mohammadjavad ketabdari

The passage of personnel and the placement of facilities on the access stairs of offshore complexes have made it very important to identify damage to these components. The modal strain energy method is one of the non-destructive and practical methods that uses changes in the dynamic properties of the structure to identify the location and determine the severity of damage in the structure. In recent years, modifications have been made to the initial version of this method, one of which is to consider the natural frequencies in locating the damage. In this paper, using the improved modal strain energy method and considering natural frequencies, a new relationship is presented to more accurately identify the location of damage in the structure, and three different damage indices in the offshore platform access bridge structure are studied and compared. The results show that the average error to accurately identify the location of damage in the average Stubbs index, the improved method and the novel method are 3.55, 2.82, and 2.21 percent, respectively, so the novel method can more accurately identify the location of damage in the structure. Also, comparing the results of different cases shows that the average damage location error decreases with increasing damage severity. The accuracy of identifying the location of the damage also increases when moving away from the supports.

Reinforcement of cement-based matrix composites with TRM and FRCM fibers have been utilized to improve the behavioral performance of reinforced concrete beams subjected to destruction in the past decades. Reinforcement and strengthening of the structural surfaces requires the use of fibers and mortar to link between them. The complexity of the interfaces between the fibers and matrix does not allow a simple and accurate model. This research created a numerical analysis approach based on the measuring and evaluating of the strength capabilities of two TRM and FRCM composites under the influence of bending stress conditions in terms of strengthening the external surfaces of the structure. In this regard, six sections of reinforced concrete beams with FLAT, STRIP and U-shaped patterns reinforced by TRM and FRCM composites under three-point loading and one beam were considered as reference. For this purpose, the impact of the link mechanism and bending moment, ultimate load capacity, energy absorption and dissipation, elastic stiffness and finally using the β reduction factor, the ultimate moment and yield stress were calculated by Abaqus software. According to behavioral results, reinforced sections with different FRCM composite patterns exhibit about 18% better performance than TRM composite.

Investigating and understanding sedimentation and erosion regimes on the coast, especially in maritime construction such as port complexes, is one of the most important processes in coastal and offshore engineering. According to empirical evidence, unfortunately most of Iran's southern and northern coasts have lost their initial and anticipated performance due to lack of attention to sedimentation problems at the design stage. Accordingly, identifying the most effective variables affecting the amount of sedimentation in the canal and relaxation pool will be of great importance. One of the specialized and specialized studies to predict the proper deposition of port areas is the use of numerical methods that can provide a proper prediction of future port conditions. In this article, the status of the port of Astara was investigated in terms of flow and sediment using the numerical model of Mike. Modeling results showed that the port is in dire straits in terms of sedimentary status and many sediments accumulate in the inlet opening of the wave, which reduces the performance of the port due to traffic in different capacities. Further studies have shown that in order to solve this problem, the port requires dredging in 5 years period. On the other hand, this dredging imposes heavy costs on the port. Therefore, given the high amount of sedimentation and disorder, it can be considered to reduce the deposition of a development phase in the surf arm.

Foroozan platform is one of the most important Iranian offshore facilities lies along the border of Iran and Saudi Arabia. As time passes by, the possibility of presence of some damage in the structural members of this platform increases. As a consequence of these damages, the operation of the platform may be disrupted and if the damage grows, especially in sensitive areas such as deck, joints or splash zone that are prone to failure, cause more damage in the future. This highlights the necessity of structural health monitoring of this platform. One of the most common structural health monitoring techniques is the modal strain energy-based damage index which is known as Stubbs index. In recent years, modifications have been made to original version of this index, one of which is to consider the natural frequencies in determining the location of damage. In this paper, using the improved modal strain energy method and considering the natural frequencies in determining the location of damage, the location and severity of damage in the Foroozan platform have been identified. One of the differences between this study and similar studies is the large number of elements of this real platform. The results showed that the improved method has a higher accuracy in locating the damage than the original method (Stubbs index). Also, single and multiple damages, with low and high intensity, were predicted with appropriate accuracy by this method.

Deck-pile pier structural system is one of the most common types of pier construction systems. Corrosion, ship collisions and huge storms cause general and extreme damages, especially in the deck and the splash zone of the wharf. If the location and severity of the damage is known at the early stages of the damage, they can be repaired as soon as possible. One of the available methods for identifying damage in structures, which is based on the changes in the dynamic properties of the structure, is the modal strain energy method. In recent years, modifications have been made to the original version of this method, the Stubbs index, one of which is the consideration of natural frequencies in locating the damage, known as the improved modal strain energy method. In the present study, using both Stubbs index method and improved method, an experimental and numerical study is performed to identify the location and determine the severity of damage in the members located in the deck and splash zone in a real LPG export deck- pile pier (pier number Fourteen) located in the port of Pars-Assaluyeh, in Persian Gulf. The results showed that the improved method has higher accuracy in locating the damage than the Stubbs index method. Also, single and multiple damage, with low and high severity, were predicted with appropriate accuracy by this method.

A set of second-order differential equations (the initial value problem) is used to analyze the vibrations of structures. This method is based on changing the second-order differential equations to the eigenvalue problem, which is usually used for modal analysis of structures. This problem involves a matrix equation with mass and stiffness as coefficient matrices. Changes in some stiffness matrix arrays change eigenvalues ​​and eigenvectors, and changes in stiffness matrices indicate damage to one or more structural members. Therefore, identifying modified arrays is very useful for monitoring the health of structures. Modified stiffness array arrays can be obtained by comparing new eigenvalues ​​and eigenvectors with old ones. The Stubbs Index (Modal Strain Energy) Stubbs (MSE) uses only special vectors to identify injuries. In the improved modal strain energy method (IMSE) proposed by Lee et al., In addition to special vectors, special values ​​are also entered in relation to the damage index. In this research, a new injury index is presented with the development of the above two indicators, which show more accurate results than them. In this study, the health monitoring of a template platform structure of Forouzan Persian Gulf oil field is compared to compare the accuracy of these three indicators. The results show that the new method is more accurate than the Stubbs and IMSE indices, especially in the presence of multiple injuries.

As one of the most important components of an offshore oil and gas complex, Catwalk (access bridge) provides support for equipment and act as a passage for staff. Therefore, any damage in this structure may result in casualties as well as financial and environmental losses. Hence, identifying the location and severity of damage in these structures is of a great importance. As a common SHM method, modal strain energy uses the changes in the dynamic properties of the structure for identifying the damage location and severity. Considering natural frequencies in the process of the damage localization is one of modifications that has been successfully applied to this method. In order to show the robustness of this method for identifying damages in real class offshore structures with a large number of elements, the improved modal strain energy (IMSE) method is applied for damage localization and quantification in the access bridge of Foroozan platform in the Persian Gulf. The results showed that the IMSE damage index is more accurate than the original Stubbs index. Both the single and multiple damages were predicted with a good accuracy with this method. However, the method was more accurate in locating the damages in horizontal elements as well as the elements far from the supports of the structure.

In this paper, a linear Lagrangian numerical model is used for simulating the solitary wave propagation over the sloped sea wall, as well as the regular wave propagation over an Impermeable submerged breakwater, called the relatively compact (GCM) hydrodynamic model of relatively compact particles (WCSPH). To simulate fluid turbulence, the SPS turbulence model, which was obtained by large eddy simulation (LES) approach, was used. The results of numerical simulations were compared with laboratory experiments. Also, the results of present numerical model were compared with the numerical model Shen et al. (2004). The results shown, the WCSPH computations produce better results than those of model Shen et al. (2004), with respect to the experimental data. The results of this study show that WCSPH method provides a useful tool to investigate the wave propagation over coastal structures.

Four-leg jacket is one of the most widely used offshore structures that is exposed to various damages during its service life. Unlike land structures, offshore structures are always exposed to waves, corrosion and damages, especially in the splash zone. At shallow to intermediate water depths, these structures are commonly used as the substructure of offshore wind turbines.  Passing their service life has made the structural health monitoring of offshore wind turbines necessary. In this research, a modified modal strain energy method is used for damage detection in deck and splash zone members which are more exposed to periodic loads of waves and high corrosive seawater than other members. The results showed the higher accuracy of the improved modal strain energy method compared to the original method (Stubbs index). Also, using improved method resulted in prediction of single and multiple damages, with low and high intensities with appropriate accuracy.

The echo reduction of an underwater vessel is one of the major concerns of its concealing problem. Recently, using scatterers in the doubly periodic distribution has attracted enormous interest. This is because of their relatively good performance and the ability to tune in the effective frequency range. In this study, a model of an acoustic echo reducing coating with internal scatterer cavities is considered. Subsequently, the major parameters that affected the acoustical performance of the layer, such as the size, the number and the location of cavities along with the thickness, for two types of spherical and cylindrical cavity geometries, were analyzed and presented. The results showed that in the layer, the larger the cavity size, the greater the echo reduction effect. Regarding the lattice constants, considering the smaller one, decays the echo reduction. However, will increase transmission loss. Also, the location of the cavity, if close to the wave entry plane, demonstrates a better echo reduction effect.

Sea keeping is vital for a floating platform as they are exposed to wave wind and marine current forces. . Therefore, in the event of damage to one or more moorings, other moorings may expose to dame too. As a consequence, analyzing the damaged mooring is of particular importance. In this paper, the effects of different layouts of damaged lines, as well as the effects of these occurrences on the hydrodynamic response of the SPAR platform are numerically investigated. The full scale of the regular wave and time-domain analysis using diffraction theory, is the conditions in the present study. In this research, modeling was carried out on a truss platform spar, which was recently installed in Kikeh oilfield on the coast of Malaysia. The validation of the model is based on the results obtained from the experimental model as well as a valid numerical code in MATLAB software. The results revealed the existence of a good agreement. In the following, numerical analysis of the different configurations of the mooring system and the damaged mooring conditions were performed. The results show that the effects of different configurations in intact mooring system states on dynamic motions of the spar platform are not significant. However, the effect of the damaged mooring lines demonstrates itself as an increase to the mean position of the platform, which was discussed in this paper.

Abnormal waves are extremely large and unusual which rarely occur, but cause serious damages. Various factors such as extreme storms, particular topography of the seabed, marine currents, wave-wave interaction with different wavelengths and frequencies may cause wave occurrence and transformation. The main objective of this study is to propose a new hybrid approach to predict the occurrence of abnormal waves using wavelet transform and support vector machines (SVM) classifier based on meteorological data. The data sets used in this paper are from two major hurricanes Dean 2007 and Irene 2011 at four locations namely, 41004 and41041 in the Gulf of Mexico. To predict the occurrence of abnormal waves, at the first extreme waves are detected using wavelet transform. The outputs of this method are considered as SVM classifier targets. Wavelet transform is applied on the significant wave height data samples. The abnormal waves are readily identified from the wavelet spectrum as an area of high energy. The inputs of SVM classifier models are historical metrological data, including: Wind direction (WDIR), Wind speed (WSPD), Sea level pressure (PRES), Air temperature (ATMP), and Sea surface temperature (WTMP). The experiment results show that the proposed method is able to predict the occurrence of extreme wave heights with height accuracy.

The absorption performance of anechoic coatings depends on the material properties, layer thicknesses and cavity distribution density and cavity size. In this paper a design method based on numerical simulation was presented by combining FEM and acoustic duct method (ADM). Analyzing of anechoic coatings was performed under active sonar impinging plane wave by normal incident angle. In this approach considering a unit cell of anechoic coating and two ducts of the fluid on its both sides, the reflection characteristics, transmission and reflection coefficients of anechoic coating were calculated using acoustic duct theory. Validation was performed by comparing the results of simulation with the available experimental data. Also a design code in ANSYS software was developed.
Finally using this code and the proposed model, the acoustical behavior of anechoic coatings was investigated. The results show that sound transmission coefficient for coating with cylindrical cavity is larger than that of spherical cavity. Furthermore unlike the transmission coefficient, for all frequencies upper than 1500 Hz, coating with cylindrical cavity has a greater echo reduction and therefore its anechoic performance is better than that of spherical cavity.

Coastal erosion has always been a serious problem in shorelines, which causes heavy damage to coastlines and public properties around the world. Rapid and uncontrolled coastal developments were started to prevent the exacerbation of erosion hazards. However in turn they have had a damaging impact on coastal ecosystems. The current study presents a comparative environmental impact assessment of two protective alternatives in coastal and shoreline structures, including traditional rubble system and a more novel one called geotube system. A case study of two breakwater structures in Bushehr and Qeshm in the south of Iran was performed and beneficial aspects of geotube system were identified.Coastal erosion has always been a serious problem in shorelines, which causes heavy damage to coastlines and public properties around the world. Rapid and uncontrolled coastal developments were started to prevent the exacerbation of erosion hazards. However in turn they have had a damaging impact on coastal ecosystems. The current study presents a comparative environmental impact assessment of two protective alternatives in coastal and shoreline structures, including traditional rubble system and a more novel one called geotube system. A case study of two breakwater structures in Bushehr and Qeshm in the south of Iran was performed and beneficial aspects of geotube system were identified.

Submerged breakwaters are a special type of breakwater associated with low wave reflection. They can also save large quantities of engineering resources from the view of economics. Although there have been previous investigations on the interaction between waves and rubble mound low-crested breakwaters, performance of impermeable submerged breakwater is somehow different from rubble mound structures. Thus, the accurate estimation of reflection and transmission coefficients is essential in designing of this kind of structures in near shore zone. In this paper, performance of impermeable trapezoidal submerged breakwater was investigated experimentally using regular waves. In the experimental plan, for three submergence depths of breakwaters different wave groups were used to measure transmission and reflection coefficients. Based on the test results, empirical expressions were formulated to describe the transmission and reflection coefficients for solid submerged breakwater under regular group waves.

In this paper wave transformation in a submerged sloped breakwater and its hydraulic performance was simulated by developing a numerical model in Fortran. The code was established by combining porous flow and a two-phase model using VOF method. Modified Navier-Stokes and k-ε equations implemented to the model to simulate the flow in porous media. Cut cell method was modified to simulate fluid transformation from sloped porous media’s boundary in more accurate way and then applied in the governing equations to increase the accuracy of the model. The validity of the present program was investigated based on the comparisons with the available experimental data. The results showed that increasing of inertia coefficient and wave period and also reduction of porosity lead to some phase lags between the incident and transmitted waves. Furthermore parametric studies were performed on effect of submerged porous breakwater crest widths and heights on transmitted waves leading to useful results for design criteria.

So far, various methods for extracting wave energy have been developed. However, most of these methods have low efficiency in shallow waters and for the small wave amplitude. The mud of the seabed is able to absorb a significant portion of wave energy in different wave lengths. In this paper inspired by this natural characteristic, the idea of a new wave energy converter with the ability to work with high efficiency in shallow water is proposed. If close to the coast, the sea floor is covered by the converter, a significant proportion of wave energy can be absorbed. The main component of this carpet of wave energy converter (CWEC) is a flexible and visco-elastic plate. In this paper, first, by using an analytical modeling, wave energy absorption capability in different sea states of Persian Gulf was considered and compared with other wave energy converters. Further investigations revealed that because of the high efficiency of this converter in shallow waters, it can be suitable for application in the Persian Gulf. Then, the new idea of using piezoelectric elements in the CWEC device was designed to increase its efficiency. The results show that the piezoelectric combined with CWEC could significantly increase the efficiency of this energy converter device.

Breaking waves have ability to transport large quantities of sediment and significant impact on coastal structures morphology. Hence, modeling of wave breaking is an important subject in coastal and marine engineering. In this research, the periodic wave breaking process on a plane slope is studied experimentally and numerically. Laboratory experiments were conducted to record water surface elevation and the wave breaking process. For the current study, a space-averaged Navier–Stokes approach together with laboratory experiments has been deployed to investigate time-dependent wave breaking processes. The developed model is based on the Smoothed Particle Hydrodynamic (SPH) method; a pure Lagrangian approach; capable of handling large deformations at free surface with high accuracy. So, a Weakly Compressible version of the Smoothed Particle Hydrodynamics (WCSPH) method together with a large eddy simulation (LES) approach was used to simulate the wave breaking on a plane slope. The results of numerical simulations were compared both qualitative and quantitative with those of laboratory experiments. Overall, good agreement was found between them. Finally, it is shown that the WCSPH method provides a useful tool to investigate surf zone dynamics.

Oscillating hydrofoils in presence of waves under the free surface as new systems for energy extraction is a hybrid renewable marine energy sources. In this system energy extraction is associated with oscillating hydrofoils operating as biomimetic systems in harmonic waves and currents in coastal regions using active pitch control. Another way of energy exploiting is used by installation of foils under the hull of the ships. Flapping foils located beneath the hull of the ship are investigated as unsteady thrusters, augmenting ship propulsion in rough seas and offering dynamic stabilization. In this system the foil undergoes a combined oscillatory motion in the presence of waves. For the system in the horizontal arrangement, the vertical heaving motion of the hydrofoil is induced by the motion of the ship in waves. The survey shows that exploiting of energy from sea using these techniques can be proposed for Iranian hybrid ships for their propulsion as secondary source of energy. Particularly North part of Persian Gulf has a proper situation for installation and operation as marine energy device in coastal regions.

Interaction between water flow and bed erodibility, which is associated with sediment transport and creat bed forms. Ripples are the smallest of the bed forms. Experiments were performed with variety slopes of 0.0005 to 0.003 and discharges of 10 to 40 L/S, on the artificial ripple in the hydraulic Laboratory of Shahrekord University.Velocity measurements were collected using an Acoustic Doppler Velocimeter. It was observed the peak value of bed shear stress was appear on the midpoint of upstream surface and the lowest value appear on the crest. From the crest to trough, the general bed shear stress was in a trend of increasing. It was also observed that in the case of ripples bed forms were consist of about 26% of total bed shear stress.

Leca lightweight particles are used for structural and semi structural concrete in different countries. In Iran it is usually used as Mass lightweight concrete، blokes and partitions. In this research an experimental work carried out using Leca concrete to assess its physical and mechanical properties and possibility of constructing high strength lightweight concrete to use as structural element in marine environment. Using leca، microsilica gel (silica soot plus super plasticizer) and cement type II، structural high cement content semi lightweight concrete was constructed. Then different characteristics such as specific weight، percentage of abrasion strength، compressive strength، specific gravity of fresh and hard concrete and intensity of bare steel bar corrosion by comparing bar corrosion potential in lightweight and ordinary concrete was obtained. The results show that the leca concrete is in the range of lightweight concrete and is suitable as semi structural and structural element. Furthermore it is found that this kind of lightweight concrete in corrosive environment behaves similar to or better than ordinary concrete. Therefore it can be used in onshore and offshore structures.

In this paper a space-averaged Navier–Stokes approach was deployed to simulate the wave propagation over coastal structures. The developed model is based on the smoothed particle hydrodynamic (SPH) method which is a pure Lagrangian approach and can handle large deformations of the free surface with high accuracy. In this study, the large eddy simulation (LES) turbulent model was coupled with the weakly compressible version of the smoothed particle hydrodynamics (WCSPH) method to simulate the wave propagation over coastal structures. The WCSPH model was employed to simulate the periodic wave propagation over impermeable trapezoidal sea wall and submerged breakwater. The numerical model results were validated against the experimental and numerical data found in the literatures and some relatively good agreements were observed. Afterwards, solitary wave propagation over impermeable trapezoidal sea wall on a sloped bed was carried out and the results of numerical simulations were compared both qualitatively and quantitatively with experimental data of Hsiao and Lin (2010). The results of this study show that WCSPH method provides a useful tool to investigate the wave propagation over coastal structures.

The application and design of concrete block mattresses for stabilization and protection of onshore pipelines utilized for seawater intake structures has been studied in this paper. The Geosynthetic products have been exploited in wide variety of applications in civil engineering such as bed erosion and pipeline stability. Mostly the combination of Geosynthetics with other materials such as concrete blocks results in better performance in adverse environmental conditions. The combination of Geosynthetic and concrete blocks which is known as concrete block mattress has received a great attention in marine purposes in the recent years due to their resistance against wave and current forces. In this study is using semi empirical relations the proper thickness of concrete blocks such that it can withstand the wave and current attacks is determine. The study revealed that the thickness should be determined based on the critical condition which is the wave breaking point.

Guyed tower is a compliant offshore platform used for drilling and extraction of oil in deep water. This platform has a flexible body and needs proper mooring system to control the deck movements. In present study this platform is analyzed in frequency domain due to irregular waves. The exiting force extracted from Pierson Moskovits spectrum using Morrison Equation. Modeling of moorings is difficult due to their variable stiffness and non linear interaction with main structure. Therefore first using static analysis data the diagram for mooring force–excursion was obtained and fitted to a polynomial of order 5. Then using this equation the spring force of moorings was linearized. Furthermore the drag term was linearized and both of these two linearized terms used in dynamic equation of motion. The results of analysis showed that errors due to these linearization on final results is negligible. Results of this research can be used for optimum design of guyed towers in deep water and its special application in Caspian Sea can be considered.

In this research a 2D model was developed to predict water level changes due to storm considering atmospheric pressure and wind stress. This model was used to simulate storm surge in Oman Sea. For boundaries of system three National Geographical Organization Merkatour Maps of 2837, 2838 and 2851 was used. The maps had a scale of 1:75000 with an Origin of coordinate coincidence of 200 latitude. To simulate the boundaries in Cartesian coordinate two digits of 0 and 1 was used to identify water and land respectively. To do this after simulating boundaries and interpolating the topographic lines of Oman Sea domain using developed code, the dynamic equations of system i.e. 2D nonlinear shallow water equations was solved using implicit and semi implicit methods. To validate the model the results of Roed & Copeer (1987) was employed for two simulated wind stresses on two rectangular and parallelogram domains with different boundary conditions. Finally the model was run on Oman Sea domain and the results was examined and discussed.