Silent VLPs At Stromboli: Implications For Slug Vs. Plug

<p>Very long period (VLP) seismic signals observed in volcanic environments are thought to be produced by magma and gas flow through conduits. Stromboli Volcano, Italy, typically produces hundreds of VLPs per day. These have been generally attributed to the flow of gas slugs through the shallow plumbing system and thus linked to the mechanism thought to drive Strombolian explosions. During a 6-day-long seismo-acoustic campaign in May 2018 (a period characterized by relatively low activity) we recorded 1900+ seismic events, the majority of which have significant energy in the VLP (2-100 s) band. We used a coincident STA/LTA trigger to identify seismic events in continuous waveform data and then used the PeakMatch algorithm (Rodgers et al., 2015) to identify seismic multiplets, with a focus on VLPs. To identify explosions, we applied the same coincident trigger to infrasound data, and manually identified gas jetting events using spectrograms and high-pass-filtered (20 Hz) waveforms. </p><p> </p><p>We identified ~250 explosions and ~600 jetting events. Seismic multiplet analysis identified two main families of repeating events. Family 1 (F1) has over 500 events and Family 2 (F2) has over 150 events based on a 0.7 correlation threshold. We find that F1 VLPs coincide in time with ~6% of explosions and ~0.8% of jetting events and F2 VLPs coincide in time with ~28% of explosions and ~2.7% of jetting events (we term these “silent VLPs”). These VLPs do not correspond with lava effusion (Marchetti and Ripepe, 2005; Ripepe et al., 2015). F2 have a higher dominant period (8-10 s) compared to F1 (3-4 s). The repeating VLPs are part of a broadband signal and the higher frequencies start after the VLP. VLP peak amplitudes are generally larger for F1 events. The dip of the VLP particle motion roughly locates the F1 and F2 VLP source centroids beneath the active crater and are stable throughout the dataset. Both VLP displacements show a small outward, large inward, and subsequent large outward motion from the crater. The lack of explosions relative to repeating VLPs does not support the slug model, where a slug rises through a conduit, generates a VLP through interactions with changes in conduit geometry, and then bursts at the lava free surface. Our observations support the plug model (Suckale et al., 2016). We suggest the “silent” VLPs are generated when the gas bubbles interact with and move into the semipermeable plug. Then the plug behaves as a mechanical filter for gas escape and allows for passive and explosive escape mechanisms.</p>

The significance of karst unconformities on overlying resource shales: Lessons learned from the Devonian Woodford Formation applied to the Permian Wolfcamp Shale

We have summarized the threefold significance of karst unconformity boundary: (1) The development of a sequence stratigraphic model for the Devonian Woodford Shale Formation is transferable to the Upper Wolfcamp in the Permian Basin, (2) demonstration of the more general application of that model beyond the Woodford to other resource shales, and (3) illustration of a modification of common sequence stratigraphy models specifically to unconventional resource shales. During early transgression, marine encroachment into the paleolows created anoxic, hypersaline marine “pockets” conducive to the preservation of organic matter. The result is deposition of thick, laterally discontinuous, organic-rich strata stratigraphically at or near the unconformity surface. This pattern of deposition and distribution of the organic-rich shale has been well-documented in the Devonian Woodford Shale and is applicable to other resource shales, in this case to the Permian Upper Wolfcamp Formation in the Central Basin Platform of the Permian Basin. The stratigraphy of the distribution of the Upper Wolfcamp on top of the Upper/Middle Wolfcamp Unconformity is similar to that of the Woodford, suggesting a similar origin and distribution. The resulting stratigraphy in both cases resembles that of the classical Exxon sea slug model except that rather than a single organic-rich deposit defining the condensed section and maximum flooding surface, a second organic-rich deposit occurs stratigraphically lower, at or near the unconformity surface. This theoretical summary can support the discovery of potential drillable target zones in the Woodford Shale and the Wolfcamp Shale.

A Two-Phase Hydrodynamic Model for Transport Pipelines in Vacuum Sewer Systems

Intermittent gas-liquid flow with an unsteady, intermittent and high-pressure drop nature is common in vacuum transport pipelines. The characteristics of intermittent flow in vacuum pipelines were analyzed. A one-dimensional transient hydrodynamic model for two-phase transport of vacuum pipelines, which consists of the film model, the liquid slug model and the mix vortex model was deduced for the first time. The model outlines the relationship between hydrodynamic parameters and presents the calculation method of pressure drop, which would be helpful to uncover the transport mechanism of vacuum pipelines and propose a more seemly system design and simulation method for availability, reliability and energy-saving considerations.

Fluid Flow Characterization in IPMC Actuated Contractile Water Jet Thruster

Contractile water jet thruster is an alternative method for Autonomous Underwater Vehicle (AUV) locomotion as well as for the AUV’s manoeuvrability control. Currently, studies on contractile water jet thruster focus more on the thrust force performance and its efficiency, such as the characterization of vortex ring formation process, the slug model L/D ratio and the influence of the thrust performance on the AUV. The aim of this paper is to discuss the fluid flow behaviour in the thruster during contraction process under different actuation frequency. This research utilized Ionic Polymer Metal Composite (IPMC) as the actuators instead of electric motor for the contractile function. The result shows that the Reynolds number of the intake flow has negative linear relation with the actuation frequency.

Dynamic Control of Biologically Inspired Pulsatile Jet Propulsion Thrusters

Inspired by the propulsion techniques employed by squid and other cephalopod, a new type of thruster was designed which utilized pulsatile jet propulsion to generate controlling forces. The thrust production from this jet actuator was characterized in a static environment and seen to be well approximated by a simple fluid slug model. A linear transfer function model was derived to describe the transient dynamics of this thruster being employed in a virtual vehicle simulation; which was developed to test the thruster with unsteady driving signals. It was predicted that an impulsive type of thrust (as is found in our jet actuator) is ideal in a non-linear damping environment, since all of the acceleration is being added to the system while its at its lowest velocity and therefore lowest drag. Due to the extremely nonlinear nature of underwater vehicle environments we developed a scaling system to classify regimes of maneuvers and characterize their dynamics independently. Assuming a simple proportional derivative control algorithm, the vehicle closed loop frequency response was predicted using the transfer function model; which was linearized according to the maneuvering regime. Within the hybrid simulation environment, the closed loop frequency response was tested empirically and seen to be well approximated by the model.

Circulation of Vortex Rings Formed From Tube and Orifice Openings

Two common configurations for generating vortex rings via jet pulses are the tube and orifice geometries. The orifice geometry forces the flow to contract as it approaches the jet exit plane, which can strongly affect vorticity flux and the circulation of the resulting ring. The author’s recent extension of the traditional slug model for vortex ring circulation (called the “pressure corrected” or PC model) accounts for the geometric differences between the tube and orifice cases, but model validation for the orifice geometry has been limited due to the lack of data for this configuration. The present study compares process of circulation generation by tube and orifice geometries using numerical simulations of finite duration jets from tube and orifice openings. Total jet slug length-to-diameter ratios (L/D) in the range of 0.5 to 3.5 and a jet Reynolds number of 2000 are considered. The numerical results confirm the underlying assumptions of the PC model. The model results for the tube geometry are within 14% of the numerical results. Incorporating the scaling of ring velocity with ejected jet length (X/D) obtained from the present numerical results improves the predictions for the orifice case, giving accuracy to within 20%. The overall geometry effect appears as a two-fold increase in circulation for the orifice case over the tube case at the same L/D.