In the performance experiment of organic Rankine cycle power generation experimental system, the load-resistance-regulation method is one of the most important regulation methods. However, the regulation law has not been clear enough to guide the experiment, which is unfavorable to the experimental research on organic Rankine cycle. In this paper the regulation law of turbine and generator by the load-resistance-regulation method is studied theoretically and experimentally. The results show that when the thermal cycle parameters keep constant, the turbine speed increases with the increase of load resistance and there is a maximum value of transmission-generator efficiency with the variation of the turbine speed; when the turbine speed and generator speed keep constant, the transmission-generator efficiency decreases and gradually tends to zero with the increase of load resistance.
The intact stability and damage stability of a model of an anemometer tower with buoyancy tank foundation are computed by the finite element software MOSES in this paper. The natural period of the anemometer tower is discussed through frequency domain analysis. The influence of a single factor, such as towing point position, wave height, wave direction and wave period, on towing stability is discussed through time domain analysis. At the same time, the towing stability under the condition of various combinations of many factors is analyzed based on the measured data of the target area. Computer simulation results show that the intact stability is preferable and the damage stability is sufficient under the condition of plenty of subdivisions. Within the scope of the buoyancy tank foundation, the higher the towing point position is, the better the stability is. Wave height has a great impact on the motion amplitude of buoyancy tank foundation, but the effect on the acceleration is not obvious; wave period has a great impact on the acceleration, while the effect on the motion amplitude is not obvious; following-waves towing is more conducive to safety than atry.
The three-stage simulation method based on LS-DYNA was introduced in this study to simulate the progressive collapse of a continuous girder bridge after a ship-bridge collision. The pile-soil dynamic interaction and the initial stress and deformation of the whole bridge before the collision were considered. By analyzing the damage, deformation, stress distribution and collapse process of the whole bridge, the results show that the displacement response of the cap beam lags behind the pile cap. The response order of the whole bridge’s components depends on their distances from the collision region. The plastic deformation of soil around piles has a positive effect on delaying the further increase in the displacement of piles. The impacted pier’s losing stability and its superstructure’s excessive deformation are the main reasons leading to the progressive collapse of the continuous girder bridge.
Prestressed steel ultrahigh-strength reinforced concrete (PSURC) beam is a new type of prestressed concrete beam, which not only has a considerable compressive strength attributed to the ultrahigh strength concrete, but also ensures a certain degree of ductility at failure due to the existence of structural steel. Five of these beams were monotonically tested until shear failure to investigate the static shear performance including the failure pattern, load-deflection behavior, shear capacity, shear crack width and shear ductility. The experimental results show that these beams have superior shear capacity, crack control ability and shear ductility. To study the shear performance under repeated overloading, seven PSURC beams were loaded in cyclic test simultaneously. The overall shear performance of cycled beams is similar to that of uncycled beams at low load level but different at high load level. The shear capacity and crack control ability of cycled beams at high load level are reduced, whereas the shear ductility is improved. In addition, the influences of variables including the degree of prestress, stirrup ratio and load level on the shear performance of both uncycled and cycled beams were also discussed and compared, respectively.
Waste cooking oil (WCO) is becoming the most promising alternative feedstock to produce biodiesel due to its low cost in China. In this study, NKC-9 ion-exchange resin and H-beta zeolite were selected as heterogeneous catalysts in the WCO esterification process and their esterification characteristics were compared by orthogonal experiments. NKC-9 resin showed higher activity and achieved a higher final conversion compared with H-beta zeolite under the same reaction conditions. Reusability experiments showed that NKC-9 resin still exhibited high activity after 5 runs. The effects of the mole ratio of alcohol to oil, reaction time, reaction temperature and the catalyst dose were investigated by multifactor orthogonal analysis. The influence of the free fatty acid (FFA) content was also investigated, and the result showed that the esterification rate could be as high as 98.4% when the FFA content was 6.3wt%.
Tung oil-based polyols were synthesized by the esterification and transesterification between Tung oilbased anhydride and butanediol. The hydroxyl values of the polyols prepared were tested and discussed. Polyurethane was prepared by using Tung oil-based polyols and/or poly(propylene glycol) as polyols and by using isophorone diisocyanate as isocyanate. The effect of the ratio of Tung oil-based polyols to poly(propylene glycol) on the properties of polyurethane prepared was investigated by the water resistance, alcohol resistance and hardness tests. The results show that Tung oil-based polyols are effective to improve the hardness, water resistance and alcohol resistance of polyurethane.
A variety of barium sulfate (BaSO4) carriers with or without mesopore structure were synthesized via precipitation reaction in aqueous solution of barium hydroxide and sulfuric acid with ethylene glycol as a modifying agent, and then calcined at various temperatures. The obtained BaSO4 was used as catalyst carriers for polystyrene (PS) hydrogenation, and BaSO4 supported palladium (Pd) catalysts with Pd content of 5wt% were prepared by using impregnation method. N2 physisorption, transmission electron microscopy, X-ray diffraction and kinetics studies were used to investigate the effect of carrier structure on the dispersion and geometric location of active metal and their catalytic activities in PS hydrogenation. It was found that the pore structure of carrier played an important role in the dispersion and location of Pd grains. The activation energy values for all the Pd/BaSO4 catalysts were around 49.1 kJ/mol, while the pre-exponential factor for Pd/BSC-6H was much higher than others. The Pd/BSC-6H without mesopores had Pd grains deposited on the external surface of the carrier, and exhibited better activity than the mesoporous catalysts. It is indicated that the utilization of Pd/BSC-6H can reduce the pore diffusion of PS coils and enabled more active sites to participate in the PS hydrogenation.
When boost power factor correction (PFC) circuit works with large scale load fluctuations, it is easy to cause a higher total harmonic distortion and a lower power factor because of traditional controllers and inductor current mode. To solve this problem, this paper proposes a PFC control system, which can operate with load fluctuations up to 1 000 W by using duty cycle feed-forward control theory to achieve smooth switching mode. The duty cycles in the next period of the control system are pre-estimated in the current cycle, which enhances the speeds of AD samplers and switching frequency, and reduces the cost and volume of the equipment to some extent. Introductions of system decoupling and feed-forward of input-voltage greatly improve the system performance. Both theoretical simulation and experimental results prove the advantage of the proposed scheme.
A wideband dual-feedback low noise amplifier (LNA) was analyzed, designed and implemented using SiGe heterojunction bipolar transistor (HBT) technology. The design analysis in terms of gain, input and output matching, noise and poles for the amplifier was presented in detail. The area of the complete chip die, including bonding pads and seal ring, was 655 μm×495 μm. The on-wafer measurements on the fabricated wideband LNA sample demonstrated good performance: a small-signal power gain of 33 dB with 3-dB bandwidth at 3.3 GHz was achieved; the input and output return losses were better than −10 dB from 100 MHz to 4 GHz and to 6 GHz, respectively; the noise figure was lower than 4.25 dB from 100 MHz to 6 GHz; with a 5 V supply, the values of OP1dB and OIP3 were 1.7 dBm and 11 dBm at 3-dB bandwidth, respectively.
This paper presented an automatic gain control (AGC) circuit suitable for FM/cw ladar. The proposed architecture was based on two-stage variable gain amplifier (VGA) chain with a novel DC offset canceller circuit, which contained an improved Gilbert cell and a Gm-C feedback loop. To keep the VGA with a linearity in dB characteristic, an improved exponential gain control circuit was introduced. The AGC was implemented in 0.18 μm standard CMOS process. Simulation and measurement results verified that its gain ranged from −20 dB to 30 dB, and bandwidth ranged from 100 kHz to 10 MHz. Its power consumption was 19.8 mW under a voltage supply of 3.3 V.