Numerical Modeling of the Ring Current and Plasmasphere

Over the last 25 years, considerable scientific effort has been expended in the development of quantitative models of the dynamics of Earth's inner magnetosphere, particularly on studies of the injection of the storm-time ring current and of dynamic variations in the shape and size of the plasmasphere. Nearly all modeling studies of ring-current injection agree that time-varying magnetospheric convection can produce approximately the ion fluxes that are observed in the storm-time ring current, but the truth of that assumption has never been demonstrated conclusively. It is not clear that the actual variations of convection electric fields are strong enough to explain the observed flux increases in ~100 keV ions at the peak of the storm-time ring current. Observational comparisons are generally far from tight, primarily due to the paucity of ring-current measurements and to basic limitations of single-point observations. Also, most of the theoretical models combine state-of-the-art treatment of some aspects of the problem with highly simplified treatment of other aspects. Even the most sophisticated treatments of the sub-problems include substantial uncertainties, including the following: (i) There is still considerable theoretical and observational uncertainty about the dynamics of the large-scale electric fields in the inner magnetosphere; (ii) No one has ever calculated a force-balanced, time-dependent magnetic-field model consistent with injection of the storm-time ring current; (iii) The most obvious check on the overall realism of a ring-current injection model would be to compare its predicted Dst index against observations; however, theoretical calculations of that index usually employ the Dessler-Parker-Sckopke relation, which was derived from the assumption of a dipole magnetic field and cannot be applied reliably to conditions where the plasma pressure significantly distorts the field; (iv) Although loss rates by charge exchange and Coulomb scattering can be calculated with reasonable accuracy, it remains unclear whether wave-induced ion precipitation plays an important role in the decay of the ring current. However, considerable progress could be made in the next few years. Spacecraft that can provide images of large regions of the inner magnetosphere should eliminate much of the present ambiguity associated with single-point measurements. On the theoretical side, it will soon be possible to construct models that, for the first time, will solve a complete set of large-scale equations for the entire inner magnetosphere. The biggest uncertainty in the calculation of the size and shape of the plasmasphere lies in the dynamics and structure of the electric field. It is still not clear how important a role interchange instability plays in determining the shape of the plasmapause or in creating density fine structure.     

适于时变幅值分析的直升机黏弹减摆器模型

针对现有适于宽幅值范围的黏弹减摆器模型一般含有动幅值参量,不便用于幅值变化的直升机旋翼/机体耦合动稳定性时域分析的问题,给出了小摆振阻尼比时,黏弹减摆器在单频及双频条件下动幅值参量的计算方法,运用该方法计算系统在收敛、中性稳定及发散3种情况下的幅值曲线,较好地反映了响应幅值在时域上的变化趋势。将改进的黏弹减摆器模型用于直升机地面共振非线性时域分析,为准确获取旋翼摆振后退型响应,给出了所需桨叶激振力矩的计算方法,在不同转速不同复模量状态下,采用该方法确定的激振力矩对桨叶进行激振激出的响应幅值与预期值误差不超过6%。对摆振后退型响应进行分析可知,系统稳定时,与线性化结果相比,计入黏弹减摆器非线性后,旋翼摆振后退型响应衰减更快,其模态阻尼在时域上呈增加趋势。      

挤压式磁流变弹性体阻尼器-转子系统的振动特性试验

 磁流变(MR)弹性体是一种由铁磁颗粒和橡胶或凝胶混合而成的磁流变固体材料,其明显优点是颗粒不会随时间而沉降,也不需要密封装置。研制了一种自定心挤压式磁流变弹性体阻尼器,并测试了支承在该阻尼器上的柔性转子系统的不平衡响应特性。试验发现,随着磁场强度增加,磁流变弹性体阻尼器的阻尼和刚度明显增大;转子系统的一阶临界转速明显提高,二阶临界振动可被抑制。采用开关控制能抑制转子通过两阶临界转速过程中的振动。研究表明,挤压式磁流变弹性体阻尼器能用于转子振动主动控制,并具有结构简单、性能稳定、控振效果明显等特点。     

用数值模拟的方法研究磁暴主相期间影响环电流分布特征的要素

环电流是距离地心2～7 Re的带电粒子围绕地球西向漂移形成的.环电流的增强将引起全球磁场的降低,反映了地磁暴的强度.磁暴主相期间,对流电场驱动等离子体片中的能量粒子经历E×B漂移与俘获注入环电流,进入损失锥的粒子沉降到大气中.本文采用磁暴主相期间环电流离子分布的模型,结合上述因素研究不同离子能量下对流电场对环电流离子通量的直接影响,以及强弱对流电场下环电流能量离子投掷角的变化,并从物理上阐述造成此种通量分布特性的原因.      

Rotordynamic characteristics prediction for scallop damper seals using computational fluid dynamics

Enhancing damping characteristic is one of the effective methods to solve the instability problem of the rotor system. The three-dimensional numerical analysis model of scallop damper seal was established, and the effects of inlet pressures, preswirl ratios, rotational speeds, interlaced angles and seal cavity depths on the rotordynamic characteristics of scallop damper seal were studied based on dynamic mesh method and multi-frequencies elliptic whirling model. Results show that the direct stiffness of the scallop damper seal increases with decreasing inlet pressure and increasing rotational speed and cavity depth. When the seal cavity is interlaced by a certain angle, which shows positive direct stiffness. The effective damping of the scallop damper seal increases with the increasing inlet pressure, the decreasing preswirl ratio and the rotational speed and cavity depth. There exists an optimal interlaced angle to maximize the effective damping and the system stability. The leakage of the scallop damper seal is significantly reduced with decreasing inlet pressure. The preswirl will reduce the leakage flowrate, and the rotational speed has a slight effect on the leakage performance. The leakage of the scallop damper seal decreases with increasing seal cavity depth.     

冲击/周期载荷作用下分布式调谐质量阻尼器对响应控制的影响

本文研究了采用分布式调谐质量阻尼器(TMD)对悬臂梁进行振动抑制的问题.首先建立了安装N个TMD的悬臂梁的动力学方程;然后通过有限单元法离散偏微分方程,使用Newmark-β法进行含TMD的悬臂梁动响应求解;最后基于数值计算模型,分别研究周期荷载与冲击荷载作用下,梁振动控制的效果.研究表明:TMD可以有效抑制悬臂梁振动...     

An innovative constraining ring rolling process for manufacturing conical rings with thin sterna and high ribs

Conical rings with thin sterna and high ribs (CRTSHR) are key bearing-load parts of aerospace equipment, which are required to be manufactured with high performance and efficiency. Traditional ring rolling is the most preferred method for manufacturing high-performance ring parts, but it can hardly achieve the forming of CRTSHR due to the extreme geometry of CRTSHR. To solve this difficulty, an innovative constraining ring rolling process (CRR) is proposed in this paper to manufacture CRTSHR. To evaluate the proposed CRR and reveal its deformation behaviors, a thermomechanical coupled FE model for CRR of CRTSHR is established. Then, the experiment for CRR of CRTSHR is performed on a modified ring rolling machine, which proves that CRR of CRTSHR is feasible and the established FE model is reliable. Based on the reliable FE model, the metal flow mode in deformed CRTSHR is analyzed, and the deformation characteristics such as the stress state, strain distribution and the evolution of power parameters in CRR of CRTSHR are revealed. Finally, the influences of key parameters such as the friction factor between ring and molds, the diameter of idle roll and the feed velocity of idle roll on CRR of CRTSHR are investigated by FE simulation.     

5B70合金大尺寸锻环成形工艺及组织性能

针对大尺寸5B70锻环性能提高需求，通过对5B70均匀化铸锭进行不同温度和应变速率下的热压缩模拟，获得应力应变数据并拟合了该合金的热加工图，以指导大尺寸锻环成形。从热加工图中得到该合金合适的热变形温度为400~450 ℃，变形速率为0.1/s左右最为合适。根据该加工图，采用相同条件的环锻工艺，制备了5B70铝镁钪合金试验件和尺寸为Ф2 900 mm×Ф2 600 mm×700 mm成品环件，并讨论了热变形工艺对成形件组织和性能的影响。结果表明，铝镁钪合金在该热变形条件下进行塑性变形，没有出现加工失稳等变形缺陷，可获得力学性能和塑性综合表现良好的铝镁钪合金成形件。     

Numerical investigation on leakage and rotordynamic performance of the honeycomb seal with swirl-reverse rings

Honeycomb seals are a crucial component to restrict the leakage flow and improve system stability for the turbomachines and aero-engines. In this work, the leakage and rotordynamic performance of honeycomb seals with the Swirl-Reverse Ring(SRR) is predicted by employing the approach of Computational Fluid Dynamics(CFD) and the multifrequency whirling model theory.Numerical results show that the positive preswirl flow and circumferential velocity can be effectively weakened for the honeycomb seal...