This paper proposes an improvement for the dynamic performance of presaturated stacked permanent magnet biased three-phase fault current limiter (PMFCL) through COMSOL finite element simulation. The nonlinear demagnetization behavior of the permanent magnet, especially in the upper part of the B-H curve with negative magnetic field intensity, has been modelled through the Jiles-Atherton method. This enables a realistic representation of the PMFCL dynamic behavior throughout its entire operations of pre-fault, fault and fault removal, respectively. The experimental measurements have been considered to validate the trends of the simulation outcomes during the entire operation of PMFCL. Extensive finite element simulation shows that the stacked design of PMFCL can increase the capability of fault current limiting with proper selection of the number and arrangement of the AC coils around the iron core (soft magnet). Results reveal that the division of AC coils into series differential connected subcoils, with an even number, can increase the limiting capability with increasing the AC coil number of turns, without exceeding the permissible tolerances of voltage drop and power losses. Moreover, this stacked design is subjected to parametric investigation for different fault types, either symmetrical or unsymmetrical, or even when changing the fault current peak value.
The velocity at the toe of a spillway is a major variable when designing a stilling basin. Reducing this velocity leads to reduce the size of the basin as well as the required appurtenances which needs for dissipating the surplus kinetic energy of the flow. If the spillway chute is able to dissipate more kinetic energy, then the resulting flow velocity at the toe of spillway will be reduced. Typically, stepped spillway is able to dissipate more kinetic energy than that of a smooth surface. In the present study, the typical uniform shape of the steps has been modified to a labyrinth shape. It is postulated that a labyrinth shape can increase the dissipation of kinetic energy through increasing the overlap between the forests of nappe will circulating the flow that in turns leading to further turbulence. This action can reduce the jet velocities near the surfaces, thus minimizing cavitation. At the same time the increasing of circulation regions will maximize the opportunity for air entrainment which also helps to dissipate more kinetic energy. The undertaken physical models were consisted of three labyrinth stepped spillways with magnification ratios (width of labyrinth to width of conventional step) WL/W are 1.1, 1.2, and 1.3 as well as testing a conventional stepped spillway (WL/W=1). It is concluded that the spillway chute coefficient is directly proportional to the labyrinth ratio and its value decreases as this ratio increases.
This research study investigates the flexural behavior of fiber reinforced polymer (FRP) bars after being subjected to different levels of elevated temperatures (100, 200 and 300°C). Three types of glass FRP bars (ribbed, sand coated, and helically wrapped) and one type of carbon FRP bars (sand coated) were used in this study. Two testing scenarios were used: a) testing specimens immediately after heating and b) keeping specimens to cool down before testing. Test results showed that as the temperature increased the flexural strength and modulus of the tested FRP bars decreased. At temperatures higher than the glass transition temperature (Tg), significant flexural strength and modulus losses were recorded. Smaller diameter bars showed better residual flexural strength and modulus than larger diameter bars. The immediately tested bars showed significant strength and modulus losses compared to bars tested after cooling. Different types of GFRP bars showed comparable results. However, the helically wrapped bars showed the highest flexural strength losses (37 and 60%) while the sand coated bars showed the lowest losses (29 and 39%) after exposure to 200 and 300℃, respectively. The carbon FRP bars showed residual flexural strengths comparable to those recorded for the GFRP bars; however, they showed lower residual flexural modulus after being subjected to 200 and 300℃.
In this paper a three phase Shunt Active Power Filter (ShAPF) is proposed to address the current related issues in a three phase Electrical Distribution System (EDS). A sliding mode controller (SMC) and an Enhanced Exponential Reaching Law based SMC (EERL-SMC) is proposed for a ShAPF to compensate the load current. The controller’s performance is tested by injecting the current harmonics into the system. A non-linear load along with different loads on the distribution side is connected in parallel in a distribution network at Point of common coupling (PCC). Modelling of the system is done using state space analysis. Stability of the system is analyzed using the state feedback approach. The reference source currents are generated using instantaneous PQ theory. For variations in the load, the THD in the source current is realized. It is found that EERL-SMC is more effective for a ShAPF in reducing the high frequency oscillations and settling time for convergence. The source voltage and current waveforms are observed to be sinusoidal in nature. Both the controllers are effective in reducing the THD levels in the source current as per the IEEE standards. A comparison between the controllers is presented in terms of settling time, THD in source current. PSCAD v4.6 is used for simulation works.
The present study examined the possibility of using rice husk (RH) inoculated with ostrich dung (OD) in the anaerobic co-digestion to produce biogas. Four digesters were conducted to observe the performance of the co-digestion process in batch scale for 25 days. Grounded RH were pretreated with five pretreatments, which were ultrasound, hydrothermal, combined hydrothermal-ultrasonic, NaOH (3% w/v) and combined 3% NaOH-ultrasound pretreatment, and these pretreatments caused an increase in biogas production by 50.72%, 34.72%, 57.9%, 60.85%, and 78.65%, respectively, compared to control. On the other hand, the same arrangement of above pretreatments led to improve the cumulative productions of methane by, 66.11%, 44.76%, 74.27%, 77.89%, 101.62%, respectively, as compared to un treated RH. Thus, combined pretreatments including 3% NaOH-ultrasound and hydrothermal-ultrasonic pretreatment is make to enhance production more of biogas and methane yields than sole pretreatments. It was stated there was well compatibility between estimated and predicted values for methane (> 0.95).
The present article reports a simple and cost-effective process to prepare the crystalline MgAl2O4 spinel using non-stoichometric amount of magnesium nitrate, aluminium nitrate by solution combustion route. Thiourea was used as a fuel and reducing agent while soaking was carried at 1000ºC with different soaking periods. After slow drying of mixed solutions at 80ºC for 4-5 hours a gel was formed and got characterized by DTA/TGA (Differential Thermal Analysis and Thermal Gravimetric Analysis) to observe the effect of temperature variation and identify the range of temperature where crystalline nature of the powder was noted. Powder sample was prepared from the gel after annealing at 1000ºC followed by soaking for 4 hours, 5 hours, 6 hours to compare the variation of particle size with respect to time. The calcined powders were characterized by XRD (X-ray powder diffraction) to determine the phases and crystal planes present in the sample, FT-IR (Fourier-transform infrared spectroscopy) to study the types of metal oxide or metal-metal bond present in the sample along with M-O coordination studies, FESEM (Field emission scanning electron microscopy) to observe the morphological structure of the sample, EDAX (Energy Dispersive X-Ray Analysis) to observe the percentage of each element present in the sample. Bulk densities were estimated from 2.4156 g/cm3 to 2.8571 g/cm3 and the rapid increase in apparent porosity of samples 7.4289%, 10.3630% and 32.51% for 4 hours 5 hours and 6 hours respectively were also noted. It had been observed that the average crystal size of spinel particles was about 48 nm, 36 nm, and 47 nm respectively. Finally, hardness of spinel was evaluated by Vicker Hardness test and evaluated to be10.52GPa (1073 HV), 4.087GPa (416.7HV) and 5.079 GPa (517.9HV).
Geological discontinuities play a significant role in the assessment of rock slope stability. Rock slope stability has been studied on the main road between Sulav and Amadiya resorts in Duhok governorate on the southern limb of Mateen anticline, to determine the expected rock slides on this road. Five (5) stations were chosen to study these rock slides that may occur on these steep slopes. All these stations within Pila Spi Formation that consists of hard dolomitic limestone and covering the areas from Sulav resort towards Amadiya district with a length of up to 2.5 Kms. The Stereographic analysis was used to study and classify the stability of these slopes. The analysis showed in all stations the possibility of plane sliding to happen on the bedding plane, and the wedge sliding between the bedding plane and planes of all joint sets, as well as the occurrence of rockfall on some stations.
Reverse osmosis (RO) technology shows common popularity in the field of water treatment as an advanced stage to eliminate the residual biogenic elements and dissolved impurities after the traditional treatment processes. This article highlights the applicability of using RO membrane technology as a post-treatment stage to treat the discharged effluent from the Gaza wastewater treatment plant. The designed experimental model reveals optimal removal efficiency between 92 and 100% for a number of physical, chemical and biological pollutants. The RO membrane unit demonstrates significant removal efficiency compared to the sand filter where the RO removal efficiency for BOD, TSS, TDS, Fecal Coliform and NO3 were 100, 97.5, 92, 100 and 100%, respectively. The quality of reclaimed wastewater was idealistic where the contents of BOD, Fecal Coliform and NO3 in the permeate were nil, and the concentrations of TDS and TSS were 20 and 296 ppm, respectively. Practically, the results confirm that the wastewater with the reclaimed quality could be used for agricultural activities with no degree of restriction according to FAO’s guidelines water quality for irrigation. According to the Palestinian Standard (PS), the quality of reclaimed wastewater is high, class (A), and it could be used without restrictions to irrigate many crops and for the purposes of groundwater replenishment. Related to energy estimation and cost analysis, the numerical model and the market analysis study demonstrate the energy of 1.23 kWh and total cost, i.e. fixed and energy costs, of 0.58 USD to produce 1 m3 of reclaimed wastewater using the RO membrane in the Gaza Strip over a projected lifespan of 5 years.
The advancement of telecommunication technologies has provided us with new promising alternatives for remote diagnosis and possible treatment suggestions for patients of diverse health disorders, among which is the ability to identify Obstructive Sleep Apnea (OSA) syndrome by means of Electrocardiograph (ECG) signal analysis. In this paper, the standard spectral bands’ powers and statistical interval-based parameters of the Heart Rate Variability (HRV) signal were considered as a form of features for classifying the Sultan Qaboos University Hospital (SQUH) database for OSA syndrome into 4 different levels. Wavelet packet analysis was applied to obtain and estimate the standard frequency bands of the HRV signal. Further, the single perceptron neural network, the feedforward with back-propagation neural network and the probabilistic neural network have been implemented in the classification task. The classification between normal subjects versus severe OSA patients achieved 95% accuracy with the probabilistic neural network. While the classification between normal subjects versus mild OSA subjects reached accuracy of 95% also. When grouping mild, moderate and severe OSA subjects in one group compared to normal subjects as a second group, the classification with the feedforward network achieved an accuracy of 87.5%. Finally, when classifying subjects directly into one of the four classes (normal or mild or moderate or severe), a 77.5% accuracy was achieved with the feedforward network.
The present work investigates the effect of the type of carbon precursor on the adsorptive proficiency of as-prepared carbon nanomaterials (CNMs) for the removal of methylene blue dye (MB) from aqueous media. A comparison study was applied to assess the growth of CNMs from the decomposition of methane (CNMY1) and acetylene (CNMY2) using response surface methodology with central composite design (RSM/CCD). The produced nanomaterials were characterized using FESEM, EDX, TEM, BET surface area, Raman, TGA, FTIR, and zeta potential. The as-prepared adsorbent displayed different morphologies and under the experimental conditions, 10 mg of CNMY1 and CNMY2 was responsible for 97.7 % and 96.80% removal of dye. The maximum adsorptive uptake predicted by Langmuir isotherm was about 250 and 174 mg/g for CNMY1 and CNMY2, respectively. The as-synthesized carbon nanomaterial in this study could be explored as a great potential candidate for dye-bearing wastewater treatment.