主蒸汽管道弯管的金属监督

薄壳理论模型显示,弯管内弧位置有最大应力,但实际上弯制导致弯管外弧减薄,加之不圆度的存在,进一步加大了弯管外弧部位的应力集中.运行中的弯管受到管道内压与外载弯矩的共同作用,其不圆度既可能减小,也可能增大或不变,"复圆"不能视作弯管蠕变损伤发展的唯一趋势.已有的试验数据证明,弯管的材质老化速度并不比直管快.因此,不能认为弯管具有管道材质老化的典型意义而轻视对直管段的组织检验.     

U形管结构参数对外压失稳临界压力的影响

利用ANSYS有限元分析软件提供的特征值屈曲分析技术,针对不同圆度偏差及弯管半径的U形管弯管段,进行了外压失稳临界压力的计算。从计算结果可知,在相同弯管半径条件下,U形管弯管段的外压失稳临界压力随管子圆度偏差的增大,外压失稳临界压力将先增大后减小。随着U形管弯管半径的增加,外压失稳临界压力的临界值会不断减小。在相同弯管半径及圆度偏差相等的条件下,U形管壁厚的减薄量对临界失稳压力值的影响更大。     

水冷壁上联箱至汽包联络管爆裂原因分析

分析了通辽发电总厂1号炉水冷壁上联箱至汽包联络管爆裂原因，认为该管材料内非金属夹杂物超标，带状组织导致韧性过低，且不圆度较大而导致在弯管外弧有较大的附加应力。在内压波动造成的疲劳载荷作用下，弯管外弧处(应力最大位置)外表面的小缺陷或组织内的非金属夹杂物等应力集中处多点萌生裂纹，并随着载荷的波动快速扩展，最终在水压试验时裂纹扩展达到临界尺寸而发生爆裂。     

感应加热小弯曲半径（1.5～3.0Dw）弯管技术的研究

以往小半径弯管的制造均采用施加反弯矩的方法,以实现控制弯管外弧侧壁厚减薄率,理论分析结果认为,采用不均匀感应加热弯制小半径弯管是可行的,并通过工艺试验证明,提高弯管内,外弧侧的加热温度差,可有效地控制弯管外弧侧的壁厚减薄率,为小半径弯管机床的优化设计和工艺制定提供了参考依据。     

电站弯管不圆度量具改进及测量分析

探讨弯管不圆度的相关概念,介绍电站弯管不圆度的测量意义及测量方法,详述用于电站弯管不圆度测量的卡钳配测量尺测量法、带表外卡规测量法、数显式外卡规测量法,对各种测量方法的优缺点进行分析比较。     

弯管运行失效特性研究的新进展

主蒸汽管道是发电设备的重要构件,在运行中主要承受蠕变载荷。随着运行时间的延长。材料将发生形变、损伤,直至管道破裂失效。这就使管道有一定的运行寿命。同直管段相比,弯管有一些特点。在弯制过程中,外弧侧管壁厚度减薄,椭圆度增加,而且材料由于形变而产生预损伤。在运行中它承受内压力、轴向力和弯矩作用。因此,弯管将在运行载荷作用下,产生不均匀的形变和损伤。那些优先出现大的形变和损伤的部位,将提前失效。     

弯管几何参数不规则度对弯头应力的影响

管子弯头的几何参数的不规则度(失圆度)表现为以下三种形式:(1)管壁厚度变化,弯头外侧减薄,内侧增厚;(2)成椭圆(正椭圆或不对称椭圆);(3)内侧皱褶(波浪度).这些几何参数不规则度的形成及其表现程度主要决定于弯管方法和工艺水平,并对弯头产生不同程度的危研究室.因此不同类型的管子(如一般钢管、不锈钢管、有色金属管,小径薄壁管、大径厚壁管等)必须采用恰当的弯管方法(如冷弯、热弯或中频弯制等)以保证弯管质量.     

45°焊制斜三通应力增强系数的试验研究

４５°焊制斜三通应力增强系数的试验研究何志敏，董邦平一、前言管道在内压、持续外载、热胀冷缩及其它位移等因素的作用下，弯管、三通等管件部位会产生局部应力集中，在机组启停和受其它交变载荷作用时，管道特别是管件还要承受反复的变形。因此，美国ＡＮＳＩ、Ｂ３１...     

主蒸汽管道弯管应力的试验研究

一、前言在火力发电厂主蒸汽管道系统中,弯管是易损件之一。这是因为弯管在被弯曲加工过程中所形成的椭圆度、残余应力等都会影响它的使用寿命。在同一内压作用下,弯管的应力比相同直径的直管复杂一些。两德一杂志在报导中介绍,在统计损伤管件时发现异型管件约占全部管件的50％。在我国也是弯管损坏几率大于直管损坏几率。对超期服役的主蒸汽管道更应予以关注。有些电厂不知弯管的实际应力状态,仅根据其使用时间的长短更换弯管。这种做法对主蒸汽管道的运行安全性和经济性有一定的影响。因此,通过实测、试验等途径透彻了解弯管的应力状态显得迫切需要。由于受条件的限制,现场实测仅反映出主蒸汽管道在运行中受综合因素影响的结果,至于弯管受内压、扭矩及其它载荷的影响程度,在现场实测中是难以区分的。为了弄清这些因素及管道弯制后其弯曲部     

超超临界锅炉高温再热器HR3C管屏开裂分析及应力优化

某超超临界锅炉二次高温再热器HR3C管屏投运约2 000 h时在冷弯管内弧处发生开裂，从应力水平研究分析其原因。结果表明：弯管金相组织正常，室温抗拉强度合格；裂纹处具有明显的沿晶氧化缺陷特征。弯管截面的椭圆度对弯管应力的影响较大，同时弯管冷弯后未进行固溶处理消除残余应力，在运行过程中促使弯管沿晶氧化缺陷的产生与扩展，最终导致管屏开裂。在实施弯管截面椭圆度控制、固溶处理和安装改进等优化措施后，管屏在后续运行中未发生开裂。     

弯头壁厚超标对管道设计的影响分析

在不同弯头壁厚条件下,通过管道应力计算来考察弯头壁厚变化对管道应力、管道对设备接口推力和推力矩以及管系中弹性支吊架荷载的影响.由于弯头壁厚增加,使得管系中弯头处一次应力降低,二次应力上升,使得管系对设备接口推力和推力矩增加,且推力矩的增加尤为显著,使得管系中弹性支吊点荷载增加,支吊架弹簧跳号.     

Dynamic modeling and torque estimation of FES-assisted arm-free standing for paraplegics.

This paper presents an application of recent findings in the field of redundant robotic systems' control, toward investigating the feasibility of functional electrical stimulation (FES) assisted arm-free standing for paraplegics. Twelve degrees-of-freedom (DOF) forward and inverse dynamic models of quiet standing have been developed. These models were used to investigate the minimum number of DOF that would need to be actuated in order to generate stable quiet standing in paraplegics despite internal and external disturbances. The results presented herein suggest that the proposed nonlinear dynamic model could achieve guaranteed asymptotic stability with only six active DOF, assuming that the remaining six DOF are passive, i.e., there is no active or passive torques applied to those DOF. The stability analyses were performed using a proportional and derivative (PD) controller coupled with gravity compensation. The results of this analysis suggest that if only six particular DOF are actively controlled in a paraplegic subject, this individual should be able to achieve stable quiet standing despite disturbances. This result has both clinical and system-design implications for the development of a device that will facilitate FES-assisted arm-free quiet standing. The clinical implication is, if a paraplegic patient can exert voluntary control over specified six DOF in the lower limbs, that patient, after intensive physiotherapy, will have the potential to perform quiet standing unassisted. The system-design implication is that FES-assisted arm-free standing for paraplegics is theoretically plausible if one would actively control only six out of 12 DOF in the lower limbs. The proposed solution does not require the locking of joints in the lower limbs (commonly applied in the field) or voluntary control of the upper body to compensate for the internal and external disturbances. Another important finding of this study is the existence of six different combinations of six active DOF able to facilitate stable quiet standing. This dynamic redundancy of the biological bipedal stance allows the selection of an ideal subset of six DOF in designing a neuroprosthesis for standing. This further implies that a considerably less complex FES system than previously anticipated needs to be developed for FES-assisted standing.     

高温过热器T91、T22管爆管分析

某电厂锅炉高温过热器T91、T22管在运行2万h后多次发生爆管，通过对原始管、运行管、爆管的组织和性能检测表明，爆管是由于T22管长时处于超温运行，在蒸汽侧产生大量氧化层，而氧化层在起停时剥落并沉积在下弯头附近，从而使管内流量降低，管壁金属短时过热所致。     

基于多项式极点配置的ASVG数字控制器设计

提出一种采用多项式极点配置的ASVG数字控制器设计的方法,该方法是基于d-q坐标系下建立的数学模型,进行双闭环数字控制器设计,电流内环控制器为二自由度控制器,直接从时域性能指标入手建立理想内环闭环特征多项式用多项式法进行极点配置,对指令电流和电流扰动分开控制,系统具有良好跟踪性能、抗扰性能和较好的鲁棒性;对电压外环直接...     

Reciprocal EMG control of elbow extension by FES

Elbow extension is critical in performing activities of daily living. Individuals with a C5-C6 spinal cord injury have paralyzed elbow extensors, yet retain weak to strong voluntary control of elbow flexion. Previous studies have shown that functional electrical stimulation (FES) of the triceps provides sufficient elbow extension strength and control to greatly improve function. With triceps stimulation applied at a constant level, elbow angle is controlled naturally by voluntary flexion opposing the stimulated extension-referred to as voluntary antagonist control. We have investigated an alternative reciprocal control scheme employing biceps electromyogram. (EMG) to modulate triceps stimulation. With reciprocal control, increasing biceps EMG proportionally reduces triceps stimulation. A personal computer (PC)-based lab system was designed to test the feasibility of reciprocal control. Reciprocal control increased the range of elbow moments, was stable during maintained elbow angle or isometric moment, and used less stimulation. Reciprocal control of triceps stimulation using biceps EMG is an effective method for restoring elbow extension to C5-C6 spinal cord injury patients, and could be extended to other situations where a voluntarily controlled muscle can be opposed by stimulating an antagonist     

Dynamic stability of spine using stability-based optimization and muscle spindle reflex.

A computational method for simulation of 3-D movement of the trunk under the control of 48 anatomically oriented muscle actions was developed. Neural excitation of muscles was set based on inverse dynamics approach along with the stability-based optimization. The effect of muscle spindle reflex response on the trunk movement stability was evaluated upon the application of a perturbation moment. The method was used to simulate the trunk movement from the upright standing to 60 degrees of flexion. Incorporation of the stability condition as an additional constraint in the optimization resulted in an increase in antagonistic activities demonstrating that the antagonistic co-activation acts to increase the trunk stability in response to self-induced postural internal perturbation. In presence of a 30 Nm flexion perturbation moment, muscle spindles decreased the induced deviation of the position and velocity profiles from the desired ones. The stability-generated co-activation decreased the reflexive response of muscle spindles to the perturbation demonstrating that the rise in muscle co-activation can ameliorate the corruption of afferent neural sensory system at the expense of higher loading of the spine.     

750 kV输电线路扩径导线跳股原因的分析

750 kV官兰输电线路在高海拔地区采用了LG JK-300/50扩径导线,在张力放线施工过程中,扩径导线频频发生跳股现象。扩径导线的结构特点是其发生跳股的内在原因,即其内层铝股和邻外层铝股疏绕的空隙和对外层铝股支持力的缺失,使导线的结构处于不稳定状态。当导线通过滑轮时,在较大的综合外力的挤压作用下,导线就会发生跳股。建议研究单位对导线跳股进一步进行试验研究。     

面内弯矩作用下薄壁弯头的极限载荷估算解

采用同时考虑材料和几何的非线性三维有限元数值分析技术,分析不同几何参数和不同弯曲模式下配直管连接薄壁弯头的弹塑性行为,研究几何参数和弯曲模式对弯头塑性承载能力的影响规律,获得了相应的极限载荷数值解,并在此基础上建立了极限载荷估算式.分析结果表明,在弯矩作用下,几何非线性对弯头塑性承载的影响显著;弯头在面内开弯载荷作用下的塑性行为与在闭弯载荷下的塑性行为差异很大,其塑性极限载荷值显著不同;弯头壁厚与其横截面半径的比值对弯头塑性承载能力的影响显著,其次为弯曲模式.     

汽轮发电机组转子材质缺陷引起的振动问题

用于加工汽轮发电机组转子的毛坯锻件如果存在材质不均或残余内应力过大问题时,会导致加工后的转子在运行中发生振动。讨论了因转子材质缺陷引起的机组振动的机理和振动特点,并结合近年国内出现的与材质缺陷有关的振动诊断和处理实例予以阐述。经分析,转子材质组织不均匀和残余内应力过大将引起机组带负荷工况振动爬升且随运行时间增长振动持续增大,后者将使转子出现一定程度的永久弯曲,并造成一阶临界转速下振动显著增大。