Experimental Identification Procedure Research Articles

Kissing bond detection in structural adhesive joints using nonlinear dynamic characteristics

In this paper, the effect of kissing bond on nonlinear dynamic behavior of structures with flexible adhesive joint is investigated. Bilinear characteristic due to opening and closing in kissing bond region results in nonlinear dynamic behavior of the structure such as harmonic distortion in response to harmonic excitation. So, the higher-order harmonics can be considered as Nonlinear Damage Indicator Functions (NDIF) for the purpose of damage identification. A two-dimensional (2D) finite element model of a beam connected to a rigid support via a flexible adhesive layer is used to investigate the efficiency of the proposed NDIFs in kissing bond detection. Kissing bond is introduced to the model via contact elements. NDIFs are extracted for the finite element model using single tone stepped-sine test simulation. Parameters such as amplitude of excitation, size and location of kissing bond region as well as friction between kissing surfaces, are studied. The results proved that the NDIFs are sensitive to the size and location of kissing bond. Consequently, in an experimental damage identification procedure, NDIFs can be used as an indicator of kissing bond type damages in adhesive joints.

The geometry of distributional preferences and a non-parametric identification approach: The Equality Equivalence Test

This paper proposes a geometric delineation of distributional preference types and a non-parametric approach for their identification in a two-person context. It starts with a small set of assumptions on preferences and shows that this set (i) naturally results in a taxonomy of distributional archetypes that nests all empirically relevant types considered in previous work; and (ii) gives rise to a clean experimental identification procedure – the Equality Equivalence Test – that discriminates between archetypes according to core features of preferences rather than properties of specific modeling variants. As a by-product the test yields a two-dimensional index of preference intensity.

Robust Control for a Spatially Three-Dimensional Heat Transfer Process

Reliable modeling and robust control of heat transfer processes are tasks with many applications in engineering. Such tasks are relevant, for example, in control of high-temperature fuel cells, in manufacturing of semiconductor devices, control and modeling of welding processes, and for a reliable description of tube-like gas heater structures. For this reason, control-oriented modeling procedures for spatially distributed heating systems are described in this paper. The resulting models, derived from a spatial semi-discretization employing a finite volume modeling technique, are parameterized by means of experimental identification procedures. These models are then used for the design of robust controllers as well as for state and disturbance observers. An experimental validation on a test rig available at the Chair of Mechatronics at the University of Rostock concludes this paper.

An advanced control strategy of an electrical--powered hospital bed.

This paper develops a multivariable control technique for low-level control of an intelligent hospital bed. First, multivariable hospital bed models, nominal, upper bounded and lower bounded models, are obtained via an experimental identification procedure. Based on the obtained nominal model, the triangular diagonal dominance (TDD) decoupling technique is applied to reduce a complex multivariable system into a series of scalar systems. For each scalar system, an online adaptive control strategy is then developed to cope with system uncertainties. Compared to the conventional control method, real-time experimental results showed that our proposed multivariable control technique achieved better performance. Experimental results also confirmed that desirable system performance was guaranteed under system uncertainty conditions.

Experimental Study of Steel and Glass Knitted Fabrics Thickness under Pre-Strain and Shear

In this paper the compression behaviour after different pre-strain and different shear angle of steel and glass fibre knitted fabrics will be analysed. These types of materials are used during the production of automotive windshields and other glasses in a car. The production of a windshield involves a step whereby the glass is deformed to the desired shape by using a mould. It is important that during this forming step the glass is not damaged and that the optical quality of the glass falls within the specifications of the customer. A knitted steel fibre fabric covers the mould. Since this fabric comes in direct contact with the glass, it is a key factor that determines the quality of the formed windshield. Variation of the fabric thickness can affect the optical quality of the glass. Thus far fabric very often manufacturers operate on the basis of empirical trial and error results to design their products. The challenge of the present work is to establish an experimental procedure for identification of the material laws for knitted fabrics deformation resistance. The paper describes an experimental procedure for derivation of the fabric thickness dependence on its deformation, using biaxial tension, shear and compression tests. The compression tests are performed on an Instron mechanical testing machine. During the test, a load cell (1 kN) pushes down with a constant speed of 1 mm/min onto the sample, compressing it. The load cell is attached to a cylinder which has a diameter of 70mm. The knitted fabrics was tested in the relaxed state and after pre-tension on the biaxial tester with pre-strains of 5x5%, 10x10%, 15%x15%, 0x10%, 10x0%, 0x20%, 20x0% and they was also tested after different shear angle (5°, 10°, 15°, 25°). Difference of thickness of fabrics after pres-strain is till 90 µm and for 25°shear angle is about 30 µm. Acknowledgements The work was funded by the grant 631/MOB/2011 of the Polish Ministry of Science and High Education, with the support from K.U.Leuven and N.V. Bekaert S.A.

Estimate of the axial force in slender beams with unknown boundary conditions using one flexural mode shape

This paper presents an experimental procedure for the axial load identification of slender prismatic beams with unknown boundary conditions by making use of one vibration frequency and of five amplitudes of the corresponding mode shape. In fact, this method does not require the knowledge of the effective length of the beam under examination, but only the flexural rigidity and mass per unit length. The proposed algorithm was verified by means of many numerical and experimental tests on tie-rods having different boundary conditions. Excellent estimates of the axial forces were obtained. Finally, the influence of the location of the instrumented sections on the estimation of the axial load was analyzed using a simply supported beam model.

Experimental model identification of open-frame underwater vehicles

Most of the works published on hydrodynamic parameter identification of open-frame underwater vehicles focus their attention almost exclusively on good coherence between simulated and measured responses, giving less importance to the determination of “actual values” for hydrodynamic parameters. To gain insight into hydrodynamic parameter experimental identification of open-frame underwater vehicles, an experimental identification procedure is proposed here to determine parameters of uncoupled and coupled models. The identification procedure includes: (i) a prior estimation of actual values of the forces/torques applied to the vehicle, (ii) identification of drag parameters from constant velocity tests and (iii) identification of inertia and coupling parameters from oscillatory tests; at this stage, the estimated values of drag parameter obtained in item (ii) are used. The procedure proposed here was used to identify the hydrodynamic parameters of LAURS—an unmanned underwater vehicle developed at the University of São Paulo. The thruster–thruster and thruster–hull interactions and the advance velocity of the vehicle are shown to have a strong impact on the efficiency of thrusters appended to open-frame underwater vehicles, especially for high advance velocities. Results of tests with excitation in 1-DOF and 3-DOF are reported and discussed, showing the feasibility of the developed procedure.

Modal numerical–experimental identification method for characterising the elastic and damping properties in sandwich structures with a relatively stiff core

In this paper, a mixed numerical–experimental identification procedure for characterising the storage and loss properties in sandwich structures with a relatively stiff core is developed. At the computational level, the proposed method is based upon an original structurally damped shell finite element model derived from the higher-order shear deformation theory and, at the experimental level, upon an accurate contact-free measurement setup with a loudspeaker-based excitation and a scanning laser interferometer for capturing the time responses. From the modal information extracted from two specimens with different geometries, the procedure allows the simultaneous estimation of the skin and core constitutive parameters through adequate objective functions measuring the discrepancy between the experimental data and the numerical predictions. For validation purposes, the method is then applied to two test cases for which all the influent properties could be estimated with a fairly good accuracy.

High precision massive shape control of magnetically levitated adaptive mirrors

The paper presents a control scheme that provides precise active shape control of deformable mirror shells using a very large number of control points. The proposed controller combines a low frequency centralized feedforward and a high frequency fully decentralized feedback, with each single actuator mated to a single sensor. To grant a precisely controlled shape the feedforward part requires an accurate knowledge of the system stiffness. For this purpose a viable experimental identification procedure for high dimension steady state response matrices is described and verified through realistic simulations. Finally the control methodology is applied to the model of an adaptive secondary mirror with 3360 control points. Numerical results confirm the validity of the proposed approach.

Generation Units Models for Load Dispatch Simulator

This paper presents aspects regarding Load Frequency Control (LFC) in the Romanian Power System, which, considering its characteristics, is a large system. Load Frequency Control keeps the balance of the power generation and consumption in a control area in order to maintain an acceptable system frequency. Time models for hydro and thermal generation units used by LFC in the Romanian Power System are presented in the paper. These models were obtained using experimental data provided from the system (step response tests). The model parameters were determined using an experimental identification procedure based on the Trust Region Algorithm. Finally, we proposed and tested a simulation diagram for modelling the load dispatch.

Inverse Method Based on Modal Vibration Testing for Characterizing the Elastic Properties

This paper presents a inverse method to derive the material properties from the resonance frequencies of a free-edge test specimen based on modal vibration test. A mixed numerical experimental identification procedure is used for this purpose. Finite element models of the test plate is simultaneously updating and reproduces the updating frequencies, then optimal procedure is running. The sum of the squared differences between the experimental and the finite element method numerical resonance frquencies is the objective function. To seek practical solutions, here presents a global optimization method--simulated annealing method for the determination of the elastic properties. The inverse method is applied to determine the elastic constants of aluminum , carbon/epoxy , Glass/PP composite material and double coated steel plate. The results indicate that the method can obtain very accurate elastic constants for aluminum , Glass/PP , carbon/epoxy composite material ,but for double coated steel plate , if the individual layer of the three different layers is as isotroptic material having six elastic constants , the method can obtain very accurate results , but if it is as transversely isotropic material having twelve elastic constants, the evaluating elastic constants are bad.

Compaction of aggregated ceramic powders: From contact laws to fracture and yield surfaces

This work describes a methodology based on Discrete Element Method (DEM) simulations to generate yield and fracture surfaces for aggregated ceramic powders. The DEM simulations, which consider the length scale of porous aggregates, are used as numerical triaxial experiments to obtain the behavior of a small volume element of powder under a given load. The experimental identification procedure, which relies on the Design Of Experiment method, is designed to limit the number of experiments and simulations needed to obtain the model material parameters. These material parameters, which model the interactions between aggregates in the DEM simulations are identified using two simple experiments on a Uranium diOxide powder: closed-die compaction and diametrical compression test. The yield and fracture surfaces obtained from the DEM simulations provide valuable information on the behavior of the powder for stress states that are difficult or impossible to attain in complex triaxial tests.

Using Modal Analysis and Optimization to Determine Elastic Constants of Thick Composite Plates

This paper presents an inverse method to derive the elastic constants of thick composite plates from the resonance frequencies of a free-edge test specimen based on modal vibration test. A mixed numerical experimental identification procedure is used for this purpose. The sum of the squared differences between the experimental frequencies and analytical frequencies from finite element method is chosen as the objective function. The optimization techniques, Hybrid Genetic /Simulated Annealing algorithm, have been applied to determine the elastic constants. As the objective function reaches its minimum, its corresponding design variables are the elastic constants of the material. The present method is applied to determine the elastic constants of AS4/PEKK material. The results indicate that different stacking sequences and numbers of frequencies have effects on the determination of elastic constants of the materials.

Recent Patents on In-Plane Permeability Measurement of LCM Composite Reinforcements

Optimization of Liquid Composite Molding (LCM) processes using Darcy flow numerical simulation requires inputting accurate reinforcement permeability data. Historically introduced by its author to describe infiltration phenomenon, permeability coming from Darcys law is usually used in LCM processes as a rheological parameter in order to predict the macroscopic resin motion during the filling stage. Resulting from the flow through a complex fibrous architecture, its measurement is very sensitive to the test conditions due to the high filaments flexibility and mesostructure heterogeneity. Reinforcements are currently anisotropic fibrous media and their in-plane permeability measurement requires specific facilities. Measurements can be performed in transient or steady state conditions, and in one-, two- or three-dimensional configurations. This paper describes the different existing experimental configurations, identification procedures and instrumentation techniques. Advantages and drawbacks of each method are discussed, in the particular case of 2D transient measurements, which are the most representative of Resin Transfer Molding process. Two recent patents using different instrumentation techniques are detailed. They are focused on the simultaneous identification of the in-plane principal permeability values in an anisotropic fibrous reinforcement. Some perspectives are suggested to improve the repeatability of such measurement results. Keywords: Permeability measurement, fibrous reinforcement, liquid composite molding, anisotropic porous media

Inverse method based on modal analysis for characterizing the constitutive properties of thick composite plates

This paper presents a powerful method for evaluating the constitutive properties of composite laminates through a mixed numerical–experimental identification procedure based on both the extracted mode shapes and the corresponding natural frequencies of the structure. The modal quantities are measured with a precise contact-free experimental technique and extracted numerically with an accurate shell element derived from the higher order shear deformation theory. The elastic properties are estimated with a nonlinear least squares algorithm applied to modal identification criteria. With this novel approach of combining frequency and mode based error norms, the proposed identification method allows an accurate identification of both in-plane and transverse elastic properties with a single non-destructive test. The effectiveness of the procedure is highlighted by test cases on moderately thick to thick plates.

Genomic systematic evolution of ligands by exponential enrichment (Genomic SELEX) for the identification of protein-binding RNAs independent of their expression levels

Genomic systematic evolution of ligands by exponential enrichment (Genomic SELEX) is an experimental procedure for the expression condition-independent identification of protein-binding RNAs. RNA libraries derived from genomic DNA are generated via random priming, PCR amplification and in vitro transcription. Libraries consist of genomic sequences of selected size, and fragments are flanked by constant sequences required for amplification and transcription. This RNA pool is then subjected to several rounds of selection and amplification to enrich for RNAs meeting the selection criteria. Various selection criteria are possible. Here we describe selection by affinity to a protein of interest. High-affinity ligands can then be cloned and sequenced to allow their identification. With this method, protein-binding RNAs can be discovered, nucleic acid-protein interactions can be identified, and whole protein-nucleic acid networks can be defined. This method is also suitable for discovering novel genes, including non-protein-coding RNAs, and it complements in silico approaches. It is better suited to detect protein-binding RNAs that are differentially expressed (and therefore absent from many tissues) and low-abundance RNAs than experimental procedures that start from the isolation of expressed RNAs. The protocol takes approximately 3 months to complete.

Series No. 1 Identification and HPLC Quantification of Carotenoids of the Fruit Pulp of Chrysophyllum Roxburghii

Carotenoids of the fruit pulp of Chrysophyllum roxburghii (Sinhala: laualu) amounted to about 180 mgkgl by fresh weight. The carotenoids were isolated by open column chromatography (Mg0:Celite 1:l) using mixtures of petroleum ether 40-60 C and acetone and identified by UVIvisible spectra, chemical tests, and High Performance Liquid Chromatography (HPLC) using authentic standards and a photodiode array detector (PAD). The major carotenoid was trans-violaxanthin (113 mgkg-'1. Also present was cis- violaxanthin, neoxanthin, P-cryptoxanthin monoepoxide, lutein, p-cryptoxanthin, <-carotene and p-carotene. The retinol equivalent of the pulp was only 68 RE1100 g. The study shows that Chrysophyllum roxburghii is not a good source of pro- vitamin A. Further as violaxanthin is reported to be not absorbed by humans, it is of no use as a dietary antioxidant. However, as trans-violaxanthin can be obtained in quantity in the pure crystalline state, directly from the column and has the benefit of eluting at 20% acetone away from most carotenoids, the compound will be useful as a standard for HPLC analysis of carotenoids from other fruits and leaves. hydroxy sintaxanthin. Some of these are not listed in a recent compendium on carotenoids naturally occurring in plant^.^ Further, the experimental techniques and identification procedures used in the above study are not in line with modern analysis procedures. There is, therefore, a possibility that some of these are artifacts of isolation.

Identifiability of sorption and diffusion processes using EIS: Application to the hydrogen reaction

In this work, a test is presented to determine the theoretical identifiability of electrochemical models involving adsorption and absorption of intermediate species coupled to diffusion. Analysis of theoretical identifiability is needed before the practical identification in order to know whether the model parameters may be identified globally (unique solution) or locally (a finite number of solutions), or if they are non-identifiable (infinite number of solutions). An experimental identification procedure of the system parameters is also proposed, this method being adequate even for theoretically non-identifiable models. The identifiability test is applied to the analysis of hydrogen evolution and insertion in metallic substrates. To illustrate the proposed procedure, electrochemical impedance spectroscopy (EIS) data were used for the experimental estimation of the hydrogen reaction parameters on steel electrodes.

Experimental identification of AURORA airship

An experimental identification procedure in order to determine a state space linearized model of the longitudinal dynamic of the AURORA airship and the estimation of the non dimensional aerodynamic coefficients is presented. From this procedure, the adapted theoretical model is validated through the comparison of the aerodynamics coefficients, estimated from the identified model, and those given by a prior knowledge. The real data are collected from flight test measurements and subspace based system identification techniques such as MOESP algorithm is used.

Damage detection of fiber-reinforced polymer honeycomb sandwich beams

In a framework of developing a structural health monitoring for civil infrastructure, the damage identification procedure based on dynamic response for fiber reinforced polymer (FRP) sandwich composites is evaluated. In this paper, an experimental damage identification procedure based on structural dynamic responses and using smart sensors is conducted. Damage identification is estimated from comparison of dynamic responses of healthy and damaged FRP sandwich beams. Correspondingly, based on the relationship between the changes of mechanical properties and the related changes of dynamic responses (i.e., the curvature mode shapes in this study), damage magnitude is quantified. The composite sandwich beams are made of E-glass fiber and polyester resin, and the core consists of the corrugated cells in a sinusoidal configuration. Artificial damage is created between the interface of core and faceplate and also in the core of sandwich beam to simulate core–faceplate debonding and core crushing, respectively. Using piezoelectric smart sensors, dynamic responses data is collected and dynamic characteristics of the sandwich structure are extracted, from which the location and magnitude of the damage are evaluated. As demonstrated in this study, the present dynamic response-based procedure using smart sensors can be effectively used to assess damage and monitor structural health of FRP honeycomb sandwich structures.