iraj rajabi

In addition to aerodynamic pressures, the wing of a flying boat is also subjected to combined hydrodynamic forces from the ski side (caused by landing and takeoff on the sea). In the asymmetric seating mode, the bending moment applied to the wing spars is one of the most important loading modes in the design of the wing spar structure. In the composite wing, the most critical part is the connection of the flange to the spar. In the finite element modeling of the real composite wing, which consists of a number of spars, ribs and other members, the connection of the flange to the web is done in a simple way without modeling the details of the connection.In this research, the finite element analysis of the wing spars of a flying boat with cross section I with different geometries under different types of loading (according to the standard) for different functional modes is performed. then, based on the results of the numerical analysis, general and simple design rules and guidelines are presented regarding how to connect the flange to the web of these spars.At the end, in order to validate the results of the finite element, an experimental sample has been built and tested, and the comparison of the results shows a very good match.

In this research, the optimization of the geometric parameters of the hovercraft skirt is investigated using the PSO algorithm in order to reduce the range of vibrations on the structure and increase the ride quality. At first, the dynamic equations governing the hovercraft in two states of contact with the ground surface and non-contact are presented. Based on the presented nonlinear dynamic equations, the equilibrium point of the hovercraft was extracted and by linearizing the nonlinear dynamic equations governing the heave motion of the vessel around the equilibrium point, the linear form of the governing dynamic equations was extracted. In order to reduce the vibrations and increase the ride quality with the vessel, an objective function is presented, and based on this objective function and using both forms of linear and non-linear dynamic equations, the geometric parameters of the skirt are obtained based on the intelligent PSO algorithm. Finally, it is shown that comparing the frequency and time behavior of the optimized hovercraft with the original hovercraft, the range of vibrations is reduced and the ride quality with the optimized hovercraft is greatly improved.

The Sassanid Empire was one of the two great governments of the civilized world of that day, which not only had unique characteristics in terms of political, religious, cultural and social structure, and in a word, civilization; It also stands out in terms of geography and the extent of its borders. According to historical evidence and documents, with the rise of the Parthians and the coming to power of the Sassanids, the entire social and political structure of the society, including the dynastic system, was transferred to the Sassanid era as one of the main symbols of the continuation of the power of the ruling families. Specifically, in the mentioned period - from the beginning of the Parthians to the end of the Sassanids - the administration of all the affairs of the country was in the hands of the "seven families" and these families are considered as the main foundations for the preservation, stability and continuity of their respective governments. The sphere of political influence of the discussed families in ancient times was very wide and significant in such a way that not only many times the removal and installation of kings was done by them, but sometimes the government was formed by this class. . In this regard, the present study aims to examine the role of ruling families in the Sasanian period. The choice of this topic was mostly due to the fact that, according to the researcher's searches, specific and independent researches that can provide detailed and detailed information about the ruling families, their position and their role and influence in the changes of their service period have not been done. Except for very few and scattered materials among the few researches and historical works, no specific information was found about the mentioned families and their performance.

Statement of the problem: 

One of the periods of Iran's history before Islam is the Sasanian era, which is considered one of the turning points of Iran's history in terms of time. Because this period of history is the meeting point between Islam and pre-Islam.

To investigate the political and religious situation of the Sassanid Empire before the Mehr-narseh dynasty.

The current research method is explanatory-analytical and the method of collecting documentary materials and the research tool is FISH.

Ardeshir's politics and statecraft are based on three principles: the concentration of the Sultanate and the unity of the Iranian nation, the cooperation and coordination of the Sultanate and the clergy, and the strengthening of the Mazdisani cult, and the support and supervision of farmers. First, he united with the Zoroastrian clergy and assigned a religious authority and a great scholar named Tansar to compile and collect the sacred texts. After gaining power, Ardeshir considered the unity and integrity of Iran as the most important issue of the country and his mission; Among the other factors of the tendency to unify religion and government was the presence of Far Izdi and dependence on the royal family, including the dependence on the Achaemenid dynasty. Another case in this regard is the compromise and eclecticism in Ayin and Izdan, which is evident in all aspects of Sassanid politics

At the beginning of the third century AD, the Sasanians arose from the province of Pars, the birthplace of the Achaemenids, and established a government in which the Zoroastrian clergy and Nejadeh families had a special position. In the Sasanian history, especially when the king was weak, Zoroastrian priests and elders and nobles gained more influence and power in the government system, and of course they occasionally had conflicts with each other. In order to understand the history of the Sassanids, the position of these groups and their relationship with the Sassanid family must be considered, as even the fall of the Sassanids should be viewed from this perspective. One of the clans or clan families whose prominent members gained a lot of political and even economic and religious influence in a period of Sassanid history was the family of Mehrnarseh, the great minister during the period of several Sassanid kings. In this research, in order to have a clearer vision of the history of the Sassanids in this period of time, an attempt will be made to study the position of one of the noble families of the Sassanid period, that is, the Mehrnarse family, in the history of political, religious and economic developments during the reigns of Yazgerd I, Bahram V and Yazgerd II.

Estimating dynamic behavior of high-speed Planing vessels is one of the concerns of designers of such vessels. Evaluation of the loading and center of gravity variation effects, for small vessels with different motion modes, are very important at design stages. Such effects, if not taking into account correctly, may affect the final behavior of the vessel. In this research, for investigating the effects of loading and the center of gravity variations on the behavior of a monohull planing boat, a scaled- down 1:5 model was built based on the ITTC standard and Froude method. after the preparation and balance of the model, tests of the model have been carried out in the high-speed towing tank, in calm water and two loading conditions and at four positions of center of gravity. In each run of test (total 40 tests), the resistance, trim and sinkage, have been measured, and the longitudinal and transverse dynamic stability of the model has been qualitatively evaluated. The results show that increasing the weight will increase the resistance. increasing the distance of the center of gravity position from the stern, will reduce the resistance and trim in the displacement mode and increase the resistance in the planing mode. Also, the decreasing the center of gravity distance from the stern, will reduce the resistance and increase the trim in the planing mode, but may results in the longitudinal instability of the model in some extreme conditions.

This research was carried out based on ecological monitoring of the Caspian Sea in depth of 30 meters project during 2018-2019. Sampling from the bed sediments of the southern Caspian Sea in 8 transects including Astara, Anzali, Sefidrood, Tonekabon, Nowshahr, Babolsar, Amirabad and Turkmen was done by a cat sampler. Sampling was done seasonally. The aim of this study was to investigate the species diversity, density and biomass and local distribution of different macrobenthos species. A total of 16 species were identified, belonging to 7 families which of Polychaeta, Crustacea and Bivalvia were found. In addition, Oligochaeta have been identified. The polychaeta comprised 59% of the total macrobenthos density. In contrast, Cerastoderma glaucum, although the frequency was 6.3% of the total density of macrobenthos, but comprised 59.9% of the total biomass. The results showed that the diversity indices had the highest value in spring and the lowest in summer. Polychaeta had the highest local distribution (100%) and Malacostraca Pterocuma sowinskyi and Cardiophila baeri had the lowest (8.2%). The lowest and highest mean (±SE) densities were recorded in winter and spring with 408±81.1 ind.m-2 and 1225±246.2 ind.m-2, respectively. In conclusion, the increase in biomass of bivalve molluscs versus the decrease in density can be due to the large size and having oyster shell and the increase in diversity indices in spring can be due to the presence of different species for reproduction after wintering period which is consistent with the density of macrobenthos in the spring.

The purpose of this study was to investigate the seasonal variation of distribution, abundance and biomass Streblospio gynobranchiata of substrate sediments on the Southern coasts of the Caspian Sea (Bandar Torkman and Babolsar) in 2018-2019. Sampling was done seasonally and 6 stations at depths of 5, 10 and 30 meters of the 2 transects. The results showed that the mean (±SE) of abundance and biomass were in the Babolsar transect (respectively) 207.06±51.40 ind.m-2 and 0.042±0.006 g.m-2 and seasonal study, the highest abundance and biomass in Babolsar transect with mean (respectively) 1297.47±284.95 ind.m-2 and 0.222±0.040 g.m-2. So there was a significant difference between the abundance and biomass in different seasons (p<0.05). Also showed that the mean (±SE) of abundance and biomass were in the Bandar Torkman transect (respectively) 206.51±53.07 ind.m-2 and 0.043±0.005 g.m-2. According to seasonal study, the highest abundance in Bandar Torkman transect with mean 942.27±180.07 ind.m-2 in summer and highest biomass 0.153 ± 0.03 g.m-2 recorded in spring, so there was a significant difference between the abundance and biomass in different seasons (p<0.05), which is due to their reproductive cycle. The total organic matter in different seasons was fluctuating, which could be due to the depth, substrate and ecological origin.

This study was carried out in line with the Caspian Sea Central Plateau Water Transmission Program in the southern shores of the Caspian Sea and Goharbaran region in 2013-2014. Sampling was carried out monthly at 8 stations at depths of 5, 10 and 15 meters in 2 transects. The purpose of this study was to investigate the relationships between some physico-chemical parameters of water and TOM (total organic matter), distribution, abundance and biomass of different species of Amphipoda in half-lines, depths, stations and seasons. Overall, one species of Niphargoides caspius from the Gammaridae and four species of Stenogammarus similis, Stenogammaus macrorus, Stenogammarus carausuii and Stenogammarus compenus of Pontogammaridae were identified. A total of 15118 individuals of the benthic organisms were counted, in which, S. compresus and N. caspius with 68 and 2 percentages, respectively. Overall, the mean (± standard error) density and biomass of benthic organisms during the period were 128±14.08 ind.m-2 and 0.15±0.01 g.m-2, respectively. According to Spearman test, density of S. carausuii, S. macrorus and S. similis was significantly correlated with sedimentation (sand) (p<0.01). Multivariate cluster analysis based on Spearmanchr('39')s correlation coefficient on the relationship between density and biomass of different species of Amphipoda with some environmental parameters, grain size and total organic matter (TOM) of bed sediments showed that the members of this group belonged to a sand bed and dissolved oxygen are more strongly correlated in which could be due to ecological origin of Amphipoda groups.

The effects of some environmental parameters on biomass and agar yield of Gracilariacorticata were examined under laboratory conditions. The macroalga was collected from natural tidal pool with in Bostaneh coast (the Persian Gulf) in May 2004. In the laboratory, biomass and agar yield were measured after 45 days examining effect of different temperatures (24, 27 and 32°C), photon irradiances (24, 66 and 94 photons m-2s-1), and concentrations of ammonium phosphate [unenriched seawater (0), 0.04 and 0.08gl-1] in culture. Except for concentration of ammonium phosphate, other environmental variables showed no significant relationship (P>0.05) with biomass and agar content of G. corticata. The agar yield derived from the alga cultivated at 0.08gl-1 ammonium phosphate (22.40±1.81%) was significantly greater than the other treatments that makes G. corticata one of the commercial agarophytes (p<0.05).

There exist simple theories to predict the strain of sandwich structures under a bending load and specific support conditions. Although theoretical predictions are highly effective, but the role of testing in validation of these theories and their progress is undeniable. The main goal of the present paper is to prepare a test instruction in order to minimize the error of data acquisition and their analysis. The effects of specimen thickness, place of strain gauge installation and kind of strain gauge was investigated. Characterization of mechanical properties of test specimens are another focus of the present study. Classic theories are used to validate the results of the tests. Based on the large number of tests conducted on the samples, the results show that an important source of error in between experimental and theoretical results may be incorrect installation of the strain gauge. A method to find this out, is to obtain the results of loading and unloading. The method of using the gauge factor of the strain gauge on the package gives better results. Using a circuit with three wires omits the error of wire resistance. The results of the tests on composite specimens obtained by TML Company strain gauges showed small differences with the results obtained by BLH Company strain gauges. The error between experimental and theoretical results in sandwich specimens increases by increasing the core thickness. The measurements obtained by strain gauge in compression is not reliable. An important result obtained was that a half-bridge installation of the strain gauge decreases the error so much.

This paper presents weight optimization of laminated sandwich panels with simply supported edges, subjected to out-of-plane load. Face wrinkling and intracell buckling are two famous local buckling of sandwich panels that are comprised important constraints of this optimization. A nonlinear analytical method has been exhibited using shear deformation effect and midplane displacement. Because of problem complexity and discontinuity of variables, genetic algorithm is preferred for this optimization. In this algorithm, a new method has been considered to stacking sequence and selection of facing and core materials. Finally, comparative results for various loads are presented.