E-ISSN: 2148-9386
Journal of ETA Maritime Science - JEMS Maritime Sci: 11 (2)
Volume: 11  Issue: 2 - 2023
1.Full Issue

Pages I - X

2.Protecting Intellectual Capital at Sea
Selçuk Nas
doi: 10.4274/jems.2023.67299  Page 67
Abstract |Full Text PDF

3.Comments on the Use of 3D Printing Technology in the Design of an AUV Destined for the Identification and Destruction of Underwater Mines
Mihaela Greti Manea, Catalin-Paul Clinci, Ovidiu Cristea
doi: 10.4274/jems.2023.44712  Pages 68 - 78
The International Maritime Organization and the North Atlantic Treaty Organization are today, enforcing increasingly stringent rules for maritime safety and security on a national and international scale. The need for security in the Black Sea has increased, the degree of danger has risen, and the risk of loss of life and destruction of ships or other surface or submersible marine vehicles cannot be overlooked. Autonomous underwater vehicles (AUVs) have various civil applications (targeting economic, industrial, and commercial interests), but military applications have recently gained prominence (needs for information, surveillance, and inspection, for the identification and destruction of risk obstacles). Given the high risk of destruction during the operation, solutions are being sought to enable the rapid and cost-free construction of AUVs without compromising their performance and efficiency. The paper’s novelty is provided by the mention of 3D printing technologies as a possible solution, taking into account the successes in other essential fields of science and technology. The contribution of the paper was related to the AUV’s body extremities (bow and stern), and the following factors were considered: geometric design using computer-aided design methods; hydrodynamic analysis of forms using computational fluid dynamics methods; and prototype manufacturing using 3D printing.

4.Simulation of Shockwave Effects on a Ship-like Structure due to Underwater Explosions
Alpaslan Tatlısuluoğlu, Serdar Beji
doi: 10.4274/jems.2023.82713  Pages 79 - 85
Underwater explosions that threaten the hull integrity and proper operation of navy ships’ systems and subsystems are considered from
the viewpoint of damage estimation. The commercial code LS-DYNA with the Arbitrary Lagrangian-Eulerian numerical technique is used
to analyze the shock effects on structural components of a ship-like form for three different scenarios. Computed maximum permanent
deformations are matched with the corresponding keel shock factor (KSF) values for searching a functional relationship of a linear form.
Although observed for limited simulations and therefore should be viewed with caution, the linear dependency of the maximum permanent
deformations on the KSF values implies that the KSF may be a simple indicator for estimating the extent of damage due to underwater

5.Maritime Students’ Assessment of Distance Education During the COVID-19 Pandemic
Elif Arslan, Emin Deniz Özkan
doi: 10.4274/jems.2023.92688  Pages 86 - 97
The coronavirus diseases-2019 (COVID-19) outbreak emerged in late 2019 and rapidly spread worldwide, resulting in a pandemic. The pandemic has had negative impacts on various aspects of life, particularly health and the economy. Education sector has been severely affected, as well. In Türkiye, as in many countries, face-to-face classes were replaced with distance education as a safety measure against the pandemic. Maritime education places significant emphasis on providing practical, hands-on training to its students. However, due to the COVID-19 pandemic, a shift to distance education was required, including the teaching of applied courses in this field of study. In this regard, revealing the evaluations of maritime students on distance education is an important issue that needs to be studied. Therefore, this study aims to evaluate the opinions of maritime faculty students in Türkiye regarding the technical aspects and learning process of the distance education that they received during the pandemic. To this end, the “Distance Education Evaluation Scale” was administered to students via an online platform, and the resulting data were analyzed using SPSS Statistics 25. The results show that male students have a more positive evaluation of distance education than female students. Those who participate in distance education by using mobile phones have a more negative evaluation of distance education, while successful students have a more positive evaluation of distance education. Finally, there was no significant difference according to universities and classes.

6.Analysis of Organizational Justice in Relation to Organizational Commitment in a Turkish Shipyard Organization
Nihan Şenbursa, Ramadan Tuna Türkeli
doi: 10.4274/jems.2023.57689  Pages 98 - 109
This study explored the relationships between organizational justice perception and commitment among shipyard employees in a maritime
organization in Türkiye. Data were collected using two-scale and sociodemographic questionnaires that were answered via email or hand
by 290 participants who were shipyard workers in Antalya, Türkiye. The questionnaire included the organizational justice scale consisting
of 20 questions, the organizational commitment scale consisting of 18 questions, and 7 questions about demographic characteristics.
To analyze the data, IBM SPSS 26 was used. A simple linear regression analysis technique was used to determine the effects between
scales. Moreover, interviews were conducted with the employees using the semistructured interview method. It was determined that there
was a positive, high-level relationship between organizational justice scale subdimension scores and total scores and this relationship
was statistically significant. It was also shown that there was a positive, low-level relationship among the organizational commitment
subdimensions’ scores of the employees and that the relationship was statistically significant. Regression analysis identified that the
organizational justice scale total scores of the employees had a statistically remarkable impact on the organizational commitment scale
total scores.

7.Advancing Computational Hydroacoustics for Marine Propellers: Investigating the Limits of Incompressible Solvers in Far-Field Noise Prediction
Ömer Kemal Kınacı, Cihad Delen
doi: 10.4274/jems.2023.35761  Pages 110 - 118
As sound is a propagating pressure wave, it is important to obtain the hydrodynamic pressure oscillations in the fluid to calculate propeller noise. Numerical hydroacoustic simulations generally assume incompressible flow. Time delays in sound propagation are neglected due to the incompressibility assumption, leading to physically infeasible results in the far field. However, recent works have shown that incompressible solvers can comfortably be used in the near field. This work focused on the effect of distance on the accuracy of the incompressible solver and investigated the hydrodynamic and hydroacoustic properties of a model-scale Duisburg Test Case (DTC) propeller by the finite volume-based computational method. Open-water experiments on a 1/59.407 model-scale DTC propeller were carried out at the Ata Nutku Ship Model Testing Laboratory in Istanbul Technical University. Open-water numerical simulations were performed to determine the hydrodynamic and hydroacoustic properties of the propeller and validated with the hydrodynamic performance of the open-water propeller. Thrust and torque coefficients and open-water efficiency were compared with experiments. The Ffowcs-Williams and Hawkings equation was coupled with the incompressible solver using impermeable surfaces in hydroacoustic predictions of the hybrid solver. Pressure oscillations in the time domain at 21 receivers were used to calculate the sound pressure levels in the vicinity of the propeller. Results of incompressible and hybrid solvers were compared to determine the reach of incompressible solvers for hydroacoustic predictions. It was revealed that discrepancy starts after a 1.5-2D propeller.

8.Experimental Study of the Heave and Pitch Motions of an Inverted Bow Hull
Abolfath Askarian Khoob, Majid Askari Sayar, Karim Akbari Vakilabadi, Hassan Ghassemi
doi: 10.4274/jems.2023.28291  Pages 119 - 126
In this study, the experimental heave and pitch motion responses of inverted bow hulls in regular head waves were investigated. Comparison of the pitch and heave motion responses of two modified versions of an NA8-14 British Ship Research Association reference fishing vessel with 45 and 60 degrees inverted bows was performed. The findings showed that decreasing the inversion angle of the bow to 45 degrees improves the dynamic performance of the model. Moreover, the interactions between the heave and pitch motions led to the frequent appearance of “kinks” in coupled form in response to the heave and pitch motions.

9.Volatility Transmission Between Container and Dry Bulk Freight Markets During the COVID-19 Pandemic
Reha Memişoğlu, Seçil Sigalı
doi: 10.4274/jems.2023.66487  Pages 127 - 135
Shipping is a highly volatile, cyclical, and capital-intensive industry defined by extreme highs and lows. This makes information regarding volatility in this market material and relevant for decisions related to portfolio diversification, forecasting, and hedging in the maritime industry. Understanding how volatility is disseminated across the shipping market can help shipping companies to improve operational efficiency by making them more responsive to market changes. When shipping companies can anticipate market changes, they can swiftly respond and adjust their operations accordingly. In addition, volatility transmission in the shipping industry is crucial for policymakers seeking to improve the economic outlook of individuals and business entities that depend on the shipping industry. By monitoring the flow of volatility between shipping markets, they can promote effective pro-industry economic policies by more accurately estimating the effects of introducing new shocks to one freight market on another one. Therefore, understanding the volatility transmission between the container and dry bulk freight markets could provide an effective risk management mechanism that improves decision- making in shipping. This study analyzes volatility transmission between the container and dry bulk freight markets during the coronavirus disease-2019 pandemic using an asymmetric BEKK-GARCH(1,1) model that can also serve as a weak efficiency test. The results indicate that there was bidirectional volatility transmission between the container and dry bulk freight markets during the pandemic and that transmission from the container to dry bulk freight market was dominant. These findings support the price formation hypothesis of shipping, which states that dry bulk freight rates will follow container freight rates when freight rates exhibit an upward trend. Furthermore, the statistical significance of volatility transmission suggests that container and dry bulk freight rates can be used as a prediction mechanism for each other, serving as a market inefficiency indicator for both freight markets.

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