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The main intention of the present study is to reduce wind, wave, and seismic induced vibrations of jackettype offshore wind turbines (JOWTs) through a newly developed vibration absorber, called tuned liquid column gas damper (TLCGD). Using a Simulink-based model, an analytical model is developed to simulate global behavior of JOWTs under different dynamic excitations. The study is followed by a parametric study to explore efficiency of the TLCGD in terms of nacelle acceleration reduction under wind, wave, and earthquake loads. Study results indicate that optimum frequency of the TLCGD is rather insensitive to excitation type. In addition, while the gain in vibration control from TLCGDs with higher mass ratios is generally more pronounced, heavy TLCGDs are more sensitive to their tuned frequency such that ill-regulated TLCGD with high mass ratio can lead to destructive results. It is revealed that a well regulated TLCGD has noticeable contribution to the dynamic response of the JOWT under any excitation. 相似文献
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Dependence of correlations between spectral accelerations at multiple periods on magnitude and distance 
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下载免费PDF全文 In this paper, the dependence of correlations between spectral accelerations at multiple periods on magnitude (M) and distance (R) has been investigated. For this purpose, a relatively large dataset of ground motion records (GMRs), containing 1551 records with a wide range of seismic characteristics, was selected. It is shown that the difference in the correlation coefficient is statistically meaningful when the general GMR dataset is divided into two subsets based on an arbitrary M or R. The observed difference is more meaningful in the case of magnitude when compared with distance. The general dataset of GMRs was then divided into four separate subsets based on optimum values of M and R, so that the four obtained subsets were given the greatest dissimilarity in terms of the correlation coefficients. The correlation coefficients between spectral accelerations at multiple periods were calculated in the case of the four subsets and compared with the available correlations in the literature. The conditional mean spectrum was also calculated by means of the conventional correlation coefficients, as well as by using the proposed M and R dependent correlation coefficients. The results show that, despite the commonly available findings in the literature, this dependence is significant and should not be neglected in the conditional spectra calculation process. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Ground motion record simulation for structural analysis by consideration of spectral acceleration autocorrelation pattern 总被引：1，自引：1，他引：0
A novel approach is introduced to generate simulated ground motion records by considering spectral acceleration correlations at multiple periods. Most of the current reliable Ground Motion Record(GMR) simulation procedures use a seismological model including source, path and site characteristics. However, the response spectrum of simulated GMR is somewhat different when compared with the response spectrum based on recorded GMRs. More specifi cally, the correlation between the spectral values at multiple periods is a characteristic of a record which is usually different between simulated and recorded GMRs. As this correlation has a signifi cant infl uence on the structural response, it is needed to investigate the consistency of the simulated ground motions with actual records. This issue has been investigated in this study by incorporating an optimization algorithm within the Boore simulation technique. Eight seismological key parameters were optimized in order to achieve approximately the same correlation coeffi cients and spectral acceleration between two sets of real and simulated records. The results show that the acceleration response spectra of the synthetic ground motions also have good agreement with the real recorded response spectra by implementation of the proposed optimized values. 相似文献
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V. Ghaffarian S. M. Mousavi M. Bahreini N. Shoaei Parchin 《International Journal of Environmental Science and Technology》2017,14(6):1197-1208
Applying biodegradable polymers in membrane preparation for separation processes is expected to be helpful in solving waste disposal problem. In this study, biodegradable blend membranes of cellulose acetate (CA)/poly(butylene succinate) (PBS) were prepared and the microorganisms possessing the ability of degrading them were isolated from soil. The isolates were classified into two groups of bacteria and fungi. The membranes biodegradation after cultivation by the isolates in liquid media was further confirmed by weight loss measurement, Fourier transform infrared analysis and scanning electron microscopy. Findings revealed that CA degradation could be improved in the blend membrane structure. Moreover, strain BG106 and BG111 could degrade the membranes at the fastest rate among the other bacteria and fungi, respectively. To our knowledge, BG111 was found to belong to Alternaria sp. and this is the first report of its PBS degradation activity. Moreover, the PBS degradability of BG104 (B. Safensis), BG105 (Achromobacter insuavis) and BG106 (Brevibacterium halotolerans) strains was reported for the first time. 相似文献
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Ore grade is the most important source of uncertainty in a mining operation which plays an important role to classify run-of-mine (ROM) material into ore and waste parcels. As a widely used method, kriging estimator is used to estimate the grade of ore blocks. In conventional mining practices, if the estimated grade of a parcel is above the cut-off grade, this parcel is classified as ore, otherwise, is labelled as a waste parcel. An alternative approach is to simultaneously consider the grade of parcels and the economic consequences of sending parcels to destinations by applying simulation-based methods. In this study, kriging and simulation-based methods including loss and profit functions are applied on a real-world case study to classify ore/waste material based on the initial exploration data. Then, the actual known data, collected from blast holes samples, are compared with the estimated results in order to validate the performance of the presented methods. Outcomes show that simulation-based methods can perform better and show more adjustability with real data. 相似文献
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This study presents single‐objective and multi‐objective particle swarm optimization (PSO) algorithms for automatic calibration of Hydrologic Engineering Center‐ Hydrologic Modeling Systems rainfall‐runoff model of Tamar Sub‐basin of Gorganroud River Basin in north of Iran. Three flood events were used for calibration and one for verification. Four performance criteria (objective functions) were considered in multi‐objective calibration where different combinations of objective functions were examined. For comparison purposes, a fuzzy set‐based approach was used to determine the best compromise solutions from the Pareto fronts obtained by multi‐objective PSO. The candidate parameter sets determined from different single‐objective and multi‐objective calibration scenarios were tested against the fourth event in the verification stage, where the initial abstraction parameters were recalibrated. A step‐by‐step screening procedure was used in this stage while evaluating and comparing the candidate parameter sets, which resulted in a few promising sets that performed well with respect to at least three of four performance criteria. The promising sets were all from the multi‐objective calibration scenarios which revealed the outperformance of the multi‐objective calibration on the single‐objective one. However, the results indicated that an increase of the number of objective functions did not necessarily lead to a better performance as the results of bi‐objective function calibration with a proper combination of objective functions performed as satisfactorily as those of triple‐objective function calibration. This is important because handling multi‐objective optimization with an increased number of objective functions is challenging especially from a computational point of view. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Water flow is greatly influenced by the characteristics of the domain through which the process occurs. It is generally accepted that earth materials have extreme variations from point to point in space. Consequently, this heterogeneity results in high variation in hydraulic properties of soil. In order to develop an accurate predictive model for transport processes in soil, the effects of this variability should be considered. In this study a two‐dimensional stochastic finite element flow model was developed for simulation of water flow through unsaturated soils. In this model, the stochastic partial differential governing equation of water flow, obtained from implementation of the perturbation‐spectral stochastic method on classical Richard's equation, was solved using a finite element method in the space domain and a finite difference scheme in the time domain. The effective hydrological parameters embedded in the mathematical model depend on time derivatives of capillary tension head; this makes possible to consider the hysteresis due to large‐scale variability of soil hydrological properties. The model is also capable of simulating infiltration and evaporation events and rapid change in the land surface boundary condition from one type event to another, based on a scheme used in the model for implementation of land surface boundary condition. The model was validated with the data obtained from a layered lysimeter test. The model was also used to simulate water flow under a long irrigation furrow. The results obtained with this model show better agreement with experimental measurements in comparison with a deterministic model. The possible reason for this agreement is that in the developed model, the influence of the variability of the properties of soil and effects of parameter hysteresis on water flow and water content redistribution are considered. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Ali Kafaei Mohammadnejad Seyyed Mohammad Mousavi Mohammad Torabi Mehdi Mousavi Amir Hossein Alavi 《Environmental Earth Sciences》2012,67(1):53-70
This study presents new attenuation models for the estimation of peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD) using a hybrid method coupling genetic programming and simulated annealing, called GP/SA. The PGA, PGV, and PGD were formulated in terms of earthquake magnitude, earthquake source to site distance, average shear-wave velocity, and faulting mechanisms. A worldwide database of strong ground motions released by Pacific Earthquake Engineering Research Center (PEER) was employed to establish the models. A traditional genetic programming analysis was performed to benchmark the proposed models. For more validity verification, the GP/SA models were employed to predict the ground-motion parameters of the Iranian plateau earthquakes. Sensitivity and parametric analyses were carried out and discussed. The results show that the GP/SA attenuation models can offer precise and efficient solutions for the prediction of estimates of the peak time-domain characteristics of strong ground motions. The performance of the proposed models is better than or comparable with the attenuation relationships found in the literature. 相似文献
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A total of 163 free-field acceleration time histories recorded at epicentral distances of up to 200 km from 32 earthquakes with moment magnitudes ranging from M w 4.9 to 7.4 have been used to investigate the predictive capabilities of the local, regional, and next generation attenuation (NGA) ground-motion prediction equations and determine their applicability for northern Iran. Two different statistical approaches, namely the likelihood method (LH) of Scherbaum et al. (Bull Seismol Soc Am 94:341–348, 2004) and the average log-likelihood method (LLH) of Scherbaum et al. (Bull Seismol Soc Am 99:3234–3247, 2009), have been applied for evaluation of these models. The best-fitting models (considering both the LH and LLH results) over the entire frequency range of interest are those of Ghasemi et al. (Seismol 13:499–515, 2009a) and Soghrat et al. (Geophys J Int 188:645–679, 2012) among the local models, Abrahamson and Silva (Earthq Spectra 24:67–97, 2008) and Chiou and Youngs (Earthq Spectra 24:173–215, 2008) among the NGA models, and finally Akkar and Bommer (Seism Res Lett 81:195–206, 2010) among the regional models. 相似文献