نشریه هیدروفیزیک
سال ششم شماره 2 (پیاپی 11، پاییز و زمستان 1399)

An accurate knowledge and understanding of wind-driven wave characteristics is one of basic requirements in marine activities and environmental studies. The present research deals modeling wind-driven wave with irregular triangular computational mesh grid in the Caspian Sea. Then, the wind-driven wave field of the Caspian Sea has been analyzed in the 2000 - 2020 period. For this purpose, the SWAN numerical model with irregular computational mesh grid was used to simulate wind-driven wave characteristics using Era-Interim reanalysis data with accuracy of 0.125 degree. The results of the modeling were validated with the measurements data in Nowshahr, Amirabad and Anzali buoys position. To increase the forecast accuracy, the model with different AGROWTH and the Whitecapping coefficients was evaluated in the Caspian Sea. Then the monthly average sea surface wind and the significant wave height field extracted for a period of 20 years. Also, dominant wind-driven wave patterns were extracted using the Empirical Orthogonal Functions (EOF) analysis method in the study area. The results show that three first main components of the EOF analysis are respectively about 70%, 20% and 5% of the total anomaly pattern of the wind-driven waves in the Caspian Sea. Therefore we can interpret separately the effect of the local waves on the general wind-driven wave pattern of the Caspian Sea.

Engineers every day by day need more to estimate longshore sediment transport rate for the design of ports and coastal structures, , determine the rate of dredging and its costs, and identify long-term reactions to sediment changes along the shoreline; Using a comprehensive formula to calculate and predict longshore sediment transport rate (LSTR) is critical to starting and continuing engineering projects.The equations in the literature so far only included a number of effective parameters in each region that did not provide an accurate estimate of the LSTR along the coast in the complexity of coastal sediment transport. Due to the complexity of flow and sediment in different conditions of coastal dynamics, engineers need to choose equations that, in addition to meeting their needs in different conditions, also provide a relatively accurate forecast of LSTR.In this research, first all the parameters that effect on the LSTR were investigated, secondly using dimensional analysis, the dimensionless and dimensional parameters are related to each other and we obtained equations. Thirdly, we used the Incomplete Self Similarity Theory (ISST) for predicting the flexible equation in different coastal dynamics conditions for calculates the LSTR in different type of coasts. Finally, we used 10,967 data over a 51-year period, the various LST equations were compared with the CERC and Kamphiuse and Bayram equations (CKB) and the least error was related to ISST equation and then CKB.

Despite the existence of the regulations that penalize wastewater discharging into water sources, repeated violations in terms of discharging has been occurred for many years. Therefore, identifying the pollutant source is of high significance. Pollution introduced into the river is transmitted to the downstream via the advection-dispersion process. Direct advection-dispersion equation (Direct ADE) or positive time step can be solved using traditional numerical and analytical methods. In the true solution, the upstream Pollutant concentration time pattern is already specified, and the aim is to find the temporal and spatial distributions of pollutant concentration at downstream.In contrast, in inverse solution, a totally different approach is adopted. Inverse solution of ADE in the form of negative reverse time step falls into the category of the partial differential equations (III-posed), and the answers to this equation do not achieve convergence. Therefore, the quasi-reversibility method is used. The quasi-reversibility method is basically built upon the addition of the stability term, which includes the fourth-order term and the stabilization coefficient and plays a major role in the convergence of the inverse answers to ADE. In the next step, ADE and stability term are solved by Fourier transform (FT). This solution leads to a highly oscillatory integral using FT. By solving this integral, Pollutant sources time pattern (time series) can be identified. To resolve the integral, two hypothetical examples (simple and intricate) were used, and the validation of the numerical results indicates the high capability of the analytical model.

In this study, using filed data measurement and time series spectral analysis on velocity factors, the period for diurnal and semidiurnal tide elements of the current were determined. The direction of the residual currents showed a surface current into the Persian Gulf and another current out of the Gulf. This indicates that in this region, the anticlockwise gyre takes place at the same time as time stratification and thermocline. The velocity of the residual current is about 10 cm/s and the velocity of the tidal current is measured at 50 cm/s. the diagrams show that the tidal current has affected the temperature up to the 30 m depth and in lower depth, it has less effect on temperature. It also has a stronger effect in spring than in winter. Therefore, moving from surface to depth, as the water temperature decreases, the effect of the tide on the temperature is decreased. The maybe related to the formation of temperature gradient and thermocline in the spring or the back and forth movement of the tidal current which created the waves and caused the increase in the temperature and decrease in the salinity. Where there are stronger layers, there is a stronger gradient as well as stronger tide effect. Also, the effect of the tide on salinity on the surface is very weak while it is stronger in some depths which may be related to the area topography and back and forth movement of the tide current.

In this study, to investigate the seasonal changes in some biological parameters of the Persian Gulf, a coupled physical-biological ROMS model is used. The biological model coupled with the physical model has seven state variables includes two nutrients, phytoplankton, chlorophyll, zooplankton and small and large detritus (N2PChlZD2). The results show that the pattern of seasonal changes in chlorophyll-a in the Persian Gulf can be divided into two regions. The first region is the northwestern part, where the growth of chlorophyll begins in spring and extends eastwards along the southern coasts until late summer and early autumn. The amount of chlorophyll-a in this region throughout the year is higher than the other parts of the Gulf and also peaks in early spring. The second region, which includes the middle and east parts of the Persian Gulf blooms in summer and peaks from late summer until early autumn. Moreover the results also show that the pattern of growth and expansion of chlorophyll-a in the Persian Gulf are independent of the Sea of Oman pattern, and its changes follow the pattern of Persian Gulf currents. In addition, the results show that there is a high concentration of nitrate in the northwest of the Persian Gulf, that it is a good reason for beginning of the phytoplankton blooms from the northwestern part of the Persian Gulf and its extension to the other parts along with the regional currents.

Significant Wave Height (Hs) prediction is used in the analysis of marine systems including marine structural engineering and sediment transport. The Gulf of Mexico faces tropical storms shaped hurricane annually that affects the height of waves in this region, Therefore it is important to have precise estimation of the significant wave height. In this paper, we review previous studies and train artificial neural network model, to predict the effect of different wind speed powers and shear velocity in predicting the wave height in the next hours. The results showed that the presence of different wind speed powers increases the accuracy of predicting Hs relative to the wind shear speed. To increase the prediction accuracy, autocorrelation of the wave height data recorded in this region was used and a suitable model was presented. In this model was calculated power 2.3 of wind speed to predict the height of the next 3, 6 and 8 hours and power 1.9 to predict the height of the next 12 hours. Finally, the prediction results were compared with previous studies, and indicated the higher prediction accuracy.

Thermoplastic polyurethane elastomer (TPUs) were synthesized by poly (oxytetramethylene) glycol (PTMG), hexamethylenediisocyanate (HDI) and 1, 4- Butanediol (BD) at three different molar ratios (1:4.2:3, 1:2.1:1, 3:4.2:1).The effect of stoichiometric balance on the acoustic and damping properties was evaluated. Fourier Transformed Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffractometry (WAXS), Scanning Electron Microscope (SEM), specific gravity, Dynamic Mechanical Thermal Analysis (DMTA) and specific gravity were used to investigate the structures. PUUEs chemical structures were characterized by FTIR. The data on the scattering of the wide-angle X-ray is ascribed to the TPU matrix hard parts phase segregation.The results of DSC and XRD backed up the amorphous and crystalline type of PUEs with 12 and 33 wt % of hard segment (HS), respectively. Changing in molecular structure cases changing in hard segment and specific gravity. This was enhanced in HS, leading to changing in storage modules and damping factor. Damping factor decrease 75% and velocity and acoustic absorption coefficient, in room temperature and 1Hz frequency, changes 200%.

In this paper, a numerical model for calculating the density and electron current of quantum wells of AlGaN / GaN transistors is presented by considering hydrostatic pressure, which enables the effect of pressure on mutual conductivity, quantum well subbands, surface and volume leakage currents and finally check for minimum noise. In this model, a self-consistent solution of Schrodinger and Poisson equation is used to obtain a two-dimensional electron gas density in which up to five energy subbands are considered. An increase in hydrostatic pressure is equivalent to creating a virtual gate adjacent to a real gate., which increases the quantum well depth, current and electron density, cross-conduction, leakage currents, and finally the minimum noise. As the pressure increases, the quantum well subbandes are compressed downward, and the electron-dependent energy increases and the quantum confinement increases. Also, at any desired frequency and drain-source current, increasing the pressure increases the minimum noise. The calculated results are in good agreement with the available experimental data.

In this paper the thermos-acoustic properties of graphene oxide thin film samples synthesized using the vacuum filtration method on the porous Polyvinylidene fluoride membranes have been investigated experimentally. To this end the electric impedance of the samples measured after mounting proper electrodes. In spite of minor fluctuation, the measured impedances are constant and pure resistive. In the following by applying AC voltage in the frequency range 150Hz-20kHz, the radiated sound pressure level of the samples have been measured using the sound level meter. The results indicate that the frequency of the radiated sound waves is twice the frequency of the exciting voltage, as expected in the thermos-acoustic effects. In addition it is found that the radiated sound pressure level of the samples increase monotonically by frequency and the exciting electric voltage and decreases by the resistance of the samples. Investigation of the sound pressure as function of the frequency represents an additional peak in the frequency of applied voltage.

Coastal monitoring is one of the important factors in managing natural resources. The purpose of this research, was detection of the coast and coastline in year 2018 AD in the Gulfport area. In this study, data from Terra satellite, Landsat 8 satellite an Sentinel 2A were used for the studied area and the NDWI index was calculated. Reducing clouds filter was used and NDWIAster image to indicate range of land and water was filtered and thresholded. After running filter for reducing holes and noises on maked image, it was considered as coast. Then, with running an edge detector filter on the coast image, the coastline was detected. The precision of detection of coast and coastline was calculated based on a reference image with the quantities of PSNR, SSIM and Correlation coefficient. The numerical results showed that the best edge detector filter was Robinsons' filter. The amount of cloud cover on processed images and the spatial resolution of the images are factors that have impressed to detection quality.

Among the air-to-water projectiles, the gyroscopic stabilizes ones, have economic and operational advantages over other types. The air stability of such projectiles can be achieved with the gyroscopic effect of the spin. However, maintaining stability of the projectile inside the cavity, is a challenging effect from design and practical point of view. Therefore, it will be important to figure out parameters which effects on the underwater projectile stability. It should be noted that experimental study of the underwater projectile dynamics requires a very precise and expensive equipment. Hence, the numerical approach can be used in the design process. The first section of the study, proposed a dynamic model of an air-to-water supercavitating cylindrical projectile. The 6DOF dynamics of the projectile investigated using the Star-CCM+ commercial code. The model's ability to simulate the water entry physical phenomena validated via within literature experimental results and both are in good agreement. Then, the water entry of the projectile was simulated in two situations of having spin and without spinning dynamic, and the results were compared. The results of this study show that, in the oblique water entry process, the existence of circular motion will not have a significant effect on the dynamic and kinematic behavior of the cylindrical projectile. This research proves that, the high-speed oblique water entry dynamics of a supercavitating projectile can well approximated with planar motion in the x-y plate. Proof of this assumption can lead to significant simplifications in laboratory and numerical modeling of such dynamics in the future.

Nature and living organisms provide an abundance of creative designs that can be used to solve many technical and engineering problems. Fast swimming shark skin is covered with low drag microstructures which is a good source of inspiration from nature for numerous engineering applications. The main objective of this research is to explore the abilities of additive manufacturing methods and to use 3D printing technology to fabricate drag-reducing riblet surfaces. Thus, the shark skin imitated riblet surfaces have been designed and fabricated in micron scale by using a yellow resin specially-formulated for 3D printers and the DLP technique. Then, a closed channel made of Plexiglas with its bottom surface covered with a riblet surface has been designed and constructed to evaluate the ability of these surfaces in reducing the pressure drop. An engineering system including a pump, rotameter, water tank, connecting tubes, differential pressure transmitter, power supply and monitor has been installed to measure the amount of pressure drop across the channel for various riblet surfaces. The tests have been performed for different Reynolds numbers and various riblet surfaces, and the pressure drop results have been compared with empirical data for a channel with simple sample. The findings indicate the ability of riblet surfaces in reducing the pressure drop across the channel.