轴承座动刚度偏低的振动特征与诊断处理

针对某型号125MW汽轮发电机组大修后定速时和满负荷时出现振动故障的问题,进行数据分析和诊断,正确判断出机组振动偏大的原因是轴座动刚度偏低。为此,提出具体的处理方案,在短时间内消除了振动故障,机组正常并网发电。     

基于磁致变刚度的微振动隔振器动态特性研究

磁敏弹性体是智能材料家族中的新成员,其储能模量(刚度)可由外加磁场控制,利用磁敏弹性体的这一特性,以其作为变刚度元件设计了面向精密设备的磁致变刚度微振动隔振器.采用扫频与定频试验探讨了微振动隔振器动态隔振特性.结果表明,在励磁电流激励的磁场控制下,磁敏弹性体刚度随激励磁场实时变化,导致系统产生移频效应,使隔振器在宽频范...     

Static and dynamic evaluation of the influence of supplementary hip-joint stiffness on crutch-supported paraplegic stance

Paraplegic persons can stand with hip-knee-ankle-foot orthoses (HKAFO) and crutches. However, current HKAFOs restrict body movement extensively, which may impede functional upper-body movements. A more compliant body support using a more compliant orthosis or well-controlled functional electrical stimulation system may increase freedom of movement to the user, but should not impede stability and required arm support. In the current study, we investigated the consequences of varying stiffness applied at the hip to postural stability and required crutch force during paraplegic stance. Experiments were performed on five paraplegic persons with spinal cord lesions varying from Tl to T12. Static postures and dynamic responses to perturbations were tested for varying hip stiffness and crutch placements. The minimal hip-joint stiffness for stable stance appeared to depend on lesion level. In contrast to the predictions of a previous modeling study, no statistically significant influences of hip-joint stiffness or crutch-to-foot distance on posture and applied crutch forces were found. It is hypothesized that the main reasons of this discrepancy are the active upper-body efforts the paraplegic HKAFO users are still able to exert and the remaining flexibility of the upper trunk and shoulder region, which is present despite the restrictions of the orthosis.     

Modulation effects of epidural spinal cord stimulation on muscle activities during walking.

Epidural spinal cord stimulation (ESCS) combined with partial weight bearing therapy (PWBT) has been reported to facilitate recovery of functional walking for individuals after chronic incomplete spinal cord injury (ISCI). Muscle activities were analyzed in this report to examine the modulation effect of ESCS on muscle recruitment during gait training. Two ISCI individuals participated in the study and both are classified as ASIA C with low motor scores in the lower limbs. Stimulating electrodes were placed at the epidural space over T10-L2 spinal segments, along the midline in participant 1 (S1), and off-midline in participant 2 (S2). Surface electromyograms (EMGs) from leg muscles under both ESCS ON and OFF conditions recorded during treadmill gait were analyzed in time-frequency domains. ESCS application produced acute modulations in muscle activities in both participants, but the observed pattern, magnitude, and spectral content of the EMGs differed. In S1, ESCS induced a significant shift in the temporal pattern of muscle activity toward normal comparing with that when ESCS was OFF, though without eliciting noticeable change in frequency distribution between ESCS ON and OFF conditions. When ESCS was applied in S2, a modulation of EMG magnitude was observed and, consequently, improved joint kinematics during walking. In this case, a stimulation entrainment appeared in time-frequency analysis. The results suggest that ESCS activates neural structures in the dorsal aspect of the spinal cord and facilitates gait-related muscle recruitment. The exact effects of ESCS depend on the electrode placement and possibly injury history and residual functions, but in general ESCS produces a positive effect on improved walking speed, endurance, and reduced sense of effort in both ISCI subjects.     

基于长过程动态仿真的风电接入对系统频率控制影响研究

风电的快速波动特性及与系统频率解耦特性使得风电接入后系统频率稳定性受到影响,在不同的风电穿透功率下,电网需有选择性地将风电纳入到系统的日前或日内调度计划中,如何确定风电接入对系统频率控制的影响是个难题。基于电力系统仿真软件DIgSILENT/PowerFactory建立了电力系统长过程调度决策仿真平台,平台为包含调度和电站上下两层的控制结构,可对风电接入后系统的长时间频率响应过程进行仿真。最后以某实际电网为例,仿真风电接入后对系统频率控制的影响,从而确定风电调度运行方案,验证模型的有效性。     

惯性与黏性对动载下混凝土强度的作用机理

通过分析混凝土试件内部的真实应力,探讨了动力荷载作用下惯性和黏性对混凝土性能的作用原理。采用理论分析和数值模拟的方法,从单自由度、多自由度角度分析了惯性与材料破坏时间的关系,并在此基础上分析了惯性的作用机制、探讨了混凝土内部水分与黏性对混凝土动力性能的作用机理。此外,还对目前动力荷载下混凝土强度提高的经验公式进行了深入分析,进一步阐释了混凝土动力实验中骨料断裂和多裂纹破坏等实验现象以及混凝土自身强度、初始静荷载等对混凝土动力性能的影响。研究成果可为正确分析室内实验结果和提取更为准确的混凝土结构动力分析参数提供参考。     

电力系统长动态过程仿真及自并励磁影响分析

以某大型区域电网严重事故为背景,基于PSCAD/EMTDC进行建模和仿真,对比研究励磁方式对电力系统动态过程的影响.仿真中,同步发电机励磁系统分别采用自并励模型和三机他励模型.两种模型下的仿真结果都基本重现了该事故从N-1及次发展到N-9直到振荡结束各个阶段的基本特征,同时表明,两种励磁方式下的仿真结果虽有差异,但没有质的差别.与他励方式相比,自并励方式在该事故的各个阶段包括振荡期间并没有对电力系统稳定产生不利的影响.     

电力系统长动态过程仿真及自并励磁影响分析

以某大型区域电网严重事故为背景,基于PSCAD/EMTDC进行建模和仿真,对比研究励磁方式对电力系统动态过程的影响。仿真中,同步发电机励磁系统分别采用自并励模型和三机他励模型。两种模型下的仿真结果都基本重现了该事故从N-1及次发展到N-9直到振荡结束各个阶段的基本特征,同时表明,两种励磁方式下的仿真结果虽有差异,但没有质的差别。与他励方式相比,自并励方式在该事故的各个阶段包括振荡期间并没有对电力系统稳定产生不利的影响。     

Unilateral and bilateral subthalamic nucleus stimulation in Parkinson's disease: effects on EMG signals of lower limb muscles during walking.

The effects of subthalamic nucleus (STN) stimulation on the spatio-temporal organization of locomotor commands directed to lower limb muscles were studied in subjects with idiopathic Parkinson's Disease (PD) by recording the EMG activity produced during steady-state walking in representative thigh (rectus femoris, RF, and semimembranosus, SM) and leg (gatrocnemius medialis, GAM, and tibialis anterior, TA) muscles, under four experimental conditions: basal stimulation OFF, unilateral (right and left) stimulation ON, and bilateral stimulation ON. Locomotor profiles of all of the muscles tested were found to be substantially affected by STN stimulation, either in terms of restoration/enhancement of the main activity bursts or normalization of recruitment timing thereof. Responses showed relatively higher statistical significance in the distal groups (GAM and TA) and, within them, for the EMG components called into action over the ground-contact (ankle dorsiflexors) and midstance (ankle plantarflexors) phases of the stride cycle. In line with data obtained from clinical rating, unilateral stimulation produced less consistent EMG changes compared with bilateral stimulation. However, at variance with clinical effects, which prevailed on the side of the body contralateral to stimulation, EMG responses to unilateral stimulation were usually symmetrical. Results indicate that the impact of STN stimulation on locomotor activation of lower limb muscles in PD is characterized by: 1) substantial effects exhibiting differential topographical (distal versus proximal) and stride-phase (stance versus swing) consistency and 2) absence of the lateralized actions typically observed for the clinical signs of the disease. Interaction with the activity of functionally different executive systems might account for the observed pattern of responsiveness.     

The effect of wrist angle on electrically evoked hand opening in patients with spastic hemiplegia.

This paper studied the effect of wrist angle on the amount of hand opening achieved by electrical stimulation in people with spastic hemiplegia. With their forearm in pronation, subjects were asked to relax while their affected wrist was passively moved in steps of about 15 degrees from full flexion into extension. Trains of stimuli were applied to the long finger extensor muscles through surface electrodes on the forearm. At each wrist position stimulation was turned on for a few seconds until hand opening equilibrated. Wrist angle and fingertip positions were recorded using a three-dimensional (3-D) motion analysis system. Maximal displacements between thumbtip and each fingertip occurred when the wrist was fully flexed. As the wrist was extended, hand aperture achieved by electrical stimulation progressively declined, reaching zero at 40 degrees of wrist extension. We conclude that electrical stimulation can significantly increase the grasp aperture of the hemiplegic hand, but this is strongly dependent on wrist posture and accompanying voluntary effort.     

Assessing long-term effects of demand response policies in wholesale electricity markets

Different policies have been implemented around the world seeking to deliver demand response potential in the electricity markets. Externalities, namely the CO₂ externality, have been one of the key concerns in the debate on the effectiveness of different policies regarding demand response development. Although most previous researches have centred on the short-term assessment of different policy choices to tackle the CO₂ externality, little work has been focused on the long-term impacts, such as changes in welfare and investment dynamics, in consequence of the implementation of such policies. This paper relies on a long-term market simulation model to examine long-term dynamics of two specific policies presently used by policy makers. The first policy relates to the correction for the externality by setting a CO₂ price at a level equal to the social cost of the associated CO₂ emissions. The second policy consists in subsidizing carbon-free technologies such as demand response. We test for each policy two different scenarios regarding the possibility of internalization of the CO₂ externality. The results show that in the long-run different policies should affect both investments and social costs, a market-driven development of demand response with the internalization of the CO₂ externality being the most efficient approach.     

一种竞赛型双足竞步机器人设计与研究

机器人的应用研究是目前研究热点,双足机器人是一种仿生类型的机器人,能够实现机器人的双足行走和相关动作。本文应用单片机控制技术、电机驱动技术等,设计了一种双足竞步机器人,并给出了机器人的硬件结构和控制程序,通过实验验证了本文所设计的双足竞步机器人到达到了设计预期和要求。通过3年的实践和应用扩展,本文所设计的双足机器人具有稳定性好、运行速度快的优点,结构简单、制作成本低,具有一定的扩展应用价值和意义。     

The effect of nonsinusoidal voltage on intrinsic aging of cable andcapacitor insulating materials

This paper investigates the effect of nonsinusoidal voltage, i.e. voltage affected by the presence of harmonics, on intrinsic aging of cable and capacitor insulating materials, i.e. cross-linked polyethylene (XLPE) and polypropylene (PP). The results of life tests under sinusoidal and distorted voltage, the latter obtained superimposing one or more harmonics on the 50 Hz component, are processed by statistical techniques derived from design-of-experiment procedures. It is shown that the factor predominant on aging acceleration due to the voltage distortion is voltage-peak increase, but also waveform slope and voltage rms value have statistical significance. Life models are obtained for XLPE and PP insulating materials, which show the endurance of the two materials to aging under nonsinusoidal conditions     

Metabolic and functional effects of low-potassium cardioplegic solutions for long-term heart preservation

Cardioplegic solutions used to arrest the heart during open heart surgery and cardiac transplantation are based on potassium as a cardioplegic agent in a concentration range of 13–35 mM. However, high to moderate K⁺ concentrations increase Ca²⁺ influx and impair endothelial function. We have therefore evaluated the possible advantage of a lower potassium concentration in a new cardioplegic solution (named CRMBM solution) designed for long-term heart preservation. Nine isolated perfused rat hearts were submitted to 8 h of hypothermic ischemia after cardioplegic arrest, followed by 60 min of reflow at 37°C. Two cardioplegic solutions were compared: (1) the CRMBM solution with 10 mM potassium (K-10 group), and (2) the CRMBM solution with 4 mM potassium (K-4 group). The quality of heart preservation was assessed by a metabolic study using P-31 magnetic resonance spectroscopy (energy metabolism and intracellular pH) combined to a functional evaluation and a measure of cellular integrity (biochemical assays in effluents and tissues). Decreasing the potassium concentration to 4 mM improved heart preservation, as shown by a higher functional post-ischemic recovery represented by the rate pressure product and a better preservation of cellular integrity. The evolutions of intracellular pH and high energy phosphate levels during ischemia and reflow were similar in both groups.     

Gas dynamic and force effects of a solid particle in a shock wave in air

Shock wave interaction with an adiabatic solid microparticle is numerically simulated. In the simulation, the shock wave is initiated by the Riemann problem with instantaneous removal of a diaphragm between the high- and low-pressure chambers. The calculation is performed in the two-dimensional formulation using the ideal gas equation of state. The left end of the tube is impermeable, while outflow from the right end is permitted. The particle is assumed to be motionless, impermeable, and adiabatic, and the simulation is performed for time intervals shorted than the time of velocity and temperature relaxation of the particle. The numerical grid is chosen for each particle size to ensure convergence. For each particle size, the calculated hydraulic resistance coefficient describing the particle force impact on the flow is compared with that obtained from the analytical Stokes formula. It is discovered that the Stokes formula can be used for calculation of hydraulic resistance of a motionless particle in a shock wave flow. The influence of the particle diameter on the flow perturbation behind the shock front is studied. Specific heating of the flow in front of the particle is calculated and a simple estimate is proposed. The whole heated region is divided by the acoustic line into the subsonic and supersonic regions. It is demonstrated that the main heat generated by the particle in the flow is concentrated in the subsonic region. The calculations are performed using two different 2D hydro codes. The energy release in the flow induced by the particle is compared with the maximum possible heating at complete termination of the flow. The results can be used for estimating the possibility of gas ignition in front of the particle by a shock wave whose amplitude is insufficient for initiating detonation in the absence of a particle.     

Fast solution method for evaluation of long-term dynamic processes in power systems with provision for island operation

A fast, simple and efficient solution method for evaluation of long-term dynamic processes in power systems with provision for island operation is proposed. The original systems of nonlinear differential equations that describe the dynamics of hydro and steam power plants, for a relatively large time step (1–2 s), are transformed into very simple decoupled difference (algebraic) equations, using linearization, decomposition, diagonalization and Cauchy's formula. This secures a fast, efficient and stable numerical integration process with low memory requirements. The differential equation, used for the evaluation of the dynamics of the uniform frequency change, is also transformed in an appropriate manner, while the resultant difference equation is further incorporated into the model of the electrical network. The full model formed in this way is simultaneously solved iteratively, using a specially developed fast decoupled procedure, which has very good and reliable convergence characteristics. The validity of the procedure developed is tested on analyses of the dynamic behavior of the Yugoslav power system, for the case of large multiple disturbances which lead to the interruption of the parallel operation with UCPTE.     

Perturbation analysis of power systems: effects of second- and third-order nonlinear terms on system dynamic behavior

The study of nonlinear behavior near an equilibrium point is of considerable importance in power system stability analysis. In this paper, a systematic analytical procedure based on normal form (NF) theory is proposed for studying the influence of high order terms arising from the Taylor series expansion of the system model on power system dynamic behavior. Using this method, a third-order model of the power system is proposed in which weak system nonlinearities are explicitly represented. Analytical expressions are then developed that provide approximate solutions to system performance near a singularity and techniques for interpreting these solutions in terms of modal functions are given. The application of these procedures is illustrated on a single-machine infinite-bus system using a classical representation, but the results can be extended to accommodate more complex systems.     

The function of the finger intrinsic muscles in response to electrical stimulation.

The actions of the dorsal interosseous, volar interosseous, and lumbrical muscles were investigated using applied electrical stimulation and recording the moments that were generated across the metacarpophalangeal joint in flexion/extension and abduction/adduction, the proximal interphalangeal joint in flexion/extension, and the distal interphalangeal joint in flexion/extension. These measurements were made isometrically at various joint angles and levels of stimulation with both able bodied subjects and persons who had sustained tetraplegia. It was determined that the dorsal interossei, including the first, were strong abductors of the fingers and generated a significant moment in metacarpophalangeal (MP) joint flexion and interphalangeal (IP) joint extension. The volar interossei were the primary adductors of the fingers, as well as providing a significant moment in MP joint flexion and IP joint extension. The lumbrical muscles were found to be MP joint flexors and IP joint extensors, although the moments that were generated were on average 70% lower than the interossei. The role of the lumbricals as finger abductors or adductors could not be determined from the data. This information on the actions and moment generating capabilities of the intrinsic muscles led to the incorporation of the interossei into electrically induced hand grasp provided by an implanted neuroprosthesis. The evaluation of the intrinsic muscles in the neuroprosthesis was accomplished by recording the moment generating capabilities of these muscles across each of the joints of the finger. These muscles were capable of generating moments that were 80-90% of the average attained by the able bodied subjects, and have provided a substantial improvement to the electrically induced hand grasp.     

三峡水库动态汛限调度对气体过饱和减缓效果研究

由于三峡大坝泄洪而导致的下游河道溶解气体过饱和,对长江中游的水生态特别是鱼类将造成不利影响。为了减缓这种影响,采取一定措施减缓下游河道的气体过饱和现象十分必要。通过水库调度,尽量减少水库出库流量从而减少弃水是一种最为有效和可行的方案。本文设计了4种不同汛限水位的动态汛限调度方案,根据水库调洪计算方法,在丰、平、枯三种典型水文年型下汛期对下游气体过饱和的减缓效果进行比较,结果表明采用动态汛限调度方式可有效缓解坝下溶解气体过饱和现象。本文还对三峡动态汛限调度的可行性进行了简要分析。     

面向东北电网调峰辅助服务市场交易主体的分摊上限动态机制设计

东北电网现行的调峰辅助服务市场机制难以应对市场结构变化带来的交易主体实际调峰收益低于预期、积极性降低等问题,且难以满足未来我国以新能源为主体的新型电力系统发展需求。在介绍东北电网现行调峰辅助服务市场费用分摊机制的基础上,分析其局限性,提出面向市场参与主体的分摊上限动态调整机制,以保障调峰供应方的调峰收益;构建以市场交易主体综合收益最高为目标的动态分摊上限数学模型,并提出用于评估调峰辅助服务市场的指标体系。基于辽宁省电网实际运营数据的算例结果验证了所提机制的合理性与有效性。