Automating event location monitoring for induced seismicity

Permanent reservoir monitoring is important for cases of induced seismicity in which there may be a risk to people or to the environment. In such cases, accurately locating microearthquakes and assessing their hazard level can help keep production at safe levels. The process can benefit greatly from the use of automation. With the shift toward full-waveform microearthquake location algorithms and workflows, greater accuracy and information can be retrieved compared to that offered by traditional traveltime estimation techniques, but the complexity of these workflows and run-time costs can be higher. Results are presented from an automatic elastic event location and moment tensor inversion workflow that has been highly parallelized on clustered computer hardware. Run times that previously took up to several days to complete using a manually intensive execution of the workflow now can be achieved in approximately 1 hour. Some 180 events recorded at the Groningen gas field and ranging in magnitude from 0.1 to 3.4 MW (ML) have been located and analyzed with the automatic workflow. The results indicate equivalent location accuracy when compared to the manually intensive workflow execution. However, larger errors are noted in the depth positions of some events and in the range and nature of the focal mechanism, as derived from moment tensor inversion. High grading of the manual and automatic results has been performed and used to study the geomechanical behavior of the microearthquakes in the Groningen region, which exhibit mainly dip-slip, double-couple motion, in areas of previous production activity.

Numerical Analysis of Influence of the Hull Couple Motion on the Propeller Exciting Force Characteristics

The numerical calculation was performed for the KRISO Container Ship (KCS) hull-propeller-rudder system with different freedom hull motion by employing the Reynolds-Averaged Navier-Stokes (RANS) method and adopting the overset grid. Firstly, the numerical simulation of hydrodynamics for a bare hull with the heave and pitch motion is carried out. The results show that the space non-uniformity of a nominal wake in the disk plane with motion is comparable to the case without motion. However, the time non-uniformity increases sharply and it has a significant positive relationship with the motion amplitude. Then, the propeller exciting force is calculated in the case including single heave, single pitch and their couple motion. It was found that both the ship and propeller hydrodynamic performance deteriorated dramatically due to the hull motion. Furthermore, the spectrum peak at the motion frequency is dominant in all the peak values and the larger the amplitude is, the higher the motion frequency peak is expected to be. For the propeller bearing force, the effect of the different hull motions appears as linear superimposition. However, the superimposition of different hull motions enlarges the propeller-induced fluctuating pressure in a single motion.

INVESTIGATION OF TORSIONAL DEFLECTION AS AN UNDESIRED MOTION IN ATOMIC FORCE MICROSCOPY WITH SIDEWALL PROBE

In this paper an analytical model is presented for the Micro-Cantilever (MC) of Atomic Force Microscopy with Side Wall probe (AFM-SW) in the tapping excitation mode. In this model the couple motion of the MC is taken into account while the torsional motion is considered as an undesirable motion which is coupled with the vertical motion. To this end, the effect of several parameters, namely; probe mass, probe dislocation, sidewall extension length, and tip sample interaction force is investigated on the occurrence probability of torsional and vertical motions. It is found that the probe dislocation is the prerequisite factor of the undesired motion happening. For sake of validation, the analytical results are compared against the previously published results, and an excellent agreement is observed.

A Passive Dynamic Approach for Flapping-Wing Micro-Aerial Vehicle Control

This article outlines a new control approach for flapping-wing micro-aerial vehicles (MAVs), inspired both by biological systems and by the need for lightweight actuation and control solutions. In our approach, the aerodynamic forces required for agile motions are achieved indirectly, by modifying passive impedance properties that couple motion of the power stroke to the angle of attack (AoA) of the wing. This strategy is theoretically appealing because it can exploit an invariant, cyclical power stroke, for efficiency, and because an impedance-adjusting strategy should also require lower bandwidth, weight, and power than direct, intra-wingbeat control of AoA. We examine the theoretical range of control torques and forces that can be achieved using this method and conclude that it is a plausible method of control. Our results demonstrate the potential of a passive dynamic design and control approach in reducing mechanical complexity, weight and power consumption of an MAV while achieving the aerodynamic forces required for the types of high-fidelity maneuvers that drive current interest in autonomous, flapping-wing robotics.