改良Load-sharing评分对胸腰段脊柱骨折手术的指导价值

目的探讨改良Load-sharing评分对胸腰段脊柱骨折手术治疗方法选择的指导价值。方法选取2012年9月至2014年9月我院收治的69例胸腰段脊柱骨折患者为研究对象,根据改良Load-sharing评分选择不同的手术方式,对于评分为4~6分的患者应用后路手术;对于评分≥7分且保留完整骨折椎后方结构、不伴有脱位的患者,应用前路手术＋骨折椎体次切＋前路植骨术;对于评分≥7分且骨折椎后方结构破坏或伴有脱位的患者,应用前后路联合手术＋骨折椎体次切＋前路植骨术。观察记录临床治疗效果。结果所有患者的后凸角、椎管占位及椎体压缩于手术后均得到恢复,与手术前比较差异具有统计学意义（P〈0.05）。40例不完全性神经功能损害患者中,3级神经功能恢复者2例,2级神经功能恢复者14例,1级神经功能恢复者24例。根据Denis分级对术后腰痛评价分级,P1 49例,P2 14例,P3 6例。术后31例恢复原来从事工作或体力劳动,32例更换较轻松工作或轻体力劳动,6例生活能自理但不能参加正常工作及劳动。结论改良Load-sharing评分对胸腰段脊柱骨折手术治疗方法的选择具有重要指导价值。

Planetary Gear Profile Modification Design Based on Load Sharing Modelling

In order to satisfy the increasing demand on high performance planetary transmissions, an important line of research is focused on the understanding of some of the underlying phenomena involved in this mechanical system. Through the development of models capable of reproduce the system behavior, research in this area contributes to improve gear transmission insight, helping developing better maintenance practices and more efficient design processes. A planetary gear model used for the design of profile modifications ratio based on the levelling of the load sharing ratio is presented. The gear profile geometry definition, following a vectorial approach that mimics the real cutting process of gears, is thoroughly described. Teeth undercutting and hypotrochoid definition are implicitly considered, and a procedure for the incorporation of a rounding arc at the tooth tip in order to deal with corner contacts is described. A procedure for the modeling of profile deviations is presented, which can be used for the introduction of both manufacturing errors and designed profile modifications. An easy and flexible implementation of the profile deviation within the planetary model is accomplished based on the geometric overlapping. The contact force calculation and dynamic implementation used in the model are also introduced, and parameters from a real transmission for agricultural applications are presented for the application example. A set of reliefs is designed based on the levelling of the load sharing ratio for the example transmission, and finally some other important dynamic factors of the transmission are analyzed to assess the changes in the dynamic behavior with respect to the non-modified case. Thus, the main innovative aspect of the proposed planetary transmission model is the capacity of providing a simulated load sharing ratio which serves as design variable for the calculation of the tooth profile modifications.

Load Sharing Behavior of Star Gearing Reducer for Geared Turbofan Engine

Load sharing behavior is very important for power-split gearing system, star gearing reducer as a new type and special transmission system can be used in many industry fields. However, there is few literature regarding the key multiple-split load sharing issue in main gearbox used in new type geared turbofan engine. Further mechanism anal- ysis are made on load sharing behavior among star gears of star gearing reducer for geared turbofan engine. Compre- hensive meshing error analysis are conducted on eccentricity error, gear thickness error, base pitch error, assembly error, and bearing error of star gearing reducer respectively. Floating meshing error resulting from meshing clearance variation caused by the simultaneous floating of sun gear and annular gear are taken into account. A refined mathematical model for load sharing coefficient calculation is established in consideration of different meshing stiffness and support- ing stiffness for components. The regular curves of load sharing coefficient under the influence of interactions, single action and single variation of various component errors are obtained. The accurate sensitivity of load sharing coefficienttoward different errors is mastered. The load sharing coef- ficient of star gearing reducer is 1.033 and the maximum meshing force in gear tooth is about 3010 N. This paper provides scientific theory evidences for optimal parameter design and proper tolerance distribution in advanced devel- opment and manufacturing process, so as to achieve optimal effects in economy and technology.

Load Dependent Series-Parallel Systems with Common Bus Performance Sharing Mechanism

A series-parallel system was proposed with common bus performance sharing in which the performance and failure rate of the element depended on the load it was carrying. In such a system,the surplus performance of a sub-system can be transmitted to other deficient sub-systems. The transmission capacity of the common bus performance sharing mechanism is a random variable. Effects of load on element performance and failure rate were considered in this paper. A reliability evaluation algorithm based on the universal generating function technique was suggested. Numerical experiments were conducted to illustrate the algorithm.

New model for load-sharing k-out-of-n:G system with different components

On the basis of capacity flow model, a new model is developed for a load-sharing k-out-of-n： G system consisting of different components, to describe the increase of the same component＇s failure rates under different loads. All components have exponential life distributions and are nonrepairable in the system. Reliability of load- sharing 2-out- of-3： G system is calculated and some special cases for the system are discussed. The calculation and discussions show that the model is right and practical.

Dynamic load sharing behavior of transverse-torsional coupled planetary gear train with multiple clearances

A new nonlinear transverse-torsional coupled model with backlash and bearing clearance was proposed for planetary gear set. Meanwhile, sun gear and planet's eccentricity errors, static transmission error, and time-varying meshing stiffness were taken into consideration. The differential governing equations of motion were solved by employing variable step-size Rung-Kutta numerical integration method. The behavior of dynamic load sharing characteristics affected by the system parameters including input rate, sun gear's supporting stiffness and eccentricity error, planet's eccentricity error, sun gear's bearing clearance, backlashes of sun-planet and planet-ring meshes were investigated qualitatively and systematically. Some theoretical results are summarized at last which extend the current understanding of the dynamic load sharing behavior of planet gear train, enrich the related literature and provide references for the design of planetary gear train.

Load-sharing Characteristic of Multiple Pinions Driving in Tunneling Boring Machine

The failure of the key parts, such as gears, in cutter head driving system of tunneling boring machine has not been properly solved under the interaction of driving motors asynchronously and wave tunneling torque load. A dynamic model of multi-gear driving system is established considering the inertia effects of driving mechanism and cutter head as well as the bending-torsional coupling. By taking into account the nonlinear coupling factors between ring gear and multiple pinions, the influence for meshing angle by bending-torsional coupling and the dynamic load-sharing characteristic of multiple pinions driving are analyzed. Load-sharing coefficients at different rotating cutter head speeds and input torques are presented. Numerical results indicate that the load-sharing coefficients can reach up to 1.2-1.3. A simulated experimental platform of the multiple pinions driving is carried out and the torque distributions under the step load in driving shaft of pinions are measured. The imbalance of torque distribution of pinions is verified and the load-sharing coefficients in each pinion can reach 1.262. The results of simulation and test are similar, which shows the correctness of theoretical model. A loop coupling control method is put forward based on current torque master slave control method. The imbalance of the multiple pinions driving in cutter head driving system of tunneling boring machine can be greatly decreased and the load-sharing coefficients can be reduced to 1.051 by using the loop coupling control method. The proposed research provides an effective solution to the imbalance of torque distribution and synchronous control method for multiple pinions driving of TBM.

Dynamic load sharing characteristics and sun gear radial orbits of double-row planetary gear train

A new non-linear bending-torsional coupled model for double-row planetary gear set was proposed, and planet's eccentricity error, static transmission error, and time-varying meshing stiffness were taken into consideration. The solution of differential governing equation of motion is determined by applying the Fourier series method. The behaviors of dynamic load sharing characteristics affected by the system parameters including gear eccentricities error, ring gear's supporting stiffness, planet's bearing stiffness, torsional stiffness of first stage carrier and input rotation rate were investigated qualitatively and systematically, and sun gear radial orbits at first and second stage were explored as well. Some theoretical results are summarized as guidelines for further research and design of double-row planetary gear train at last.

LOAD SHARING AND CONTACT OF HOURGLASS WORM GEARING

Based on solid modeling, the geometry and the FE model of the hourglass worm gearing are established. By the hybrid method of FEM and penalty function, the load sharing among tooth paris and the stress of contact teeth are calculated, the contact zones and the distribution of the contact pressure are investigated. The variation of the contact states with the load is investigated by comparision of its contact patterns under different loads.

双路电源的主动均流电路系统研究

广泛使用的低成本电源管理芯片或直流电源模块通常并未集成输出均流控制功能,因此不能直接并联输出使用。而使用特殊的电源管理芯片或是额外的均流控制电路会提高电源电路的复杂程度,造成电路成本的提高。针对此应用场景,提出了一种具有主动均流功能的双路电源开关,作为负载开关或电源多路复用器应用于电路之中,利用开关电流的方法均分输出电流,在几乎不增加电路成本的同时对两路电源进行均流。阐述了所提双路电源开关的工作原理与参数设计方法,并通过仿真与实验证明了所提方法的正确性与可行性。

配筋空心方钢管高强混凝土纯弯构件受力性能有限元分析

目的 研究配筋空心钢管高强混凝土构件的抗弯性能,推动其在建筑结构中的应用。方法 采用有限元分析软件ABAQUS建立配筋空心钢管混凝土构件有限元模型,在验证模型准确的基础上,分析构件的受力全过程及钢材屈服强度、混凝土抗压强度、钢管壁厚、钢筋直径、普通钢筋数量对构件受弯性能的影响。结果 纯弯试件在荷载作用下受力过程可分为3个阶段:弹性阶段、弹塑性阶段和强化阶段;试件破坏形态均为受弯破坏,表现出较好地延性。结论 组合构件在弯矩作用下可以很好地协同工作;钢材屈服强度和钢管壁厚的增加对构件承载力的提高影响最显著,建议配置普通钢筋数量在6~8根为最优。

不同螺栓等级下共享铁塔挂载连接件承载性能研究

为研究螺栓等级对挂载连接件承载性能的影响,选取了4.8级普通螺栓(KL-4.8)与8.8级摩擦型高强螺栓(KL-8.8)连接的挂载连接件进行静力试验研究。采用ABAQUS有限元分析软件对其受力性能进行模拟,使用可靠的数值模型系统分析螺栓等级和螺栓直径对连接件承载性能的影响。结果表明:在水平荷载作用下,两种不同螺栓等级连接的挂载连接件节点处均未出现滑移;两种连接件的破坏模式基本一致,左右两侧方钢管底部及右侧方钢管顶部均出现断裂;KL-8.8的整体刚度、极限承载能力以及变形能力均高于KL-4.8;当采用4.8级普通螺栓连接且承载力低于74.13 kN时,螺栓直径不宜小于18 mm,否则螺栓杆会发生剪切变形;当采用8.8级和10.9级高强螺栓连接时,双板件连接处节点偏于刚性连接,挂载连接件的整体刚度和极限荷载主要取决于方刚管、挂载铁杆等其他部件;挂载连接件在承载过程中通过双板件与主材之间的摩擦力和螺栓抗剪来抵抗外载,实际工程中应根据挂载重量合理选择螺栓参数。

桩承式加筋垫层路堤荷载分担改进计算模型

桩承式加筋垫层路堤中的关键荷载传递机制是多种现象的组合,包括路堤填土中的土拱效应、加筋垫层的张拉膜效应和地基土的支撑作用,然而,目前针对此方面的研究尚不完善。本文首先以考虑土体被动土压力发挥程度及桩间土应力非均匀分布改进的Hewlett土拱模型为改进载体;其次,假定加筋垫层为上、下部受均布荷载作用的简支梁,截面拉应力完全由加筋体承担,压应力完全由垫层材料承担,同时考虑地基土反力与梁最大挠度相关,引入地基反应系数,从而建立改进的桩承式加筋垫层路堤荷载分担计算模型;最后,通过工程实例与模型参数分析,验证本文计算模型的可靠性与准确性。研究结果表明:在路堤填筑过程中,土拱效应逐渐完全发挥,促进路堤荷载向桩体转移;随着地基土固结,桩体承担的路堤荷载也在逐渐增大;路堤填土高度、填土内摩擦角、桩间距对桩体荷载分担影响较大,加筋体抗拉模量对其影响较小。

有源前端组网的直流船舶电网高能效运行控制

直流船舶电网为航运业绿色转型提供了有效可行的解决方案。考虑到实际船舶的运行工况,本文提出一种分层协调控制策略,主要用于有源前端组网的直流船舶电网中功率单元协调运行的设备层控制系统和功率层控制系统。其中,设备层控制系统负责实现发电机组转速的无静差跟随与不同容量柴油发电机组间的动态/稳态功率共享;功率层控制系统负责提升母线电压质量,提高系统能效。最后,利用仿真与半实物仿真系统对控制策略进行验证,结果表明该控制策略可有效提高系统运行能效,最高节省约10%的燃油。

虚拟电厂两阶段准线型需求响应优化及收益共享-风险共担决策方法

末端分散式资源的需求响应(demand response,DR)是支撑电力系统灵活调节的重要形式,但末端资源通常规模大且单体容量小,迫切需要虚拟电厂(virtual power plant,VPP)等市场主体进行聚合代理,从而间接参与电网公司的调节服务。聚焦于准线型需求响应这一新兴的响应模式,重点研究VPP内部分散式资源的利益-风险互动协调策略,提出面向准线型DR的VPP两阶段优化及收益共享-风险共担决策方法,构建VPP与电网、内部用户互动协调新模式。首先,在准线型激励下VPP以整体收益最大化为目标,考虑柔性负荷响应积极度与新能源准确度因子,进行日前-日内两阶段DR优化;其次,在收益共享-风险共担决策方法下,VPP与柔性负荷共享准线型激励、与新能源共担不确定性风险,并以改进的Shapley法对内部柔性负荷进行利益分配。仿真结果表明,相较于传统DR,准线型DR给出全时段响应目标,更具有优越性;共享-共担决策吸引柔性负荷参与VPP调节,促使VPP与用户双赢。

重载行星轮系安装误差对系统均载性能的影响

行星轮安装误差的存在会导致行星轮系产生不均载问题,进而会影响减速器的传动性能和寿命。以往的研究未明确定义不同角度下的安装误差对系统均载性能的影响,并且关于多行星轮对系统均载影响的研究(在不同安装误差和不同输入功率下)也较少。为此,研究了实际应用中行星轮系安装误差对系统均载性能的影响。首先,以重载四行星轮系为研究对象,建立了行星轮径向和切向安装误差的综合误差表达形式;然后,基于轮系的传动模型,分析了单行星轮不同安装误差角和误差数值对系统均载的影响;最后,在单行星轮的基础上分析了不同工况和误差配置下多行星轮对系统均载的影响。研究结果表明:行星轮的切向安装误差对系统均载影响最大,径向安装误差对系统均载影响最小,当单行星轮安装误差数值为60μm,安装误差角θ从径向往切向方向靠近时,行星系统的均载系数增大了9.6%;误差绝对值越大,均载系数越大,当单行星轮安装误差数值从-30μm到-60μm时,系统的均载系数增大了4.6%;多行星轮存在切向安装误差对系统均载的影响可以用有效误差来衡量;齿轮承载范围内,随着输入功率的增大,安装误差对系统均载的影响逐渐减小。

Shared-nothing并行数据库系统查询优化技术

查询优化是并行数据库系统的核心技术 .该文介绍作者自行研制的一个 Shared- nothing并行数据库系统PBA SE/ 2中独特的两阶段优化策略 .为了缩减并行查询优化庞大的搜索空间 ,PBASE/ 2将并行查询优化划分为顺序优化和并行化两个阶段 .在顺序优化阶段对并行化后的通信代价进行预先估算 ,将通信开销加入顺序优化的代价模型 ,同时对动态规划搜索算法进行了修正和扩展 ,保证了顺序优化阶段得到的最小代价计划在并行化后代价仍然最小 .并行化阶段的优化目标是实现查询工作量在系统内多种资源上的负载平衡 ,提出了资源负载平衡因子的概念 ,并且通过启发式规则、任务调度等机制保证了并行查询执行计划的优化性 .

高压水道钢筋混凝土夹心钢板衬砌研发与性能验证

针对高压水道中钢筋混凝土衬砌内水外渗以及钢板衬砌易于溃屈问题,研发了一种高压水道钢筋混凝土夹心钢板衬砌,主要由内层钢筋混凝土-钢板-外层钢筋混凝土组成。为验证新型衬砌性能,进行了高内外水交替作用下模型试验,研究衬砌变形受力及荷载分担变化情况。结果表明:外水压力作用下衬砌处于受压状态,各部分荷载分担比较为固定,钢板部分所受压应力仅为1.47 MPa,远低于临界应力20.25 MPa,失稳溃屈的风险极小;内水压力作用下衬砌处于受拉状态,随着内水压力的增加,内层混凝土会先于外层混凝土开裂,未开裂前衬砌各部分荷载分担比基本固定;开裂后混凝土部分分担荷载降低、钢板与围岩所分担荷载增加,钢板所受拉应力为28.01 MPa,远低于其极限强度。相较于传统衬砌,新型衬砌结构在高压水道环境下具有更优越的性能。

低加速力波动感应线圈型发射器的外电路设计

感应线圈型发射器中每级驱动线圈都会对电枢产生脉冲形式的电磁推力,导致电枢在发射过程中加速力波动较大。过大的加速力峰值以及加速力波动都可能对载荷造成不利影响甚至损坏其内部携带的敏感电子器件,因而限制了感应线圈型发射器在实际工程应用中的价值。针对上述问题,提出一种多电容分时触发的新型驱动电路,并通过分析电容值和电枢触发位置变化对发射器发射效率的影响,说明了该电路的可行性。设计三种模式的驱动电路进行对比,研究结果表明:相比于其他电路触发模式,提出的分时触发模式在初始储能相同和电枢出口速度近似的情况下,电磁加速力峰值降低了2.04 kN,加速力波动降低了2.36 kN。因此,采用分时触发电容的驱动外电路,可以有效降低电枢的加速力峰值和加速力波动,并为携带敏感载荷的感应线圈型发射器的设计提供了参考价值。