Among numerous offshore structures used in oil extraction, jacket platforms are still the most favorable ones in shallow waters. In such structures, log piles are used to pin the substructure of the ...platform to the seabed. The pile＇s geometrical and geotechnical properties are considered as the main parameters in designing these structures. In this study, ANSYS was used as the FE modeling software to study the geometrical and geotechnical properties of the offshore piles and their effects on supporting jacket platforms. For this purpose, the FE analysis has been done to provide the preliminary data for the fuzzy-logic post-process. The resulting data were implemented to create Fuzzy Inference System （FIS） classifications. The resultant data of the sensitivity analysis suggested that the orientation degree is the main factor in the pile＇s geometrical behavior because piles which had the optimal operational degree of about 5° arc more sustained. Finally, the results showed that the related fuzzified data supported the FE model and provided an insight for extended offshore pile designs.
Tropical cyclones may be destructive in the coastal region, such as the Gonu tropical cyclone, which affected the Arabian Peninsula and parts of southern Iran in 2007. In this study, a coupled MIKE ...21/3 HD/SW (hydrodynamic/spectral wave) model was used to simulate the inland flooding inside the Sur port during the Gonu tropical cyclone. The MIKE 21 Cyclone Wind Generation (CWG) tool was utilized to generate the cyclone’s wind and pressure field. The required input data were obtained from the International Best Track Archive for Climate Stewardship (IBTrACS) and imported into the CWG tool. In this study, the wind and pressure fields were compared between the analytical vortex model and European Centre for Medium-Range Weather Forecasts (ECMWF) data during the Gonu cyclone passage. Moreover, by developing a new model, artificial Mangroves’ effect on inland flooding was investigated. The results show that, contrary to the ECMWF data, the analytical vortex models well captured the storm event’s wind and pressure field. Furthermore, the flood hazard is calculated based on the inundation depth, flow velocity, and area’s vulnerability. The flood hazard map shows that 5% of the coast is at high-risk, 49% is at medium-risk, and 46% is at low-risk class in the Sur port. By applying Mangroves as flood risk reduction, the high-risk area is almost completely removed. However, medium and low-risk zones increase by 50% and 50%, respectively. This information could be helpful in disaster risk reduction and coastal management in the future.
A simple dynamic model of an offshore jacket platform is developed based on the scaled hydro-elastic model of the jacket to estimate the dynamic response of the system. The finite element model of ...the platform is updated numerically by using the experimental modal analysis (EMA) results. Dynamic characteristics of the improved simple dynamic model (SPM) and idealized model are specified based on updated model properties. The effects of the experimental test are studied to investigate the dynamic response of a scaled model of an offshore jacket platform through the SPM and idealized models. Seismic response of the jacket platform is studied by using the idealized model under an earthquake acceleration. The effects of marine growth and the corrosion are considered within the calculation process by considering the jacket mass and stiffness variation. The developed SPM and idealized model provide a feasible and effective approach for evaluating the dynamic response of the offshore jacket platform. The results indicate the importance of the experimental studies in validating the numerical results and reducing the uncertainties for the fixed marine structures.
Abstract
The discrepancy between the theoretical and experimental results is defined as one of the main reasons for updating the analytical models of the structures based on experimental data sets. ...Although various updating methods have been proposed in the literature, the capability of the approaches on controlled systems is yet to be investigated. In this paper, a numerical model updating method is proposed considering both parametric and structural uncertainties on a passive controlled complex structural system. The method is applied on a three-dimensional offshore jacket platform model including an attached Tuned Liquid Column Gas Damper (TLCGD) damping system. The effect of the damper parameters on updating the numerical model is investigated for the first time using a Laser Doppler Vibrometer (LDV) as a non-contact measuring system. The maximum decrement is occurred using a sine function which seems to be because of the sinusoidal nature of the experimental data. According to the results, the discrepancy between the numerical and experimental data can be decreased by 75 percent utilizing non-contact measurements and discrepancy functions. The results also indicate that by calibrating the gas pressure and the total liquid column length of the TLCGD damping system, as the most important parameters of the damper, the discrepancy is decreased almost 66 percent. The proposed method of updating the FE model for the controlled systems is beneficial for the old sophisticated controlled practical systems that increasing their life time span is essential.
•The capability of a model updating approach is investigated on a controlled system.•The updating method is proposed considering both parametric and structural uncertainties.•The efficiency of the method is studied using a non-contact measuring system.•Based on the results the highest decrement is occurred as the most important parameters of the damper are taken into account in the tenth scenario.•Calibration of the gas pressure and the total liquid column length of the TLCGD have significant roles in updating the controlled system.
Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local ...erosion. In this study, we investigate the flow patterns around refractive and right-angle groins. In particular, we analytically compare the flow characteristics around a refractive groin and study the degree of accuracy that can be achieved by using a right-angle groin of various projected lengths. To compare the flow characteristics, we replaced the right-angle groin with an approximation of a refractive groin. This replacement had the least effect on the maximum velocity of flow in the channel. Moreover, we investigated the distribution of the density variables of temperature and salinity, and their effects on the flow characteristics around the right-angle groin. A comparison of the flow analysis results in baroclinic and barotropic conditions reveals that the flow characteristic values are very similar for both the refractive and right-angle groins. The geometry of the groin, i.e., right-angle or refractive, has little effect on the maximum speed to relative average speed. Apart from the angular separation, the arm length of the groin in downstream refractive groins has less effect on other flow characteristics than do upstream refractive groins. We also correlated a number of non-dimensional variables with respect to various flow characteristics and groin geometry. These comparisons indicate that the correlation between the thalweg height and width of the channel and groin arm＇s length to projection length have been approximated using linear and nonlinear formulas regardless of inner velocity in the subcritical flow.
Structural vibration is one of the main engineering concerns in recent decades especially in offshore structures due to the dynamic environment and accessibility. Among different methods, applying a ...device within the primary system for mitigating the vibration through system damping increment is one of the most promising methods. In this study, a combined novel Magneto-Rheological Tuned Liquid Column Gas Damper (MR-TLCGD) as a damping system is introduced for the first time in structural control field and the efficiency of the system is investigated on a three dimensional fixed offshore jacket platform under both wave and earthquake excitation. The performance of the system is studied through considering different values of yield stress and gas pressure as of the main parameters of MR fluid and gas damper. The results are compared to a previously studied Tuned Liquid Column Gas Damper (TLCGD) system. Based on the results, utilizing an MR-TLCGD system in an offshore structure can be defined as a proper choice for reducing structural vibration. It can be concluded that considering an appropriate value for yield stress and gas pressure, regardless of the results limitation for this case study, is of great importance in practical cases.
•A combined novel Magneto-Rheological Tuned Liquid Column Gas Damper (MR-TLCGD) damping system is introduced for the first time.•The efficiency of the damping system, MR fluid's yield stress and gas pressure are investigated under wave and earthquake incidence.•Utilizing an MR-TLCGD in an offshore platform causes more reduction in structural vibration in comparison with TLCGD damping system.•Considering an appropriate value is of great importance for both yield stress and gas pressure values.
A non-destructive method is proposed in this study for damage detection of a composite panel using random decrement (RD) signature technique and artificial neural network (ANN) algorithm. For this ...purpose, a 10-layer rectangular composite panel is built and the experimental test is carried out employing contact and non-contact sensing equipment to capture the vibration characteristics of the system. The experimental scenarios are defined using both intact and damaged models in two pinned and fixed supporting condition. The free damping response of the structure is extracted by RD method and employed for training the ANN neurons. The proposed ANN-RDT method is compared with the multimode random decrement technique (MRDT) and analytical mode decomposition- random decrement technique (AMD-RDT) method in damage detection process considering two error indexes. It is shown that the present method performs better than the MRDT and AMD-RDT. According to the results, the proposed approach is shown to be effective for diagnosing the presence of damage in both specified supporting systems. The trained algorithm performed more successful in the scenarios with pinned conditions with a damage closer to the supports. As indicated, the efficiency of the method is highly sensitive to location of the damage and sensors along with the type of the support. The experimental non-contact data is also shown to be significantly beneficial to utilize a simpler linear equation and also to gain the system dynamic characteristics.
Structural integrity monitoring of jacket structures is an attractive challenge faced by researchers worldwide. Because of numerous uncertainties in marine environments, using statistical methods to ...reduce the detrimental impacts of uncertainties on model updating and damage detection results are unavoidable. In this study, a new Bayesian model updating framework is proposed using incomplete Frequency Response Function (FRF) data. In this methodology, the incomplete measurements issue is not dealt with the model reduction or data expansion method and the number of data in the objective function is increased using FRF at different excitation frequencies. The experimental verification of a scale 2D fixed platform is implemented to reveal the validity of the proposed methodology. Several numerical damage scenarios are simulated to investigate the effect of noisy data, FE model uncertainties, incomplete measurement, and added mass in the damage detection procedure. According to the results, the introduced method is entirely successful in the model updating and damage detection of the jacket platform. The results also indicate the lower effects of uncertainties and noise levels in damage detection outcomes.
•A new model updating and damage detection Bayesian framework using the incomplete noisy data was proposed.•The model reduction or data expansion methods do not need to solve the incomplete measurement problems.•The Bayesian method was used for the damage identification of the marine structures for the first time.•The experimental verification of a scaled 2D fixed platform was operated to validate the proposed methodology.•The effects of noisy data, FE model uncertainties, incomplete measurement and added mass on the results were investigated.
A developed tuned liquid multiple columns gas damper, introduced as a TLMCGD damper, is proposed in this study and its capability is assessed on an offshore jacket platform under regular and ...irregular waves and also earthquake incidence. The proposed damping system includes a combination of performance of both tuned liquid multiple columns damper (TLMCD) and tuned liquid column gas damper (TLCGD). The number of multiple columns and gas pressure are defined as of the main parameters of the damper and their performance are investigated through various values under earthquake. According to the results, a passive optimum TLMCGD system can decrease the structural response of the system up to 22, 60, and 55 percent under regular wave, irregular wave, and earthquake, respectively. The whole structural response of the system reduces as the number of columns and the value of gas pressure increases up to a certain amount. To investigate the effectiveness of gas pressure in performance of the damper, various gas pressure values are considered for different 4 to 10-column TLMCGD dampers. By increasing the value of the gas, the displacement RMS reduces significantly. The highest decrement occurs as 50 to 100 bar gas pressure is specified for the gas springs of the dampers. Still more investigation is required to evaluate other key parameter of the system within an experimental study which is left for future studies.
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