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Volume 14, Number 1, March 2024

This paper investigates the impact of local joint flexibility (LJF) on the fatigue life of jacket-type offshore platforms. Four sample platforms with varying geometric properties are modeled and analyzed using the Opensees software. The analysis considers the LJF of tubular joints through the equivalent element and flexible link approaches, and the results are compared to rigid modeling. Initially, modal analysis is conducted to examine the influence of LJF on the frequency content of the structure. Subsequently, fatigue analysis is performed to evaluate the fatigue life of the joints. The comparison of fatigue life reveals that incorporating LJF leads to reduced fatigue damage and a significant increase in the longevity of the joints in the studied platforms. Moreover, as the platform height increases, the effect of LJF on fatigue damage becomes more pronounced. In conclusion, considering LJF in fatigue analysis provides more accurate results compared to conventional methods. Therefore, it is essential to incorporate the effects of LJF in the analysis and design of offshore jacket platforms to ensure their structural integrity and longevity.

Key Words
fatigue damage; local joint flexibility; modal analysis; offshore jacket platform; spectral fatigue analysis

Behrouz Asgarian, Parviz Kuzehgar and Pooya Rezadoost: Faculty of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran

In this paper, the authors explore the modeling and control of a point absorber wave energy converter, which is connected to the electric grid via a power converter that is based on a linear permanent magnet synchronous generator (LPMSG). The device utilizes a buoyant mechanism to convert the energy of ocean waves into electrical power, and the LPMSG-based power converter is utilized to change the variable frequency and voltage output from the wave energy converter to a fixed frequency and voltage suitable for the electric grid. The article concentrates on the creation of a predictive control system that regulates the speed, voltage, and current of the LPMSG, and the modeling of the system to simulate its behavior and optimize its design. The predictive model control is created to guarantee maximum energy output and stable grid connection, using Matlab Simulink to validate the proposed strategy, including control side generator and predictive current grid-side converter loops.

Key Words
back to back converter; LPMSG; multi-level inverter; point absorber; predictive control; wave energy harvestin

Abderrahmane Berkani and Karim Negadi: L2GEGI Laboratory, Department of Electrical Engineering, Faculty of Applied Science, University of Tiaret,
BP 78 Zaaroura, 14000, Tiaret, Algeria
Mofareh Hassan Ghazwani, Ali Alnujaie and Hassan Ali Ghazwani: Department of Mechanical Engineering, Faculty of Engineering, Jazan University,
P.O. Box 114, Jazan, 45142, Kingdom of Saudi Arabia
Lazreg Hadji: Department of Civil Engineering, University of Tiaret, BP 78 Zaaroura, Tiaret, 4000, Algeria

The interaction of the blade of surface-piercing propellers (SPPs) with the water/air surface is a physical phenomenon that is difficult to model mathematically, so that such propellers are usually designed using empirical approaches. In this paper, a newly developed mechanism for measuring the torque of SPPs in an open water circuit is presented. The mechanism includes a single-component load cell and a deformable torque sensor to detect the forces exerted on the propeller. Deformations in the sensor elements lead to changes in the strain gauge resistance, which are converted into voltage using a Wheatstone bridge. The amplified signal is then recorded by a 16-channel data recording system. The mechanism is calibrated using a 6-DoF calibration system and a Box-Behnken design, achieving 99% accuracy through multivariate regression and ANOVA. Finally, the results of performance tests on a 4-blade propeller were presented in the form of changes in the torque coefficient as a function of feed rate. The results show that the new mechanism is 8% more accurate than conventional empirical methods.

Key Words
experimental test; manufacturing; statistical study; surface-piercing propellers

Masoud Zarezadeh, Nowrouz Mohammad Nouri and Reza Madoliat: School of Mechanical Engineering, Iran University of Science and Technology, Narmak,
Heydarkhani St., Tehran, 16846-13114, Iran

In order to achieve the best performance, the automatic control with advanced technology is made of sheathed steel to withstand a wide range of wave loads. This model shows how to control the vibration of the fiber panel as a solution using the new results from the Lyapunov stability question, a modification of the bat that making it easy to calculate and easy to use. It is used to reduce the storage space required in this system. The results show that the planned worker can compensate effectively for the unplanned delay. The results show that the proposed controller can compensate for delays and errors. Fuzzy control (predictive control) demonstrated the external vibration can be reduced.

Key Words
evolved control systems; offshore platforms; predictive control; time delays

C.C. Hung, Faculty of National Hsin Hua Senior High School, Tainan, Taiwan
T. Nguyen: Ha Tinh University, Dai Nai Ward, Ha Tinh City, Vietnam;
C.Y. Hsieh: National Pingtung University Education School, No.4-18, Minsheng Rd., Pingtung City,
Pingtung County 900391, Taiwan

Ocean surface currents have an essential role in the Earth's climate system and significantly impact the marine ecosystem, weather patterns, and human activities. However, predicting ocean surface currents remains challenging due to the complexity and variability of the oceanic processes involved. This review article provides an overview of the current research status, challenges, and opportunities in the prediction of ocean surface currents. We discuss the various observational and modelling approaches used to study ocean surface currents, including satellite remote sensing, in situ measurements, and numerical models. We also highlight the major challenges facing the prediction of ocean surface currents, such as data assimilation, model-observation integration, and the representation of sub-grid scale processes. In this article, we suggest that future research should focus on developing advanced modeling techniques, such as machine learning, and the integration of multiple observational platforms to improve the accuracy and skill of ocean surface current predictions. We also emphasize the need to address the limitations of observing instruments, such as delays in receiving data, versioning errors, missing data, and undocumented data processing techniques. Improving data availability and quality will be essential for enhancing the accuracy of predictions. The future research should focus on developing methods for effective bias correction, a series of data pre-processing procedures, and utilizing combined models and xAI models to incorporate data from various sources. Advancements in predicting ocean surface currents will benefit various applications such as maritime operations, climate studies, and ecosystem management.

Key Words
ocean current modelling; ocean current prediction challenge; ocean current prediction opportunities; ocean surface current prediction

Ittaka Aldini: Department of Electrical and Information Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia;
Indonesian Agency for Meteorology, Climatology, and Geophysics, Jakarta, Indonesia
Adhistya E. Permanasari and Risanuri Hidayat: Department of Electrical and Information Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia
Andri Ramdhani: Indonesian Agency for Meteorology, Climatology, and Geophysics, Jakarta, Indonesia

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