فصلنامه علوم و فناوری دریا
سال نوزدهم شماره 73 (بهار 1394)

In this article we have discussed seakeeping different body types. As we know seakeeping ability of a vessel or offshore structure to the desired buoyancy is such that if a vessel or floating structures، seakeeping good، bad sea conditions can also have acceptable performance. Numerical Investigation movements with heave and pitch of three type hull of Wigley، Series 60 and DDG 51 floating in front of the regular wave and validation of numerical results are compared with experimental results to predict seakeeping floating ship in effect Maxsurf Ratios software deals have. It should be noted that the shape and size of ship movements of the body، but the results of this study cannot be used in similar cases.

Clutter is one of the main reasons which produce sonars'' false alarms. Clutter modeling is the first step for recognizing، controlling and removing this phenomenon. The precision of the clutter''s model، in approximating the statistical parameters of clutter، is the challenging point. The probability density function of the clutter distribution is usually determined by the K-distribution; so that the shape parameter of this distribution (α) is conversely related to the statistical parameters of the false alarm rate. This paper uses the clutter''s model in the surface of the array of hydrophones and then analyzes the shape parameter''s precision of the obtained distribution. In the following، the accuracy of the calculated shape parameter will be compared by other criterion parameters which describe the sonar''s clutter.

Grain size analysis is one of the most important tools for classifying sedimentary environments. Although for this analysis demography computations are common، but these methods are time-consuming and difficult. As grain size is critical in sediment erosion، accumulation، and transportation، so it''s important to use a more efficient method for grain size analysis. This research conducted to determine the sediment texture and grain size distribution in the Caspian Sea، Noor coastal area، by sediment sampling and application of the GRADISTAT program. Results indicate that in general، the texture of sediments in Noor coastal area is sandy and its D10، D50 and D90 are 1. 251Ф، 2. 605Ф and 2. 693Ф، respectively.

Simulating and predicting of marine statistical data such as wind and wave are of the most needed information of sea and ocean. In this regard، several methods and models have been created for simulating wind and wave including spectral and numerical models، semi-experimental and experimental methods. One of the proposed methods in this area is the nonlinear dynamics and chaos theory. In the dynamic systems literature، the term chaos is used to refer to situations where complex and random-looking behaviors arise from simple nonlinear deterministic systems which can be predictable. In this paper in order to define the dynamic parameters of strong breeze speed and significant wave height، daily data form the buoy in Asaluyeh Port during 2007-2008 were utilized. Nonlinear dynamics were carried out by phase space reconstruction and calculating the delay time، embedding dimension، correlation dimension and maximum Lyapunov exponent. Results indicate the chaotic behavior of significant wave height (with a correlation dimension of 6. 7) and stochastic behavior of strong breeze.

In this paper، a combination methods to separate of overlapping radar pulses، is presented. The advantages of this method، is less processing capacity and providing the possibility to create parallel processing in each cluster. Also، by using time domain analysis، not only recognizes the PRI type and differentiate subgroups in each clusters، but also uses time as a tool for clustering. The flowchart of the proposed method and detail of the procedure are described in this paper. The clustering algorithm can be done in real time and their accuracy is increased، because of continuous processing. The computer simulation and results، in the following papers will be presented.

Ballast water is held in tanks and/or cargo holds of ships to provide stability and maneuverability during a voyage when ships are not carrying cargo require more stability due to rough seas. Ballast water maybe either fresh or saline. Aquatic species arrive through a variety of mechanisms unintentionally when attached to vessel hulls or carried in vessel ballast water and intentionally when imported for aquaria display، as live seafood for human consumption، or as a transplant to increase sport fishing opportunities. Ballast water is an important way of transferring aquatic nuisance species (ANS) all over the world. ANS include algae، shellfish، developing larvae، eggs and other microorganisms. Due to the lack of natural predators in the new environment، they are often able to thrive and outgrow the native species. This domination can cause massive ecological، economic، and public health problems such as degradation of habitat، alteration of water quality، blockage of flow in drainage and irrigation canals، or even transition of diseases to humans. The International Maritime Organization (IMO) regards the introduction of harmful aquatic organisms and pathogens to new environments via ballast water، as one of the four greatest threats to the world’s oceans. At least one foreign marine species is introduced into a new environment every nine weeks. In this paper the ballast water management methods is explained under three categories، the exchange، the treatment and the isolation of the ballast water. The advantages and disadvantages of these methods are also discussed.