فصلنامه دریا فنون
سال ششم شماره 2 (پیاپی 16، تابستان 1398)

Target tracking by bearing-only measurements is one of the main methods for passive tracking of underwater moving targets. In this problem, the choice of filter type and accuracy of estimates from target state variables have always been the most important topics, but in many cases and applications of this kind of tracking, the presence of outliers in the measurements are unavoidable which reduce the accuracy of estimates or stability in the performance of the tracking filters. In this paper, to overcome this problem, a new method based on a robust M-estimation in fifth-degree cubature Kalman filter structure is presented. In this method, the outlier in the measurement is detected, and the weight of this malicious data is reduced using Huber's weight function. Analysis of the underwater target tracking problem are discussed in three situations: without the presence of outliers, the presence of small outliers in some continuous measurements and the presence of large outliers. This analysis indicates the effectiveness of the proposed method so that the accuracy of the estimates made by the selected filter is still at an acceptable level.

Performance of Power Line Communications (PLC) and Underwater Acoustic Communications (UWA) Channels is affected by limiting factors of fading, attenuation, multipath propagation and impulsive noise. Classically, Fourier-Based Orthogonal frequency division multiplexing (OFDM) modulation is utilized to overcome these limitations. However, this modulation suffers from some drawbacks like low spectral efficiency and high peak to average power ratio. Due capability of wavelet-based OFDM in overcoming these limitations and also lack of sufficient knowledge about its performance in impulsive noise channels, this paper is devoted to suggestion of wavelet-based OFDM for PLC and UWA Channels and evaluates its performance for different wavelet families and in the presence of impulsive noise mitigation methods and general models of channel and noise. The results demonstrate that wavelet-based OFDM not only increases spectrum efficiency in comparison with Fourier-Based OFDM, but also provides better performance in the terms of average bit error rate and high peak to average power ratio.

Sea keeping is vital for a floating platform as they are exposed to wave wind and marine current forces. . Therefore, in the event of damage to one or more moorings, other moorings may expose to dame too. As a consequence, analyzing the damaged mooring is of particular importance. In this paper, the effects of different layouts of damaged lines, as well as the effects of these occurrences on the hydrodynamic response of the SPAR platform are numerically investigated. The full scale of the regular wave and time-domain analysis using diffraction theory, is the conditions in the present study. In this research, modeling was carried out on a truss platform spar, which was recently installed in Kikeh oilfield on the coast of Malaysia. The validation of the model is based on the results obtained from the experimental model as well as a valid numerical code in MATLAB software. The results revealed the existence of a good agreement. In the following, numerical analysis of the different configurations of the mooring system and the damaged mooring conditions were performed. The results show that the effects of different configurations in intact mooring system states on dynamic motions of the spar platform are not significant. However, the effect of the damaged mooring lines demonstrates itself as an increase to the mean position of the platform, which was discussed in this paper.

In this paper, the dynamic responses of the KVLCC2 tanker at differents speeds have been evaluated using a numerical method. Ship movements and the forces acting on it have been determined accurately based on computational fluid dynamics method using OpenFoam open source code. Free surface of the two phase flow has been simulated using interFoam and interDyMFoam solvers. The amplitude of ship's heave and pitch motions have been determined in the regular head waves at various speeds. The regular second order stokes wave is generated using the input speed technique. In order to verify the accuracy of the numerical results obtained from the present study, the values of the heave motion, rolling angle, thrust coefficient, as well as added resistance compared with the validated experimental results presented by other researchers. In addition, free surface contours and important flow parameters have been extracted. Also, heave and pitch RAO changes are presented and compared with valid experimental results. These simulations are carried out at different speeds and current numerical results have acceptable accuracy compared with experimental data. By comparing the average force applied to the hull in the waves with the amount of calm water resistance, the amount of added resistance is determined at different speeds. The ratio of the added resistance to the total resistance decreases with increasing the Froude number. Due to the hull form of the tanker, the calm water resistance has a higher growth rate relative to added resistance. Such an analysis, using virtual wave making techniques and simulating dynamic behavior Conforms to reality, can provide more accurate results than potential methods and can be used in a wider range of marine applications.

In this paper, lifting line theory(LLT) and finite volume method (FVM) have been used for numerical simulation of hydrodynamic performance of marine propeller. The LLT is based on the potential flow and vortex theory to quickly design and analyze the marine propeller. On the other hand, the FVM is based on the discretization of the Navier-stocks equations. In this paper, the accuracy and efficiency of these two methods have been investigated for analyzing the performance of the submerged propeller. In order to validate the methods, the geometry and experimental results of the VP1304 and DTMB4119 propellers have been used. For studying the hydrodynamic performance of marine propeller,the torque and thrust coefficients versus advance ratio were computed by FVM and LLT. For all of the advance ratios, the FVM provides acceptable thrust and torque coefficients. Wheras its preprocessing and processing times are high. In return, the LLT in low advance ratios did not calculate the satisfactory results. Wheras it needs short cpu time to process.Therefore it is suitable for parametric studies.

Providing fresh water is of the most crucial issues in each countries. So, there exists an increasing need for research and development on the systems like desalinations. Salinity is one of the most important adverse environmental effects of such plants. Literature review shows that there are few researches on the investigation of jet behavior of the multiport system or the shallow water condition using CFD approach. On the other hand, utilization of multiport and rosette systems in high capacity desalination plants is increasing. In this regard, in this paper, effect of port spacing and configuration on brine pollution dispersion in these systems in the shallow water regime are being investigated for the Kangan petrochemical plant using ANSYS FLUENT. Results show that S/dF>2 is conservative and overestimated and S/dF>1 is suffiecient to meet the requirements of the jet dependency. Also, for rosettes, S/dF>2 is underestimated and S/dF>5 is proposed in this regard.

A three dimensional numeric oceanic model sensitive to wind tension based on primitive equations in the earth’s spherical coordinates modified by array of sigma vertical coordinate is designed to simulate the Sound velocity structures in the Northwest Indian Ocean.Wind speed data from the ECMWF database in 2018 as well as measuring of temperature salinity data, are extracted from WOA18 database. To predict temperature and salinity, after applying the wind stress and initial data on temperature and salinity, the model will be used in each of the months of winter (December 2017, January and February 2018) and summer season (June, July And August 2018). In order to compare vertical sound velocity, seasonal mean of measured and predicted temperature and salinity are used in Mackenzie equation. The results of this comparison show good compatibility between the sound velocity structure obtained from measurements and predictions. The results of the numerical model and also the measurements show that the sound channel is formed under the thermocline layer and is not affected by seasonal changes.

The effects of evaporation on the ocean mixed layer in the presence or the absence of Langmuir circulation (LC) and wave breaking (WB) is studied through the Large Eddy Simulation. We have used approximate parameters of summer monsoon for defining the experimental simulations. The simulations were conducted for 33.5 hours and we ignored the first 9.5 hours of results and the simulated parameters is investigated during 24 hours period. We can mention that there is a good matching between diurnal variations of TKE and SST with diurnal changes of latent heat flux in the presence of evaporation and absence of Langmuir circulation and wave breaking and TKE in this case increased between 25 to 100 percent related to the case on the absence of evaporation. Although, evaporation in the presence of LC and WB decreased SST, around 0.060 C in a 24 hours period, but as expected, it decreased SST in the case of presence of LC and WB less than it (0.050 C). Meanwhile, it was found that, evaporation in the absence of LC and WB causes a slight decrease in velocity shear and shear production and an increase in dissipation rate (approximately double), pressure transport, and TKE transport. These two terms of TKE budget balance with dissipation rate close to the sea surface and the diurnal changes of TKE profile is observable just in this case. However, the most effect of adding the presence of evaporation to the presence of LC and WB in TKE budget is summarized to decreasing of shear production in the middle part of ocean mixed layer. It is also found that, in the presence of evaporation, presence or absence of LC and WB doesn't affect the profile of turbulent heat flux; similar to the evaporation which doesn’t change the Stokes production.

Results of the physical oceanography study in the southern coastal waters of the Caspian Sea were analyzed using field measurements data. The measurements were carried out in the region using acoustical current meter and CTD profiler. The observations were done over ten sampling stations with a maximum depth of 200 m depth during a physical oceanography research. During the marine cruise, CTD probe was released into the seawater column from sea surface to the bottom. Acoustic current meter were deployed by bottom mounted frame over the continental shelf of the sea. Physical parameters such as temperature, salinity, density and current (dynamical parameter) were measured and recorded. The collected data showed good knowledge about formation a seasonal thermal stratification, water column stability, alongshore, and cross shore components of wind and current in the region. The current over the southern continental shelf of the Caspian Sea was significant in terms of speed, and are mainly caused by winds (wind driven) on the areas. The wind area was mainly from the north and northwest areas on the studied area, while surface water flows on the continental shelf from the west and northwest toward the east. At the beginning of autumn vertical structure showed stratification across upper layer with stability at boundaries. In December, thermal and density stratification was not observed in water column.

In this paper a dynamic and discrete berth allocation problem with objective of minimizing total departure delay in Shahid-Rajaee container port is studied. The matter in Shahid-Rajaee container port is low depth of its access channel. When low-depth tide occurs, vessels with deep-draft are not able to pass the channel. Thus they have to wait until high-depth tide occurs and the draft of access channel reach to a passable depth for the vessels. The proposed model is a mix integer linear programming model that is able to consider the effect of tidal phenomenon with each accuracy degree. For evaluating validation of the proposed model first the proposed model is compared to existing operations of Shahid-Rajaee container port. The results show that applying the proposed berth allocation model can improve operations and significantly decrease vessel delayed departures. Next sensitivity analysis for depth of the access channel is proposed. The results have shown dredging of the access channel could have significant influence in reducing departure delays and improving the operation quality of Shahid-Rajaee container port.