فصلنامه دریا فنون
پیاپی 1 (بهار و تابستان 1392)

The Joint Tactical Information Distribution System (JTIDS) is the communication terminal of Link-16. JTIDS is a hybrid direct sequence/frequency-hopping spread spectrum system. In this paper, we investigate the performance of Link-16/JTIDS in additive white Gaussian noise (AWGN) when an alternative structure for the physical layer data transfer scheme is employed. The proposed structure makes an effort to optimize the double pulse structure and solve some problems in the old structure. New jamming mitigation method for JTIDS is possible by chip to chip comparing in double pulse structure and symbol decision. In this paper, an analytic upper bound on the probability of symbol error of CCSK is derived for the 32-chip CCSK sequence chosen for JTIDS.In general, the results show that the proposed double-pulse structure outperforms the old double-pulse structure and the single-pulse structure.

In this paper, first the advantages of laser communication link in terms of passive defense - against being heard, no frequency interference, a high data rate and low chance for communication origin tracking- are investigated. Then, the transmitter and receiver which are designed with ZEMAX software are analyzed. Considering environmental effects and using power value on receiver optic's detector, BER value is calculated numerically. Finally, based on average intensity analytical formula, the amount of power in the receiver, and Sea water transmission function, communication link's parameters are investigated during a year, 1390 in Strait of Hormuz and compared with Chabahar link parameters at the same time. Results are shown with graphs obtained from calculation.
The role of using laser communication links are analyzed to improve Camouflage, Concealment and Decoy (CCD) doctrine and to increase military capability and authority of Navy.

Range Doppler algorithm from synthetic aperture radar raw data is processed to produce the final image. The filtering algorithm based on Fourier domain is running for the azimuth and range. To save time fast Fourier transform in the azimuth-frequency and time-range domains for range cell migration correction is used. This domain, Range Doppler domain is called and range cell migration correction is defined and implemented in this domain. Synthetic aperture radar images to improve the clarity of this paper and the algorithm using fractional Fourier transform compared to the classical Fourier transform method is implemented.

In this paper, we focus on a novel parallel manipulator for utilizing in motion simulator of a high speed boat. First, we record behaviour of the high speed boat using accelerometers with a special data acquisition. Next, a novel parallel manipulator is introduced and its inverse kinematics, workspace, velocity and acceleration analysis are performed. Also, according to recorded experimental data of the high speed boat, the feasibility of using the proposed novel parallel manipulator in motion simulator of the high speed boat and necessitates of the use of washout filters is explored. Finally, validation of the analytical equations is compared by ADAMS simulation software.

To evaluate the designed wave measurement sensor, an inclusive software for simulation of sea waves and the sensor was implemented and presented. A typical sensor would be heave, roll and pitch sensors which are used in buoys. The complexity of determinations for transformation of buoy movements may be the main motivation to simulate all processing for such wave sensors. In this paper, the evaulvation of designed sea wave sensor was considered using an implemented software. The software covered estimation of IMU calibration, processing of heave, pitch and roll and estimation of spectral values. A comparison between wave effective height and wave mean direction with OCEANOR buoys was performed with fine agreement. The performance of system due to different designed parameters was assessed and designations were optimized.

In this paper, the responses of a floating barge in waves under hydrodynamic loads are investigated using the BEM-based ANSYS AQWA software. Usually marine vehicles are faced to sea waves with different heights and frequencies during their life. Due to different loads, their locations and tonnages a barge in operational conditions may have different drafts. Furthermore, in most of the time, the loading is more than regular tonnage, which causes critical situations of sea keeping. The aim of this paper is to study the effect of wave direction and barge draft on coupled motions of a floating barge in six degrees of freedom. For this purpose at first the results at design waterline are compared and verified with Newman’s results. Then responses are evaluated in different water lines and wave directions. Results show that the maximum values of Froude Krylov and diffraction forces occur in Yaw motion for 45⁰ waves of 12 seconds period. However the Froud Krylov-diffraction forces occur in roll motion for ±90⁰ waves of 8 second period. Nevertheless, there are not any perceptible changes in structural responses for waves with periods greater than 19 seconds.