Technical Services - Ningbo Shangong Center of Structural Monitoring & Control Engineering Co., Ltd.

Health monitoring system for civil engineering structure
Fiber grating temperature sensing system in electric power field and petrochemical industry
Variation control scheme

The large-scale civil engineering structures are expensive and undertake the important social function; their service life can be up to decades, even a century; the coupling of multi-disasters like environment erosion, material aging and long-term effect, fatigue effect or mutation effect of load etc will inevitably lead to the accumulation of damages and attenuation of resistance of structure and system; thus the ability of resistance to natural disaster, even the normal environmental effect is also reduced which will result in catastrophic sudden accidents under the extreme case. So it has important and practical significance for scientific decision making of detection, maintenance and control of major engineering structures, ensuring the safe operation of structure to set operating health monitoring system on the important civil structure as to monitor the degree of change of the structural working behaviors under all-weather conditions, grasp the cases of the accumulation of damages of structure and the decrease of degree of safety.

Definition of "Health Monitoring" (Ou jinping (2002)): Structural intelligent monitoring integrates various software and hardware including intelligent sensing elements, data wired and wireless acquisition and real-time processing, structural damage identification, health diagnosis and reliability prediction as well as telecommunication and data management. It is the symbol of development and combination of engineering theory and a concentrated expression of modern structural experimental technique. It marks the development and integration of the high and new technology

Structural health monitoring system consists of sensor subsystem, data acquisition, processing and storage subsystem, structural safety assessment subsystem, wired/wireless long-distance transmission subsystem, remote monitoring and data management subsystem.

Sensor subsystem
Determine the minimum quantity of sensors in terms of optimization theory on sensor. The total quantity of sensors is determined by considering the characteristics of the structure being monitored, scale of investment and importance of the structure as well as a certain redundancy.
For entire variable monitoring sensor, the optimal position is generally determined according to optimal sensor placement theory and modal information of the structure.
For local variable monitoring sensor, it is generally placed in the part which bears the maximum stress and is easily damaged and the area which will have greater influence on the whole structure if damaged.

Data acquisition, processing and storage subsystem
This subsystem includes three parts: data acquisition, data processing and data storage. Among other things, data acquisition is to acquire the electric signals which are collected by the data acquisition instrument; data processing is to conduct FFT, filtering and de-noising and abnormal value removal on the signals; data storage is to store the data acquired in a computer or directly in the database server in the form of text files or binary files which will facilitate the future data analysis or safety assessment.

Structural safety assessment subsystem
Analyze the health conditions of the current structure by analysis of the data acquired through relevant model analysis algorithm.

Wired/wireless long-distance transmission subsystem
Realize data long-distance transmission by establishing wired/wireless network

Remote monitoring and data management subsystem
Through digital signal transmission network, perform the remote real-time monitoring and management function on health conditions of structure and the whole motoring system, which can provide technical support for safe operation of structure, realize the real-time safety assessment on structure by local users and distant specialists and improve accuracy and reliability of the safety assessment.

Electric unit usually works at high voltage and large current. Some device defects could cause abnormal rise in the temperature of components. For example, electric unit has a great number of conductor crimp connections and socket connections which could lead to the increase of contact resistance if not tight and abnormal operation of device and even burn. Applying temperature sensing technique to discover abnormality in the temperature of electrical unit is very important for ensuring safe and reliable operation.

In petrochemical system, the place where large-scale oil tanks are located belongs to inflammable and explosive location. If monitoring is conducted during temperature rise, fire forecast is given in time at the early stages and corresponding measures are taken, the loss of the accident can be reduced to the minimum level. But for technical reasons, supporting facilities are still not available at present. Fire accidents occur from time to time, thus more attention has been given to conduct temperature and fire detecting on large-scale oil tank.

The traditional sensors conform to standards on prevention of explosion. But due to the potential power supply problems existing in the sensor itself, it still could act as a source of ignition in some cases. Therefore, the traditional sensors cannot meet the requirements for sensing temperature at high voltage or in the environment where oil tanks are located.

Fiber grating temperature sensing system is explosion-proof and insulative with the advantages of high precision, high reliability and ease installation and high durability; therefore it is an ideal product for sensing temperature in inflammable and explosive locations in petrochemical industry and electric power field.

Be explosion-proof and insulative and safe in nature: Fiber grating temperature sensing system is an all optical monitoring system in its true sense, because this system and the monitoring site do not need power supply at all. The system is safe in nature and the characteristics of being explosion-proof, severe electromagnetic interference resistant and lightning strike-proof is much superior to that of electrical signal sensor and other technical schematic.

High precision and reliability: Fiber grating sensor adopts absolute measurement and light source attenuation, and line losses do not affect measurement precision. Among all types of fiber sensors, the fiber grating sensor has higher measurement precision.

Ease installation and high durability: Fiber grating sensor can be customized according to specific measuring point. The sensor is simple in structure and made of materials, which has high corrosion resistance; it can be installed with oil but without power and can provide long-term real-time online monitoring. Installation and maintenance for it are easy.

Variation and impact widely exist in various structures, for example, the periodic variation of buildings occurring under the action of wind load; random vibration of offshore platform occurring due to joint action of complicated external forces such as wind, waves, and ice; and severe variation of the car body occurring when going on a rough ground. Variation and impact usually cause fatigue accumulative damage of structure and shorten service life of works. In addition, it is usually associated with noise pollutant which has adverse effect on the health of operators and the surrounding people.

In order to increase service life of works and reduce its noise pollution, our company will provide the solution for variation and impact which is based on the latest variation control theory and the most advanced intelligent damper control technique. Implementation methods of this solution include several steps:

i. Make structural analysis and environmental load analysis for the controlled object and establish the dynamics model;
ii. On the basis of comprehensive consideration of dynamics features, importance and economic factors of the controlled object, put forward the implementation scheme of intelligent variation control system or passive energy dissipation shock absorber.
iii. Primarily design variation control system (device) and simulate it on computer to draw the theoretical variation control effect;
iv. Customize variation control system (device) as per design and conduct device performance test and field trial operation test;
v. Compared the field operation result with the theoretical result, if the error exceeds the allowable range, return to step three and redesign the system (device).

Intelligent control system is a closed loop linear control system based on state feedback in principle. It consists of magneto-rheological fluid damper, control algorithm integrated circuit, sensor and power supply controller, of which the magneto-rheological fluid damper is the core element. Due to application of intelligent controllable magneto-rheological fluid, the precise stepless control over damping force by the power supply with low power can be easily implemented.

Passive energy dissipation shock absorber usually adopts a viscous damper of which the damping force cannot be adjusted. It is a very effective and economical vibration control device when mechanics features of the controlled object are simple and vibration frequency domain is narrow.