船舶风翼液压系统小角度回转控制策略研究

为了优化风翼回转液压系统在小角度转动时的控制策略,选用一种升力系数较大的多段翼风翼,根据风翼模型风洞实验数据得出风翼气动特性曲线。基于实验数据设计目标船风翼回转液压驱动系统,建立AMESim仿真模型并在液压实验台中验证其正确性。围绕船舶风翼小角度转动的需求,确定正弦启动和制动控制信号,进而确定风翼小角度转动时液压驱动系统启动和制动最佳控制策略。结果表明：风翼回转液压驱动系统启动和制动采用正弦控制信号,且启动和制动时间为2～3 s时系统压力波动较小,有利于液压系统的稳定运行。     

液电混合挖掘机回转驱动系统运行特性及能效

液压挖掘机作业时,上车回转系统频繁起制动。由于惯性大、起动压力高,造成大量的溢流损失;制动时上车回转系统的动能通过液压马达出口的制动阀转化为热能,能量浪费大。为了降低挖掘机回转过程的能耗,提出液电混合挖掘机回转驱动系统。在回转过程中,电机作为主驱动控制上车回转系统的回转速度,液压马达-蓄能器回收上车回转系统制动动能,并在起动时辅助电机驱动回转系统。首先对主要元件进行参数设计,然后建立原机回转系统和所提系统的联合仿真模型,对2种回转系统的运行特性和能效特性展开研究。结果表明:与原机系统相比,所提系统在1个回转工作循环内能耗降低37.26%～53.29%,并抑制了上车回转系统的回摆现象,提高整机运行的平稳性。     

一种大型液压挖掘机回转系统节能技术的研究

针对某大型液压挖掘机现有回转系统存在回转制动能量浪费严重的现象,提出一种新液压回转制动能量回收系统,利用蓄能器回收其回转制动阶段的制动能,下次回转启动与变量泵共同驱动回转马达。阐述了两种系统液压原理的异同,在AMESim中建立模型并进行仿真分析。仿真结果表明:新系统可以降低变量泵的功耗和吸收系统压力波动,回转制动能量回收率为28.5%,回收制动能量再利用率为76.3%,蓄能器能量回收利用率为21.7%,节能效果明显,可以有效改善其能耗问题。     

油液混合动力挖掘机回转系统仿真分析

为了回收挖掘机回转平台制动过程中的制动能量,设计了油液混合动力挖掘机回转系统,利用蓄能器回收回转平台的制动能量。阐述油液混合动力回转系统和普通回转系统液压原理的不同,建立AMESim模型并进行仿真分析。仿真结果表明:油液混合动力挖掘机回转系统在一定程度上降低了液压泵的功率损耗和液压马达的压力波动;在节能方面,蓄能器的能量回收效率达到70.0%,再利用效率达到72.8%,利用率较高,达到节能的目的。     

基于优化非线性控制的液压制动系统压力跟踪仿真研究

为提高车辆制动过程中控制系统的响应速度,设计车辆液压制动非线性PID控制优化系统,并对制动压力跟踪效果进行仿真。给出车辆液压制动系统平面图,分析车辆行驶和制动过程中液压系统的工作原理。采用数学模型对车辆液压制动系统进行简化,针对输入的不确定性设计了非线性PID控制系统。采用遗传算法对非线性PID控制系统进行优化,给出了液压制动非线性PID控制系统的优化流程。在不同初始状态和不同压力信号条件下,采用MATLAB软件对制动压力跟踪误差进行仿真,并与优化前的仿真结果进行对比和分析。结果表明:在非线性PID控制系统中,液压制动压力跟踪误差较大,控制参数调整速度较慢;在遗传算法优化后的非线性PID控制系统中,液压制动压力跟踪误差较小,控制参数调整速度较快。采用遗传算法优化非线性PID控制系统,可以提高整个系统的反应速度,获得良好的制动效果。     

基于AMESim的摇臂式清仓机液压系统动态特性的研究

针对摇臂式清仓机液压系统进行研究,利用AMESim仿真软件分别搭建了液压系统截割回路、支撑回路和回转回路的仿真模型,并对其动态特性进行仿真及分析,得到各回路对应的压力、流量、转速随时间变化的曲线。仿真结果表明:该液压系统具有压力波动小、调速范围广、回转平稳的特点。     

双马达主被动复合驱动挖掘机回转系统特性

液压挖掘机由于上车回转平台转动惯量大、工作中高频次起制动,导致大量的制动动能转化为控制阀阀口热能浪费掉。为此,提出双马达主被动复合驱动挖掘机回转系统,主动系统采用阀口独立回路,应用泵阀复合、压力流量匹配控制策略抑制回转平台起动过程的节流和溢流损失,利用阀口独立回路多自由度控制的优点解决制动阶段转台冲击和反转问题;被动系统采用液压马达-蓄能器组合,回收利用回转平台制动动能;在空载制动过程中,通过增压缸向蓄能器补充油液。建立回转系统机电液联合仿真模型,并对所提系统的运行特性与能量特性进行分析。结果表明：满载和空载制动阶段蓄能器能量回收率分别为79%和72%,利用增压缸解决了蓄能器油液回收不足问题,较传统回转系统能耗降低54.3%。     

回转缓冲阀在起重机液压系统中的应用研究

针对起重机在吊重回转制动时出现压力冲击大,引起重物左右摆动、停止耗时长的问题,利用AMESim软件建立回转制动系统的简化模型,进行问题分析,并对系统中的回转缓冲阀进行参数优化,对比优化前后的回转制动缓冲效果。仿真和实测结果表明:合理设计回转缓冲阀的技术参数,才能有效降低液压系统的压力冲击,提高起重机作业效率。     

基于AMESim液压可控停车顶系统仿真研究

液压可控停车顶是驼峰溜放车辆的新型自动化减速装置,提高了铁路编组场调车的自动化水平。以液压可控停车顶为研究对象,开展基于AMESim软件的系统建模与仿真分析。在分析液压可控停车顶系统工作原理及控制方式的基础上,利用AMESim软件中的机械库、液压库及信号控制库构建了液压可控停车顶系统仿真模型,分析系统在非制动状态、待制动状态和制动状态下的顶杆位移、顶杆速度、液压制动缸上下腔压力、蓄能器气囊容积及压力的动态性能。仿真结果显示:液压可控停车顶可实现非制动状态、待制动状态和制动状态的切换,制动状态下具有减速缓冲作用。液压可控停车顶建模仿真分析为系统的优化设计提供一定的参考。     

四驱电动车液压再生制动系统制动能效的研究

为定量分析四驱电动汽车液压制动能量再生系统的制动效能和蓄能能力,设置再生制动系统单独制动仿真。液压二次元件以泵的形式运行,建立蓄能器数学建模,对汽车制动时的受力进行运动学分析,然后在AMESim软件上搭建仿真模型。由于蓄能器最低工作压力是影响蓄能器效能的关键参数,进而也是影响液压制动能量再生系统制动效能的关键因素,所以赋予蓄能器不同的最低工作压力进行对比仿真分析。仿真结果表明:当蓄能器最低工作压力为17 MPa时,在保证四驱电动车液压再生制动系统有较高的制动能效的同时,可以获得较高的蓄能器效能。     

超声辅助对共沉淀法制备富锂锰基正极材料Li[Li_0.144Ni_0.136Co_0.136Mn_0.544]O₂性能影响的研究

通过超声辅助共沉淀法成功制备了富锂锰基正极电极材料,研究了不同的超声时间对材料形貌、结构和电化学性能的影响。研究发现,超声辅助能够使材料颗粒更加均匀,结构更合理,有利于材料电化学性能的提升。当合成前躯体材料超声时间为8h时,复合材料的放电比容量最好,在0.1C的初始放电比容量为327.8 mAh g_-1,均高于未超声的复合材料的265.2 mAh g_-1,1C下循环50圈后放电容量为181.6 mAh g_-1,保持率为84.8%。通过循环伏安法测试和电化学交流阻抗测试,发现超声后的复合材料还原氧化峰电流更大,电荷转移阻抗更小,具有较好的倍率性能。     

Investigation of the microwave dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics for application in coplanar patch antenna

In this paper, the dielectric properties of Ca_1−xMg_xLa₄Ti₅O₁₇ ceramics at microwave frequency have been studied. The diffraction peaks of Ca_(1−x)Mg_xLa₄Ti₅O₁₇ ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm³ can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (_r) and quality factor (Q × f) of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τ_f) of −9.6 ppm/°C can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.     

High-speed deposition of Y-Si-O films by laser chemical vapor deposition using Nd:YAG laser

Y-Si-O films were prepared by laser chemical vapor deposition (LCVD) with a Nd:YAG laser using TEOS (tetraethyl orthosilicate) and Y(dpm)₃ precursors. The effects of laser power (P_L), deposition temperature (T_dep) and total chamber pressure (P_tot) on the phase, microstructure and deposition rate of Y-Si-O films were investigated. At P_L < 102 W (T_dep < 1140 K), amorphous Y-Si-O films were obtained independent of P_tot. At P_tot = 0.6 kPa, mixture phase films of Y₂SiO₅ (the X1 phase) and Y₂Si₂O₇ (the α, β, δ and y phases) were obtained at P_L = 102 W (T_dep = 1210 K), while single phase X1-Y₂SiO₅ films were prepared at P_L > 139 W (T_dep > 1280 K). Y₂Si₂O₇ mixture phase films were obtained at P_tot = 3.5 kPa and Y₂Si₂O₇ and Y₂SiO₅ (the X2 phase) mixture phase films were obtained at P_tot = 7.5 kPa independent of T_dep. Amorphous Y-Si-O films showed a dense, glassy microstructure. Faceted columnar grains grew on the Y-Si-O films at P_tot = 0.6 kPa, whereas rounded cauliflower-like grains grew at P_tot = 7.5 kPa. The R_dep increased with increasing P_L and T_dep and reached a maximum of 430 μm h⁻¹ at P_tot = 0.6 kPa, P_L = 186 W and T_dep = 1310 K.     

Structure, microstructure and electrical properties of (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics

The ternary system (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBi_0.5Li_0.5TiO₃ (abbreviated to BNKLT-x/y) was synthesized by conventional oxide-mixed method. The phase structure, microstructure, and dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction patterns showed that pure perovskite phase with rhombohedral structure can be obtained in all the ceramics. The grain size varied with x and y. The temperature dependence of dielectric constant and dielectric loss revealed there were two phase transitions which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic). Either increasing x or y content can make T_m (the temperature at which dielectric constant _r reaches the maximum) increase. With the addition of Bi_0.5K_0.5TiO₃, the remanent polarization P_r increased but the coercive field E_c decreased. With the addition of Bi_0.5Li_0.5TiO₃, P_r increased obviously and E_c increased slightly. Due to the stronger ferroelectricity by modifying Bi_0.5K_0.5TiO₃ and Bi_0.5Li_0.5TiO₃, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: P_r = 31.92 μC/cm², E_c = 32.40 kV/cm, _r = 1118, tan δ = 0.041, d₃₃ = 203 pC/N and K_p = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials.     

Microwave dielectric properties and its compatibility with silver electrode of Li2MgTi3O8 ceramics

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature and microwave dielectric properties of Li₂MgTi₃O₈ ceramic have been investigated. The pure Li₂MgTi₃O₈ ceramic shows a relative high sintering temperature (∼1000 °C) and good microwave dielectric properties as Q × f of 40,000 GHz, ?_r of 27.2, τ_f of 2.6 ppm/°C. It was found that the addition of a small amount of BCB can effectively lower the sintering temperature of Li₂MgTi₃O₈ ceramics from 1025 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 0.5 wt% BCB added Li₂MgTi₃O₈ ceramic sintered at 900 °C for 2 h exhibited good microwave dielectric properties of Q × f = 36,200 GHz (f = 7.31 GHz), ?_r = 26 and τ_f = −2 ppm/°C. Compatibility with Ag electrode indicates this material can be applied to low temperature-cofired ceramics (LTCC) devices.     

Mg-substituted ZnNb2O6-TiO2 composite ceramics for RF/microwaves ceramic capacitors

Microstructure and microwave dielectric properties of Mg-substituted ZnNb₂O₆-TiO₂ microwave ceramics were investigated. Mg acted as a grain refining reagent and columbite phase stabilization reagent. With an increasing Mg content, the amount of ixiolite (Zn, Mg) TiNb₂O₈ decreased, and the amount of (Zn_0.9Mg_0.1)_0.17Nb_0.33Ti_0.5O₂ and columbite increased. ZnO-Nb₂O₅-1.75TiO₂-5 mol.%MgO exhibited excellent dielectric properties (at 950 °C): ?_r = 35.6, Q × f = 16,000 GHz (at 5.6 GHz) and τ_f = −10 ppm/°C. The material was applied successfully to make RF/microwaves ceramic capacitor, whose self-resonance frequency was 19 GHz at low capacitance of 0.13 pF.     

Dielectric function and the crystal structure of MeV ion implanted LiNbO3

The behavior of the dielectric functions of MeV ion-implanted LiNbO₃ was studied using THz spectroscopy. Single crystal LiNbO₃ specimens were implanted with 3 MeV Au ions at four different levels of ion fluence (1 × 10¹², 1 × 10¹³, 1 × 10¹⁴ and 1 × 10¹⁵ cm^− 2). The optical spectra of the specimens were then measured in two ranged values: (1) reflectance THz range spectra from 40 to 700 cm^− 1 and (2) reflectance ultraviolet, visible, and near-infrared spectra from 250 to 2000 nm. The THz spectra were analyzed by fitting with the dielectric function model proposed by Brendel. The dielectric function model explained well the experimental spectra of the ion-implanted LiNbO₃. The dielectric function shows that the ion-implanted layers were amorphous phase at the fluence of 1 × 10¹⁴ and 1 × 10¹⁵ cm^− 2, whereas the layers at 1 × 10¹² and 1 × 10¹³ cm^− 2 maintained the crystal phase but significantly suppressed the phonon resonances. The volume of ion-implanted layers expanded about 8% with the fluence of 1 × 10¹⁴ and 1 × 10¹⁵ cm^− 2, i.e. after amorphization, These results show that the ion implantation significantly affected the lattice vibration mode and the structure even at very low ion fluence.     

Ultraviolet and violet upconversion luminescence in Ho-doped Y2O3 ceramic induced by 532-nm CW laser

Ultraviolet and violet upconversion luminescence spectra of holmium-doped Y₂O₃ were produced under the excitation of a compact continues-wave 532 nm solid-state laser. Emissions around 306, 362, 412, 390 and 428 nm can be assigned to the transitions of ³D₃ → ⁵I_J (J = 8, 7, 6), ⁵G₄ → ⁵I₈ and ⁵G₅ → ⁵I₈, respectively. Power dependence and upconversion dynamics analysis demonstrated that both the energy transfer upconversion (ETU) and the excited state absorption (ESA) processes were involved in the population of ³D₃ state via the coupled intermediate states ⁵S₂/⁵F₄. Fluorescence spectra in the visible and infrared ranges showed that ⁵G₄ and ⁵G₅ states were populated by the ESA process from ⁵I₆ and ⁵I₇ states, respectively, while the ⁵I₆ and ⁵I₇ states were radiatively populated from the excited ⁵S₂/⁵F₄ states. Upconversion mechanisms have been evaluated based on a rate equation model.     

Relationships between Zr substitution for Ti and microwave dielectric properties in Mg(ZrxTi1−x)O3 ceramics

The influence of Zr substitution for Ti on the microwave dielectric properties and microstructures of the Mg(Zr_xTi_1−x)O₃(MZ_xT) (0.01 ≤ x ≤ 0.3) ceramics was investigated. The quality factors of Mg(Zr_xTi_1−x)O₃ ceramics with x = 0.01-0.05 were improved because the solid solution of a small amount of Zr⁴⁺ substitution in the B-site could increase density and grain size. An excess of Zr⁴⁺ resulted in the formation of a great deal of secondary phase that declined the microwave dielectric properties of MZ_xT ceramics. The temperature coefficient of resonant frequency (τ_f) of Mg(Zr_xTi_1−x)O₃ ceramics slightly increased with increasing Zr content, and the variation in τ_f was attributed to the formation of secondary phases.     

Effects of rare-earth elements on the glass-forming ability and mechanical properties of Cu46Zr47-xA17Mx （M = Ce, Pr, Tb, and Gd） bulk metallic glasses

Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr, Tb, and Gd) bulk metallic glassy (BMG) alloys were prepared by copper-mold vacuum suction casting. The effects of rare-earth elements on the glass-forming ability (GFA), thermal stability, and mechanical properties of Cu₄₆Zr_47−x Al₇M _x were investigated. The GFA of Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr) alloys is dependent on the content of Ce and Pr, and the optimal content is 4 at.%. Cu₄₆Zr_47−x Al₇Tb _x (x = 2, 4, and 5) amorphous alloys with a diameter of 5 mm can be prepared. The GFA of Cu₄₆Zr_47−x Al₇Gd _x (x = 2, 4, and 5) increases with increasing Gd. T _x and T _p of all decrease. T _g is dependent on the rare-earth element and its content. ΔT _x for most of these alloys decreases except the Cu₄₆Zr₄₂Al₇Gd₅ alloy. The activation energies ΔE _g, ΔE _x, and ΔE _p for the Cu₄₆Zr₄₂Al₇Gd₅ BMG alloy with Kissinger equations are 340.7, 211.3, and 211.3 kJ/mol, respectively. These values with Ozawa equations are 334.8, 210.3, and 210.3 kJ/mol, respectively. The Cu₄₆Zr₄₅Al₇Tb₂ alloy presents the highest microhardness, Hv 590, while the Cu₄₆Zr₄₃Al₇Pr₄ alloy presents the least, Hv 479. The compressive strength (σ _c.f.) of the Cu₄₆Zr₄₃Al₇Gd₄ BMG alloy is higher than that of the Cu₄₆Zr₄₃Al₇Tb₄ BMG alloy.