A new catalogue of normal-mode splitting function measurements up to 10 mHz

The splitting of the Earth's free-oscillation spectra places important constraints on the wave speed and density structure of the Earth's mantle and core. We present a new set of 164 self-coupled and 32 cross-coupled splitting functions. They are derived from modal spectra up to 10 mHz for 91 events with Mw ≥ 7.4 from the last 34 yr (1976–2010). Our data include the 2001 June 23 Peru event (Mw = 8.4), the Sumatra events of 2004 (Mw = 9.0) and 2005 (Mw = 8.6), the 2008 Wenchuan, China event (Mw = 7.9) and the 2010 Chile event (Mw = 8.8). The new events provide significant improvement of data coverage particularly in continental areas. Almost half of the splitting functions have never been measured before. In particular, we measured 33 new modes sensitive to mantle compressional wave velocity, 10 new inner-core sensitive modes and 22 new cross-coupled splitting functions. These provide new constraints on the large-scale compressional structure of the mantle and the odd-degree structure of the mantle and inner core and can be used in future inversions of heterogeneous Earth structure. Our new splitting function coefficient data set will be available online

Tonga slab deformation: The influence of a lower mantle upwelling on a slab in a young subduction zone

There are fundamental geographic variations in the deformation of slabs in the transition zone. The seismic energy release and morphology of the Tonga slab show that it is deforming faster and has accumulated more deformation than any other slab. We show that Tonga overlies the edge of the large-scale Pacific superplume. There is no substantial aseismic penetration into the lower mantle beneath Tonga, consistent with initiation of subduction during the Eocene. Other major subduction systems overlay seismically fast structures. For long-lived subduction systems, the lower mantle tends to pull down on slabs while in Tonga the lower mantle pushes upward, partially accounting for the intense deformation. The perturbation to the state of slab stress due to large-scale mantle flow is 10 to 40 MPa — nearly as large as that expected from slab pull

Splitting function measurements for Earth's longest period normal modes using recent large earthquakes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95155/1/grl27754.pd

A new catalogue of normal-mode splitting function measurements up to 10 mHz

The splitting of the Earth's free-oscillation spectra places important constraints on the wave speed and density structure of the Earth's mantle and core. We present a new set of 164 self-coupled and 32 cross-coupled splitting functions. They are derived from modal spectra up to 10 mHz for 91 events with Mw ≥ 7.4 from the last 34 yr (1976–2010). Our data include the 2001 June 23 Peru event (Mw = 8.4), the Sumatra events of 2004 (Mw = 9.0) and 2005 (Mw = 8.6), the 2008 Wenchuan, China event (Mw = 7.9) and the 2010 Chile event (Mw = 8.8). The new events provide significant improvement of data coverage particularly in continental areas. Almost half of the splitting functions have never been measured before. In particular, we measured 33 new modes sensitive to mantle compressional wave velocity, 10 new inner-core sensitive modes and 22 new cross-coupled splitting functions. These provide new constraints on the large-scale compressional structure of the mantle and the odd-degree structure of the mantle and inner core and can be used in future inversions of heterogeneous Earth structure. Our new splitting function coefficient data set will be available online

Numerical study of time-periodic mixing ventilation: effect of amplitude

© Healthy Buildings Europe 2017. All rights reserved. Conventional ventilation methods often supply fresh air to the room with a steady supply flow rate, which might induce stagnant recirculation cells and stagnation zones that are characterized by high concentrations of contaminants. This paper presents computational fluid dynamics (CFD) simulations of isothermal mixing ventilation with a transient supply flow rate in a generic room. The time-periodic supply flow rate is described by a sine function with different amplitudes. It is shown that time-periodic forcing triggers the stagnant recirculation cells to continuously shift throughout the room, thereby reducing average (passive gaseous) concentration levels in the occupied zone volume compared to the steady supply of fresh air. The concentrations are lower when larger amplitudes are applied. The analysis indicates a reduction in contaminant concentration by up to 24% and an increase of the contaminant removal effectiveness by 24% for time-periodic supply conditions compared to steady supply, which offers new perspectives on healthy and sustainable ventilation for, among others, residential buildings, office rooms, ship cabins, train cabins and cars.status: publishe

Instantaneous characteristics of interacting opposing plane jets in a generic enclosure measured with PIV

Knowledge of the instantaneous flow behaviour of interacting opposing jets, in addition to knowledge of the mean flow, is important for science and practice. Whereas studies often focused on axisymmetric jets, analyses for plane jets are scarce in general and for plane jets in an enclosed domain (i.e. not a (semi-)open environment) in particular, as e.g. encountered in airplane cabin ventilation. In this paper, 2D particle image velocimetry measurements are performed to study isothermal interacting opposing plane wall jets and plane free jets in a generic empty reduced-scale water-filled enclosure. Inlet Reynolds numbers vary from 3450 to 4650. The analyses encompass an inspection of the global flow patterns (in the vertical midplane) and of the flow components (e.g. interaction zone, merged jet, return flows, recirculation cells), using distribution plots, correlation functions and fast Fourier transforms. Vortical structures are also visualised and tracked over time. It is shown that the transient interaction of the opposing wall jets drives a merged jet that resembles a flapping turbulent plane jet. Remarkable are the occasional deviating (more unstable) flow patterns that appear. Furthermore, many vortical structures are present that could enhance mixing within the enclosure. The opposing free jets mainly show quasi-periodic oscillations with a given frequency (Strouhal number around 3.3 × 10–3), comparable to opposing plane free jets mentioned in the literature. Also in this configuration, many different vortices are present that can grow considerably large while transported through the flow domain. Both configurations show a potential for contaminant lock-up (stagnation zones)

CFD study of the flow field driven by interacting jets in a generic enclosure

Mixing ventilation flows consisting of interacting jets (as in airplane cabins) can be highly turbulent and unsteady. The aim of this study is to assess the performance of Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) simulations in predicting the isothermal flow resulting from interacting wall jets in a generic enclosure. Three k-ε turbulence models are employed: the standard k-ε and RNG k-ε models with near-wall modelling, and a low-Reynolds number version of the k-ε model. Comparison of the simulations with (time-averaged) PIV measurements reveals a good overall prediction of the velocity and turbulent kinetic energy by all models. Local deviations from the experiments can be attributed to the inability of the steady RANS method to capture the unsteady jet interaction