فصلنامه علوم و فناوری دریا
سال بیست و پنجم شماره 99 (پاییز 1400)

The issue of air aspiration is a major challenge for AUVs’ propulsion systems working based on combustion engines. Some AUVs have snorkels to take fresh air from sea surface, so keeping heights of these AUVs is important. A reliable and safe bilge sub-system survives the AUV in emergency cases. In this paper, a three layers supervisory control system has been employed to handle a bilge subsystem dealing with faults (e.g., pump failures) and allows to keep the inlet of the AUV’s snorkel upon sea water. The highest layer of the supervisory control system as a mission layer is modeled by a decision tree and the decision tree is built on petri net models. In addition, our results represented the bilge might not be sufficient to deal with the effects of water ingress. Using an accumulator in the supervisory control system to keep the height can improve fault tolerant of AUV after water ingress.

Floating structures play an important role in exploring the oil and gas from the sea. The motion response of the structure should be kept within a certain range to prevent damage to the risers and transmission pipes and, most importantly, the oil processing system. In this study, vertical acceleration of semisubmersible platform was simulated under regular wave in AQWA software. The results were compared to experimental results done in the marine technology center of university technology Malaysia. Semi motions in six degrees of freedom subjected to regular wave were investigated in time and frequency domains. Damping coefficients, added masses and wave forces under different incident wave angles and finally response amplitude of operations (RAOs) was obtained in the frequency domain. By transferring the data to the time domain and solving, the vertical acceleration was obtained. Acceleration causes crew seasickness, the worst of which occurs during a 20-second period. The Surge RAO have the highest value in the 20-second period equal to 5.5 and the Yaw RAO have the lowest value of 0.032 in the 20.91-second period. Comparing the obtained results with the laboratory results, it can be seen that the simulation performed on the motion of the semi-submersible platform has an average error of 10.41%.

Surface temperature, evaporation and wind are the three main factors in water circulation in the Persian Gulf. This study was conducted to investigate the effect of climate change in the region on the growth and technical and economic development of Iranian maritime transport with a case study of Imam Khomeini port. For this purpose, monthly data from rainfall, temperature, wind and the amount of unloading and loading of oil and non-oil products were collected for 2008. The rate of change in each of the loading and unloading parameters during the months of the year and the rate of difference between loading and unloading were assessed by applying meteorological factors using the T-test. Finally, using multivariate linear regression, the relationships between each variable were determined by the amount of loads and unloads. According to the results of this study, the amount of precipitation in this port has the lowest rate and its effect on all loading and unloading operations is not significant. However, the effect of wind is negative for most loads, and the amount of this effect on the discharge of non-oil materials is very significant. Also, the difference between unloading and loading of non-oil materials is high, so that the amount of unloading of these materials compared to loading them in the same conditions is about 4 times, and this indicates the low export of non-oil materials. However, the amount of oil materials exports is much higher than its imports.

In this research for the study of geochemical changes and heavy metals contaminations in Gorgan Bay deposits, 5 sedimentary cores (K1,K3,K5,N1) were collected by using a gravity corer from different part of Gorgan bay. After geochemical analysis, the trend of each element was drawn up. The concentration range of toxic elements: arsenic (2.89-10.18 ppm), lead (9.88-43.8 ppm), copper (6.01-45.2 ppm), zinc (22.8-106.18 ppm), nickel (8.78-105.4 ppm), cobalt (5.38-44.18) and chromium (15.3-140.9 ppm) were obtained. Generally, the highest concentration of elements was observed in the surface parts of the cores and the lowest concentration was perceived at depths more than 50 cm. Enrichment factor index (EF) for all elements exception core K7 was less than 1-1.5 indicated natural sources for elements. Based on the average value of Cd, mcd, RI, the sediment contamination degree was defined as low pollution (expect in surfaces considerable), low contamination and low ecological risk, respectively. The pollution load index (PLI) was between 1 and 2, representative low pollution. Finally, the comparison of the concentration of selected elements in this area with the American and Canadian sediment quality guidelines signified the ranges between low risk to dangerous and harmful.

Todays, transit of goods is one of the most lucrative trades in the world, and naturally the countries that are in the path of transit corridors can benefit the most from this trade. The purpose of this study is presenting a model of transit development with the blue ocean approach in the Amirabad Port Special Economic Zone, in which the identified strengths, weaknesses, opportunities and threats were analyzed using the SWOT technique. The data collection tool in this research is a questionnaire, which has been distributed and collected among fifty port and maritime specialists. Also, the research method is descriptive-survey. After reviewing and during the mentioned steps, it was concluded that the strategy of Amirabad Port Special Economic Zone is in offensive state and for this reason, an offensive strategy should be applied.

This paper is dedicated to design of a low cost and GPS independent navigation system and also implementation of that on a boat. Exact position estimation of a boat is very important and critical in maritime security. There are several different methods for maritime navigation including Doppler navigation, GPS and INS as the three most common methods. With regard to high cost of Doppler navigation due to its expensive sensors, probability of GPS signals lost or distortion and also for cumulative errors in INS and pricey cost in its ultra-accurate types, in this research an open loop estimation method is presented using only heading angle and velocity of the vehicle. Due to lack of speed sensor, velocity of the boat is simulated by adding noise to the speed values measured by GPS. Furthermore real data of a magnetometer are used as the boat's heading angle measurements. In order to assess the suggested algorithm, two different tests are carried out in Mazandaran Sea and the speed and heading angle of the boat are stored during the mission and then off-line implementation of the proposed method is accomplished in MATLAB. Comparing the results with GPS measurements indicates acceptable and desirable performance of the suggested method.