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A novel approach is introduced for reliable prediction of the retention time of morphine and its derivatives, which have widespread use in medical and pharmaceutical applications. A core correlation is introduced based on the number of carbon and hydrogen atoms as well as the number of ester, noncyclic ether, and ketone functional groups from experimental data of 42 compounds. An improved correlation is developed to increase the reliability of the core correlation by inserting a correcting function. The reliability of two correlations is tested and compared with the best available complex method based on a backpropagation artificial neural network (BP-ANN) for further 15 compounds. The values of root mean squared error (RMSE) of core and improved correlations for the test set are 0.5681 and 0.4832 min, which are lower than those reported by BP-ANN (0.6052 min). Cross-validations of the improved correlation corresponding to the coefficients of determination for leave-one-out (Q2LOO) and the fivefold cross-validation (Q25CV) are close to its the coefficient of determination (R2 = 0.982), which confirms goodness-of-fit, goodness-of-prediction, accuracy, and precision of the novel model.

In this paper the transmission error and the strain field are analysed for two gear pairs, with different lightweight designs, reflecting the common industrial practice. The methodology used for the analysis is based on a hybrid FE-Analytical approach implemented in a multibody solver which allows to achieve a good accuracy with a low computational effort. The specific formulation allows to well describe the deformation field of the gear body from which the strain values can be computed at specific locations in the FE model. The numerical method used in this work is validated both in terms of transmission error and strain field, using the results obtained from an experimental campaign performed on a high-precision gear test rig.

© 2016 Elsevier Ltd This paper presents a technique for offline time synchronization of data acquisition systems. The technique can be applied when real-time synchronization of data acquisition systems is impossible or not sufficiently accurate. It allows for accurate synchronization based on the acquired dynamic response of the structure only, without requiring a common response or the use of a trigger signal. The synchronization is performed using the results obtained from system identification, and assumes linear dynamic behavior of the structure and proportional damping of the structural modes. A demonstration for a laboratory experiment on a cantilever steel beam shows that the proposed methodology can be used for accurate time synchronization, resulting in a significant improvement of the accuracy of the identified mode shapes. publisher: Elsevier articletitle: Offline synchronization of data acquisition systems using system identification journaltitle: Journal of Sound and Vibration articlelink: http://dx.doi.org/10.1016/j.jsv.2016.06.015 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved. ispartof: Journal of Sound and Vibration vol:381 pages:264-272 status: published

© 2018 Elsevier Ltd This paper presents an algorithm for the localization of forces applied to a structure. The force estimation is performed in the frequency domain based on a limited number of sensors and a linear dynamic system model and it involves minimizing an objective function penalized with a group sparsity term. The minimization of this objective function is formulated as a second order cone program, which is solved using an interior point method. This allows for a reduction of the calculation time when compared to other algorithms that are currently available to enforce group sparsity on the forces, especially for large scale problems. The presented algorithm is first verified using numerical simulations. Next, a validation is performed using data obtained from a field test on a footbridge, where two locations on the bridge deck are excited using hammer impacts and the force localization is performed assuming a total of 108 possible force locations. ispartof: MECHANICAL SYSTEMS AND SIGNAL PROCESSING vol:115 pages:593-606 status: published

Vibration measurements of the fuel assembly of a nuclear reactor are a very useful tool to determine the health and lifetime of the reactor core. The importance of these measurements is exacerbated in the new generation of heavy liquid metal reactors, where the fuel assembly is exposed to a corrosive molten metal coolant at 300 $^\circ$ C and where the space between the individual fuel pins is limited to a few millimeters. In this paper, we consider fibre Bragg gratings as potential candidates for carrying out fuel pin vibration measurements in such an environment. We describe a dedicated method to integrate fibre Bragg gratings in a fuel pin, and we subject this pin to conditions close to those encountered in a real heavy liquid metal reactor. More specifically, we report on the performance of draw tower gratings used as a vibration sensor when the fuel pins are immersed in heavy liquid metal at 300 $^\circ$ C for up to 700 h. The performance evaluation is based on monitoring the signal-to-noise ratio of the grating's spectral response as a function of time. We show that accurate detection of the Bragg peak becomes very challenging after 400 h of exposure. Additionally, we succeed to extend the useful lifetime with a factor of two by using an appropriate integration of the fiber in the fuel pin and by using an alternate peak detection algorithm.

Nowadays, it is possible to manufacture smart composite materials with embedded fiber optic sensors. These sensors can be exploited during the composites' operating life to identify occurring damages such as delaminations. For composite materials adopted in the aviation and wind energy sector, delaminations are most often caused by impacts with external objects. The detection, localization and quantification of such impacts are therefore crucial for the prevention of catastrophic events. In this paper, we demonstrate the feasibility to perform impact identification in smart composite structures with embedded fiber optic sensors. For our analyses, we manufactured a carbon fiber reinforced plate in which we embedded a distributed network of fiber Bragg grating (FBG) sensors. We impacted the plate with a modal hammer and we identified the impacts by processing the FBG data with an improved fast phase correlation (FPC) algorithm in combination with a variable selective least squares (VS-LS) inverse solver approach. A total of 164 impacts distributed on 41 possible impact locations were analyzed. We compared our methodology with the traditional P-Inv based approach. In terms of impact localization, our methodology performed better in 70.7% of the cases. An improvement on the impact time domain reconstruction was achieved in 95.1% of the cases.

© © 2016 Elsevier Ltd. All rights reserved. This paper presents a verification of a joint input-state estimation algorithm using data obtained from in situ experiments on a footbridge. The estimation of the input and the system states is performed in a minimum-variance unbiased way, based on a limited number of response measurements and a system model. A dynamic model of the footbridge is obtained using a detailed finite element model that is updated using a set of experimental modal characteristics. The joint input-state estimation algorithm is used for the identification of two impact, harmonic, and swept sine forces applied to the bridge deck. In addition to these forces, unknown stochastic forces, such as wind loads, are acting on the structure. These forces, as well as measurement errors, give rise to uncertainty in the estimated forces and system states. Quantification of the uncertainty requires determination of the power spectral density of the unknown stochastic excitation, which is identified from the structural response under ambient loading. The verification involves comparing the estimated forces with the actual, measured forces. Although a good overall agreement is obtained between the estimated and measured forces, modeling errors prohibit a proper distinction between multiple forces applied to the structure for the case of harmonic and swept sine excitation. publisher: Elsevier articletitle: Verification of joint input-state estimation for force identification by means of in situ measurements on a footbridge journaltitle: Mechanical Systems and Signal Processing articlelink: http://dx.doi.org/10.1016/j.ymssp.2015.12.017 content_type: article copyright: Copyright © 2016 Elsevier Ltd. All rights reserved. ispartof: Mechanical Systems and Signal Processing vol:15 pages:245-260 status: published

Incore temperature measurements are crucial to assess the condition of nuclear reactor components. The sensors that measure temperature must respond adequately in order, for example, to actuate safety systems that will mitigate the consequences of an undesired temperature excursion and to prevent component failure. This issue is exacerbated in new reactor designs that use liquid metals, such as for example a molten lead-bismuth eutectic, as coolant. Unlike water cooled reactors that need to operate at high pressure to raise the boiling point of water, liquid metal cooled reactors can operate at high temperatures whilst keeping the pressure at lower levels. In this paper we demonstrate the use of optical fibre sensors to measure the temperature distribution in a lead-bismuth eutectic cooled installation and we derive functional input e.g. the temperature control system or other systems that rely on accurate temperature actuation. This first-of-a-kind experiment demonstrates the potential of optical fibre basedinstrumentation in these environments. We focus on measuring the surface temperature of the individual fuel rods in the fuel assembly, but the technique can also be applied to other components or sections of the installation. We show that these surface temperatures can be experimentally measured with limited intervention on the fuel pin owing to the small geometry and fundamental properties of the optical fibres. The unique properties of the fibre sensors allowed acquiring the surface temperatures with a resolution of 30 mK. With these sensors, we assess the condition of the test section containing the fuel assembly during different steps of the operation of the facility, including the heating and verification of the vacuum of the loop as well as the filling and draining of the LBE loop. We also identify a simulated electrical shut-down and heating circuit failure in the primed installation. (C) 2015 Elsevier B.V. All rights reserved.

Composite materials are nowadays widely used in several applications, especially in the aerospace field. Despite the numerous advantages that composites can offer, the health monitoring of this type of structures is challenging. A major challenge regards the detection and monitoring of delaminations. In the case of aeronautical structures, delaminations are often caused by impacts with external objects. Therefore, the capability of detection, localization and reconstruction of occurring impacts becomes an essential health monitoring tool for the estimation of the remaining structure lifetime. In this paper, we propose a new procedure for the reconstruction of impacts, based on the structural model and on measured vibration data. The procedure is tested over a carbon fiber reinforced composite plate, instrumented with surface mounted fiber Bragg grating sensors. The experimental results show that the proposed algorithm (VS-LS) can localize and reconstruct the impact forces with at least three times better accuracy than the classical pseudo-inverse method. (C) 2016 Elsevier Ltd. All rights reserved.

Wind induced ovalling vibrations were observed during a sto rm in October 2002 on several empty silos of a closely spaced group consisting of 8by 5 thin-walled silos in the port of Antwerp (Belgium). In the present study, it is investigatedif the observed ovalling oscillations can be numerically predicted. To this end, the silo structur es are modeled using a finite element (FE) model and the wind flow around a single silo is investigat ed using 3D computational fluid dynamics (CFD) simulations. A wind tunnel experiment w as set up to validate the CFD simulations. To explain the onset of the wind induced ovalli ng vibrations, the interaction of the wind field with the structural vibrations has to be taken intoaccount. Therefore, the complex interplay of both fields is investigated with both one-way an d two-way coupling simulations. It is interesting to compare the results of both coupling app roaches to assess the necessity of performing the computationally much more time-consuming t wo-way coupling simulations. It is found in both coupling approaches that the mode shapes with t he lowest natural frequencies are excited dynamically. The results in the one-way coupling si mulations differ however from those in the two-way coupling, demonstrating the importance of pe rforming fully coupled simulations for suchlike aeroelastic problems.

This paper presents a technique for offline time synchronization of data acquisition systems for linear structures with proportional damping. The technique can be applied when direct synchronization of data acquisition systems is impossible or not sufficiently accurate. The synchronization is based on the acquired dynamic response of the structure only, and does not require the acquisition of a shared sensor signal or a trigger signal. The time delay is identified from the spurious phase shift of the mode shape components that are obtained from system identification. A demonstration for a laboratory experiment on a cantilever steel beam shows that the proposed methodology can be used for accurate time synchronization, resulting in a significant improvement of the accuracy of the identified mode shapes.

The increasing complexity of mechanical structures makes the measurement of dynamic loadings on the structure non practical, since the applied forces can not be measured in a direct way. Recently, a vast category of inverse algorithms have been developed in order to solve the load identification problems. In contrast with forward methods that compute the output (effect) of a system subject to inputs (cause), inverse methods offer the possibility to compute the input parameters of a system with known output data and the system model. Inverse problems suffer in general from instability problems due to high condition number. They are almost always under-determined and highly sensitive to measurement errors. Optimization techniques based on regularized cost functions are the most popular remedies to this problem. This paper deals with a sensitivity analysis of the classical regularization techniques, compared to a newly developed method (G-FISTA). The aim is to reconstruct applied loads on structures in noisy environments. Multiple simulation studies are done considering several situations of noise level, point force locations and sensor configurations. This study shows that the location and time history of discrete forces on structures can be better estimated using structured-sparse penalty functions techniques. A detailed noise study is done using the pseudo-inverse, Tikhonov and G-FISTA methods in frequency domain, and their performances are evaluated.

The identification of system parameters using forward approaches is not always practical due to the rising complexity of modern structures, leaving no chance for direct parameter measurements. In contrast to forward methods, inverse techniques have been gaining popularity, since the advent of high performing computers. This approach consists of the computation of input parameters of a system, with known "output data" and the "system model". When the number of equations (sensors) becomes lower than the amount of unknowns (input parameters), the problem becomes underdetermined and most of the time highly sensitive to input perturbations, leading to infinity of existing solutions. The discrete force identification problem in mechanics consists of estimating a set of two unknown parameters based on measured structural responses: the impact force locations and their corresponding time history. In this article we propose a new approach to identify forces on structures, by making use of an iterative optimization technique. This algorithm creates a new mathematical setting for the inverse problem, and then solves it using a mixed cost function of group-penalized least squares. We also briefly mention some of the most famous existing methods for inverse problems in frequency domain, such as classical pseudo-inverse, Iterative weighted pseudo- inverse, regularization and penalized techniques. This study shows that the location and time history of discrete forces applied on a beam structure can be better estimated using this new iterative and penalization technique (G-FISTA).

The identification of system parameters using forward approaches is not always practical due to the rising complexity of modern structures, leaving no chance for direct parameter measurements. In contrast to forward methods, inverse techniques have been gaining popularity, since the advent of high performing computers. This approach consists of the computation of input parameters of a system, with known output data and the system model. When the number of equations (sensors) becomes lower than the amount of unknowns (input parameters), or when the condition number of the system is high, the problem does not have a unique solution. The system becomes under-determined and highly sensitive to input perturbations. The discrete force identification problem in mechanics consists of estimating the applied force locations and their corresponding time history based on measured structural responses. In this article, the applicability of a recently proposed force identification technique (G-FISTA) will be tested using a real-life measurement on a footbridge. This iterative algorithm promotes structured sparsity in the force vector. This algorithm creates a new mathematical setting for the inverse problem, and then solves it using a mixed cost function of group-penalized least squares. This study shows that the location and time history of discrete forces applied on a footbridge can be correctly estimated using the proposed technique.

In-core vibration measurements are crucial in view of preventing excessive vibration already in the design stage or assessing component integrity during operation. This issue is exacerbated in new reactor designs that use liquid metals, such as for example a molten lead-bismuth eutectic, as coolant. In this paper we demonstrate the use of optical fibre sensors to measure the vibration induced by the coolant flow in a lead-bismuth eutectic cooled installation and we apply modal analysis techniques to derive modal parameters of the system. This first-of-a-kind experiment demonstrates the potential of optical fibre based instrumentation in these harsh environments. We focus on measuring the vibration of the individual fuel rods in the fuel assembly, but the technique can also be applied to other components or sections of the installation. We show that the vibration on the fuel rods can be experimentally measured with limited intervention on the fuel pin owing to the small geometry and fundamental properties of the optical fibres. With these sensors, we determine the vibration amplitude and modal parameters of the fuel assembly containing the fuel rods during different steps of the operation of the facility, including the initial start-up of the coolant circulation as well as during continuous operation.

The dynamic response of a cantilever wing at small and large angles of attack was tested using the Active Aeroelastic Test Bench (AATB) in the wind tunnel at low wind velocity 8 m/s, Re ≈ 120, 000). The compliant wing was excited at the root of the wing with a small 2◦ pitch angle. Advantage was taken from the fact that the AATB allows for arbitrary excitation of the wing in pitch and plunge at its constrained root. This property is exploited in order to excite the wing with an odd random phase multisine. The response of the instrumented wing was recorded by using both fibre Bragg grating (FBG) optical strain gauges and piezoelectric accel-erometers. Using the spectral properties of the applied odd random phase multisine, the level of stochastic nonlinear distortions and the Best Linear Approximation (BLA) of the FRF was estimated for different angles of attack. A clear increase of the level of stochastic nonlinearities was observed when increasing the angle of attack up to 17.5◦. These distortions were mainlyfocussed around the resonance frequencies and in the very low frequency range. This latter could only be observed in the measurements of the FBG strain gauges due to the high pass filter effect of the piezoelectric accelerometers. Comparison of the identified BLA with gust response measurements showed that in general good predictions from the BLA model were possible when the Signal to Distortion Ratio (SDR) was above 10 dB. For the tested wing this was for angles of up to 12◦. Above this angle all resonance frequencies were still well approx-imated both in frequency and amplitude, however, a very important low frequency contribution was missing from the predicted data.

The design of mechanical structures requires the knowledge of acting dynamic loads. However, for some of these structures, e.g. aircraft wings and tall buildings, the external forces can not be measured directly. With the advent of high performance computers and reliable modal analysis techniques, accurate models of the structure are available. Inverse techniques offer the possibility to recover the systems input forces from noisy vibration data of the structure, given the structural model. More particularly, the discrete force identification problem consists of estimating a set of two unknown parameters based on measured structural responses: the force locations and the corresponding time history. Regularization and optimization techniques can solve the ill-conditioned load identification problem. In this article, we consider a scenario where external excitation loads are applied on a structure. We reconstruct the applied force history from the measured vibration data. The proposed algorithm creates a new mathematical setting for the inverse problem, and then solves it using a mixed cost function of group-penalized least squares. Several simulations and experiments in this study show that the location and time history of discrete forces on real structures can be better estimated using the proposed (G-FISTA) technique.