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11.
Soil-Structure Interaction Analysis of Jack-up Platforms Subjected to
Monochrome and Irregular Waves
As jack-up platforms have recently been used in deeper and harsher waters, there has been an increasing demand to understand their behaviour more accurately to develop more sophisticated analysis techniques. One of the areas of significant development has been the modelling of spudcan performance, where the load-displacement behaviour of the foundation is required to be included in any numerical model of the structure. In this study, beam on nonlinear winkler foundation (BNWF) modeling—which is based on using nonlinear springs and dampers instead of a continuum soil media—is employed for this purpose. A regular monochrome design wave and an irregular wave representing a design sea state are applied to the platform as lateral loading. By using the BNWF model and assuming a granular soil under spudcans, properties such as soil nonlinear behaviour near the structure, contact phenomena at the interface of soil and spudcan (such as uplifting and rocking), and geometrical nonlinear behaviour of the structure are studied. Results of this study show that inelastic behaviour of the soil causes an increase in the lateral displacement at the hull elevation and permanent unequal settlement in soil below the spudcans, which are increased by decreasing the friction angle of the sandy soil. In fact, spudcans and the underlying soil cause a relative fixity at the platform support, which changes the dynamic response of the structure compared with the case where the structure is assumed to have a fixed support or pinned support. For simulating this behaviour without explicit modelling of soil-structure interaction (SSI), moment-rotation curves at the end of platform legs, which are dependent on foundation dimensions and soil characteristics, are obtained. These curves can be used in a simplified model of the platform for considering the relative fixity at the soil-foundation interface. 相似文献
12.
The design and planning of soil vapor sampling for vapor intrusion assessment require an estimate of the time for vapor migration from the contamination source to reach steady state prior to vapor sampling and analysis for volatile organic compounds (VOCs). This study presents the model derivation, analytical solutions, as well as the assumptions and limitations of a one-dimensional VOC vapor transport model based on diffusion in porous media and equilibrium partitioning of VOCs in solid, aqueous, and vapor phases. The model assumes a finite domain with boundary conditions that represent the scenarios of vapor migration in the real environment. The derivation of the conceptual model is presented along with its practical use and implications as illustrated through case examples. Consideration of the upper (or exit) boundary condition along with the distance between the source and the applicable boundary, rather than the distance from the source to the measurement point, are shown to be critical in the time estimates as compared to an expression typically used and cited in guidance documents. The study reveals the importance of defining a conceptual model and relevant boundaries in assessing near steady state conditions, and suggests a tiered approach in refining the estimate with increasing level of effort for practical applications in vapor assessment. 相似文献
13.
Parisa?Almasi Saeid?SoltaniEmail author 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(5):1171-1182
The present study attempts to investigate potential impacts of climate change on floods frequency in Bazoft Basin which is located in central part of Iran. A combination of four general circulation models is used through a weighting approach to assess uncertainty in the climate projections. LARS-WG model is applied to downscale large scale atmospheric data to local stations. The resulting data is in turn used as input of the hydrological model Water and Energy Transfer between Soil, plants and atmosphere (WetSpa) to simulate runoff for present (1971–2000), near future (2020–2049) and far future (2071–2100) conditions. Results demonstrate good performance of both WetSpa and LARS-WG models. In addition in this paper instantaneous peak flow (IPF) is estimated using some empirical equations including Fuller, Sangal and Fill–Steiner methods. Comparison of estimated and observed IPF shows that Fill–Steiner is better than other methods. Then different probability distribution functions are fit to IPF series. Results of flood frequency analysis indicate that Pearson III is the best distribution fitted to IPF data. It is also indicated that flood magnitude will decrease in future for all return periods. 相似文献
14.
The complex stream bank profiles in alluvial channels and rivers that are formed after reaching equilibrium has been a popular topic of research for many geomorphologists and river engineers. The entropy theory has recently been successfully applied to this problem. However, the existing methods restrict the further application of the entropy parameter to determine the cross-section slope of the river banks. To solve this limitation, we introduce a novel approach in the extraction of the equation based on the calculation of the entropy parameter (λ) and the transverse slope of the bank profile at threshold channel conditions. The effects of different hydraulic and geometric parameters are evaluated on a variation of the entropy parameter. Sensitivity analysis on the parameters affecting the entropy parameter shows that the most effective parameter on the λ-slope multiplier is the maximum slope of the bank profile and the dimensionless lateral distance of the river banks. 相似文献
15.
Parisa Sarzaeim Omid Bozorg-Haddad Elahe Fallah-Mehdipour Hugo A. Loáiciga 《Environmental Earth Sciences》2017,76(14):498
Iran is a developing country with arid and semiarid regions. Poor management of water resources combined with the effects of climate change is leading to the drying of several rivers and wetlands. Several planned water development projects, primarily for agricultural expansion, will be implemented in the coming years which could worsen impacts on vulnerable aquatic ecosystems. Proper water resources management is essential to meet present and future residential, environmental, industrial, and agricultural demands in semiarid regions. This paper presents projections of how the availability of water resources will change in the Karkheh river basin of Iran for the period 2010–2059 employing sustainability criteria in the form of time-based reliability, volumetric reliability, resiliency, and vulnerability. This paper’s results show that consideration of environmental receptors as a stakeholder of water use places limitations on agricultural development within the Karkheh river basin. 相似文献
16.
Natural Hazards - Climate change is currently one of the most important environmental issues. Dendrochronology is frequently used to identify the climatic changes most closely associated with... 相似文献
17.
Shear wave splitting is a well-known method for indication of orientation, radius, and length of fractures in subsurface layers. In this paper, a three component near offset VSP data acquired from a fractured sandstone reservoir in southern part of Iran was used to analyse shear wave splitting and frequency-dependent anisotropy assessment. Polarization angle obtained by performing rotation on radial and transverse components of VSP data was used to determine the direction of polarization of fast shear wave which corresponds to direction of fractures. It was shown that correct implementation of shear wave splitting analysis can be used for determination of fracture direction. During frequencydependent anisotropy analysis, it was found that the time delays in shearwaves decrease as the frequency increases. It was clearly demonstrated throughout this study that anisotropy may have an inverse relationship with frequency. The analysis presented in this paper complements the studied conducted by other researchers in this field of research. 相似文献
18.
Bahi Jalili Seh‐Bardan Radziah Othman Samsuri Abd Wahid Fardin Sadegh‐Zadeh Aminudin Husin 《洁净——土壤、空气、水》2013,41(4):356-364
Leachate derived from bioleaching process contains high amount of metals that must be removed before discharging the water. Aspergillus fumigatus was isolated from a gold mine tailings and its ability to remove of As, Fe, Mn, Pb, and Zn from aqueous solutions and leachate of bioleaching processes was assessed. Batch sorption experiments were carried out to characterize the capability of fungal biomass (FB) and iron coated fungal biomass (ICFB) to remove metal ions in single and multi‐solute systems. The maximum sorption capacity of FB for As(III), As(V), Fe, Mn, Pb, and Zn were 11.2, 8.57, 94.33, 53.47, 43.66, and 70.4 mg/g, respectively, at pH 6. For ICFB, these values were 88.5, 81.3, 98.03, 66.2, 50.25, and 74.07 mg/g. Results showed that only ICFB was found to be more effective in removing metal ions from the leachate. The amount of adsorbed metals from the leachate was 2.88, 21.20, 1.91, 0.1, and 0.08 mg/g for As, Fe, Mn, Zn, and Pb, respectively. The FT‐IR analysis showed involvement of the functional groups of the FB in the metal ions sorption. Scanning electron microscopy revealed that surface morphological changed following metal ions adsorption. The study showed that the indigenous fungus A. fumigatus was able to remove As, Fe, Mn, Pb, and Zn from the leachate of gold mine tailings and therefore the potential for removing metal ions from metal‐bearing leachate. 相似文献
19.
Measurement of compressional, shear, and Stoneley wave velocities, carried out by dipole sonic imager (DSI) logs, provides
invaluable data in geophysical interpretation, geomechanical studies and hydrocarbon reservoir characterization. The presented
study proposes an improved methodology for making a quantitative formulation between conventional well logs and sonic wave
velocities. First, sonic wave velocities were predicted from conventional well logs using artificial neural network, fuzzy
logic, and neuro-fuzzy algorithms. Subsequently, a committee machine with intelligent systems was constructed by virtue of
hybrid genetic algorithm-pattern search technique while outputs of artificial neural network, fuzzy logic and neuro-fuzzy
models were used as inputs of the committee machine. It is capable of improving the accuracy of final prediction through integrating
the outputs of aforementioned intelligent systems. The hybrid genetic algorithm-pattern search tool, embodied in the structure
of committee machine, assigns a weight factor to each individual intelligent system, indicating its involvement in overall
prediction of DSI parameters. This methodology was implemented in Asmari formation, which is the major carbonate reservoir
rock of Iranian oil field. A group of 1,640 data points was used to construct the intelligent model, and a group of 800 data
points was employed to assess the reliability of the proposed model. The results showed that the committee machine with intelligent
systems performed more effectively compared with individual intelligent systems performing alone. 相似文献
20.
Shear wave velocity is a critical physical property of rock, which provides significant data for geomechanical and geophysical studies. This study proposes a multi-step strategy to construct a model estimating shear wave velocity from conventional well log data. During the first stage, three correlation structures, including power law, exponential, and trigonometric were designed to formulate conventional well log data into shear wave velocity. Then, a Genetic Algorithm-Pattern Search tool was used to find the optimal coefficients of these correlations. Due to the different natures of these correlations, they might overestimate/underestimate in some regions relative to each other. Therefore, a neuro-fuzzy algorithm is employed to combine results of intelligently derived formulas. Neuro-fuzzy technique can compensate the effect of overestimation/underestimation to some extent, through the use of fuzzy rules. One set of data points was used for constructing the model and another set of unseen data points was employed to assess the reliability of the propounded model. Results have shown that the hybrid genetic algorithm-pattern search technique is a robust tool for finding the most appropriate form of correlations, which are meant to estimate shear wave velocity. Furthermore, neuro-fuzzy combination of derived correlations was capable of improving the accuracy of the final prediction significantly. 相似文献