Numerical Simulation Test Research Articles

Factors Influencing the Stability of a Slope Containing a Coal Seam in a Goaf

Our aim in this study was to analyze the major and minor factors affecting the stability of a slope containing a coal seam in a goaf. Based on engineering experience, we first identified nine factors that may affect slope stability, of which we determined eight that may substantially affect slope stability through a single-factor numerical simulation analysis. Then, we arranged 27 groups of numerical simulation tests with eight factors and three levels with the orthogonal test method, and we determined the ranking of the major and minor influencing factors through a range of variance analyses. The results showed that the influence of each factor was ranked as the roadway width > coal seam position > slope gradient > coal seam thickness > coal seam internal friction angle > coal seam cohesion > coal seam dip angle. Among these, the roadway width, coal seam position, and slope gradient were the major factors affecting slope stability; coal seam thickness, coal seam internal friction angle, coal seam cohesion, and coal seam dip angle were the minor factors. In this study, we combined the goaf and slope containing the coal seam, and we couple analyzed the factors influencing the stability of the slope containing the coal seam in the goaf. Our findings provide a scientific basis for the treatment and protection of slopes containing coal seams in goafs in the future and have a practical engineering importance for the analysis of the excavation stability of road-cutting slopes in goafs.

Study on Coal Seepage Characteristics and Secondary Enhanced Gas Extraction Technology under Dual Stress Disturbance

During the mining of coal seams with outburst hazard, abnormal gas emissions in front of the coal mining working face (CMWF) may induce gas overrun. To address this technical problem, this study analyzed the permeability variation of coal in front of the CMWF at different stress paths through physical experiments, numerical simulation and on-site tests. The spatial-temporal evolution law of the unloading area of the working face under dual stress disturbance caused by hydraulic punching (HP) and coal seam mining was explored; next, a secondary enhanced extraction technology was proposed and applied in the Shoushan No. 1 Coal Mine, Henan Province, China. The results reveal the following: (1) the coal permeability decreases linearly with increasing confining pressure (CP) and axial pressure (AP) under Stress Paths 1 and 2 (that is, fixed AP and CP). (2) The coal permeability is negatively related to the distance from the stress peak point under Stress Paths 3 and 4 (that is, AP and CP are, respectively, the vertical stress and horizontal stress before the stress peak). (3) As the distance from the peak stress declines, the reduction amplitude of coal permeability in the test area first decreases, and then increases, under Stress Paths 5 and 6 (that is, the vertical stress as CP and the horizontal stress as AP). The plastic damage range of coal around the HP cavities expands due to the dual impact of HP and coal seam mining, which can realize both regional unloading and provide channels for gas extraction within 60 m in front of the CMWF. According to the gas extraction concentration of boreholes, the coal body in front of the CMWF is divided into three zones: efficient, effective and original extraction zones. The efficient extraction zone is within 20 m in front of the CMWF, with an average gas extraction concentration of over 30%. In the effective extraction zone, the gas extraction concentration falls with the increase in the distance from the CMWF. The original extraction zone is beyond 50–60 m, and the borehole gas concentration stabilizes below 10%. The number of extraction boreholes in the stress disturbance area of the middle-floor gas extraction roadway accounts for 5–10% of the total number of boreholes, but its maximum monthly extraction volume can reach 38.5% of the total volume.

Study on Stability and Control of Surrounding Rock in the Stopping Space with Fully Mechanized Top Coal Caving under Goaf

Under the condition of fully mechanized top coal caving in close-distance coal seams, the surrounding rock of the stopping space easily loses stability during the withdrawal of mining equipment in the working face because the lower coal seam working face is located under the goaf and the overburden rock has a large range of complex interaction. Field investigation, theoretical analysis, laboratory experiment, similar simulation experiment, numerical simulation, and field industrial tests are used to carry out the research on the stability and control of the surrounding rock in the large section stopping space under the goaf in this paper. The research conclusions are as follows. (1) It is determined that the lower coal seam working face can only stop mining under the goaf, and the reasonable stopping position under the goaf should ensure that the key block fracture line of the main roof is behind the support. (2) The interaction law between the main roof’s key blocks of the upper and lower coal seams is analyzed, and the catastrophic conditions for sliding instability and rotary instability of the main roof’s key blocks of the upper and lower coal seams are obtained. (3) “Anchorage with push and pull equipment-Embedded anchorages and trays” integral anchoring technology is developed. The dimensions of the push and pull equipment are determined. (4) Through numerical simulation of the distribution characteristics of the anchor cable pre-stress field, the asymmetric control scheme of “Partition long and short anchor cables + Integral polyurethane mesh + Embedded anchorages and trays for roof protection” is determined. The rock pressure observation shows that the withdrawal of the working face equipment is implemented safely.

The low frequency pressure pulsation and control of the open-jet wind tunnel

An open jet wind tunnel has low-frequency pressure pulsation in common wind speed range due to its unique structural form, which seriously damages the quality of flow field in the test section. The low-frequency pressure fluctuation performance and control mechanism of Jilin University open jet and return flow wind tunnel are investigated by experiments and numerical simulation. The results show that the low-frequency pressure fluctuation is a narrow pulse phenomenon that only occurs in certain intervals, and several velocity intervals may be found in the same wind tunnel. The reliability of the numerical simulation is verified by comparing the peak frequency and amplitude of pressure fluctuation in numerical simulation and wind tunnel tests. A simplified model similar to and amplifying the phenomenon is established. The flow structure and vortex evolution are analyzed via detached eddy simulation. In the test section, large-scale shedding vortices are formed at the nozzle exit, introducing periodic pulsating instantaneous velocity and acting with the collector to form an edge-feedback. This acoustic feedback forms resonance with the pipeline circuit, resulting in poor flow field quality. In accordance with the mechanism of nozzle jet, two methods of controlling pulsation are proposed: spoiler and flow-follow device. The study shows that the effects of two methods are abrupt, and the frequency of pressure pulsation is changed. The spoiler destroys the complete structure of vortex ring in free jet and develops into a complementary double vortex ring structure, which is highly sensitive to size factors. The flow-follow device supplements the velocity loss of the free jet at the nozzle and develops into a double vortex ring with master–slave structure in the middle of the test section. Its vibration reduction effect is greatly affected by the flow velocity. It takes effect in an appropriate range where the flow velocity is higher than the nozzle velocity. If the follow velocity is extremely low, the flow-follow device cannot change the original jet structure. If the follow velocity is extremely high, the momentum of the fan will be greatly reduced, the flow field will be unstable, and another order of pulsation may be induced. This work lays a solid foundation for further understanding the aerodynamic characteristics and optimization mechanism of open jet wind tunnel.

Numerical and Experimental Study on Combustion Characteristics of Micro-Gas Turbine Biogas Combustor

The use of biogas in land-based gas turbines for power generation is a promising approach to reducing greenhouse gases and our dependence on fossil fuels. The focus of this research was to investigate the fuel/air mixing and combustion performance in an DLE (dry low emission) type can combustor designed for a micro-gas turbine. The fuel and air mixing uniformity was studied considering the air flow characteristic and fuel injection performance through the numerical simulation. The influence of the fuel/air mixing characteristics on the combustion characteristics was studied by numerical simulation and experimental tests. The combustion characteristics studied included the temperature field in the combustor, the pattern factor at the combustor outlet, combustion efficiency, and pollutant emission characteristics. The results show the position of the fuel nozzle has little effect on the mixing uniformity due to the limited mixing space for the micro-gas turbine combustor, while there are optimal fuel nozzle diameters to generate the suitable fuel jet momentum for the mixing process. The fuel/air mixing characteristics had an obvious influence on the combustion performance for the studied DLE combustor. The increase in the fuel air mixing uniformity can decrease the NOx emissions and generate a better temperature distribution at the combustor outlet. The increased mixing uniformity may decrease the combustion efficiency and increase the CO emissions of the micro-gas turbine combustor.

Physical-mechanical behaviors of stainless steel plate-lattice built by material extrusion additive manufacturing

Additive manufacturing (AM) technology has been widely adopted for the fabrication of metal lattices due to its freeform design capability over traditional manufacturing methods. However, the prevalent laser-based AM technologies possess high energy and investment consumption, and relatively low manufacturing speed, hampering their widespread adoption in building metal lattice components. In this study, an integrated approach of material extrusion AM, debinding, and sintering was introduced to produce 17–4 PH stainless steel plate-lattice structures in a time-efficient and cost-effective way. Three types of plate-lattice structures, namely body-centered cubic (BCC), face-centered cubic (FCC) and their combination (BCC-FCC), were successfully fabricated. Physical-mechanical behaviors, including physical deformation and compressive properties, were investigated through modeling, simulation, and experiments. Specifically, the shrinkage of the final sintered parts was predicted by the analytical modeling and characterized by experimental observation, the results of which showed a good consistency. The plate-lattice structure exhibited equiaxed grains on each surface, with a small portion of lath martensite observed at the top surface. Numerical simulation and compression test were conducted to reveal the compressive modulus, yield strength, and the fractural response at large compressive strains. All three types of plate-lattices possessed a lower compressive modulus than the simulated value, but still exhibited extraordinary yield strength under the compressive force compared to the truss-based or triply periodic minimal surface lattices. The successfully built metal plate-lattice structure verifies the great potential of material extrusion AM process, showing a great promise to fabricate complex metal lattice for large scale applications.

Asymmetric molten pool morphology in wire-arc directed energy deposition: Evolution mechanism and suppression strategy

Symmetric molten pool morphology is essential and fundamental in manufacturing three-dimensional (3D) components by wire-arc directed energy deposition (DED) method. However, when the molten metal droplets are deposited on non-level surfaces, various inclined substrates lead to undesirable molten pool behaviors, asymmetrical weld bead morphologies, or even formation of defects, which are mainly triggered by the gravity. Therefore, the evolution mechanism and suppression strategy of the asymmetric molten pool morphology on the inclined surface are necessary for the fabrication of 3D components. Herein, experimental and simulation analysis was carried out to reveal the evolutionary mechanism of molten pool and forming characteristics of wire-arc DED on various inclined surfaces, and a printing strategy was proposed to suppress the asymmetric molten pool morphology. First, a series of deposition experiments based on variable tilted substrates was conducted to evaluate the influence mechanism of weld bead morphology, and a characteristic parameter was introduced to quantitatively analyze the influence of inclination angle on the forming morphologies of weld beads. Second, in order to better comprehend the evolution of the asymmetric molten pool morphology, 3D numerical simulation and high-speed photography test were conducted to investigate the evolution of temperature field, velocity field, and fluid dynamics during the deposition on variable substrates. Finally, based on the theory of equilibrium of forces, a strategy was proposed to suppress the undesirable fluid flow pattern and eliminate the asymmetric morphology of single bead. Besides, for the multi-bead deposition process, this paper proposed an alternate printing strategy to alleviate asymmetric molten morphology and improve the forming quality. The feasibility of the proposed methods were verified via comparative quantitative evaluation. • Evolution mechanism of molten pool in wire-arc DED is systematically investigated. • Adverse effect of gravity on the mass transfer behavior of molten pool is revealed. • The influencing mechanisms of asymmetric morphology of molten pool are explored. • Printing strategies are proposed to eliminate the asymmetric weld bead morphology.

Loads Experiment Research on Key Components of Umbrella Wind Turbine Regulating Mechanism

Taking the key components of the umbrella wind turbine regulating mechanism as the research object, the main stress concentration parts were determined by numerical simulation, and the strength of the key components was checked. Through the wind tunnel test, the variation of the stress on the key components of the adjustment mechanism with the shrinkage angle of the umbrella wind turbine under the actual operating conditions was tested. The results show that the stress on the connecting rod and the small hub increases first and then decreased with the increase of the shrinkage angle, and both reach the maximum stress under the working condition of 45°. The stress of the large hub decreased with the increase of the shrinkage angle. The safety and reliability of the power regulating mechanism of the umbrella wind turbine was verified by numerical simulation and wind tunnel test, which laid a research foundation for the subsequent structural optimization and improvement of the umbrella wind turbine.

Destabilization Mechanism and Stability Control of the Surrounding Rock in Stope Mining Roadways below Remaining Coal Pillars: A Case Study in Buertai Coal Mine

To study the stability control of stope mining roadways below remaining coal pillars, the present study investigates the destabilization mechanism of coal pillars and roadways in sections under the dual action of supporting pressure on the floor of the remaining coal pillar in the overlying coal seam and the mining at the working face of the lower coal seam and clarify the principle of surrounding rock stability control based on theoretical analysis, numerical simulation, and industrial testing. The results yielded the following findings. After the stope mining of the overlying coal seam working face, the stress transfer of the T-shaped remaining coal pillar significantly increased the vertical stress of the lower coal seam. The lateral support pressure generated by the stope mining at the lower coal seam working face further aggravated the stress concentration in the coal, leading to severe compression-shear failure of the surrounding rock. As the sectional coal pillar becomes wider, the roadway gradually avoids the area of peak superimposed support pressure. The vertical stress curve of the sectional coal pillar shifts from single-peaked to asymmetrically double-peaked, and the stress difference between the two roadway ribs and the stress concentration coefficients decrease continuously. A stability control method of long anchor cable reinforcement support is proposed. In-situ industrial testing showed that the surrounding rock deformation was basically stable during the service period of the 42202 stope mining roadway, thus achieving the stability control of the stope mining roadway.

Design and Research of Slope-Pendulum Wave Energy Conversion Device

Wave energy is a kind of clean energy that is rich in reserves and has not been exploited on a large scale. The slope-pendulum wave energy conversion (S-PWEC) device has been optimized in structure and its capture efficiency has been increased. Taking the selection of the Zhejiang sea area as the research background, this paper performs numerical simulation and array WEC experimental testing of S-PWEC under 66 major sea conditions. The experimental results show that S-PWEC adds a slope structure to the bottom, which can effectively improve the motion response ability and resistance to extreme sea conditions. In the regular wave and irregular wave tests, the electron power output efficiency can be increased by 13.24% and 10.06%, respectively; in the array WEC experiment, the diffraction effect and radiation effect will affect the work of the array WEC, and the optimal arrangement distance can be selected to maximize the power output of the WEC system.

Genetic algorithm tuned adaptive discrete-time sliding mode controller for grid-connected inverter with an LCL filter

The development of a two-stage cascaded control strategy for a single-phase grid-connected inverter with an LCL filter based on inverter-side current is proposed. The main objective of the proposed controller is to minimize both the grid current tracking error and the current total harmonic distortion and to overcome the system resonance introduced because of the third-order LCL filter. In the first part, a feed-forward controller calculates the reference values for the system states at the steady-state operation with no external disturbance. In contrast, an adaptive discrete-time sliding mode controller is used for disturbance rejection caused by parameter uncertainties in the second stage. The proposed control approach also considers the nonlinear behavior of the pulsed nature of the inverter’s hard switching pulse width modulation modulator. The grid-side current is taken as in-phase to the grid voltage for the inverter-side reference values calculation. Numerical simulation and experimental tests were performed to validate the proposed control strategy’s faster dynamic response under external disturbances and parametric uncertainties. An improvement of approximately 18% in THD was recorded against the variation of grid-side impedance ranging from 50%–150% over the conventional discrete sliding mode control These results demonstrate the robustness and effectiveness of the proposed controller to integrate the solar photovoltaic energy sources seamlessly.

Effect of ultrasonic vibration characteristics on mechanical properties of stainless steel laser weld

The laser welding efficiency of stainless steel is high, but the welding quality is still insufficient. In order to improve the welding performance of stainless steel, a controllable ultrasonic laser welding system was designed in the paper. Through numerical simulation and experimental test, the influences of ultrasonic vibration on the mechanical properties of weld were obtained. For the simulation study, the sound vibration coupling scheme was applied to the welding model. The closed environment model was established, and the characteristic frequency and sound pressure distribution of ultrasonic were simulated and analyzed by COMSOL software. In the aspect of performance test, through the real-time monitoring of the welding system, the effect of ultrasonic on the molten pool area, molten pool flow rate and metal vapor pressure is obtained. Under different ultrasonic excitation frequencies, the changes of weld microstructure, wear morphology, hardness and oxidation were studied. The results show that ultrasonic vibration can significantly improve the wear resistance, hardness and corrosion resistance of stainless steel welds. The ultrasonic energy efficiency at the second-order characteristic frequency is higher, the flow rate in the molten pool is low, and the joint quality is better.

Stability Influencing Factors and Control Methods of Residual Coal Pillars with Solid Waste Materials Backfilling Method

Affected by coal mining activities, the remaining coal pillars are very likely to be destabilized and cause safety accidents. The backfilling of the remaining goaf can maintain the stability of the coal pillar well, but the coal pillar in the unfilled zone may still be unstable. In this paper, the effect of backfilling materials on coal pillars and the reinforcement method are discussed using numerical simulation, statistical mathematics, elastic mechanics, and mechanical test methods. The results show that: backfilling with solid waste materials and reinforcing the coal pillar could maintain the stability of the bottom goaf, where the backfill body height is the main factor in the strength of the coal pillar. The propagation of the confining stress of the backfill body on the pillar in the unfilled zone is the primary way to influence the coal pillar strength. Changing the backfill body height filling can affect the coal pillar strength. By analyzing the propagation law of confining stress in the coal pillar, the minimum backfill body height is determined to be 7 m. Combined with mechanical tests and the Mohr–Coulomb criterion, the minimum confining pressure required to maintain the coal pillar stability under the peak ground pressure is analyzed. The ratio of solid waste materials is determined based on this. Field tests have proved that the coal pillar remains stable when the goaf is not filled, and the cement/fly ash ratio is 1:4, which can ensure product safety. The research has significant value and significance for the governance of the remaining coal pillars and production safety.

Predictive method for the macroscopic mechanical properties of concrete at ultra-low temperatures

Based on the randomness of the concrete meso-structure and the influence of damage at the interface layer, a predictive method for the mechanical properties of concrete at ultra-low temperatures is proposed in this paper. In this method, the mechanical properties of aggregate and mortar materials at ultra-low temperatures are input parameters, the concrete random meso-structure is constructed using the Monte Carlo method, and the interface damage models using interface normal tensile failure are established. Based on the homogenization theory, the concrete macroscopic mechanical properties at ultra-low temperature can be predicted by statistical analyses of numerical simulation tests. The results showed that the properties were consistent with reported results, which verified the correctness of the proposed method.

Wind Load Similarity Relations for Parabolic Trough Collectors

Abstract Large-scale parabolic trough collectors (PTCs) are generally installed in flat, open areas. Their specific costs ($/m2) are dependent on wind load-based structural design factors. To help estimate these wind loads, validated numerical simulations were used to develop similarity relations for large-scale PTCs. First, similarity relations of wind pressure, force, and lift/drag coefficients were deduced between a full-sized model (FM) and a scaled-down experimental similarity model. Second, the wind loads on the similarity model were simulated with a computational model to analyze the pressure distributions and aerodynamic performance under different wind speeds and pitch angles. Third, the computational method was extended to compute wind loads on a LS-2 collector (a commercial-scale PTC designed by LUZ International Ltd). The numerical results had a close agreement with the experiment results, on the whole, achieving a mean relative error in the drag coefficients of 5.1%, 3.8% in the lift coefficients and 5.0% in the moment coefficients, which indicated that the simulation model was valid. Further, compared with the shear stress transport model for the atmospheric boundary layer (ABL) along with large eddy simulations for the ABL, the k–ɛ turbulence model has better accuracy. Finally, practical similarity equations were proposed which can be used to estimate the wind loads on a range of PTC designs in a wide range of conditions. The mean relative error of these practical similarity equations was found to be within 12.0%. Overall, this study reports a validated set of similarity equations that can be used to bypass costly numerical simulation and/or wind tunnel testing for the estimation of wind loads on the large-scale PTCs (e.g., the EuroTrough) installed in flat, open areas.

A New Reconstruction Algorithm for Geometric Shape of Static Overhead Transmission Lines

This paper proposes a reconstruction algorithm for the geometric shapes of static overhead transmission lines that is based on the spatial coordinate data (obtained by field mapping) and the corresponding inclination data (obtained by attitude sensors). The algorithm takes the piecewise cubic Hermite interpolation function as the basic framework and corrects the aforementioned two types of data based on the “minimum energy principle” of the transmission line system. The introduction of a new energy function in modified energy method (MEM) overcame the shortcomings of conventional energy method (CEM) in fairing strategy, and the new Fairing Criterion made result curves more consistent with the mechanical properties of transmission lines. In the numerical simulation tests, the two energy methods were compared in terms of load type, horizontal span, elevation difference, and anti-disturbance ability, which showed that MEM has a higher reconstruction accuracy (average Euclidean distance is less than 1 cm) and better robustness than CEM. Meanwhile, the key parameters involved in the algorithm were discussed to guide the application in practical engineering. In addition, measurement tests under non-uniform icing were carried out in the field test station, and the results showed that the maximum relative error is less than 0.1%.

Experimental Study of the Damage and Failure Characteristics of the Backfill-Surrounding Rock Contact Zone.

Due to obvious differences in the properties of the filling body and surrounding rock, deformation always develops near the contact zone. Thus, determining the damage and failure characteristics of the contact zone between the backfill and surrounding rock is a precondition for safe production in mines. Taking Jinchuan mine as study area, the backfill-surrounding rock contact zones are divided into three models according to their different geometric shapes, namely, a linear model, embedded model, and multiple broken line model. A combined numerical simulation and physical model test method was adopted in this study. The research results show that the damage in the linear model begins at the seam, the failure is mainly concentrated in the filling body, and shear failure is dominant. The damage in the embedded model initially occurs around the inflection points, while the damage in the multiple broken line model initially occurs at the seams, and cracks always appear on the vertical contact surface first. Among the three contact models, the stability increases as follows: embedded > multiple broken line > linear. Moreover, the filling body enclosed by surrounding rock is the most stable, and the surrounding rock located in the footwall is more stable than the filling body located in the footwall. The conclusions of this study provide a theoretical basis for designing a mining scheme for Jinchuan mine and other mines with similar geological conditions and mining methods, and they provide a reference for studying the mechanical properties and stability of composite materials.

Design and Experiment with a Double-Roller Sweet Potato Vine Harvester

The yield of sweet potato vines is large, making it a good source of food. However, it is difficult to harvest sweet potato vines due to creeping and intertwining. Therefore, according to the domestic sweet potato planting model, this paper designed a double roll sweet potato vine harvester which can complete the operations of vine picking, vine killing, conveying and header harvesting at one time. The machine adopts the process of front roll vine picking, rear roll vine killing and rod bar lifting. The key components of the vine picking device, vine killing device and lifting device were designed and calculated. A numerical simulation test of the vine harvesting process was carried out by using the discrete element numerical simulation method. It was determined that the length of the vine picking rod from the outside to the inside is 175 mm, 150 mm and 105 mm, respectively, and the inclination angle of the end is 160°. There are six vine killing knives on each vine killing knife plate. The inclination of the lifting device is 50°and the conveying speed is 3 m/s. Using the box Behnken experimental design method, taking the vine picking roller speed, vine killing roller speed and ground clearance as the experimental factors, and taking the sweet potato vine harvest rate, stubble height and potato injury rate as the evaluation indexes, a quadratic regression orthogonal test was carried out, the effects of various factors on the evaluation indexes were analyzed, and the experimental factors were optimized and verified. The experimental results showed that the optimal parameter combination is as follows: the rotation speed of vine picking roller should be 716 r/min, the rotation speed of vine killing roller should be 1960 r/min and the ground clearance should be 16 mm. With these parameters, the harvest rate of sweet potato vines is 93.1%, the stubble height is 29.5 mm and the potato injury rate is 0.174%. As such, the harvester meets the requirements for the mechanized harvesting of sweet potato vines and is of great significance as a light and simplified product for the sweet potato industry.

High quality of an absolute phase reconstruction for coherent digital holography with an enhanced anti-speckle deep neural unwrapping network.

It is always a challenge how to overcome speckle noise interference in the phase reconstruction for coherent digital holography (CDH) and its application, as this issue has not been solved well so far. In this paper, we are proposing an enhanced anti-speckle deep neural unwrapping network (E-ASDNUN) approach to achieve high quality of absolute phase reconstruction for CDH. The method designs a special network-based noise filter and embeds it into a deep neural unwrapping network to enhance anti-noise capacity in the image feature recognition and extraction process. The numerical simulation and experimental test on the phase unwrapping reconstruction and the image quality evaluation under the noise circumstances show that the E-ASDNUN approach is very effective against the speckle noise in realizing the high quality of absolute phase reconstruction. Meanwhile, it also demonstrates much better robustness than the typical U-net neural network and the traditional phase unwrapping algorithms in reconstructing high wrapping densities and high noise levels of phase images. The E-ASDNUN approach is also examined and confirmed by measuring the same phase object using a commercial white light interferometry as a reference. The result is perfectly consistent with that obtained by the E-ASDNUN approach.

An Integrated Test-Based Nonlinear Aeroelastic Analysis Method to Freeplay-Induced Limit-Cycle Oscillations

The nonlinear limit-cycle oscillations induced by aileron rotational freeplay are investigated by numerical simulation and flutter wind tunnel tests. An integrated nonlinear aeroelastic analysis method and procedure based on the nonlinear system identification technology is proposed. Based on the characteristics of the structure, a low-speed nonlinear flutter wing-aileron model that considers both the linear flutter test and the nonlinear limit-cycle oscillation test with aileron rotational freeplay is designed. The wind tunnel tests are conducted with the model, and the stable limit-cycle oscillation is observed by accelerometers under the linear flutter boundary with a 0° angle of attack. Higher-order harmonic vibration is also observed with a low proportion compared to the fundamental oscillation, and the limit-cycle oscillation grows gradually with the increase of airspeed until flutter occurs. The comparison of numerical and experimental investigation shows high consistency.