based Planar Wavefront Model to Estimate Seismic Rocking Spectra Using Translational Spectra

AbstractA new and simple planar wavefront model is presented for synthesizing the Fourier spectra of the seismic rocking ground motion (i.e., seismic ground rotation about a horizontal axis) at a s...

A Numerical Model of the SEIS Leveling System Transfer Matrix and Resonances: Application to SEIS Rotational Seismology and Dynamic Ground Interaction

Abstract Both sensors of the SEIS instrument (VBBs and SPs) are mounted on the mechanical leveling system (LVL), which has to ensure a level placement on the Martian ground under currently unknown local conditions, and provide the mechanical coupling of the seismometers to the ground. We developed a simplified analytical model of the LVL structure in order to reproduce its mechanical behavior by predicting its resonances and transfer function. This model is implemented numerically and allows to estimate the effects of the LVL on the data recorded by the VBBs and SPs on Mars. The model is validated through comparison with the horizontal resonances (between 35 and 50 Hz) observed in laboratory measurements. These modes prove to be highly dependent of the ground horizontal stiffness and torque. For this reason, an inversion study is performed and the results are compared with some experimental measurements of the LVL feet’s penetration in a martian regolith analog. This comparison shows that the analytical model can be used to estimate the elastic ground properties of the InSight landing site. Another application consists in modeling the 6 sensors on the LVL at their real positions, also considering their sensitivity axes, to study the performances of the global SEIS instrument in translation and rotation. It is found that the high frequency ground rotation can be measured by SEIS and, when compared to the ground acceleration, can provide ways to estimate the phase velocity of the seismic surface waves at shallow depths. Finally, synthetic data from the active seismic experiment made during the HP3 penetration and SEIS rotation noise are compared and used for an inversion of the Rayleigh phase velocity. This confirms the perspectives for rotational seismology with SEIS which will be developed with the SEIS data acquired during the commissioning phase after landing.

Recording active-seismic ground rotations using induction-coil magnetometers

Most of the current rotational sensing technology is not geared toward the recording of seismic rotations’ amplitudes and frequencies. There are few instruments that are designed for rotational seismology, and the technology for building them is currently being developed. There are no mass industrial producers of seismic rotation sensors as there are for geophones, and only one current sensor model can be deployed on the ocean bottom. We reviewed some current rotational-seismic acquisition technologies, and developed a new method of recording rotations using an existing, robust and field-deployable technology that had seen extensive use in large exploration surveys: induction-coil magnetometers. We conducted an active seismic experiment, in which we found that magnetometers could be used to record seismic rotations. We converted the magnetometer data to rotation-rate data, and validated them by comparing the waveforms and amplitudes with rotation rates recorded by electrokinetic rotation sensors.

Rotational motions from the 2016, Central Italy seismic sequence, as observed by an underground ring laser gyroscope

We present the analysis of rotational and translational ground motions from earthquakes recorded during October-November 2016, in association with the Central Italy seismic sequence. We use co-located measurements of the vertical ground rotation rate from a large ring laser gyroscope and the three components of ground velocity from a broad-band seismometer. Both instruments are positioned in a deep underground environment, within the Gran Sasso National Laboratories of the Istituto Nazionale di Fisica Nucleare. We collected dozens of events spanning the 3.5-5.9 magnitude range and epicentral distances between 30 and 70 km. This data set constitutes an unprecedented observation of the vertical rotational motions associated with an intense seismic sequence at local distance. Under the plane-wave approximation we process the data set in order to get an experimental estimation of the events backazimuth. Peak values of rotation rate (PRR) and horizontal acceleration (PGA) are markedly correlated, according to a scaling constant which is consistent with previous measurements from different earthquake sequences. We used a prediction model in use for Italy to calculate the expected PGA at the recording site, obtaining consequently predictions for PRR. Within the modelling uncertainties, predicted rotations are consistent with the observed ones, suggesting the possibility of establishing specific attenuation models for ground rotations, like the scaling of peak velocity and peak acceleration in empirical ground-motion prediction relationships. In a second step, after identifying the direction of the incoming wavefield, we extract phase-velocity data using the spectral ratio of the translational and rotational components. This analysis is performed over time windows associated with the P-coda, S-coda and Lg phase. Results are consistent with independent estimates of shear wave velocities in the shallow crust of the Central Apennines.

Comparison of Observed and Synthetic Near‐Fault Dynamic Ground Strains and Rotations from the 2004 Mw 6.0 Parkfield, California, Earthquake

Comparison of Observed and Synthetic Near‐Fault Dynamic Ground Strains and Rotations from the 2004 Mw 6.0 Parkfield, California, Earthquake

Interchange rotation factors and player characteristics influence physical and technical performance in professional Australian Rules football

ObjectivesTo examine the effects of match-related and individual player characteristics on activity profile and technical performance during rotations in professional Australian football. DesignLongitudinal observational study. MethodsGlobal positioning system data and player rating scores were collected from 33 professional Australian football players during 15 Australian football League matches. Player rating scores were time aligned with their relative total and high-speed running (HSR) distance (>20kmh−1) for each on ground rotation. Individual players’ maximal aerobic running speed (MAS) was determined from a two-kilometre trial. A multilevel linear mixed model was used to examine the influence of rotations on physical activity profiles and skill execution during match play. ResultsRotation duration and accumulated distance resulted in a trivial-to-moderate reduction in relative total and HSR distances as well as relative rating points. The number of disposals in a rotation had a small positive effect on relative total and HSR distances and a large positive effect on relative rating points. MAS was associated with a moderate-to-large increase in relative total distance, but had a large negative effect on relative rating points. Previous rotation time, stoppages and the number of rotations in the quarter had a trivial-to-small negative effect on relative total and HSR distances. A greater speed (mmin−1) was associated with a trivial increase in rating points during a rotation, while there was a trivial decrease in relative total distance as rating points increased. ConclusionThe complex relationship between factors that influence activity profile and technical performance during rotations in Australian football needs to be considered when interpreting match performance.

Subtracting Tilt from a Horizontal Seismometer Using a Ground‐Rotation Sensor

Abstract We demonstrate the use of a high‐precision ground‐rotation sensor to subtract wind‐induced tilt noise in a horizontal broadband seismometer at frequencies above 10 mHz. The measurement was carried out at the LIGO Hanford Observatory using a low‐frequency flexure‐beam‐balance with an autocollimator readout and a T240 seismometer, located in close proximity to each other. Along their common horizontal axis, the two instruments show significant coherence below 100 mHz, which increases as a function of wind speed due to floor tilt induced by wind pressure on the walls of the building and the ground outside. Under wind speeds of 10–15 m/s, correcting the seismometer for measured ground rotation lowered the signal by a factor of ∼10, between 10 and 100 mHz. This article describes the instruments used, shows representative data for low and high wind speeds, and discusses the tilt subtraction and possible limitations.