Dynamic analysis of piezoceramic actuation effects on plate vibrations

This paper presents a simulation model for the active vibration control of a rectangular plate using piezoceramic elements of arbitrary shape. Experiments using multiple PZT patches were carried out to validate the model. An analysis was then undertaken to determine the dynamic effect of the piezoactuators. Numerical results showed that piezoactuators enhance the modal coupling of the structure under certain circumstances. Special attention should be paid to higher-order modes in both simulation and the development of active control strategies. Actuators of different shapes have been tested to show their influence on the dynamic behaviour of the structure. It was noted that actuators shapes affect the structure more in off-resonance regions than near resonance. This effect however remains weak as long as the actuators possess the same area and do not possess significantly different width to length dimensions.     

Experimental researches on sliding mode active vibration control of flexible piezoelectric cantilever plate integrated gyroscope

The flexible appendages of spacecrafts in aerospace applications demand to be lighter and larger. Thus, they are susceptible to excessive vibration response due to external disturbances or attitude maneuvering. Some of the flexible appendages are cantilever plate structures, such as solar panels and plate shape antennas. Usually, the coupled bending and torsional vibration of cantilever plate will be caused. To decouple the bending and torsional vibration for measuring and driving, gyroscope and PZT patches are used as sensors and actuators by utilizing optimal placement. The motion of equation of the presented piezoelectric plate system is derived. And a kind of discrete-time sliding mode variable structure control (VSC) algorithm is proposed to suppress vibration of the flexible plate. The experimental comparison studies are conducted. The experiments demonstrate that the proposed methods can suppress vibration significantly for cantilever plate.     

Robust control of plate vibration via active constrained layer damping

In this paper, the theoretical modeling of a plate partially treated with active constrained layer damping (ACLD) treatments and its vibration control in an H_∞ approach is discussed. Vibration of the flat plate is controlled with patches of ACLD treatments, each consisting of a viscoelastic damping layer which is sandwiched between the piezo-electric constrained layer and the host plate. The piezo-electric constrained layer acts as an actuator to actively control the shear deformation of the viscoelastic damping layer according to the vibration response of the plate excited by external disturbances. In the first part of this paper, the Mindlin–Reissner plate theory is adopted to express the shear deformation characteristics of the viscoelastic damping layer, meanwhile GHM (Golla–Hughes–McTavish) model of viscoelastic damping material and FEM (finite element model) are incorporated to describe the dynamics of the plate partially treated with ACLD treatment. In the second part, particular emphasis is placed on the vibration control of the first four modes of the treated plate using H_∞ robust control method. For this purpose, an H_∞ robust controller is designed to accommodate uncertainties of the ACLD parameters, particularly those of the viscoelastic damping core which arise from the variation of the operation temperature and frequency. Disturbances and measurement noise are rejected in the closed loop by H_∞ robust controller. In the experimental validation, external disturbances of different types are employed to excite the treated plate. The results of the experimental clearly demonstrate that the proposed modeling method is correct and the ACLD treatments are very effective in fast damping out the structural vibration as compared to the conventional passive constrained layer damping (PCLD).     

Free linear vibration and buckling of super-elliptical plates resting on symmetrically distributed point-supports on the diagonals

This computational study reports the free vibration frequencies (corresponding to the first three symmetrical and antisymmetrical modes), and the minimum buckling load (in case of in-plane uniform pressure along the periphery) of point-supported super-elliptical plates of uniform thickness. The plate perimeter was defined by a super-elliptic function with a power corresponding to the shape ranging from an ellipse to a rectangle. The analysis was based on the classical theory of thin plates and the computations were carried out by the Ritz method. The geometrical boundary conditions were satisfied by the Lagrange multipliers. The results were compared with those of rectangular plates and good agreement was obtained.     

Model-based design and experimental validation of active vibration control for a stress ribbon bridge using pneumatic muscle actuators

This paper describes the development of an active vibration control system for a light and flexible stress ribbon footbridge. The 13 m span carbon fiber reinforced plastic (CFRP) stress ribbon bridge was built in the laboratory of the Department of Civil and Structural Engineering, Berlin Institute of Technology. Its lightness and flexibility result in high vibration sensitivity. To reduce pedestrian-induced vibrations, very light pneumatic muscle actuators are placed at handrail level, introducing control forces. First, a reduced discretized analytical model is derived for the stress ribbon bridge. To verify the analytical prediction, experiments without feedback control are conducted. Based on this model, a delayed velocity feedback control strategy is designed. To handle the nonlinearities of the muscle actuator, a subsidiary force control is implemented. Then the control performance from numerical simulation is verified by experiments under free vibration. As a result, analytical analyses agree well with experimental results. It is demonstrated that handrail-introduced forces can efficiently control the first mode response.     

Experimental and numerical study on reinforcement effect of plate anchors or flip anchors on model slopes

Flip anchors are a kind of ground anchor that rotate and open in the ground to attain pull-out resistance without the use of grout. Compared to ordinary grouted ground anchors, flip anchors can be driven into the existing ground quickly and are suitable for the emergency reinforcement of slopes. However, little research has been done on the slope reinforcement effect of flip anchors. In this paper, experiments on a model slope reinforced by plate anchors or flip anchors were conducted. During the experiments, vertical loading with a rigid loading plate was applied to the shoulder of the model slope to investigate its stability. Experiments were firstly conducted with and without model plate anchors under a plane strain condition. Then, experiments were conducted using actual flip anchors under a three-dimensional condition. In these experiments, the depth of the anchor plates, h, and the installation state of the anchor heads of the flip anchors (open or closed anchor head condition) were varied. After the experiments, corresponding numerical simulations (FEM) were conducted, and a subloading t_ij model was applied to describe the soil behaviour. The numerical method used in this research successfully reproduced the reinforcing effect of the flip anchors. According to the test and calculated results, compared with the cases without reinforcement and with plate anchors, the effectiveness of the flip anchors for slope stability was verified. Moreover, the flip anchors installed under the closed anchor head condition required a larger displacement to produce a reinforcing effect than the anchors installed under the open anchor head condition.     

Simulation and analysis on control effectiveness of TRVs in district heating systems

Based upon an existing building and heating system with thermostatic radiator valves (TRVs), an integrated model is developed for simulating the thermal and hydraulic behavior of the heating system under various operation cases. According to the simulation results, the effectiveness of TRVs in reducing overheating has been studied. The results indicate that when the set value of the TRV is kept at 2-3, its effectiveness in reducing the overheating phenomena caused by an excessive water flow rate is less than 60%. If the overheating phenomena is caused by an excessive supply water temperature and radiator area, the effectiveness of the TRV can reach about 80%; the TRV's effect becomes more obvious with increasing overheating degree; however, about 20%-40% of overheating loss still needs to be resolved by improving improper operation adjustment and design. Considering these results, a control strategy is proposed, in which the supply water temperature is adjusted daily according to the flow performance of the system, and the pump is operated with frequency conversion and constant pressure difference. Further simulation indicates that, under the new control strategy, the variation of the heat supply quantity of the system can match the heat load change, and the flow rate of the system can be controlled at an appropriate range.     

Vibration of a standing plate with simply supported vertical sides and weakened by a horizontal hinge

A rectangular standing plate under self weight has simply supported vertical sides and weakened by a horizontal internal hinge. Using Levy separation, the governing equations reduce to an ordinary differential equation with non-constant coefficients. The difficult boundary value problem is then turned into two deterministic initial value problems. Fundamental frequencies for four kinds of common edge conditions are determined. It is found that the hinge, similar to self weight, decreases the frequency, and in certain cases promotes buckling.     

Modeling and control of power flow in a double-beam system

The vibrational power flow in a double-beam system is investigated theoretically and experimentally in this paper. A novel large displacement piezoelectric actuator assembly, comprising two curved THUNDER actuators, is used to connect the two beams and provide both passive and active isolation at the same time. A simulation model is proposed to describe the coupled mechanical and electrical properties of the new actuator assembly. Modal expansion approach is used to study the power transmissions between the two beams which are mechanically and electrically coupled via the actuator mounts. The effectiveness of both active and passive isolation has been investigated. The optimal control voltage for each actuator is obtained by minimizing the time-averaged power transmitted into the receiver beam. Results show a significant reduction in vibration power transmission. A correlation between the control effort and the mode shapes to be controlled is shown to exist.     

Influence of geometry and material properties on the axial vibration of a rock bolt

A continuous dynamic model for the axial vibration of a rock bolt system is presented. The model comprises three sections: the fixed length, bonded into the rock, the free length, which is not coupled to the rock, and the protruding length, which extends beyond the rock. The head assembly is modelled as a discrete mass and a spring, and a further discrete mass is included, representing a testing device that can be attached to the protruding end. Each section is modelled as a continuous elastic rod governed by the wave equation, with suitable compatibility conditions applied between the sections and boundary conditions, which also account for the effect of the discrete components, applied at the ends. Solutions in non-dimensional form are substituted into the boundary conditions to allow the natural frequencies to be calculated, and it is shown that two possible solutions for the mode shapes can be used for the fixed length—an exponential solution or the classical sinusoidal solution—depending on the stiffness of the grout relative to that of the bar. The conditions for which the two solutions are valid are developed, and changes in the frequency ratio with changes in length ratio, and the stiffness ratios of the grout and the anchor head relative to the stiffness of the fixed length of the anchorage are examined. Generally, the state of a bolt after installation is unknown and this does not provide proper assurance of the safety of the structure for which the bolts are used. The model provides a viable tool for helping to assess the condition of the bolt by using the natural frequencies associated with areas of the bolt of particular interest, e.g. the free length. The results show how the changes in the stiffness and/or length ratios affect the dynamics associated with fixed length of the bolt and the quality of the bonding installation. A case study is presented showing how the model can be used effectively to interpret real data.     

层合板壳振动控制LQR方法的理论推导

从层合板壳弹性力学基本方程出发,考虑各种因素影响,导出统一形式的振动方程,利用LQR最优控制理论,根据能量原理确定了Q,R,求出符合条件的最优控制集中力,等效分布荷载的表达式及位移衰减函数。     

新型板式全热交换器研制--产品研制及实验

讨论了国内外评价全热交换器性能的主要指标,介绍了一种新型全热交换器的基本结构、主要特点以及实验结果。结果表明,由于采用了纳米气体分离复合膜作为热质交换材料,该全热交换器具有以下特点：a）全热交换效率高达75％以上,高于其他形式的同类产品;b）取消了传统的波纹瓦楞纸支撑结构,空气阻力大幅度下降;c）在较高的迎面风速下,仍然有较高的换热效率;d）热质交换材料的孔径只有2nm,细菌、病毒和气体均无法通过,实现了零泄漏;e）由于采用了板式换热器的可拆卸结构,加上材料良好的疏水性,因此芯体可以拆卸,大大延长了换热器寿命。     

An internal assessment of the thermal comfort and daylighting conditions of a naturally ventilated building with an active glazed facade in a temperate climate

An active facade is often used to promote the flow of air through a building, however in order to ensure that this process is effective the facade should face a southerly orientation. This means that not only solar energy is transferred across the glazing but in sunny periods shading is needed to prevent excess brightness levels occurring on the working areas where it may result in the luminance distributions not complying with current lighting requirements. The building investigated is located in Sheffield, England and is one of the University of Sheffield's recently built green buildings. It has a high thermal mass which is used to promote the use of night cooling. This paper reports the initial findings of an internal assessment of the thermal comfort and daylighting conditions in such a building. The results have indicated that such designs are to be commended for their passive use of solar energy and can provide a high quality working environment.     

Experimental and numerical study on vibration control effects of a compound mass damper

A compound mass damper (CMD) was put forwarded based on the joint vibration control effects of tuned liquid damper and colliding particles. A series of shaking table tests were designed in order to investigate the dynamic response of a single degree of freedom bent frame structure with or without the damper (CMD, tuned mass damper, and tuned liquid damper) under three different kinds of earthquake waves. It is shown that the vibration reduction performance of CMD is generally better than the traditional dampers no matter from peak response attenuation rate or root mean square response attenuation rate. The vibration reduction effect of traditional dampers is susceptible to the characteristics of earthquake waves, whereas CMD is effective in a broader frequency bands. Also, the vibration reduction effect of CMD is not sensitive to the amplitude of earthquake waves, which means the system has good robustness. In addition, CMD has the advantage of fast start‐up. The numerical simulation results of the CMD are obtained through certain simplifications, and are in good agreement with the experimental results, which further verifies the damping effect of the proposed damper and provides a simplified method for its engineering design.     

Study on a discrete-time dynamic control model to enhance nitrogen removal with fluctuation of influent in oxidation ditches

The aim of study was proposed a new control model feasible on-line implemented by Programmable Logic Controller (PLC) to enhance nitrogen removal against the fluctuation of influent in Carrousel oxidation ditch. The discrete-time control model was established by confirmation model of operational conditions based on a expert access, which was obtained by a simulation using Activated Sludge Model 2-D (ASM2-D) and Computation Fluid Dynamics (CFD), and discrete-time control model to switch between different operational stages. A full-scale example is provided to demonstrate the feasibility of the proposed operation and the procedure of the control design. The effluent quality was substantially improved, to the extent that it met the new wastewater discharge standards of NH₃-N < 5 mg/L and TN < 15 mg/L enacted in China throughout a one-day period with fluctuation of influent.     

钢框架结构软钢阻尼器振动控制的试验及理论研究

本文通过试验研究和理论分析探讨极低屈服点软钢阻尼器的减震效果。对建造在野外的三层钢框架结构输入该结构在历年地震观测中采集到的地震波记录进行了拟动力试验。本次拟动力试验选用了4条地震波记录,各分为有阻尼器和无阻尼器的两种情况共计进行了8次试验。试验结果表明软钢阻尼器具有明显的减震效果。并采用能够同时考虑应变硬化和刚度退化现象的SkeletonShift模型模拟阻尼器的恢复力特性,对该结构进行了弹塑性地震反应分析。地震观测、拟动力试验以及计算机分析结果所表现出的各地震反应具有较好的一致性,说明拟动力试验技术应用于模拟结构的地震反应,可得到令人满意的结果。     

Shaking table test and numerical simulation on vibration control effects of TMD with different mass ratios on a super high‐rise structure

In this paper, the influence of mass ratio on the vibration control effects of tuned mass damper (TMD) on a super high‐rise building has been investigated. A 1/45 scaled model of a super high‐rise building was constructed, and the TMD with the mass ratio of 0.01, 0.02, and 0.03, respectively, was suspended on the top. Shaking table test and the corresponding numerical simulation were carried out to make a further understanding of the damping mechanism. The structural performance with or without TMD was comparatively studied. The results show that larger mass ratio can improve the control effects under frequent earthquake, but the control effects increase little with the increase of mass ratio under rare earthquake due to structural damages, accompanied by stiffness degradation and nonlinear behavior of the main structure. In addition, some suggestions on the mass ratio selection are also proposed to generalize its applications.     

新型CFRP棒-钢组合构件的强度特性数值分析

空间结构正在向着超大跨度发展,结构自重是限制其实现这种跨越能力的重要原因。碳纤维复合材料(CFRP)具有轻质高强的特点,为这一问题的解决提供了有效的途径。提出了一种新型CFRP棒-钢组合构件作为构成大跨度空间结构的基本单元,发挥CFRP材料轻质高强的特点,同时解决在构成大跨度空间结构时CFRP构件间的连接问题。首先,给出了CFRP棒-钢组合构件的结构形式,分析其可行性;其次,给出了分析模型的关键参数,以Hashin理论为基础,利用ABAQUS中用户材料子程序UMAT,开发了适用于实体单元、具有脆性破坏准则的复合材料本构模型子程序;最后,分析了6种不同长度组合构件的受压强度特性,结果表明,CFRP棒-钢组合构件具有很好的承载能力,但是其极限承载力具有一定的离散性,需要更进一步通过具体模型试验,结合数值分析的结果给出其设计方法。     

Experimental study on the seismic behavior of a shear wall with concrete‐filled steel tubular frames and a corrugated steel plate

Shear walls and core tubes in shear walls constitute the core anti‐earthquake vertical systems of high‐rise buildings. This paper proposes a new type of composite shear wall with concrete‐filled steel tubular frames and corrugated steel plates. The seismic behavior of the new shear wall is studied using a cyclic loading test and damage analysis. The failure mode, load‐carrying capacity, ductility, stiffness degradation, hysteresis behavior, and energy dissipating capacity exhibited in the test are studied. The test results show that when the proposed wall is broken, the tension side of concrete‐filled steel tubes is torn. The concrete at the bottom of the wall is detached and peels off along the through cracks. The energy dissipation capacity of concrete walls is more fully utilized. The proposed wall exhibits excellent deformability, energy dissipation capacity, and the stiffness degradation was slower than that of other walls. The use of corrugated steel plate significantly improved the seismic performance while simultaneously increasing the ductility and reducing the damage. In addition, this paper modified the energy dissipation factor in the Park & Ang model based on the situation of the specimen and experiment. It can be used to evaluate the damage degree of this new type of shear wall.