جستجوی مقالات مرتبط با کلیدواژه « Self » در نشریات گروه « فنی و مهندسی »

Maneuverability is an important aspect of marine vehicle design. With the development and utilization of ocean resources, maritime transportation is becoming increasingly busy. Stopping ability has great effect on the safety of ship maneuvering for those large ships. Therefore, it is necessary to study the behavior of the ship during the stopping maneuver to ensure the safety of navigation. In this study, the stopping maneuver has been investigated directly and with interaction between the ship's hull and propeller, Reynolds Averaged Navier-Stokes (RANS) equations and Star-CCM+ commercial software. well-known vessel KVLCC2 have been selected to study the parameters of the stopping maneuver. In order to reach the design speed of the ship, the self-propulsion test has been carried out using a PI integral controller. Verification and validation of the results have been studied according to ITTC recommendations. By comparing the results obtained in the self-propulsion test as well as the stopping maneuver with some available experimental data, a good accuracy was obtained and the details of the flow parameters, including pressure distribution and wake pattern, were analyzed

Nowadays, fiber-metal laminates (FMLs) have gained many applications in aviation, marine and automotive industries. These structures include thin metallic face sheets bonded to the composite prepregs. Internal damages in FMLs are difficult to detect and repair by conventional methods. To overcome this, in the present study a self-healing polymeric system based on chopped hollow glass tubes has been introduced and employed to recover the flexural strength of Al-2024/E-glass-epoxy/Al-2024 specimens after damage. The micro-tubes were located next to each other in pairs and filled with restorative agents (epoxy resin amine hardener). The aim of this study was to find a suitable volume fraction and also the optimum time to achieve the maximum healing efficiency. Various volume fractions of filled tubes containing 5, 8 and 11 vol.% healing agent together with different time passing period of 3 and 5 days after primary damage were employed. The results demonstrated that the maximum healing efficiency for flexural strength (89%) was observed for the specimen with 8 vol.% healing agent after passing 5 days from the time of damage creation

Introduction of self compacting concrete has brought huge technological advances. Use of SCC facilitated the concrete placing between the rebars, without need of external vibration, and just through the weight of concrete itself. This paper investigated the effects of high temperature on hardened properties of self compacting concrete (SCC) containing powdery admixture. For this purpose, self compacting concrete control (non-pozolan) specimen of ACI 237R-07 mixed design has been used in accordance with instructions. First, in order to ensure the satisfaction of tolerance related to quality control of SCC in fresh mode; slump flow, L box, T50 and V funnel were performed. Then the hardened specimens containing various minerals admixture (metakaolin, fly ash. silica fume and zeolite) were 91 days old heated to elevated temperatures (300, 500, 700 0C) to evaluate mechanical properties. Furthermore the ultrasonic pulse velocity test as non-destructive methods to estimate the compressive strength of specimen is presented.

self-compacted concrete(SCC) is a concrete that can flow in the space between reinforcement without separation and compact only by their own weight. In this study, the effect of using silica fume, metakaolin, rice husk ash and fly ash with different ratios of 10% and 20% by weight of cement in self-compacting concrete containing magnetic water is concered. The fresh properties of self compacted concrete were's tested by means of slump flow, T50, V-funnel, L-box and visual stability index(VSI). The hardened properties were assessed, using compressive strength at the ages of 7 and 28 days. Also splitting tensile strength and water absorption test were assessed at the age of 28 days. In addition, concrete specimens were made using tap water and magnetic water, was passed through a magnetic field of 0.8 Tesla. The results show that pozzolanic materials are suitable in properties of self-compacting concrete containing magnetic water in terms of flowability and viscosity. Moreover, magnetic water can reduce the amount of superplasticizer, required for SCC, up to 45%. Also the results of hardened SSC show an improvement in mechanical and durability properties of concrete. The usage of silica fume with ratio 20% by weight of cement in self-compacting concrete containing magnetic water, increases the compressive and splitting tensile strengths by 48% and 35% respectively and decreases amount of water absorption by 55% at the age of 28 days.

The diffusion of nitrate pollution in watersheds is due to complex biochemical and hydrological procedures linked to the cycle of nitrogen and water. Nitrate load comes from different sources such as wastewater treatment plants, runoff of fertilized lawns and cropland, failing on-site septic systems, runoff of animal manure storage areas, and industrial discharges that contain corrosion inhibitors. Loss of nitrate to surface and groundwater can reduce farm productivity, harm the environment, and affect drinking water quality. Large uncertainties and limited physical understanding of the water quality such as nitrate barricade the process-based modeling and seek a black box relationship between driving and resultant variables. Therefore, in this paper Multi-Station (MS) modeling of nitrate of the Little River Watershed (LRW) has been done. Hence, MS nitrate modeling is considered whereby nitrate loads of the inside and outlet of the LRW could be predicted. As a more explanation, the nitrate of upper sub-basins are employed for predictions of the interior sub-basins nitrate loads, and then, central sub-basins are participated in outlet nitrate prediction of the LRW. So, MS model can prepare a reliable platform to get information about the amount of nitrate in crucial places of the LRW. For this purpose, two scenarios with distinct views are used for MS nitrate modeling to identify the suitable strategy for future hydro-environmental researches. In the first scenario, Markovian characteristics of the streamflow-nitrate process are proposed as the base of the MS model, where antecedent of streamflow and nitrate time series of sub-basins are shared in nitrate modeling. On the other hand, non-linear feature extraction criterion of MI that is more suitable measure regarding the linear measure of Correlation Coefficient (CC) is employed for the selection of appropriate inputs of the Least Square SVM (LSSVM) and Feed Forward Neural Network (FFNN) models to avoid from the time consuming trial-error process of input selection. In the second scenario, seasonality-based characteristics of the streamflow-nitrate process are focused. Where, streamflow and nitrate time series of the sub-basins are decomposed by the wavelet transforms at a suitable level for clarifying spectral and temporal information of the time series. Then, as a new feature extraction method, both SOM and MI are respectively employed for clustering homogeneous sub-series and selecting cluster's proper agents, to be fed into LSSVM and FFNN models for MS nitrate load modeling of the LRW.

In this study, Ti2AlC ternary carbide by mixing of Ti, Al and C powders and by self-propagating high temperature combustion synthesis method has been synthesized. 2Ti:2Al:1C and 2Ti:2Al:0.5C compounds and carbon sources such as graphite, activated carbon and carbon black were used in order to evaluate the variables of composition and carbon source in the synthesis of Ti2AlC Max phase. First, the primary powders were weighed. Then, the supposed mixed powders were dry grinded for 3 hours. Then, they have been formed in pills under 80 MPa pressure. After applying the self-propagating high temperature combustion synthesis process on the samples, X-ray diffraction analysis and field emission transmission electron microscopy were used to study the phase composition and to observe the microstructure, respectively. Ultimately, determined the maximum amount of synthesized Ti2AlC Max phase was 74 Wt. % and it is related to the sample with 2Ti:2Al:0.5C compound in which the activated carbon is used to provide carbon. Also it was observed that with an increase of 0.5 to 1 mole percent of carbon in the raw materials, weight percent of Ti2AlC MAX phase in the reaction products sharply reduced.

In this study, the effect of nano-alumina addition on the properties of high-alumina low-cement self-flowing refractory castables was studied. For this reason, the reactive alumina in the refractory castable composition was substituted by nano-alumina powder. Then, the self-flow characteristics such as; self-flow value and working time of high-alumina low-cement refractory castables were studied. Besides, the physical and mechanical properties, phase composition and microstructure of these refractory castables were studied after drying at 110 °C and firing at 1250 and 1450 °C. The results showed that the nano-alumina addition has a great effect on the self-flow characteristics and mechanical strength of these refractory castables. With addition of nano-alumina particles, the self-flow value and working time tends to decrease due to high surface area of nano-alumina particles. By use of 1 wt.% nano-alumina content in the castable composition, the alumina self-flowing castable with adequate working time can be obtained according to standard values of self-flowing castables. The decrease in porosity and, increase in mechanical strengths after drying is obtained by adding nano-alumina. The phase analysis and microstructure evaluations showed that CA6 phase can be form at lower temperatures (1250 °C) with the addition of nano-alumina. CA6 platy formation leads to increase of porosity in the microstructure. But, the because of bonding behavior of platy CA6, the mechanical strengths are considerably increased after firing.

In terms of mechanical behavior, human’s speaking and generating voice is a sophisticated process which is resulted in interaction between flowing air through the larynx and oscillating functionality of vocal folds. The sulcus vocalis is one of the individual cases of scarring in which the superficial lamina propria is absent over the length of the vocal fold and can procreate several disorders in voice generation. In this study, for the first time, the effects of sulcus vocalis on vibrating functionality of vocal folds have been assessed by employing finite element numerical modeling. Two-dimensional models of either healthy or sulcus vocal folds were implemented which each one is coupled and solved via LS-dyne software. Also, the three e-layer linear elastic model was utilized for the structure phase and the arbitrary Lagrangian-Eulerian (ALE), incompressible continuity, and Navier- Stokes relations were used for the fluid domain. Type II patients’ self-excited oscillations have been exhibited and compared with the healthy model. The results of the healthy model were assessed and compared with numerical and experimental results of previous studies. Moreover, the influences of the sulcus not only on the flow components but also on the oscillating functionality of the vocal folds have been evaluated. The results indicated that the frequency of vocal folds’ vibrations and the value of volume flux tends to be remarkably declined and boosted up respectively.

Self lubricating coatings are one of the conventional protective coatings in aerospace and power plant industries which have the suitable stability and performance at high temperature. In this research, co-deposition of alumina and silver particles within Ni-P electroless coating were implemented on mild carbon steel substrate. The effect of heat treatment on the hardness of the coatings was investigated and morphology and cross section of the coatings were evaluated by Scanning Electron Microscopy (SEM). The tribological behavior of the coatings was evaluated by pin-on disc method and by using 52100 steel pins at ambient and high temperature and the wear rate was measured by 3d optical profiler. Also, lubrication mechanism was investigated by using energy dispersive spectroscopy analysis (EDS) and wear track micrographs. The results showed that the wear resistance and lubrication of Ni-P-Ag-Al2O3 hybrid coating were increased simultaneously and high temperature self-lubricating characteristics of the hybrid coating have been enhanced by the diffusion of silver through the coating and the production of silver-rich tribofilms.

Asphalt concrete is a self-healing material which can repair damages automatically when it is exposed to rest periods. Healing of an asphalt concrete is the recovery of its stiffness and strength due to closure of the internal cracks. Nevertheless¡ healing rate in ambient temperature¡ especially at low temperature¡ is slow and traffic circulation can''t be closed during reaching sufficient healing. Furthermore¡ self-healing of asphalt concrete is much dependent on temperature and pavement healing will increase at high temperatures. In this research¡ microwave heating was used in order to increase asphalt concrete self-healing capacity through temperature increase. Varying amounts of carbon fiber and steel wool were added to the asphalt mixture to increase thermal efficiency by microwave heating. According to the results of type and optimum wool percent test¡ it was observed that samples with carbon fibers have better efficiency compared to other mixtures with steel wool. Also¡ optimum carbon fiber percent was obtained as 0.2% of mixture''s total mass. Moreover¡ in order to investigate self-healing process in asphalt mixture¡ fatigue life test¡ Cantabro durability test and indirect tensile test were conducted on the samples. Test results showed that heating causes an increase in healing rate of fatigue life and tensile strength and failure samples can recover part of their lost properties. Also¡ healing rate increases with temperature rise¡ as well. Also¡ it was revealed that heating should not be applied very late. Cantabro durability test results showed if heating is applied between the rotations¡ aggregate separation will be reduced because of increasing cohesion between bitumen and aggregates.