分散制御型多点加振による大型構造物の振動試験法の検討

A control method has been developed to always excite a multi-degree-of-freedom system efficiently at a resonance frequency. When an excitation point corresponds to a vibration detection point in the multi-degree-of-freedom system, a phase lag at a resonance frequency and a phase lead at an anti-resonance frequency alternately appear in the vibration characteristics, and the phase lag becomes 90° at all the resonance frequencies. Therefore, if a controller that has a phase lag of 90° and a constant gain in a wide frequency range is used, self-excited vibration is generated at all the resonance frequencies. The self-excited vibration mode in the multi-degree-of-freedom system with local feedback control can be freely switched by dynamic stimulation. However, it can be also disadvantage in the point of changing against the desire. In this paper, a cross feedback control is added to the local feedback control to excite and stabilize the self-excited vibration modes. The cross feedback control mutually exchanges control signal between adjacent local feedback controllers. Giving the sign of the cross feedback gain corresponding to natural vibration modes can assist formation of the self-excited vibration modes. At first, we verified all the natural vibration modes are excited by adding cross feedback control. Additionally, we verified the desired natural vibration can be maintained against a disturbance. Finally, we verified amplitude of the vibration is maintained against changing mass and dumping.

A control method has been developed to always excite a multi-degree-of-freedom system efficiently at a resonance frequency. When an excitation point corresponds to a vibration detection point in the multi-degree-of-freedom system, a phase lag at a resonance frequency and a phase lead at an anti-resonance frequency alternately appear in the vibration characteristics, and the phase lag becomes 90° at all the resonance frequencies. Therefore, if a controller that has a phase lag of 90° and a constant gain in a wide frequency range is used, self-excited vibration is generated at all the resonance frequencies. The self-excited vibration controller can be expressed as the sum of the positive velocity feedback control with a high gain in a high frequency domain and the integral control of the displacement with a high gain in a low frequency domain. A local feedback controller for each actuator consists of a self-excited vibration controller, a saturation element that limits excitation force, and a negative velocity feedback controller that provides damping. A driving at a resonance point system using many actuators with local feedback control, that is, decentralized control, is excellent in its adaptability to the environment, in its extendibility, and in its fault tolerance. In addition, the self-excited vibration mode can be freely switched on by changing the frequency of the sine wave that causes the self-excited vibration.

Step-type compound planetary gear sets are widely applied in vehicle systems. Comprehensive dynamic model of step-type compound planetary gear sets, which includes translational, rotational vibrations and static transmission errors, was established. Natural vibration characteristics of the system, such as natural frequencies and vibration modes, were analyzed. Belt shape distribution characteristics of its natural frequencies was researched. According to vibration characteristics of both central components and planets, natural vibration modes of the system are classified into three types: central components translational vibration and planets random vibration, central components rotational vibration and planets identical vibration, central components static and adjacent planets reverse vibration mode.

Parallel welded steel truss component is widely used in construction, tower, bridges, aerospace and other fields. And the welding residual stress is distributed complicatedly in many areas and directions, which will definitely deform the welded steel truss or even crack it. So, it is necessary to do aging treatment to avoid such thing happened, as well as improve the accuracy and reliability. Vibratory stress relief (VSR) is a new kind of technology which may eliminate the residual stress in metal component with high efficiency, energy-saving, environment protection and low cost compared with thermal stress relief (TSR). But its technical effects vary with the vibration parameters. To the parallel steel truss structures, the excitation parameter of VSR is determined by welding residual stress distribution and the natural mode of vibration. The residual stress concentration areas can get enough vibration, if the parallel steel truss component vibrates with different kinds of natural mode of vibration, which will obtain good effect of eliminating stress. Firstly, the inherent vibration mode of parallel welded steel truss component is measured by the modal analysis technology. Secondly, multiple intrinsic modes are chosen according to principle of making all the welding residual stress concentration regions and directions get enough vibration and then main technical parameters are determined such as excitation frequency, excitation point and support point. In this paper, two examples are given out: the specimen 1is treated with the transverse bending vibration mode and torsion vibration mode respectively according to the above method. As for specimen 2, it is treated with 3 exciting frequencies which are located automatically by the vibration aging machine. The residual stresses of the two specimens are measured before and after their vibrations with blind holes method. Results show that after vibration aging, the welding residual stress peak figure of the Specimen 1 is reduced by an average of 48.65% and the mean value of that dropped by an average of 32.50%. Correspondingly, the residual stress peak value of the Specimen 2 shows a decline of 3.38%, its average fell by an average of 2.55%.

Quadruped animals switch gait patterns with walking frequency for energy-effective walking. This is similar to the phenomenon that excited natural vibration modes are switched with vibration frequency in a MDOFs system. Therefore, in this paper, it is assumed that quadruped animals walk by using the natural vibration of their own musculoskeletal systems. In the simplest rigid-body-link model consisting of a body and four legs, there are the natural vibration modes similar to the gait patterns (trot, pace and gallop) of quadruped animals. However, all the natural frequencies in the model exist near the natural frequency in the free leg, and are accordingly different from the walking frequencies of actual quadruped animals. In the rigid-body-link model added a scapular and a pelvic on observations of quadrupted walking, the natural frequency of the gallop mode corresponding to high speed walking raises greatly and approaches the walking frequency. If the physical characteristics of horses were applied to the rigid-body-link model added the leg's joints, the natural vibration in the model is close to the gait patterns of horses.

This paper describes measurement of natural vibration of acoustic space by multi-point excitation using decentralized control. A set of acoustic excitation system consists of a speaker, a microphone, and a local feedback controller. The acoustic excitation system handles the frequency range from 100Hz to 500Hz higher than a mechanical vibration system does. So the phase lag of an actuator, the dead time by propagation of sound, and the dead time by sampling of a controller influence the local feedback control. First, the various phase lag in the acoustic excitation system are identified. The speaker has the second vibration property derived from mechanical resonance, and the first delay property derived from induced voltage of coil. The propagation of sound from the speaker to the microphone causes the dead time. Sampling time of the controller also causes the dead time from the input signal to the output signal. Second, the way to compensate these phase lag in the acoustic excitation system is proposed. Resonance of the speaker makes the phase decrease 180 degree at the resonant frequency. To suppress a change in the phase in the frequency range from 100Hz to 500Hz, the resonant frequency moves to less than 100 Hz. The phase lead and the phase lag after the resonant frequency movement are compensated by the second order phase lag-lead element. The natural vibration of one-dimensional/two-dimensional acoustic space is self-excited by the acoustic excitation system with the phase compensation. By closing the feedback loop, the first mode natural vibration is excited. By adding sinusoidal signal from outside, all natural vibration in the frequency range from 100Hz to the 500Hz is self-excited (forced entrainment).

This article studies optimization design of Vibratory stress relief (VSR) technology parameter for large welded components. The test is carried through a large welded truss. It first analysis key factor of the influence on VSR technology effect. And then by modal analysis, we’ve got the natural frequency and natural modes of the specimen , The optimization design is based on residual stress distribution and natural modes of component for VSR process parameters. Test pieces are treated by vibration. before and after vibration, residual stress of the specimens is measured by the method of blind hole.The results showed that vibration mode is a key factor in determining the effect of VSR. Stress distribution is more complex for large welded components.As accordance by selecting a few of vibration modes, for VSR main technical parameters design, it can get enough vibration displacement in the areas and directions of component with residual stress. Thus we can have a good effects to relief welding residual stress.Three major parameters (Excitation frequency, excitation point, support points) are related with vibration mode. They are decided by selecting vibration mode. Excitation force is decided based excitation frequency as well as the size of the exciter eccentric , to get the right excitation force by adjusting the size of the exciter eccentric under the condition of the selected excitation frequency.

In this study, a 3D model of a two‐step sine movable tooth drive is developed in the UG software. The finite element model (FEM) analysis package, ANSYS, is used to calculate the natural frequencies and vibration modes of the drive system. The results show that the first twenty natural frequencies can be classified into five families, including the total system vibration mode, single‐element vibration mode, two‐element vibration mode, three‐element vibration mode, and four‐element vibration mode. The effects of the system parameters on the natural frequencies and the vibration modes are investigated. The track amplitude, the movable tooth radius, the radius of the movable tooth rotation, and the number of movable teeth affect the natural frequencies and vibration modes of the drive system.

Based on the principle of axial active magnetic bearing system with single degree of freedom, the difference between magnetic system vibration mode and the traditional bearing system vibration mode were described. Initial four order natural frequencies and vibration mode were calculated by the module of modal analysis of ANSYS11. Axial displacement and control current influence on natural frequencies and vibration mode were also analyzed. At last they were compared with the results of experimental modal analysis. Analysis shows that there was a certain difference between the results of finite element method and experimental model analysis, but the difference was small. It provided theoretical basis for flexible system design and dynamic design.

A schematic description of a stand based on a digital speckle interferometer with a diffuse reference wave is given, which makes it possible to determine the natural frequencies and vibration modes of the blades in real-time. In the frequency range of 100 ... 3000 Hz, an experimental study of the vibration characteristics of a turbine rotor blade of a gas turbine engine was carried out, under free boundary conditions, which were achieved by placing the blade on soft silicone racks. Blade dimensions: height along the trailing edge - 288 mm, a chord in the middle section - 88.5 mm. 7 modes of vibrations have been identified. The technology of creating a solid-state geometric model of a rotor blade based on a faceted body obtained by 3D scanning with an accuracy of 0.01 mm is presented. The finite element method, using the Lagrange variation principle, is used to calculate the values of natural frequencies and vibration modes of a blade based on the developed geometric model. Concerning the frequency range 100 ... 3000 Hz, using the Ansys Workbench software package, a series of calculations of the resonant frequencies of the blade, by the finite element method, in the range of variation of the values of mechanical properties was carried out: Young's modulus E = 200 ... 230 GPa; Poisson's ratio μ = 0.26 ... 0.3. The density of the material: ρ = 7830 kg / m³, determined experimentally, by the method of hydrostatic weighing. The final element used in the calculation is (tetrahedron) SOLID 187; the minimum element size is 0.6 mm. The total number of elements is about 1.5 ∙ 10⁶. Based on the two-dimensional spline interpolation of the calculated data, the dependence of the standard deviation of the calculated and experimental values on the adopted mechanical properties of the material of the rotor blade is built. In the range of values E = 215 ... 217 GPa and μ = 0.295 ... 0.3, the minimum standard deviation of the calculated frequencies from their experimental values is 0.73%. Provided the value of the standard deviation of frequencies is 1%, the range of values of mechanical properties will be: E = 211 ... 220 GPa and μ = 0.26 ... 0.3. It is shown that narrowing the studied range of values of Young's modulus and Poisson's ratio does not significantly affect the results obtained.

In this paper, a micro electromagnetic harmonic drive system is proposed. Considering Van der Waals force, dynamics equation of the flexible ring for the micro drive system is deduced and resolved. Using the equations, the effects of the molecule force on the natural frequencies and vibration modes of the drive system are investigated. Results show that considering molecule force, natural frequencies of the flexible ring are reduced and its vibration modes are changed. For lower order modes, smaller clearance between the flexible ring and stator, smaller thickness of the flexible ring and larger radius of the flexible ring, the effects of the molecule force on the natural frequencies and vibration modes are more obvious.

A method for determining the location and depth of a notch has been developed on the basis of the results of a finite-element analysis of natural vibration modes of a cantilever with a notch. A phenomenological relationship is obtained that relates the degree of cantilever damage to the characteristic features of its natural vibration modes. A new diagnostic sign of the degree of cantilever damage is proposed, which is the angle between the tangents on the plot of the natural form of the fourth vibration mode. An approximate equation is deduced that describes the dependence of the angle between the tangents at the “break” point of the shape of the fourth vibration mode on the depth of a notch in the cantilever.

ACOUSTIC INSULATION PROVIDED BY A SINGLE WALL SEPARATING TWO CONTIGUOUS TUNNELS VIA BEM

Free Vibration Modes Analysis of Femur Bone Fracture Using Varying Boundary Conditions based on FEA

This paper deals with the problem of multiple crack identification for beam-like structures from a natural vibration mode. A simplified expression for natural vibration modes of a beam with an arbitrary number of cracks has been obtained explicitly in terms of the crack parameters. The obtained solution allows not only a new form of the eigenvalue problem for a multiple cracked beam to be derived, but it is also straightforward to formulate the standard inverse problem of multi crack identification from measured mode shape. The proposed procedure in combination with the well known regularization method enables both location and size of multiple cracks to be consistently identified from the sparsely and noisy measured data. The robustness of the technique that can be called the crack scanning method has been illustrated and validated by the numerical simulation results.