Real-time structural measurement (RTSM) for control devices

Abstract

Relative displacements related to a structure are measured for use of a feedback signal in real time for the structural monitor of active and semi-active vibration. The monitors reduce structural movement caused by any source of natural or artificial vibration. A pre-stressed axial element is installed between two different points of the structure using a fixed connector and a flexible one. As the structure vibrates in response to an external “source”, a relative displacement is caused between two connecting points of the axial element, which can be measured based on the rotation φ of the flexible connector of the axial element. Discrete displacement can be obtained in real time of the whole structure where the axial element is installed. A modal monitor through active or semi-active devices can improve the structural behavior in some cases.

Claims

1. A system to measure in real-time dynamic displacements of structures relative to a reference, the system comprising: one or more axial elements installed and pre-stressed between two connection points of a flexible structure having a base; and a rotation measuring sensor configured to measure rotation between a reference of the structure and the axial elements, wherein the measuring sensor is placed at a fixed-to-the-base connection or alternatively at a fixed-to-the structure connection which forms the connection points of the axial elements to the structure, to obtain a relative displacement between the reference and the axial elements, measured in perpendicular direction to the axial elements, and obtained by multiplying a length of the axial elements by a tangent function of the measured rotation φ between the reference and the axial elements, wherein the relative displacement obtained can be used in controlling structural vibrations due to natural causes selected from the group consisting of earthquakes, wind, sea waves, and human generated actions through machines, people movement, vehicles, explosions, or other sources, wherein the system further comprises another axial element, also pre-stressed and installed between another two connection points of the flexible structure wherein one of said another two connection points is selected to be a node of a higher mode of the structure, to filter the contribution of this higher mode in the measured displacement.

2. The system according to claim 1, further comprising displacement sensors between the axial elements and the flexible structure to obtain a displacement shape of the structure at discrete points by measuring the relative structural displacements perpendicular to the axial element.

3. The system according to claim 1, comprising two or more pre-stressed axial elements to measure more than one relative displacement between two points of the flexible structure where one of the two points is a modal node in the flexible structure to identify independent modal contributions to the obtained displacement.

4. The system according to claim 1, wherein two or more axial elements are installed in the flexible structure for measuring the rotational motions, rocking motions, or any other differential motions of the structure.

5. The system according to claim 1, wherein the same axial element measures displacement in two principal directions of the structure using a bi-directional or spherical hinge of the axial element where one or more sensors are installed to measure displacements in the two principal directions of a structure.

6. The system according to claim 1, wherein the measuring sensor to obtain the relative displacement between the reference and the axial pre-stressed elements is a displacement sensor selected from the group consisting of a laser sensor, a potentiometer, an inclinometer, an accelerometer used as an inclinometer, a gyrocompass, a gyroscope, and other sensors used to measure rotations.

7. The system according to claim 1, wherein the axial elements are materialized as a lamella of carbon fibre or any other material with similar physical properties that minimize perturbations introduced into the measurements by natural vibrations of the axial elements and attain similar or better signal-to-noise ratios.

8. The system according to claim 1, wherein the fixed-to-the-base connection and the fixed-to-the-structure connection for the axial elements, connects to points of the flexible structure, capable of allowing rotations of the axial elements.

9. The system according to claim 8, wherein other types of connections that allow rotations of the axial elements to the structure are used.

10. The system according to claim 1, further comprising a metallic grip system used to anchor the axial elements.

11. The system according to claim 10, wherein other types of anchorage systems of axial elements are used.

12. Use of the system for measuring relative dynamic structural displacements according to claim 1, for being used in any type of buildings, planes, ships, trains, automobiles, bridges, towers, chimneys, industrial structures, equipment, lifelines, any kind of machinery, and others.

13. Use of the system for measuring relative dynamic structural displacements according to claim 12, for real-time active and semi-active structural vibration control caused by natural or human induced structural vibrations.

14. Use of the system for measuring relative dynamic or static structural displacements according to claim 12, for structural health monitoring, system identification, or others than vibration control of an active or semi-active vibration control device.

Description

DESCRIPTION OF DRAWINGS

(1) Below, the invention will be described by referring to the figures in the Appendix, where:

(2) FIG. 1 schematically shows a model structure (2), where two axial elements (1) and (4) of different lengths are installed in order to measure the relative displacement of the structure (2) in real time.

(3) FIG. 2 shows the fixed and flexible connections of the axial element (1) and (4) to the structure (2). In the case presented herein, the axial element materializes as a carbon fiber sheet.

(4) Left: front view and right: cross-section of the connection.

(5) 1 axial element/2 structure/3 relative displacement sensor between the axial element and the structure/4 second axial element/5 fixed connection/6 flexible connections/7 threaded bars/8 steel plates/9 screws/10 bolts/11 laser sensor

DETAILED DESCRIPTION OF THE INVENTION

(6) The invention refers to a solution to measure the relative displacements of the structures in real time, using the signal, for example, to monitor an active or semi-active structural monitor device. Applications are also possible in other areas, as in the health monitoring of the structural vibration.

(7) The invention consists in an axial element (1) (FIG. 1), which is installed between two different points of a structure (2). As an example, FIG. 1 schematically shows a frame of the building. The invention can be also used in any structure (bridges, seaports, warehouses, transmission lines, etc.). Should the structure (2) starts moving due to earthquake, wind, rotation of machinery, persons, vehicles or any other source, the rotation φ of the axial element (1) can be measured. Knowing the rotation of the axial element (1), the relative displacement of the axial element (1) can be obtained with respect to the not distorted structure at different heights h.sub.i through:
q.sub.i=φ.Math.h.sub.i

(8) With sensors (3), which measure the relative displacement s.sub.i between the axial element (1) and the structure (2) at different heights h.sub.i, the relative displacement of the structure (2) with respect to the not distorted structural configuration can be obtained through:
u.sub.i=q.sub.i+s.sub.i=φ.Math.h.sub.i+s.sub.i
u.sub.o and s.sub.o are equal to zero, because there is no relative displacement between the axial element (1) and the structure (2) where the axial element is connected to the structure (2).

(9) With the axial element installed (1) it is possible to obtain the full discrete form of the structural displacement in real time. If only the displacement is of interest, the floor sensors (3) are not necessary.

(10) By introducing a second axial element (4) of a different length into the same structure (2), it is possible to determine the contribution of the upper mode in the total displacement. This can be useful if modal displacements are used as feedback signal to monitor active or semi-active devices. As an example, let us assume that the contribution of the third mode displacement can be set aside, as well as the upper mode of the structure (2). After the displacement in real time corresponding to the first structural mode, measurement can be made if an axial element (4) is installed where the structure (2) has a node for the second mode of vibration. In practical applications, the assumption that the third mode and the upper mode have not much participation in the total structural displacement is, in some cases, appropriate. With the displacement of the first mode measured n.sub.1,0 in the point where the second mode passes through point zero, the first mode's form of discrete displacement can be obtained in real time:
η.sub.1=v.sub.1.Math.η.sub.1,o
v.sub.1 represents a normalized vector that describes the first mode of the structure (2). This vector can be for example estimated by numerical simulations of the structure (2) or by procedures of parametric or non-parametric structural identification. The in real time discrete displacement form of the second mode can be calculated through:
η.sub.2=u−η.sub.1

(11) The axial element (1, 4) is pre-stressed, so that the natural frequencies of the axial element are significantly greater than the natural frequencies of the structure (2). This prevents the natural vibrations of the axial element (1, 4) from introducing unacceptable disruptions in the rotation signal φ measured between the axial element (1, 4) and the structure (2). The high frequencies of the axial element (1, 4) can be achieved using a material for the axial element (1, 4) of low mass density and that can be pre-stressed at high axial loads. As an example of the case shown in FIG. 2, the axial element (1, 4) materializes through a laminar carbon sheet that meets these requirements very well.

(12) In FIG. 2 a possible configuration is shown for the fixed connection (5) and for the flexible connection (6) between the axial element (1, 4) and the structure (2). The flexible connection (6) allows pre-stressing the axial element (1, 4) through two threaded bars (7). In the case of the carbon fiber sheet as material of the axial element (as shown in FIG. 2), the carbon fiber can be fixed keeping a sheet between two steel plates (8), which are pre-stressed together by several screws (9). For a different material of an axial element (1, 4) other connections can be necessary (5) and (6) to the structure (2) and other fixings of the axial element.

(13) The bolt (10) in FIG. 2 allows the rotation of the plane (joint) between connections (5) and (6) and fixing the steel plates (8) of the axial element (1, 4). This rotation φ between the axial element (1, 4) and the structure (2) can be measured with different types of sensors, such as potentiometers, inclinometers, accelerometers used as inclinometers, gyrocompasses, gyroscopes or displacement sensors with the laser sensor (11) shown in FIG. 2.

(14) If inclinometers or accelerometers are used, depending on the excitation inlet expected of the structure (2) and the position where φ is measured, it is necessary to consider that these sensors also measure absolute movements of the building. Due to this, additional sensors must be installed directly in the structure (2), so that the relative rotation between the axial element (1, 4) and the structure (2) can be determined by subtracting the two signals. If a displacement sensor as the laser sensor (11) shown in FIG. 2 is used, the sensor measures the relative displacement between the connection (5) or (6) and the steel plate (8). This displacement measured can lead to the relative target displacement in real time q.sub.i without calculating rotation φ first.

(15) It should be considered that the points of the structure (2), where the axial element (1, 4) is connected, experience structural rotation. Except for the use of a gyrocompass or a gyroscope to measure rotation φ, the sensors used measure the relative rotation between the axial element (1, 4) and the point where this axial element (1, 4) is installed.

(16) In such cases, the rotation of the structure (2) where the axial element (1, 4) is connected, distorts the measurement of the relative target displacement. It is therefore important to measure the relative rotation φ in a point of the structure, where its rotation can be set aside. In the case of a building, this could be underground, as shown in FIG. 1.

(17) Only for simplicity, in FIG. 1 measurements in real time are only in one direction of the structure (2). The invention can be also applied to measure the displacements of a structure (2) in real time, with an axial element in each of the two perpendicular directions. With a second sensor (11), the rotation of the axial element (1, 4) in the perpendicular direction can be measured to remove the displacement of the plane of the structure shown in FIG. 1. In such cases, connecting the axial element (1, 4) to the structure (2) with a bidirectional joint is necessary.

(18) For bidirectional displacements of a structure (2), installing the sensors (3) in the axial element can be necessary, as well as measuring the axial element (1) to the structure (2) and not inversely. In such cases, contact-free displacement sensors should be used (for example, laser sensors). Their weight should be considered in the design, since the sensors (3) installed in the axial element (1) will reduce the frequencies of the axial elements. The latter should be always away from the structure frequencies.