双缓冲腔环形间隙对凿岩机缓冲系统动态特性的影响

分析了液压凿岩机双缓冲系统的结构特点,应用孔口节流理论确定了缓冲活塞的静平衡位置,基于应力波传递原理得到了缓冲活塞的回弹速度,考虑油液的压缩特性推导出一级缓冲腔压力公式,由间隙流量公式得到了二级缓冲腔压力,在此基础上建立了缓冲活塞的运动微分方程.应用Matlab工具对双缓冲系统的动态特性进行了仿真,分析了不同环形间隙下缓冲活塞的运动规律,探讨了环形间隙对一级和二级缓冲腔压力的影响.提出与环形间隙和活塞最大行程的比值相关的间隙行程系数η.仿真结果表明,间隙行程系数与双缓冲系统的特性密切相关,存在最优范围.搭建了实验台,通过实验对缓冲系统的数学模型进行了验证.      

Dynamics of Mechanical Actions on Materials. Part 11. System with Two Irreversibly Deformable Bodies

A rheological model and the dynamics of an open mechanical system are considered including the elastic element of a machine and a composite body consisting of two successively joined irreversibly deformable bodies with a single degree of freedom under the action of an external force. On loading the system below the elastic limit for both bodies the motion of the mechanical system is described by a second order classical dynamic system. Above the elastic limit for one of the bodies system movement is described by a third order dynamic system, and above the elastic limit for both bodies by a dynamic system consisting of two third order differential equations. The solution of this dynamic system has the nature of damping oscillation with an increase in damping factor as there is an increase in the ratio of elastic stiffnesses and strain hardenings to the viscous resistances of the deformable bodies.

     

Dynamics of Mechanical Actions on Materials. Part 11. System with Two Irreversibly Deformable Bodies

A rheological model and the dynamics of an open mechanical system are considered including the elastic element of a machine and a composite body consisting of two successively joined irreversibly deformable bodies with a single degree of freedom under the action of an external force. On loading the system below the elastic limit for both bodies the motion of the mechanical system is described by a second order classical dynamic system. Above the elastic limit for one of the bodies system movement is described by a third order dynamic system, and above the elastic limit for both bodies by a dynamic system consisting of two third order differential equations. The solution of this dynamic system has the nature of damping oscillation with an increase in damping factor as there is an increase in the ratio of elastic stiffnesses and strain hardenings to the viscous resistances of the deformable bodies.     

四辊轧机主传动系统轴向窜动问题分析与改善

通过对 R2 轧机主传动系统轴向窜动问题进行分析,确定轧机上下辊系发生轴向窜动的原因分别是辊缝调整时万向接轴水平长度的变化和轧辊交叉产生的轴向力。通过采取提高主电机轴向阻尼止推装置的阻尼效果以降低扁头套与扁头之间的临界摩擦力以及通过调整下辊系的交叉状态以降低辊间轴向力等措施,使 R2 轧机主传动系统轴向窜动问题得到有效解决,避免了重大设备事故的发生。     

井下电动铲运机静液压系统控制方式的比较与探讨

对井下电动铲运机静液压系统的机械伺服控制和电气伺服控制方式进行比较和分析 ,设计成功机、电、液一体化的液压伺服控制系统 ,可实现静液压驱动系统的无级变速、静液压驱动系统与制动系统的联动 ,且耐潮、抗冲击、耐震动     

瞬间液相扩散复合法生产钢质蜂窝夹芯减振板

 采用瞬间液相扩散复合原理生产钢质蜂窝夹芯减振板的关键问题之一是中间夹层助复剂的选择和配制。采用正交设计方法设计了一种以铜为基体元素、锌为主要合金元素，再添加微量元素和稀土铈，以降低熔点，提高润湿性和塑性，并可在中低温下使用的助复剂。利用瞬间液相扩散复合原理及特点，使用这种自制的助复剂对蜂窝夹芯减振板进行了复合，并测试了其力学性能和减振性能。结果表明，设计的蜂窝夹芯减振板可满足力学性能要求并提高了减振性能。     

链斗式挖掘船液压主驱动方案刍议

以采金船为范例，阐述了链斗式挖掘船主驱动的工作特性及要求，对目前三种典型机械传动布置方案的优缺点作了客观分析，指出斗键生驱动引用液压技术的条件已趋成熟．在此基础上进一步提出直接液压驱动和多点单级减速液压驱动两种实施方案，并与现有的多种机械传动方案全面比较后，肯定了液压驱动方案的发展应用前景．     

液压凿岩机双缓冲系统性能参数优化设计

针对以往分析凿岩机入射应力波为定值的情况,基于应力波在不同介质中传递原理,计算经过多次透射和反射到达缓冲活塞的应力波大小,并运用傅里叶级数推导入射应力波模型.采用应变片实验法测试入射应力波波形,依据实验结果对入射应力波模型进行修正.基于牛顿力学理论,构建双缓冲系统的蓄能器等效刚柔耦合模型和双缓冲机构模型.借助Matlab工具,分析缓冲活塞运动规律以及一、二级缓冲腔压力变化规律.采用多目标优化方法对双缓冲系统的性能参数进行优化,获得双缓冲系统性能参数的最优参量:缓冲流量8.5 L·min-1、环形间隙0.017 mm、蓄能器初始充气压力2.3 MPa以及工作压力7.6 MPa.      

Hydraulic Damping of Saturated Poroelastic Soils During Steady-State Vibration

A theoretical study of the steady-state response of a saturated poroelastic soil column during compressional and rotational harmonic vibrations is presented. Hydraulic damping due to Biot flow is evaluated for top-drained and double-drained boundary conditions and for compressional and rotational motions using the theory of a damped single-degree-of-freedom system. For compressional motions, the dynamic response of gravels and sands is highly influenced by the compressibility of the pore fluid. More hydraulic damping occurs as soil hydraulic conductivity increases and as the column boundary conditions change from top drained to double drained. On the other hand, hydraulic damping for rotational motions is significantly less than that for compressional motions and is dependent on a dimensionless hydraulic conductivity parameter Ks. For Ks within the range of 10?3–100, hydraulic damping may have an important contribution to total soil damping, especially at small strain levels.     

冷带轧机两侧压下系统自适应同步控制研究

驱动冷带轧机的液压伺服系统由伺服阀和不对称液压缸组成。建立了某650mm冷带轧机的位置系统的非线性数学模型,并且给出了其参数。首先针对操作侧和传动侧压下位置子系统简单设计了控制器。由于两侧子系统的参数不同,例如总的质量、摩擦阻尼系数和液压缸活塞的初始位置不同等,会造成压下位置的不同步。为了解决这一问题,利用模型参考自适应控制的思想,设计了压下位置自适应同步控制器,该控制器也可用于倾辊控制。仿真结果表明两侧的位置误差能够很好地趋近于零或倾辊给定信号,系统的同步控制精度能够得到有效保证,并能够在一定程度上改善出口带材的板形质量。     

Dynamics of mechanical action on materials. IX. Preset movement of a system

The dynamics of an open mechanical dissipative system involving a viscoelastic strain hardenable body above and below its elastic limit is considered when the force generated with movement is governed by the kinematics of a machine with preset movement. The dynamic origin is clarified for the nonlinear part of the tensile curve beyond the elastic limit for a viscoelastic body to which “nonliear elasticity” is attributed. It is demonstrated that it arises as a result, a transient relaxation process. On completion of this process a force is established within the system governed by viscous flow of the body and corresponding to its yield point. As a result of the change in controlling parameters and the effect of a delay a bistable state arises for the system beyond the elastic limit leading to its macroscopic acoustic activity.     

Element Level System Identification with Unknown Input with Rayleigh Damping

A novel system identification procedure is proposed for nondestructive damage evaluation of structures. It is a finite element-based time-domain linear system identification technique capable of identifying structures at the element level. The unique features of the algorithm are that it can identify a structure without using any input excitation information and it can consider both viscous and Rayleigh-type proportional damping in the dynamic models. The consideration of proportional damping introduces a source of nonlinearity in the otherwise linear dynamic algorithm. However, it will also reduce the total number of damping coefficients to be identified, reducing the size of the problem. The Taylor series approximation is used to transform a nonlinear set of equations to a linear set of equations. The proposed algorithm, denoted as the modified iterative least square with unknown input algorithm, is verified with several examples considering various types of structures including shear-type building, truss, and beams. The algorithm accurately identified the stiffness of structures at the element level for both viscous (linear) and proportional (nonlinear) damping cases. It is capable of identifying a structure even with noise-contaminated response information. An example shows how the algorithm could be used in detecting the exact location of a defect in a defective element. The algorithm is being developed further and is expected to provide an economical, simple, efficient, and robust system identification technique that can be used as a nondestructive defect detection procedure in the near future.     

轧机液压压下系统非线性振动诱因分析

具有液压压下系统的轧机被广泛应用在板带生产过程中,为解决液压压下系统引起的轧机非线性振动问题,在闭环控制情况下分别研究了不同阻尼系数、泄漏系数以及控制器比例系数3种系统参数对压下系统垂振的影响。考虑压下缸非线性液压弹簧力建立了轧机液压压下系统垂振模型,通过振动位移时域图和位移-速度相图分析了不同系统参数与系统垂振的相关性。仿真结果表明,由于轧机液压压下系统采用传统PID控制器,液压系统本身阻尼系数、泄漏系数等具有慢时变特性,会使得原有PID控制可能出现功能失效情况,造成系统垂振的发生,该研究为后续设计控制器消除液压系统参数变动引起的垂振有一定的理论和工程实际意义。     

太钢六轧厂2300mm轧机电气系统改造的设计与应用

简要介绍了太钢六轧厂2300mm轧机电气系统改造工程的主传动、液压系统、辅助传动系统、自动化系统的改造内容以及基本控制功能。主传动采用西门子SIMADYND系统取代旧系统,辅助传动系统采用西门子6RA70系列和欧陆590+系列直流调速器,自动化系统采用S7-300型PLC。系统设计先进,可靠性好,在冶金行业内具有很好的参考价值。     

Range of Validity of the Transient Damping Leakage Detection Method

In a recent paper, an elegant, efficient, and easy to apply transient-based leakage detection method was proposed. The method exploits the fact that friction and leakage damp the modes of transient waves in a different manner. The method involves six major assumptions. These are: (1) the periodic motion in time of each mode is linearly independent of all other modes; (2) the amplitude of the induced transient is small; (3) the magnitude of the leak is small in comparison with the flow rate; (4) the wall friction can be represented by the Darcy–Weisbach equation; (5) the transient is initiated by an instantaneous small amplitude disturbance; and (6) the pipe system is a simple reservoir–pipe–valve type system or reservoir–pipe–reservoir type system. These six assumptions are relaxed and the validity of the transient damping method is assessed. The analysis shows that the first four assumptions do not pose any serious restriction to the applicability of the damping rate method provided that the mathematical model, used to generate the transient head trace in the leak-free pipe, accurately represents the frictional damping in the system. On the other hand, Assumptions (5) and (6) restrict the applicability of the method to systems that do not involve internal boundary conditions, such as junctions and pumps, and to transients triggered by impulses whose duration is smaller than the wave travel time. Extension of this method to complex pipe systems requires that the linearized waterhammer equations are solved under more general initial and boundary conditions. In addition, more investigation in relation to the frequency content of the input signal and its importance in leakage detection is warranted. The general framework used to derive the damping rate method has led to an efficient and direct algorithm for identifying leaks and future research should seek ways to adapt this framework to more complex pipe systems.     

天钢高速线材厂集卷液压系统的分析

天钢集团高速线材厂集卷区是高线厂的关键部位,是线材成型的必经之路,其主要动作靠液压系统驱动,液压系统的运转正常与否对集卷区主要设备的运转起着决定性的作用,文章对保证该液压系统正常运转的因素进行了分析并提出了解决办法.     

Dynamic Characteristics of SDOF Structure with Maxwell Element

Dynamic characteristics are analytically investigated for a single degree of freedom structure with a Maxwell element (SSME). Eigenvalues are obtained analytically and approximated by a perturbation method. Then, cases are sorted by a stiffness ratio λ: the ratio of a structural spring to an auxiliary spring. For a small λ, the optimal damping ?c provides the maximum damping ratio. For a large λ, the lower and upper critical dampings ?a and ?b provide duplex eigenvalues. These values are approximated by simple terms. To reduce transient response, λ should be large, and ? should be around ?c, ?a, and ?b, which provide the SSME with large damping. For a stationary excitation, the optimal damping ?d is introduced to produce the minimum peak deformation. In fact, ?d is larger than ?c and ?b, and provides larger stiffness and a smaller damping ratio. For a seismic excitation, some cases with ?d might reduce deformation more than those with ?c and ?b, but must support larger stress in the Maxwell element. Thus, ? should be based on design constraints.     

Measuring Vertical Profiles of Hydraulic Conductivity with In Situ Direct-Push Methods

U.S. EPA (Environmental Protection Agency) staff developed a field procedure to measure hydraulic conductivity using a direct-push system to obtain vertical profiles of hydraulic conductivity. Vertical profiles were obtained using an in situ field device—composed of a Geoprobe direct-push drive, threaded steel pipes with an open-slotted section, and a drive point at the bottom—PVC tubing, and a peristaltic pump. Simple mathematical formulas were derived for estimating hydraulic conductivity from the field measurements. The field procedure and mathematical formulas were applied in an unconfined sand aquifer. A vertical profile of hydraulic conductivity at a measurement location was plotted with the value obtained from a conventional slug test from a nearby monitoring well. The hydraulic conductivity in the middle of the aquifer was found to be an order of magnitude higher than that at the water table depth. The conductivity from the slug test at the monitoring well was half of the maximum value in the profile. The in situ direct-push method provided valuable information on site characterization in a short time, with minimal disturbance and without installing additional wells.     

Mathematical Formulation and Validation of a Mixed Finite Element–Finite Difference Model for Simulating Phreatic Surfaces

The phreatic surface in an unconfined aquifer exists as a movable interface between the saturated and unsaturated zones. The movement of the phreatic surface depends on recharge, hydraulic conductivity, porosity, and horizontal and vertical flows. The location of the phreatic surface helps define the variably saturated flow domain in the subsurface. The variably saturated flow process in the subsurface is described by a parabolic partial differential equation. In this equation, the hydraulic conductivity and soil moisture capacity are used as the subsurface characteristics. The location of the phreatic surface is governed by a first-order partial differential equation. The governing parabolic partial differential equation is solved using a variational finite element formulation. The first order phreatic surface equation is then solved by loosely coupling with the governing parabolic partial differential equation describing the variably saturated flow. In the present study, a two-dimensional space is used to investigate the movement of the phreatic surface in a variably saturated unconfined flow domain. Based on the time-varying solutions of hydraulic heads, the location of the phreatic surface is simulated in a finite two-dimensional space.     

In vivo studies of an implantable energy convertor for skeletal muscle powered cardiac assist

A device that harnesses the mechanical energy of skeletal muscle contracting in a linear configuration has been implanted in goats. This energy convertor transforms muscle work to hydraulic energy that could drive a variety of cardiac assist devices. The device is mounted with a rib clamp and plate affixed to the sternum by cortical bone screws. A transcutaneous hydraulic line carries a silicon based working fluid to an external system that controls the muscle load. In 60 to 70 kg goats, the latissimus dorsi insertion was reattached to the energy convertor. A Telectronics myostimulator with intramuscular electrodes stimulated the latissimus dorsi. In acute implants, hydraulic pressures in excess of 150 psi were obtained. Chronic implantation of the device allowed system evaluation in the conscious unanesthetized animal. Two weeks after implant, hydraulic pressures in excess of 200 psi were obtained and energy transferred to the external loading system exceeded 1 J per contraction. Six weeks after implant, the device continued to cycle freely. These initial results are very promising and suggest an implantable energy convertor is feasible. Development of an energy convertor is an important step toward tether-free skeletal muscle powered cardiac assist devices.