Design,Development and Testing of the JTech Bolt for Use in Static,Quasi-Static and Dynamic Domains

Designing a rock reinforcement element requires knowledge of:geomechanical behaviour,interaction of the reinforcement element with rock mass and the element’s mechanistic response in static and dynamic environments.Using this knowledge the JTech bolt was developed and subjected to a thorough program to test,gather data and validate the bolt performance in varying domains.By conducting FE(finite element)modeling,the simulation reviews the JTech bolt design evaluating the effects of threadbar geometric variation,threadbar and nut engagement results under high stress,coating friction response and effects of thread tolerance extremes on the failure mode.These results determine safety factors,tolerances and quality management criteria.Once manufactured,in-situ system testing,laboratory and underground short encapsulation testing,resin mixing testing,double shear testing and dynamic testing at varying velocity and mass,determine the system’s capacity and effectiveness in static,quasi-static and dynamic mining environments.In this paper,the process and results are described.

Dynamic Domain Decomposition Method and Its Application on Nonlinear Problem

In this paper,domain decomposition method（DDM） for numerical solutions of mathematical physics equations is improved into dynamic domain decomposition method（DDDM） . The main feature of the DDDM is that the number,shape and volume of the sub-domains are all flexibly changeable during the iterations,so it suits well to be implemented on a reconfigurable parallel computing system. Convergence analysis of the DDDM is given,while an application approach to a weak nonlinear elliptic boundary value problem and a numerical experiment are discussed.

Dynamic Harmonic Domain Modelling of Space Vector Based SSSC

This paper presents analytical frequency domain method for harmonic modeling and evaluation of Space Vector Pulse Width Modulation (SVPWM) based static synchronous series converter (SSSC). SVPWM is the best among all the PWM techniques. It gives a degree of freedom of space vector placement in a switching cycle. Dynamic modeling technique is used for space vector modulation (SVM) based voltage source converter that is adapted as a static synchronous series converter (SSSC) for harmonic analysis using dynamic harmonic domain. Performance of the SSSC is evaluated in dynamic harmonic domain simulation studies in MATLAB environment. The switching function spectra are necessary for harmonic transfer matrix which is calculated using Fourier series. This paper presents the analysis of harmonics for space vector based SSSC during steady state and dynamic condition.

RC-Circuit-Like Dynamic Characteristic of the Magnetic Domain Wall in Flat Ferromagnetic Nanowires

We investigate the dynamic behavior of the magnetic domain wall under perpendicular magnetic field pulses in fiat ferromagnetic nanowires using micromagnetic simulations. It is found that the perpendicular magnetic field pulse can trigger the magnetic domain wall motion, where all the field torques axe kept on the plane of nanowire strip. The speed of magnetic domain walls faster than several hundreds of meters per second is predicted without the Walker breakdown for the perpendicular magnetic driving field stronger than 200mT. Interestingly, the dynamic behavior of the moving magnetic domain wall driven by perpendicular magnetic field pulses is explained by charging- and discharging-like behaviors of an electrical RC-circuit model, where the charging and the discharging of magnetic charges on the nanowire planes are considered. The concept of the RC-model-like dynamic characteristic of the magnetic domain wall might be promising for the applications in spintronic functional devices based on the magnetic domain wall motion.

Dynamic Resonant Frequency Bands of Suspension System of Vehicles with Varying Speeds Based on Time⁃Frequency Spectrum

The dynamic responses of suspension system of a vehicle travelling at varying speeds are generally nonstationary random processes,and the non-stationary random analysis has become an important and complex problem in vehicle ride dynamics in the past few years.This paper proposes a new concept,called dynamic frequency domain(DFD),based on the fact that the human body holds different sensitivities to vibrations at different frequencies,and applies this concept to the dynamic assessment on non-stationary vehicles.The study mainly includes two parts,the first is the input numerical calculation of the front and the rear wheels,and the second is the dynamical response analysis of suspension system subjected to non-stationary random excitations.Precise time integration method is used to obtain the vertical acceleration of suspension barycenter and the pitching angular acceleration,both root mean square(RMS)values of which are illustrated in different accelerating cases.The results show that RMS values of non-stationary random excitations are functions of time and increase as the speed increases at the same time.The DFD of vertical acceleration is finally analyzed using time-frequency analysis technique,and the conclusion is obviously that the DFD has a trend to the low frequency region,which would be significant reference for active suspension design under complex driving conditions.

A Trajectory Planning Method of Automatic Lane Change Based on Dynamic Safety Domain

Traditional research on automatic lane change has primarily focused on high-speed scenarios and has not considered the dynamic state changes of surrounding vehicles.This paper addresses this problem by proposing a trajectory planning method to enable automatic lane change at medium and low speeds.The method is based on a dynamic safety domain model,which takes into account the actual state change of surrounding vehicles,as well as the upper boundary of the safety domain for collision avoidance and the lower boundary of comfort for vehicle stability.The proposed method involves the quantification of the safety and comfort boundaries through parametric modeling of the vehicle.A quintic polynomial trajectory planning method is proposed and evaluated through simulation and testing,resulting in improved safety and comfort for automatic lane change.

Deep-learning enabled atomic insights into the phase transitions and nanodomain topology of lead-free(K,Na)NbO_(3) ferroelectrics

Lead-free K_(x)Na_(1-x)NbO_(3)(KNN)perovskites have garnered increasing attention due to their exceptional ferropiezoelectric properties,which are effectively tuned via polymorphic structures and domain dynamics.However,atomic insights into the underlying nanomechanisms governing the ferroelectricity of KNNs amidst varying factors such as composition,phase,and domain are still imperative.Here,we perform molecular dynamics simulations of phase transitions and domain dynamics for KNNs with various K/Na ratios(x=0.25∼1.0)by using ab-initio accuracy deep learning potential(DP).As a demonstration of its transferability,the newly developed DP model shows quantum accuracy in terms of the equation of states,elastic constants,and phonon dispersion relations for various KNbO_(3)and K_(0.5)Na_(0.5)NbO_(3).Furthermore,intricate temperature-dependent phase transitions and domain formation of KNNs are extensively and quantitatively captured.Simulations indicate that for KNNs with compositions x ranging from 0.25 to 1.0,the paraelectric-to-ferroelectric phase transition of KNNs is driven primarily by the order-disorder effect,while the displacive effect is dominant in the subsequent ferroelectric phase transitions.Specifically,flux-closure or herringbone-like nanodomain patterns arranged with 90°domain walls formed close to the experimental observations.Detailed analyses reveal that favorable 90°domain wall formation becomes more challenging with increasing Na content due to distinct oxygen octahedron distortion arising from the different ionic radii of K/Na atoms.It is envisioned that the combination of unified DP and atomistic simulations will help offer a robust solution for more accurate and efficient in silico explorations of complex structural,thermodynamic,and ferroelectric properties for relevant energy storage and conversion materials.

Long dynamic range spread spectrum optical domain reflectometer

The performance of an optical time domain reflectometer(OTDR) is significantly improved using spread spectrum technology. The concept of spread spectrum OTDR(SSOTDR) is proposed, the theoretical basis and simulation results of the new method are given, and the problem of direct application of bipolar spread spectrum codes to OTDR and despreading in the optical domain are solved. The simulation results show the feasibility of the SSOTDR, which exhibits better dynamic range reported to date for a practical long-haul OTDR system without using conventional average technique.

Domain wall dynamics driven by a circularly polarized magnetic field in ferrimagnet:effect of Dzyaloshinskii-Moriya interaction

In this work,we study the domain wall motion in ferrimagnet driven by a circularly polarized magnetic field using the collective coordinate theory and atomistic micromagnetic simulations,and we pay particular attention to the effect of Dzyaloshinskii-Moriya interaction(DMI).Similar to the case of antiferromagnetic domain wall,ferrimagnetic wall moves at a speed which is linearly dependent on the DMI magnitude.In addition,it is revealed that the DMI plays a role in modulating the domain wall dynamics similar to that of the net spin density,which suggests another internal parameter for controlling domain wall in ferrimagnets.Moreover,the results show that the domain wall dynamics in ferrimagnets is much faster than that in ferromagnets,which confirms again the great potential of ferrimagnets in future spintronic applications.

Correlation of cooperatively localized rearrangement on the "fluidized domain" in glass substances (or polymers) to their fragility Ⅲ:Theory of dynamic fragility at isochoric state

A set of universal equations on the reduced stress relaxation modulus with K-W-W stretched exponential function has been derived from the dynamics of α and β structural relaxation processes. In the present work, the K-W-W decay function is used to define the three types of relaxations (single α, single β relaxation and α-β co-relaxation), then their average times of relaxation are theoretically calculated from the reduced shear stress relaxation modulus and the relaxation time spectrum function H(τ). When the average time of co-relaxation, the reference temperatures (ficitive Tf and glass transition Tg) and the isostructural parameter achieved from the conditions of isostructural glass state are introduced into the reduced shear stress relaxation modulus (GT) under the equilibrium state, a set of correlations between isochoric fragility index (mvα, mvβ and mvαβ) and the coupling strength (α and β) under the reference temperatures are derived from the exact definition of isochoric fragility. So the theory of dynamic fragility for glass substances at isochoric state is developed. The theory can predict the following main features of structural relaxations and behavior of isochoric fragility: the temperature dependence of peak relaxation frequency exhibits a bifurcation with a pair of single α and single β relaxations; the temperature dependence of Stickel equation on 1/T exhibits two crossovers with VFTH(1) and VFTH(2) at the temperatures of Tf and Tg regime; there are two linear correlations between isochoric fragility index (mvα and mvβ) and the coupling strength. Fine agreements between the theoretical calculation and experimental results are obtained.

Enhanced piezoelectric properties and depolarization temperature in textured(Bi_(0.5)Na_(0.5))TiO_(3)-based ceramics via homoepitaxial templated grain growth

Enhanced piezoelectric response was usually achieved in(Bi_(0.5) Na_(0.5))TiO_(3)(BNT)-based ceramics with sacrifice of depolarization temperature T_(d),seriously limiting their usage range in electromechanical applications.In this work,we propose to explore piezoelectric anisotropy and domain engineering in composition&microstructure-controlled textured ceramics to resolve this issue.[001]c-textured 0.94(Bi_(0.5) Na_(0.5))TiO_(3)–0.06BaTiO_(3)(0.94BNT-0.06BT)ceramics with Lotgering factor F_(001)-91%were fabricated through homoepitaxial templated grain growth(TGG)via using 0.94BNT-0.06BT microplatelet templates.The textured samples exhibited more ordered domains with facilitated domain switching behavior,being consistent with saturated high polarization achieved at lower electric fields.Increasing F_(001) to above 60%enables rapid enhancement of piezoelectric response.Notably,compared to non-textured counterpart,the maximally textured ceramics exhibited-236%enhanced piezoelectric coefficient(d_(33)-302 pC/N)and-280%enhanced piezoelectric voltage coefficient(g_(33)-49.8×10^(−3)Vm/N),together with slightly increased depolarization temperature(T_(d)-106℃).Moreover,those values are approaching or even higher than the single-crystal values.This work not only provides important guidelines for design and synthesis of novel textured ceramics with improved comprehensive electrical properties,but also can expand application fields of BNT-based ceramics.

Identification method for helicopter flight dynamics modeling with rotor degrees of freedom

A comprehensive method based on system identification theory for helicopter flight dynamics modeling with rotor degrees of freedom is developed. A fully parameterized rotor flapping equation for identification purpose is derived without using any theoretical model, so the confidence of the identified model is increased, and then the 6 degrees of freedom rigid body model is extended to 9 degrees of freedom high-order model. Bode sensitivity function is derived to increase the accuracy of frequency spectra calculation which influences the accuracy of model parameter identification. Then a frequency domain identification algorithm is established. Acceleration technique is developed furthermore to increase calculation efficiency, and the total identification time is reduced by more than 50% using this technique. A comprehensive two-step method is established for helicopter high-order flight dynamics model identification which increases the numerical stability of model identification compared with single step algorithm. Application of the developed method to identify the flight dynamics model of BO 105 helicopter based on flight test data is implemented. A comparative study between the high-order model and rigid body model is performed at last. The results show that the developed method can be used for helicopter high-order flight dynamics model identification with high accuracy as well as efficiency, and the advantage of identified high-order model is very obvious compared with low-order model.