Exploring the gravity-driven failure of a cohesive granular column.

Fault growth and rupture history based on displacement distribution along the Luoshan Fault, NW China

In the development of adhesives, an understanding of the fracture behavior of the bonded joints is inevitable. Two typical failure modes are known: adhesive failure and cohesive failure. However, a molecular understanding of the cohesive failure process is not as advanced as that of the adhesive failure process. In this study, research was developed to establish a molecular understanding of cohesive failure using the example of a system in which epoxy resin is bonded to a hydroxyl-terminated self-assembled monolayer (SAM) surface. Adhesive failure was modeled as a process in which an epoxy molecule is pulled away from the SAM surface. Cohesive failure, on the other hand, was modeled as the process of an epoxy molecule separating from another epoxy molecule on the SAM surface or breaking of a covalent bond within the epoxy resin. The results of the simulations based on the models described above showed that the results of the calculations using the model of cohesive failure based on the breakdown of intermolecular interactions agreed well with the experimental results in the literature. Therefore, it was suggested that the cohesive failure of epoxy resin adhesives is most likely due to the breakdown of intermolecular interactions between adhesive molecules. We further analyzed the interactions at the adhesive failure and cohesive failure interfaces and found that the interactions at the cohesive failure interface are mainly accounted for by dispersion forces, whereas the interactions at the adhesive failure interface involve not only dispersion forces but also various chemical interactions, including hydrogen bonds. The selectivity between adhesive failure and cohesive failure was explained by the fact that varying the functional group density affected the chemical interactions but not the dispersion forces.

The research quantitatively explores the linking properties between the circular plate anchor and the granular assembly during the failure process under the subject of a specified pullout force given to the anchor using three-dimensional discrete particle simulations. This circular anchor is created as a hard cluster of spherical grains and is initially buried at a depth in the granular assembly. The numerical method is constructed based on the frictional interaction force law. The linking dynamic is characterized by the variation of the drag force acting on such anchor due to interaction with grains at the bottom of the frustum which is formed during the uplifting movement of the anchor. The results show that the drag force acting on the anchor first reaches a nearly constant value corresponding to the loading phenomenon at small anchor movement, reflecting the plastic deformation of granular bed as a result of particle rearrangement, and then fluctuates in a wide range, this range increases with increasing the anchor movement as a result of the unloading/reloading events. These loading/unloading/reloading events provide evidence for the linking properties between the anchor movement and granular assembly, which are highlighted by the density and intensity of force network within the frustum.

Geophysical granular flows, involving rapidly flowing granular materials, can exhibit volume‐enhanced mobility. Lacking a mechanistic understanding of such size effects limits the applications of lab‐scale findings to natural events. Using discrete element method simulations, we find that increasing granular system size suppresses energy‐dissipating velocity fluctuations while promoting sustained creeping motion. This nonlocal phenomenon of granular materials enhances the mobility in various granular column collapse scenarios. This mechanism is reflected in the rheological data, which deviate from traditional rheology but are collapsed under a recent power‐law rheology that incorporates velocity fluctuations. Moreover, this size‐dependent power‐law rheology exhibits universality in transient simulations with varied flow geometries, slope angles, and base roughness. This rheologically consistent framework, spanning inertial to quasi‐static states, bridges small‐scale investigations and continuum models for large‐scale simulations, enabling improved predictive capability of the entire flow processes, from initiation to deposition, in natural geophysical flows.

With the growing stress on today's power system, it is operated much closer to its stability limit. Under such circumstances it is highly desirable that one must be able to assess the security and stability of the electric power system when exposed to disturbances/faults. In the post-fault transient analysis of interconnected systems, the transient energy margin which is a complex function of prefault system conditions, structure of fault (type and location) and network topology at the specified fault clearing time gives a quantitative idea about the stability of the system. High adaptation capabilities of artificial neural networks make them capable of synthesizing the complex mapping that transform the input features in to a single-valued space of energy margin. Appropriate input feature selection has a direct bearing on the consistency and accuracy of mapping. This issue has been addressed in the present paper by comparing the prediction results based on approaches (Sobajic and Pao, 1989), (Sobajic and Pao 1992), (Jeyasurya, 1993) in the time domain, energy domain and its corresponding time domain calibration. Subsequent to the above comparison, the much haunting question of whether to train the network in the energy or time domain has been answered satisfactorily. It has been observed that fault clearing time is a key parameter that anticipates the success of possible calibration of energy margin results into the time domain. Test cases for prediction have been collected from many different operating conditions in power systems. Multilayer perceptron model with ADAPTIVE LEARNING ALGORITHM is used to carry out the present studies.

We examine stationary regimes in granular materials from a dynamical systems theory perspective. The aim is to enrich the classical view of the critical state regime in granular materials, and more broadly, to improve the fundamental understanding of the underlying mesoscale mechanisms responsible for macroscopic stationary states in complex systems. This study is based on a series of discrete element method simulations, in which two-dimensional assemblies of nonuniformly sized circular particles are subjected to biaxial compression under constant lateral confining pressure. The lifespan and life expectancy of specific cluster conformations, comprising particles in force chains and grain loops, are tracked and quantified. Results suggest that these conformational clusters reorganize at similar rates in the critical state regime, depending on strain magnitudes and confining pressure levels. We quantified this rate of reorganization and found that the material memory rapidly fades, with an entirely new generation of force chains and grain loops replacing the old within a few percent strain.

Active normal faults in the Central Apennines accommodate ongoing crustal extension and have generated significant earthquakes (up to Mw ~7) during historical and instrumental times. However, several fault systems, including the Gran Sasso fault system (GSFS), lack documented surface-rupturing earthquakes, raising questions about their structural maturity, role in accommodating the extension in this region, and their potential to generate future large-magnitude events.Here, we investigate the relationship between fault geometry, cumulative displacement, and slip rate along the Gran Sasso fault system located 19km north of L’Aquila, a system consisting of two major normal faults with an overall length of ~46 km. These include(i) the Campo Imperatore fault, consisting of two segments measuring roughly 20 km and 8 km, and (ii) the Assergi fault, which extends about 18 km along the western flank of the Gran Sasso massif. Both faults exhibit a consistent average W-E orientation with secondary structure tending WNW-ESE. Our aim is to assess the structural maturity and seismic significance of the GSFS within the broader Apennine fault network.Using high-resolution Pleiades satellite imagery combined with existing geological maps and field observation, we mapped in detail the active fault trace and identified displaced geomorphic markers. The analysis focuses on two main fault segments, the Campo Imperatore and Assergi segments, along which a well-preserved Holocene fault scarp is continuously expressed. Scarp height was measured accurately along strike using several complementary approaches, including field-based observations, topographic profiles extracted from high-resolution DEMs, and the automated ScarpLearn algorithm (Pousse et al., 2022), which identifies and quantifies fault scarp morphology together with associated uncertainties. Preliminary results indicate that vertical displacement varies between ~2 and 16 m, locally reaching up to ~20 m along the Campo Imperatore segment. These results are analyzed in relation to fault architecture to assess how geometric complexities, such as relay zones and step-overs, influence displacement distribution along strikeField investigations and detailed mapping along the Campo Imperatore fault allowed the identification of three key sites where fluvial terraces and glacial moraines are displaced and can be used as geomorphic markers of fault slip. Samples were collected for ^36Cl cosmogenic exposure dating of these surfaces. When combined with measured offsets, these exposure ages provide constraints on average late Quaternary slip rates and on the long-term activity of the fault, under the assumption that the dated surfaces record cumulative displacement since their abandonment.

an extended CFD-DEM model based on micropolar fluid and its application in geological engineering

SummaryThree‐dimensional Discrete Element Method simulations have been performed to study the deformation of cross‐anisotropic granular materials under principal stress rotation (PSR), for rotation planes oriented at different angles θ with respect to the bedding plane. The simulations have been conducted with a novel technique for applying specified stresses at three‐dimensional boundaries. The results are qualitatively in agreement with experimental results from literature. Cumulative volume contraction is always observed under continuous PSR and increases with increasing θ. The dilatancy rate decreases with increasing number of PSR cycles, tending to zero. The noncoaxiality angle between the strain increment and the stress in the PSR plane increases with increasing number of cycles, reaching the same asymptotic value for samples of various densities and for various θ. Periodic oscillations of the dilatancy rate and noncoaxiality angle within each PSR cycle are observed with an increasing oscillation magnitude with increasing θ, due to the larger fabric anisotropy within the PSR plane. When θ = 30 or 60°, significant noncoaxial strain accumulation occurs in the plane perpendicular to the PSR plane due to the oblique angle between the PSR plane and the bedding plane, echoing the major principal fabric direction's being neither parallel nor perpendicular to the PSR plane. The macroscopic behavior of the samples is related to the microscopic parameters including coordination number and fabric anisotropy. With increasing number of cycles, the difference between normalized stress/strain/fabric increment tensors tends to become constant, with only a small lag between each pair, irrespective of θ.

In this paper, the application of Discontinuous Deformation Analysis (DDA), a powerful numerical method, to the simulation of rock mass failure problems has been discussed. It has been shown that the failure along discontinuous surfaces can be easily simulated by use of the method based on the Mohr-Coulomb failure criterion. For the failure (separation) of an individual block, we suggest that dense artificial meshes are made within the block, and the same strengths of the block itself are assigned to the cohesion, friction and tensile parameters of the artificial discontinuous surfaces. Then, the same algorithm as for the general discontinuities can be adopted.The new approach has been successfully applied to the simulation of a huge rock collapse at Toyohama tunnel, a very sad accident happened in Hokkaido in Feb., 1996. The collapse picture obtained from the simulation is quite in agreement with that from the spot. It is the first time that the progressive failure processes of the event are re-shown in detail. We believe that the simulation is very helpful on investigation of the failure mechanism and process, which can provide useful knowledge for preventing such kind of events in future.

Experimental investigation in extinction of turbulent non-premixed disk stabilized flames

Purpose of the work. The purpose of this work is to study a nonlinear correction device for an automatic control system for a DC electric drive, which provides an approach to the optimal operating mode according to the criterion of speed and accuracy, while simultaneously determining the stability conditions and limits of the system's performance. Research methods. The work uses mathematical modeling, the theory of optimal control based on the minimax principle, the harmonic linearization method for stability analysis, as well as numerical methods to determine the optimal parameters of the phase-leading link. Structural diagrams of DC electric drives and models with relay characteristics were used, which made it possible to study the influence of nonlinear correction on the dynamic properties of the system. Results. In the process of research, a structural diagram of a DC electric drive with a nonlinear regulator, including a phase-leading link and relay elements, was constructed. A method for approximating the optimal control law using the minimax principle is proposed, which ensures minimization of deviations from the optimal regime in a wide range of input amplitudes. Dependencies between the parameters of the phase-leading link and the magnitude of the system error deviation are established, which made it possible to formulate criteria for selecting its time constants. Analytical expressions for estimating the signal switching moment are obtained, the normalized relations between the amplitude and the switching time are constructed, which determine the quality of the control process. It is shown that the proposed nonlinear corrector allows to reduce the time of the transient process and reduce the error magnitude without a significant increase in overshoot. The analysis of the system stability using the harmonic linearization method made it possible to determine the critical values of the gain coefficients and self-oscillation frequencies. It is established that the presence of a nonlinear corrector significantly affects the dynamic characteristics and at the same time narrows the limits of stability. The constructed graphs of the critical gain and self-oscillation frequency depending on the nonlinear link parameter allowed us to determine clearly the areas of stable and unstable operation of the DC electric drive. Thus, the results confirm that the use of a nonlinear correction device provides an increase in the system speed and a decrease in the error, but requires consideration of a compromise between the quality of regulation and the margin of stability. Scientific novelty. The work substantiates a new approach to the synthesis of DC electric drive control systems based on nonlinear dynamic correction. The application of the minimax principle for approximating the optimal control law is proposed and its effectiveness in a wide range of input influences is shown. For the first time, a comprehensive analysis of the relationship between the parameters of the nonlinear link and the system stability limits is carried out. Practical value. The results of the work can be used in the design of electric drives operating in modes with high requirements for speed and regulation accuracy. The proposed approaches contribute to the creation of more effective control algorithms that take into account the trade-off between speed, accuracy, and system stability.

Comparison between inductive and resistive SFCL in terms of current limitation and power system transient stability

Accurately capturing internal crack evolution and deformation is essential for understanding rock failure and improving disaster prediction. However, traditional methods mainly focus on surface cracks and struggle to reveal the spatial characteristics of crack propagation, limiting insights into rock damage mechanisms. This study proposes a framework for automatically and visually characterizing crack behavior and deformation evolution by integrating in-situ X-ray computed tomography (XCT), deep learning, and digital volume correlation (DVC) techniques to address this limitation. This framework enhances crack identification accuracy and internal deformation field analysis. First, in-situ XCT scanning experiments were conducted to dynamically capture the crack propagation process in sandstone samples with an initial single defect. Next, a U-Net-based image segmentation approach was employed to improve crack extraction accuracy from CT images, enabling precise characterization of internal crack behavior. Finally, DVC technology was utilized to compute three-dimensional (3D) full-field displacement and strain distributions, facilitating the visualization and quantitative analysis of internal rock deformation mechanisms. The results indicate that the displacement difference between monitoring points on both sides of a crack enables the quantitative classification of crack types. Crack behavior in sandstone generally exhibits a mixed combination of opening, shearing, and tearing modes. Moreover, the heterogeneous displacement field distribution within the sandstone influences spatial variations in crack behavior. After crack formation, the internal strain field exhibits significant localization, which largely governs the sample’s failure process. The distribution characteristics of the ε yy and ε xy strain fields closely correspond to the internal crack morphology, demonstrating that their evolution effectively characterizes the internal rock damage process.

In February 1998 a new and unique form of power generator, the Powerformer TM , was introduced into the marketplace. The Powerformer can be operated at transmission system level voltage without the need for a step up transformer and consequently has unique system support capabilities. The aim of the research work, presented in this thesis, was to investigate the unique aspects of the Powerformer from a power system perspective, in order to facilitate optimal power system operation and security.The main focus of the research undertaken by the author of this thesis was to investigate the impact of Powerformer on the relative voltage stability of a power system. The driving force behind the author's desire to look at the impact of the Powerformer on power system voltage stability and security was the realisation that voltage stability issues are becoming increasingly important. The focus for today's modem power transmission systems is undergoing a radical shift from a purely publicly provided service to a financially driven commodity. This ultimately means that power systems are increasingly under pressure to be utilised to their fullest capacity without the need to install new, expensive and sometimes socially unpopular system equipment and facilities. The problem with this situation is that a system's stability can be affected greatly by loading conditions. When a system is heavily loaded the voltage stability limit, rather than the transient angle stability limit constrains its operation. It is for this reason that voltage stability concerns in particular are increasingly being discussed in the literature and becoming an issue for power system operators. A number of different static and dynamic system analysis techniques have been reviewed and compared in this thesis, with the results of these comparisons presented and discussed in this thesis. Amongst the methods discussed in this thesis, methods for use in voltage stability analysis and assessment have been proposed and presented by the author of this thesis. The most suitable techniques are being utilised to determine how the Powerformer can aid in safe system operation under a number of different system contingencies in a number of different test systems, including the 600+ bus Queensland Transmission System. Particular emphasis has been placed in this research on long-term system dynamics. Two major aspects of the Powerformer that differ it from conventional are the lack of a step up transformer and the ability of the Powerformer stator to be overloaded for longer periods than conventional power generators. The lack of a step up transformer means that power that would normally be lost can be supplied to the system and that the high voltage bus, normally on the opposite side of the step up transformer, is directly controlled. The overload capability of the Powerformer means that it can supply reactive power support to the power system for a longer period than a conventional generator. Investigations undertaken into the Powerformer have shown it to have a potentially beneficial ability to allow greater system loading capability and therefore system security margins and a potentially beneficial impact on the time to voltage collapse following a system contingency.