فهرست مطالب

Maritime Technology - Volume:10 Issue: 18, Spring-Summer 2023

International Journal of Maritime Technology
Volume:10 Issue: 18, Spring-Summer 2023

  • تاریخ انتشار: 1402/02/11
  • تعداد عناوین: 6
  • Ehsan Asadi Asrami*, Mohammad Moonesun Pages 1-26

    To obtain the hydrodynamic forces acting on a solar-powered AUV, and to investigate the effects of the free surface, a model of this type of vessel was simulated in ANSYS FLUENT 18 commercial software. To validate the data, a vessel with a scale of 1: 1 compatible with the installation of photovoltaic panels was built and tested in the towing tank of the National Iranian Marine Laboratory (NIMALA). The standard k-ε model and multi-block mesh were used to simulate the three-dimensional unsteady viscous flow around these cases: individual struts, the body without struts, and the body with struts. Three depth-to-diameter ratios ( h d =3.6 , 4.5 , 5.2 ) and six Froude numbers in the range of 0.06 ~  0.35, equivalent to the Reynolds range 2.4×10 05 to 1.4× 10 06 , were used to obtain lift and drag coefficients. The findings of this study were used to create a solar AUV. The maximum percentage of struts contribution in the total resistance force is 62 percent. The generated resistance effect, caused by struts and their attachment to the body, also plays a significant role. According to the current study data for the analyzed model, its maximum value is around 41 percent.

    Keywords: solar AUV, hydrodynamic coefficients, CFD, towing tank
  • Nima Khanmoradi*, Mohammad Moonesun, Sara Jafari Horestani Pages 27-36

    The aim of the present study is calculation of the resistance and resistance coefficient of a diver on the water surface and near surface. The results of this article are useful for designing different types of water scooters. This study uses a computational fluid dynamics methodology by considering the effects of free surface. SST K-ω turbulent model is implemented in the Star-CCM+ application and is applied to the flow around a three-dimensional bare hull of an adult human. Three common swimming positions are considered: a ventral position with the arms extended at the front, a ventral position with the arms placed alongside the trunk and a ventral position with one arm extended at the front and another arm placed alongside the trunk. The flow velocities between 0.5 and 2.25m/s with increasing step of 0.25m/s are considered in the simulations which are typical speed of swimmers. According to the resistance coefficient vs Froude number diagrams, submerged diving with two hands alongside the trunk is produces lower resistance. Also, resistance in near surface swimming is lower than surface swimming in lowest speeds. But in higher speeds, that changes and resistance in surface swimming is lower than the other. The results of this research can be used for designing all types of marine propulsion vehicles, water scooter, and all swimming thrusters.

    Keywords: human body, diver resistance, swimmer resistance, CFD, resistance coefficient, free surface simulation
  • Amirreza Zafarjoo, Ruhollah Amirabadi* Pages 37-51

    Most of the fixed offshore platforms in the Persian Gulf have survived more than 25-year design life and have suffered from significant damages in this period. Seismic acceleration modifications and changes in seismic criteria of API-2EQ-2014 increase the importance of seismic assessment of the offshore platforms in the Persian Gulf. This paper presents a case study for modeling and evaluating the seismic behavior of an existing damaged fixed offshore platform in the Persian Gulf with consideration of actual structural damages as per provided subsea inspection reports and comparing with the intact condition of the platform to obtain the effect of assessment initiators like; actual damages and increased spectral acceleration as per API2EQ 2014 in the structural integrity of the fixed offshore platforms under the seismic loads in Persian gulf. Following the actual jacket inspection reports, Excessive corrosion, flooding of some members, marine growth, and anode wastage are the significant damages on this platform. Spectral nonlinear and static-dynamic analysis with SACS12.00 software considering the pile-soil interaction in the three following scenarios have been performed to verify structural seismic assessment. The first scenario contains a damaged platform with a lighter topside, the second scenario is a damaged platform with a heavier topside, and the third one includes the intact platform with initial design assumptions and criteria. The evaluation of the structure in three parts of the jacket members, joints, and piles has been done under the ALE & ELE earthquake levels. According to the results, jacket legs have the significant effect on the structural seismic strength. In abnormal level earthquake, the first plasticization occurs in the deck legs which are connected to the topside and the piles below the seabed. The comparison of the RSR values ​​indicates that the initial assumption in platform design criteria has been stringent and uneconomical in the past. Also, the actual presented damages do not have much effect on the seismic strength of the structure. A Comparison of the Joint and member capacity illustrates a more significant impact of uniform corrosion on joint capacity than member strength. Finally; buckling in the deck legs at the splash zone and yielding in the Piles near the sea bed causes the global collapse of the structure.

    Keywords: assessment, seismic, jacket, fixed platform, offshore, offshore platforms
  • Mehran Sabz Gashtasebi*, Homayoun Yousefi, Mohammad Amin Kouhbor Pages 52-63

    Blockchain is a novel and disruptive technology that has the potential to transform the current international business and trade processes that rely on traditional intermediaries. It is a distributed ledger that verifies and records transactions using a peer-to-peer network over time in a sequence of blocks, secured by cryptographic functions that are complex, immutable and tamper-proof. International maritime trade, which is the main mode of global transportation, expects to change its business model by adopting blockchain, which enables a decentralized architecture of international transactions without intermediaries and facilitates paperless trade. Moreover, blockchain aims to address the problems and inefficiencies that plague maritime trade. However, there are key factors that influence the adoption of blockchain in maritime trade that need to be investigated in order to successfully implement this technology in the future. This study examined the impact of blockchain technology on maritime trade and identified the factors affecting its acceptance in Iranian maritime trade using the research background, literature review and interviews with experts who were PMO managers. These factors were validated by the Delphi method and then categorized and prioritized using the theoretical framework of technology, organization, environment (TOE) and analytical hierarchy process. The results indicated that “blockchain benefits” in the “technology” dimension, “human resource capability” in the “organization” dimension and “government support and policy” in the “environment” dimension were ranked first. These findings could assist the stakeholders in Iran’s maritime trade, such as ports, customs, government agencies, and transportation logistics companies, in developing strategies for the successful adoption and advancement of blockchain and enhancing their organizational competitiveness.

    Keywords: Blockchain, disruptive technology, maritime trade, paperless trade, distributed ledger, ahp
  • Kasra Pourkermani* Pages 64-69

    Baltic Dry Index (BDI) is shipping freight-cost index which is reported daily by Baltic Exchange. The index is a benchmark for the prices of ship chartering contracts which is a proxy for the maritime economy, BDI is heavily used by financial traders to predict the world economy, the volatility forecast has an important implication for all the investors and hence in this paper the daily forecast performance of different models is evaluated.

    Research methodology

    The daily forecast performance of conditional and unconditional volatility of 12 long memory GARCH-type models based on the root-mean-square error (RMSE) is evaluated. Because all return series were skewed and fat-tailed, each conditional volatility model was estimated under a skewed Student distribution.


    According to the idea that the accuracy of Value-at-Risk (VaR) estimates was sensitive to the adequacy of the volatility model used, the result showed that the 250-day moving average models, exponential smoothing, and (component GARCH) CGARCH function better than other models based on RMSE standard. The results of hybrid models such as Dibold-Mariano statistics showed that there was no significant difference between the predictive power of 250 days moving average (MA250) and CGARCH.

    Practical implications

    BDI was widely regarded as a benchmark for the world economy by traders and hedge fund managers.


    we examine the science of volatility prediction in BDI which has not been performed before.

    Keywords: Conditional volatility, unconditional volatility, GARCH, Baltic Exchange Dry Index
  • Ali Katoozi, Miralam Mahdi* Pages 70-81

    In this study, to numerically investigate the consequence of bubble collision on the pressure distribution due to cavitation collapse, the bubble behavior around NACA0015 2D hydrofoil has been simulated using the Eulerian-Lagrangian perspective. Macroscopic examination of the cavitation flow was determined by the homogeneous mixture model (Eulerian method) and the bubble motion path based on the applied forces using Newton's second law and the development of numerical code (Lagrange method). Bubble oscillations were obtained from the modified Rayleigh-Plesset-Keller-Herring equation. To study the effect of bubbles colliding (bubble with wall and bubble with the bubble), the model of vertical elastic forces and vertical and tangential viscosities used by Heitkam et al. To pair the obtained results and solve them, the fourth-order Runge-Kutta method with variable time step has been used, which has increased the data solving speed up to 10 times. From the Keller& Kolodner relationship, a pressure wave emitted from the collapse of a spherical bubble and the model of Soyama et al, the total energy of the cavitation-induced shocks, which is the result of the accumulation of all the shocks on each other, is obtained. The results showed that the effects of increasing the radius by decreasing the cavitation number are the same, when the bubble colliding with the wall is applied and when it is not and by decreasing the cavitation number, the bubble growth rate increases, and by increasing the bubble radius, the erosion intensity increases. The process of bubble growth starts earlier in the case of collision with the wall than in the case in which the collision did not occur, therefore, the cavitation number has little effect in this case and is related to the impact effects. The result of the impact of the bubble on the wall and the bubble with the bubble reduces the maximum radius compared to the case where the effect of the impact is not considered and also reduces the amount of erosion. The possible place of erosion is located at the end of the cavitation cavity, and possible damage can be prevented by strengthening this place. The results were compared with other published works and had acceptable accuracy.

    Keywords: Bubble collision, Cavitation flow, Erosion intensity, Eulerian-Lagrangian method, Bubble dynamics