Hasil untuk "Harbors and coast protective works. Coastal engineering. Lighthouses"

Bambang Agus Kironoto, Miskar Maini, Adam Pamudji Rahardjo et al.

Sediment transport in open channels plays a significant role in shaping turbulent flow structures, influencing sediment dynamics and flow resistance. Transport regimes are classified into equilibrium, where sediment inflow and outflow are balanced, and nonequilibrium, characterized by bed degradation. This study experimentally investigated the turbulence characteristics of sediment-laden, low-velocity open-channel flows under two conditions: sediment-feeding (SF) flows representing equilibrium and nonsediment-feeding (NSF) flows representing degradation-type nonequilibrium conditions. Laboratory experiments were conducted in a 10-m recirculating flume using a 16-MHz acoustic Doppler velocimeter (ADV). Velocity and turbulence profiles were collected under fixed- and movable-bed configurations using two sediment types (d50 = 1.55 and 1.85 mm) simulating tropical riverbeds. Analyses of velocity profiles, turbulence intensities, Reynolds shear stress, mixing length, eddy viscosity, energy spectra, velocity correlations, and turbulence scales were performed. The results reveal clear distinctions between the SF and NSF flows, particularly near the bed. Sediment feeding reduces the near-bed velocity gradient (du/dy), suppresses near-wall turbulence, and shifts the turbulence intensity peak upward to y/H ≈ 0.15. It also significantly reduces the Reynolds shear stress, whereas changes in the eddy viscosity near the bed are less pronounced because of the dominant velocity gradients. A hybrid model combining exponential and power-law terms is proposed to better represent the turbulence intensity and shear stress profiles under sediment-feeding conditions. Spectral analysis confirmed that, despite the 50 Hz sampling limit of the ADV, the inertial subrange follows Kolmogorov's −5/3 law, although the dissipation range was not captured, and microscale estimations remain approximate. Compared with sediment feeding, increased bed roughness reduces turbulence scales, whereas bed mobility effects are secondary. Shear velocity estimates derived from the Clauser, energy gradient, and Reynolds shear stress methods indicate that turbulence-based methods yield more consistent results in sediment-laden flows. These findings advance the understanding of sediment–turbulence interactions and improve sediment transport modeling for low-velocity open channels. Furthermore, these insights can be applied to enhance predictive modeling, optimize sediment management strategies, and support the design of more resilient river engineering structures, particularly in tropical systems.

Wenguang Luo, Yan Pan, Jing Lu et al.

Understanding wind-induced sediment resuspension is essential for predicting turbidity dynamics and nutrient cycling in shallow lakes. This study investigates the spatial variability of sediment resuspension under different hydrodynamic conditions and quantifies the influence of wind-driven forces on sediment stability. A controlled laboratory experiment was conducted using a wind-generation system comprising 13 rows of fans positioned at varying distances and angles with respect to three distinct regions (A, B, and C). Turbidity variations exhibited a strong linear correlation with the dimensionless parameter (W2/H) (R2 = 0.85–0.92), where W represents wind frequency (Hz) and H denotes water depth (m). This parameter effectively captures resuspension sensitivity. Further analysis showed that W, which reflects the proximity to the wind source, integrates the effects of both wind angle and position. Using the 50 NTU water quality threshold, critical (W2/H) values were determined as 2787, 7176, and 16,771 for regions A, B, and C, respectively—corresponding to wind frequencies of 17 Hz, 27 Hz, and 41 Hz at a depth of 0.1 m. Accordingly, regions B and C require approximately 1.6 and 2.5 times more wind energy than region A to reach the same turbidity level. These findings establish a quantitative relationship between wind-driven turbulence and sediment transport, providing insight into the spatial heterogeneity of sediment stability. This research offers both theoretical and practical implications for water quality management, including optimizing artificial aeration, mitigating eutrophication, and improving sediment regulation strategies in shallow lake ecosystems.

Oscar Ferreira

Early warning systems for coastal erosion and flooding are currently primarily designed for local applications, offering high-resolution, site-specific predictions. Only a few early warning systems (EWS) are used at large regional or national scales. There is also a lack of standardised indicators and thresholds, which vary widely across systems and hinder cross-regional applicability. While current EWS perform well in binary hazard detection (Yes/No hazard; 80–95% accuracy), they struggle to accurately classify intermediate hazard levels. A lack of comprehensive field datasets has impeded rigorous validation for most systems, with many assessments relying on qualitative observations. Improving the reliability of the EWS requires improving their validation against field data obtained during storms and regular updating of the topobathymetric data to include the actual pre-storm morphology. Currently, most EWS rely on outdated or synthetic morphological inputs, which increases prediction uncertainty. The computational constraints of physics-based models may prevent warnings from being issued in time and have led to the adoption of surrogate approaches that depend on robust training datasets. Furthermore, most systems focus solely on hazard detection, paying limited attention to the risk to assets or populations. Future development must prioritise stakeholder engagement and the co-design of systems that incorporate both hazard and risk assessments, in order to improve their usefulness and facilitate decision-making by end users.

Abdulvahed Khaledi Darvishan, Shahrbanoo Pourbakhshi, Alireza Riyahi Bakhtiari

Understanding sediment sources and budgeting is crucial for effective watershed management and soil conservation. This study employs n-alkanes as biomarkers to trace sediment origins in a small watershed in Northern Iran, comparing the contribution of degraded forests, coniferous afforestation, and natural forests. Soil and vegetation samples were collected from different land use/land covers, while bed sediment samples were obtained from multiple points along the main stream. The distribution patterns of n-alkanes in sediment samples were analyzed in relation to those found in soil and vegetation samples. Additionally, several key indices including the carbon preference index (CPI), aquatic plant proxy (Paq), Hydrocarbon vegetation index (HVI), total organic carbon (TOC), total nitrogen (TN), and soil particle size distribution were measured to further refine source attribution. Using principal component analysis (PCA) and the FingerPro package in R, the contribution of different sediment sources was pinpointed. According to the PCA, the three sediment sources were well separated from each other. The results were striking: degraded forests accounted for the largest contribution at 45.10 %, followed by planted forests at 28.12 % and natural forests at 26.78 %. Considering the area of each land cover, the specific contribution of degraded forest and planted forest to sediment yield were 10.87 % and 7.14 % per hectare, nearly three times and two times that of natural forests (3.78 % per hectare), respectively. Our analysis, validated with a 70 % accuracy rate through the GOF index as well as field evidences, demonstrates that sediment fingerprinting with n-alkanes can effectively reveal erosion patterns and sediment yield rates between different types of forest land use. This insight is crucial for future soil conservation using appropriate afforestation species, ensuring that land management practices are aligned with long-term sustainability goals.

Carolina Billet, Guadalupe Alonso, Matías Dinápoli et al.

Satellite-derived shorelines (SDSs) are increasingly used to monitor beach morphology worldwide, yet their application remains poorly validated in microtidal environments strongly influenced by atmospheric forcing. In this study, the performance of CoastSat and CoastSat.slope using nine years of in situ beach profiles from six sandy beaches in Buenos Aires (Argentina) was evaluated. The analysis compares alternative sea level forcings—including global tidal predictions (FES2022), a regional barotropic model with meteorological forcing (MSAS), and wave setup from reanalysis products—and evaluates the effect of using locally trained classifiers on shoreline detection. The results show that locally trained classifiers markedly reduced RMSE values, from 9–21 m with the default classifier to 7–12 m with the locally trained one, while the MSAS model consistently outperforms FES2022 for sea level corrections across all sites. CoastSat.slope provided effective slope estimates for tidal corrections but tended to overestimate values relative to field data. Sensitivity tests confirmed that overestimation has a smaller impact on water level correction than underestimation, explaining why validation metrics improved when using CS.slope-derived slopes. These findings translate into actionable guidelines: (i) prioritize regional sea level models when nontidal variability is large; (ii) apply wave setup corrections cautiously in microtidal coasts; and (iii) use locally trained classifiers in heterogeneous or urbanized beaches. Overall, this study demonstrates that with appropriate parameterization, CoastSat is a reliable tool for shoreline monitoring in atmospherically forced, microtidal coasts, and its methodological insights are transferable to other low-energy, data-scarce regions worldwide.

Sadra Shadkani, Yousef Hemmatzadeh, Amirreza Pak et al.

Accurately predicting suspended sediment concentration (SSC) in fluvial systems is essential for environmental monitoring, flood management, and riverine engineering applications. This study introduces a novel hybrid approach for forecasting SSC by leveraging advanced deep learning algorithms. Daily datasets from the U.S. Geological Survey, including discharge (Q) and SSC measurements, were analyzed from 2007 to 2017 at two key locations on the Mississippi River: Chester (CH) and Thebes (TH). The proposed framework integrates feedforward neural networks (FFNN), long short-term memory (LSTM) networks, stochastic gradient descent (SGD), and radial basis function (RBF) models, augmented with a first-order differencing technique. Additionally, hybrid models, including Supervised FFNN-LSTM and Supervised FFNN-SGD, were developed to enhance predictive performance. The dataset was partitioned into training (70%, 2,747 d) and testing (30%, 1,178 d) subsets, with daily temporal resolution. Six input scenarios incorporating lagged parameters were evaluated using performance metrics, including the correlation coefficient (CC), Nash–Sutcliffe efficiency (NSE), scatter index (SI), and Willmott’s index (WI). Sensitivity analysis identified SSCt-1 (i.e., one day before) as the most influential predictor for short-term forecasting. Among the models, the SFFNN-LSTM-6 achieved the highest performance, with CC values of 0.976 for CH and 0.960 for TH, demonstrating the ability to predict SSC effectively even in the absence of current-day discharge data. The proposed hybrid models exhibited exceptional robustness across diverse flow regimes, including extreme environmental conditions, establishing a reliable tool for SSC forecasting in complex fluvial systems.

Jing Guo, Zihan Pan, Xiaomin Yan et al.

Elucidating the historical variation of biogenic elements and source provenance in coastal areas is crucial to better understand environmental evolution and organize ecological management. In this study, the spatiotemporal distribution of biogenic elements (carbon (C), nitrogen (N), phosphorus (P), and silicon (Si)), and carbon and nitrogen isotopes (δ13C and δ15N), respectively in sediment were explored to illustrate elemental changes and determine sources of sedimentary organic matter (SOM) in the coastal regions of northern Beibu Gulf (CNBG). C, N, and P contents exhibited a general decreasing pattern from estuaries to offshore areas, probably due to terrigenous inputs and sediment textures. Since Si was mainly associated with diatoms, lower Si was attributed to the depression of phytoplankton growth by oyster beds in estuaries of Fangcheng Bay and the Maowei Sea. Based on a δ13C and δ15N three-end-member mixing model, it revealed that the average contribution of terrigenous plants and shellfish biodeposition for SOM were 56.00% and 22.39% in the intensive mariculture region (IMR), indicating that terrestrial sources and mariculture biodeposits played a prominent role as SOM sources. Additionally, according to three lead 210 (210Pb) dated sediment cores, it was found that elemental contents and elemental burial rates increased along with the coastal development after 1980s, particularly since 2006 when the Beibu Gulf Economic Zone was established. Multiple Linear Regression results showed that C and N contents and sedimentation rates were responsible for the variation of carbon burial rates during the past decades. More importantly, the significant positive relation between elemental contents and population, and gross domestic product (GDP) growth further proved a close relation between environmental evolution in the CNBG and the socioeconomic development of Guangxi Province. Moreover, the different trends of SOM source contribution for three sediment cores demonstrated the evolution characteristics among different coastal environments. The elevated δ13C and δ15N manifested the increasing contribution of marine phytoplankton (46.83%–69.33%) to SOM in Sanniang Bay recently, where frequent occurrence and decomposition of algal blooms resulted in more SOM. The dominant fraction of terrestrial sources (76.50% ± 13.27%, where ± indicates a standard deviation bound) to SOM in Lianzhou Bay implied the significant impacts of riverine inputs and fishing activities during the last century. This study indicates human activities have led to the continuous increase in nutrients, which has caused ecological risks such as algal blooms in the CNBG, thus, the mitigation of coastal eutrophication needs close attention.

Hao Hou, Wei Zhu, Cheng Lin et al.

Fluid mud, characterized by a bulk density < 1.2 g/cm3, has various adverse environmental effects; furthermore, it can pose challenges for maritime navigation, as fluid mud is an important factor for determining the depth of navigation channels. Notably, the formation of fluid mud by mixing sand and clay is a complex process. Fluid mud typically occurs on the surface of sediment beds in river estuaries, where the confluence of freshwater and saltwater in such regions promotes particle flocculation. The current study is the first to document the occurrence of fluid mud in Lake Taihu, China. The formation mechanisms were investigated through a comprehensive field and laboratory characterization program. The presence of large flocs was confirmed through this program, prompting further investigation into the role of organic matter. The results indicated that polysaccharides played a crucial role in promoting the aggregation of inorganic particles into flocs. In Lake Taihu, cyanobacterial accumulation zones, which are rich in extracellular polymeric substances (EPS), were primarily found in downwind bays, which also served as the sediment deposition areas. Notably, flocs with a size of ∼80 μm contributed to the formation of highly loose fluid mud in the region, with the density varying from 1.09 to 1.13 g/cm3. Overall, the current study advances the current literature on hydrogeology and sedimentology, particularly with respect to the characterization and formation of fluid mud in lakes.

Saman Shabani, Yuntong She, Carlos Frederico Lange

The erosion of riverbanks led to significant environmental and infrastructure challenges, leading to soil loss, structural damage, and flooding. Since the 1970s, erosion control structures such as geobags have been widely utilized to protect riverbanks. The geobags provide several advantages, including improved durability and cost-efficiency, compared with traditional rip-raps. To design geobags, it is necessary to understand how the geobags will perform under hydraulic loading. Despite numerous fluvial studies focusing on geobag stability, no study examined how a single bag behaves under current loads, and none of the models simulated the motion of bags. This research investigated geobag movement within the channel bed with overset mesh techniques using computational fluid dynamics (CFD). Additionally, an image processing technique was employed to evaluate the borders of the geobags within the channel. By conducting the simulation, the drag and friction forces acting on the single bag were carefully analyzed, and the effects of the shape, fill ratio and material of the geobags were determined. The failure velocity of geobags following the same pattern was determined based on a correlation with the experiment.

Leonardo Zandonadi Moura, Jean-Michel Martinez, William Santini et al.

This study aims to evaluate sediment transport processes in the Madeira River, a high-load Amazon tributary altered by the Jirau run-of-river hydropower dam. A methodology for sensitivity analysis and calibration of the HEC-RAS one-dimensional morphodynamic model is developed. It integrates multiple model to measured comparisons, including conventional monitoring and water color remote sensing data. The study underscores the value of employing products derived from satellite imagery, refining model differentiation and improving the spatial and temporal resolution of sediment transport predictions. A simple, regionally significant method of estimating depth-integrated concentrations form surface index concentrations is discussed, showing that for high concentrations a 1.10–2 multiplicative factor suffices. Sensitivity analysis highlights the dominant influence of sand content in the upstream sediment load and the necessity of using the Krone–Partheniades transport formula to simulate fine sediment retention. The calibrated model estimates a sediment retention efficiency of 21.3% in the backwater-affected reach over a five-year period, with over 90% of the sand fraction being deposited. Results suggest that the wash load threshold for this system is medium to coarse silts and clay-silt flocs larger than 0.016 mm. These are the key size classes to understand deposition of fines. Flocculation processes may play a role, requiring adjustments in the input sediment load grain size distribution. A multivariate sediment rating curve, incorporating tributary discharge dynamics, enhances model performance, particularly in reproducing seasonal concentration variations in the backwater reach. These findings provide insights into the best practices for sediment modeling in high-load rivers impacted by hydropower and highlight the importance of multi-objective calibration approaches.

El Mehdi Chagdali, Kamal El Kadi Abderrezzak, Sébastien Erpicum et al.

This study experimentally assesses the influence of varying the inlet boundary condition on the flow patterns in rectangular shallow reservoirs. Two types of inlet boundary conditions were compared: a free surface inlet channel, and a pressurized circular inlet jet positioned at three different elevations over the flow depth (centroid of the inlet jet situated at 25%, 50%, or 75% of the flow depth). The outlet boundary condition was a free surface channel in all cases. Twenty-two experiments were done with two distinct reservoir lengths (length-to-width ratios of 1.1 and 2.0) and three hydraulic boundary conditions (Froude numbers of 0.14, 0.16, and 0.21). Velocity fields were measured with Large-Scale Particle Image Velocimetry (LSPIV) at the surface, and with an Acoustic Doppler Velocity Profiler (ADVP) at several cross sections. The flow patterns are greatly influenced by the inlet boundary condition and the reservoir geometry, but to a lesser extent by the hydraulic boundary condition. For an inlet circular jet located near the reservoir bottom, an unstable flow type, changing over time in a chaotic manner, was observed regardless of the reservoir length and of the inlet flow rate. The same type of unstable flow pattern was observed for a relatively long reservoir and the lowest tested flow rate, irrespective of the vertical positioning of the inlet jet. In all other tested configurations, a steady reattached jet was found in the reservoir equipped with a pressurized inlet jet. In addition to providing new knowledge on flow patterns in shallow reservoirs with an inlet jet, the experimental data presented here will prove valuable for evaluating flow computational models.

Wenbo Zhu, Yan Lu, Chengyang Zhou et al.

The current study investigates the impact of burrowing activities by crab species in the tidal flats of the Yellow River Delta in China on the hydraulic resistance characteristics of water flow, particularly the regulatory effect of biological activity on hydraulic parameters. Although there are many models that attempt to describe the resistance to water flow, these models tend to ignore the influence of such things as biological structures, geomorphological features, and artificial constructs in complex natural water bodies, resulting in insufficient predictive accuracy of the resistance coefficients and Manning's roughness coefficients. In this paper, a new theoretical model is developed to achieve the construction of a model for predicting the hydrodynamic resistance characteristics of crab-hole regions affected by water flow by introducing a cross-sectional area correction coefficient to improve the accuracy of the calculation. The experimental results show that there is a significant positive correlation between the drag coefficient, and the hydraulic radius, and cave density, and a negative correlation with the Reynolds number, and the modification for the sidewall and bed effect greatly improves the representativeness of the measured data. In addition, a new theoretical model is proposed to improve the prediction of drag and Manning's roughness coefficient, and the prediction results are in good agreement with the measured data. The improved drag coefficient calculation model proposed in this paper improves the applicability to the research object and helps to establish a more accurate hydrodynamic model.

Aage Kristian Olsen Alstrup, Carl Chr. Kinze, Natacha Mia Kristensen et al.

The white-beaked dolphin (<i>Lagenorhynchus albirostris</i>) is the second most frequently stranded cetacean species along the Danish coastline. The northern North Sea, the Skagerrak, the Kattegat and the Danish straits are part of the species distributional range. Here, we present eight incidents of breeding activity for the white-beaked dolphin in the inner Danish waters, reviewed from yearly reports made by the National Contingency Plan concerning strandings of marine mammals in Denmark from 2009 to 2023, Danish Wildlife Diseases Surveillance reports from 2014 to 2023 and the citizen science database Naturbasen in the period 2002 to 2023. Three pregnant females, three lactating females and one calf were found stranded in the inner Danish waters. Besides this, there have been live sightings of a female with a newborn calf. We conclude that the white-beaked dolphin is breeding in the inner Danish waters.

Mark R. Jury, Luis E. Alfaro-Garcia

This study analyses climate variability on the north coast of Peru to understand how the local weather is coupled with anomalous ocean conditions. Using high-resolution satellite reanalysis, statistical outcomes are generated via composite analysis and point-to-field regression. Daily time series data for 1979–2023 for Moche area (8S, 79W) river discharge, rainfall, wind, sea surface temperature (SST) and potential evaporation are evaluated for departures from the average. During dry weather in early summer, the southeast Pacific anticyclone expands, an equatorward longshore wind jet ~10 m/s accelerates off northern Peru, and the equatorial trough retreats to 10N. However, most late summers exhibit increased river discharge as local sea temperatures climb above 27 °C, accompanied by 0.5 m/s poleward currents and low salinity. The wet spell composite featured an atmospheric zonal overturning circulation comprised of lower easterly and upper westerly winds > 3 m/s that bring humid air from the Amazon. Convection is aided by diurnal heating and sea breezes that increase the likelihood of rainfall ~ 1 mm/h near sunset. Wet spells in March 2023 were analyzed for synoptic weather forcing and the advection of warm seawater from Ecuador. Although statistical correlations with Moche River discharge indicate a broad zone of equatorial Pacific ENSO forcing (Nino3 R~0.5), the long-range forecast skill is rather modest for February–March rainfall (R² < 0.2).

Marcan Graffin, Mohsen Taherkhani, Meredith Leung et al.

Coastal morphological changes can be assessed using shoreline position observations from space. However, satellite-derived waterline (SDW) and shoreline (SDS; SDW corrected for hydrodynamic contributions and outliers) detection methods are subject to several sources of uncertainty and inaccuracy. We extracted high-spatiotemporal-resolution (~50 m-monthly) time series of mean high water shoreline position along the Columbia River Littoral Cell (CRLC), located on the US Pacific Northwest coast, from Landsat missions (1984–2021). We examined the accuracy of the SDS time series along the mesotidal, mildly sloping, high-energy wave climate and dissipative beaches of the CRLC by validating them against 20 years of quarterly in situ beach elevation profiles. We found that the accuracy of the SDS time series heavily depends on the capability to identify and remove outliers and correct the biases stemming from tides and wave runup. However, we show that only correcting the SDW data for outliers is sufficient to accurately measure shoreline change trends along the CRLC. Ultimately, the SDS change trends show strong agreement with in situ data, facilitating the spatiotemporal analysis of coastal change and highlighting an overall accretion signal along the CRLC during the past four decades.

Masayuki Banno

Long-term in situ monitoring of beach morphology is indispensable for capturing the processes of foreshore morphological changes, and thus many beach monitoring campaigns have been conducted globally. Here, we review the various foreshore beach processes attributable to cross-shore sediment transport, which have been elucidated through long-term beach monitoring. Historical in situ beach monitoring has revealed many daily–annual-scale cyclic foreshore beach morphological changes and shoreline changes; however, many shorter- and longer-term processes remain unresolved, for example, the short-term response to tidal fluctuations and the long-term response to sea level rise. The cost per area surveyed of state-of-the-art equipment will gradually decrease over time, and the accuracy, resolution, and volume of information obtained from the monitoring methods, which are still in the early stages of development, will improve as research progresses. Continued long-term monitoring and acquisition of previously unmeasured monitoring data through the development of monitoring methods are expected to help elucidate unresolved beach processes.

Mahdi Saleh, Rouhollah Amirabadi, Mahdi Sharifi

Significant advantages of FPSO in the ability to transfer and extract from offshore wells have led to their widespread applications. Kind of different modules is installed on the top of these platforms, where one of the major engineering concerns is choosing the location of these modules on the FPSO platform deck in order to reduce the effects of environmental forces. Typically, these modules are analyzed and designed based on the maximum linear acceleration extracted from the shipchr('39')s spectral analysis, using a quasi-static method. The main purpose of this research is the analytical study of these modules response under dynamic excitation due to the wave effect. This research has been done in two parts. First, the dynamic response of different parts of the shipchr('39')s deck has been analyzed under the effect of wave force and proper location for these modules is recommended. For this purpose, first with modeling and analysis performed in MAXSURF software, the shipchr('39')s dynamic responses at different points of the deck have been calculated. Then these modules have been analyzed against the deck response considering base isolation at the module bases in the second part. The obtained response has been applied to two modules as a case study in Sap2000 software. The result shows that base shear and displacement have a verity response in the function of base isolation stiffness. Due to the extension of the shipchr('39')s deck and the serious differences in the acceleration spectrum at different locations of the deck, in order to select the optimal stiffness, the locations of the desired module must also be considered.

Saeed Darvishi Alamouti, Mohammad Reza Bahaari, Majid Moradi

Monopiles are common foundations for offshore structures such as wind turbines and they are commonly used as fender piles in port structures. In such structures, especially in OWTs, the ratio of pile length to diameter (L/D) is small which makes the pile behave as a rigid structure. However, the pile flexural (bending) stiffness still affects the pile load-displacement characteristics and maybe should not be ignored in the pile design. In this study, the effect of pile flexural stiffness on a short monopile subjected to static lateral load is investigated.  The modeled pile has aspect ratio of 5 (L/D=5) which is driven into medium sand. The main characteristics of pile static lateral behavior including lateral resistance, stiffness, deflections, bending distribution and toe-kick are investigated and results are discussed. Results show that in the studied case, the pile behavior pattern is in the middle of flexible and completely rigid pile and therefore bending stiffness has meaningful effects on some important parameters related to monotonic performance.

Hassan Sayyaadi, Abolfazl Motekallem

This paper presents a three dimensional simulation of the vortex induced vibrations of three elastic cylinders in regular triangle arrangement at high Reynolds number. The motion of every single cylinder, which is free to oscillate in two degrees of freedom in a uniform flow and has the same mass and natural frequency in both X and Y directions, is modeled by a mass spring damping system. The displacement and lift forces for each cylinder are analyzed with five spacing ratios L/D changing from 2.5 to 6.5. The results indicate that the downstream cylinders are usually undergone serious fluctuating lift forces. It is found that the simultaneous resonance in the X and Y directions may occur for the downstream cylinders. The stream wise oscillation of downstream cylinders could be as large as 0.54D, and the maximum transverse amplitude of three cylinders can reach to 2.30D. It is indicated that the cross flow oscillation amplitude of three cylinders significantly increased compared with the flow induced vibration of a single elastic cylinder and the stream wise oscillation of downstream cylinders is unneglectable for vortex induced vibration of multi cylinder system.