Dynamic Instability Mechanism Research Articles

Analysis of swallowtail mutation instability of slope with weak interlayer under blasting disturbance

Abstract The stability analysis of slope under blasting disturbance is one of the important research topics in blasting engineering and geotechnical engineering. Based on the dynamic instabil-ity mechanical model of slope with weak interlayer, the mechanical effect of blasting dis-turbance on slope system is analyzed. The swallowtail mutation model of slope system under blasting disturbance is established. Two methods to determine slope stability under blasting disturbance are proposed: safety factor method and double judgment method. Through the analysis of the dynamic instability mechanism of the slope system under the effect of blast-ing disturbance, it is concluded that: (1) the greater the amplitude of blasting disturbance vibration, the worse the stability of the slope system, and the greater the possibility of land-slide disaster. The slope landslide disaster caused by blasting disturbance mainly occurs in the middle and late stage of blasting disturbance (0.17 ∼ 0.5s). (2) When the period of blast-ing vibration wave (T > 1s), the frequency of blasting disturbance wave can be appropriately increased, which is conducive to reducing the impact of blasting disturbance on slope stabil-ity. When the period of blasting disturbance wave (T < 1s), proper adjustment of blasting disturbance frequency will not have a direct impact on the stability of slope. (3) With the increase of the incident angle of blasting vibration wave, the change of the dynamic self-stability critical height of the slope system shows a trend of increasing, and the in-creasing rate is decreasing. The greater the incident angle of blasting vibration wave, the worse the stability of slope system. Proper reduction of the incident angle of blasting vibra-tion wave is beneficial to improve the stability of slope system. Finally, the rationality and applicability of thse proposed double judgment method are verified based on the actual con-ditions of the current slope in Laoyingzui.

Numerical and experimental investigation on autoparametric resonance of multi-system structures

The analysis of dynamic stability in frame structures has always been a critical issue in engineering and mechanical design. Autoparametric resonance instability problems present a more complex dynamic instability mechanism than general parametric resonance, and determining the unstable regions of frame structures with multiple subsystems requires consideration of the coupled vibration of each subsystem. Unfortunately, existing approximate formulas are inadequate to analyze the stable boundary of autoparametric resonance in frame structures. To address this issue, this paper proposes a novel method called the dynamic axial force transfer coefficient (DTC) method to investigate the spatial dynamic instability characteristics of complex frame structures under parametric excitation due to autoparametric resonance. The proposed method, in conjunction with the harmonic balance method and the finite element method (FEM), established the global finite element equation of the frame and derived the stable boundary equation of autoparametric resonance for general frame structures. A complex spatial frame model is built to verify the effectiveness of the DTC method, and a comprehensive parametric analysis is conducted to investigate the dynamic instability mechanism of autoparametric resonance, including structural damping, static load coefficient, connection and boundary conditions of subsystems, and cross-sectional dimensions of subsystems. The results show that autoparametric resonance stability analysis of frame structures should consider the design parameters of each subsystem independently. In addition, strong coupling interaction between subsystems may induce autoparametric internal resonance of structure subjected to dynamic load. An autoparametric resonance test of a Γ-shaped frame is presented to further verify the proposed method. The test reveals the mechanism of the strong coupling effect, which may lead to a high risk of structural failure. More importantly, the DTC method can accurately determine the unstable boundary of multi-system frame structures, which is consistent with conventional methods (EGE) and experimental results, and predict the strong coupling effect of practical structures. The proposed method is simpler and more convenient than the existing methods for stability analysis of the autoparametric resonance of general frame structures, and can provide more effective guidance for structural design.

Unveiling the dynamic instability mechanism of microstructure transformation in faceted oxide eutectic composite ceramics

Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior. Herein, the microstructure transformation of faceted Al2O3/Er3Al5O12 thermal emission eutectic composite ceramics is explored over wide ranges of compositions (13.5 mol%–22.5 mol% Er2O3) and solidification rates (2–200 μm/s). Entirely coupled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%–22.5 mol% Er2O3 at low solidification rates. The competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature criterion. In addition, the mechanisms of irregular eutectic spacing selection and adjustment under different solidification rates are revealed based on Magnin–Kurz model. A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface undercooling. According to the well microstructure tailoring, the flexural strength of Al2O3/Er3Al5O12 eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low fluctuation. The eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refining microstructure. The as-designed Al2O3/Er3Al5O12 composites with microstructural tailoring have great potential as integrations of structural and functional materials.

Dynamic instability mechanism of post-buckled FG nanotubes transporting pulsatile flow: size-dependence and local/global dynamics

For bistable structures such as post-bucked nanotubes, the size-dependence may have influences on both local and global dynamics. A local/global dynamic instability study of post-buckled nanotubes transporting pulsatile flow is conducted for the first time. To model the size-dependence of both the solid and fluid, the nonlocal strain gradient beam model coupled with surface elasticity is established, and the slip-flow model is introduced. The governing equations are derived based on Zhang-Fu's refined beam theory and von Kármán type geometric relationship. A new computation mode is developed that combines the two-step perturbation- Galerkin truncation, incremental harmonic balance method (IHBM), and Runge-Kutta method to obtain the stability boundary and amplitude-frequency bifurcation diagram. Also, the dynamic characteristics in different parameter regions are presented through displacement-time history diagram, phase diagram, Poincaré map and spectrum diagram. The complex motions of local attractor- two-well chaos- global snap-through, and hysteresis are observed. Subsequently, the nonlinear dynamic instability mechanism and the physical significance of stability boundary are revealed. It is revealed that the structural size-dependence have dual effects and may change the bifurcation topology, such as the change of motion from local attractor to global attractor, and from periodic motion to chaotic motion.

Study on the Dynamic Instability Mechanism of the Rock Formation in the Multifault Structure Zone of the Stope

Under the influence of tectonism in geological activities, most fault structures appear in groups. Multiple fault structures can induce a variety of mine dynamic disasters, which significantly affect the safety of mine production. To study the dynamic instability mechanism of the strata in the multifault structure zone of the stope when mining, a numerical model of multiple fracture structures was established. At the same time, the mechanism of the dynamic instability of the rock formation in the multifault structure zone of the stope has been studied through similar simulation experiments and on-site data analysis. The research results show that the stress-affected areas of the faults in the multiple-fault structure area overlap, and the stress evolution law of the fault will distinguish its independent dynamic evolution model. The multifault structure area has a multifault overall evolution law model. In this model, there is a synergy between the fault layers, and the maximum value of stress concentration is diagonally distributed. Under the influence of mining, the fault structure will be activated to change the stress field distribution form of the stope. The two faults in multiple structural areas have a joint mechanism, which plays a key role in controlling the dynamic instability process of the surrounding rock of the stope. The first activated faults in the multiple-fault structure area will undergo secondary activation under the influence of subsequent fault activities. The evolution law of cracks in the overburden of similar simulation experiments confirms that the early active F1 fault will be affected by the subsequent F2 fault activity. The mine pressure data measured on-site verifies the reliability of the numerical simulation experiment and the similar simulation experiment.

Failure characteristics and meso-deterioration mechanism of pre-stressed coal subjected to different dynamic loads

The study of dynamic fracture mechanism of pre-stressed coal is of great importance to the coal bursts prevention and the coal pillar reinforcement subjected to the dynamic disturbance. In this paper, the effect of pre-static load and dynamic load on the initiation fracture evolution and destruction states of coal were studied using experimental and theoretical approaches. The results show that the coal usually splits into several blocks along the dominant fractures when subjected to the static load. The increase of pre-static load can make the post-peak dynamic stress–strain curve of the specimen gradually transform from type II to type I. The dynamic load plays the same role as that of pre-static load in terms of the effect on the dynamic stress–strain curve, but different in dynamic failure state of the coal. The enhancement of the former will make the dominant fracture expansion and leading the dynamic failure of coal gradually transform from the surface peeling to failure into several large pieces along the dominant fractures, while the increase of the latter will provid increasing kinetic energy to activate the internal fracture expansion of the specimen, and causing the failure state of the specimen transform from the surface peeling to the complete destruction into pieces. For the specimen with the surface peeling failure form, the peeling degree of the specimen depend on both the length of the fracture and the distance of the fracture to the free surface. Based on these results, the dynamic instability mechanism and protection focus of coal pillars under coupled static and dynamic loads were further discussed.

Analytical and experimental studies on out-of-plane dynamic parametric instability of a circular arch under a vertical harmonic base excitation

The out-of-plane dynamic stability of an arch under a vertical periodical base excitation is investigated by using both analytical and experimental methods. When the excitation frequency is near twice the out-of-plane natural frequency of the arch, an out-of-plane divergent vibration is induced, which will eventually leads to an out-of-plane dynamic parametric instability of the arch. Firstly, Hamiltonian principle is employed to derive the in-plane dynamic equations, and analytical solutions for the dynamic axial compressive force and bending moment in pre-stability state are obtained and verified by numerical simulations. Then the mode shape functions for the out-of-plane dynamic instability are analytically determined and the out-of-plane dynamic instability regions are obtained by Bolotin's method. Factors affecting the critical excitation frequencies of the out-of-plane dynamic instability regions, such as the arch's included angle, the slenderness ratio, and the logarithmic decrement, are thoroughly analyzed and verified via the method of multiple scales. Lastly, laboratory tests are carried out for the out-of-plane parametric resonance instability of fix-ended circular arches with various included angles and slenderness ratios. The critical excitation frequencies of dynamic instability regions of the tested arches are determined by increasing and decreasing the excitation frequency, and the experimental results agree with the theoretical counterparts very well. The main contributions of this work include: (1) obtaining an analytical solution of out-of-plane dynamic instability regions for the arch under a vertical harmonic base excitation; (2) applying a newly-designed experimental system to conduct the out-of-plane dynamic instability tests; (3) proposing a method of time domain analytical solution to determine the critical excitation frequencies of the out-of-plane dynamic instability region, and (4) discussing the dynamic instability mechanism for base-excited arches.

Dynamic-Instability Mechanism of Double-Layer Spherical Shell under Harmonic Loading

Based on dynamic instability theory, by incremental dynamic analysis method, large-scale parameters-analysis is carried on double-layer Kiewitt shell under harmonic loading，with weight effects and double non-linear effect calculated and Failure-amplitude is determined. Further exploring on the relationship between excitation frequency changes and failure-amplitude and between initial imperfection effect and load reduction are also conducted.

Dynamic Instability Mechanism and Vibration Control of Radial Gate Arms

The failures of the low head radial gates for hydraulic structures are commonly caused by the dynamic instability of arms (struts) under dynamic loads during gate opening and closing operations. For understanding the dynamic instability mechanism of radial gate arm, the dynamic stability of radial gate arm with I-section was analyzed with the consideration of bending, torsion and warping by using parametric resonance theory, and the boundaries of main dynamic instability regions were obtained. In order to avoid severe vibrations of radial gate arms, two vibration control measures were proposed. The study provides useful and valuable information for design and safe operation of radial gates.

Impact of LTC in power system nonlinear behaviour: algorithm and bifurcation analysis

A numerical algorithm, based on initial value problem, using local parameterisation continuation technique is proposed in this paper for the bifurcation analysis of a sample power system model with Load Tap Changer (LTC). Bifurcation diagrams of steady state solutions are constructed by the application of the proposed algorithm. From the bifurcation diagrams, the existence of various bifurcation points such as Unstable Hopf Bifurcation (UHB), Stable Hopf Bifurcation (SHB), Cyclic Fold Bifurcation (CFB), Saddle Node Bifurcation (SNB) and Period Doubling Bifurcation (PDB) are identified with the use of tools of nonlinear dynamics. The role of LTC on the occurrence of Hopf bifurcation, SNB, incidence of dynamic and static voltage collapse and in augmenting the loadability limit of a sample power system is analysed. It is shown that LTC can only be temporarily relied upon to stop or delay the dynamic instability mechanism.

The Effect of Infinitesimal Damping on the Dynamic Instability Mechanism of Conservative Systems

The local instability of 2 degrees of freedom (DOF) weakly damped systems is thoroughly discussed using the Liénard‐Chipart stability criterion. The individual and coupling effect of mass and stiffness distribution on the dynamic asymptotic stability due to mainly infinitesimal damping is examined. These systems may be as follows: (a) unloaded (free motion) and (b) subjected to a suddenly applied load of constant magnitude and direction with infinite duration (forced motion). The aforementioned parameters combined with the algebraic structure of the damping matrix (being either positive semidefinite or indefinite) may have under certain conditions a tremendous effect on the Jacobian eigenvalues and then on the local stability of these autonomous systems. It was found that such systems when unloaded may exhibit periodic motions or a divergent motion, while when subjected to the above step load may experience either a degenerate Hopf bifurcation or periodic attractors due to a generic Hopf bifurcation. Conditions for the existence of purely imaginary eigenvalues leading to global asymptotic stability are fully assessed. The validity of the theoretical findings presented herein is verified via a nonlinear dynamic analysis.

Probing the domain structure of FtsZ by random truncation and insertion of GFP

Random transposon-mediated mutagenesis has been used to create truncations and insertions of green fluorescent protein (GFP), and Venus-yellow fluorescent protein (YFP), in Escherichia coli FtsZ. Sixteen unique insertions were obtained, and one of them, in the poorly conserved C-terminal spacer, was functional for cell division with the Venus-YFP insert. The insertion of enhanced GFP (eGFP) at this same site was not functional; Venus-YFP was found to be superior to eGFP in other respects too. Testing the constructs for dominant negative effects led to the following general conclusion. The N-terminal domain, aa 1-195, is an independently folding domain that can poison Z-ring function when expressed without a functional C-terminal domain. The effects were weak, requiring expression of the mutant at 3-5 times the level of wild-type FtsZ. The C-terminal domain, aa 195-383, was also independently folding, but had no activity in vivo. The differential activity of the N- and C-terminal domains suggests that FtsZ protofilament assembly is directional, with subunits adding primarily at the bottom of the protofilament. Directional assembly could occur by either a treadmilling or a dynamic instability mechanism.

On the behaviour of open-topped oil storage tanks in high winds. Part III. A structural dynamic instability mechanism?

On the behaviour of open-topped oil storage tanks in high winds. Part III. A structural dynamic instability mechanism?

Stability of stationary and rotating discs under edge load

The dominant dynamic instability mechanism in circular cutters, grinding wheels and the like is a moving load resonance excited by a constant transverse load at the “critical rotation speed.” The critical speed theory is extended here to include the effects of concentrated in-plane edge loads similar to loading occurring in engineering processes. The theoretical analysis shows the critical speed is only sensitive to edge load when the resonance mode and the mode of static edge load buckling are identical. This always occurs with large edge load, but it is not the case with the smaller edge loads typical of engineering processes. These analyses are confirmed through prediction and measurement of static buckling loads for centrally clamped discs with in-plane, concentrated loads inclined between 0° and 80° to the edge normal.