Merging fluxgate and induction coil data collected from Eskdalemuir geophysical observatory to produce low-noise, one-second data

This report describes the use of one-second MFS-07 induction coil and DMI FGE89J fluxgate magnetometer magnetic field data recorded at Eskdalemuir Geophysical Observatory in order to compute an "improved" one-second time series for frequencies higher than specified fluxgate operating band. The DMI instrument is a true one-minute system though it can produce one-second data which are relatively noisy in the 0.2 - 0.5 Hz band. The induction coils are sensitive for periods between 0.1 Hz and 50 Hz allowing their high frequency response to complement the low frequency to DC response of the DMI instrument. A numerical technique is adapted from published algorithms developed for merging one-second data recorded at Niemegk observatory in Germany. Our goal is to combine the long-term stability of the DMI fluxgate magnetometer with the low-noise of the induction magnetometer to capture the natural magnetic field for frequencies down to 0.5Hz. Magnetic field data with long-term stability in the low frequency end and also providing information at high frequencies are useful in the study of space weather storms. We have determined the improvement by examining the merged time series, computing the coherence and phase of the one-second merged data with that of the induction coil and fluxgate magnetometer data for the two horizontal components as well as plotting the spectrograms of fluxgate and merged frequencies of interest. We repeated our analysis using data from an instrument capable of meeting the INTERMAGNET one-second definitive data standard, the LEMI-025 fluxgate magnetometer, to compute a separate merged one-second time series as an independent check. We find that a high coherence exists between the two merged time series (LEMI-025/induction coil and FGE89J/induction coil), without phase difference. Spectrograms of the merged time series reveal micro-pulsations that are otherwise masked by the inherent noise from either fluxgate instruments at the frequency band where Pc1 pulsations occur (0.2-0.5Hz). The Pc1 pulsation in the one-second merged time series from Eskdalemuir observatory is also identified in the equivalent spectrogram of the Niemegk observatory from the same day. This proves that the numerical technique created to capture natural field variations in the 0.2-0.5Hz band can be applied effectively for this UK observatory

Block compressed storage and computation in the large-scale reservoir simulation

The block compressed storage and solving methods in reservoir simulation are explored to resolve large sparse linear equations emerging in three-phase black oil model. In this paper, the active nodes are compressed firstly, and then the block main diagonal elements, nonzero block elements in lower triangular and upper triangular are separately stored into three real arrays. Owing to the coefficient matrix arising in the reservoir simulation being symmetrical, the addresses of block elements in lower triangular are deposited in three integer arrays. This block compressed storage method can save lots of memory and reduce the search frequencies of non-zero elements. On the basis of such compression storage, the block incomplete LU preconditioned generalized minimal residual method (GMRES) is adopted to solve the equations, showing that it is an effective method possessing fast convergence and good stability. Testing of black oil model example reveals that the block compressed storage and solving methods are effective in solving the large-scale reservoir simulation. Key words: reservoir simulation, black oil model, active nodes compression, block compressed storage, block ILU factorization, block generalized minimal residual metho

Research on the Temperature Field and Frost Heaving Law of Massive Freezing Engineering in Coastal Strata

In this study, based on the background of massive freezing engineering in coastal strata, the thermal physical parameters and some freezing laws of soil were obtained through soil thermal physical tests and frozen soil frost heaving tests. When the freezing temperatures were −5°C, −10°C, −15°C, and −20°C, the frost heaving rates of the soil were 0.53%, 0.95%, 1.28%, and 1.41%, and the frost heaving forces of the soil were 0.37 MPa, 0.46 MPa, 0.59 MPa, and 0.74 MPa, respectively. In the range of test conditions, the frost heaving rate and the frost heaving force of the soil increased with the decrease of the freezing temperature, and the relationship was roughly linear with the temperature. The entire cooling process could be roughly divided into three stages: active freezing stage, attenuation cooling stage, and stability stage. The range of the frozen soil expansion did not increase linearly with the decrease of the freezing temperature, and there was a limit radius for the frozen soil expansion. A three-dimensional finite element model was established to simulate the temperature field and frost heaving of the soil under the on-site working conditions. The entire frost heaving process could be roughly divided into two stages. The calculated temperature values and the frost heaving force values were compared with the on-site measured values, and the results verified that the numerical calculation could accurately reflect the temperature field and frost heaving law of the formation