Suppression System Research Articles

Design and Field Application of DC and Harmonic Suppression System for Neutral Current in 220 kV Substation

Design and Field Application of DC and Harmonic Suppression System for Neutral Current in 220 kV Substation

Macro fiber composite-based active and efficient suppression of low-frequency vibration of thin-walled composite beam

Low-frequency vibration of thin-walled materials, which are widely used in aircrafts, can lead to fatal damage of aircraft components and even serious accidents. Efficient suppression of such low-frequency vibration is a promising way to avoid the above issue. Here, we propose a macro fiber composite (MFC) based self-feedback system for active suppression of low-frequency vibration of thin-walled composite beams, taking advantage of the excellent sensing and actuating features of MFCs. The self-feedback system composed of two MFCs, which were attached on the upper and lower surface of the thin-walled composite beams. One of the MFCs acted as sensors for continuously sensing the vibration signals and the other one was utilized to generate inverse vibration to efficiently suppress the detected vibration. The vibration suppression ratio could reach to 82.09% at the resonant frequency of 67 Hz. Importantly, the bandwidth with more than 50% vibration suppression ratio was about 52 Hz. Our proposed design could be suitable for various thin-walled materials, such as carbon fiber plate, epoxy plate, and steel plate, opening up a new avenue for active and efficient suppression of low-frequency vibration.

Optimizing firefighting agent consumption and fire suppression time in buildings by forming a fire feedback loop

The paper presents experimental research findings for the characteristics of physical and chemical processes in the seat of fire at different stages of fire development and suppression. Combustion product temperatures and composition, as well as the luminous intensity of the flame were recorded. The research was carried out using a model of class A fire. The most effective combinations of technical equipment were determined that are necessary and sufficient for early fire detection, timely suppression initiation, combustion and smoldering completion. The minimum volumes of a firefighting liquid (water) necessary and sufficient to suppress combustion were determined. The benefits of using feedback systems during firefighting were substantiated. These systems optimize the consumption of fire-extinguishing agents and time of fire suppression by monitoring the fire behavior in real time. Recommendations were made on the engineering of automatic indoor fire suppression systems that optimize the conditions of firefighting and minimize threat to people’s lives and health.

Investigation of optimal selection and atomizing characteristics of nozzles for ultrasonic dry-mist dust suppression system

ABSTRACT In order to provide insightful guidance for the selection of nozzles and the determination of operating conditions of ultrasonic dry-mist dust suppression system, this study collected six different types of ultrasonic dry-mist nozzles and investigated their atomizing characteristics in depth. Through comparison, the optimal nozzles were applied to engineering site and the dust suppression performance was measured. According to the present research results, the spraying ranges of No. 3, No. 5 and No. 6 nozzles among six different types of nozzles are below 170 cm, suggesting these nozzles are not suitable for far-distance dust suppression. Among the rest three types of nozzles, No. 4 nozzle (ST-47 nozzle) performs best in terms of overall performance, which can not only possess great spraying range but also produce the droplets at the dry-mist level size. Therefore, No. 4 nozzle is applicable to dry-mist dust suppression system in most cases. As the air supply pressure increases, the air flow rate of ST-47 nozzle increases gradually in exponential form while the water flow rate drops exponentially, accompanied with constant increasing ratio of gas-to-liquid flow rate. As the water supply pressure increases, the air flow rate of ST-47 nozzle decreases gradually in exponential form, while the water flow rate increases exponentially, accompanied with constant decreasing ratio of gas-to-liquid flow rate. As regard to the other atomizing parameters, the spraying range increases as the increasing air supply pressure but decreases as the increasing water supply pressure; both the droplet size and atomizing angle decrease as the increasing air supply pressure but increase as the increasing water supply pressure. The optimal operating condition for ST-47 ultrasonic dry-mist nozzle was determined as p L = 0.1 MPa and p air = 0.5 MPa. Under that optimal operating condition, the total dust and respirable dust suppression efficiencies after the application of ultrasonic dry-mist dust suppression system during coal transport on the belt can reach up to 94.1% and 96.1%, respectively.

Application of multi-parametric characterization to water-based fire suppression systems in compartment fire scenarios

A new predictive fire suppression model has been developed and applied to a compartment room environment with various fire locations to clarify the suppression mechanisms of water mist and sprinkler systems. To effectively mitigate the combustion process, an in-depth framework has been developed, which includes the thermal fluidic interactions and utilizes statistical approaches for water droplets characterization. Efficiencies and effectiveness of both systems under different operating conditions were investigated with a multi-parametric approach that uniquely traces the accumulative mass fluxes, penetrability and number counts of droplets. Different fire suppression scenarios were identified based on combustion behaviors, and the suppression systems’ performance was evaluated based on spray coverage, penetrability, water utilization rate and potential water damage. The current study finds that water mist systems significantly outperform sprinkler systems in suppressing centered fires from both time (within 0.55 s) and utilization rate (up to 6.78%) perspective, while sprinkler systems can effectively suppress fires within a larger area, but their water utilization rate is as low as 0.07%. For water mist systems, although the water utilization rate can be 37 times higher than sprinkler systems, their effective suppression coverage area is small, which provided directions for future improvement.

Fire extinguishing and explosion suppression characteristics of explosion suppression system with N2/APP after methane/coal dust explosion

The study aims to examine the suppression performance of an inhibitor after a methane/coal dust explosion. The design of an explosion suppression system included the carrier gas of nitrogen (N2) with an inhibitor of ammonium polyphosphate (APP). The study investigated fire extinguishing and explosion suppression of methane/coal dust by N2/APP in a vertical pipe. Flame propagation characteristics were measured by a high-speed camera, micro-thermocouple, and pressure sensor. The residues after the explosion were characterized chemically by X-ray photoelectron spectroscopy, and the thermal decomposition characteristics of coal dust and APP in the N2 atmosphere were analyzed by synchronous thermal analysis. Experimental results show that the explosion suppression system can effectively hinder the flame propagation of methane/coal dust explosion. The flame height, bottom velocity, and temperature were all weakened significantly. The optimum level of suppressant minimizes the explosion pressure and suppresses the flame significantly. In addition, the fire extinguishing and explosion suppression mechanisms of N2/APP were summarized. The suppression method used in this study blocks the explosion after it occurs rather than preventing it through premixed inerting.

Wildlife Monitoring and Anti-Smuggling System for Trees in Forest with Deforestation, Fire and Smoke Detection with Fire Suppression System

Remote sensing has presented a systematic, replicable, and geographically comprehensive picture of the expected large amount of biodiversity. Materials, planning data, policies, and monitoring the forest sector would be more beneficial for appropriate estimations of forest efficient expenditure. A wildfire is an uncontrolled fire that harms both natural and societal resources. When the fire begins to burn and spreads quickly over the forest, it causes enormous damage. Some of the causes of wildfire include lightning, extremely hot and dry weather, a lack of rain, and human ignorance. This project creates an IOT foundation for a system that detects jungle fires. The fire detection system that has been described allows for the early identification of fire before it spreads across a large region. After the fire is discovered, water starts pumping ferociously. With the use of a GPS module, the institution receives the device's precise position. Included the is an Internet - of - things solution for escaping tree trafficking.

Ensuring the seismic resistance of a building using a geotechnical seismic insulating screen

This paper considers the issue related to the protection of buildings and structures against seismic influences and the prevention, exclusion, or reduction of seismic hazards. The catastrophic destruction of modern «earthquake-resistant» buildings in Turkey and Taiwan has shown that existing methods of strengthening and reinforcing structures are not perfect and require further study. Analysis of existing approaches to ensuring seismic resistance showed that seismic insulation and seismic suppression systems still do not have a scientific and technical justification for the effectiveness of their operation from the point of view of ensuring the stability of structures. The estimation-dynamic models of the «base-seismic insulation-structure» system developed to date do not always make it possible to simulate the joint work of their interaction during an earthquake and account for the transformation of the seismic impact on the structure. An alternative technique has been devised, a geotechnical seismic insulation screen, as a seismic insulation system that reduces the intensity of seismic loads on the structure and ensures its seismic resistance. In a specific example, the effectiveness of this seismic insulation system is confirmed. This seismic insulation technique in the form of damper screens is characterized by reliability and manufacturability in ensuring the seismic resistance of objects under construction. The results of computational and experimental modeling of the interaction of an earthquake-insulated structure with a ground base found that the values of axial forces and bending moments in a building with a seismic insulating screen are less than in a building without seismic insulation by 30‒40 %. The geotechnical seismic insulation screen makes it possible to advance the development of new seismic insulation techniques and determine their effectiveness. This technique will also be effective when strengthening the base and seismic insulation systems of historical monuments, protecting them against seismic and dynamic influences.

Improved Model Predictive Current Control of NPC Three-Level Converter Fed PMSM System for Neutral Point Potential Imbalance Suppression

For the neutral point clamped (NPC) three-level converter fed permanent magnet synchronous motor (PMSM) system, the performance of the conventional model predictive current control (MPCC) algorithm will be deteriorated if the amplitude of the neutral point potential (NPP) is large. Additionally, the adjustment process of the weighted coefficients of the conventional MPCC algorithm is complex because of numerous control terms in the cost function. To solve the above issues, an improved MPCC algorithm is proposed in this paper. Firstly, Newtonian iteration is used to transfer the stator current into stator voltage in the cost function. Then, the NPP term in the conventional cost function can be eliminated by introducing the partition control of the NP potential, which also eliminates the whole adjustment process of weighting coefficients. Finally, based on the amplitude of the NPP, the amplitude and phase angle of medium and small vectors are modified to improve the control performance of the torque and flux. Experimental results show that the fluctuation of the neutral point potential can be suppressed rapidly. Meanwhile, the performance of the torque, flux and current are also improved compared with the conventional MPCC.

Research on Stray-Light Suppression Method for Large Off-Axis Three-Mirror Anastigmatic Space Camera.

The stray-light suppression of a large off-axis three-mirror anastigmatic space camera has been a hot topic, and this study proposes a composite stray-light suppression strategy that effectively suppresses stray light using the combination of a baffle, retaining ring, and internal antistray light measures. Additionally, the light barrier of the third mirror with a three-layered structure was designed to further optimize the composite stray-light suppression system. At the stray-light simulation analysis stage, in view of the limitations of the Torrance–Sparrow scattering analysis model, an analysis model with wide adaptability is proposed, which can be applied to the stray-light simulation analysis of large-size mirrors with rough surfaces. The simulation results indicate that the point source transmittance of the composite stray-light suppression strategy proposed in this paper is of the order of 10−5 before installing the light barrier of the third mirror, and the veiling glare index of the full field of view is less than 5.8%. After installing the light barrier of the third mirror, the point source transmittance reached the order of 10−8, and the veiling glare index of the full field of view was less than 1.31%. Moreover, the influence of the light barrier of the third mirror on the modulation transfer function of the system was less than 2.3%. The modulation transfer function test of the large-width off-axis three-mirror anastigmatic space camera in a simulated vacuum on-orbit environment was completed, and the test results indicated that the negative impact of the light barrier of the third mirror on the modulation transfer function was less than 3.6%. Moreover, an out-of-field imaging test of the space camera was conducted and the results showed that the image was clear, and the SNR reached 80 dB. The simulation and experimental results prove that the solution in this study can effectively solve the problem of stray-light suppression for large off-axis three-mirror anastigmatic space cameras.

Sensitivity analysis of road tunnel resilience through data-driven stochastic simulation

Abstract A probabilistic resilience model for tunnels exposed to disruptive events is vital to understanding and estimating the functionality loss and its recovery time due to these events. Performing sensitivity analysis will help to identify the critical parameters contributing to tunnel resilience. This paper aims to identify tunnel resilience’s sensitivity for parameters such as traffic volume, fire suppression systems, changes in maintenance, and operation parameters using a simulation model that estimates overall tunnel resilience for a given period. Overall universal compatibility of the simulation model is checked for twenty-two tunnels using information from the US National Tunnel Inventory (NTI), and resilience correlation is established. The results show that resilience loss due to fire and accidents are directly correlated with traffic volume. A significant reduction in the loss due to fire can be found by installing a fire suppression system. Increasing the service life of equipment and frequency of inspection and repair contributes to an increase in a tunnel’s resilience index. A resilience correlation study for the twenty-two tunnels showed that an average resilience index for these tunnels is 96.57%. Linear correlations can be made between tunnel length and traffic loss due to fire and operation. Accidents and fire events are correlated with average traffic in the tunnel. Tunnel speed limit, age, number of lanes, and bores do not show a considerable effect on disruptive events. Overall, the study shows that the proposed simulation model can encompass various disruptive events to estimate the resilience of the tunnel.

Numerical Model Development for CFETR CSMC Quench Detection System

The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T/s without quench. Quench detection by voltage measurements is likely to be the fastest available technical solution to avoid coil's damage caused by quench, but the voltage detection is a real challenge due to large noise induced by the power supply in alternating current operation. The pick-up sensors, comprising the co-wound wire (CWW) and the co-wound tape (CWT), are used in the CSMC quench detection system for noise compensation and suppression. To accurately compensate all related induced voltage in the multi-pulse coil system, the foremost task is to estimate the static inductance matrix between the CSMC and its pick-up sensors. In this paper, a numerical model is developed for inductance calculation and analysis. Moreover, several numerical simulations with this design model to evaluate the maximum inductive noises and quench detection signals by CWW and CWT have been conducted for the case of the worst test scenarios.

FRIT-based integral action state feedback controller tuning using PSO for a liquid slosh suppression system

This paper presents a model-free approach of controller tuning to a liquid slosh suppression system. The sloshing is the usual occurrence happening to the liquid in a moving container. An integral action state feedback controller was proposed as the selected control structure. A fictitious reference signal was formulated using the recorded input-output data generated from a one-shot experiment and later be used to design the appropriate performance index. The minimization of the performance index of the controlled system was achieved by employing the PSO algorithm. Numerical analyses using MATLAB software have been conducted to evaluate the effectiveness of the proposed model-free approach. The results manifested that the tuned controller had exhibited good transient response performance regarding the trajectory tracking of the cart motion and reduction of slosh level motion.

Nonlinear oscillator design based on phase reduction method for closed‐loop system

SummaryTo widely utilize the synchronization properties of nonlinear oscillators in the control and signal processing engineering field, a common design method for a nonlinear oscillator model would be helpful. The output response of a nonlinear oscillator excited by a periodic signal implicitly includes the information of both the instantaneous phase and the amplitude of the input signal. Explicitly expressing the dynamics of both phase and amplitude with the phase reduction method, and organizing them by the number of events in one period, could enable the design of a nonlinear oscillator model in the same manner that can synchronize with an arbitrary cyclic phenomenon in a broad sense. Assuming the cyclic phenomenon is a single periodic signal, the property of the generalized nonlinear oscillator model has the role as a common‐dimensional observer to attain the pseudo‐property of both iso‐damping and flat‐gain. Thus, this article determines the essential role of the nonlinear oscillator inserted in the closed‐loop system through investigating the input–output characteristic of the generalized nonlinear oscillator model. As a result of the numerical simulation using a simple vibration excitation and suppression system, it was found that using the generalized nonlinear oscillator model enables us to easily build the closed‐loop system including the pseudo‐property of both iso‐damping and flat‐gain.

Repression of Uyghur Muslims and the Freedom of Religious Beliefs in China

China has been accused by the international community for placing tight constraints on the religious freedom of Uyghurs in the northwest Xinjiang Uighur Autonomous Region (XUAR). It has been widely reported that China has placed in detention over a million Uyghur Muslims in order to ‘re-educate’ them to adapt to ‘Chinese culture’. It has been alleged that China is using a system of surveillance, control, and suppression of religious activity aimed particularly at Uyghurs accusing them of actively involving in separatist activity with foreign funding in order to destabilise the region. Note that, China has also brought in polices on regulation of religious affairs that makes it difficult for a religious body or a church, mosque to exist in China without prior State approval. The policy also gives unfettered power of oversight to the government over minority religious institutions and their day to day management. In light of the above, this article examines the issue of right to freedom of religion or belief in the backdrop of China’s treatment of Uyghur Muslims in the Xinjiang region. Further, this article also comments upon China’s current domestic policy regulating religion and its commitment at the international level to protect and promote freedom of religion or belief of all its citizens.

Simple adaptive V-stack piezoelectric based airfoil flutter suppression system

The suppression of aeroelastic vibrations due to flutter using a trailing edge flap is analyzed to increase the speed operability range of wings. The aeroelastic model of a 3DOF airfoil in incompressible flow is presented and an augmented state-space representation is used for the time domain analysis. A finite element model of a V-stack piezoelectric actuator, used to move the trailing edge flap, is introduced to model the actuator dynamics. The use of the simple adaptive controller is investigated to realize an adaptive flutter suppression system. A parallel feedforward compensator is tuned to make the plant almost strictly passive and a metaheuristic algorithm is used to determine the invariant parameters. Numerical simulations are carried out to verify the performance of the simple adaptive flutter suppression system in presence of speed variations and disturbances. Numerical results proved that the SAC flutter suppression system improves the closed loop system flutter boundary with respect to a gain scheduled PID controller.

A coordination control strategy for power quality enhancement of an active distribution network

Integration of power electronics-based converter-interfaced distributed generators (DGs) into the existing power systems have created several power quality related challenges. These challenges include reduced voltage rigidness at the point of common coupling (PCC), total harmonic distortion (THD), lack of inertial response and power imbalance due to unconsumed power from DGs. To address these challenges, this paper proposes a coordination control strategy which has two major objectives: (1) to regulate the apparent impedance at the PCC of the active distribution network (ADN) using coordination of DGs; (2) to use active and reactive power of battery energy storage system (BESS) for transient suppression at PCC and reactive power for power factor improvement of DGs. The proposed control strategy is applied to an ADN based on a 7 - bus test system. This study confirms that the unique method of regulating the apparent impedance of PCC using active and reactive power coordination of DGs significantly improves the power quality at the PCC of ADN. For instance, using the proposed method, the percentage overshoot (%OS) of active and reactive power injection at PCC of ADN was reduced up to 19.55% and 12.8%, respectively. Similarly, the THD of the grid current reduced from 4.71% to 2.85%.

Spacecraft attitude control and vibration suppression using magnetically suspended control & sensitive gyroscope and radial basis function network adaptive sliding mode control

For the sake of improving the agility and super-static performance of spacecraft under external disturbances, this paper puts forward an idea for using pyramid configuration of the Magnetically Suspended Control & Sensitive Gyroscope to realize dual control of attitude maneuver and vibration suppression of spacecraft. The RBF neural network is used to reduce the chattering in sliding mode control through adaptively learning the non-linear part of the system. A band-pass filter is designed to divide the attitude deviation signal fed back by the sensors into high-frequency and low-frequency parts. The control laws of gyro gimbal and magnetic suspension rotor are designed, respectively, to realize the attitude maneuver and vibration suppression simultaneously. The adaptive laws of parameters avoid the saturation of rotor deflection angle while speeding up the attitude maneuver process of spacecraft. Compared with the traditional sliding mode control methods, the proposed one not only improves the accuracy and speed of attitude control but also improves the robustness of the spacecraft attitude control and vibration suppression system. Semi-physical simulation results show the effectiveness and superiority of the proposed method.

Thermal Characteristic Analysis of Sodium in Diluted Oxygen via Thermogravimetric Approach

As the main reactor type of the fourth-generation nuclear power systems, sodium-cooled fast reactors are now designed and built worldwide. A sodium pool cooling circulation process is indispensable in a sodium-cooled fast reactor. However, the sodium pool fire design is the basis of accidents in sodium-cooled fast reactors. The fire hazard caused by the sodium–oxygen reaction and fast reactor safety have attracted extensive attention. Dry powder is widely used as an effective fire-extinguishing agent to control sodium fire. The sodium will burn in an oxygen-depleted atmosphere when using dry powder to cover fire. In this study, the change law of thermogravimetry of melted sodium is studied by thermogravimetric analysis (TGA) and the apparent activation energy (Ea) is obtained, which has a linear relationship with the oxygen concentration. The results can provide a reference for improving the engineering design standards of sodium fire suppression systems and can also be incorporated into simulation software to improve the accuracy of fire suppression simulations.

Effect of non-condensable gas in steam condensation at sub-atmospheric pressure condition

In the International Thermonuclear Experimental Reactor (ITER), a postulated Loss Of Coolant Accident (LOCA) in the Vacuum Vessel (VV) has to be managed with a pressure suppression system working at sub-atmospheric pressure. The operating conditions considerably differ from those experienced in the fission nuclear power plants such as BWR, since the ITER Tokamak works at very low pressure conditions and can withstand a maximum pressure of 0.15 MPa. For this reason, the pressure value must not exceed 10 kPa for a water temperature of 30 °C inside the Vapour Suppression Tanks (VSTs) that are the fundamental components of the Vacuum Vessel Pressure Suppression System (VVPSS). During a LOCA some non-condensable gases (mainly hydrogen and oxygen gases due to the water radiolysis or thermolysis) may be mixed in the steam and this could impair the condensation efficiency. In order to investigate the effects of non-condensable gas on DCC, we conducted a research program funded by ITER Organization at the laboratory of the University of Pisa: we designed and built a small-scale experimental rig to study the steam Direct Contact Condensation (DCC) with the presence of non-condensable gas and simulate the behaviour of a VST. Since DCC can occur with different characteristics, we ran 12 closed mode tests exploring all condensation regimes injecting a certain mass of air with the steam discharged in the subcooled water. The tests started at the saturation pressures corresponding to water temperatures ranging from 40 °C to 80 °C and ended when the free space volume reached the atmospheric pressure. From the analysis of the data acquired during the tests we observed that the condensation efficiency remained higher than 95%. We observed that despite this, the presence of a certain quantity of non-condensable gas has negative aspects on condensation: the condensation regime never reaches stability (the regimes quickly shift towards instability). Furthermore, the presence of air triggers a turbulence of the flow which interferes with the transfer of heat from the steam to the water. Not only the introduction of air into the flow increases linearly the pressure above the water head but its high temperature further contributes to the pressure increase. The air mixed with the flow also forms eddies that can trap the steam and transport it out of the water, preventing it from condensing. Apart from condensation, the most noticeable problem is the rapid increase in pressure inside the condensation tank.