一种甲乙类水声功率放大器设计

水声功率放大器是声呐发射机的重要组成部分,用来提高输出功率,驱动换能器向水中辐射足够能量的声信号。水声功放与换能器之间的阻抗匹配包括变阻匹配和调谐匹配两方面,通过阻抗匹配可以将换能器的阻值调整到一个适当的值,使得功放输出的电压和电流利用系数最高。设计了一部甲乙类水声功率放大器,并与某型换能器完成了匹配,最大功率可达170 W。

螺旋桨适伴流理论设计及参数优化设计

螺旋桨运转于舰艇艉后不均匀流场中,不均匀的流场对螺旋桨的空泡、噪声、振动以及水动力性能产生重要影响。而船舶螺旋桨适伴流理论设计及参数优化设计的目的就是在精确预报船舶艉后伴流场的条件下,合理地设计螺旋桨,使设计桨适合于所在伴流场下的运转。将伴流谐调分析法、螺旋桨侧斜及纵倾选择原则、升力线程序、升力面程序和非定常面元法程序、螺旋桨参数优化设计程序相结合,建立了螺旋桨适伴流理论设计及参数优化设计的系统,对大侧斜螺旋桨(highly skewed propeller,HSP)再设计为例,验证该系统的有效性。该系统为实现对潜艇螺旋桨的量身定制提供了理论支持。

Fabrication of Cu_2O@Cu_2O core-shell nanoparticles and conversion to Cu_2O@Cu core-shell nanoparticles in solution

Cu2O@Cu2O core-shell nanoparticles (NPs) were prepared by using solution phase strategy. It was found that Cu2O@Cu2O NPs were easily converted to Cu2O@Cu NPs with the help of polyvinylpyrrolidine (PVP) and excessive ascorbic acid (AA) in air at room temperature, which was an interesting phenomenon. The features of the two kinds of NPs were characterized by XRD, TEM and extinction spectra. Cu2O@Cu NPs with different shell thicknesses showed wide tunable optical properties for the localized surface plasmon (LSP) in metallic Cu. But Cu2O@Cu2O NPs did not indicate this feature. FTIR results reveal that Cu+ ions on the surface of Cu2O shell coordinate with N and O atoms in PVP and are further reduced to metallic Cu by excessive AA and then form a nucleation site on the surface of Cu2O nanocrystalline. PVP binds onto different sites to proceed with the reduction utill all the Cu sources in Cu2O shell are completely assumed.

Automatic Voltage Regulator Test of Three Gorges Right Bank Hydropower Station

Based on real-time digital simulations(RTDS),a laboratory environment similar to the real-time operation situation of the Three Gorges Hydropower Station is established.Then,the causes for the power fluctuation of the second generator by errors in the rotor rotating speed calculation are found,and the tuning method of the speed related parameters are given.The damping and reverse tuning characteristics of power system stabilizers(PSSs)in the digital automatic voltage regulator(AVR)are compared and investigated in the frequency range of 0.18-1.1 Hz.The efficiency of the proposed tuning method for ensuring power system stability is verified by RTDS.Finally,field tests show the validity of the laboratory test results.

COSMO-RS: An ionic liquid prescreening tool for gas hydrate mitigation

Recently ionic liquids(ILs) are introduced as novel dual function gas hydrate inhibitors. However, no desired gas hydrate inhibition has been reported due to poor IL selection and/or tuning method. Trial & error as well as selection based on existing literature are the methods currently employed for selecting and/or tuning ILs. These methods are probabilistic, time consuming, expensive and may not result in selecting high performance ILs for gas hydrate mitigation. In this work, COSMO-RS is considered as a prescreening tool of ILs for gas hydrate mitigation by predicting the hydrogen bonding energies(E_(HB)) of studied IL inhibitors and comparing the predicted E_(HB) to the depression temperature(?) and induction time. Results show that, predicted EHBand chain length of ILs strongly relate and significantly affect the gas hydrate inhibition depression temperature but correlate moderately(R = 0.70) with average induction time in literature. It is deduced from the results that, ? increases with increasing IL EHBand/or decreases with increasing chain length. However, the cation–anion pairing of ILs also affects IL gas hydrate inhibition performance. Furthermore, a visual and better understanding of IL/water behavior for gas hydrate inhibition in terms of hydrogen bond donor and acceptor interaction analysis is also presented by determining the sigma profile and sigma potential of studied IL cations and anions used for gas hydrate mitigation for easy IL selection.

Gravitational Contributions to Running of Gauge Couplings

Gravitational contributions to the running of gauge couplings are calculated by using different regularizationschemes.As the β function concerns counter-terms of dimension four, only quadratic divergences from the gravitationalcontributions need to be investigated.A consistent result is obtained by using a symmetry-preserving loop regularizationwith string-mode regulators which can appropriately treat the quadratic divergences and preserve non-abelian gaugesymmetry.The harmonic gauge condition for gravity is used in both diagrammatical and background field calculations,the resulting gravitational corrections to the β function are found to be nonzero, which is different from previous resultspresented in the existing literatures.

Methodology Approach Using Harmonic Synthesis as Simulation Method for Investigation of Power Network with Non-Linear Loads

The paper deals with analysis and synthesis of non-harmonic and non-linear sources and appliances, and their interaction with harmonic power supply network. Basic idea is based on knowledge of harmonic spectrum of the sources and/or appliances, respectively. Obviously, one need to know voltage harmonic components of voltage sources （renewable with inverters,...）, and current harmonic components generated by non-linear appliances （rectifiers,...）. Method of investigation lies on decomposition of real electric circuit into n-harmonic separated equivalent schemes for each harmonic component. Then transient analysis will be done for each scheme separately using ＂impedance harmonic matrices＂. The important fact is that each equivalent scheme is now linearized and therefore easily calculated. Finally, the effects of each investigated schemes arc summed into resulting quantities of real non-linear electric circuit.