A common method for controlling a group of parallel converters in decentralized control strategy structure in an island microgrid, the use is the droop-down characteristics of frequency ω-P and voltage E-Q. However, the problem with using this method is that the reactive power is not properly distributed (in proportion to the capacity of the micronutrients) between the micronutrients, which may lead to overload in the converters. Microgrids may also suffer from Dynamic stability problems such as power fluctuations, which can be increased by switching between active and reactive power control. To avoid this problem, the X / R ratio of transmission lines is an important parameter that should be carefully considered in the design of micronutrient controllers. By linearizing and simplifying conditions, the control system conversion function model becomes a single input-single output system, which is efficient enough to show the relationship between control parameters such as slope of droop characteristics and derivative sentences, virtual impedance, and voltage controllers. Using this model, stability conditions for different parameters are analyzed. Also, to improve power distribution stability, common droop strategies are modified by adjusting the slope as well as adding nonlinear sentence sections. This approach reduces the coupling between active and reactive power control and reduces the dependence of power distribution on grid parameters such as the X / R ratio. To evaluate the reliability of the proposed model, the simulation results in a sample island microgrid in MATLAB software are presented.

Reliable and accurate assessment of Dynamic soil behavior curves is necessary for the solution of many soil Dynamic problems, such as the site response analysis. The shear modulus and damping curves of silicate soils under different conditions have been investigated by many geotechnical researchers.Carbonate sediments are located in temperate and tropical areas and cover approximately 40% of the ocean surface. This type of soil is typically observed near offshore hydrocarbon industries, such as the Persian Gulf. Carbonate sand is the accumulation of pieces of carbonate materials, it usually originates from reworked shell fragments and skeletal debris of marine organism. Foundation problems associated with carbonate soil deposits, particularly as experienced by the offshore hydrocarbon industry have led to significant research focused on understanding the behavior of these soils.This study focuses on evaluation of Dynamic properties of Bushehr calcareous sand. The shear modulus and damping ratio of the tested sand was measured at small to large shear strains using resonant column and cyclic triaxial tests.The calcareous sand specimens were tested by a fixed-free type of resonant column apparatus (SEIKEN model). By using the resonant column apparatus, shear modulus and damping ratio of the calcareous sand for the shear strain amplitude ranging from about 10-4 % to 10-2 % were measured. The cyclic triaxial tests were conducted using a fully automated GDS triaxial testing apparatus. The cyclic tests were done on samples with shear strain amplitudes ranging from about 10-2 % to 1 %. The procedure used to perform the Dynamic and cyclic tests was the multi-stage strain-controlled loading under undrained condition.The tests were conducted in three levels of initial effective mean confining pressure equal to 40, 200, and 400 kPa. The sand specimens were constructed in relative densities lower than 50 or 80 percent, depends on the initial effective stress, in order to acquire the target relative densities (i.e.50 or 80 percent) after consolidation.The experimental results indicate that with an increased shear strain amplitude, shear modulus decreases and damping ratio increases. This trend, which was observed for all the tests, is typical behavior of soils under Dynamic loading, as observed in the previous studies.The effect of mean effective confining pressure and relative density on the normalized shear modulus (G/Gmax) curves of the Bushehr calcareous sand was investigated. Gmax is the small-strain shear modulus measured at shear strain amplitude about 10-4 %. The increase in mean effective confining pressure causes the normalized shear modulus to increase, however, it is more pronounced in low effective confining pressure. Changes of the normalized shear modulus curves (G/Gmax-g) at the range of s' m=200-400 kPa is less than that at the range of σ' m=40-200 kPa. Normalized shear modulus curves are almost independent of the changes in relative density of the sand.The results also indicate that the increased amount of initial mean effective confining pressure leads to the smaller damping ratio for the tested sand. It is also observed that damping ratio curves (D-g) are not affected strongly by relative density changes.Comparison of the tests results with the ranges and models recommended by the previous researchers reveals that the normalized shear modulus and damping ratios of the studied calcareous sand are somewhat inconsistent. In fact, there might be a necessity to modify the previous recommendations for accurate prediction of the Dynamic behavior curves of calcareous sands.

Studying the behaviour of supercavitation from the energy aspect can be divided into two sections. Studying the behavior of supercavitation in the flow field and in vicinity of the flow field. A large portion of field energy is kept in the field، and the rest of it distributed as noise (sound) out of the field. In this paper، harmonious structures of the field which are flowing as energy sources are decomposed by POD method (Proper Orthogonal Decomposition) and presented as spatial modes. The behavior of each mode and therefore behavior of supercavitation can be estimated by studying behavior of supercavitation in nearby area by decomposing the spatial modes via Helmholz decomposition to vectorial and Scalar potential function and then modelling of potential section of scalar to spherical harmonics. By investigating spatial modes، the first mode which has the highest energy is known as mean flow and by studying the intensity of spherical harmonic modes it can be shown that dipole source is an appropriate representative for field behavior in the nearby area and as a result supercavitation behavior in far feild.

Due to the lack of measurements in many regions, wave characteristics are estimated using different methods. Wave climate hindcasting/forecasting is mostly conducted by numerical models or empirical methods. Until now, different empirical methods have been developed for wave hindcasting. However, with the development of high speed processors, several sophisticated numerical models have been developed for wave prediction. These models are mostly phase-averaged spectral wave models developed in three generations. In the last two decades, third generation wave models have been used widely in academic and practical projects. In this regard, Port and Maritime Organization has produced his own model, PMO Dynamic. This model has been developed as a part of first three phases of Monitoring and Modeling of Study of Iranian Coasts project. PMO Dynamic package is a software available for engineering purposes. It has several modules that have been developed for different objectives. Wave model is the module which is used for the generation and transformation of wind waves in coastal areas. In this paper, in order to test the PMO Dynamic model capabilities, it has been applied for the prediction of wave parameters in Bushehr Bay and the results have been compared with MIKE21 SW model and measured data.

Due to the wide applications of polymeric materials, it is necessary to develop a Dynamic constitutive model to investigate their strain rate dependent mechanical behavior. In this study, the generalized strain rate dependent constitutive model was developed based on the experimental results of polymers. The experimental data of thermoset and thermoplastic polymers were used to evaluate the model. The present model includes three main components; the first component expresses the elastic stress-strain behavior of polymers. The second component models the nonlinear stress-strain behavior of the material using the Johnson-Cook model and the third component predicts the ultimate strength of polymers. Then, by combining the generalized strain rate dependent constitutive model and the plasticity micromechanical model of Huang, the shear behavior of glass/epoxy composites is predicted. This model, called Dynamic constitutive-micromechanical model, removed dependency of composite mechanical behavior to the fiber volume fraction and the strain rate. Therefore, experimental characterization was reduced significantly.Finally, it was shown that the generalized strain rate dependent constitutive model and the Dynamic constitutive-micromechanical model predicted the mechanical behavior of neat polymers and glass/epoxy composites respectively, with good accuracies.

Background: In intertrochanteric fractures، Dynamic hip screw (DHS) is the most frequently used tool، but several studies did not give good results for this device in reverse-oblique and transverse fractures. Current study aimed to compare fixation results of reverse-oblique intertrochanteric and short-segment subtrochanteric fractures using Dynamic condylar screw (DCS) and DHS in patients referred to Alzahra and Kashani Hospitals in Isfahan, Iran.Methods: In a cross-sectional study، medical files of the patients referred to emergency units of the two hospitals who were diagnosed with intertrochanteric or subtrochanteric fractures and underwent DHS or DCS surgery more than 6 months before were assessed; they were invited for follow-up visit and examination. Written consent forms were taken from all the patients upon their entry; and they were examined in terms of complications including nonunion and failure of device and level of fracture improvement. These cases were evaluated by simple radiography ,too. Results obtained from examination of patients in addition to demographic information were recorded in the data collection form for each patient.Findings: Perfect union was observed in 14 (of 25) patients in DHS group and 21 (of 25) patients in DCS group (56% vs. 84%) six months after the surgery. Bone union was significantly better in DCS group (P=0.031). In addition, six months after the surgery, the devices used in 14 people in DHS group and 24 people in DCS group were fixed and the difference between the two groups was significant (P=0.001). 14 and 24 patients had total recovery in DHS and DCS groups، respectively (20% vs. 44%) with a significant difference (P=0.020).Conclusion: Considering obtained results, it can be concluded that using DCS is recommended over DHS due to severity of pain, bone union and fixation of the device.