International Journal of Coastal, Offshore and Environmental Engineering
Volume:6 Issue: 3, Summer 2021

The primary objective of this paper is probabilistic quantification of the fatigue life of tension-leg platforms (TLP) using reliability methods. The need for such methods stems from the significant uncertainty in the loads exerted on offshore structures. The scope of this paper is limited to the study of fatigue in TLP tendons. For this purpose, nonlinear time-history of force response of the TLP tendon under random-wave load is computed via MOSES software and the damage due to fatigue is estimated in accordance with the Palmgren-Miners rule. Assuming a Rayleigh distribution for stress variation and eight different sea states, the ultimate fatigue damage is computed by accumulating the damage over all individual sea states. This cumulative damage enters the limit-state function that is based on the Palmgren-Miners rule. Prevailing sources of uncertainty in this problem are those in the estimation of fatigue stresses, fatigue strength, and the Palmgren-Miners rule. Finally, reliability analysis is carried out for four different service lives using the first- and second-order reliability methods (FORM and SORM) and Monte Carlo sampling. The results indicate that FORM computes the probability of failure sufficiently accurate. It is concluded that the probability of failure increases drastically with the service life. The importance vector from the sensitivity analysis in FORM reveals that the model error is the most influential source of uncertainty on the probability of failure.

Two major research programs on the use of heuristics in decision-making exist, and each has its own set of followers. The first program was initiated by Kahneman and Tversky in the 70s. They primarily concentrated on the errors caused by using heuristics. This has now grown into many heuristics named after their associated biases. The second program was initiated by Gigerenzer and colleagues in Germany. Gigerenzer argues that although simple heuristics sometimes leads to “biased” decisions, they can deliver better answers in some situations. This is particularly true for uncertain or complex environments, where there is only a small data sample or there is no time to formally seek an optimized decision.  Gigerenzer and colleagues have generated a substantial body of evidence that humans use simple heuristics, often with great results. Like Kahneman and Tversky, Gigerenzer’s work has attracted researchers exploring the power of “Fast and Frugal” Heuristics, and how they are used by humans. This part, of the four-part paper, discusses Kahneman and Gigerenzer's findings concerning engineering decision making. Avoiding errors when using simple heuristics is discussed in Part IV.

The small microwave skin depth of sea water as well as the small penetration depth of laser signal in water impose limitations on the application of SAR and Lidar in sea surveillance systems. On the other hand, vessels travelling at sea bring about hydrodynamic anomalies in the sea water called as wake. These hydrodynamic disturbances can be detected by using some techniques such as airborne radio imaging and Extremely Low Frequency (ELF) electromagnetic signal processing. In practice, the motion of conductive sea water anomalies in the natural earth's magnetic field induces ELF magnetic wakes which can be measured via accurate magnetic sensors and detected through signal processing schemes. The physical properties of the hydrodynamic wake as well as those relating to the corresponding magnetic wake are directly related to the vessel parameters such as hull shape, speed and heading. In this work, we firstly derive and formulate the mathematical expressions relating to the aforementioned hydrodynamic and magnetic wakes. By employing derived expressions, a novel detection scheme is proposed based on constructing the 2-dimentional image of the vessel’s magnetic wake through the magnetic signals captured from an array of magnetic sensors, and finally, the relation between the spectral image of the magnetic wake and the vessel heading is studied. We will show that our proposed scheme can detect the existence of a remote vessel as well as its heading from the constructed image with high accuracy, and moreover, it does not have common limitations of existing single-sensor based heading detection schemes.

This research investigates the morphodynamic classification of beaches of Iran according to the dimensionless fall parameter (Ω) and the relative tide range (RTR). According to RTR parameter, the southern Iranian coast (Hormozgan province) is mixed wave and tide and the northern Iranian coast (Mazandaran province) is wave-dominated. By using some schemes, the beach states in the north regions of the eastern and central parts of the Mazandaran province are dissipative and in the western part it is intermediate. Also, in the south section in most of the regions of the Hormozgan province, the beach states are ultradissipative, but in some areas low tide terrace and low tide bar/rip occur.

Two numerical models of tsunami generation/propagation have been run in the Makran region. These models are one of the necessary components in the warning systems in this region. The outputs of these models are not in regular international data model standards. In order to get the best result from these models, the models’ outputs must be managed in a database system. An ideal data management system for tsunami warning system has three essential parts included: data convertor, Geographical Information System (GIS) and Relational Database Management System (RDBMS). The schematics and properties of the proposed data management system have been shown in this paper. 3D, spatial, temporal and statistical analysis of tsunami models data exported to the proposed system based on GIS capabilities and data processing routines. Some examples of data analysis of tsunami propagation in the Makran region (north of the Arabian Sea) have been shown.

Khowr-e Musa at the northwestern terminus of the Persian Gulf sedimentary basin is the widest and ‎longest inshore marine outcrop in the entire coast of the iran at present. In this research, the tidal Current velocity and tidal water level ‎in the Khowr-e Musa estuary was modeled in a 15-day ‎period from 18th of November 2006 by using the Telemac two-dimensional hydrodynamic software. For this purpose, the irregular mesh in two dimensions was selected from the smallest mesh ‎of 70 meters to the largest mesh of 210 meters. The topography of the area was added to the ‎grid of mesh by using an interpolation method. Then TPXO database tidal data applied along ‎the boundary of model. The friction coefficient was calculated using the Stickler theory with ‎the value of 40 m1/2s-1 and the model was executed with a time step of 10 seconds. After Sensitivity analysis and calibration, the model was ‎validated by using measurement data that’s provided by the ports and maritime organization. The results showed a good correlation of 94% between the results of the water surface level of modeling the tidal and measurement data and correlation of 73% between the results of the current velocity of modeling the tidal and measurement data, so the TELEMAC two-dimensional hydrodynamic model is suitable for studying the tidal current.