平台式重力仪航空重力测量数据后处理技术研究

针对航空重力测量对数据后处理的要求,结合平台式重力仪系统的组成与工作原理,在重力异常信号的频域特征基础上,设计出一套有严格频域规范的航空重力数据后处理流程,并对某海域实测数据进行了处理。结果表明,重力异常值内符合精度为12条东西测线达到0.43mGal/140s和0.84mGal/100s,4条南北测线达到0.39mGal/140s和0.79mGal/100s;以同测线GT-2A单次测量结果为标准值统计标准差,12条东西测线为0.72mGal/140s和0.98mGal/100s,4条南北测线为1.41mGal/140s和1.53mGal/100s。结果表明,设计的航空重力测量数据后处理方法可以实现重力异常信号的高精度提取。     

脉冲爆震载荷作用下转子系统动力学特性

针对脉冲爆震涡轮发动机(PDTE)气动载荷具有周期性、非定常的特点,应用有限元法建立了PDTE转子系统动力学特性计算模型。在验证计算模型准确性的基础上,研究了周期性、非定常轴向力和扭矩对转子系统动力学特性的影响。研究结果表明:与传统燃气涡轮发动机相比,PDTE转子系统同时存在弯曲振动、轴向振动和扭转振动。脉冲爆震燃烧室的气动载荷会改变转子系统的弯曲刚度,但对气动载荷合理设计后,其对弯曲振动的影响较小。周期性、非定常轴向力引起转子系统轴向振动,且轴向振动特性主要受零频和1阶轴向共振频率处响应的影响。PDTE工作时滚珠轴承的轴向支反力会不断变向,在设计滚珠轴承时应予以考虑。周期性、非定常扭矩引起转子系统扭转振动,1阶扭转共振频率分量在扭转振动响应中占优。      

Numerical investigation of flow mechanisms of tandem impeller inside a centrifugal compressor

This study numerically investigated a single stage centrifugal compressor ‘‘Radiver’’ with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance. The results demonstrate that tandem design and clocking fraction (λ_s) significantly affects the compressor performance. The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller. The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary. In order to restrain the inducer wake and exducer shock losses, parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained. The modified tandem impeller with 25% clocking arrangement shows an 8.45% stall margin increase and maintains the total pressure ratio and efficiency as the conventional design, which proves the potential of tandem impeller to improve compressor stage performance. It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.     

捆绑火箭POGO振动动力学模型的研究

确定了捆绑火箭POGO振动动力学模型中蓄压器的最佳安装位置,简化了液体捆绑火箭动力学模型。基于AMESim软件搭建捆绑火箭动力学仿真模型,分析了蓄压器的安装位置对捆绑火箭POGO振动系统的系统阻尼比的影响,以及贮箱、直管、泵和推力室产生的作用力对系统阻尼比的影响。结果表明:蓄压器安装在芯级氧路和助推氧路的系统阻尼比提升最大,POGO振动的抑制效果最好;推力室产生的作用力对系统阻尼比的影响占主导地位,故仅需考虑推力室产生的作用力,以简化捆绑火箭POGO振动动力学模型。该研究可应用于POGO振动的仿真过程。     

耦合热、动载荷的超超临界汽轮机迷宫密封动力特性

密封汽流激振严重影响超超临界汽轮机的安全运行,采用DEFINE_CG_MOTION和DEFINE_PROFILE控制宏建立转子的涡动方程,通过Workbench流固耦合方法计算热、动载荷下密封齿形变,根据快速傅里叶变化得到机组运行时的密封动力特性,并对转子稳定性进行分析。结果表明:蒸汽可导致密封齿膨胀变形,温度对密封齿长度变化影响可达1%~1.5%,压力和离心作用对其影响较小。热、动载荷使迷宫密封直接刚度减小,直接阻尼先增加后减小,交叉刚度先减小后增加,动力系数的最大变化为原来的2倍。35~55 Hz内转子稳定裕度急剧下降,转子对密封汽流激振更敏感。热、动载荷引起的压力波动集中在低频范围,密封周向压力波动可增高18.5 kPa。密封高压区的压力波幅剧增是汽流激振显著的主要原因。      

变体辅助的无人机栖落机动模糊控制设计

无人机（Unmanned aerial vehicle， UAV）的栖落机动是一种大幅度的俯仰运动，易引起升降舵操纵力矩饱和。本文以变体方式增强无人机的俯仰操纵能力，并研究其对应的控制设计方法。首先对栖落机动建立了纵向动力学模型，并通过采用轨迹线性化和张量积变换方法转换得到T-S模糊模型。基于Lyapunov稳定理论和平方和方法，设计了满足控制输入约束的栖落机动多项式模糊控制器。对非变体与变体下的栖落机动控制过程进行了仿真，结果验证了控制律的有效性，并且表明变体辅助的无人机具有更强的操纵性能，能提高栖落机动中升降舵的抗饱和能力。     

横向振动下螺栓连接失效及影响因素研究

针对螺栓连接结构在横向振动下的失效问题进行试验研究,首先,对比相同条件下普通螺母与防松螺母的失效过程,结果表明普通螺母仅出现松动失效,而防松螺母会先出现部分松动,再因螺栓根部疲劳断裂而完全失效。同时在不同类型防松螺母中,Hard-lock螺母和施必牢螺母防松效果明显优于其他防松螺母。其次,考察拆卸次数、振动频率、幅值等因素对螺栓连接失效的影响规律,发现多次拆卸会改变普通螺母的失效形式;相对于振动频率,振动幅值和预紧力对螺栓失效的影响较大。     

用于叶片减振的压电材料分布拓扑优化

提出一种可用于实际叶盘结构的压电分支阻尼器拓扑优化方法,可以给出总质量受约束的压电材料在叶片上的最佳分布,达到尽可能大的模态阻尼比。通过理论推导说明:压电阻尼器所产生的模态阻尼比仅取决于模态机电耦合系数,且该系数只与压电材料的几何形状以及模态应力场有关。进一步结合压电本构关系,基于应力分量的线性加权给出了有限的压电材料在叶片上铺设位置“优先级”的判断指标。给出了基于叶盘结构有限元模型的压电材料拓扑优化方法,通过替换单元类型和材料参数的方式对压电材料进行布置,并给出了多模态族优化、极化方向设置、电极铺设等问题的解决方案。在一个接近真实的叶盘模型上应用了此优化方法。结果表明,仅使用质量占叶片质量10%的压电材料,就可以为多个模态提供约12%的阻尼比。      

L-band nighttime scintillations at the northern edge of the EIA along 95°E during the ascending half of the solar cycle 24

The characteristics of nighttime ionospheric scintillations measured at the L-band frequency of 1.575 GHz over Dibrugarh (27.5°N, 95°E, MLAT ～ 17°N, 43° dip) during the ascending half of the solar cycle 24 from 2010 to 2014 have been investigated and the results are presented in this paper. The measurement location is within or outside the zone of influence of the equatorial ionization anomaly depending on solar and geomagnetic activity. Maximum scintillation is observed in the equinoxes irrespective of solar activity with clear asymmetry between March and September. The occurrence frequency in the solstices shifts from minimum in the June solstice in low solar activity to a minimum in the December solstice in high solar activity years. A significant positive correlation of occurrence of scintillations in the June solstice with solar activity has been observed. However, earlier reports from the Indian zone (～75°E) indicate negative or no correlation of scintillation in June solstice with solar activity. Scintillations activity/occurrence in solstices indicates a clear positive correlation with Es recorded simultaneously by a collocated Ionosonde. In equinoxes, maximum scintillations occur in the pre-midnight hours while in solstices the occurrence frequency peaks just after sunset. The incidence of strong scintillations (S₄ ≥ 0.4) increases with increase in solar activity. Strong (S₄ ≥ 0.4) ionospheric scintillations accompanied by TEC depletions in the pre-midnight period is attributed to equatorial irregularities whereas the dusk period scintillations are related to the sporadic-E activity. Present results thus indicate that the current location at the northern edge of the EIA behaves as low as well as mid-latitude location.     

Thrusting maneuver control of a small spacecraft via only gimbaled-thruster scheme

The thrust vector control (TVC) scheme is a powerful method in spacecraft attitude control. Since the control of a small spacecraft is being studied here, a solid rocket motor (SRM) should be used instead of a liquid propellant motor. Among the TVC methods, gimbaled-TVC as an efficient method is employed in this paper. The spacecraft structure is composed of a body and a gimbaled-SRM where common attitude control systems such as reaction control system (RCS) and spin-stabilization are not presented. A nonlinear two-body model is considered for the characterization of the gimbaled-thruster spacecraft where, the only control input is provided by a gimbal actuator. The attitude of the spacecraft is affected by a large exogenous disturbance torque which is generated by a thrust vector misalignment from the center of mass (C.M). A linear control law is designed to stabilize the spacecraft attitude while rejecting the mentioned disturbance torque. A semi-analytical formulation of the region of attraction (RoA) is developed to ensure the local stability and fast convergence of the nonlinear closed-loop system. Simulation results of the 3D maneuvers are included to show the applicability of this method for use in a small spacecraft.