• International Journal of Control, Automation, and Systems
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• v.2 no.4
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• pp.494-500
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• 2004

The wing rock phenomenon is a high angle of attack aerodynamic motion manifested by limit cycle roll oscillations. Experimental studies reveal that direct control and manipulation of leading edge vortices, through the use of 'blowing' techniques is effective in the suppression of wing rock. This paper presents the design of a robust controller for the experimental implementation of one such 'blowing' technique - recessed angle spanwise blowing (RASB), to achieve wing rock suppression over a range of operating conditions. The robust controller employs Takagi - Sugeno fuzzy system, which is fine-tuned by experimental simulations. Performance of the controller is assessed by real-time wind tunnel experiments with an 80 degree swept back delta wing. Robustness is demonstrated by the suppression of wing rock at a range of angles of attack and free stream velocities. Numerical simulation results are used to further substantiate the experimental findings.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.8
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• pp.725-734
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• 2011

At high angles of attack, aircraft dynamics can display an oscillatory lateral behavior that manifests itself as a limit cycle known as wing rock. In this paper, a classical and neural network based adaptive control design methods of adaptively stabilizing the oscillatory motion by adapting uncertainties are described in detail. All methods are simulated and compared using a model for an 80o swept delta wing.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1047-1059
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• 2018

This paper focuses on the cracking and fragmentation process in rock materials containing a pair of non-parallel flaws, which are through the specimen thickness, under vertical compression. Several numerical experiments are conducted with varying flaw arrangements that affect the initiation and tensile wing cracks, shear crack growth, and crack coalescing behaviors. To obtain realistic numerical results, a parallelized peridynamics formulation coupled with a finite element method, which is able to capture arbitrarily occurring cracks, is employed. From previous studies, crack initiation and propagation of tensile wing cracks, horsetail cracks, and anti-wing cracks are well understood along with the coalescence between two parallel flaws. In this study, the coalescence behaviors, their fragmentation sequences, and the role of an x-shaped shear band in rock material containing two non-parallel flaws are discussed in detail on the basis of simulation results strongly correlated with previous experimental results. Firstly, crack initiation and propagation of tensile wing cracks and shear cracks between non-parallel flaws are investigated in time-history and then sequential coalescing behavior is analyzed. Secondly, under the effect of varying inclination angles of two non-parallel flaws and overlapping ratios between a pair of non-parallel flaws, the cracking patterns including crack coalescence, fragmentation, and x-shaped shear band are investigated. These numerical results, which are in good agreement with reported physical test results, are expected to provide insightful information of the fracture mechanism of rock with non-parallel flaws.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.2
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• pp.23-32
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• 2001

Rock masses are usually discontinuous in nature, as a result of various geological processes they have underdone and they contain rock joints and bridges. Crack propagation and coalescence processes mainly cause rock failures in tunnels. In this study, we focused on the crack initiation, propagation and coalescence process of rock materials containing two pre-existing open cracks arranged in different geometries. During uniaxial compression, wing crack initiation stress, wing crack propagation angle, and crack coalescence stress of Diastone gypsum and Yeosan Marble specimens were examined. And crack initiation, propagation, and coalescence processes were observed. Shear, tensile and mixed (shear+tensile) types of crack coalescence occurred. To compare the experimental results with Ashby & Hallam model, crack coalescence stress was normalized and it generally agreed with the experimental results.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.307-319
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• 2011

Cyclic loading due to traffic, excavation and blasting causes microcrack growth in rocks over long period of time, and this type of loading often causes rock to fail at a lower stress than its monotonically determined strength. Thus, the crack growth and coalescence under cyclic loading are important for the long-term stability problems. In this research, experiments using gypsum as a model material for rock are carried out to investigate crack propagation and coalescence under monotonic and cyclic loading. Both monotonic and cyclic tests have a similar wing crack initiation position, wing crack initiation angle, cracking sequence and coalescence type. Three types of crack coalescence were observed; Type I, II and III. Type I coalescence occurs due to a shear crack and Type II coalescence occurs through one wing or tension crack. For Type III, coalescence occurs through two wing or tension cracks. Fatigue cracks appear in cyclic tests. Two types of fatigue crack initiation directions, coplanar and horizontal directions, are observed.

• Tunnel and Underground Space
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• v.11 no.3
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• pp.217-224
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• 2001

Rock masses are usually discontinuous in nature due to various geological processes and contain rock joints and bridges. Crack propagation and coalescence processes in rock bridge mainly cause rock failures in slopes, foundations, and tunnels. In this study, we focused on the crack initiation, propagation and coalescence process of rock materials containing two pre-existing open cracks arranged in different geometries. Specimens of 120${\times}$60${\times}$25 mm in size, which were made of Yeoman Marble, were prepared. In the specimens, two artificial cracks were cut with pre-existing crack angle ${\alpha}$, bridge angle ${\beta}$, pre-existing crack length 2c and bridge length 2b. Wing crack initiation stress, wing crack propagation angle, and crack coalescence stress were measured and crack initiation, propagation and coalescence processes were observed during uniaxial compression. Crack coalescence types were classified and analytical study using Ashby and Hallam model (1986) was performed to be compared with the experimental results.

• Computers and Concrete
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• v.17 no.6
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• pp.723-737
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• 2016

In this paper an approach was described for determination of direction of sliding block in rock slopes containing planar non-persistent open joints. For this study, several gypsum blocks containing planar non-persistent open joints with dimensions of $15{\times}15{\times}15cm$ were build. The rock bridges occupy 45, 90 and $135cm^2$ of total shear surface ($225cm^2$), and their configuration in shear plane were different. From each model, two similar blocks were prepared and were subjected to shearing under normal stresses of 3.33 and $7.77kg/cm^{-2}$. Based on the change in the configuration of rock-bridges, a factor called the Effective Joint Coefficient (EJC) was formulated, that is the ratio of the effective joint surface that is in front of the rock-bridge and the total shear surface. In general, the failure pattern is influenced by the EJC while shear strength is closely related to the failure pattern. It is observed that the propagation of wing tensile cracks or shear cracks depends on the EJC and the coalescence of wing cracks or shear cracks dominates the eventual failure pattern and determines the peak shear load of the rock specimens. So the EJC is a key factor to determine the sliding direction in rock slopes containing planar non-persistent open joints.

• Geomechanics and Engineering
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• v.19 no.1
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• pp.49-60
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• 2019

Crack instability propagation during coal and rock mass failure is the main reason for electromagnetic radiation (EMR) generation. However, original cracks on coal and rock mass are hard to study, making it complex to reveal EMR laws and mechanisms. In this paper, we prefabricated cracks of different inclinations in coal and rock samples as the analogues of the native cracks, carried out uniaxial compression experiments using these coal and rock samples, explored, the effects of the prefabricated cracks on EMR laws, and verified these laws by measuring the surface potential signals. The results show that prefabricated cracks are the main factor leading to the failure of coal and rock samples. When the inclination between the prefabricated crack and axial stress is smaller, the wing cracks occur first from the two tips of the prefabricated crack and expand to shear cracks or coplanar secondary cracks whose advance directions are coplanar or nearly coplanar with the prefabricated crack's direction. The sample failure is mainly due to the composited tensile and shear destructions of the wing cracks. When the inclination becomes bigger, the wing cracks appear at the early stage, extend to the direction of the maximum principal stress, and eventually run through both ends of the sample, resulting in the sample's tensile failure. The effect of prefabricated cracks of different inclinations on electromagnetic (EM) signals is different. For samples with prefabricated cracks of smaller inclination, EMR is mainly generated due to the variable motion of free charges generated due to crushing, friction, and slippage between the crack walls. For samples with larger inclination, EMR is generated due to friction and slippage in between the crack walls as well as the charge separation caused by tensile extension at the cracks' tips before sample failure. These conclusions are further verified by the surface potential distribution during the loading process.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.173-180
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• 2002

The specimens with three discontinuities have been tested in uniaxial compression. The geometry of discontinuities is changed by three different parameters: flaw inclination angle, continuity, and spacing. From the tips of the discontinuities wing and secondary cracks are observed. Wing cracks initially propagate curvilinear direction and follow loading direction after some distance from the tip of the discontinuities. Two different types of secondary cracks have been observed from the study: quasi-coplanar secondary cracks and oblique secondary cracks. From the test nine different types of coalescence are observed and they show a correlation with flaw angle and ligament angle. It is attempted to simulate the observed results by using FROCK(Fractured ROCK). FROCK is a code based on the hybridized DDM(Displacement Discontinuities Method) . It is shown that FROCK has quite potential of modeling of rock fracture processes.

• Journal of Aerospace System Engineering
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• v.17 no.5
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• pp.34-41
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• 2023

This paper applies the icing effect and wing rock uncertainty to small unmanned aerial vehicles (UAVs), which have recently attracted attention. Attitude control simulations were performed using various control methods. First, the selected platform, the Skywalker X8 UAV with blended wing-body (BWB) configuration, was linearized for both its baseline form, and a form with applied icing effects. Subsequently, using MATLAB SimulinkⓇ, simulations were conducted for roll and pitch attitude control of the baseline configuration and the configuration with icing effects, employing disturbance observer-based PID control, model reference adaptive control, and model predictive control. Furthermore, the study introduced wing rock uncertainty simultaneously with icing effects on the configured model-a combination not previously explored in existing research-and conducted simulations. The performance of each control Method was compared and analyzed.