The use of damping to absorb vibration is not a new technology, in the aerospace, aviation, military, firearms, automotive and other industries have long been the application of a variety of dampers (or shock absorbers) to reduce vibration and dissipate energy. From the 1970s, people began to gradually transfer these technologies to buildings, bridges, railroads and other structural engineering, its development is very rapid. In particular, hydraulic viscous dampers, which have a history of more than 50 years, have been accepted by the structural engineering community in the U.S. Before, it has experienced a large number of experiments, rigorous review, repeated demonstration, especially the long process of seismic testing.
-Widely used in aerospace, aviation, military, machinery and other industries, decades of successful application of the history
-Started in the 1980s in the U.S. East and West of the two seismic research centers and other units to make a lot of experimental research, published dozens of related papers
In the 1990s, the National Science Foundation and the Institute of Civil Engineering and other units organized two large-scale joint, by a third party to make the comparative test, gave an authoritative test report for professors and engineers to refer to
- In the affirmation of the above results on the basis of almost all the relevant agencies, norms review, affirmation and provide for the application of the approach
- Management through, brought hundreds of structural engineering practical application of the test report. Hundreds of structural projects have been realized. These structural projects have successfully survived earthquakes, high winds, and other disasters.
Engineering structural damping and dampers
The twentieth century, especially in the last two or three decades people have made great efforts to improve the ability of buildings to resist vibration, and has achieved remarkable results. The most proud of this achievement is the "structural protection system". People have gone beyond the traditional concept of strengthening beams, columns, and walls to improve vibration resistance, and have skillfully avoided or minimized damage from earthquakes and wind by combining them with the dynamic properties of the structure. Base isolation (Base Isolation), the use of various dampers (Damper) energy absorption, energy consumption system, high-rise buildings on the roof of the mass *** vibration damping system (TMD) and active control (Active Control) vibration damping system are already towards the engineering practice. Some have become indispensable protection measures to reduce vibration. Especially for the unpredictable earthquake, the destruction mechanism is not very clear multi-dimensional vibration, these structures to protect the system becomes more important.
These structural protection systems in the least controversial, beneficial and harmless system to be the use of dampers to absorb the unpredictable seismic energy. The use of damping to absorb seismic energy is not a new technology, in aerospace, military, firearms, automotive and other industries have long been applied to a variety of dampers to reduce vibration and dissipate energy. From the seventies of the twentieth century, people began to gradually transfer these technologies to construction, bridges, railroads and other projects, its development is very rapid. By the end of the twentieth century, nearly 100 structural projects around the world have used dampers to absorb energy and reduce vibration. By 2003, Taylor alone had installed 110 buildings, bridges, and other structural structures worldwide.
Taylor Taylor company from 1955 after a long period of a large number of aerospace, military industry test, the first experiments will be the application of this technology to the structure of the project, in the U.S. Earthquake Research Center for a large number of shaker model experiments, computer analysis, published dozens of papers on the subject. Structural damper is the key to durability, time and temperature changes under the stability of the Taylor company's damper after a long period of testing and a variety of comparative analysis, the products of other companies is difficult to look forward to its back. The development of the corresponding design specifications in the United States are based on Taylor's damper products. Its products are technologically advanced, constructed reasonably and reliably, with a high degree of technical transparency, and can be manufactured according to the designer's requirements for a variety of uses. Each product undergoes the most rigorous testing before leaving the factory and is given a hysteresis curve. Taylor Taylor company from the world's more than 130 projects, 32 bridges in the actual application, has accumulated a lot of practical experience.
Classification of dampers:
Damper: used for vibration damping;
Snubber: used for vibration isolation, allowing movement at low speeds, and locking at speeds or accelerations exceeding the corresponding values, forming a rigid support.
The damper is just a building block. Damper: used for vibration damping; Snubber: used for shockproof, low-speed allows movement, in the speed or acceleration exceeds the corresponding value of locking, the formation of rigid support.
At present, there are a variety of applications: spring dampers, hydraulic dampers, impulse dampers, rotary dampers, wind dampers, viscous dampers, etc.
[Editorial] Principle of Controlled Passive Electromagnetic Dampers and Preliminary Experimental Research
Introduction
The vibration of high-speed rotating machines is a relatively prominent and difficult to solve the problem. These machines have high rotational speeds and operate above the critical speed or even several orders of critical speed. Therefore, in order to ensure their safe operation, in addition to ensuring careful design and precise manufacturing and installation, usually also use dampers to reduce vibration. Extruded oil film dampers and electromagnetic dampers are two commonly used dampers. In this paper, a new controllable passive electromagnetic damper is designed.
Structure and working principle of controllable passive electromagnetic damper
Figure 1 shows the schematic diagram of controllable passive electromagnetic damper. It has no displacement sensor. Its structure is similar to the extruded oil film damper: the rotor (1) of the rotating machine is supported on an iron core (3) through rolling bearings (2) or plain bearings. The core is then supported by a spring (4) in the machine base (5). The support stiffness of the spring can be designed according to the requirements of use, for the main stiffness of the support system. Four electromagnets (6) are placed concentrically around the core on the base. Each magnet coil on the role of the same size of DC excitation voltage.
Figure 2 illustrates the additional stiffness and damping produced by the controlled passive electromagnetic damper as a function of frequency. It can be seen that the value of the additional stiffness is negative over the entire frequency range and the negative stiffness value decreases as the frequency increases. In the high frequency region the stiffness value is almost zero. This damping characteristics are just in line with the requirements of rotating machinery, low-frequency large damping high-frequency small damping characteristics. After the size of the controlled passive electromagnetic damper is determined, the stiffness and damping values depend only on the static excitation current or excitation voltage. Changing the value of the excitation voltage can change the stiffness and damping, and thus this damper is controllable.
Experimental setup
Figure 3a shows the experimental setup: a slender shaft, supported on a common rigid ball bearing at one end and on the electromagnetic damper support shown in Figure 1 at the other end. The rotor is driven by a DC motor. The vibration and rotational speed of the shaft are detected by eddy current sensors and photoelectric sensors, respectively. The vibration and rotational speed signals are acquired by a computer through an AD board. Fig. 3b shows the flat plate radial spring that provides the stiffness of the main support. The spring is made of elastic aluminum and is machined by wire cutting. Its stiffness value is calculated and optimized by finite elements. There are two springs placed side by side on one electromagnetic damper support to ensure symmetry and facilitate system modeling. Theoretical calculations and experimental tests show that the first order critical speed of this rotor is about 3900revs/min.
Experimental
The variation of rotor vibration with rotational speed is tested at different excitation voltages. The experimental data is given in Fig. 4. The four curves in the figure represent the case where the excitation voltage is 0 volts, 9 volts, 12 volts and 15 volts respectively. It can be seen that as the excitation voltage increases, the damping provided by the electromagnetic damper increases. This results in suppression of rotor amplitude from 0.185 mm to 0.56 mm and the damping effect is significant. It can also be seen from the figure that the critical speed of the rotor is reduced due to the presence of negative electromagnetic stiffness. This agrees well with the results in Fig. 2, where the additional negative electromagnetic stiffness is very small near the critical speed of 65 HZ and thus it has little effect on the critical speed. At an excitation voltage of 15 volts, the critical speed of the rotor only decreases to 3780revs/min.
Conclusion
The passive electromagnetic damper used in the rotor system achieves good vibration damping results. The damping mechanism of this damper is passive and the magnitude of damping is controllable with the magnitude of the excitation voltage. Compared with the extruded oil film damper, the passive electromagnetic damper has most of the advantages of electromagnetic bearings over ordinary bearings; compared with the active electromagnetic damper, the overall structure of the passive electromagnetic damper is simple, low cost and higher reliability. Therefore, this is a very promising and effective vibration damping device for high-speed rotors.
This paper introduces the principle of the passive electromagnetic damper in the linear range and only carries out the preliminary vibration damping experiments of the passive electromagnetic damper, more non-linear characteristics of the research and optimization of the design will be reported in the future.