فصلنامه دریا فنون
سال پنجم شماره 4 (پیاپی 14، زمستان 1397)

Low noise amplifier is one of the most used blocks in a radar reciever such as fire control radar. In this paper, a broadband amplifier is proposed applying for the frequency range 2.5 to 5.5 GHz. The input stage of this circuit is defined as common-source. A standard 0.13 CMOS technology is used for simulation. Amplifier has a good stability thorough the frequency range of operation. The third order linearity is improved by derivative superposition method. the complementary transistors in the input stage was used to achieve good IP2 for proposed LNA. The simulation results show that the LNA achieved the maximum gain of 11.3 dB, input and output return loss lower than -8 dB, A minimum noise figure 2.3 dB in 2.5-5.5 GHz, an IP3 of -3.2dBm and an IP2 of +13.3 dBm. The power consumption is 18 mw from a 1.5V supply.

Gas sensors generally have the task of absorbing and detecting gas molecules on a sensitive material that in this paper, using zigzag type graphene nanotubes and Armchair type without applying gas and applying gas, will be simulated and analyzed using ATK software. Due to the characteristic electronic gas sensor including the voltage-current characteristic can detect the toxic molecules found in the tissues of the body. Selective toxic molecule In this article is Sulfur dioxide which is one of the known toxic gases and as a chemical compound in the form of gas at room temperature with the chemical formula SO2. By studying the results of simulations, can see the high sensitivity of the graphene nano-type armchair type than the zigzag type to detect the gas.

In this paper, the effect of the compressor pressure ratio, the input temperature to the gas turbine and the recovery pressure of the steam boiler is investigated by examining the simultaneous generation of electricity and heat from the perspective of economical exergy and exergy. The results show that the energy efficiency and exergy of the CHP cycle are greater than the gas turbine cycle and are the most common exergy loss in the combustion chamber. Exergy efficiency increases and then decreases by increasing the compressor pressure to an optimal amount. As the input temperature increases to the turbine gas, the exergy efficiency increases, the loss of exergy, and the rate of cost of the exergy casualties decreases. By increasing the temperature of the saturated vapor in the CHP cycle, the energy efficiency decreases but the exergy efficiency increases.

Wet Cooling towers (WET) that are widely used in different industries and air conditioning systems to remove excessive heat, have disadvantages and limitations. Cooling towers are one of the biggest heat andmass transfer devices that are in wide spreaduse. To overcome these limitations, Counter Flow Shower Cooling Tower (SCT) which is within the Wet Cooling Towers(WCT) category is presented. In this paper, analyzing heat and mass transfer in counter current open cooling towers. Using a computer program, the numerical solution will be executed and the effect of proper environmental and geometrical parameters will be reviewed and compared with experimental results in the recourses. Moreover, the effect of velocity variation, enthalpy, humidity, temperature and droplet diameter on the cooling efficiency of the tower will be investigated. It was concluded that amongst all mentioned parameters, the droplet diameter has the most impact upon decreasing the output temperature of the cooling tower. By changing geometrical parameters(tower height increase and droplet diameter reduction), the outlet temperature of the SCT in different ambient condition could be improved. these towers have high efficiency in dry-cool and dry-hot regions.

In the present study, the four-stroke marine diesel engine power generation cycle is studied and thermodynamic analysis is carried out. First and second law of thermodynamics analyzes have been on different components of the cycle in order to determine the effect of each components on the cycle performance and to improve the effeciency of them. Also, the effect of ambient air temperature on engine performance has been studied to determine the effect of temperature on engine performance during the combustion process. This model results have been compared with the experimental data, good agreement between the results confirmed the accuracy of the present model. The results show that turbine has the best performance of the first and second law of thermodynamic efficiency. Charge air cooler has the lowest efficiency of second low about 36.65%, and the diesel engine efficiency is 45%. The highest exergy destruction is occurred in the diesel engine about 85.54% and lowest exergy destruction is occurred in the oil cooler exchanger about 0.51 %. About 32 percent of the fuel energy remains in the exhaust gases. According to the results, the diesel engine, charge air cooler and exhaust gases are the best components for improving cycle performance. Finally, based on the results, diffrent ways have been suggested to reduce losses and waste heat.

Hydrodynamic coefficient estimation is an essential part of underwater vehicle dynamic model design procedure. Due to existence errors in analytical calculation methods, results of the methods are not reliable. Also, determination of the coefficients by experimental test is a difficultly and costly work. This procedure due to nonlinear behavior of the system has some problems. A suitable solution is using estimators for the coefficient estimations that the estimators can present suitable estimation of coefficients using experimental tests. Also, the estimator output can be used in the design of the system adaptive control. In this paper, equations of motion of an autonomous underwater vehicle (AUV) in six degree of freedom for coefficients estimation are properly modeled. Then, using of Extended Kalman Filter (EKF) and reduced order measurement with respect to similar methods, all of viscous damping coefficients are estimated. The method is implemented on an actual AUV and the results indicate a good performance of proposed method.

The purpose of this study is numerical investigation of the simultaneous effect of reservoir geometric shape on the plan and its slope on the model as well as the flood wave fluctuates due to dam break. The downstream bed is considered as dry. Characteristics of flow due to dam break in two reservoirs are studied and compared under long and wide geometric shapes and reservoir bottom slopes of 0%, 2%, 3.5% and 5%. The modeling is carried out in 3D mode using Flow3D software. The results indicate that in the wide reservoir with increasing the slope of the reservoir bottom, the water level is not significantly different in the downstream and upstream of the dam, but severe variations of the water level is observed in the wide reservoir at all slopes at the downstream of the gate. The reason for these variations can be due to the shape of the tank because surges occur after the sudden opening of the gate while these waves are dissipated over the reservoir in the long reservoir. In the long reservoir and at the upstream points of the gate the level water is decreased by increasing the slope of the reservoir bottom and the lowest water level is observed for the slope of 5%. At the downstream points of the gate in the long reservoir the water level decreases with the increase in the reservoir slope and over time at t=7s the loss of water level drop for slopes of 3.5% and 5% is more than other slopes.

AbstractApplying wind energy as a source of renewable and alternative fuels is very important. Given that the sea is the more stable and fast winds, so most of the countries that have access to the sea, are in particular attention to the installation of wind turbines in the sea. New problem arise with the installation wind turbines in the sea, which is due to additional sea states such as wave and current loads. Therefore modeling and analysis of offshore wind turbines under wave and wind loads is essential. In this research the offshore wind turbine with tripod platform has been modeled and analyzed under wave and wind excitations. Then it considers the effects of wave and wind parameters on the response of strucuture. The results show that increasing the waves and the wind parameters does not increase the response of the structure necessarily. Also effect of these parameters on the structural response is different.

Using control tools is one of the efficient methods to reduce the responses of marine structures. The use of dampers in jacket marine structures can help to reduce the dynamic response of the structure with increasing damping and without changing the structural stiffness. In this research, for vibration control of the Resalat oil platform in the Persian Gulf under irregular wave loads, rubber bearing base isolation system along with viscous dampers are utilized. The Morison equation is used for wave force formulation, as well as to model the time history of irregular waves, Jonswap spectrum is utilized. In this study, rubber bearing base isolator with three different effective damping ratios and viscous damper with different damping coefficients were used to investigate the effect of each control tool on structural responses. In addition, to achieve the optimal response, the structure studied in two different conditions; the structure with rubber bearing isolator, and the structure with rubber bearing isolator plus viscous dampers. The results showed that the use of rubber bearing isolator with viscous damper has a better performance on the jacket platform response. It also reduced the base shear of the structure, which could lead to a reduction in the cross-section of the piles.

Image restoration is a critical step in many vision applications. Due to the poor quality of Passive Millimeter Wave (PMMW) images, especially in marine and underwater environment, developing strong algorithms for the restoration of these images is of primary importance. In addition, little information about image degradation process, which is referred to as Point Spread Function (PSF), makes the problem more challenging. Blind image deconvolution is a popular approach for image restoration, which can estimate the original image and the degradation function simultaneously. This is an ill-posed inverse problem and requires regularization to be solved. In addition to the type of regularization functions, the value of regularization parameters can drastically affect the output result. In this paper, we propose an optimized main function for improving the resolution of Passive Millimeter Wave (PMMW) images based on the semi-blind deconvolution and propose a Particle Swarm Optimization (PSO) algorithm for selecting optimum values of regularization parameters in blind image deconvolution. A new cost function is defined for the optimization process which is useful in image restoration. The algorithm has been tested on standard images and evaluated using standard metrics. Two real PMMW images blurred by an unknown degradation function are also used in this algorithm to obtain a sharp deblurred image with an estimate of the PSF. Simulation results show that the proposed method improves the quality of the estimated PSF and the deblurred image.