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41.
Hydraulic actuators are typically used in a real‐time hybrid simulation to impose displacements to a test structure (also known as the experimental substructure). It is imperative that good actuator control is achieved in the real‐time hybrid simulation to minimize actuator delay that leads to incorrect simulation results. The inherent nonlinearity of an actuator as well as any nonlinear response of the experimental substructure can result in an amplitude‐dependent behavior of the servo‐hydraulic system, making it challenging to accurately control the actuator. To achieve improved control of a servo‐hydraulic system with nonlinearities, an adaptive actuator compensation scheme called the adaptive time series (ATS) compensator is developed. The ATS compensator continuously updates the coefficients of the system transfer function during a real‐time hybrid simulation using online real‐time linear regression analysis. Unlike most existing adaptive methods, the system identification procedure of the ATS compensator does not involve user‐defined adaptive gains. Through the online updating of the coefficients of the system transfer function, the ATS compensator can effectively account for the nonlinearity of the combined system, resulting in improved accuracy in actuator control. A comparison of the performance of the ATS compensator with existing linearized compensation methods shows superior results for the ATS compensator for cases involving actuator motions with predefined actuator displacement histories as well as real‐time hybrid simulations. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
42.
A magneto‐rheological (MR) damper is a semi‐active device where the damper force capacity is controlled by varying the input current into the damper. In this paper, the dynamics of MR dampers associated with variable current input is studied. Electromagnetic theory is used to model the dynamics of an MR damper including the eddy current effect and the nonlinear hysteretic behavior of damper material magnetization. A nonlinear differential equation that relates the input current to the damper with a constant equivalent current is proposed. The nonlinear differential equation is combined with the Maxwell Nonlinear Slider (MNS) model to create the variable current MNS model to predict the damper force under variable input current and random damper displacement loading. The model is evaluated by comparing the predicted response of a large‐scale MR damper to the measured damper response from experiments. The experiments include a real‐time hybrid simulation of a 3‐story building structure with a large‐scale MR damper subjected to the design earthquake. The exceptional agreement observed between the predicted and experimental results illustrate the robustness and the accuracy of the variable current MNS model. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
43.
Debris flow in metropolitan area — 2011 Seoul debris flow 总被引：4，自引：2，他引：2
Chan-Young Yune Yun-Ki Chae Joongcheol Paik Gihong Kim Seung-Woo Lee Heung-Seok Seo 《山地科学学报》2013,10(2):199-206
A large number of debris flows occurred simultaneously at around 8:30 to 8:50 a.m. on July 27, 2011, at the center of Seoul, Korea. This area is located in the southern part of Seoul and is a densely populated district. As a result of the debris flow event, 16 people were killed, 30 houses were buried, and 116 houses were damaged around Umyeon Mountain, a relatively small mountain with a height of 312.6 m. Since the debris flow event, field investigations on the initiation and transportation zones of debris flows have been carried out. Rainfall data were collected from the automatic weather stations (AWSs) which are operated by the Korea Meteorological Administration (KMA). Video files recorded by residents were also acquired and used to analyze the flow characteristics of the debris flow. Field investigation shows that about 40 debris flows occurred around Umyeon Mountain and most of the debris flows were initiated by small slope failures. The effects of the precipitation that triggered the debris flows were analyzed as well. A landslide hazard map which considers slope gradient and aspect, strength of soil, hazard record, rainfall conditions, and vegetation, was constructed and compared with the initiation zones of debris flows. 相似文献
44.
Jee-Hyun Jung Young Sun Chae Ha Na Kim Moonkoo Kim Un Hyuk Yim Sung Yong Ha Gi Myung Han Joon Geon An Eunsic Kim Won Joon Shim 《Ocean Science Journal》2012,47(3):209-214
This study describes the spatial variation and the duration of the impacts from the Hebei Spirit oil spill using specific biochemical indices in resident benthic fish. Enzymatic activities and biliary PAHs metabolites were higher at the site closer to the spill area in four months after spill incident. Regarding our results of detoxification response, markers of Phase I followed a similar trend in accordance with levels of biliary metabolites, while markers of phase II and GST appeared relatively unchanged. 相似文献
45.
Local variability in temperature, humidity and radiation in the BaekduDaegan Mountain protected area of Korea 总被引：1，自引：1，他引：0
CHAE Heemun LEE Hyunju LEE Sangsin CHEONG Yukyong UM Gijeung MARK Bryan PATRICK Nathan 《山地科学学报》2012,9(5):613-627
A novel embedded sensor network records changes in key climatic-environmental variables over a range of altitude in the BaekduDaegan Mountain (BDM) of Gangwon Province in Korea, a protected mountain region with unique biodiversity undergoing climate change research. The investigated area is subdivided into three horizontal north-south study areas. Three variables, temperature (T, ℃), relative humidity (RH, %), and light intensity (LI, lumens m -2 , or lux, lx), have been continuously measured at hourly intervals from June, 2010 to September, 2011 using HOBO H8 devices at 10 fixed study sites. These hourly observations are aggregated to monthly, seasonal and annual mean values, and results are summarized to inaugurate a long-term climate change investigation. A region wide T difference in accordance with altitude, or lapse rate, over the interval is calculated as 0.4℃100 m -1 . T lapse rates change seasonally, with winter lapse rates being greater than those of summer. RH is elevated in summer compared to other seasons. LI within forestland is lower during summer and higher during other seasons. The obtained results could closely relate to the vegetation type and structure and the terrain state since data loggers were located in forestland. 相似文献
46.
In this paper, centrifuge model tests were conducted in order to understand the deformation characteristics and behavior of sand compaction piles (SCPs) reinforced grounds in relation to area replacement ratios and penetration ratios. To simulate ground stress conditions, preliminary compaction was conducted to form grounds that maintained a certain level of strength. SCPs were installed in the grounds using compaction methods, and the relationship between loads and settlement as well as stress under rigid loading conditions were compared and analyzed. In addition, finite element analyses were conducted in order to verify the results of the centrifuge model tests and assess the effects of penetration ratios and depths on variations in stress. According to the results of the analyses, stress concentration ratios gradually decreased as depths increased, and the decreasing rate increased as penetration ratios decreased. However, in regions close to the surface layer in depth in which SCPs were installed, stress concentration ratios showed almost the same range regardless of penetration ratios. Stress concentration ratios showed proportional relations with penetration ratios. However, they showed similar values in regions close in depth to the surface of the ground. In particular, they showed very close ranges at penetration ratios of 100% and 80%. 相似文献
47.
The behavior due to rainfall infiltrating the ground plays a role in landslides, groundwater recharge and various other ground
responses. Most of these geotechnical behaviors have a correlation between soil pore space and soil volumetric water content
in the unsaturated and saturated soil porous media. Therefore, the soil porosity associated with soil pores and the distribution
of volumetric water content are significantly important hydrological characteristics. In the case of shallow slope failure
such as landslide, the infiltration activity due to the connectivity of soil pore spaces in a porous media is induced. Slope
failure may be attributed to the effect of a wetting front with the slope due to liquid infiltration, which changes the volumetric
water content, soil matric suction and shear strength of the slope. This study was performed with an unsaturated injection
test using a frequency domain reflectometry (FDR) dielectric device which measures the dielectric constant of unsaturated
soil and the study then proposed the unsaturated dielectric mixing models to calculate soil porosity and effective porosity
of unsaturated soils. From the experimental results the ratio of effective porosity to porosity of soils are measured in a
range of 70–85%. These experimental results show a decrease of about 5–10% for unsaturated soil compared to the ratio of effective
porosity to porosity of saturated soil. The infiltration passages of tracer material are restricted within the pore connectivity
in the unsaturated soil which is caused by dead-pores in the soil. Using the FDR device and the unsaturated dielectric mixing
models, we can consider the acquisition of physical properties to detect the infiltration activity, the response of the dielectric
constant along with the injected tracer and hydrological parameters for the unsaturated soil porous media. 相似文献
48.
Soonyoung Yu Pyeong-Koo Lee Seong-Taek Yun Sang-Il Hwang Gitak Chae 《Environmental Earth Sciences》2017,76(9):338
Volatile organic compounds (VOCs) detected in stormwater were compared with VOCs present in emission sources, air, groundwater, and influent to sewage treatment plants in Seoul to understand their fate and transport in the urban hydrological system. Stormwater is a carrier of non-point source pollutants and contains VOCs from land surfaces and air. Samples of stormwater and influent to sewage treatment plants were collected and analyzed for 61 VOCs, while the VOCs in emission sources, air and groundwater were investigated through literature reviews for comparison. The results showed that the most frequently detected VOCs in stormwater were similar to those in air. However, the atmospheric concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary-butyl ether (MTBE) were too low to explain their frequent detection and high concentrations in stormwater. As a result, land surfaces seem to be a primary source of these VOCs in stormwater. Comparison of the VOCs in stormwater and groundwater showed that toluene and MTBE were frequently detected in both media, but more often and at higher concentrations in stormwater. This finding indicates that stormwater recharge is a source of toluene and MTBE in groundwater. Regarding groundwater, land surfaces seem to be a primary source of toluene, while urban air is the primary source in the case of MTBE. Specifically, the MTBE values in air were sufficiently high to explain its levels in groundwater, which had continually increased and remained low afterward. Furthermore, the high ratios of TEX (toluene, ethylbenzene, and xylenes) to benzene and MTBE in stormwater indicated that TEX had additional sources other than vehicles, most likely hydrocarbon solvents. These solvents seem to be a primary source of TEX and other frequently detected VOCs in stormwater. However, trichloroethylene (TCE), tetrachloroethylene (PCE) and their dechlorination intermediates were far more frequently detected and at higher concentrations in groundwater than in stormwater. Additionally, their concentrations frequently exceeded the water-quality criteria. It seems that halogenated solvents had produced contamination plumes of these chlorinated VOCs in the Seoul aquifer. Based on VOCs detected in Seoul, stormwater was mixed with groundwater in combined sewers and flowed into sewage treatment plants. The results imply that organic solvents should be handled with extreme care to protect groundwater quality. 相似文献
49.
Aurelia coerulea is a bloom forming jellyfish that first appeared before 1980 in the western and southern Korean seas and which has been blamed for huge economical losses in all fields of marine activities. As a preventive measure to reduce economical losses, polyp removal was undertaken at Lake Shihwa, Lake Saemangeum, and Masan Bay, Korea. In the course of efforts during 2 years to remove polyps, polyps were surveyed, quantified, and removed. In these areas, the initial total polyp abundance was 5.04 × 109 and 46.25% of them were removed; Lake Shihwa the highest rates of removal and Lake Saemangeum the lowest. These efforts to remove polyps prevented the appearance of 1.20 × 109 medusae, corresponding to 78.28 × 106 kg. The cost of polyp removal was evaluated and compared with that of medusae removal. The ratio between the cost of polyp removal and that of medusae removal ranged between 0.78–3.14%, indicating large cost savings for polyp removal undertakings. However, the effect of polyp removal varied from positive to none, and we assumed that the cleared surface for polyp removal, quantity of removed polyp, and existence of polyps’ hotspots in neighboring areas were the causes of the non-effectiveness of polyp removal undertakings. 相似文献
50.
Magneto‐rheological (MR) dampers are a promising device for seismic hazard mitigation because their damping characteristics can be varied adaptively using an appropriate control law. During the last few decades researchers have investigated the behavior of MR dampers and semi‐active control laws associated with these types of dampers for earthquake hazard mitigation. A majority of this research has involved small‐scale MR dampers. To investigate the dynamic behavior of a large‐scale MR damper, characterization tests were conducted at the Lehigh Network for Earthquake Engineering Simulation equipment site on large‐scale MR dampers. A new MR damper model, called the Maxwell Nonlinear Slider (MNS) model, is developed based on the characterization tests and is reported in this paper. The MNS model can independently describe the pre‐yield and post‐yield behavior of an MR damper, which makes it easy to identify the model parameters. The MNS model utilizes Hershel–Bulkley visco‐plasticity to describe the post‐yield non‐Newtonian fluid behavior, that is, shear thinning and thickening behavior, of the MR fluid that occurs in the dampers. The predicted response of a large‐scale damper from the MNS model along with that from existing Bouc–Wen and hyperbolic tangent models, are compared with measured response from various experiments. The comparisons show that the MNS model achieves better accuracy than the existing models in predicting damper response under cyclic loading. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献