We measured shear wave velocities in the shallow subsurface by applying seismic interferometry to earthquake records from eight vertical borehole arrays in eastern Hokkaido, Japan. We detected an increase of several percent in the seismic velocity during January to March due to seasonal frost dynamics. The velocity changes associated with seasonal frozen soil are affected by the frost depth and the extent of freezing, while the frost depth and the extent of freezing are mainly controlled by the cumulative temperature and the current temperature, respectively. Thus, a weighted cumulative freezing degree day is proposed to consider these two factors and used for stage division of the annual freeze‐thaw cycle. Based on the results of observation, we present an empirical model to relate the velocity changes with the weighted cumulative freezing degree days, which allows us to estimate the influence of seasonal frozen soil on near‐surface seismic velocity.
This paper presents a simulation analysis method of degradation behavior for electro-hydraulic servo valve (EHSV). Unlike traditional statistical methods, our work is motivated by the failure mechanism of erosion wear. We assume that degradation trend of flow characteristic is related to structure wear in the valve components. Hence, in this paper, twin flappernozzle servo valve is considered as an example to analyze the degradation behavior in a simulation way. First, erosion wear rates at the precise structure are obtained in hydraulic oil of contaminant class 12 by the Computational Fluid Dynamics (CFD) models. Then, degradation trends of null leakage are simulated under different erosive wear conditions. Finally, the relationship between wear in the valve structure and degradation in null leakage is obtained by the testing data. The simulation results show that erosion wear happens at three sites i.e. the flapper surface, the nozzle outlet and sharp edges of the spool. Moreover, erosion wear of sharp edges greatly influences the flow rate of null leakage. The feasibility of our approach in analyzing degradation trend of hydraulic components is validated by the simulation experiments.
Keywords resonant column, frozen silt, shear modulus, damping ratio, Hardin-Drnevich model IntroductionLarge frozen regions are distributed around the world, as in subarctic countries [1,2]. Compared to soil under normal conditions (15°C to 25°C), under which pore water remained in a liquid state inside the soil, the dynamics of frozen ground varies significantly with the seasons, resulting in different vibratory responses for building and civil engineering structures; even seismic damage is related to the season. The seasonal influences were demonstrated in the seismic damage caused by the earthquake swarm that occurred in Dedu county, China, in 1986. These earthquakes occurred in the summer and winter; the stiffer buildings suffered more during the winter earthquake events, while the more flexible buildings were damaged during the summer events [3]. Research on the frequency of building during an Alaskan winter illustrates that the firstorder mode frequency of reinforced concrete frame structures with a shallow foundation increases nearly 50% over construction performed during the summer [4].There are many researchers studying the shear modulus and damping ratio of normal soil [5][6][7][8][9][10], also some researchers have made significant achievements using specific soils [11][12][13][14][15]. Common used testing devices are resonant column apparatus (RCA) and dynamic triaxial apparatus (DTA), and the utilization frequency of DTA is higher than RCA. But in fact, the resonant column test (RCT) at normal temperatures (15°C to 25°C) is relatively reliable, and certain codes, such as the Chinese standard (SL237-1999) and the American standard (D4015-92) [16,17], have proven to be useful.In contrast, research on the shear modulus and damping ratio of frozen soil is limited [3,[18][19][20]. These researches revealed each factor that affects the modulus and damping to a different extent. However, the equipment performance and technological level required for a low temperature environment are more complex than those found in normal temperature tests. For all of the research noted above, there is a limit to the equipment's capabilities as well as some issues with the methodology, as shown in the following list.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.