فصلنامه دریا فنون
سال نهم شماره 2 (پیاپی 28، تابستان 1401)

Passive Millimeter Wave Imaging Systems (PMWIS) are used to detect hidden objects. Millimeter waves, generated by thermal radiation, pass through textiles, smoke, fog, and living tissue, and these types of systems create high resolution images and they do not need external incident wave. In this research, a PMWIS at a frequency of 35 GHz has been designed and simulated and the basic parameters of this system such as spatial resolution and temperature have been calculated for the intended application. An Antipodal Fermi Tapered Slot Antenna (AFTSA) was designed and built with the Substrate Integrated Waveguide (SIW) and Grounded Coplanar Wave Guide (GCPW) impedance converter. The gain and radiation pattern of the antenna and the reflector antenna were calculated so that it had a suitable spatial resolution for the use of hidden object detection. The proposed system with linear scanning method (Raster) is able to form an image with a spatial resolution of 3.35 cm at a distance of 1.5 m from center of the antenna reflector and a temperature resolution of 0.11 k. In this system, the desired spatial resolution can be obtained by changing the position of the antenna and the more complex scanning methods.

Nowadays, wireless ad-hoc and sensor networks area is one of the hottest research topics in computer networking. Some challenges in these networks are traffic performance, energy consumption and security. Solving the traffic issues and data communication challenges in the networks can be through various strategies on which among them modifying the network layer and routing algorithms is very important solution. On the other hand, among the existing sensor networks, underwater sensor networks are encountering much serious problems in terms of energy source limit and batteries. In this paper, the aim is to enhance the energy consumption in dense acoustic underwater sensor networks utilizing vector-based routing (VBF) such that with creating cubic depth zoning (CDZ), energy consumption is reduced while the traffic performance does not experience any loss. Computer simulation results explicitly demonstrate that in the VBF-based routing protocols, depth zoning is effective to use less energy sources and increase battery lifetimes. Also, the effectiveness in more dense networks is stronger.

In this paper, an all-MOSFET voltage reference circuit with low power consumption to improve ship-to-shore communications, improve staff welfare and optimize fleet-level performance is proposed. The complementary to absolute temperature (CTAT) voltage is generated by an NMOS diode connected transistor. In differential propotional to absolute temperature (PTAT) voltage generator, the use of a cross coupled NMOS and PMOS transistors pairs significantly increases the temperature coefficient of the PTAT voltage. so only one stage of differential PTAT voltage generator is sufficient to neutralize the negative TC of the CTAT voltage generated by NMOS diode connected, which reduces power consumption and chip area. The results of the simulation of the proposed voltage reference circuit in 0.18 μm CMOS technology shows that this circuit can supply a reference voltage of 0.557 V at a supply voltage of 1 V with. TC is calculated 23.4 ppm /° C in the temperature range of -50°C to 120° C. Power consumption is 14.4 nW and the total area is 0.0037 mm2. Also, the power supply rejection ratio (PSRR) and line regulation (LR) are 34 dB and 0.038 %/V, respectively.

In this paper, nonlinear vibration analysis for an orthotropic composite material thin cylindrical shell on the viscoelastic foundation and under internal moving ring type pressure load has been investigated. In this regard, using Sanders thin shell theory along with considering shear deformation and rotary inertia, kinematic relations for the strain-displacements relations with simplifications are rewritten and the resultants components of edgewise normal forces, bending moments and lateral shear force with respect to the membrane and bending strains considering relations for extensional, coupled bending-extensional and lateral shear stiffness matrices are extracted. Then, governing coupled partial differential equations for edgewise normal forces, bending moments and lateral shear forces in axial, radial and circumferential directions under internal moving pressure load are derived. Applying Galerkin method and using assumed mode summation technique for the shell with simply-supported end boundary conditions, an analytical solution for dynamic modal response are obtained. Using a computer code written in the environment of MATLAB mathematical software, modal response for laminated composite cylindrical shell are calculated. The validity of the obtained results is conducted with comparing with the ones in the literature. The effect of variation of different geometrical parameters including radius and thickness of the shell, speed of internal pressure load and types of lay-up of laminates on the dynamic deflection response of the shell are all investigated.

Cylindrical piles are commonly used in coastal and offshore engineering as support structures for piers, offshore platforms and wind turbines. In this research wave impact to consecutive cylindrical piles was numerically simulated by Smoothed Particle Hydrodynamics (WCSPH).The Simulation was performed by unsteady state Navier-Stokes Equations in Lagrangian form. Modelling the real fluid in simulation, the SPS Turbulent method with laminar viscosity was applied in momentum equations. WCSPH has the advantage of exact free surface simulation. But applying this method and especially with turbulent methods causes large errors in pressure field and wave forces. Therefore due to large and unphysical oscillations in pressure field, Riemann Solvers was used to modify the WCSPH. Furthermore due to using diffusion terms in momentum equations, the corrected gradient of kernel was applied. The developed method with non-conservative Riemann solvers with corrected gradient of kernel was called SPH-T-NCR against the non-modified method called SPH-T. Validating the numerical model, the horizontal wave force was compared to three dimensional dam break experimental data. Good agreement was seen between SPH-T-NCR results and those of experimental. Then the resulting force of a regular wave to one and three cylindrical piles was computed. Furthermore the flow pattern around the piles was simulated.

The use of high-speed planing vessels has been developing and along with the development of their application, research and development of knowledge related to different areas of these vessels, including hydrodynamic analysis is being developed. Today, with the development of computers and the development of simulation software, much research in the field of vessel hydrodynamics is done by numerical simulation. In this paper, a planing vessel is investigated using STAR-CCM+ commercial software in regular oblique wave conditions with different directions. To validate the results, due to the fact that in the published articles, there was no laboratory test or similar simulation in oblique wave conditions, the simulation validation was performed using laboratory test results in headsea condition. In the planing boat behavior, it was observed that by deviating the wave from the headsea condition, the intensity of the slamming impact is reduced until the slamming impact is eliminated and the acceleration behavior approaches the linear state. The effect of the oblique wave on the heave and pitch is less and with increasing the deviation of the wave from the headsea condition, the amplitude of roll increases.

In this paper, an innovative method for damage detection for the plate model, along with longitudinal and transverse stiffeners in the side hull of the ship based on the finite element model updating based on the wavelet transform of correlation function is presented. The proposed algorithm is used to estimate the parameters of plate model, along with longitudinal and transverse stiffeners in the side hull of the ship. By the solution of the sensitivity equation through Least-squares method, the finite element model of the structure is updated for estimation of the location and severity of structural damages, simultaneously. The results of the model updating using noise contaminated data indicate the high accuracy of and robustness of the method against modeling and measurement errors.

Floating breakwaters have widely been used in the past and at the present. These types of structures have some important advantages in comparison with the rubble mound breakwaters, particularly in relation to the environmental issues. In the past, most of the studies for these kinds of breakwaters have been focused on flat beds, however, in practice, uneven bed topographies, especially in shallow coastal areas, can be an effective factor in performance of these structures. For the current study, the effect of various geometries of bed forms on performance of floating breakwaters was investigated using Flow-3D software. The incident waves to the model were irregular types and the wave energy spectrum was JONSWAP. The uneven bed forms were investigated in two categories. For the first group, singular uneven bed forms were considered whereas for the second category continuous uneven forms were considered.First, to investigate the effect of different geometries of single bed forms, three common modes of these bed forms as rectangular, trapezoidal with an angle of 70 degrees and a parabolic have been considered. Also, in order to investigate the effect of bed form height on floating breakwater performance, these uneven forms have been studied at different heights. The continuous bed forms were then simulated in two forms of sinusoidal and dunes with different dimensions. Based on the results of this research, it was found that the rectangular uneven bed form of the singular forms had a great influence on improvement of efficiency of the floating breakwater and with increasing its height the performance of breakwater increased. It was also found that the continuous bed form performed better than the all singular uneven forms modes With corresponding height. Finally, the numerical results showed that among the continuous uneven forms of dune shapes,

The extraction of electricity from sea waves in areas with long beaches is particularly important. The prediction of waves by semi-empirical methods is specifically important to evaluate the wave energy potential. Therefore, in this study, the SPM semi-empirical method was used to analyze and predict the waves of the southern shores of the Caspian Sea to determine the energy production potential. First, First, the prediction of wind-induced waves in three stations of Anzali, Noshahr and Amirabad was conducted, Subsequently, the obtained results from the prediction were compared with the measured data relates to the waves in these three stations, which represented a good agreement between the predicted and measured data. Then, the potential of power generation at 8 stations on the southern coast of the Caspian Sea was investigated including Astara, Ramsar, Bandar Anzali, Chalus, Noshahr, Babolsar, Mahmoudabad and Amirabad for a 10-year period from 2006 to 2016 by using wave forecasting and available power generation relationships. Comparison of average energy production in three stations of Astara, Ramsar and Bandar Anzali with other stations showed that the western parts of the southern shores of the Caspian Sea have more potential for energy production from waves. Also, seasonal analysis of energy production based on one-year period data showed that winter and summer seasons had the highest and lowest amount of power generation and wave density, respectively.

This paper investigates the flexural vibration of Timoshenko beams using hybrid modeling. The Timoshenko beam equation is solved by a new analytical method, and then modeled as a series of interconnected distributed and lumped elements. Natural frequencies of a uniform beam with various boundary conditions are calculated using the distributed lumped modeling technique (DLMT). The results obtained by this method are verified with the results of other techniques. The method is then employed for calculating natural frequencies of a submarine propeller shaft using Timoshenko beam theory. The results are compared and verified with frequencies and mode shapes obtained by FEM using ANSYS software. The frequencies obtained by DLMT and FEM are differed less than 5 percent, which confirms the DLMT results. It is shown that the presented method provides accurate results, while it can be simply and effectively applied to the complicated systems.