Fault Surface Research Articles

Crack propagation and fatigue life estimation of spur gear with and without spalling failure

Spur gears are most commonly used to transmit power, and speed variation from one shaft to another shaft. Spalling more frequently occurs surface fault in the gears and sometimes it causes severe damage to the gear tooth. This paper focuses on the effect of spalling on the fatigue life of spur gear. The simulation study is conducted in two parts. In the first part, the Johnson-Cook Damage model is used for the spall generation on the tooth surface. After that, the spalling results are imported as input into the crack initiation /crack propagation model and calculated the rate of crack growth of fatigue crack is based on Paris law implemented in user-defined subroutine Abaqus software. User-defined subroutine code is also validated with the comparison of the numerical and experimental results available in the literature. Cracks with different initial lengths are placed in the deeper cavities of spalling and the crack propagation analysis is conducted using XFEM. The study is conducted for four different backup ratios with cracks of three different initial lengths. The fatigue crack growth life of spur gears is investigated using different crack lengths and backup ratios. Further, a comparison has been made between the fatigue life of a spur having a spalling fault with the fatigue life of spur gear that does not have spalling fault present on its surface. It has also been found in this study that spur gear having cracks originating from the spall region have a less fatigue life as compared to the spur gear without spalling. With the increase in backup ratio from 0.3 to 3.3, an exponential increase in fatigue life is observed. However, the fatigue life of spur gear without the presence of spalling fault has higher fatigue for all backup ratios.

Seismic source identification of the 9 November 2022 Mw 5.5 offshore Adriatic sea (Italy) earthquake from GNSS data and aftershock relocation

The fast individuation and modeling of faults responsible for large earthquakes are fundamental for understanding the evolution of potentially destructive seismic sequences. This is even more challenging in case of buried thrusts located in offshore areas, like those hosting the 9 November 2022 Ml 5.7 (Mw 5.5) and ML 5.2 earthquakes that nucleated along the Apennines compressional front, offshore the northern Adriatic Sea. Available on- and offshore (from hydrocarbon platforms) geodetic observations and seismological data provide robust constraints on the rupture of a 15 km long, ca. 24° SSW-dipping fault patch, consistent with seismic reflection data. Stress increase along unruptured portion of the activated thrust front suggests the potential activation of longer portions of the thrust with higher magnitude earthquake and larger surface faulting. This unpleasant scenario needs to be further investigated, also considering their tsunamigenic potential and possible impact on onshore and offshore human communities and infrastructures.

Estimation of the Hurst exponents of irregularly sampled subsurface fault geometries by the lifting scheme

SUMMARY Seismic fault surfaces have complex geometries over a broad-scale range. The Hurst exponent (H) is an important parameter characterizing the complexity of fault geometries. This exponent of seismic faults has only been estimated at outcrops and from surface traces of large earthquakes. This is because geometry data of subsurface faults usually have large uncertainties and many gaps. This study examined the applicability of the lifting scheme, which is one of the wavelet transform methods, to estimate H of irregularly sampled geometry of subsurface faults. We analysed the surface geometry of the subducting oceanic plate at the Nankai trough, Japan, which is part of the fault plane of interplate earthquakes. The geometries of the subducting plate were estimated along six survey lines by integrating seismic refraction and reflection surveys. Two-way traveltimes of reflected waves from the plate surface, which were measured from the reflection survey data, were converted to depth using the velocity structure estimated by refraction survey. The intervals between sampled points were irregular because the reflected waves were obscured or invisible in some places. The Hurst exponents were estimated from the scale dependence of the wavelet coefficients that were derived by the lifting scheme without interpolation. Analyses of the synthetic data simulating the irregularly sampled plate geometries indicated that the lifting scheme yields stable but largely biased estimates of H, especially for small H (<0.5). We introduced the empirical bias correction to achieve an unbiased estimation of the exponent. The analysis of plate geometry at the Nankai trough was conducted at narrow-scale ranges with consideration for the accuracy of velocity structures. We may conclude that H of five survey lines across the trough axis is > 0.8, and that of a line along trough is > 0.7. These estimated exponents had large uncertainties due to analyses at narrow-scale ranges, but were close to the estimates in studies of the surface traces of large earthquakes.

Strong-motion simulation for the 1944 Tonankai earthquake based on the statistical green’s function method and stochastic representation of complex source process

Precisely evaluating the source, path, and site terms in a broadband frequency range is indispensable for quantitatively predicting strong motions. We conducted a generalized spectral inversion of strong motion in Japan to delineate both the spectral amplitude and phase characteristics for statistical Green’s functions. To predict ground motion from future megathrust earthquakes, we also need to model a kinematic source with a stochastic representation of the slip and rupture velocities on the fault surface. In this fundamental study, we first reported the basic features of statistical Green’s functions used for summation. We then demonstrated the construction of a kinematic source with distinctive strong-motion-generation areas with spatially random slip and rupture velocity variations. After the summation of statistical Green’s functions following the constructed kinematic source, we found that the peak ground accelerations and peak ground velocities of synthetics for the Mw8.2 1944 Tonankai earthquake are in good agreement with those of the well-established empirical formula in Japan because the medians of the synthetic values are well within the average plus/minus one standard deviation of the formula. Based on the simulation results of conducted parametric studies, we observed relatively small but meaningful effects of random slip distribution, as well as relatively small effects of random rupture velocity perturbation. In conclusion, our implementation of the complex source model and the empirically obtained statistical Green’s function used as an element source can be a viable combination for broadband (0.1 to 20 Hz) strong-motion simulations, realistic in terms of the amplitude and duration, without any hybrid scheme.Graphical

A multiscale analysis of adjacent fault dislocation mechanism induced by tunnel excavation based on continuous-discrete coupling method

Tunnelling usually causes adjacent fault dislocation that further induces serious disasters and threats, such as earthquakes, while its physical mechanism is still not clear. In this paper, we establish a multiscale numerical model of tunnel excavation adjacent to a fault by a coupled continuous-discrete method. The discrete element method (DEM) is employed to simulate the meso-mechanical behaviours of the fault fracture zone, and the finite difference method (FDM) is used to describe the macrodynamic characteristics of the hanging wall and footwall. A synthetic rock mass (SRM) model is developed to build the fractured rock to present the discontinuity and heterogeneity of the fault zone. The macro and meso mechanism of fault dislocation induced by tunnel excavation are analyzed, respectively. Results show that the fault experiences a different local dislocation form changing from upward movement to downward movement along the fault surface at the macro-scale. The weak transfer ability of the fault for deformation between the hanging wall and footwall, the reduced macro shear strength of the fault during the unloading process, and the meso joint slip and intact rock failure in the fault fracture zone are three main reasons for fault dislocation. The random distribution characteristics of the joints have remarkable influence on fault deformation. The fault slips more easily when the joint dip is close to the fault orientation. A higher joint density and a larger joint length provide a favourable environment to accumulate more connected joint surface, resulting in a larger slip displacement. Sensitivity analyses are conducted on several critical parameters including tunnel location, fault thickness, and stress condition, with the purpose of evaluating the safety of a potential tunnel site and predicting the potential seismic risks when tunnelling adjacent to a fault.

Numerical simulation study on the spontaneous rupture process and its influencing factors of the 2001 MS 8.1 Kunlun earthquake in China

On November 14, 2001, the MS 8.1 Kunlun earthquake occurred in the west of Kunlun Mountain pass in the East Kunlun fault zone of the Qinghai-Tibet Plateau, China. The field investigation and the results of kinematic inversion indicate that it is a strike-slip earthquake with a complex rupture process. The study of the spontaneous rupture process of this earthquake and its influencing factors is of great significance for understanding the occurrence mechanism of continental large earthquakes. First, based on the results of geological survey and kinematic inversion, a three-dimensional non-planar fault model is established. Then, using the curved-grid finite difference method (CG-FDM), the dynamic rupture process of the 2001 MS 8.1 Kunlun earthquake is numerically reproduced by adjusting the parameters for numerical simulation experiments. On this basis, the influence of background stress field, fault geometry and friction coefficient on the surface slip distribution, seismic moment rate function and rupture velocity are discussed respectively. The results show that the important reasons for the super-long rupture scale and super-shear rupture velocity of this earthquake may be the clockwise rotation of the maximum horizontal principal compressive stress along the NNE ∼ NE direction and the low friction coefficient distribution on the whole fault surface. The difference between the dynamic and static friction coefficients along the fault strike may be non-uniform, and it may be larger on the main fault than that on the secondary fault. This will result in a higher level of stress drop on the main fault, leading to the occurrence of super-shear rupture and the slip distribution with the Kusai Lake as the macroseismic epicenter. The large local geometric variation along the strike of the main fault may also have some influence on the distribution of co-seismic slip and the location of the super-shear rupture. In addition, the numerical simulation results in this paper confirm the conclusion that the East Kunlun fault zone has low friction coefficient.

Gravity and magnetic models at Rangitoto Volcano, Auckland Volcanic Field, New Zealand: Implications for basement control on magma ascent

In small-volume volcanism, pre-existing crustal structures can influence magma ascent processes. Rangitoto volcano in the Auckland Volcanic Field, New Zealand, provides a possible example of magma-structure interaction as this volcano was emplaced adjacent to an outcrop of a regional-scale basement fault, the Islington Bay Fault. In this study, we evaluated the magmatic plumbing system of Rangitoto using gravity and magnetic data acquired over the volcano and the adjacent, non-volcanic Motutapu Island. We modelled the Rangitoto internal architecture and magma plumbing using 2.5D forward and 3D inverse modelling methods. Both models are constrained by petrophysical data, while drill hole logs are only used to constrain the 2.5D model. Our model endmembers suggest that parallel magma pathways are present below the Rangitoto summit cones. In 3D magnetic models, this is evidenced by a fault-aligned pair of high-susceptibility bodies. Interpreting our models in conjunction with previously published geological and geophysical models allows us to hypothesise that the fault-parallel alignment of Rangitoto magma pathways reflects the primary influence of the Islington Bay Fault over the Rangitoto magma ascent. Magma diversion at shallow levels by other finer structures intersecting and adjacent to the fault could explain why Rangitoto erupted 3.5 km west of the Islington Bay Fault surface trace.

Seismic displacement prediction methods, procedure, comparison and application

The methodology in the seismic design of slopes has evolved with technological advancement and the development of geotechnical engineering. Since methods with great limitations such as pseudo-static analysis to rigorous methods that require a lot of information for a better understanding of the behavior of the soil such as the dynamic analysis.
 This article develops the procedure, comparison, and application of methods for estimating seismic displacements, which are the Newmark (1965), Sarma (1975), Makdisi & Seed (1978) and Bray, Macedo & Travasarou (2018). Each of these methods considering the criteria of each one to obtain permanent displacements, such as yield acceleration, degraded period, spectral acceleration, magnitude, etc.
 As an applicative case, a rockfill dam and core central 50 m high placed in sandstone strata and moraine deposits interspersed with shale intrusions is shown, as seismic scenarios the Lima 1974 earthquake, the Attic 2001 earthquake and the earthquake were used. of Pisco 2007, considering both NS and EW directions. Likewise, the response spectrum on the base of the failure surface, resulting from a nonlinear seismic response analysis from 3 columns in the dam, is considered as information. The methods of Newmark (1965), Sarma (1975), Makdisi & Seed (1978), and Bray, Macedo & Travasarou (2018) were applied, obtaining deformation results between 1 to 30 cm that according to their order of magnitude represent a stable condition for the dam.

RETRACTED ARTICLE: Method of surface defect detection for agricultural machinery parts based on image recognition technology

At present, the large use of agricultural machinery for agricultural production has increased the efficiency of agricultural production, thus greatly improving the speed of agricultural production, and also greatly increasing the demand for agricultural machinery. Under the current market scenario, the surface quality of agricultural machinery will have a certain degree of impact on its grade pricing and competitiveness. To find product surface defects in the process of product quality control, product surface fault detection is very important in the process of product quality control. Traditional surface defects are mainly detected manually, which will lead to low efficiency and error prone. In order to solve and find the problems of surface defects and low accuracy of agricultural machinery, this paper proposes a method of inspection of surface micro defects based on image recognition technology. Canny operator is used to extract the weakness of the fault edge, and the algorithm of corrosion function is used to remove the relatively small structural elements in the image, so that the boundary becomes part of the internal contraction, complete the filling of the specified holes, connect the two points that meet the set value, on the other side, the integrity of the second image edge is defective, and complete the identification and detection of the defect section according to the defect type, Complete defect edge images can be obtained by adjusting characteristic defect behavior parameters, so as to complete defect category identification and inspection. In the simulation experiment, the proposed method can accurately detect various small defects of parts, and produce appropriate detection results.

Using InSight Data to Calibrate Seismicity From Remote Observations of Surface Faulting

AbstractWe use a scaling relationship between fault length and scalar moment to predict seismicity from the Cerberus Fossae graben using shear modulus and fault lengths. Cerberus Fossae is 20–40° (1,200–2,300 km) from the InSight lander and matches the location of 21 recorded seismic events withMw ≥ 3. These unique seismic observations make an ideal laboratory to test our method of predicting seismicity on another planet using surface fault observations. Terrestrial faults have observed patterns of rupture depth distributions and segmentation. We use these patterns and magnitudes of detected marsquakes to predict moment release of events in Cerberus Fossae over a range of plausible Martian rupture vertical slip extents (VSEs) of 2, 20, and 40 km, which are rooted in estimates of crustal thickness, elastic thickness, and seismicity depth. We sum individual events for each case to determine cumulative moment release and use deformation duration to determine annual moment release. Predicted seismicity rates are dependent on the duration of deformation, which in this case is well constrained to 2–10 Ma. We compare our results to events recorded at Cerberus Fossae by InSight and find that seismicity rates for the cases with a 40 km maximum VSE or no limit on VSE are within an order of magnitude of observed seismicity. Faults with maximum VSEs of 2 km best match observed magnitudes. Our approach, using only observed fault lengths, segmentation, seismogenic thickness estimates, and deformation duration, produces seismicity estimates that are as accurate as methods that take rupture offset into account.

A Mixed‐Flux‐Based Nodal Discontinuous Galerkin Method for 3D Dynamic Rupture Modeling

AbstractNumerical simulation of rupture dynamics provides critical insights for understanding earthquake physics, while the complex geometry and heterogeneous material properties of natural faults make numerical method development challenging. The discontinuous Galerkin (DG) method is suitable for handling these complexities. In the DG method, the fault boundary conditions can be conveniently imposed through the upwind flux by solving a Riemann problem based on a velocity‐strain elastodynamic equation. However, the universal adoption of upwind flux can cause spatial oscillations in cases where elements on adjacent sides of the fault surface are not nearly symmetric. Here we propose a nodal DG method with an upwind/central mixed‐flux scheme to solve the spatial oscillation problem and thus reduce the dependence on mesh quality. Our method can achieve high scalability in parallel computing under different orders of accuracy. We verify the new method by comparing simulation results with those from other methods on a series of published benchmark problems with complex fault geometries, heterogeneous materials, off‐fault plasticity, roughness, thermal pressurization, and various versions of fault friction laws. Finally, we demonstrate that our method can be applied to simulate the dynamic rupture process of the 2008 Mw 7.9 Wenchuan earthquake along realistic fault geometry, including branches, step‐overs and a previously neglected sub‐parallel fault segment, offering a high potential to systematically explore the influences of fault zone properties on earthquake rupture dynamics.

Likelihood of Primary Surface Faulting: Updating of Empirical Regressions

Abstract Surface faulting is a common phenomenon for crustal earthquakes and is an important source of localized hazard to buildings and infrastructure. Nevertheless, not all earthquakes of a given magnitude generate surface faulting. To correctly assess the hazard posed by surface fault displacement, it is critical to use reliable regressions of the likelihood of surface faulting. Such regressions are derived from empirical data and the ones currently used in engineering practice are based on datasets acquired several years ago. The aim of this work is to update the regressions characterizing the likelihood of primary surface faulting (i.e., P(Slip|m)). We systematically analyze Mw≥5.5 earthquakes that occurred in 1992–2018, with hypocentral depths lower than 20 km and epicenter onshore. We obtain information on the occurrence or non-occurrence of primary surface faulting for 363 earthquakes (87 with primary surface faulting and 276 without). We derive empirical regressions of P(Slip|m) from the entire dataset as well as for normal, strike-slip, and reverse earthquakes, and discuss the potential sources of aleatory and epistemic uncertainty. A sensitivity analysis shows that the P(Slip|m) term has a significant impact on the hazard curve expressed as the annual frequency of exceeding a given displacement value. We argue that the regressions presented in this work can be incorporated in models for probabilistic fault displacement hazard assessment, ultimately providing a better evaluation of the hazard.

Training the creation, visualization and interpretation of fault maps for the subsurface – using tectonic geomorphology

Abstract Fault mapping is essential for understanding subsurface geological structure. However, effective training of students in developing and understanding fault patterns in 3D seismic imagery is impeded by the time-investment needed to acquire competence using software and then creating depth-structure maps of stratal horizons. Here an exercise is laid out that can achieve the desired experience – using the young fault systems of Afar (Djibouti), where former land-surface-defining basalt flows are offset by arrays of normal faults. The top-basalt surface, displayed on GoogleEarth, is in effect a depth-structure map and the gaps (‘fault-loss’) in this surface approximate to exposed fault surfaces. The mapping exercise is described and illustrated here step-wise. The fault system is gradually mapped out to reveal examples of long-continuous faults, branching patterns, relaying faults and isolated fault segments. Alternative criteria for identifying faults can be examined, with analogies in seismic interpretation. This can inform discussion of the approaches and uncertainties inherent in mapping faults in the subsurface. The study may be extended to consider the pattern of early–syn-rift depositional systems. Collectively these tasks can be progressed within an hour or so, providing effective insights into the structure of normal fault systems that cannot be replicated by conventional fieldwork.

Carbonates and intermediate-depth seismicity: Stable and unstable shear in altered subducting plates and overlying mantle

A model for intermediate-depth earthquakes of subduction zones is evaluated based on shear localization, shear heating, and runaway creep within thin carbonate layers in an altered downgoing oceanic plate and the overlying mantle wedge. Thermal shear instabilities in carbonate lenses add to potential mechanisms for intermediate-depth seismicity, which are based on serpentine dehydration and embrittlement of altered slabs or viscous shear instabilities in narrow fine-grained olivine shear zones. Peridotites in subducting plates and the overlying mantle wedge may be altered by reactions with CO2-bearing fluids sourced from seawater or the deep mantle, to form carbonate minerals, in addition to hydrous silicates. Effective viscosities of magnesian carbonates are higher than those for antigorite serpentine and they are markedly lower than those for H2O-saturated olivine. However, magnesian carbonates may extend to greater mantle depths than hydrous silicates at temperatures and pressures of subduction zones. Strain rates within altered downgoing mantle peridotites may be localized within carbonated layers following slab dehydration. A simple model of shear heating and temperature-sensitive creep of carbonate horizons, based on experimentally determined creep laws, predicts conditions of stable and unstable shear with strain rates up to 10/s, comparable to seismic velocities of frictional fault surfaces. Applied to intermediate-depth earthquakes of the Tonga subduction zone and the double Wadati-Benioff zone of NE Japan, this mechanism provides an alternative to the generation of earthquakes by dehydration embrittlement, beyond the stability of antigorite serpentine in subduction zones.

Numerical investigation of progressive damage and associated seismicity on a laboratory fault

Understanding rock shear failure behavior is crucial to gain insights into slip-related geohazards such as rock avalanches, landslides, and earthquakes. However, descriptions of the progressive damage on the shear surface are still incomplete or ambiguous. In this study, we use the hybrid finite-discrete element method (FDEM) to simulate a shear experiment and obtain a detailed comprehension of shear induced progressive damage and the associated seismic activity. We built a laboratory fault model from high resolution surface scans and micro-CT imaging. Our results show that under quasi-static shear loading, the fault surface experiences local dynamic seismic activities. We found that the seismic activity is related to the stress concentration on interlocking asperities. This interlocking behavior (i) causes stress concentration at the region of contact that could reach the compressive strength, and (ii) produces tensile stress up to the tensile strength in the region adjacent to the contact area. Thus, different failure mechanisms and damage patterns including crushing and sub-vertical fracturing are observed on the rough surface. Asperity failure creates rapid local slips resulting in significant stress perturbations that alter the overall stress condition and may trigger the slip of adjacent critically stressed asperities. We found that the spatial distribution of the damaged asperities and the seismic activity is highly heterogeneous; regions with intense asperity interactions formed gouge material, while others exhibit minimal to no damage. These results emphasize the important role of surface roughness in controlling the overall shear behavior and the local dynamic seismic activities on faults.

Study on the Effect of Small Faults on the Gas Content in No. 3 Coal Seam of the Changping Mine Field.

To study the influence of small faults on the gas content of Coal Seam 3# in the Changping mine field, the influence scope and degree of small faults on Coal Seam 3# and gas content in the Changping mine field are analyzed based on the field measured data such as the gas content on both sides of the fault, the initial speed of gas emission, and the solidity coefficient of the coal seam, combined with the FLAC3D stress simulation results, and the influence area of small faults is zoned from the perspective of gas control. The analysis results show that the measured gas content in the hanging wall of SF250 fault with a drop of 1.3 m and SF353 fault with a drop of 1.9 m is 7.14 and 9.47 m3/t, respectively, and the gas content in the footwall is 5.29 and 7.41 m3/t, respectively. The gas content in the hanging wall is obviously higher than that in the footwall; the gas content in the coal seam near the small fault surface is slightly lower. With the increase of the distance from the fault surface, the gas content in the coal seam decreases first and then increases; the firmness coefficients of hanging wall coal of small fault are 0.40 and 0.45, respectively, and those of footwall coal are 0.73 and 0.75, respectively. The firmness coefficient of hanging wall coal seam is obviously smaller than that of footwall coal seam. The closer it is to the fault surface, the smaller the firmness coefficient of coal is, and the greater the initial gas release speed is; the permeability coefficient of the coal seam far from the fault surface in the hangingwall of the small fault shows a decreasing trend after an increasing trend. The maximum stress of the coal seam is 21.85 MPa at 14 m from the hangingwall of the fault to the fault, and the minimum stress of the coal seam is 2.79 MPa at 1 m from the footwall of the fault to the fault. The stress of the hangingwall of the fault is greater than that of the footwall of the fault, and the stress concentration area is 14 m from the hangingwall of the fault to the fault.

Substantial Upper Plate Faulting Above a Shallow Subduction Megathrust Earthquake: Mechanics and Implications of the Surface Faulting During the 2016 Kaikoura, New Zealand, Earthquake

AbstractThe 2016 moment magnitude 7.8 Kaikoura, New Zealand, earthquake occurred at the southern end of the Hikurangi subduction zone where the upper plate above the shallow megathrust is exposed sub‐aerially. As a result, the substantial co‐seismic deformation in the upper plate above the megathrust rupture was observed geologically and geodetically. We explore the relationship between this surface faulting and the subduction megathrust rupture and find that the greatest upper plate fault slip occurred coincident (in time and location) with the megathrust rupture. Models of Coulomb stress change demonstrate that these surface faults become positively loaded as the upper plate rebounds during the megathrust event, favoring fault slip. In addition, during the megathrust rupture these faults terminate against an uncoupled subduction plate interface. We simulate the effects of decoupling at the base of these faults and find that very large fault slip is an expected consequence of this decoupling, allowing near‐complete strain release. In contrast, typical strike‐slip faults, pinned at their base, would have lower amounts of fault slip. These two conditions—increased Coulomb stress and basal decoupling—combine to produce the extreme co‐seismic upper plate faulting observed above the shallow Kaikoura megathrust earthquake. Similar conditions occur in other global subduction zones, but in most subduction zones the region above the coupled megathrust is underwater and poorly observed. Our analysis of the Kaikoura earthquake indicates a need to reevaluate patterns of strain accumulation and release in these regions, rather than assuming simple models of elastic rebound.

Depth prediction by using various velocity models of Khasib Reservoir in East Baghdad field, Iraq

In this study, the variance seismic attribute was used to track fault geomorphology, which interpreted in time. To convert these fault surfaces and isochron maps to depth, the velocity model was prepared. Therefore, 14 velocity models for depth conversion were built by using different equations in East Baghdad Field, central Iraq to depth conversion assessment and select a precise model from many candidates of velocity models to generate an accurate depth map. All the velocity models are divided into two main velocity layers. The upper-velocity layer represents the tertiary sequences, while the lower-velocity layer represents the Upper Cretaceous sequences. Three criteria are made in this study (mis-tie value, standard deviation analysis, and blind well test) to select the best depth map. The results reveal the velocity model-7 is better to use because the depth map of the Khasib Reservoir, which produced from model-7 shows less mis-tie between estimated and real depth, less standard deviation values, and lower errors at EB 24 and 26 well locations. The corrected depth map of Khasib Reservoir shows three structure noses. Two of them opened toward the NW direction, while the southern structural nose opened toward the SW direction with a minor enclosure.

Reconfiguration control allocation of actuator faults for tailless aircraft with low aspect ratio

The triaxial attitude control of the tailless aircraft depends heavily on the effectiveness of the actuators. Still, the actuators have redundancy characteristics, cross-coupling of rudder effect, and so on. Therefore, the reconfigurable control allocation of the tailless aircraft under typical actuator faults is deeply studied in this paper. The effectiveness and rationality of the incremental control allocation method based on quadratic programming are thoroughly verified for application to maximize the residual control ability of the aircraft, ensure that the aircraft can still complete the flight mission typically, and guarantee flight safety. According to the research principle of surface failures from slight to severe, three typical rudder surface faults are designed successively: Efficiency loss of single actuator, single actuator stuckness, and double actuators combined stuckness. On this basis, the mechanism of reconfiguration allocation after actuator failures is studied, and the residual control ability of the actuator after loss is fully explored. What’s more, the range of allowable reduction of efficiency of each actuator and the acceptable stuck angle range of each actuator are explored, and the most severe failure in the combination of double actuators stuck is obtained. The attitude controller is designed with incremental backstepping (IBKS). The reconstruction allocation adopts a quadratic programming allocation method based on an effective set solver, which can be seamlessly connected with the IBKS method to improve the control accuracy and disturbance immunity effectively.

Magnetic fabric analyses of basin inversion: a sandbox modelling approach

Abstract. A magnetic fabric analysis is a useful tool to display deformation in nature and in models. In this study, three sandbox models represent basin inversion above a velocity discontinuity (base plate). After complete deformation of each model, samples were taken in different parts of the models (along faults and areas away from faults) for magnetic fabric analysis. Model I, which simulates basin formation during extension, shows two kinds of magnetic fabric: an “undeformed”/initial fabric in areas away from faults and a normal fault-induced fabric with a magnetic foliation that tends to align with the fault surface. Models II and III were extended to the same stage as Model I but were subsequently shortened/inverted by 1.5 cm (Model II) and 4 cm (Model III). Both inverted models developed “thrusts” during inversion. The thrusts show an alignment of magnetic foliation parallel to the fault surfaces that depends on the maturity of the thrust. Our results highlight that thrusting is more efficient in aligning the magnetic fabric along them compared to normal faults. Moreover, models II and III reveal a magnetic fabric overprint towards a penetrative strain-induced fabric (magnetic lineation perpendicular to shortening direction) with increasing strain in areas away from thrusts. Such overprint shows a gradual transition of a magnetic fabric to a penetrative strain-induced fabric and further into a thrust-induced fabric during shortening/inversion. In contrast, extension (Model I) developed distinct magnetic fabrics without gradual overprint. In addition, pre-existing normal faults are also overprinted to a penetrative strain-induced fabric during model inversion. They define weak zones within the main pop-up imbricate and steepen during model inversion. Steepening influences the magnetic fabric at the faults and, in general, the strain propagation through the model during inversion. The magnetic fabric extracted from the models presented here reflect the different stages of basin development and inversion. This study is a first attempt of applying magnetic fabric analyses on models simulating inverted basins. This study illustrates the possibility of applying a robust tool, i.e. magnetic fabric analyses, to sandbox models, whose initial, intermediate, and final stages are well documented, to understand fabric development in inverted tectonic regimes.