International Journal of Coastal, Offshore and Environmental Engineering
Volume:7 Issue: 1, Winter 2022

Humans are thought of as predictably irrational, primarily due to apparent inconsistencies in their decision-making.  When presented with the same information on different occasions, the same people often draw different conclusions. There is a noise in the decision-making of individuals, whether in the same or a different environment. Humans are likened to a faulty scale; every time you weigh the same thing you get a different answer. This variation is more pronounced when we examine decisions by different decision-makers. Noise in decisions implies that humans’ internal gauges are imprecise and that their dial rests on a different position when confronted with the same choice at different times. Decision errors can relate to; correlation, causal reasoning, probabilistic reasoning, thinking statistically, hypothetical thought, dubious justification, not seeing everything, and even seeing something which is not there. This part of this series of papers attempts to clarify errors in engineers’ decision-making processes and describe how to avoid them.

Bangladesh has a coastline of 710 km and a long sandy beach. Moderate and high waves causes erosion along the coastline. Concrete block revetment is widely used for shore protection in Bangladesh. As per Coastal Engineering Manual, concrete block revetment stability is limited to wave height of 1.5 m. Studies reveal that the significant wave heights are greater than 1.5 m in the most parts of coastline of Bangladesh. Therefore, in some places, the concrete block revetment has failed. Revetment constructed with Tetrapod, X-bloc, Core-loc etc. are recommended to use for high waves. However, those armor units are not suitable in the context of Bangladesh considering its cost, construction and placement. Moreover, any hard protection may stop the erosion and protect the shoreline, but the sandy beach may be lost. Geotube breakwater is low cost structure for dissipating wave energy to some extent. In this study, laboratory experiments have been carried out for wave height 1.76 m to 2.40 m (as prototype) with two layer protection consisting of concrete block revetment at the shore and submerged geotube breakwater at shallow water. Concrete block size has been calculated using Pilarczyk formula for prototype wave height 1.5 m and scaled down using surf coefficient for laboratory model. Seventeen laboratory runs have been conducted and analysis of the experimental results reveal that two layer protection is effect to protect the shore from high waves. An equation has been established to design the shore protection works along the coastline experienced by high waves.

In this study, a semi-active control system is assessed over a numerically updated model to achieve the most promising numerical results and to keep the performance of the numerical model as close to the prototype behavior as possible. Numerical model updating is performed based on the experimentally captured non-contact sensing data considering uncertainties. The elastic modulus of the jacket elements is specified as the calibration parameter. A mathematical function -optimized using Particle Swarm Optimization (PSO) algorithm- is also employed to reduce the structural uncertainties of the numerical model. Eight MR dampers both in X and Y directions are located in a platform numerical model. Modified Newmark-Beta method besides optimized parameters of instantaneous optimal control algorithm are utilized to predict the response of the system. The performance of the updated model is evaluated under environmental loads. The results indicate the importance of model uncertainty reduction in improving the accuracy of simulation results in a complex system. Based on the results using a non-contact sensing technology such as Laser Doppler Vibrometer (LDV) system is strongly recommended in practical cases due to great sensitivity capabilities and also no direct contact requirements.

The aim of the current study is to determine the equilibrium beach profiles of the coasts of Babolsar and Nowshahr in the southern Caspian Sea. Using depth field data collected from two beaches in the period from 2018 to 2019, seasonal beach profiles and equilibrium beach profiles of the study area were extracted. To investigate the type and transfer of bed sediments, samples were collected from depths of 0.5, 1.5, 3 and 5 meters and were transferred to the laboratory for granulation. The results show the predominant type of sediments in Babolsar and Nowshahr are fine sand with an average of 82.39% and 82.12%, respectively. Also, the percentage of fine-grained sediments, including very fine sand and silt have increased from nearshore to offshore. In the west-east, the median diameter of sediment and the profile slope decreased, from there, the erosion and deposition rate in the two regions has changed. In the western regions, the diameter of beach sediments is more than in the eastern regions due to strong sea currents and relatively coarse-grained sediments from the rivers of western Mazandaran, as well as human activities.

In this study, the performance of some models for predicting the wave runup level is investigated. To do so, they are compared with each other over a database of 1390 field and laboratory data points. This comparison has actually two aims The first one is to investigate the models using all data points and the second one is to consider the influence of wave breaking type on the accuracy of the formulas. The latter goal is achieved by dividing the data points based on the type of wave breaking using the Iribarren number. It is also important to mention that most of the models used here for comparison have been optimized by Power et al. in 2019 so that more accurate outcomes would be obtained by them. These models depend on certain wave and beach parameters, including wave height, wave length, wave period, and seabed slope. The results of the comparison have been demonstrated using several statistical characteristics (e.g. RMSE, R2, etc.) so that a good understanding could be obtained from the behavior of each formula. At first, when the type of wave breaking is not considered in the comparison and all data points are used, the optimized formula derived from both studies of Holman and Atkins et al. seems to be the most accurate one with the least prediction error. Then, when the data points are divided into groups based on the wave breaking type (i.e. spilling and plunging), different outcomes are achieved. The optimized formula proposed by Poate et al. has almost the best performance in the case of spilling type and the formula of Power et al. is the most accurate one when considering the plunging type, showing that the type of wave breaking plays an important role in the accuracy of wave runup level prediction formulas.

Fixed pile-founded offshore platforms installed in the seismic-prone areas are exposed to the risk of earthquake-induced disastrous failure and costly operation interruption. Accordingly, the development of applied seismic evaluation methodologies for these infrastructures is a matter of utmost importance. In the context of performance-based earthquake engineering (PBEE), probabilistic seismic assessments of fixed pile-founded offshore platforms have been investigated, here. A three-dimensional (3D) finite element model of a recently installed platform located in the South Pars Oil and Gas field of the Persian Gulf has been made. Soil-pile-structure interaction, as well as dynamic site response effects, has been considered. Probabilistic seismic demand modeling (PSDM) has been employed to manifest the efficient and sufficient ground motion intensity measures (IMs) which can rigorously predict the structural engineering demand parameters (EDPs). Derived from probabilistic seismic demand analysis (PSDA), the superb results have been also evaluated by means of the predominantly used method of incremental dynamic analysis (IDA). On the other hand, the drawn findings contributed to representing the fragility curves of the fixed pile-founded offshore platforms. The demonstrated results are highly recommended to be considered in related research.