Soil-pile-structure interaction effects on the seismic response of a cooling tower     

Kijun Ahn  Phillip L. Gould 《地震工程与结构动力学》1989,18(4):593-609

A study of the effects of soil-pile-structure interaction on the response of rotational shell structures supported by a group of vertical piles is presented. The interaction effects are included in the dynamic analysis through the development of a frequency dependent boundary system at the interface between the shell and the underlying foundation. The substructure method is used to simplify the connection problem between the shell and the pile foundation. A free vibration analysis of a cooling tower is carried out to investigate the dynamic properties of rotational shells with four different foundation stiffnesses. The effects of soil-pile-structure interaction on the response in the shell are demonstrated by a complex response analysis of a cooling tower.  相似文献   

Analysis of GPS RTK performance using external NOAA tropospheric corrections integrated with a multiple reference station approach     

Yong Won Ahn  G. Lachapelle  S. Skone  S. Gutman  S. Sahm 《GPS Solutions》2006,10(3):171-186

For high-accuracy geodetic applications, time-variable tropospheric propagation delay errors limit global positioning system real-time kinematic positioning accuracy. Potential improvements in positioning accuracy are evaluated by using the National Oceanic and Atmospheric Administration (NOAA) real-time tropospheric corrections (herein called NOAA model) within a multiple reference station network approach. The results are compared with those for modified Hopfield tropospheric model corrections, for six scenarios in three geographical regions in the U.S. National Geodetic Survey network of Continuously Operating Reference Stations, for baseline lengths of 60~150 km. Analyses are conducted at rover locations for relatively humid days, and misclosures for various double difference observations are computed; these observations include each frequency (L1 and L2) and three linear combinations [wide lane, ionosphere free (IF), and geometry free]. The effectiveness of the network approach is demonstrated, with overall performance improvements of 15 and 19%, using the modified Hopfield and the NOAA model, respectively. The IF linear combination, a measure of tropospheric and orbital errors, shows a 3% improvement for the NOAA model compared with the modified Hopfield model.  相似文献   

Interdecadal change of interannual variability and predictability of two types of ENSO     

Hye-In Jeong  Joong-Bae Ahn  June-Yi Lee  Andrea Alessandri  Harry H. Hendon 《Climate Dynamics》2015,44(3-4):1073-1091

A significant interdecadal climate shift of interannual variability and predictability of two types of the El Niño-Southern Oscillation (ENSO), namely the canonical or eastern Pacific (EP)-type and Modoki or central Pacific (CP) type, are investigated. Using the retrospective forecasts of six-state-of-the-art coupled models and their multi-model ensemble (MME) for December–January–February during the period of 1972–2005 along with corresponding observed and reanalyzed data, we examine the climate regime shift that occurred in the winter of 1988/1989 and how the shift affected interannual variability and predictability of two types of ENSO for the two periods of 1972–1988 (hereafter PRE) and 1989–2005 (hereafter POST). The result first shows substantial interdecadal changes of observed sea surface temperature (SST) in mean state and variability over the western and central Pacific attributable to the significant warming trend in the POST period. In the POST period, the SST variability increased (decreased) significantly over the western (eastern) Pacific. The MME realistically reproduces the observed interdecadal changes with 1- and 4-month forecast lead time. It is found that the CP-type ENSO was more prominent and predictable during the POST than the PRE period while there was no apparent difference in the variability and predictability of the EP-type ENSO between two periods. Note that the second empirical orthogonal function mode of the Pacific SST during the POST period represents the CP-type ENSO but that during the PRE period captures the ENSO transition phase. The MME better predicts the former than the latter. We also investigate distinctive regional impacts associated with the two types of ENSO during the two periods.  相似文献   

Site flatfile of Korea meteorological administration’s seismic stations in Korea     

Cho  Hyung-Ik  Lee  Moon-Gyo  Ahn  Jae-Kwang  Sun  Chang-Guk  Kim  Han-Saem 《Bulletin of Earthquake Engineering》2022,20(11):5775-5795

Bulletin of Earthquake Engineering - This study constructed a flatfile with the information useful to satisfy the site characterization requirements of Korea Meteorological Administration’s...  相似文献   

On the use of a four-parameter kappa distribution in regional frequency analysis     

Thomas Rodding Kjeldsen  Hyunjun Ahn  Ilaria Prosdocimi 《水文科学杂志》2017,62(9):1354-1363

  相似文献   

An evaluation of inversion models for retrieval of inherent optical properties from ocean color in coastal and open sea waters around Korea     

Palanisamy Shanmugam  Yu-Hwan Ahn  Joo-Hyung Ryu  Balasubramanian Sundarabalan 《Journal of Oceanography》2010,66(6):815-830

This study was aimed to investigate three inversion models (currently in use with Moderate Resolution Imaging Spectroradiometer and Sea-viewing Wide Field-of-view Sensor data processing), namely constrained Linear Matrix (LM), Quasi-analytical algorithm (QAA) and GSM semi-analytical models (GSM). These models were applied to large bio-optical data sets (collected from coastal and open sea waters around Korea) to retrieve inherent optical properties (IOPs) such as absorption coefficients of phytoplankton (a _ph ), colored dissolved and detrital organic matters (a _cdm ), and particulate backscattering coefficient (b _bp ) at five wavelengths (412, 443, 490, 510, and 555 nm). The derived IOP products were compared with in situ a _ph , a _cdm and b _bp coefficients measured for the same remote sensing reflectance (R _rs (λ)) data sets used in the models and the uncertainties of the three models were assessed based on the standard statistical procedures (mean relative error MRE, root mean square error RMSE, slope, and coefficient of determination R ²). It was found that all the three models tended to yield significant errors with varying magnitude at different wavelengths. Overall performance of the models assessed based on the above statistical means was found in the following order: LM > GSM > QAA for retrieving the a _ph , LM > GSM > QAA for retrieving the a _cdm , and QAA > GSM > LM for retrieving the b _bp . Our analyses suggest that these models will require additional refinements with a full parameterization by a fully suited data set in order to produce accurate retrievals of IOPs in coastal and open sea waters around Korea.  相似文献   

Experimental study on the gap entrance profile affecting rudder gap cavitation     

Bu-Geun Paik  Kyung-Youl Kim  Jong-Woo Ahn  Yong-Soo Kim  Sung-Pyo Kim  Je-Jun Park 《Ocean Engineering》2008,35(1):139-149

The unsteady cavity patterns around the gap of the conventional and newly developed semi-spade rudders for marine ships are visualized qualitatively using a high-speed CCD camera. Time-resolved PIV analysis is also performed with the bubble tracers to study the flow behavior over the rudder surface. In addition, pressure measurements are conducted on the rudder surface and inside the gap to find out the flow characteristics around the gap entrance of the rudder. Both the rudders are tested without a propeller wake at the various cavitation numbers and at the rudder deflection angle of −8°θ10°. The strong cavitation patterns around the conventional rudder gap are significantly reduced by adopting a newly developed entrance profile, and a time-resolved velocity field is found to be very effective in catching the vortical cavity flow around the rudder gap. The stagnation point near the gap entrance of the conventional rudder can cause unsteady cavity flow. However, the developed rudder has very stable pressure distribution along the horn surface and decreases the pressure inside the gap because of the modification of the gap entrance. The pressure distribution around the gap of the suction side is closely related to the variation of the rudder deflection angle. The cavitation inception speed is delayed by about 4 knots in the angle range of −5°θ5° by employing the developed profile of the gap entrance.  相似文献   

Recent Primary Production and Small Phytoplankton Contribution in the Yellow Sea during the Summer in 2016     

Hyo Keun Jang  Jae Jung Kang  Jae Hyung Lee  Myungjoon Kim  So Hyun Ahn  Jin-Yong Jeong  Mi Sun Yun  In-Seong Han  Sang Heon Lee 《Ocean Science Journal》2018,53(3):509-519

The high nutrient concentration associated with the mixing dynamics of two warm and cold water masses supports high primary production in the Yellow Sea. Although various environmental changes have been reported, no recent information on small phytoplankton contribution to the total primary production as an important indicator for marine ecosystem changes is currently available in the Yellow Sea. The major objective of this study is to determine the small (< 2 μm) phytoplankton contribution to the total primary production in the Yellow Sea during August, 2016. In this study, we found relatively lower chlorophyll a concentrations in the water column than those previously reported in the central waters of the Yellow Sea. Moreover, the overall contribution of small phytoplankton (53.1%) to the total chlorophyll a concentration was considerably higher in this study than that (10.7%) observed previously. Based on the N/P ratio (67.6 ± 36.6) observed in this study, which is significantly higher than the Redfield ratio (16), we believe that phytoplankton experienced P-limiting conditions during the study period. The average daily carbon uptake rate of total phytoplankton in this study was 291.1 mg C m^-2 d^-1 (± 165.0 mg C m^-2 d^-1) and the rate of small phytoplankton was 205.7 mg C m^-2 d^-1 (± 116.0 mg C m^-2 d^-1) which is 71.9% (± 8.8%) of the total daily carbon uptake rate. This contribution of small phytoplankton observed in this study appears to be higher than that reported previously. Our recent measured primary production is approximately 50% lower than the previous values decades ago. The higher contributions of small phytoplankton to the total chlorophyll a concentration and primary production might be caused by P-limited conditions and this resulted in lower chlorophyll a concentration and total primary production in this study compared to previous studies.  相似文献   

Time‐varying,nonlinear suspended sediment rating curves to characterize trends in water quality: An application to the Upper Hudson and Mohawk Rivers,New York     

Kuk‐Hyun Ahn  Scott Steinschneider 《水文研究》2019,33(13):1865-1882

This work proposes two modelling frameworks for diagnosing temporal variations in nonlinear rating curves that describe suspended sediment–discharge relationships. A variant of the weighted regression on time, discharge, and season model is proposed and is compared against dynamic nonlinear modelling, a newly developed nonlinear time series filter based on sequential Monte Carlo sampling. Both approaches estimate a time series of rating curve parameters, with uncertainty, that can be used to diagnose variability in the sediment–discharge relationship over time. We evaluate the models with a variety of synthetic scenarios to highlight their ability to estimate signals of known rating curve change. Results reveal important bias‐variance trade‐offs unique to each approach, and in general, suggest that dynamic nonlinear modelling is better suited for rapid rating curve changes, whereas the weighted regression on time, discharge, and season variant more precisely estimates slow change. The techniques are then applied in two case studies in the Upper Hudson and Mohawk Rivers in New York. We conclude with a discussion of the implications of dynamic rating curves for the management of water quality in riverine and estuary systems.  相似文献   

Scientific instrumentation for the 1.6 m New Solar Telescope in Big Bear     

W. Cao  N. Gorceix  R. Coulter  K. Ahn  T. R. Rimmele  P. R. Goode 《Astronomische Nachrichten》2010,331(6):636-639

The NST (New Solar Telescope), a 1.6 m clear aperture, off‐axis telescope, is in its commissioning phase at Big Bear Solar Observatory (BBSO). It will be the most capable, largest aperture solar telescope in the US until the 4 m ATST (Advanced Technology Solar Telescope) comes on‐line late in the next decade. The NST will be outfitted with state‐of‐the‐art scientific instruments at the Nasmyth focus on the telescope floor and in the Coudé Lab beneath the telescope. At the Nasmyth focus, several filtergraphs already in routine operation have offered high spatial resolution photometry in TiO 706 nm, Hα 656 nm, G‐band 430 nm and the near infrared (NIR), with the aid of a correlation tracker and image reconstruction system. Also, a Cryogenic Infrared Spectrograph (CYRA) is being developed to supply high signal‐to‐noise‐ratio spectrometry and polarimetry spanning 1.0 to 5.0 μm. The Coudé Lab instrumentation will include Adaptive Optics (AO), InfraRed Imaging Magnetograph (IRIM), Visible Imaging Magnetograph (VIM), and Fast Imaging Solar Spectrograph (FISS). A 308 sub‐aperture (349‐actuator deformable mirror) AO system will enable nearly diffraction limited observations over the NST's principal operating wavelengths from 0.4 μm through 1.7 μm. IRIM and VIM are Fabry‐Pérot based narrow‐band tunable filters, which provide high resolution two‐dimensional spectroscopic and polarimetric imaging in the NIR and visible respectively. FISS is a collaboration between BBSO and Seoul National University focussing on chromosphere dynamics. This paper reports the up‐to‐date progress on these instruments including an overview of each instrument and details of the current state of design, integration, calibration and setup/testing on the NST (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献