In the Carboniferous–Permian period, several organic-rich black shales were deposited in a marine–continental transitional environment in the Linfen area on the eastern margin of the Ordos Basin. Integrated sedimentological and organic geochemical analyses are performed on an outcrop in order to clarify the relationship between paleoenvironment and organic matter accumulation. The results of this study show that the marine–continental transitional strata of the Upper Carboniferous Benxi Formation to Lower Permian Taiyuan and Shanxi Formation exposed in the Linfen area are composed of sandstone, shale, coal, and limestone. Total organic carbon (TOC) contents of the studied samples were mainly distributed in the range of 0.59%–35.4%, with an average of 7.32%. From Benxi Formation to Shanxi formation, the humidity gradually increased, and the climate gradually changed from hot and humid to warm and humid during Carboniferous to Permian. The deposition of the Shanxi Formation ended with the climate returning to hot and humid, having an oxic-suboxic conditions and a high paleoproductivity. Paleoredox conditions and paleoproductivity are the two vital factors controlling the formation of organic matter in black shales. The transitional environment characterized by oxic-suboxic, relatively high deposition rate, and various source of organic matter, although different from the marine environment, provides a good material basis for the deposition of organic-rich shales.
An O-tube flume is a horizontal closed-circuit flume that can be driven by an inline impellertype pump to produce steady and/or oscillatory flow over a mobile seabed.An O-tube has the ability to reproduce large combined wave and current conditions near the seabed, typical of (cyclonic) storm conditions.In this paper, we investigate the hydrodynamics of an O-tube and show applications of this technology.First, we derive a dynamic equation to explain the coupling between pressure and flow rate within the O-tube.This result can be thought of as an extension of the classical hydrodynamic equations developed for U-tubes and allows for improved control of the flow within the O-tube by providing a prediction of the non-linear interaction between steady flow (i.e.currents) and unsteady flow (i.e.waves).We demonstrate this improved control by comparing measurements of flow rate taken from an O-tube with the dynamic equation.Secondly, we present velocity measurements to give a detailed description of the flow field within the O-tube, including mean flow profiles and seabed shear stress.Finally, we conclude the paper by providing two example applications of the facility to study sediment transport and scour.
Our research aim is to investigate the buffet alleviation effect of static or vibrating bulges attached on the forebody surface of the model. Experiments and numerical simulations on a model consisting of a sharp-edged, 70°-leading edge sweep delta wing and twin swept back vertical tails were conducted. Models with different bulges were tested and computed at 10 and 20 m/s of free stream velocity at angles of attack ranging from 20°–50°. Dynamic strain gauge and multichannel data acquisition and analysis system were employed for the measurement of unsteady root strain on the vertical tails. Experimental and computational results show that both static and vibrating bulges behave effectively as a novel tool to alleviate tail buffet, and the alleviation effect depends largely on the vibrating frequency. Besides, one-sided bulge can only alleviate the buffeting response for the tail of the same side, and it has no obvious alleviation effect for the opposite tail. Results of the spectral analysis reveal that there are generally three peaks of spectral density for aircrafts of this configuration, and bulges used in this paper could alleviate tail buffeting, but the total lift and drag of the whole model show no obvious deviation compared to the base model and the dominant frequency of the vibration of the tails has not shifted.
The dynamic vibration absorber, which is adopted to suppress the unbalanced vibration of rotor, is optimized for the optimal parameters in this paper. This paper proposes a parameter optimization method for dynamic vibration absorbers and seeks parameters of a dynamic vibration absorber with better vibration suppression performance. Firstly, the frequency response function of the dynamic vibration absorber-rotor coupling system is obtained by using the finite element method. Then, basing on the optimal mathematical model, the optimal design variables are solved with the adaptive particle swarm optimization algorithm. Also, an example is used to prove the validity of the optimization design method mentioned in this paper. Further, in order to master the influence of deviation from the optimal value on the suppressing vibration effect, the vibration suppression performance changes of the dynamic vibration absorber whose parameters deviate from the optimal value are analyzed. The results show that: compared with conventional design method, this method is more superior; The dynamic vibration absorber with optimal parameters has better vibration suppression performance; At the same degree deviated from the optimal value, the stiffness has a more remarkable influence on the vibration suppression performance than damping for suppressing the first resonance; For the dynamic vibration absorber which is adopted to suppress the fixed-frequency vibration, the influence of stiffness deviation on the vibration suppression performance appears an obvious interval which is related to working speed.
Aiming at the problems of difficulty in obtaining images of rail surface defects, wide range of defect types, unpredictability of defects and slow defect detection speed, we propose an algorithm for rail surface defect detection based on a convolutional neural network multi-scale-cross FastFlow model (MSC-FastFlow). The pre-training model is used to extract multi-scale features to ensure the extraction speed while doing a good job of image feature extraction. A scale normalized cross fast flow is used as a probability distribution estimation to obtain a standard Gaussian distribution of the image, and the anomaly score is achieved by the distance from the center of the distribution for detect detection as well as locating defects. The comprehensive experimental results show that the unsupervised defect detection method can automatically detect defects without any defect samples, achieving 98.2% and 97.42% detection accuracy at the image level and pixel level, respectively, with a detection speed of 0.08s per image, which is better than existing algorithms for rail surface defect detection and can be well applied in practical projects.
Flow mechanisms around two cylinders in tandem arrangement above a scoured bed have been investigated using the three-dimensional unsteady Navier–Stokes equations with the Spalart–Allmaras improved delayed detached-eddy simulation model. A turbulent inlet boundary layer generation method is adopted to obtain more realistic inlet boundary conditions. First, uniform flow over a single cylinder at Re = 3900 and flow over a single cylinder above scoured beds at Re = 6000 were simulated to validate the numerical model, boundary layer generation method, and mesh density effect. Second, two cylinders in the tandem arrangement above scoured beds with six different pitch ratios L/D are investigated numerically in terms of instantaneous vortex characteristics, the hydrodynamic force, and time-averaged flow fields. The simulation results in scoured beds are compared with simulations under the near flat wall and wall-free conditions. The major findings can be summarized as follows. (1) When L/D≤2.0, the wake of two tandem cylinders is dominated by the intermittent shedding, and the downstream sand dune in the scoured bed hinders the Kármán vortex formation at the rear of the downstream cylinder. Lift force fluctuations of the two cylinders have small amplitudes, and their spectra show a multi-peak distribution and no dominant peak frequency in the spectrum of the upstream cylinder. A squarish cavity-like recirculation zone is formed between two cylinders at L/D=2.0. (2) When L/D≥3.0, the periodic vortex shedding is evident in the wake of the upstream cylinder, and the small sand berm between two cylinders has an impact on the bottom shear layer of the upstream cylinder. The downstream cylinder is periodically impacted by the vortices shed from the upstream cylinder. Lift force spectra of the upstream and downstream cylinders have the same peak frequency. (3) Due to the influence of scoured bed and the inlet boundary layer, the time-averaged lift coefficient of the upstream cylinder remains negative when L/D≥1.5, and the critical spacing for drag inversion is relatively smaller compared with under wall-free conditions. The negative pressure coefficient values of the upstream cylinder are smaller than the values in near flat wall and wall-free conditions.
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