Damping zǔní
In electricity, it almost means response time.
In mechanical physics, the reduction of system energy damping vibration is not entirely caused by "resistance". As far as mechanical vibration is concerned, one is that the mechanical energy of the system is reduced and converted into internal energy because of the heat generated by friction resistance. This kind of damping is called friction damping. The other is that the system causes the vibration of the surrounding particles, so that the energy of the system gradually radiates to the surrounding area and becomes the energy of waves. This kind of damping is called radiation damping.
Friction needs stable time! Pointer multimeter, when the pointer is stable!
Linear viscous damping is the most commonly used damping model in mechanical systems. The magnitude of damping force R is proportional to the velocity of the moving particle, and the direction is opposite, and R=-C, where C is the viscous damping coefficient, and its value must be determined by vibration test. Because the mathematical solution of linear system is simple, other forms of damping are often converted into equivalent viscous damping in engineering according to the principle of equal energy loss in a period. The motion of the object varies with the damping coefficient of the system. For example, in a vibration system with degrees of freedom, [973-0 1] is called the critical damping coefficient. Where is the mass of the particle and k is the stiffness of the spring. The ratio of actual viscous damping coefficient c to critical damping coefficient c is called damping ratio. < 1 is called underdamping, and the object logarithmically attenuates vibration; > 1 Over-damping, the object slowly returns to the equilibrium position without vibration. Underdamping has little effect on the natural frequency of the system, but the amplitude of free vibration decays quickly. Damping can also significantly reduce the amplitude of forced vibration near the * * * vibration zone, while damping has little effect on the amplitude far away from the * * * vibration zone. The newly emerging large damping materials and squeezed oil film bearings have obvious vibration reduction effects.
In some cases, viscous damping can not fully reflect the actual situation of energy dissipation in mechanical systems. Therefore, when studying mechanical vibration, hysteresis damping, proportional damping, nonlinear damping and other models are also established.
In electricity, it almost means response time.
In mechanical physics, the reduction of system energy damping vibration is not entirely caused by "resistance". As far as mechanical vibration is concerned, one is that the mechanical energy of the system is reduced and converted into internal energy because of the heat generated by friction resistance. This kind of damping is called friction damping. The other is that the system causes the vibration of the surrounding particles, so that the energy of the system gradually radiates to the surrounding area and becomes the energy of waves. This kind of damping is called radiation damping.
Friction needs stable time! Pointer multimeter, when the pointer is stable!
Linear viscous damping is the most commonly used damping model in mechanical systems. The magnitude of damping force R is proportional to the velocity of the moving particle, and the direction is opposite, and R=-C, where C is the viscous damping coefficient, and its value must be determined by vibration test. Because the mathematical solution of linear system is simple, other forms of damping are often converted into equivalent viscous damping in engineering according to the principle of equal energy loss in a period. The motion of the object varies with the damping coefficient of the system. For example, in a vibration system with degrees of freedom, [973-0 1] is called the critical damping coefficient. Where is the mass of the particle and k is the stiffness of the spring. The ratio of actual viscous damping coefficient c to critical damping coefficient c is called damping ratio. < 1 is called underdamping, and the object logarithmically attenuates vibration; > 1 Over-damping, the object slowly returns to the equilibrium position without vibration. Underdamping has little effect on the natural frequency of the system, but the amplitude of free vibration decays quickly. Damping can also significantly reduce the amplitude of forced vibration near the * * * vibration zone, while damping has little effect on the amplitude far away from the * * * vibration zone. The newly emerging large damping materials and squeezed oil film bearings have obvious vibration reduction effects.
In some cases, viscous damping can not fully reflect the actual situation of energy dissipation in mechanical systems. Therefore, when studying mechanical vibration, hysteresis damping, proportional damping, nonlinear damping and other models are also established.
As we all know, obstacles such as friction that attenuate free vibration are called damping. The "special" components placed on the structural system can provide resistance to motion and reduce the energy of motion, which is called dampers.
Using damping to absorb energy and reduce vibration is not a new technology. In aerospace, aviation, military industry, guns, automobiles and other industries, various dampers (or shock absorbers) have been used to reduce vibration and dissipate energy. Since 1970s, people have gradually applied these technologies to buildings, bridges, railways and other structural projects, which have developed very rapidly. In particular, the hydraulic viscous damper with a history of more than 50 years experienced a long process of a large number of experiments, strict examination and repeated argumentation, especially earthquake tests, before it was accepted by the American structural engineering community. The following process 1 summarizes it.
The development of the United States:
Widely used in aerospace, aviation, military industry, machinery and other industries, has been successfully applied for decades.
Since 1980s, he has done a lot of experimental research in two earthquake research centers in the United States and published dozens of related papers.
In the 1990s, the National Science Foundation and the Civil Engineering Society of the United States organized two large-scale joint comparative experiments made by a third party, and gave authoritative test reports for the reference of professors and engineers.
On the basis of affirming the above achievements, the application method has been affirmed and stipulated after the review of almost all relevant institutions and norms.
The approval of the management department has brought hundreds of practical applications of structural engineering. These structural projects have successfully withstood the test of earthquakes, strong winds and other disasters and are very successful.
Shock absorption and damper of engineering structure
In the twentieth century, especially in the last two or three decades, people have made great efforts to improve the anti-vibration ability of buildings and achieved remarkable results. The most proud of this achievement is the "structural protection system". People jumped out of the traditional concept of strengthening the anti-vibration ability of beams, columns and walls, and combined with the dynamic performance of the structure, skillfully avoided or reduced the damage of earthquakes and winds. Base isolation, various energy absorption systems using dampers, mass vibration reduction system (TMD) and active control vibration reduction system of high-rise building roofs have all gone to engineering practice. Some have become indispensable protective measures to reduce vibration. Especially for unpredictable earthquakes and multidimensional vibration with unknown failure mechanism, the protection system of these structures becomes more important.
Among these structural protection systems, the least controversial and beneficial thing is to use dampers to absorb this unpredictable seismic energy. Using damping to absorb energy and reduce vibration is not a new technology. In aerospace, military, gun, automobile and other industries, various dampers have been used to reduce vibration and energy dissipation. Since 1970s, people have gradually transferred these technologies to buildings, bridges, railways and other projects, which have developed very rapidly. By the end of the 20th century, nearly 65,438+000 structural projects around the world had used dampers to absorb energy and reduce vibration. By 2003, Taylor alone had installed 1 10 buildings, bridges or other structures all over the world.
Taylor Taylor Company started from 1955 and has undergone a lot of long-term inspections in aerospace and military industries. In the first experiment, this technology was applied to structural engineering. A large number of shaking table model experiments and computer analysis were done in the American Earthquake Research Center, and dozens of related papers were published. The key of structural damper is its durability and stability under the change of time and temperature. Taylor damper has been tested for a long time and compared with other companies' products. The corresponding design codes in the United States are all based on Taylor damper products. Its products have advanced technology, reasonable and reliable structure and high technical transparency, and can be used to manufacture dampers suitable for various purposes according to the requirements of designers. Every product has passed the most rigorous test before leaving the factory, and the hysteresis curve is given. Taylor Taylor Company has accumulated a lot of practical experience from the practical application of more than 32 global 130 projects and bridges.
Classification of dampers:
Damper: used to reduce vibration;
Buffer: used for shock prevention, allowing low-speed movement, locking when the speed or acceleration exceeds the corresponding value, forming a rigid support.
The damper is just a component. When used in different places or different working environments, it has different shock absorption effects. Buffer: used for shock prevention, allowing low-speed movement, locking when the speed or acceleration exceeds the corresponding value, forming a rigid support.
At present, there are various applications: spring damper, hydraulic damper, pulse damper, rotary damper, wind damper, viscous damper and so on.
[Edit this paragraph] The principle and preliminary experimental study of controllable passive electromagnetic damper.
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The vibration problem of high-speed rotating machinery is a prominent and difficult problem. The speed of this machine is very high, and it runs at the critical speed or even above several critical speeds. Therefore, in order to ensure its safe operation, in addition to ensuring careful design and accurate manufacturing and installation, dampers are usually used to reduce vibration. Squeezed oil film damper and electromagnetic damper 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
Fig. 1 is a schematic diagram of the controllable passive electromagnetic damper. It has no displacement sensor. Its structure is similar to that of squeeze film damper: the rotor (1) of rotating machinery is supported on the iron core (3) through rolling bearing (2) or sliding bearing. The iron core is supported on the machine base (5) by a spring (4). The supporting stiffness of the spring can be designed according to the use requirements, which is the main stiffness of the supporting system. Four electromagnets (6) are concentrically placed around the iron core on the machine base. The same DC excitation voltage is applied to each electromagnetic coil.
Fig. 2 shows that the additional stiffness and damping produced by the controllable passive electromagnetic damper vary with frequency. It can be seen that the value of additional stiffness is negative in the whole frequency range, and the negative stiffness decreases with the increase of frequency. The stiffness value is almost zero in high frequency region. This damping characteristic is just in line with the characteristics of high damping at low frequency and low damping at high frequency required by rotating machinery. After the size of the controllable passive electromagnetic damper is determined, the stiffness and damping value only depend on the static excitation current or excitation voltage. The stiffness and damping can be changed by changing the excitation voltage, so the damper is controllable.
Experimental device
Fig. 3a shows the experimental device: an elongated shaft, one end of which is supported on a common rigid ball bearing, and the other end of which is supported on the electromagnetic damper bracket shown in fig. 1. The rotor is driven by a DC motor. The vibration and rotation speed of the shaft are detected by eddy current sensor and photoelectric sensor respectively. Vibration signal and rotational speed signal are collected by computer through AD board. Fig. 3b is a flat radial spring providing rigidity of the main support. The spring is made of elastic aluminum and is machined by wire cutting. The stiffness value is calculated and optimized by finite element method. There are two springs placed side by side on the support of electromagnetic damper to ensure symmetry and facilitate system modeling. Theoretical calculation and experimental test show that the first critical speed of the rotor is about 3900 rpm.
Empirical test
Under different excitation voltages, the variation of rotor vibration with speed was tested. Figure 4 shows the experimental data. The four curves in the figure represent the excitation voltages of 0 V, 9 V, 12 V and 15 V respectively. It can be seen that with the increase of excitation voltage, the damping provided by electromagnetic damper also increases. This reduces the amplitude of the rotor from 0. 185mm to 0.56mm, and the vibration reduction effect is obvious. It can also be seen from the figure that the critical speed of the rotor decreases due to the existence of negative electromagnetic stiffness. This is very consistent with the results in Figure 2. Near the critical speed of 65HZ, the additional negative electromagnetic stiffness is very small, so the influence on the critical speed is very small. When the excitation voltage is15v, the critical speed of the rotor only drops to 3780 rpm.
conclusion
Passive electromagnetic damper has achieved good vibration reduction effect in rotor system. The damping mechanism of this damper is passive, and the damping can be controlled by the excitation voltage. Compared with squeeze film damper, passive electromagnetic damper has the biggest advantage that electromagnetic bearing is superior to ordinary bearing. Compared with active electromagnetic damper, passive electromagnetic damper has the advantages of simple overall structure, low cost and high reliability. Therefore, it is a promising and effective high-speed rotor vibration reduction device.
This paper introduces the principle of passive electromagnetic damper in linear range, and only carries out the preliminary vibration reduction experiment of passive electromagnetic damper. More research and optimization design of nonlinear characteristics will be reported later.