Arbitrary Conditions Research Articles

A New Method for Predicting the Crack Propagation Process of Brittle Rock Under Thermo-Hydro-Mechanical Loading Conditions

Prediction on the crack propagation process of brittle rock under Thermo-Hydro-Mechanical (THM) loading conditions is very important for crack-arrest design and disaster prevention in deep rock engineering. Although currently existing fracture criteria can successfully predict crack initiation under arbitrary loading conditions, very few quantitative methods are available for predicting the crack propagation process of brittle rock under single loading condition, let alone THM loading conditions. In this paper, a new THM coupling fracture theory is established to predict the crack propagation process (including the crack initiation, stable and unstable propagation of Mode I or Mode II fracture), where the calculation formulae of Mode I and Mode II wing-tip stress intensity factors are deduced by a new superposition method with higher accuracy than the conventional superposition method and simpler form than the complex function method. Uniaxial compression tests and self-designed THM coupling tests of pre-cracked specimens are conducted to measure stress-strain curves and fracture trajectories under different loading conditions. Research results show that mechanism of crack initiation is the same as that of unstable propagation in both uniaxial compression and THM coupling tests. As the temperature and hydraulic pressure are increased and the confining pressure is decreased, the mechanisms of crack initiation and unstable propagation are changed from Mode II to Mode I. Mode I fracture has smaller loads of crack initiation load and unstable propagation and larger length of crack stable propagation than Mode II fracture. Test results agree very well with prediction ones, which proves the validity of the new THM coupling fracture theory. This fracture theory can be further extended to predict the multi-crack propagation process under THM loading conditions.

Coupled Lateral and Torsional Vibration of Rub‐Impact Rotor during Hovering Flight

When aircraft make a maneuvering during flight, additional loads acting on the engine rotor system are generated, which may induce rub‐impact faults between the rotor and stator. To study the rub‐impact response characteristics of the rotor system during hovering flight, the dynamic model of a rub‐impact rotor system is established with lateral‐torsional vibration coupling effect under arbitrary maneuvering flight conditions using the finite element method and Lagrange equation. An implicit numerical integral method combining the Newmark‐β and Newton–Raphson methods is used to solve the vibration response. The results indicate that the dynamic characteristics of the rotor system will change during maneuvering flight, and the subharmonic vibrations are amplified in both lateral and torsional vibrations due to maneuvering overload. The form of the rub‐impact is different during level and hovering flight conditions: the rub‐impact may occur at an arbitrary phase of the whole cycle under the condition of level flight, while only local rub‐impact occurs during hovering flight. Under the both flight conditions, the rub‐impact has a large effect on the spectral characteristics, periodicity, and stability of the rotor system.

Zero-power tip-tilt control of a magnetically levitated platform by lateral displacement of hybrid-electromagnets

This papers discusses a method of magnetic levitation which allows a levitated platform to remain both level and zero-power under arbitrary eccentric loading conditions. A hardware system is proposed and developed which laterally displaces hybrid electromagnets (HEMs) to counteract the moments caused by eccentric loads. In this system, the displaced HEMs are the same HEMs which are used for the levitation of the platform. A mathematical formulation is provided to explain the control methodology, and data from successful experimental trials of the developed hardware is discussed.

The modified early age strains development model for the case of two-way restraint conditions

This paper proposes a design model (2D MSDM) for assessment the early-age stress-strain parameters of two-axially restrained expansive concrete elements. The analytical model allows defining the restrained expansion strains and corresponding self-stresses in case of arbitrary restraint conditions in orthogonal directions by taking into consideration the elastic-plastic behavior of concrete during the expansion period. The results of solution according to the proposed model were compared with the experimental results of expansive concrete elements with orthogonal confinement carried out by authors and other researchers.

ArchLab: a MATLAB tool for the Thrust Line Analysis of masonry arches

Abstract According to Heyman’s safe theorem of the limit analysis of masonry structures, the safety of masonry arches can be verified by finding at least one line of thrust entirely laying within the masonry and in equilibrium with external loads. If such a solution does exist, two extreme configurations of the thrust line can be determined, respectively referred to as solutions of minimum and maximum thrust. In this paper it is presented a numerical procedure for determining both these solutions with reference to masonry arches of general shape, subjected to both vertical and horizontal loads. The algorithm takes advantage of a simplification of the equations underlying the Thrust Network Analysis. Actually, for the case of planar lines of thrust, the horizontal components of the reference thrusts can be computed in closed form at each iteration and for any arbitrary loading condition. The heights of the points of the thrust line are then computed by solving a constrained linear optimization problem by means of the Dual-Simplex algorithm. The MATLAB implementation of presented algorithm is described in detail and made freely available to interested users (https://bit.ly/3krlVxH). Two numerical examples regarding a pointed and a lowered circular arch are presented in order to show the performance of the method.

Метод запобігання надзвичайним ситуаціям внаслідок пожеж шляхом короткочасного прогнозування загорянь

A parametric model for predicting the current recurrence of the state of the airspace of premises in the conditions that are characteristic of real premises on the basis of the use of an arbitrary plural of dangerous factors of fire. The developed model depends on two parameters that are defined by a priori and affect the result of the recurrence of the recurrence of the conditions of the airspace of the premises. The new scientific result is determined by the theoretical substantiation of the developed model of prediction of recurrence of the growth of the airspaces of the airspace. The proposed model has two properties. The first one is associated with the possibility of use in theoretical studies of the detection of early inflammation of various materials in arbitrary conditions of modern premises. The second one is to practice the real measurements of hazardous fire factors of the airspace of premises. In accordance with the proposed model of prediction of current recurrence of the state of the air environment of premises in the fire of materials based on the measurement of an arbitrary set of dangerous fire factors, a control algorithm of the method of prevention of emergency situations as a result of fires in premises is developed. The control algorithm consists of six successive functionally linked blocks. The developed control algorithm allows us to offer an appropriate method for preventing emergencies as a result of fire in premises by predicting the recurrence of appliance of the airspace of the premises, which occurs on the basis of the current discrete measurement of an arbitrary plurality of dangerous fire factors. The procedure for application of the proposed method includes six successive functional procedural elements.

Coupling-Independent Real-Time Wireless Resistive Sensing Through NonlinearPTSymmetry

We report the realization of coupling-independent, robust wireless sensing of fully passive resistive sensors. $\mathcal{P}\mathcal{T}$-symmetric operation obviates sweeping, permitting real-time, single-point sensing. Self-oscillation is achieved through a fast-settling nonlinearity whose voltage amplitude is proportional to the sensor's resistance. These advances markedly simplify the reader. A dual time-scale theoretical framework generalizes system analysis to arbitrary operating conditions and a correction strategy reduces errors due to detuning from $\mathcal{P}\mathcal{T}$-symmetric conditions by an order of magnitude.

Probabilistic fatigue surrogate model of bimodal tension process for a semi-submersible platform

Mooring-line tension typically involves a bimodal process in which a wave-frequency component and a low-frequency component are induced by dynamic wave loading. The non-Gaussian characteristics make fast frequency domain estimation inaccurate. Although the time-domain fatigue damage is believed to be the most reliable method, it is computationally expensive; thus, in the present study, surrogate models including artificial neural network and kriging models are constructed for fatigue-damage prediction of the bimodal tension process to improve the accuracy and efficiency compared with the simple frequency- and time-domain approaches. A parametric study is conducted to investigate the spectrum parameters and correction factor for the bimodal tension process, and the fatigue damage under arbitrary wave conditions is evaluated using interpolation techniques for long-term fatigue analysis. The fatigue failure probability of mooring lines under dynamic environmental loads is calculated using the surrogate models and various spectral fatigue techniques. The results indicate that with a finite database of time-domain fatigue damage, the proposed surrogate models-based approach can provide a significantly more accurate assessment of the fatigue failure probability than spectral-based approaches.

Diseño, Construcción y Capacidades del Large Universal Shell Element Tester

El Large Universal Shell Element Tester (LUSET) es un nuevo dispositivo de ensayos, desarrollado en la ETH Zúrich, el cual facilita el estudio del comportamiento mecánico, a escala real, de elementos lámina de hormigón armado sujetos a solicitaciones en sus tres dimensiones (esfuerzos combinados de elementos tipo losa y membrana). En este artículo se presentan los motivos que condujeron al desarrollo del LUSET y, adicionalmente, se describen sus componentes, el software de control y los sistemas de medición. Finalmente, se presenta una breve descripción de la serie de ensayos usada para validar la funcionalidad del LUSET, así como, un resumen de sus posibilidades.

Control of instability by injection rate oscillations in a radial Hele-Shaw cell

Small spatial perturbations grow into fingers along the unstable interface of a fluid displacing a more viscous fluid in a porous medium or a Hele-Shaw cell. Mitigating this Saffman-Taylor instability increases the efficiency of fluid displacement applications (e.g., oil recovery), whereas amplifying these perturbations is desirable in, e.g., mixing applications. In this work, we investigate the Saffman-Taylor instability through analysis and experiments in which air injected with an oscillatory flow rate outwardly displaces silicone oil in a radial Hele-Shaw cell. A solution for linear instability growth that shows the competing effects of radial growth and surface tension, including wetting effects, is defined given an arbitrary reference condition. We use this solution to define a condition for stability relative to the constant flow rate case and make initial numerical predictions of instability growth by wave number for a variety of oscillations. These solutions are then modified by incorporating reference conditions from experimental data. The morphological evolution of the interface is tracked as the air bubble expands and displaces oil between the plates. Using the resulting images, we analyze and compare the linear growth of perturbations about the mean interfacial radius for constant injection rates with and without superimposed oscillations. Three distinct types of flow rate oscillations are found to modulate experimental linear growth over a constant phase-averaged rate of fluid displacement. In particular, instability growth at the interface is mildly mitigated by adding to the base flow rate provided by a peristaltic pump a second flow with low-frequency oscillations of small magnitude and, to a lesser extent, high-frequency oscillations of large amplitude. In both cases, the increased stability results from the selective suppression of the growth of large wave numbers in the linear regime. Contrarily, intermediate oscillations consistently destabilize the interface and significantly amplify the growth of the most unstable wave numbers of the constant flow rate case. Numerical predictions of low-frequency oscillations of opposite sign (initially decreasing) show promise of even greater mitigation of linear instability growth than that observed in this investigation. Looking forward, proper characterization of the unsteady, wetting, and nonlinear dynamics of instability growth will give further insight into the efficacy of oscillatory injection rates.

Oxygen Vacancies in Perovskite Oxide Piezoelectrics.

The excellent electro-mechanical properties of perovskite oxide ferroelectrics make these materials major piezoelectrics. Oxygen vacancies are believed to easily form, migrate, and strongly affect ferroelectric behavior and, consequently, the piezoelectric performance of these materials and devices based thereon. Mobile oxygen vacancies were proposed to explain high-temperature chemical reactions half a century ago. Today the chemistry-enabled concept of mobile oxygen vacancies has been extrapolated to arbitrary physical conditions and numerous effects and is widely accepted. Here, this popular concept is questioned. The concept is shown to conflict with our modern physical understanding of ferroelectrics. Basic electronic processes known from mature semiconductor physics are demonstrated to explain the key observations that are groundlessly ascribed to mobile oxygen vacancies. The concept of mobile oxygen vacancies is concluded to be misleading.

Comparison of naturalistic and arbitrary discriminative stimuli during schedule thinning following functional communication training

AbstractWe replicated and extended research on incorporating naturalistic discriminative stimuli into schedule thinning following functional communication training with three boys with autism spectrum disorder who engaged in severe behavior. Comparing naturalistic to arbitrary discriminative stimuli, two participants demonstrated differentiated communication in fewer sessions when arbitrary stimuli were used, while the third participant mastered the discriminations in a comparable number of sessions. Although previous research has demonstrated success in rapidly thinning the schedule with arbitrary stimuli, we extended this line of research by evaluating the extent to which differentiated communication would maintain during rapid schedule thinning in both naturalistic and arbitrary conditions. Two participants' communication remained differentiated, and in both conditions, during rapid schedule thinning. However, neither discrimination maintained for the third participant. Results are discussed in terms of the existing literature and directions for future research.

Process design for 5-axis ball end milling using a real-time capable dynamic material removal simulation

For repairing turbine blades or die and mold forms, additive manufacturing processes are commonly used to build-up new material to damaged sections. Afterwards, a subsequent re-contouring process such as 5-axis ball end milling is required to remove the excess material restoring the often complex original geometries. The process design of the re-contouring operation has to be done virtually, because the individuality of the repair cases prevents actual running-in processes. Hard-to-cut materials e.g. titanium or nickel alloys, parts prone to vibration and long tool holders complicate the repair even further. Thus, a fast and flexible material removal simulation is needed. The simulation has to predict suitable processes focusing shape deviations under consideration of process stability for arbitrary complex engagement conditions. In this paper, a dynamic multi-dexel based material removal simulation is presented, which is able to predict high-resolution surface topography and stable parameters for arbitrary processes such as 5-axis ball end milling. In contrast to other works, the simulation is able to simulate an unstable process using discrete cutting edges in real-time.

Control and Experimental Verification of a Bidirectional Nonisolated DC–DC Converter Based on Switched-Capacitor Converters

This article presents a bidirectional nonisolated dc-dc converter based on switched-capacitor converters intended for electric railway system applications. It consists of plural main converters with two power devices per converter, plural auxiliary converters each of which is formed by cascaded chopper cells, and small-sized inductors for current control. The dc-dc converter can achieve zero-current switching (ZCS) for all power devices used in the main converters under arbitrary load conditions and an arbitrary voltage ratio of high-voltage-side voltage and low-voltage-side voltage. Consequently, square-wave currents can be removed from both the high- and low-voltage sides of the converter. The validity of the operating principles as well as the control methods proposed in this article is verified by experiments using a 200-V, 2-kW downscaled model.

Identifying cloud, precipitation, windshear, and turbulence by deep analysis of the power spectrum of coherent Doppler wind lidar.

Researches on the atmospheric boundary layer (ABL) need accurate measurements with high temporal and spatial resolutions from a series of different instruments. Here, a method for identifying cloud, precipitation, windshear, and turbulence in the ABL using a single coherent Doppler wind lidar (CDWL) is proposed and demonstrated. Based on deep analysis of the power spectrum of the backscattering signal, multiple lidar products, such as carrier-to-noise (CNR), spectrum width, spectrum skewness, turbulent kinetic energy dissipation rate (TKEDR), and shear intensity are derived for weather identification. Firstly, the cloud is extracted by Haar wavelet covariance transform (HWCT) algorithm based on the CNR after range correction. Secondly, since the spectrum broadening may be due to turbulence, windshear or precipitation, the spectrum skewness is introduced to distinguish the precipitation from two other conditions. Whereas wind velocity is obtained by single peak fitting in clear weather condition, the double-peak fitting is used to retrieve wind and rainfall velocities simultaneously in the precipitation condition. Thirdly, judging from shear intensity and TKEDR, turbulence and windshear are classified. As a double check, the temporal continuity is used. Stable wind variances conditions such as low-level jets are identified as windshear, while arbitrary wind variances conditions are categorized as turbulence. In the field experiment, the method is implemented on a micro-pulse CDWL to provide meteorological services for the 70th anniversary of the China's National Day, in Inner Mongolia, China (43°54'N, 115°58'E). All weather conditions are successfully classified. By comparing lidar results to that of microwave radiometer (MWR), the spectrum skewness is found be more accurate to indicate precipitation than spectrum width or vertical speed. Finally, the parameter relationships and distributions are analyzed statistically in different weather conditions.

Identification of Life Models for Li-Ion Batteries Using Penalized Regression and Bilevel Optimization

Reduced-order physics-based life models are extremely useful for rapidly predicting battery state-of-health and for simulating battery lifetime in arbitrary aging conditions. However, identification of well-parameterized models is difficult. This is because, for maximum usefulness in predicting lifetime under a variety of conditions, aging test data exhibits many degradation mechanisms, which all need to be accurately modeled. However, because aging tests are time-consuming and expensive, especially for large-format batteries, a minimum of tests are conducted while probing many stress factors. Building a well-parameterized model is then very challenging: an under-parameterized model will neglect critical degradation modes, and an over-parameterized model will extrapolate poorly to new testing conditions. To complicate this matter, the functional form of the model for any individual degradation rate can be very difficult to identify. In this work, the statistical tools of penalized regression and bilevel optimization are used to help identify both the functional forms of and optimize the parameters of reduced-order life models, accelerating identification of robust models. Model robustness is demonstrated through traditional statistics methods of cross-validation and sensitivity analysis, uncertainty quantification through bootstrap resampling and Monte-Carlo simulation, and simulation of real-world use cases.

(Invited) Atomistic Understanding on the Surface of GaAs By Ab Initio Thermodynamics; From Equilibrium Shape to Growth Shape

The III-V semiconductor nanowires (NWs) have attracted substantial attention as an ideal system for the study on the growth mechanism and electronic device applications. For the precise manipulation of the nanowire growth, understanding on the temperature–pressure (T–P) dependent variation in surface energy and reconstruction which governs the anisotropic interaction between vapor sources and crystal solids is crucial. Unfortunately, the quantitative values of the variation in surface energy cannot be obtained only using the conventional electronic structure calculation. To overcome this difficulty, we have developed a reliable ab initio thermodynamic method by which the T–P dependent surface energy is predicted from the atomic-scale calculations on: surface reconstructions of InAs1; equilibrium crystal shapes of GaAs and InAs2; and anisotropic adsorption and growth conditions of GaAs NW3.In this talk, we present an ab initio thermodynamics approach by combining the atomic-scale calculation with the thermodynamic treatment to take a step forward in the theoretical modeling on the growth of polar GaAs <111> nanowire by calculating the change in Gibbs free energy during the nucleation and growth process. By comparing the nucleation rate between different stacking sequences, the formation probability of stacking fault or wurtzite segment was quantitatively predicted under arbitrary vapor-phase growth conditions. The predicted T–P dependent probability from atomic-scale calculation is directly comparable to the experiments and remarkably consistent with the available results to date, elucidating the fundamental asymmetric growth mechanism. Our ab initio approach is truly independent of any empirical data, bridging to the experimentally controllable variables. This simulation can be applied to various nanomaterials, including two-dimensional materials as well as other III-V and II-VI NWs, where the precise control of the stacking sequence is significant for their properties.[1] Yeu et al., Sci. Rep., 2017, 7, 10691[2] Yeu et al., Sci. Rep., 2019, 9, 1127[3] Yeu et al., Appl. Surf., Sci., 2019, 497, 143740

Operating modes of dual-grating dielectric laser accelerators

In this work, we present a comprehensive theoretical description of the Lorentz force in dual-grating dielectric laser accelerators (DLA). Here we examine the dual-grating DLA under arbitrary illumination conditions, both single-side and dual-side drive. We improve upon previous descriptions of these forces by providing a unified description of all possible operating modes of these devices, and classify the modes into three categories. In particular, we predict the existence of the previously observed ``line modes'' and a novel ``elliptical mode'', provide an experimental demonstration of this new mode, and suggest a possible application for it in improving the resolution of attosecond-scale streak cameras. Finally, we examine several complementary methods of tuning a dual-grating DLA to a desired operating mode---particularly dual-drive phase rotation and translational offset of the grating teeth.

New analytical expressions of photovoltaic solar module physical parameters: Effects of module temperature and incident solar irradiance

In this work, we present three methods to extract model physical parameters of a photovoltaic solar module modelled by a single-diode electronic circuit. The model physical parameters we are looking for are photocurrent Iph , saturation current Is , ideality factor η, series resistance Rs and shunt conductance Gp . The first method is based on exact solution of module characteristic equation, the second one uses exact expression of dynamic conductance and the third one makes use of exact expression of the integral of translated current-voltage characteristics (I-Isc ). In all these extraction methods, we achieve numerical fitting of experimental data of output current, differential conductance and area under translated characteristics with suitable analytical expressions to get model physical parameters at standard test conditions (STC). Then, we assume these values as initial conditions and derive exact analytical expressions reporting effects of module temperature and incident solar irradiance on photocurrent, saturation current and ideality factor using temperature coefficients provided as well as irradiance coefficients extracted from module manufacturer datasheet. We examine new analytical expressions of model physical parameters in the case of Shell SQ80 photovoltaic solar module at arbitrary operating conditions of module temperature and solar irradiance. We evidence good agreement between experimental characteristics and forecasted analytical characteristics generated by new analytical expressions.

Ultimate Strength Prediction of Fibrous Composites only upon Independently Measured Constituent Properties

This study presents an accurate and easy-to-use micromechanical model to predict the ultimate strength of unidirectional polymer composites under an arbitrary load condition only upon independently measured constituent properties. In this model, the micromechanical method based on generalized model of cells (GMC), which effectively predict the nonlinear deformation of unidirectional composites, is used to analyze the repeating unit cells of composites. At the same time, a unified plastic theory (i.e. modified Ramaswamy-Stouffer model) is incorporated into the GMC's analytical framework to describe viscoplastic behaviors of matrix phase. Additionally, because of the stress concentration effect which causes the difference between the matrix in-situ and original strength behaviors, a stress concentration factor is introduced in order to utilize the measured constituent properties directly. The prediction results with SCF match better with the experimental results than the prediction results without SCF. In addition, the prediction results show that the presence of thermal residual stress and material plastic effects generally has important influence on the strength prediction of a composite.