Probabilistic approach for active control of structures: experimental verification     

Jae‐Seung Hwang  Kyung‐Won Min  Sang‐Hyun Lee  Hongjin Kim 《地震工程与结构动力学》2005,34(3):207-225

In our previous study (Earthquake Engineering and Structural Dynamics 2003; 32 :2301), we have developed a probabilistic algorithm for active control of structures. In the probabilistic control algorithm, the control force is determined by the probability that the structural energy exceeds a specified target critical energy, and the direction of a control force is determined by the Lyapunov controller design method. In this paper, an experimental verification of the proposed probabilistic control algorithm is presented. A three‐story test structure equipped with an active mass driver (AMD) has been used. The effectiveness of the control algorithm has been examined by exciting the test structure using a sinusoidal signal, a scaled El Centro earthquake and a broadband Gaussian white noise; and, especially, experiments on control have been performed under different conditions to that of system identification in order to prove the stability and robustness of the proposed control algorithm. The experimental results indicate that the probabilistic control algorithm can achieve a significant response reduction under various types of ground excitations even when the modeling error exists. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Vertical distribution of giant jellyfish, <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> using acoustics and optics     

Seonghun Kim  Kyounghoon Lee  Won Duk Yoon  Hyungbeen Lee  Kangseok Hwang 《Ocean Science Journal》2016,51(1):59-65

Nemopilema nomurai jellyfish, which are believed to complete their development in the East China Sea, have started migrating into the Yellow Sea in recent years. We obtained biomass estimates of this species in the Yellow Sea using bottom trawl fishing gear and sighting surveys over a 5-year period. These methods are effective for obtaining N. nomurai jellyfish density estimates and information about the community distribution near the bottom or surface of the sea. To verify the vertical distributions of giant jellyfish between, we used hydroacoustic equipment, including an optical stereo camera system attached to a towed sledge and an echo counting method with scientific echosounder system. Acoustic and optical data were collected while the vessel moved at 3 knots, from which the distribution and density of N. nomurai jellyfish were analyzed. Subsequently, the camera system was towed from a 7 m mean depth to sea level, with the detection range of the acoustic system extending from an 8 m depth to the bottom surface. The optical and acoustic methods indicated the presence of vertical distribution of 0.11³ (inds/m³) and 0.064 (inds/m3), respectively. However, the vertical distribution indicated that around 93% of individuals occurred at a depth range of 10–40 m; thus, a 2.4-fold greater density was estimated by acoustic echo counting compared to the optical method.  相似文献   

Rare earth element fingerprints in Korean coastal bay sediments: Association with provenance discrimination     

Jeongwon Kang  Han Jun Woo  Seok Jang  Kap-Sik Jeong  Hoi-Soo Jung  Ha Gi Hwang  Jun-Ho Lee  Jin Hyung Cho 《Ocean Science Journal》2016,51(3):305-316

Rare earth elements (REEs: La-Lu) in surface sediments collected from the mouth and middle tidal flats of Gomso Bay, South Korea, in August 2011 and May 2012 were analyzed to investigate the fine-grained sediment provenance. The upper continental crust (UCC)-normalized light REEs (LREEs: La to Nd) were more enriched than the middle REEs (MREEs: Sm to Dy) and heavy REEs (HREEs: Ho to Lu), resulting in large (La/Yb)_UCC (1.9 ± 0.4) to (Gd/Yb)_UCC (1.4 ± 0.2) ratios. The monthly (La/Yb)_UCC values differed between the mouth and middle tidal flats due to deposition of fine-grained sediments that originated from distant rivers (the Geum and Yeongsan) and the Jujin Stream, located on the southern shore of the inner bay. We observed relative reductions in the (La/Yb)_UCC value and REE content in the sediments from the mouth of the bay compared with those from Jujin Stream sediments. Confined to the middle tidal flat around the KH Line of Jujin Stream, the sediments, most enriched in LREEs but depleted in Eu, were distributed in August as strong Jujin Stream runs. Here, we suggest that an increase in LREE/HREE and decrease in MREE/LREE ratios can be used as a proxy to identify the Jujin Stream provenance in mixed riverine sediments and to trace Jujin Stream sediments within the Gomso Bay tidal flat, especially in the summer rainy season.  相似文献   

Physical and finite element modeling of lateral stability of offshore skirted gravity structures subjected to iceberg impact load     

Mandar M. Dewoolkar  Jeaan Hwang 《Ocean Engineering》2008,35(16):1615-1626

Static stability mainly against sliding of a typical, relatively large skirted gravity structure was investigated using three-dimensional finite element modeling. The numerical model was validated against centrifuge test results. A specific set of dimensions was chosen to model a typical skirted gravity structure in a centrifuge with two types of foundation soils: uniform saturated sand and a clay zone sandwiched between two sand layers. Soil shear strength parameters used in the finite element models were estimated from in-flight cone penetration resistance measurements obtained in the centrifuge. Numerical parametric studies were conducted using the validated finite element model. The parameters included were the depth and strength of the clay zone and the inclination of external load. It is shown that a relatively simple three-dimensional finite element model was effective in providing information that would be needed to design such a critical and expensive offshore structure. Basic Mohr-Coulomb strength parameters and moduli based on cone penetration resistance measurements and published empirical correlations were appropriate in modeling the soils in the finite element simulations.  相似文献   

Radium tracing of submarine groundwater discharge (SGD) and associated nutrient fluxes in a highly-permeable bed coastal zone, Korea   总被引：2，自引：0，他引：2  

Guebuem Kim  Jae-Woong Ryu  Dong-Woon Hwang 《Marine Chemistry》2008,109(3-4):307

In order to estimate submarine groundwater discharge (SGD) and SGD-driven nutrient fluxes, we measured the concentrations of nutrients, ²²⁴Ra, and ²²⁶Ra in seawater, river water, and coastal groundwater of Yeongil Bay (in the southeastern coast of Korea) in August 2004 and February 2005. The bottom sediments over the shallow areas of this bay are composed mainly of coarse sands. Large excess concentrations of ²²⁴Ra, ²²⁶Ra, and Si supplied from SGD were observed in August 2004, while these excess concentrations were not apparent in February 2005. Based on the mass balance for ²²⁴Ra, ²²⁶Ra, and Si, which showed conservative mixing behavior in seawater, SGD was estimated to be approximately 6 × 10⁶ m³ day^− 1 (seepage rate = 0.2 m day^− 1) in shallow areas (< 9 m water depth) in August 2004, which is much higher than the SGD level typically found in other coastal regions worldwide. During the summer period, SGD-driven nutrients in this bay contributed approximately 98%, 12%, and 76% of the total inputs for dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicate (DSi), respectively. Our study implies that the ecosystem in this highly permeable bed coastal zone is influenced strongly by SGD during summer, while such influences are negligible in winter.  相似文献   

Trace metals in seawater and copepods in the ocean outfall area off the northern Taiwan coast   总被引：3，自引：0，他引：3  

Fang TH  Hwang JS  Hsiao SH  Chen HY 《Marine environmental research》2006,61(2):224-243

The distribution, partitioning and concentrations of trace metals (Cd, Cr, Cu, Fe, Mn, Pb and Zn) in seawater, including dissolved and particulate phases, and in copepods in the ocean outfall area off the northern coast of Taiwan were investigated. Normalization of metal concentrations to the background metal concentration to yield relative enrichment factors (EF), which were used to evaluate the contamination of dissolved and particulate trace metals in seawater around the ocean outfall. The EF results indicated that the outfall area was significantly contaminated by dissolved Fe and Zn, and by particulate Fe, Cr, Cu, Pb and Zn. In addition, most trace metals were chiefly in the particulate phase. The average percentage of total metal concentrations (dissolved plus particulate phases) bound by suspended particulate matter followed the sequence Al(95%) = Mn(95%) > Pb(88%) > Cu(86%) > Fe(72%) > Zn(32%) > Cr(17.5%) > Cd(3.4%). Therefore, metal contamination is better evaluated in solid phase than in the dissolved phase. The concentration ranges of trace metals in the copepods, Temora turbinata, Oncaea venusta and Euchaeta rimana, near the outfall were: Cd, 0.23-1.81 microg g(-1); Cr, 16.5-195 microg g(-1); Cu, 14-160 microg g(-1); Fe, 256-7255 microg g(-1); Mn, 5.5-80.8 microg g(-1); Pb, 2.6-56.2 microg g(-1); Zn, 132-3891 microg g(-1); and Al, 0.21-1.13%. Aluminum, and probably Fe, seemed to be the major elements in copepods. The concentrations of trace metals in copepods, especially Temora turbinata, near the outfall were generally higher than those obtained in the background station. The mean increase in bioconcentration factor of metals in copepods ranged from 4 to 7 and followed the sequence Al(6.4) > Cu(6.2) > Fe(6.0) > Zn(5.7) > Pb(5.6) > Cr(5.5) > Cd(5.1) > Mn(4.7). Therefore, marine copepods in the waters of northern Taiwan can accumulate trace metals over background concentrations and act as contamination indicators.  相似文献   

Southwestward intrusion of korea strait bottom cold water observed in 2003 and 2004     

Chang?-Woong?ShinEmail author  Cheolsoo?Kim  Sang?-Kyung?Byun  Dongchull?Jeon  Sang?-Chull?Hwang 《Ocean Science Journal》2006,41(4):291-299

Hydrographic surveys were carried out four times in the western channel of the Korea Strait in March and August 2003 and in June and November 2004. The bottom cold water, which was lower than 10°C, appeared in the channel trough except in March 2003. It flowed southwestward along the shelf of Korean coasts in August 2003 and in November 2004. The width and the maximum speed of the intrusion current were about 20 km and approximately 25 cm s^-1, respectively, off Ulsan, Korea. The volume transport of the bottom cold water was estimated 0.019 Sv (Sv≡10⁶ m³ s^-1) in August 2003 and 0.026 Sv in November 2004.  相似文献   

Acoustic Characteristic of Sailfin Sandfish (Arctoscopus japonicus) in Dokdo,Republic of Korea     

Myounghee Kang  Rina Fajaryanti  Sangchul Yoon  Bokyu Hwang 《Ocean Science Journal》2020,55(2):289-301

The aim of this study is to determine the acoustic characteristics of sailfin sandfish over a wide frequency range. The acoustic survey was conducted in Fe  相似文献   

Lateral cyclic response of an aluminum model pile in sand     

Jiunn-Shyang Chiou  Zhi-Wei Xu  Cheng-Chang Tsai  Jin-Hung Hwang 《Marine Georesources & Geotechnology》2018,36(5):554-563

Lateral cyclic load tests were performed on an aluminum model pile in dry sand. Two levels of loading were adopted to represent different service load conditions. The maximum number of loading cycles was 1,000. From the test results, it was found that the even though in the service load condition, the pile response was still affected by cyclic effects and a larger load level would produce more significant influence. In a global point of view, the lateral displacement and maximum moment increased with loading cycles, while the secant stiffness within a cycle decreased with cycles. The cyclic effect was more significant on the lateral displacement than on the moment. In a local point of view, cyclic loading would degrade the equivalent subgrade stiffness for the soil shallower than about seven times diameter. In addition, the secant subgrade stiffness within a cycle increased with loading cycles. Some experimental relationships of lateral pile response and loading cycles were built and compared with those in the literature.  相似文献   

Large-scale laboratory measurements of solitary wave inundation on a 1:20 slope     

Yu-Hsuan Chang  Kao-Shu Hwang  Hwung-Hweng Hwung   《Coastal Engineering》2009,56(10):1022-1034

The run-up flow and related pressure of solitary waves breaking on a 1:20 plane beach were investigated experimentally in a super tank (300 m × 5 m × 5.2 m). Swash flow measurements of flow velocities are compared with an existing analytical solution. By incorporating an analytical solution, the hydrodynamic pressure for a quasi-steady flow state is determined and compared with laboratory data. Concerning the evident extra pressure exerted by the impact of swash flow, an empirical drag coefficient for a circular plate is also suggested in the present study.  相似文献