TECHNICAL FIELD

This invention relates to dynamically attenuating silo vibration, in general, and in particular to a dynamic vibration attenuation system, a dynamically attenuated silo, and an associated method for dynamically attenuating silo vibration.

BACKGROUND ART

The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

Silos are well known in the art. A silo is generally a structure for storing bulk materials, typically particulate material, and such silos are often used in agriculture to store grain, or bulk material applications such as bulk storage of coal, cement, carbon black, woodchips, food products, sawdust, or the like. A further application of silos is in the resources industry, where typically ore is stored in silos, such as for train loading systems, or the like.

The flow of bulk solids in silos can be accompanied by dynamic pulsations and self-excited vibrations. The frequency of these pulsations can be larger than 1 Hz, and sometimes vibrations in the audible range can occur. The latter is typically called silo noise, silo honking or silo music, where the noise often appears intermittently with a sound similar to that of a truck horn.

Distinct shocks appearing at irregular intervals of seconds to hours can also occur in silos, which are typically called silo quaking or silo thumps. Depending on the properties of the ground supporting the silo, shocks can spread out far into the surroundings. Silo quaking and silo honking can thus affect the environment, are unpleasant for personnel nearby and can damage a silo structure.

Silo vibrations are commonly caused or induced by material discharge and vary from an audible noise to a vigorous and unpleasant vibration of a floor on which the silo rests. These vibrations may be harmless, i.e. just a source of discomfort or nuisance, or they could lead to catastrophic failure of the silo or surrounding structures, as well as health problems for personnel exposed to strong noise and vibration.

Research has shown that the vibration amplitudes and frequencies of silo quake are not consistent across each discharge cycle. Each discharge cycle may produce a different accelerogram containing different vibration amplitudes and frequencies, thus making it extremely difficult for traditional dynamic structural analysis methods to accurately predict the response of a silo structure during discharge, which makes it very difficult to design a silo with suitable vibration dampers to reduce the amplitudes of vibrations accordingly.

The present invention was conceived with these shortcomings in mind.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a material silo comprising:

a silo structure for operatively receiving and/or discharging particulate material;

a sensor arrangement configured for operatively sensing, over a period comprising a plurality of instances of time, due to material movement via the silo, a displacement of the silo structure, a weight of granular material in the silo, and a flow rate of granular material received and/or discharged from the silo;

a processor arranged in signal communication with the sensor arrangement, and configured to calculate, at each instance of time, a resultant dynamic force from the sensed displacement, weight and flow rate; and

a damping arrangement operatively responsive to the processor and configured to dynamically dampen the resultant dynamic force in order to maintain vibration amplitudes in the silo structure below a user-selectable threshold.

Typically, the processor is configured to calculate the resultant dynamic force, at each instance of time (t), according to:
Σf(t)=(m(t)−dm){umlaut over (x)}(t)+(2δ(t)√{square root over (k(t)(m(t)−dm))}){dot over (x)}(t)+k(t)x(t)
Where, for the silo:x(t) is the displacement at instance of time t;{dot over (x)}(t) is the velocity at instance of time t;{umlaut over (x)}(t) is the acceleration at instance of time t;m(t) is the time-variant mass at instance of time t;dm is the change in the mass at instance of time t;δ(t) is the critical damping ratio at instance of time t;k(t) is the stiffness at instance of time t; andΣf(t) is the resultant dynamic force at instance of time t.

It is to be appreciated by the skilled addressee that sensing of the displacement, vibration, mass and/or flow rate of the silo over the period facilitates calculation of a resultant displacement, velocity and/or acceleration of the silo at an instance of time. As such, the calculated resultant force may comprise elements of such mass, displacement, velocity and/or acceleration.

Typically, the sensor arrangement comprises sensors selected from a group consisting of accelerometers, vibrometers, displacement sensors, load cells, strain gauges, weight scales, microphones, flow meters and other sensors suitable to facilitate calculation of the above formula.

Typically, the sensor arrangement is configured to capture a vibration, a displacement, a weight of the granular material, and a flow rate at each instance of time and/or incremental change in the time-variant mass of the granular material during discharge.

Typically, the processor comprises any suitable central processing unit having electronic circuitry configured to perform arithmetic, logical, control and/or input/output (I/O) operations as specified by a set of instructions.

Typically, the processor includes a memory arrangement with a database for storing a suitable set of instructions, including user-definable silo characteristics.

In one example, the user-definable silo characteristics are selected from a group comprising the critical damping of the silo, the stiffness of the silo structure, a geometry of the silo, structural material properties of the silo, structural member properties comprising the silo, static and/or dynamic load forces of the silo structure, vibration damper properties and locations on the silo structure, silo support properties, and/or any data necessary to enable accurate dynamic analysis of the silo structure.

Typically, the damping arrangement comprises at least one damper selected from a group consisting of an active mass damper, an active stiffness damper, a semi-active mass damper, a semi-active stiffness damper, a passive mass damper, a passive stiffness damper, and structural strengthening means.

According to a second aspect of the invention there is provided a dynamic vibration attenuation system for a granular material silo operatively receiving and/or discharging particulate material, said system comprising:

a sensor arrangement configured for operatively sensing, over a period comprising a plurality of instances of time, due to material movement via the silo, a displacement of the silo structure, a weight of granular material in the silo, and a flow rate of granular material received and/or discharged from the silo;

a processor arranged in signal communication with the sensor arrangement, and configured to calculate, at each instance of time, a resultant dynamic force from the sensed displacement, weight and flow rate; and

a damping arrangement operatively responsive to the processor and configured to dynamically dampen the resultant dynamic force in order to maintain vibration amplitudes in the silo below a user-selectable threshold.

Typically, the processor is configured to calculate the resultant dynamic force, at each instance of time (t), according to:
Σf(t)=(m(t)−dm){umlaut over (x)}(t)+(2δ(t)√{square root over (k(t)(m(t)−dm))}){dot over (x)}(t)+k(t)x(t)
Where, for the silo:x(t) is the displacement at instance of time t;{dot over (x)}(t) is the velocity at instance of time t;{umlaut over (x)}(t) is the acceleration at instance of time t;m(t) is the time-varying mass at instance of time t;dm is the change in the mass at instance of time t;δ(t) is the critical damping ratio at instance of time t;k(t) is the stiffness at instance of time t; andΣf(t) is the resultant dynamic force at instance of time t.

Typically, the processor is configured to calculate a dynamic response of the silo, at each instance of time (t), with the calculated dynamic force and mass of granular material remaining inside the silo obtained in accordance with the above formula.

Typically, the sensor arrangement comprises sensors selected from a group consisting of accelerometers, vibrometers, displacement sensors, load cells, strain gauges, weight scales, microphones, flow meters and other sensors suitable to facilitate calculation of the above formula.

Typically, the sensor arrangement is configured to capture a displacement, a vibration, a weight of the granular material, and a flow rate at each instance of time and/or incremental change in mass of the granular material during discharge.

Typically, the processor comprises any suitable central processing unit having electronic circuitry configured to perform arithmetic, logical, control and/or input/output (I/O) operations as specified by a set of instructions.

Typically, the processor includes a memory arrangement with a database for storing a suitable set of instructions, including user-definable silo characteristics.

In one example, the user-definable silo characteristics are selected from a group comprising the critical damping of the silo, the stiffness of the silo structure, a geometry of the silo, structural material properties of the silo, structural member properties comprising the silo, static and/or dynamic load forces of the silo structure, vibration damper properties and locations on the silo structure, silo support properties, and/or any data necessary to enable accurate dynamic analysis of the silo structure.

Typically, the damping arrangement comprises at least one damper selected from a group consisting of an active mass damper, an active stiffness damper, a semi-active mass damper, a semi-active stiffness damper, a passive mass damper, a passive stiffness damper, and structural strengthening means.

According to a third aspect of the invention there is provided a method for dynamically attenuating silo vibration, said method comprising the steps of:

sensing, over a period comprising a plurality of instances of time, a displacement of the silo, a weight of granular material in the silo, and a flow rate of granular material discharged from the silo;

calculating, at each instance of time, a resultant dynamic force from the sensed displacement, weight and flow rate; and

dynamically damping the resultant dynamic force in order to maintain vibration amplitudes in the silo below a user-selectable threshold.

Typically, the step of calculating is performed by a processor configured to calculate the resultant dynamic force, at each instance of time (t), according to:
Σf(t)=(m(t)−dm){umlaut over (x)}(t)+(2δ(t)√{square root over (k(t)(m(t)−dm))}){dot over (x)}(t)+k(t)x(t)
Where, for the silo:x(t) is the displacement at instance of time t;{dot over (x)}(t) is the velocity at instance of time t;{umlaut over (x)}(t) is the acceleration at instance of time t;m(t) is the mass at instance of time t;dm is the change in the mass at instance of time t;δ(t) is the critical damping ratio at instance of time t;k(t) is the stiffness at instance of time t; andΣf(t) is the resultant dynamic force at instance of time t.

Typically, the step of sensing is performed by a sensor arrangement comprising sensors selected from a group consisting of accelerometers, displacement sensors, vibrometers, load cells and flow meters and other sensors suitable to facilitate calculation of the above formula.

In one example, the step of calculating comprises calculating, at each instance of time, a dynamic response of the silo structure, at each instance of time (t), with the calculated dynamic force and mass of granular material remaining inside the silo obtained from the above formula.

Typically, the step of damping is performed by a damping arrangement comprising at least one damper selected from a group consisting of an active mass damper, an active stiffness damper, a semi-active mass damper, a semi-active stiffness damper, a passive mass damper, a passive stiffness damper, and structural strengthening means.

According to a fourth aspect of the invention there is provided a computer programme product which, when executed by a suitable processor, facilitates performance of the method according to the third aspect of the invention, by a suitable computer system.

According to a fifth aspect of the invention there is provided a computer programme product which, when executed by a suitable processor, facilitates performance of a method of modelling silo vibration, said method comprising the steps of:

simulating, over a period comprising a plurality of instances of time, due to material flow through a silo, a displacement of the silo, a weight of granular material in the silo, and a flow rate of granular material discharged from the silo;

calculating, at each instance of time, a resultant dynamic force from the simulated displacement, weight and flow rate; and

calculating resultant dynamic damping forces required for dynamically maintaining vibration amplitudes in the silo below a user-selectable threshold.

Typically, the steps of calculating are performed by the processor configured to calculate the resultant dynamic force, at each instance of time (t), according to:
Σf(t)=(m(t)−dm){umlaut over (x)}(t)+(2δ(t)√{square root over (k(t)(m(t)−dm))}){dot over (x)}(t)+k(t)x(t)
Where, for the silo:x(t) is the displacement at instance of time t;{dot over (x)}(t) is the velocity at instance of time t;{umlaut over (x)}(t) is the acceleration at instance of time t;m(t) is the mass at instance of time t;dm is the change in the mass at instance of time t;δ(t) is the critical damping ratio at instance of time t;k(t) is the stiffness at instance of time t; andΣf(t) is the resultant dynamic force at instance of time t.

