THE DESIGN AND IMPLEMENTATION OF SELF-COMMISSIONING TECHNIQUES FOR A VECTOR-CONTROLLED INDUCTION MOTOR DRIVE

ABSTRACT

This paper presents the design and implementation of self-commissioning techniques for a vector-controlled induction motor drive. Two key techniques are involved in the self-commissioning of a vector-controlled induction motor drive. The identification of the electric and mechanical parameters of motor and load, and the tuning of controller parameters that are to meet performance specifications in the various vector control loops, are proposed. The proposed techniques are further verified by experiments. Close simulation and experimental results are obtained.     

Identification of linear time‐invariant system with deterministic disturbances

Abstract

The identification of linear time‐invariant SISO discrete systems that have a deterministic disturbance in the output is proposed. The method is purely algebraic so that the system is identified exactly. The persistent excitation of input sequence is discussed and a necessary and sufficient condition is developed.     

Computational Time Reversal for NDT Applications Using Experimental Data

A model-based non destructive testing (NDT) method is proposed for damage identification in elastic structures, incorporating computational time reversal (TR) analysis. Identification is performed by advancing elastic wave signals, measured at discrete sensor locations, backward in time. In contrast to a previous study, which was purely numerical and employed only synthesized data, here an experimental system with displacement sensors is used to provide physical measurements at the sensor locations. The performance of the system is demonstrated by considering two problems of a thin metal plate in a plane stress state. The first problem, which represents passive damage identification, consists in finding the location of a small impact region from remote measurements. The second problem is the identification of the location of a square hole in the plate. The difficulties one encounters in applying this identification method and ways to overcome them are described. It is concluded that while this is a viable model-based identification method, which may lead, after further development, to a practical NDT procedure, one must be careful when drawing conclusions about its performance based solely on numerical experiments with synthesized data.     

Mode of drug binding to DNA determined by optical tweezers force spectroscopy

Abstract

Optical tweezers were employed to investigate the effects of small DNA-binding molecules on the low-force (≤ 15 pN) stretching behaviour of single DNA molecules. As the canonical B-DNA helix is not perturbed in this force regime, the effects on DNA elasticity observed upon drug binding provide useful insight into how DNA-binding drugs may alter in vivo processes. In this study, the effects of agents with different DNA binding modes were analysed. DNA force—extension curves were recorded in the presence of netropsin, a purely minor groove-binding antibiotic drug, ethidium bromide, an intercalating fluorescent dye, and berenil, an antiprotozoal drug proposed to exhibit both intercalative and minor groove-binding modes. Applying an approximation of the worm-like chain model, which describes the low-force stretching behaviour, the results were analysed in terms of the DNA contour length and persistence length. From these single molecule studies it was observed that minor groove-binding and intercalating modes of DNA-binding could be distinguished based on changes to DNA elasticity.     

Effect of electrical and mechanical poling history on domain orientation and piezoelectric properties of soft and hard PZT ceramics

Abstract

The superior piezoelectric properties of all polycrystalline ferroelectrics are based on the extent of non-180° domain wall motion under electrical and mechanical poling loads. To distinguish between 180° and non-180° domain wall motion in a soft-doped and a hard-doped lead zirconate titanate (PZT) ceramic, domain texture measurements were performed using x-ray and neutron diffraction after different loading procedures. Comparing the results to measurements of the remanent strain and piezoelectric coefficient allowed the differentiation between different microstructural contributions to the macroscopic parameters. Both types of ceramic showed similar behavior under electric field, but the hard-doped material was more susceptible to mechanical load. A considerable fraction of the piezoelectric coefficient originated from poling by the preferred orientation of 180° domains.     

Phase instability and nonlinear effects in a mechanically synthesized FeB nanocrystalline alloy

Results are presented of investigations of the processes taking place during the mechanical formation of FeB alloy. It was observed that there are critical rates of introduction of damage and defect concentrations above which the system becomes unstable and two branches of nonequilibrium steady states appear. During grinding, transitions of a cyclic nature are observed between these states. It is noted that the evolution of the system is determined by the dynamics of the fluctuations and in this sense, the mechanical synthesis reaction may be unpredictable. It is established that the powder grinding process and mechanical formation of an alloy from atomic components cannot be treated on a purely mechanical or mechanochemical basis. They must be viewed as part of the general problem of nonlinear dynamic systems far from thermodynamic equilibrium. Pis’ma Zh. Tekh. Fiz. 24, 35–40 (July 26, 1998)     

Physical basis for model with various inelastic mechanisms for nickel base superalloy

Abstract

Two mechanical behaviour models for N – 18 alloy are proposed. The material is a powder metallurgy nickel base superalloy hardened by 60% volume of the ordered γ′ phase. The behaviour of alloy N – 18 is modelled by classical constitutive equations involving plasticity and creep. The experimental data used include stress relaxation and creep tests. An updated version of the first model is proposed and compared to the experimental data set. A new model is also presented with equations based on physical concepts. Material parameter identification is performed for each model, and experimental results are in good agreement with theoretical simulations.     

Double bridge circuit for self‐validated structural health monitoring strain measurements

In structural health monitoring (SHM) applications, sensor faults and structural damage need to be assuredly discriminated. A self‐diagnosis strain sensor operating in a continuous online SHM scenario is considered. The strain sensor is based on full electric resistance strain gauge Wheatstone bridges. The state of the art shows that such a sensor has not yet been developed. The loop current step response (LCSR) is a well‐known method to detect strain gauge debonding. However, applying the LCSR method to a full strain gauge Wheatstone bridge has some limitations analysed in this paper. To enable the use of the LCSR method in an online SHM scenario, the double bridge circuit is proposed in this work. Two new strain gauge debonding fault detection methods and a new debonding fault isolation method—based on the double bridge circuit measurements—are proposed and evaluated. Two new sensor fusion weighting approaches are also proposed and evaluated—to achieve strain gauge debonding fault tolerance on the double bridge circuit. The experimental results show that the proposed methods can detect, isolate, and tolerate a strain gauge grid debonding fault and can be applied in an online SHM self‐diagnosis sensor scenario.     

Identification of continuous‐time delayed systems using an input pulse of arbitrary shape

Abstract

This article resolves difficulties of continuous identification often encountered in field testing, such as unsteady initial states, unknown disturbances, and noise‐corrupted measurements. The unique feature of the proposed method is that it divides the identification problem into two simpler estimation problems based on pulse testing of arbitrary shape. Sequential algorithms are developed to deal with the first estimation problem subjected to the zero portion of the input and then to solve the remaining problem subjected to the arbitrary portion of the input. The method provides a convenient way to fit model predictions to output measurements in the face of unknown initial states and static disturbances. Simulation results demonstrate that the use of the integral filter renders the method rather robust with respect to noise and model structure mismatch.     

基于续尺度卷积网络的10 MW漂浮式风力机筋腱损伤识别EI北大核心CSCD

为提升复杂环境中漂浮式风力机平台筋腱结构隐性损伤识别率,基于卷积神经网络(convolutional neural network,CNN),提出连续多尺度卷积神经网络(continues-multi-scale convolutional neural network,CMS-CNN),建立“端到端”的损伤识别模型。为验证CMS-CNN方法的有效性,以10 MW漂浮式风力机为研究对象,对损伤位置、程度进行故障诊断,结果表明:连续多尺度模型比传统多尺度的诊断结果更佳;横荡加速度受环境载荷影响较小,基于此响应信号所训练的CMS-CNN诊断模型更可靠;CMS-CNN模型可在筋腱结构微弱损伤时实现精准定位,亦能完成结构隐性损伤程度识别。     

Effects of high temperature mechanical damage on physical properties of unidirectional Ti/SiC metal matrix composite

Abstract

A miniaturised test system was used to investigate how the thermal and electrical properties of a unidirectionally reinforced titanium alloy (Ti–6Al–4V)/SiC (SM1140+)metal matrix composite change with mechanical damage at elevated temperature. Thermal conductivity and expansion measurements were obtained in the longitudinal and transverse direction both before and after short term strength and creep tests and at intervals during tests to assess changes in interface characteristics as functions of mechanical or thermal damage. The mechanical tests included monotonic stress–strain and ramp creep at temperatures between 500 and 650°C. The changes in thermal properties were compared with model predictions for the dependence of thermal properties on interface characteristics. The agreement was good for thermal expansion changes but not for thermal conductivity. This was ascribed to the nature of the damage at the interface that probably still allowed thermal transport but not mechanical load transfer.     

Methods for process-related resin selection and optimisation in high-pressure resin transfer moulding

ABSTRACT

A framework for process-related resin selection and optimisation is proposed in the context of research and development for industrial applications of high-pressure resin transfer moulding. The first stage involves validation of the reaction kinetics model by differential scanning calorimetry and characterisation of viscosity, storage- and viscous-shear moduli by dynamic mechanical analysis in a rheometer as a function of time. It also includes capillary pressure measurements of curing resin impregnating a fibre yarn. Process-related resin selection criteria are based on the optimisation of cycle time, including filling time against gel time, micro-infiltration time and demould time. The proposed framework and associated test and analysis methodologies are applied to three epoxy resin systems in connection with carbon fibre reinforcement.     

Investigation into the creeping polarization and strain in PZT-855 under combined mechanical and electrical loadings

The time-dependent remnant polarization and remnant strains evolving with time are measured and modeled on initially unpoled ferroceramic PZT-855 under a compressive stress and an electric field. Experiments reveal that the compression stress significantly inhibits the hysteresis loop curves of the electric displacement and the strain since the two hysteresis loop curves against the applied electric field become narrower and narrower as the compression stress becomes larger and larger. Moreover, the compression stress decreases the coercive electric field significantly when compared to that under an applied purely electric field. The variable tendency of the coercive filed in the present case seems like a power-law curve. It is also seen that the compression stress significantly influences the variable features of the remnant polarization and remnant strains against time although the time-dependent feature still remains. In particular, the larger the compression stress is, the smaller the remnant polarization and remnant strains are. For some extreme cases, the remnant strain transfers from a tensile strain to a compressive strain. The power-law formulation proposed by Liu and Huber (J Eur Ceram Soc 29:2799?C2806, 2006) is extended to model the present experimental data. However, unlike those under purely electric fields, as the mechanical loading varies from 0 to 100 MPa, the predicted saturation of the remnant polarization appears much earlier than the present experimental data. This limits the application of the power-law model. Further theoretical investigations are needed which will be given in a sequel.     

High-speed impact of electromagnetically sensitive fabric and induced projectile spin

This work deals with the dynamic contact of a rigid body with a deformable electromagnetically sensitive fabric structure, represented by a network model. Of particular interest are the electromagnetically induced forces generated on the fabric, which are proportional to the external electric field (E ^EXT ) and the velocity crossed with the external magnetic field (v × B ^EXT ). These forces transmit reactions to the rigid contacting object, which can induce rotational motion. Modeling and simulation of this effect can be useful in ballistic shielding applications, because the rotation of an incoming, ogival, projectile allows it to be more easily impeded. A modular formulation for the deformation of impacted fabric structures, represented by a network model, is developed in this paper, characterized by (1) stretching of interconnected yarn networks, described by simple constitutive relations, including yarn damage, (2) interaction with impacting objects, incorporating contact with friction and (3) electromagnetic sensitivity and actuation, demonstrating how the Lorentz force can be harnessed to break symmetric deformation patterns in order to induce spin onto an incoming object, whether that object is electromagnetically sensitive or not.     

Digital watermarking based on fractal image coding

Abstract

With advances in computer network and multimedia technology, digital media are rapidly proliferating, and thus the issue of copyright protection for electronic publishing is receiving great attention. To achieve the goal of copyright protection, the digital watermarks are used to identify the owner of a certain image, so as to prevent illegal copying. Digital watermarking is the technique that embeds an invisible signal including owner identification and copy control information into multimedia data such as audio, video, and images. A new digital watermark approach based on fractal image coding is proposed in this paper. We present a way to use the fractal code as a means of embedding a watermark into image. The proposed approach has been shown to be resistant to general attacks, like StirMark. Moreover, someone who owns the decryption key can simply extract the digital watermark from the watermarked image without resorting to the original image.     

Modeling and Measuring All the Elements of an Ultrasonic Nondestructive Evaluation System II: Model-Based Measurements

Abstract

In Part I: Modeling Foundations [1], a comprehensive model of an ultrasonic nondestructive evaluation (NDE) flaw measurement system was developed. Here, it will be shown that this comprehensive model can be used to completely characterize commercial measurement systems where all the elements of the system can be either modeled explicitly or measured, using purely electrical measurements. When combined, these models and measurements are shown to be able to predict accurately the measured signals in an ultrasonic test.     

Evaluation of Damage in Concrete Under Uniaxial Compression by Measuring Electric Response to Mechanical Impact

The paper proposes a method of evaluating damage in concrete under uniaxial compression. The evaluation procedure is based on measuring the electric response to mechanical impact. Measurements are made periodically while the external load is gradually increased. The experiment is carried out using samples of normal weight concrete. The algorithm for evaluating concrete degradation under uniaxial compression is based on analyzing signals in terms of time and frequency. The paper analyzes a number of measured and computed parameters of the electric response: the energy attenuation coefficient of the electric responses; the correlation coefficient of the signal spectra prior to and during the loading; the spectral centroid of the signal spectrum and the frequency of the dominant spectral peak. Experimental results show that the array of the collected data allows for evaluation of cracking processes in concrete under an external compressive load. The proposed method can be used to monitor the development of damage in concrete under uniaxial compression.     

The crack surface anomalous scaling and its connection with the size-scale effects

The size-scale effects is one of the most important research topics in solid mechanics. Several theories have been proposed in order to describe the scaling of mechanical properties in fracture mechanics of quasi-brittle materials such as concrete, rock, wood and a broad class of fibrous or particulate composites. In the last two decades they were investigated by means of several techniques, including renormalisation group theory, intermediate asymptotics, dimensional analysis, statistics of extremes among the others. One of the most successful approaches is the fractal one. It is based on the assumption of a fractal-like damage localization at the mesostructural level and on the linking of mechanical properties to the fractal dimensions of the damage domains. In particular, the fractal dimension of fracture surface an be linked to the scaling properties of toughness. On the other side, recent experimental researches have shown that fracture surfaces present an anisotropic propagation in the longitudinal and transverse directions. To describe such anisotropy, it does not appear sufficient to characterize the fracture surface by a single fractal dimension, but the anomalous scaling (Morel et al., Physical Review E 58, 6999–7005 [1998]) should be introduced. This approach has proved to be very effective in describing the R-curve behaviour (Morel et al., International Journal of Fracture 114, 307–325 [2002]). Dealing with the size-scaling effects, a scaling law for both fracture toughness and tensile strength has been recently proposed. In this work, we point out some inconsistencies of the proposed approach, suggesting a more consistent way to derive the scaling laws and a correction on the scaling exponent at the larger scales. The phenomenon of scaling in notched and un-notched structures is summarized in a unified framework and the anomalous scaling is applied to the case of unnotched specimens, showing how it captures correctly only the convexity of the scaling law in a bilogarithmic plane and not the real asymptotes, thus indicating that the anomalous scaling can not be considered as a satisfactory explanation to the size-scale effects.     

Wigner–Ville distribution based diffraction phase microscopy for non-destructive testing

ABSTRACT

The paper proposes an approach for non-invasive measurement of displacement derivatives and defect identification using an optical interferometric technique based on diffraction phase microscopy. Our approach relies on the application of Wigner–Ville distribution method in diffraction phase microscopy for directly extracting the phase derivative information, which is subsequently utilized for non-destructive deformation metrology. In addition, the proposed method offers good computational efficiency and robustness against noise for fast defect inspection. The performance of the proposed method is validated by experimental results.