CN112526596A - Perfect seismic wave absorption device - Google Patents

Abstract

Earthquakes are one of the most damaging natural disasters to humans and building facilities. The existing anti-seismic method has limited effect on 8-level earthquake. In the invention, a small-volume local resonance structure device is provided, which faces seismic waves in an arrangement mode of a plurality of columns of parallel underground vertical wells, the front-row vertical wells are shorter, the rear-row vertical wells are gradually longer, and the length of the rearmost columns reaches the size of the wavelength of the seismic waves. Such an array would block and fully absorb an 8-level seismic event.

Description

Perfect seismic wave absorption device

Technical Field

The present disclosure relates to subterranean devices that block and absorb seismic waves.

Technical Field

Earthquakes are one of the most damaging natural disasters to humans and building facilities. Over the past few decades, there have been many studies that have proposed various methods to mitigate the damage of earthquakes to building facilities, but the effect has been limited for 8-level earthquakes, and until recently some methods have been proposed to attenuate the seismic waves before they reach the building. Modern buildings can resist 7-grade earthquakes, so 8-grade and above earthquakes need to be additionally provided with earthquake-proof protection measures. Most of the earthquake's frequency spectrum is concentrated in a certain range, the higher the magnitude, the lower the frequency. The 8-level seismic frequency is about 1Hz, and the shock absorption of the seismic frequency is extremely difficult. The most destructive of seismic waves in a region sufficiently far from the epicenter is the Rayleigh waves, while the longitudinal and transverse waves are significantly less destructive due to geometric attenuation. The huge disasters caused by two major earthquakes in 2016 indicate that the human beings have long paths to walk against the earthquakes, and great breakthroughs in technology are urgently needed.

Phononic crystals and locally resonant metamaterials provide one viable option. Periodically distributed and injected into underground hollow circular pipe or concrete filled square steel pipe to form phononic crystal, and can block seismic wave in specific frequency band according to Bragg scattering principlePhys. Rev. B59 (19): 12169 (1999)]. These feasibility studies, which verify the barrier of seismic waves with phononic crystals at a theoretical level, reveal three requirements for seismic damping of 8 th order. The first is that the period of the phononic crystal should be comparable to the seismic wave wavelength, and the period of the phononic crystal against 8-level earthquakes in soft formations should be on the order of 100 meters. The second is that the attenuation of the seismic by the phononic crystal is highly dependent on the perfect distribution of the crystal. A large scale, highly uniform formation of at least several hundred meters in size is required for the phononic crystal, and any irregular and uneven soil and rock distribution can significantly reduce the seismic isolation performance of the phononic crystal. Similarly, changes in soil moisture caused by sunlight exposure or rain wetting can affect the wave velocity of seismic waves in the formation and the stop band frequency of phononic crystals. The third condition is that each cell making up the phononic crystal needs to be of sufficient size and weight to achieve the required intensity for scattering seismic waves. Because of these limitations, while a phononic crystal may be a method of low frequency seismic damping, or other vibration source damping, it is not a viable method of 8-level seismic damping.

Local resonance acoustic metamaterial composed of mass oscillator, film and base [ invention-1, US 8,960,365]Another method is provided. By taking the essence of the material, each independent local resonance structural unit in the local resonance acoustic metamaterial independently plays a role and is not influenced by other units. The overall function of the metamaterial array is the sum of the functions of all the individual building blocks, without having to rely on precise distribution to form bragg scattering. The geometric dimensions and dimensions of the absorber are such that the mutual interference of the scattered seismic waves is no longer the main cause of the attenuation of the seismic wavesThe seismic wave wavelength is irrelevant and can be greatly reduced. The resonant frequency of a local resonant structure is the core parameter that determines the frequency of the attenuated seismic waves. The array formed by the local resonance structure similar to the cladding sphere seems to have good and even perfect shock absorption effect on seismic wavesExtreme Mechanics Letters8: 30–37 (2016)]But in practice the seismic isolation effect of the array is greatly overestimated because the researchers neglect the dissipation of the local resonance structure. The direct result is that small perturbations at the resonant frequency will amplify the displacement of the transducer by a factor of several hundred. Since the base of each local resonance structure is tightly fixed in the ground, the displacement of 10 cm on the ground caused by 8-level earthquake can enlarge the displacement amplitude of the vibrator of the local resonance structure to dozens of meters, which cannot be realized by any current design. In addition, all proposed individual structures are of the scale of several meters to several tens of meters, and the individual structures weigh several to several tens of tons. When seismic waves come, the first few seconds of vibration may cause these large structures to detach from the surrounding mud layer, or even topple over, and fail, rendering the barrier unable to block subsequent seismic waves.

Until now, all seismic wave blocking researches based on the local resonance structure still stay at the qualitative and conceptual verification level, and the influence of actual dissipation is not considered. To go further up, rigorous, quantitative studies must be performed based on actual material parameters. Since most modern buildings are resistant to class 7 earthquakes, there is a practical need for barriers that can attenuate class 8 earthquakes to class 7 or below. For this purpose, our inventive subsurface seismic wave barrier must have 4 conditions: (1) the barrier should have a decay frequency range centered around 1Hz, ranging from about 0.5Hz to about 2 Hz. (2) The vibrator of the local resonance structure still has enough vibration space when the ground surface is displaced by 10 cm. (3) The barrier should have sufficient structural strength and good contact with the surrounding mud layer to ensure its barrier function within about 100 seconds of the duration of the seismic wave. (4) The attenuation of the barrier to the 8 th order seismic waves is close to 20 db because it is only then possible to ensure that the structure behind the barrier is not damaged.

Disclosure of Invention

In the patent of the invention, a local resonance structure with small volume is provided, and the local resonance structure is applied to a method for blocking 8-level earthquake and even completely absorbing the earthquake. The method satisfies the four requirements. The method comprises the following steps: and a plurality of metamaterial shock absorbers disposed in a plurality of shafts dug into the ground, wherein spaces in the shafts not occupied by the metamaterial shock absorbers are filled with soil. Wherein the shaft has various lengths and diameters. Wherein said wells are arranged in substantially parallel rows, each of said rows having the same length and diameter. The length of the front row of the vertical wells is shorter than the wavelength of the absorbed seismic waves, the length of the rear row of the vertical wells is sequentially increased in an increasing mode until the length is equal to the wavelength of the absorbed seismic waves, and the length of each rear row of the vertical wells is not increased. The metamaterial shock absorber comprises an elongated corrugated metal sheet, two ends of the elongated corrugated metal sheet are fixed on a substantially rigid two-dimensional plane frame, and one or more substantially rigid object blocks are placed at the suspended part of the elongated corrugated metal sheet, so that a superstructure vibrator is formed. The vibration modal frequency of the object block and the strip-shaped corrugated metal sheet when vibrating together is determined by the dimension of the two-dimensional plane frame, the dimension and the corrugated structure of the strip-shaped corrugated metal sheet and the dimension and the weight of the object block. The superstructure vibrator is completely surrounded by a substantially rigid shell, on which the frame of the superstructure vibrator is fixed. As an option, the remaining space within the rigid shell is filled with a liquid.

Drawings

FIG. 1(A) a plurality of weighted membrane dampers are embedded in an array of shafts excavated into the ground. The top left of the figure shows the side section of the array and the bottom left is a top view of the hoistway. The right figure is a schematic structural diagram of the weighted membrane absorber.

FIG. 1(B) is a weighted membrane damper for a mass.

FIG. 1(C) two-proof-mass weighted membrane vibration absorber.

Fig. 1(D) free vibration spectra of two vibration absorbers.

FIG. 2(A) seismic wave transmission for a 300 meter long single row shaft as a function of effective mass density of a weighted membrane absorber in the shaft.

FIG. 2(B) the scattering energy density of the wedge array well shown in FIG. 1(A) as a function of seismic frequency.

Detailed Description

Underground attenuator

Tuned mass dampers are damping devices for specific frequencies that were invented a hundred years ago. Dynamic mass for the dynamic action of the absorber on its base

Is described by the expression

（1）

Wherein

Is the static mass of the vibrator and,

is the operating frequency of the vibration absorber and,

is the frequency of the vibration or vibrations,

is the quality factor of the image to be processed,

。

the weighted membrane absorber of invention-1 is a compact and lightweight tuned mass absorber with one or more operating frequencies. Fig. 1(a) shows a schematic structure of the vibration absorber. A weight 101 is attached to the wall of the container 103 by an elastic strip or sheet 102. The movement of the weight 101 in the direction perpendicular to the elastic piece 102 is subjected to the elastic restoring force in the direction perpendicular to the elastic piece 102, and becomesA substantially simple harmonic oscillator, the weight being an oscillator. This is substantially the same as the principle of the structure in invention-2 (US 7,395,898B 2 (2008)). The walls of the container 103 act as a rigid frame in invention-1. Fig. 1(B) shows a real sample absorber-1. The original soft rubber film of invention-2 was replaced with a corrugated metal sheet 111 of 0.1 mm thickness in the absorber-1 of the invention, both ends of which were fixed to a rigid frame 112. A M6 nut 113 is fastened to the corrugated sheet 111 as a weight of a damper. Fig. 1(C) shows a two-nut absorber sample, which is seen from free vibration spectrum curves 121, 122 of absorber-1 and absorber-2 of the sample shown in fig. 1(D) and has a plurality of vibration modes around 10 Hz. The free vibration spectrum (curve 121) of absorber-1 has resonance peaks at 10.5 Hz and 9.1 Hz, indicating that it has a vibration-damping effect at these two frequencies. The folds of the steel sheet are energy concentration positions, the large curvature provides more energy dissipation than the plane, and a point of grease is coated on the folds to enhance viscous damping dissipation and reduce quality factors

Thus, the absorber of FIG. 1(B) has a quality factor of 10Hz

It is only about 30, and the quality factor of a flat steel sheet can reach more than 1000 generally. From these experimental measurements and numerical simulations, we estimate that a corrugated steel sheet with a length of 300 mm, combined with a mass with a weight of 20 g, can form a vibration absorber with a resonant frequency as low as 1 Hz. If the mass is kept constant at 2 g, the length of the corrugated steel sheet is 560 mm.

A number of said corrugated steel sheet dampers are embedded in the earth 104 and may be used to damp seismic waves 105. Although there are many possible arrangements of the absorbers, in the present patent we only consider embedding the absorbers in a well structure 106 having a depth as shown in fig. 1 (a). The perimeter of each of the absorbers is filled with the same soil 104 as outside the well. For 8-order earthquakes such as those with wavelengths over 100 metersIn terms of seismic waves, the absorber moves with the surrounding soil like a mass point, and behaves like a 'super-soil' with a dynamic mass of formula (1), and the dynamic mass density is equal to the sum of the dynamic masses of all corrugated steel sheet absorbers in a unit volume. Using a diagonal matrix for dynamic mass density of super soil

Description of not havingYThe components are due to Rayleigh waves in the modelYThe direction is not displaced. As a representative example, we chose

,

= 1000 Kg/m³，

Is given by formula (1), wherein

= 1 Hz，Q= 10. Mass density of this value

The well space corresponding to about 1/8 is the condition occupied by the vibration absorber. With vibration-dampers being vertical only in directionZVibrating in a direction, whereby the mass density is anisotropicXThe direction is only the static mass.

FIG. 2(A) shows the transmission coefficient curves for different dynamic mass densities of wells with a depth of 300 m in a single row, for example, a mass density multiple of 5 means the dynamic mass density of the super-soil in equation (1)

To do so

A resonant frequency of 1Hz andQno = 10 is changed. Other multipleAnd so on. Curve 201 is the transmission coefficient simulation of a 1Hz seismic wave after propagation through the well. According to the proportionality rule we derive, the transmission coefficient remains constant when the dynamic mass density multiplied by the frequency is constant. Thus, the seismic frequency and the resonant frequency of the super-soil are both increased to 10Hz, and the dynamic mass density is determined by

Is reduced to

The new transmission coefficient is completely consistent with the mass density related data point 202 and the curve 201, and the simply derived proportional rule is verified through numerical simulation. This can also be used to estimate the attenuation of seismic waves at other frequencies. An important speculation is that a lower dynamic mass density, or a smaller number of absorbers, is required for the attenuation of high frequency seismic waves, which may well guide the design of the damping device and reduce costs. The law of proportionality is also an expression of the law of acoustic mass density. Our seismic local resonance vibration absorber essentially exploits the dynamic mass effect, resulting in mass amplification and maximization of energy dissipation by resonance.

Perfect absorber

The above example is a good seismic barrier, but produces considerable reflections. Considering the small reflection coefficient of shallow wells, we designed a wedge-shaped well array as shown in FIG. 1(A) to achieve perfect absorption. The first 9 columns of wells were 10, 20, 30, 40, 50, 60, 70, 80, 90 meters deep, respectively, and the last 5 columns of wells were all 100 meters deep. All wells were filled with super soil at a frequency of 1 Hz. Fig. 2(B) shows a reflection coefficient curve 211, a transmission coefficient curve 212, and an absorption coefficient curve 213, and an incident wave intensity curve 214. Within the given frequency range, the reflection coefficient is less than 0.04 and the transmission coefficient is a minimum of 0.13, corresponding to an attenuation of 17.7 db. The maximum value of the absorption coefficient reached 0.982. If two rows of wells 100 meters deep are added after the wedge array, the transmission attenuation can exceed 20 db.

It is contemplated that various other changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the subject matter, may be made by those skilled in the art without departing from the spirit of the invention and the scope of protection as defined in the appended claims.

Claims (13)

1. A seismic wave absorbing metamaterial structure, comprising:

and a plurality of metamaterial shock absorbers disposed in a plurality of shafts dug into the ground, wherein spaces in the shafts not occupied by the metamaterial shock absorbers are filled with soil.

2. The seismic wave absorbing metamaterial structure of claim 1, wherein the vertical shafts have various lengths and diameters.

3. The seismic wave absorbing metamaterial structure of claim 1, wherein the vertical wells are arranged in substantially parallel rows, each row having the same length and diameter.

4. The seismic wave absorbing metamaterial structure as in claim 1, wherein the length of the forward row of the vertical wells is shorter than the wavelength of the targeted absorbed seismic waves, and the length of the backward row of the vertical wells is sequentially increased until the length is equal to the wavelength of the targeted absorbed seismic waves, and the length of each backward row of the vertical wells is not increased.

5. The seismic wave absorbing metamaterial structure of claim 1, wherein the metamaterial absorber comprises elongated corrugated metal sheets, both ends of the elongated corrugated metal sheets are fixed on a substantially rigid two-dimensional planar frame, and one or more substantially rigid blocks are placed at the suspended part of the elongated corrugated metal sheets so as to form the superstructure vibrator.

6. The metamaterial shock absorber according to claim 1, wherein: the vibration modal frequency of the object block and the strip-shaped corrugated metal sheet when vibrating together is determined by the dimension of the two-dimensional plane frame, the dimension and the corrugated structure of the strip-shaped corrugated metal sheet and the dimension and the weight of the object block.

7. A seismic wave absorbing metamaterial structure, comprising:

and a plurality of metamaterial shock absorbers disposed in a plurality of shafts dug into the ground, wherein spaces in the shafts not occupied by the metamaterial shock absorbers are filled with soil.

8. The seismic wave absorbing metamaterial structure of claim 7, wherein the vertical shafts have various lengths and diameters.

9. The seismic wave absorbing metamaterial structure of claim 7, wherein the vertical wells are arranged in substantially parallel rows, each row having the same length and diameter.

10. The seismic wave absorbing metamaterial structure of claim 7, wherein the length of the forward row of the vertical wells is shorter than the wavelength of the targeted absorbed seismic waves, and the length of the backward row of the vertical wells is sequentially increased until the length is equal to the wavelength of the targeted absorbed seismic waves, and the length of each backward row of the vertical wells is not increased.

11. The seismic wave absorbing metamaterial structure of claim 7, wherein the metamaterial absorber comprises elongated corrugated metal sheets, both ends of the elongated corrugated metal sheets are fixed on a substantially rigid two-dimensional planar frame, and one or more substantially rigid blocks are placed at the suspended part of the elongated corrugated metal sheets so as to form the superstructure vibrator.

12. The metamaterial shock absorber according to claim 7, wherein: the vibration modal frequency of the object block and the strip-shaped corrugated metal sheet when vibrating together is determined by the dimension of the two-dimensional plane frame, the dimension and the corrugated structure of the strip-shaped corrugated metal sheet and the dimension and the weight of the object block.

13. The metamaterial shock absorber according to claim 7, wherein: the superstructure vibrator of claim 12, completely surrounded by a substantially rigid shell, said frame of said superstructure vibrator being fixed to said rigid shell, the remaining space inside said rigid shell being filled with a liquid.

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