This paper proposes a self-excited induction generator model with saturation effect for power generating mode in a remote site. The model is led through the space vector mathematical formalism and allows one to analyze the steady and dynamic states. It is developed for a squirrel cage induction machine. This model provides magnetizing inductance variation able to influence the build-up and the stabilization of voltage generation when the load changes. The final result is a realistic approach model which takes into con- sideration the dependency of the magnetizing inductance versus magnetizing current. This novel model is validated through experimental measurements to demonstrate its validity and practicability.
B a c k g r o u n d: Near Infrared Spectroscopy (NIRS) is considered a reliable assessment method of a balance between cerebral oxygen demand and supply. One of forms of anaesthesia applied during extensive abdominal surgical procedures is the epidural anaesthesia. Its application in addition to the general anaesthesia is a commonly accepted form of anaesthesia in patients undergoing abdominal surgery. The aim of this study was to verify the hypothesis that epidural blocks may have eff ects on cerebral saturation in patients undergoing abdominal surgery under general anaesthesia.
M e t h o d s: Cerebral saturation was monitored intrasurgically. Reduction of cerebral oxymetry by over 25% in relation to the baseline, or cerebral oxymetry value below 50% was considered clinically significant.
R e s u l t s: One hundred and one (101) subsequent and non-randomised patients, age between 35 and 84 years (mean 64 ± 10) qualifi ed for major abdominal surgeries were enrolled. In 14 (13.9%) patients of 101 enrolled a clinically signifi cant reduction of cerebral saturation was observed. In 50 (49.5%) of the enrolled patients, the epidural anaesthesia was applied along the general anaesthesia. A clinically signifi cant reduction of cerebral saturation was observed in 9 of them. No statistically significant association was found between the application of epidural anaesthesia and development of cerebral desaturation.
C o n c l u s i o n: The application of epidural anaesthesia caused no clinically significant reduction of cerebral saturation during the general anaesthesia in course of major abdominal surgical procedures.
The ways of the improvement of the method for the determination of steel losses in the electrical devices of basic types are substantiated. The method is refined by taking into account the magnetic system properties at high saturation. The presence of the interrelation between the special features of the domain structure movement and the shape of the hysteresis loop is proved for laminated cores. It enabled the explanation of the causes for the abnormally high values of the losses in the steel and the atypical shapes of the hysteresis loops at its high saturation. The empiric dependence for the determination of steel losses is obtained. It provides for the high convergence of the calculated and experimental data at the actual degree of saturation and can be used in the direct-current operation of the analyzed devices.
The paper presents a detailed description of one of the newest methods of vacuum saturation of reinforcing preforms in gypsum molds. As an appropriate selection of the infiltration time is a crucial problem during realization of this process, aim of the analysis shown in the paper is to present methods of selection of subatmospheric pressure application time, a sequence of lowering and increasing pressure, as well as examining influence of structure of reinforcing preforms on efficiency of this process. To realize the aim, studies on infiltration of reinforcing preforms made of a corundum sinter of various granulation of sintered particles with a model alloy were conducted. The infiltration process analysis was carried out in two stages. The first stage consisted in investigation of influence of lengthening of sucking off air from the reinforcing preforms on efficiency of this process. In the second stage, an analysis of influence of a two-staged infiltration process on saturation of the studied materials was conducted. Because the studied preforms were of similar porosity, the obtained differences of the saturation level of particular preforms have shown, that the saturation process is influenced mostly by size of pores present in the reinforcement. Because of these differences, each reinforcement type requires individual selection of time and sequence of the saturation process. For reinforcements of higher pore diameter, it is sufficient to simply increase air sucking off time to improve the saturation, while for reinforcement of smaller pore diameter, it is a better solution to apply the two-staged process of sucking off air. Application of the proposed analysis method allows not only obtaining composite castings of higher quality, but also economical optimization of the whole process.
This paper presents a predictive torque and flux control algorithm for the synchronous reluctance machine. The algorithm performs a voltage space phasor pre-selection, followed by the computation of the switching instants for the optimum switching space phasors, with the advantages of inherently constant switching frequency and time equidistant implementation on a DSP based system. The criteria used to choose the appropriate voltage space phasor depend on the state of the machine and the deviations of torque and flux at the end of the cycle. The model of the machine has been developed on a d-q frame of coordinates attached to the rotor and takes into account the magnetic saturation in both d-q axes and the cross saturation phenomenon between both axes. Therefore, a very good approximation of this effect is achieved and the performance of the machine is improved. Several simulations and experimental results using a DSP and a commercially available machine show the validity of the proposed control scheme.
We demonstrated a tunable Q-switched ytterbium-doped fiber laser (YDFL) using MoWS2/rGO nanocomposite as passive saturable absorber. Further, the Mo1−xWxS2/rGO nanosheets, with x proportion of 0.2, are synthesized using hydrothermal exfoliation technique. The proposed nanocomposite-PVA based thin film is fabricated by mixing the MoWS2/rGO nanosheets with polyvinyl alcohol (PVA). The fabricated thin film is sandwiched between two fiber ferrules to realize the proposed saturable absorber (SA). Further, the proposed MoWS2/rGO-PVA based thin film SA exhibits a fast relaxation time and a high damage threshold which are suitable to realize a Q-switched pulsed laser with a tunable wavelength range of 10 nm that extends from 1028 nm to 1038 nm. For the highest pump power of 267.4 mW, the generated Q-switched pulses exhibit a narrow pulse width of 1.22 μs, the pulse repetition rate of 90.4 kHz, the highest pulse energy of 2.13 nJ and its corresponding average power of 0.193 mW. To the best of author’s knowledge, this is the first realization of a tunable Q-switching fiber laser in a 1 μm wavelength using MoWS2/rGO nanocomposite saturable absorber.
In this study, the compressive deformation of crushed sandstone was tested using a crushed rock deformation-seepage test system, and the effects of various factors, including crushed rock grade, grade combination, water saturation status, and stress loading method (i.e., continuous loading or cyclic loading and unloading), on the compressive deformation of crushed sandstone was analyzed from four perspectives including stress-strain, bulking coefficient, deformation mechanism and energy dissipation. The results indicate that the stress-strain relations of crushed sandstone are closely associated with all factors considered, and are well represented by exponential functions. The strain observed for a given applied stress increased with increasing crushed rock grade throughout the loading period. Crushed sandstone grades were combined according to a grading index (n), where the proportion of large-grade rocks in the sample increased with increasing n. The bearing capacity of a water-saturated crushed sandstone sample with n = 0.2 was less than that of an equivalent dry sample for a given applied stress. The stress-strain curve of a water-saturated crushed sandstone sample with n = 0.2 under cyclic loading and unloading was similar to that obtained under continuous loading. Observation and discovery, the deformation mechanism of crushed sandstone was mainly divided into four stages, including crushing, rupture, corner detachment and corner wear. And 20% of the work done by testing machine is used for friction between the crushed sandstone with the inner wall of the test chamber, and 80% is used for the closing of the void between the crushed sandstone, friction sliding, crushing damage.
W publikacji przedstawiono wybrane wyniki badań laboratoryjnych dotyczące ograniczania dopływu wody złożowej do odwiertów wydobywczych gazu i ropy. Przeanalizowano wpływ nasycenia wodą gazonośnych utworów miocenu z rejonu zapadliska przedkarpackiego na ich przepuszczalność względną dla gazu. Dokonano przeglądu literatury pod kątem oceny rezultatów uzyskanych w zabiegach zmniejszania przepuszczalności względnej skał gazonośnych i roponośnych dla wody. Na podstawie testów laboratoryjnych dokonano próby oceny skuteczności zmian przepuszczalności względnej dla solanki i azotu próbek piaskowca szydłowieckiego pod wpływem oddziaływania czterech wyselekcjonownych produktów chemicznych w postaci polimerów oraz mikrożeli. Badania laboratoryjne wykazały, że trend zmian przepuszczalności jest również silnie powiązany z zastosowanym produktem - modyfikatorem przepuszczalności względnej (RPM). Ponadto, skuteczność działania cieczy zabiegowej zależy od prędkości przepływu (wydatku przepływu) solanki przez testowaną próbkę skały - skuteczność działania testowanego preparatu jest tym większa, im wydatek przepływu solanki jest mniejszy. Wyniki testów wykazały selektywne działanie badanych produktów. W przypadku produktu nr 1 uzyskano średnie spadki przepuszczalności na poziomie 60% dla solanki oraz 18% dla gazu. W przypadku zastosowania produktu nr 2 opartego na technologii mikrożeli zaobserwowano znaczące obniżenie względnej przepuszczalności skały dla wody, z małym wpływem na przepuszczalność dla węglowodorów. Zmiany przepuszczalności dla solanki testowanych próbek piaskowca zawierały się w przedziale od 65 do 90%, a dla gazu wynosiły około 50%.