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The limited availability of analytical solutions and the high cost associated with experimental testing motivate the use of computational tools to assess the dynamic behavior of load-bearing components, especially when a wide design space must be explored, as is often the case with composite structures. In this context, a novel high-order accurate discontinuous Galerkin formulation for transient and free-vibration analysis of multilayered plates and shells is presented and numerical validated. The starting point of the formulation is a generalized structural theory for multilayered shells with arbitrary curvature based on the expansion of the displacement covariant components throughout the shell thickness. The variational statement of three-dimensional elastodynamics allows deriving the strong form of the governing differential equations, which form the basis to obtain the corresponding discontinuous Galerkin weak statements. As the order of the through-the-thickness expansion and the order of the discontinuous Galerkin basis functions are free parameters, the proposed approach allows tuning the order of accuracy of the computed solution throughout both the shell thickness and the shell modeling domain. Numerical results are reported and discussed for several validation test cases in terms of h - and p -convergence analyses, demonstrating the high-order accuracy, robustness, and computational savings of the formulation. • Transient and free-vibration analysis of laminated shells with general curvature. • An Equivalent-Single-Layer theory using the covariant components of displacement. • A high-order accurate discontinuous Galerkin formulation for shell dynamics. • Numerical solutions obtained using structured and implicitly-defined meshes. • h p -convergence analyses for various plate and shell geometries. [ABSTRACT FROM AUTHOR]

Some aspects of engineering dynamics, such as nonlinearities and transient motion of many interconnected parts, remain difficult to handle today. To comply with increasing demands on resilience and safety, the dynamics of large machines need to be better understood. Complex network methods, already present in many scientific disciplines, provide a tool set complementary to conventional methods of system analysis. This work aims at providing a new, function-based view on mechanical systems by generating functional networks. To this end, a network algorithm is applied to sets of cyclically coupled Duffing oscillators as a common example of a complex nonlinear mechanical system. In the functional network, each node represents an oscillator while the direction of the network edges represents a functional coupling. Results show that the network method is capable of identifying dynamical transitions and synchronization between components, as well as determining the number of different states present within a system. Additionally, the time evolution of the component interactions, especially in response to a disturbance, is studied via a sliding-window approach. The results of this analysis might hopefully open new ways for a more efficient system analysis through optional sensor placement, and for effective countermeasures against unwanted dynamics through improved analysis of transient dynamics. [Display omitted] • Network analysis reveals functional dependencies within a set of coupled oscillators. • Functional networks help uncover phase space dimensionality. • Network perspective allows tracking of propagation of disturbance in dynamical system. [ABSTRACT FROM AUTHOR]

• Formulation of transient flows in a pipeline with distributed leakage is developed by Fourier series analysis. • Analytical expressions are systematically validated by different numerical applications and experimental data. • Results analysis and discussion are conducted for the impacts of distributed leakage on transient waves. For health monitoring and condition assessment in water pipelines, most of the current transient-based leak detection studies simulate a practical leakage as a discrete point via the orifice equation. However, a solid evidence is yet to illustrate the validity of this simplification. Therefore, this study aims to fill this gap, by relaxing the assumption of leaks as dicrete points, and considering longitudinal crack-shaped leakages of various size. The analytical solutions based on the Fourier series in a typical reservoir-pipeline-reservoir are developed to analyze the time-domain pressure signals in transient operation. The proposed analytical solutions are numerically validated against the method of characteristics for different leaky scenarios including the leak ratio and longitudinal-crack length. Good agreement between the two methods demonstrates the effectiveness and accuracy of the derived analytical solution. For the distributed outflow along the entire pipe manifold, the numerical validation of the proposed analytical solution is provided by extracting data from the literature. The comparison among the time-domain signals of discrete and distributed leakage revealed that a longitudinal crack can slightly smoothen the pressure peaks with minor changes in amplitudes. [ABSTRACT FROM AUTHOR]

Several vibration harvesting parameters must be obtained through experiments due to the complexity of olive branches. However, the pure test method significantly reduces the efficiency of equipment development. Therefore, in this study, we proposes a research method based on a combination of finite element simulation and vibration tests to address this problem. SolidWorks was used to establish a three-dimensional model of an olive tree including some smaller branches, The natural frequency and modal vibration modes of olive trees were determined by modal analysis. Furthermore, the vibration parameters were determined by harmonic response analysis. Then, the vibration motor was tested at five frequencies (10, 15, 20, 25, and 30 Hz), and the results were compared with the transient analysis results. The results show that the vibration response is more intense in the medium frequency range (18.66–28.96 Hz). It is inefficient and uneconomical to harvest all olives by applying force to the trunk. It is more effective to apply vibration force to the lateral branch to lessen the damage inflicted to the tree. An excitation force of 5220 N at 25 Hz to the left branch is suitable for harvesting the olive fruit. The average correlation coefficient of the maximum resultant acceleration observed in the tests and its simulated value was 0.63, indicating that the model can predict the vibration response reliably. Finally, the results of the harmonic response analysis were verified by transient analysis. This study can serve as a reference for the design of vibration harvesters. • A three-dimensional model of an olive tree including some small branches was established. • Optimal parameters were determined through modal and harmonic response analyses. • Actual vibration response of olive tree was investigated using the transient analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] Decreasing inlet methanol partial pressure and methanol space velocity during methanol-to-olefins (MTO) catalysis on HSAPO-34, HSSZ-13, and HSSZ-39 increases cumulative ethylene-to-propylene ratio by a factor of ~2.3x, ~2.4x, and ~2.2x, respectively. The composition of hydrocarbons occluded in the catalyst when compared at a similar turnover number during MTO suggests that decreasing methanol concentration in the catalyst bed decreases the extent of methylbenzene homologation within the pool of entrained aromatics, resulting in increments in the concentration of aromatic precursors to ethylene relative to those for propylene. Ethylene-to-propylene ratio changed by a factor of ~1.3x within one catalyst turnover and <10 s on-stream after a step-change in the inlet methanol pressure; in this duration the speciation of entrained methylbenzenes is unchanged as less than 1 mol C mol H+ −1 was converted to hydrocarbons, revealing that instantaneous ethylene and propylene selectivity depends sensitively on local methanol concentration. These mechanistic insights identify local methanol concentration as the salient parameter in modulating product selectivity during MTO on window-cage type materials. [ABSTRACT FROM AUTHOR]

• A method for studying mechanisms, the Analysis of Coverage Transients (ACT) is described. • The ACT method compares transient coverages in inert gas and reactive atmospheres. • The method is applied to the hydrodeoxygenation (HDO) of γ-valerolactone (GVL) on Ni 2 P/MCM-41. • The method uses an in situ spectroscopy, in this case, X-ray absorption spectroscopy. • Combined kinetic and spectroscopic results gave a consistent picture of the key steps of GVL HDO. The understanding of catalytic mechanisms is enhanced by the observation of surface intermediates at reaction conditions using spectroscopic techniques, but this is insufficient, as the observed species may not be involved in the reaction. This work describes a general method of analysis of hydrogenation or oxidation reactions which uses transient spectroscopic data to determine whether an adsorbed species is a reactive intermediate or a spectator on the surface. The assumptions and limitations of the method are summarized. Although the technique is approximate, it is easy to implement, and provides order-of-magnitude estimates of the rate of reaction of an intermediate. The method consists of measuring the change of coverage of the species with time, dθ/dt, during adsorption in inert gas or at reaction conditions. An example is given with the hydrodeoxygenation of the model compound γ-valerolactone (GVL) using a Ni 2 P/MCM-41 catalyst, one of the most effective catalysts reported for the transformation. The reaction is relevant to the upgrading of bio-oil derived from pyrolysis of lignocellulosic feedstocks. The kinetics of the reaction and observation by in situ infrared spectroscopy of adsorbed GVL and its transformation to pentanoic acid are consistent with a Langmuir-Hinshelwood mechanism. Analysis by in situ transient X-ray absorption fine structure shows that the adsorbed GVL is a true reaction intermediate. [ABSTRACT FROM AUTHOR]

• Aerobic-anaerobic ethanol switches on ceria surfaces lead to new steady state acetaldehdye formation rates. • Water and CO 2 , unlike acetaldehyde and CO 2 , can be used in the estimation of surface reduction during anaerobic induction periods. • Hydrogen pretreatment can be used to vary the initial prevalence of catalytic dehydrogenation over ceria surfaces. • Phenol co-feeds can be used to selectively eliminate catalytic dehydrogenative routes. Quantitative analyses of four sets of aerobic/anaerobic ethanol conversion transients point to the evolution of a native high-surface-area cerium oxide surface that effects the reduction half of the ethanol oxidation turnover to catalyzing, exclusively, nonoxidative ethanol dehydrogenation upon complete surface reduction. Aerobic–anaerobic switches at 498 K lead to new steady state dehydrogenation rates, rather than termination of catalytic acetaldehyde formation. Concurrent termination of oxygen imbalances (reflecting ceria reduction) and induction periods (reflecting active site creation) in anaerobic experiments point to ethanol dehydrogenation turnovers owing their provenance to surface reduction. Implausibly high vacancy densities obtained from analysis of oxygen imbalances when using acetaldehyde and CO 2 formation rates, unlike those obtained when using water and CO 2 formation rates, point to the catalytic origin of at least part of the acetaldehyde formed during both aerobic–anaerobic switches and anaerobic induction periods. Normalized water molar flow rates, used as a measure of the relative contributions of catalytic and stoichiometric routes to acetaldehyde formation, evince a transition from stoichiometric ethanol oxidation to catalytic ethanol dehydrogenation upon progressive surface reduction. High-temperature hydrogen pretreatments can be used to manipulate both the initial contribution of ethanol dehydrogenation to overall acetaldehyde formation as well as the fractional surface reduction that ethanol, rather than molecular hydrogen, effectuates. Alpha hydrogen-free titrants such as phenol, on the other hand, can be used to titrate sites contributing to catalytic alkanol dehydrogenation without altering the prevalence of stoichiometric routes responsible for site creation in the first place. The combination of transient experiments used herein capture, with clarity, the evolution in catalytic function of high-surface-area cerium oxide toward ethanol upon progressive reduction that originates from its stoichiometric conversion over a native, fully oxidized surface. Not unimportantly, the results also point to an avenue for the water-free synthesis of alkanals over reducible metal oxides. [ABSTRACT FROM AUTHOR]

The microclimate of naturally ventilated greenhouses, which are extensively used in tropical regions to produce various food or commercial crops, is highly dependent on the efficiency of ventilation that varies according to the local climate and the main characteristics of the greenhouse. Numerical simulation facilitates the spatial analysis of air flows for different types of greenhouse and their effect on the internal microclimate. The objective of this work focused on the use of a transient CFD-2D model for the study of natural ventilation in three types of greenhouses, the traditional Colombian wood (TG) greenhouse and two alternative types of multi-span greenhouses (curved - DMG and gothic - GMG) that are characterised by having larger ventilation areas both on the sides and on the roof. The model was validated by experiments performed in the DMG greenhouse through the collection of temperature and air velocity data by means of anemometry techniques, developing an accurate relationship between the simulated and experimental data. The results of the simulations showed that both DMG and GMG have ventilation rates 3.4 times higher than those found in the TG. This is reflected in the more homogeneous thermal spatial distribution with the average temperatures which were reduced by 2.8 °C with respect to the TG. • Transient CFD simulations were developed to study greenhouses natural ventilation. • The CFD model was successfully calibrated through experimental tests. • Ventilation rates and thermal behavior were calculated for the simulated greenhouses. • Ventilation rates were 3.5 and 4.3 times higher in alternative greenhouse designs. • Multi-tunnel greenhouse temperature was 2.8 °C lower than the one of the traditional. [ABSTRACT FROM AUTHOR]

Axial piston pumps are the key component in power hydraulic systems. Flow and pressure ripple signals, which can reflect the flow dynamics of the axial piston pump, are important information sources for condition monitoring. Therefore, the characteristics of flow and pressure ripple signals should be investigated for further condition monitoring and fault analysis. However, measuring high-frequency flow ripple directly can be difficult, and the pressure ripple is not only affected by pump dynamics but also affected by the transient pressure wave propagation. However, in practical applications, the hydraulic pipeline system is complex due to the space constraint of the equipment, and the influence of the pipeline system cannot be ignored when modeling pressure ripple. This paper proposes a novel two-stage method for fault simulation of the pumps that considers the influence of the pipeline system on the pressure ripple. Firstly, the surrogate pipeline model with free parameters is calibrated using ITA to capture the characteristics of the complex practical pipeline system. Secondly, the calibrated model is applied to the fault simulation of axial piston pumps. A detailed 3D CFD model of the pump is built up, and the flow ripple at the pump outlet from the numerical model is used as an approximation of the real flow ripple of the pump, which serves as one of the boundary conditions of the surrogate pipeline model. After calibrating the model, the CFD model of the pump is used to simulate internal failures in the pump. Two failure cases are studied: a faulty slipper and a faulty cylinder. The simulated signal of the proposed model matches the experimental signal well under the healthy and faulty conditions, which confirms the effectiveness of the proposed method. • A novel two-stage method for fault simulation of axial piston pumps is proposed. • In the first stage, the surrogate pipeline model is calibrated using ITA. • In the second stage, the calibrated model is used for fault simulation. • Two failure cases are studied, a pump with a faulty slipper or a faulty cylinder. [ABSTRACT FROM AUTHOR]

We proposed a provably stable FDTD subgridding method for accurate and efficient transient electromagnetic analysis. In the proposed method, several field components are properly added to the boundaries of Yee's grid to make sure that the discrete operators meet the 2nd-order and 4th-order summation-by-parts (SBP) properties. Then, by incorporating the simultaneous approximation terms (SATs) into the finite-difference time-domain (FDTD) method, the proposed FDTD subgridding method mimics the energy estimate of the continuous Maxwell's equations at the semi-discrete level to guarantee its stability. Furthermore, to couple multiple mesh blocks with different mesh sizes, the interpolation matrices are also derived. The proposed FDTD subgridding method is accurate, efficient, easy to implement and integrate into the existing FDTD codes with only simple modifications. At last, four numerical examples with fine structures are carried out to validate the effectiveness of the proposed method. • A SBP-SAT FDTD subgridding technique is proposed to solve TM electromagnetic problems. • A few additional field components are added on the boundaries of Yee's cell to make operators meet the SBP properties. • The proposed subgridding technique is theoretically stable. • Interpolation matrices between coarse and fine mesh blocks are detailed derived to guarantee the stability and accuracy. [ABSTRACT FROM AUTHOR]

Dihydropyrimidine dehydrogenase (DPD) is an enzyme that uses an elaborate architecture to catalyze a simple net reaction: the reduction of the vinylic bond of uracil and thymine. Known DPDs have two active sites separated by approximately 60 Å. One active site has an FAD cofactor and binds NAD(P) and the other has an FMN cofactor and binds pyrimidines. The intervening distance is spanned by four Fe 4 S 4 centers that act as an electron conduit. Recent advancements with porcine DPD have revealed unexpected chemical sequences where the enzyme undergoes reductive activation by transferring two electrons from NADPH to the FMN via the FAD such that the active form has the cofactor set FAD•4(Fe 4 S 4)•FMNH 2. Here we describe the first comprehensive kinetic investigation of a bacterial form of DPD. Using primarily transient state methods, DPD from E. coli (EcDPD) was shown to have a similar mechanism to that observed with the mammalian form in that EcDPD is observed to undergo reductive activation before pyrimidine reduction and displays half-of-sites activity. However, two distinct aspects of the EcDPD reaction relative to the mammalian enzyme were observed that relate to the effector roles for substrates: (i) the enzyme will rapidly take up electrons from NADH, reducing a flavin in the absence of pyrimidine substrate, and (ii) the activated form of the enzyme can become fully oxidized by transferring electrons to pyrimidine substrates in the absence of NADH. [Display omitted] • The first transient kinetic analysis of dihydropyrimidine dehydrogenase from a bacterium. • Dihydropyrimidine dehydrogenase (DPD) from E. coli has the same cofactor content as mammalian DPDs. • Much like the mammalian enzyme, DPD from E. coli undergoes reductive activation. • Unlike the mammalian enzyme, effector roles for NADPH and pyrimidine are respectively diminished and absent. [ABSTRACT FROM AUTHOR]

Addressing the need for more computationally efficient and accurate simulation tools for Lamb wave-based structural health monitoring (SHM) systems, this paper proposes the use of refined theories for the study of the wave propagation phenomena in thin-walled structures. When dealing with complex structures, classical plate models can be insufficiently accurate whereas 3D finite elements soon reach their limits due to the high computational requirements in ultrasonic wave analysis. As a solution to these issues, a finite element framework based on the Carrera's unified formulation (CUF) is presented for the simulation of Lamb waves in continua. Different structural theories are discussed and tested, showing that the Lamb modes can be well represented using beam elements with enriched kinematics. The validity and convergence rates of the proposed models are assessed through benchmark solutions. An example of damage detection in a typical reinforced panel is included to show the potential of the method. [ABSTRACT FROM AUTHOR]

This paper attempts in analysing the transient dynamic response behaviour of multi layered hybrid composite plates by a modified higher order refined zigzag theory (HRZT). An improved C0 continuous model is developed based on the refined higher order zigzag theories (HRZT) with warping effect for multilayered plates using eight noded isoparametric quadratic plate bending element to get the stress distribution across the thickness under dynamic load in a realistic manner. The continuity condition of transverse shear stresses is ensured with the help of 3D equilibrium equation at the interfaces of two adjacent layers along with the shear stress free condition at the outermost faces of a laminate. A computer code is developed with the help of MATLAB software package. The hybrid laminate is modeled by placing carbon fibres in the outermost layers and glass fibres in the rest and thus the flexural behaviour is improved. The experimental study on the transient dynamic response of hybrid laminates is also performed. Transient dynamic response obtained from the finite element based numerical model is verified by comparing the time history data obtained numerically and experimentally. The interlaminar stresses are also extracted and recorded under dynamic loading condition. The displacement and the stress components of laminated plates under static load are also computed in the present study and the results are compared with the theoretical outcome obtained in the relevant literature for validation of the present FE formulation. An exhaustive study on glass and hybrid fibre reinforced laminates is carried out to investigate the effectiveness of the hybrid laminate in terms of the response data of laminates with mono fibre as well as multiple (hybrid) fibres. [ABSTRACT FROM AUTHOR]

Conservation of energy, spurious-free, and optimal convergence are among the most favorite ingredients of a discontinuous Galerkin finite-element time-domain method (DG-FETD) for the analysis of transient electromagnetic problems. Unfortunately, due to the reliance on dissipative upwind flux to suppress spurious modes, most existing DG-FETDs possess only one or two of them. In this paper, we present a novel two-dimensional DG-FETD method, which combines all of the three advantages. The proposed method is based on the electric field E and magnetic field H , whose approximation spaces are composed of Whitney's edge functions. To inhibit the spurious modes while keeping the conservation of numerical energy, the numerical flux with dissipation is not adopted. Instead, a carefully designed interface condition along with the non-dissipative central flux is employed for this purpose. That is, across each face of an element except for those coinciding with boundaries of the computational domain, if E is strongly enforced to be tangential continuous then the continuity of H is weakly imposed, and vice versa. For the convenience of complying with this requirement and without loss of the inherent parallelism of the DG-FETD method, two partially staggered sets of subdomains are built for E and H , respectively. These subdomains are made up of sub-elements generated through a refinement of each cell on the initial mesh into four similar elements. The final discrete system is advanced with a second order leap-frog time-stepping scheme. A series of numerical examples demonstrate that the present method is robust and much more superior to the conventional DG-FETD methods. [ABSTRACT FROM AUTHOR]

Abstract It is well known that rotating beams are stretched due to centrifugal forces. Accordingly, it can be speculated that the stretching effect for rotating curved beams leads to changes of the curvature. But this speculation has been not verified and reported in existing literatures. In this paper, a dynamic model of curved beams is derived by using the Absolute Nodal Coordinate Formulation based on radial point interpolation method (ANCF/RPIM), and the transient analysis of curved beams rotating at the steady state angular speed are especially performed by using the ANCF/RPIM. The results show that the curvature of curved beams is reduced due to centrifugal forces. These configuration changes have an important influence on frequency characteristics. Thus, modal analysis should take account of the configuration changes by using steady states which can be obtained in a manner of static analysis. The "static external force" for steady states is a non-zero centrifugal force, while centrifugal forces are identically equal to zero in the original ANCF. To this end, this paper uses a floating frame to describe overall rotations of beams, and defines the nodal coordinates located on the floating frame to describe configurations of beam. Based on this description, new ANCF dynamic equations can be easily obtained by using coordinate transformation of the original ANCF dynamic equations, in which the centrifugal forces are not equal to zero. The results show that the configurations in steady and transient states are very close, and transient states are almost located in both sides of the steady state. Therefore, steady states can be regarded approximately as equilibrium positions of vibrational curved beams. By using steady states, the new ANCF dynamic equations can be linearized to determine frequencies of curved beams. Finally, the effects of curvature changes on the frequencies of curved beams, especially "dynamic softening" effect, are investigated, and the reason that these effects are caused in curved beams is explained in detail. [ABSTRACT FROM AUTHOR]

Abstract The paper presents experimental and theoretical studies of wave phenomena accompanying transient edge waves (EW) excitation by a piezoelectric transducer attached at the edge of an elastic plate. Theoretical investigations are conducted on the basis of the three-dimensional elastodynamic theory. The boundary value problem describing non-stationary wave motion is solved with the use of integral transforms and the modal expansion technique. The asymptotic analysis with the wavenumber considered as a small or large parameter is applied to the three-dimensional problem. In the first case (long-wave vibrations) the approximate formulae for the fundamental EW's pole and corresponding residue are derived. These relations take into account the influence of the transverse shear load arising because of coupling between long-wave integral and Saint-Venant's boundary layer. In the second case (short-wave vibrations) an infinite series of poles corresponding to higher order EW is revealed. Results of numerical investigations of EW dispersion properties and waveforms are presented and used for an analysis of experimental data acquired with the use of Laser Doppler vibrometry. It is shown that the contribution of EW is predominant in the wave-field excited by the load under consideration. A good agreement between theoretical predictions and measurements is demonstrated. For the calculation of transient wave-field three different models of actuator-plate interaction are developed: in the low-frequency range the interaction is considered as a static one, while the lower and higher eigenfrequencies of the actuator are taken into account in the medium- and high-frequency ranges respectively. For the low-frequency range, an explicit analytical formula is derived for calculation of EW contribution into the transient wave-field. In the high-frequency range, the excitation of the first higher order EW is predicted by the numerical solution and observed experimentally. Graphical abstract Image 1 Highlights • Edge waves excited by a transducer at the edge of a plate are studied. • Contribution of edge waves is predominant in the transient wave-field at the edge. • An explicit analytical formula for calculation of edge wave contribution is derived. • Laser vibrometry measurements verify theoretically predicted properties of edge waves. • Excitation of a higher order edge wave is observed in the experiments. [ABSTRACT FROM AUTHOR]

A Sonic Black Hole (SBH) in a retarding duct structure incorporates two indispensable physical processes, i.e., wave energy focalization and dissipation, to entail slow-sound effect and broadband sound absorption. Original SBH design, however, involves a large number of inner rings inside the duct to produce the required impedance changes. In this study, a SBH configuration with perforated boundary (SBH-PB) is examined, in which perforated acoustic boundaries are used to achieve enhanced SBH effects. Upon a dedicated treatment of the perforated boundary (PB) with the backing cavity, the transfer matrix method (TMM) is adopted to analyze the acoustic characteristics of the SBH-PB and to explore the underlying physical mechanisms. The adoption of the PB is shown to bring about threefold benefits: increased accuracy of the TMM modeling owing to the weakened coupling among the backing cavities in the SBH-PB, enhanced sound absorption through micro-perforations, and the realization of SBH effects with a reduced number of inner rings. To visualize the slow-sound effect, the change of sound speed is examined through transient simulations using finite element method by capturing the wavefront propagation inside the duct. Finally, for the first time, an acoustic duct system replicating the transient simulations is developed to experimentally demonstrate the slow-wave phenomenon in the time domain. The proposed structure holds promises for sound wave manipulation and the development of acoustic noise control devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eddy-currents analysis formulation associated with a spiral pulse. • Mathematical derivation of resultant eddy waveforms using the circuit equation. • TMIM computational framework for transient spiral eddy-current analysis. • Spiral waveform eddy-currents analysis results were cross-validated against Ansys. Eddy currents are induced in the metallic structures of MRI machines due to the rapid switching of gradient fields generated by gradient coils. Several undesirable effects are associated with the induced eddy currents such as heat, acoustic noise, and MR image distortions. Accurate transient eddy currents numerical computations are required to predict and ameliorate such effects. Spiral gradient waveforms are of importance, particularly for fast MRI acquisition applications. For mathematical convenience, previously published work is mostly concerned with transient eddy currents computations associated with trapezoidal gradient waveforms; where spiral gradient waveforms were not considered. We recently presented preliminary transient eddy currents computations induced by an amplitude-modulated sinusoidal pulse in the scanner's cryostat. In this work, we present a full computational framework for transient eddy currents induced by a spiral gradient waveform. A mathematical model for transient eddy currents involving the spiral pulse was derived and presented in detail using the circuit equation. Computations were implemented using a tailored multilayer integral method (TMIM) and results were compared to Ansys eddy currents analysis for cross-validation. The transient response of resultant fields generated by both an unshielded transverse coil driven by a spiral waveform was computed showing high agreement between Ansys and TMIM; albeit with high computational efficiency concerning time and memory. For further validation, computations for a shielded transverse coil were performed showing how eddy currents effects are reduced. [ABSTRACT FROM AUTHOR]

The objective of this work is to study the influence of error induced by gas film in micro-scale on the static and dynamic behavior of a shaft supported by the aerostatic bearings. The static and dynamic balance models of the aerostatic bearing are presented by the calculated stiffness and damping in micro scale. The static simulation shows that the deformation of aerostatic spindle system in micro scale is decreased. For the dynamic behavior, both the stiffness and damping in axial and radial directions are increased in micro scale. The experiments of the stiffness and rotation error of the spindle show that the deflection of the shaft resulting from the calculating parameters in the micro scale is very close to the deviation of the spindle system. The frequency information in transient analysis is similar to the actual test, and they are also higher than the results from the traditional case without considering micro factor. Therefore, it can be concluded that the value considering micro factor is closer to the actual work case of the aerostatic spindle system. These can provide theoretical basis for the design and machining process of machine tools. [ABSTRACT FROM AUTHOR]

Smooth running and rapid response are the desired performance goals for the transient motions of servo mechanisms. Because of the uncertain and unobservable transient behaviour of servo mechanisms, it is difficult to evaluate their transient performance. Under the effects of electromechanical coupling, the stator current signals of a permanent-magnet synchronous motor (PMSM) potentially contain the performance information regarding servo mechanisms in use. In this paper, a novel method based on analysing the stator current of the PMSM is proposed for quantifying the transient performance. First, a vector control model is constructed to simulate the stator current behaviour in the transient processes of consecutive speed changes, consecutive load changes, and intermittent start-stops. It is discovered that the amplitude and frequency of the stator current are modulated by the transient load torque and motor speed, respectively. The stator currents under different performance conditions are also simulated and compared. Then, the stator current is processed using a local means decomposition (LMD) algorithm to extract the instantaneous amplitude and instantaneous frequency. The sample entropy of the instantaneous amplitude, which reflects the complexity of the load torque variation, is calculated as a performance indicator of smooth running. The peak-to-peak value of the instantaneous frequency, which defines the range of the motor speed variation, is set as a performance indicator of rapid response. The proposed method is applied to both simulated data in an intermittent start-stops process and experimental data measured for a batch of servo turrets for turning lathes. The results show that the performance evaluations agree with the actual performance. [ABSTRACT FROM AUTHOR]

The objective of this work is to analyze wave packet propagation in weakly nonlinear acoustic metamaterials and reveal the interior nonlinear wave mechanism through spectro-spatial analysis. The spectro-spatial analysis is based on full-scale transient analysis of the finite system, by which dispersion curves are generated from the transmitted waves and also verified by the perturbation method (the L-P method). We found that the spectro-spatial analysis can provide detailed information about the solitary wave in short-wavelength region which cannot be captured by the L-P method. It is also found that the optical wave modes in the nonlinear metamaterial are sensitive to the parameters of the nonlinear constitutive relation. Specifically, a significant frequency shift phenomenon is found in the middle-wavelength region of the optical wave branch, which makes this frequency region behave like a band gap for transient waves. This special frequency shift is then used to design a direction-biased waveguide device, and its efficiency is shown by numerical simulations. [ABSTRACT FROM AUTHOR]

The paper focuses on the analysis of an industrial ceramic kiln in order to improve the energy efficiency and thus the fuel consumption and the corresponding carbon dioxide emissions. A lumped and distributed parameter model of the entire system is constructed to simulate the performance of the kiln under actual operating conditions. The model is able to predict accurately the temperature distribution along the different modules of the kiln and the operation of the many natural gas burners employed to provide the required thermal power. Furthermore, the temperature of the tiles is also simulated so that the quality of the final product can be addressed by the modelling. Numerical results are validated against experimental measurements carried out on a real ceramic kiln during regular production operations. The developed numerical model demonstrates to be an efficient tool for the investigation of different design solutions for the kiln's components. In addition, a number of control strategies for the system working conditions can be simulated and compared in order to define the best trade off in terms of fuel consumption and product quality. In particular, the paper analyzes the effect of a new burner type characterized by internal heat recovery capability aimed at improving the energy efficiency of the ceramic kiln. The fuel saving and the relating reduction of carbon dioxide emissions resulted in the order of 10% when compared to the standard burner. [ABSTRACT FROM AUTHOR]

The transient analysis of sliding beams represents a challenging problem of structural mechanics. Typically, the sliding motion superimposed by large flexible deformation requires numerical methods as, e.g., finite elements, to obtain approximate solutions. By means of the classical sliding spaghetti problem, the present paper provides a guideline to the numerical modeling with conventional finite element codes. For this purpose, two approaches, one using solid elements and one using beam elements, respectively, are employed in the analysis, and the characteristics of each approach are addressed. The contact formulation realizing the interaction of the beam with its support demands particular attention in the context of sliding structures. Additionally, the paper employs the sliding-beam formulation as a third approach, which avoids the numerical difficulties caused by the large sliding motion through a suitable coordinate transformation. The present paper briefly outlines the theoretical fundamentals of the respective approaches for the modeling of sliding structures and gives a detailed comparison by means of the sliding spaghetti serving as a representative example. The specific advantages and limitations of the different approaches with regard to accuracy and computational efficiency are discussed in detail. Through the comparison, the sliding-beam formulation, which proves as an effective approach for the modeling, can be validated for the general problem of a sliding structure subjected to large deformation. [ABSTRACT FROM AUTHOR]

In this work, a thin pretwisted and delaminated composite strip is modeled using the variational asymptotic method (VAM). The original 3D problem is reduced to a 2D cross-sectional analysis and a 1D problem along the length of the strip. Damage, in the form of an embedded delamination, is accounted in the strip by following a sublaminate approach. The 1D governing elastodynamic equations of the strip model is solved using the spectral finite element (SFE) method, wherein the structure is modeled as a wave guide. In SFE method, the governing elastodynamic equations are solved in transformed frequency domain to obtain the dynamic stiffness matrix. The guided wave response of the delaminated composite structure for different loads and boundary conditions are subsequently computed. Modal and wave response from SFE using the reduced 1D model are validated by comparing results with those reported in the literature and in some cases with the results obtained from a 3D model using a direct finite element (FE) package. Modal and wave propagation analysis is performed for various dimensions of delamination and composite layup. The analysis provides insight into the dynamic characteristic of partially delaminated strip. The usage of SFE is expected to yield a faster result and lesser computation time than the conventional direct FE method for analyzing and monitoring the delaminated strip exposed to high frequency excitations. Additionally, the capability of the model to investigate the inverse problem of damage detection is demonstrated. • A reduced order computational method for dynamic analysis of strips is proposed. • Modal behavior of partially delaminated, pretwisted strip is layup dependent. • Torsional wave amplitude and wave speed are nonlinearly correlated. • Framework is computationally efficient compared to equivalent direct 3D simulations. • Parametric study of wave response for various delamination dimensions is presented. [ABSTRACT FROM AUTHOR]

In this study, the frequency spectrum of squeak noise in hip joint system is measured in experiment. The numerical reproduction of hip squeak signal involves the formulation of the finite element geometry, the analytical contact kinematics such as Hertz theory and Coulomb's law and the mode-discretization. For general approach, the contact kinematics are analytically modeled to easily adjust the contact location, the contact area, the rotation direction, the pressure distribution, the friction law, and so on. Furthermore the friction stress vectors act on the 3-dimensional spherical contact surfaces where they can be divided into the steady-sliding and its transverse slip directions. Numerical calculations for the various contact parameters are conducted to investigate the possibility of hip squeak occurrence and the nonlinear oscillations after the onset of squeak are also solved. In the transient analysis, the periodic limit cycle of hip squeaking is shown to be the stick-slip type oscillation. Then the numerical frequency spectrum is qualitatively compared with hip squeak signal measured in experiment. The stick-slip oscillation during hip squeaking and its contact behavior will be also discussed over the contact area within one period. [ABSTRACT FROM AUTHOR]

• A linear dynamic model is proposed for a flexible beam attached to a freely rotating rigid shaft. • Transient and modal analyses were performed accurately and efficiently with the proposed model. • Transient and modal analysis results of the conventional prescribed model were also obtained. • An equilateral triangular shape torque function was employed to perform the transient analysis. • The shaft mass moment of inertia was found to critically influence the prescribed model accuracy. A novel linear dynamic model is proposed for the transient and modal analyses of a flexible beam attached to a rigid shaft undergoing free rotational motion. For the proposed modeling of the shaft-beam coupled system, the shaft angular speed is modeled as the sum of a reference angular speed and generalized speed instead of the time derivative of the shaft rotation angle which has traditionally been used for the shaft dynamic modeling. Thus, the shaft-beam coupled system is linearized around the reference angular speed for deriving the equations of motion. With the proposed modeling method, the two-way inertia coupling effect between the rigid shaft and flexible beam can be considered accurately. The transient responses obtained with the proposed model are in good agreement with those obtained with a nonlinear dynamic analysis program. Moreover, due to the linearity of the proposed dynamic model, modal characteristics of the shaft-beam coupled system can be also accurately identified. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this paper is to introduce a new linear time-frequency transform to improve the detection of fault components in electric machines transient currents. Linear transforms are analysed from the perspective of the atoms used. A criterion to select the atoms at every point of the time-frequency plane is proposed, taking into account the characteristics of the searched component at each point. This criterion leads to the definition of the Adaptive Slope Transform, which enables a complete and optimal capture of the different components evolutions in a transient current. A comparison with conventional linear transforms (Short-Time Fourier Transform and Wavelet Transform) is carried out, showing their inherent limitations. The approach is tested with laboratory and field motors, and the Lower Sideband Harmonic is captured for the first time during an induction motor startup and subsequent load oscillations, accurately tracking its evolution. [ABSTRACT FROM AUTHOR]

The chaperonin-containing t-complex polypeptide 1 (CCT, also known as TRiC) assists protein folding in an ATP-dependent manner. CCT/TRiC was mixed rapidly with different concentrations of ATP, and the amount of phosphate formed upon ATP hydrolysis was measured as a function of time using the coumarin-labeled phosphate-binding protein method. Two burst phases were observed, followed by a lag phase and then a linear steady-state phase of ATP hydrolysis. The phases were assigned by (i) determining their dependence on ATP and K + concentrations and (ii) by measuring their sensitivity to the mutation Gly345 → Asp in subunit CCT4, which decreases cooperativity in ATP binding. The values of the observed rate constants corresponding to the burst phases are found to decrease with increasing ATP and K + concentrations, thereby indicating that the apo state of CCT/TRiC is in equilibrium between several conformations and that “conformational selection” by ATP takes place before hydrolysis. The amplitude of the lag phase, which follows, decreases with increasing ATP concentrations, thus indicating that it reflects a transition between states with low affinity for ATP and a state with high affinity for ATP that is predominant under steady-state conditions. A kinetic model based on the data is suggested, in which CCT/TRiC is in equilibrium between a relatively large number of states that are distinguished kinetically, in agreement with its proposed sequential allosteric mechanism. [ABSTRACT FROM AUTHOR]

During these last decades the modal instability of systems, generated by frictional contact forces, has been the subject of a huge amount of works in friction induced vibration literature. Linear and nonlinear numerical analyses have been largely investigated to predict and reproduce squeal vibrations. While nonlinear transient analysis needs large computational efforts, results of Complex Eigenvalue Analysis (CEA) suffer from an over-prediction issue and it is not able to predict correctly the mode that will become effectively unstable in case of several unstable eigenvalues. Because the CEA has been adopted as an efficient tool for brake design, a more reliable index is here proposed, from the CEA outputs and energetic considerations, to identify the mode that will become effectively unstable. A modular lumped model is developed to reproduce friction induced vibrations. The use of the eigenvalue real part, as discriminant of the system instability, is here combined with information coming from the eigenvectors, projected on the equilibrium position, to account for the energy flows involved in the squeal phenomena. This approach allows to define a Modal Absorption Index (MAI). The MAI allows for comparing unstable modes of the same system and is applied in this paper to predict, by CEA outputs, the unstable mode that will effectively result in squeal vibrations. [ABSTRACT FROM AUTHOR]

Impulsive energies are abundant throughout the natural and built environments, for instance as stimulated by wind gusts, foot-steps, or vehicle–road interactions. In the interest of maximizing the sustainability of society׳s technological developments, one idea is to capture these high-amplitude and abrupt energies and convert them into usable electrical power such as for sensors which otherwise rely on less sustainable power supplies. In this spirit, the considerable sensitivity to impulse-type events previously uncovered for bistable oscillators has motivated recent experimental and numerical studies on the power generation performance of bistable vibration energy harvesters. To lead to an effective and efficient predictive tool and design guide, this research develops a new analytical approach to estimate the electroelastic response and power generation of a bistable energy harvester when excited by an impulse. Comparison with values determined by direct simulation of the governing equations shows that the analytically predicted net converted energies are very accurate for a wide range of impulse strengths. Extensive experimental investigations are undertaken to validate the analytical approach and it is seen that the predicted estimates of the impulsive energy conversion are in excellent agreement with the measurements, and the detailed structural dynamics are correctly reproduced. As a result, the analytical approach represents a significant leap forward in the understanding of how to effectively leverage bistable structures as energy harvesting devices and introduces new means to elucidate the transient and far-from-equilibrium dynamics of nonlinear systems more generally. [ABSTRACT FROM AUTHOR]

The effect of resonance time-harmonic wave energy transmission through deep notches and its manifestation in transient wave fields is studied. This effect has been revealed during a wide-range parametric study on the basis of semi-analytical models developed in preceding paper (Glushkov et al., 2015 [1] ). Its emergence at the predicted frequencies is experimentally validated using the laser Doppler vibrometry. The analysis within the trapped mode theory provides a better understanding of the resonance phenomena observed. [ABSTRACT FROM AUTHOR]

Formation of the bivalent interaction between the Notch intracellular domain (NICD) and the transcription factor CBF-1/RBP-j, Su(H), Lag-1 (CSL) is a key event in Notch signaling because it switches Notch-responsive genes from a repressed state to an activated state. Interaction of the intrinsically disordered RBP-j-associated molecule (RAM) region of NICD with CSL is thought to both disrupt binding of corepressor proteins to CSL and anchor NICD to CSL, promoting interaction of the ankyrin domain of NICD with CSL through an effective concentration mechanism. To quantify the role of disorder in the RAM linker region on the effective concentration enhancement of Notch transcriptional activation, we measured the effects of linker length variation on activation. The resulting activation profile has general features of a worm-like chain model for effective concentration. However, deviations from the model for short sequence deletions suggest that RAM contains sequence-specific structural elements that may be important for activation. Structural characterization of the RAM linker with sedimentation velocity analytical ultracentrifugation and NMR spectroscopy reveals that the linker is compact and contains three transient helices and two extended and dynamic regions. To test if these secondary structure elements are important for activation, we made sequence substitutions to change the secondary structure propensities of these elements and measured transcriptional activation of the resulting variants. Substitutions to two of these nonrandom elements (helix 2, extended region 1) have effects on activation, but these effects do not depend on the nature of the substituting residues. Thus, the primary sequences of these elements, but not their secondary structures, are influencing signaling. [ABSTRACT FROM AUTHOR]

Dispersive transport of charge carriers in disordered nanostructured semiconductors is described in terms of integral diffusion equations nonlocal in time. Transient photocurrent kinetics is analyzed for different situations. Relation to the fractional differential approach is demonstrated. Using this relation provides specifications in interpretation of the time-of-flight data. Joint influence of morphology and energy distribution of localized states is described in frames of the trap-limited advection–diffusion on a comb structure modeling a percolation cluster. [ABSTRACT FROM AUTHOR]

Spacecraft imaging of Mars’ south polar region during mid-southern summer of Mars year 28 (2007) observed bright halo-like features surrounding many of the pits, scarps and slopes of the heavily eroded carbon dioxide ice of the South Polar Residual Cap (SPRC). These features had not been observed before, and have not been observed since. We report on the results of an observational study of these halos, and spectral modeling of the SPRC surface at the time of their appearance. Image analysis was performed using data from MRO’s Context Camera (CTX), and High Resolution Imaging Science Experiment (HiRISE), as well as images from Mars Global Surveyor’s (MGS) Mars Orbiter Camera (MOC). Data from MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) were used for the spectral analysis of the SPRC ice at the time of the halos. These data were compared with a Hapke reflectance model of the surface to constrain their formation mechanism. We find that the unique appearance of the halos is intimately linked to a near-perihelion global dust storm that occurred shortly before they were observed. The combination of vigorous summertime sublimation of carbon dioxide ice from sloped surfaces on the SPRC and simultaneous settling of dust from the global storm, resulted in a sublimation wind that deflected settling dust particles away from the edges of these slopes, keeping these areas relatively free of dust compared to the rest of the cap. The fact that the halos were not exhumed in subsequent years indicates a positive mass-balance for flat portions of the SPRC in those years. A net accumulation mass-balance on flat surfaces of the SPRC is required to preserve the cap, as it is constantly being eroded by the expansion of the pits and scarps that populate its surface. [ABSTRACT FROM AUTHOR]

In automotive disc-brake squeal, most numerical studies have been focussed on the prediction of unstable vibration modes in the frequency domain using the complex eigenvalue analysis. However, the magnitude of the positive real part of a complex eigenvalue is an unreliable indicator of squeal occurrence. Although nonlinearities have been shown to play a significant role in brake squeal, transient nonlinear time domain analyses have rarely been applied owing to high computational costs. Here the complex eigenvalue analysis, the direct steady-state analysis and the transient nonlinear time domain analysis are applied to an isotropic pad-on-disc finite element model representing a simple model of a brake system. While in this investigation, in-plane pad-mode instabilities are not detected by the complex eigenvalue analysis, the dissipated energy obtained by the direct steady-state analysis of the model subjected to harmonic contact pressure excitation is negative at frequencies of pad modes, indicating a potential for instabilities. Transient nonlinear time domain analysis of the pad and disc dynamics reveal that in-plane pad vibrations excite a dominant out-of-plane disc mode. For intermittently chaotic pad motion, the disc dynamics is quasi-periodic; and for chaotic motion of the pad, a toroidal attractor is found for the disc׳s out-of-plane motion. Nonlinear interactions between the pad and the disc highlight that different parts in a brake system display different dynamic behaviour and need to be analysed separately. The type II intermittency route to chaos could be the cause for the experimentally observed instantaneous mode squeal. [ABSTRACT FROM AUTHOR]

A new analytical solution for the motion of an elastic cylinder in a viscous fluid is derived using Laplace transforms. Unlike previously available solutions, full expressions for transient terms are given. The solution is compared with conventional treatments of this problem. It is expected to have particular value for applications related to viscosity measurement using vibrating-wire viscometers applied to higher viscosity fluids. [ABSTRACT FROM AUTHOR]

Localized faults in rotating machines tend to result in shocks and thus excite transient components in vibration signals. An iterative extraction method is proposed for transient signal analysis based on transient modeling and parameter identification through Levenberg–Marquardt (LM) method, and eventually for fault feature extraction. For each iteration, a double-side asymmetric transient model is firstly built based on parametric Morlet wavelet, and then the LM method is introduced to identify the parameters of the model. With the implementation of the iterative procedure, transients are extracted from vibration signals one by one, and Wigner–Ville Distribution is applied to obtain time–frequency representation with satisfactory energy concentration but without cross-term. A simulation signal is used to test the performance of the proposed method in transient extraction, and the comparison study shows that the proposed method outperforms ensemble empirical mode decomposition and spectral kurtosis in extracting transient feature. Finally, the effectiveness of the proposed method is verified by the applications in transient analysis for bearing and gear fault feature extraction. [ABSTRACT FROM AUTHOR]

In this paper an Euler–Bernoulli model has been used for vibration analysis of micro-beams with large transverse deflection. Thermoelastic damping is considered to be the dominant damping mechanism and introduced as imaginary stiffness into the equation of motion by evaluating temperature profile as a function of lateral displacement. The obtained equation of motion is analyzed in the case of pure single mode motion by two methods; nonlinear normal mode theory and the Galerkin procedure. In contrast with the Galerkin procedure, nonlinear normal mode analysis introduces a nonconventional nonlinear damping term in modal oscillator which results in strong damping in case of large amplitude vibrations. Evaluated modal oscillators are solved using harmonic balance method and tackling damping terms introduced as an imaginary stiffness is discussed. It has been shown also that nonlinear modal analysis of micro-beam with thermoelastic damping predicts parameters such as inverse quality factor, and frequency shift, to have an extrema point at certain amplitude during transient response due to the mentioned nonlinear damping term; and the effect of system׳s characteristics on this critical amplitude has also been discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper researches the detection of mixed eccentricity in Inverter-Fed Induction Motors. The classic FFT method cannot be applied when the stator current captured is not in steady state, which is very common in these motors. Therefore, a transform able to detect the time–frequency evolutions of the components present in the transient signal captured must be applied. In order to optimize the result, a method to calculate the theoretical time–frequency evolution of the stator current components is presented, using only the captured current. This previously obtained information enables the use of the proposed transform: the Adaptive Slope Transform, based on appropriately choosing the atom slope in each point analyzed. Thanks to its adaptive characteristics, the time–frequency evolution of the main components in a stator transient current is traced precisely and with high detail in the 2D time–frequency plot obtained. As a consequence, the time–frequency plane characteristic patterns produced by the Eccentricity Related Harmonics are easily and clearly identified enabling a reliable diagnosis. Moreover, the problem of quantifying the presence of the fault is solved presenting a simple and easy to apply method. The transform capabilities have been shown successfully diagnosing an Inverter-Fed Induction Motor with mixed eccentricity during a startup, a decrease in the assigned frequency, and a load variation with and without slip compensation. [Copyright &y& Elsevier]

This work focuses on the trailing edge flow-induced noise by studying the associated transient noise generation physics. A wavelet-based beamforming method is first performed to analyse the dynamics and correlations of the trailing edge noise problems in the time–frequency domain. The wavelet-based beamforming method is an extension of the conventional beamforming method in which the Fourier transform is substituted by the wavelet transform to perform the transient acoustic imaging. The transient process is interpretable by using this method, which is impossible for the previous conventional acoustic imaging techniques. To verify and showcase the proposed method, the velocity field obtained by particle image velocimetry is provided along with the time–frequency analysis of acoustic measurements. Next, a particular problem of trailing edge noise from an aerofoil is experimentally studied at the Reynolds number of O (1 0 5) , where the intermittent nature of the underlying aerodynamic flow structures can be inferred by the proposed wavelet-based beamforming. To provide the complementary flow-field results, a secondary experiment is performed in a different wind tunnel around the same Reynolds number. The finding of the correlation between the flow field and acoustic imaging results constitutes the key contribution of this work. Finally, the analysis of the velocity flow field and of noise source image is used to elucidate the associated flow physics. Overall, the proposed method can help to achieve deepened physical insights into various transient and moving systems in underwater and aerospace systems. • The PIV and the proposed wavelet-based beamforming method are employed. • The flow fluctuations, transient flow dynamics and the correlations are studied. • The dynamics and correlations of the trailing edge noise are analysed. [ABSTRACT FROM AUTHOR]

• The impact of harmonic/random excitation amplitude ratios on OMA methods is studied. • Novel method AOBMA extends OBMA by scaling and (weighted) averaging of orders. • Comparing OMA estimation performances using a Monte-Carlo simulation study. • AOBMA reduces estimation errors compared to OBMA in simulation and operational data. • Order-based methods (AOBMA, OBMA) surpass traditional OMA in mode shape estimation. Machinery with rotating components poses a challenge to Operational Modal Analysis (OMA) due to its periodic inputs, i.e. orders. Transient (acceleration or deceleration) runs represent a relevant test condition for structures, which experience a low amount of broadband (noise) excitation during operation. In these cases, orders present themselves as a favourable source of excitation. However, this type of excitation can result in distortions of the response spectrum at the ending frequencies of individual orders. These "end-of-order" distortions can introduce spurious or biased modal estimations. Order-based Modal Analysis (OBMA) is an OMA method, which was developed specifically for the transient test case and is not affected by end-of-order distortions. However, some downsides are associated with OBMA because it performs modal analysis for each relevant order individually. In addition to the associated analysis effort, this produces multiple sets of modal estimations with ambiguous results. This paper introduces an extension of OBMA to address these issues. The proposed method, called Averaged Order-based Modal Analysis (AOBMA), applies scaling and (weighted) averaging to extracted orders prior to the modal estimation step. A Monte-Carlo simulation study is introduced to compare the modal estimation performance of traditional OMA, OBMA and AOBMA. Different ratios of harmonic and random excitation amplitudes are simulated to gauge the impact of the excitation's composition. In addition, all methods are also applied to operational measurements from a turbofan casing during run-up. The results indicate that AOBMA produces a lower variance in the estimated modal parameters compared to OBMA. Moreover, while OMA was more successful in the estimation of closely spaced modes, it was surpassed by AOBMA and OBMA regarding the accuracy of mode shape estimations. [ABSTRACT FROM AUTHOR]

Highlights: [•] 1 J NH spin–spin coupling constants probe transient intramolecular hydrogen bonds. [•] Hydrogen bonds can be detected at low polypeptide concentrations. [•] The helical folding nucleus of GCN contains a partially populated hydrogen bond. [Copyright &y& Elsevier]

Highlights: [•] New type of excitation pulse for CPMG sequence. [•] Maximization of CPMG component, minimization of CP component. [•] Significant increase of SNR in inhomogeneous fields. [•] Reduction of transient effect in early echoes. [•] Excellent agreement between theory and experiment. [ABSTRACT FROM AUTHOR]

Abstract: Passive pneumatic tables are popularly used in precision measurements or processes for isolation of ground vibrations over frequency ranges higher than resonance frequencies of a few Hz typically. Recently, active pneumatic tables are also used often because the passive systems are liable to table excitations in the low resonance frequency ranges, causing long settling times. In studies on the active tables, disturbances onto the tables were often regarded to be unknown and, hence, feedback control algorithms were implemented. However, the disturbances are mostly due to inertial forces due to movement of equipment on the table, e.g., x–y stages. Such a movement is given relative to the table as command inputs. Since absolute motion of the table is normally measured in an active isolation table, absolute motion of the equipment can be easily estimated for calculation of the inertial force exerted onto the table by the moving equipment. Consequently, by compensating dynamic pressure inside the pneumatic chamber to counteract with the inertia force due to the equipment motion, resultant forces acting onto the table can be made zero. In this paper, how to apply the proposed feed-forward control algorithm to a 6-degree of freedom active pneumatic table with time-delay pneumatic control is presented. Performance of the inertial force compensation control evaluated through experiments is also discussed. [Copyright &y& Elsevier]

• An alternative transient modelling and leakage detection approach is proposed. • The time domain impedance function is introduced for the transient response. • PSO is integrated into impedance calibration scheme addressing wide range of surge amplitudes. • The leakage-identified impedance function substantially improves leakage detection. • Numerical and experimental verifications demonstrate the superiority of the method. An alternative approach to modeling the hydraulic transient response and leakage detection is proposed for reservoir pipeline valve systems. Exponential-function-based impedance formulations are derived in the frequency domain, which are useful for identifying the pressure response of different pipeline elements and abnormalities. The time-domain impedance function (TIF) is introduced to address the transient response for a specific pipeline system. The TIF comprehensively simulates various valve maneuvers or flowrates in either the laminar or turbulent flow regimes. The delineated TIF from the measured pressure head in the pipeline system with leakage exhibits potential for leak location prediction. The integration of the particle swarm optimization scheme into the inverse TIF algorithm provides a robust evaluation capability under a wide range of surge amplitudes. The developed leakage-identified impedance function substantially improves the leakage detection ability through transient impact isolation. Both the numerical and experimental verifications demonstrate the potential of the proposed method for leak detection as well as water hammer simulation for pipeline systems. [ABSTRACT FROM AUTHOR]

• Torsional dynamic model of PGEP with angle-varying mesh stiffness and tooth backlash. • Transient oscillation analysis during regenerative braking transition process. • Optimized torsional vibration-induced regenerative braking method designed and tested. Electric regenerative braking systems have drawn much attention in the trends of energy-saving and emission-reduction requirements for electric vehicles. However, the significant differences between regenerative braking transmission chains and the traditional ones have lead to increasing oscillation and noise of electrical powertrain. With the application of planetary-gear transmission chains, adopting an advanced regenerative braking method becomes practical. This paper develops a novel regenerative braking method for transient torsional oscillation suppression of planetary-gear electrical powertrain (PGEP), which uses an angle-varying mesh stiffness-considered transmission model and a genetic algorithm-based method for allocation of electric regenerative braking torque. Simulations are conducted with various angle-varying mesh stiffness and backlash to compare the transient torsional oscillation-suppression performance of PGEP during regenerative braking transition process. For an initial speed of 80 km/h, simulation results show that the proposed torsional oscillation-considered electric regenerative braking torque allocating method performs the best comparing with the traditional methods, which has a 55% reduction in vehicle jerk and 36% improvement in torsional oscillation of PGEP. The AVL experiment results also demonstrated that torsional oscillation-considered regenerative braking method has considerable benefits in both transient torsional oscillation suppression of PGEP as well as enhancement of driving comfort. [ABSTRACT FROM AUTHOR]

• Modeling of a single-shaft parallel hybrid powertrain for dynamic analysis. • The input of the powertrain model is the gas pressure given by a gas pressure map. • Optimization of dual mass flywheel and centrifugal pendulum vibration absorbers. • A multi-objective optimization based on the transient analysis of the model. • The Pareto fronts yield reduced torsional vibration and the inertia of the device. This research deals with an optimization of a dual mass flywheel (DMF) with centrifugal pendulum vibration absorbers (CPVAs) used in a single-shaft parallel hybrid electric vehicle (HEV) powertrain for the reduction of the torsional vibration at the rotor of the electric motor and the total moment of inertia of the DMF and CPVAs. Unlike the previous studies, this research considers the overall behavior of an entire powertrain with an in-line four-cylinder engine and a five-speed automatic transmission for the optimization of the DMF with CPVAs. For this purpose, the multibody dynamics model of the HEV powertrain is constructed and used to analyze the transient response of the system for a given gas pressure map and acceleration condition of the vehicle. Then, a multi-objective genetic algorithm is applied to determine the Pareto optimal front that yields the design parameter values of the DMF and CPVAs effective in the torsional vibration reduction and inertia minimization. The result of the optimization is compared with the HEV powertrain system with a flywheel only, and shows that the vibrations transmitted to the motor are significantly reduced in all the solutions of the Pareto front. By using the method proposed in this research, various parameter combinations of the DMF and CPVAs can be considered in the early design process. [ABSTRACT FROM AUTHOR]

• An efficient transient-based method is developed for polymeric pipe parameters identification and leak detection. • The developed method is extended from single pipeline to branched multiple-pipeline system. • Experimental tests in single and branched pipeline systems are performed for method validation. • Extensive numerical tests are applied for analyzing the influences of different factors and input signals. • Application results are discussed for practical implications to pipeline health monitoring. The widespread use of plastic pipes in different fluid conveyance systems has greatly driven the recent development and application of transient-based methods (TBMs) for leak detection in viscoelastic/polymeric pipelines. Current TBMs for viscoelastic pipe leak detection are usually achieved by a two-step procedure, namely viscoelastic parameters identification and leak detection, which requires the pre-knowledge of intact system states (i.e., non-leak) for comparative analysis. This paper presents an efficient single-step frequency domain inverse transient analysis (FDITA) method for simultaneous identifications of viscoelastic parameters and leaks in plastic pipes, so as to enhance the applicability and accuracy of TBMs. Both the single and branched polymeric pipe systems are applied for the method development and application. To this end, analytical solutions of single and branched systems from the transfer matrix method are firstly derived to represent the transient frequency responses of viscoelastic pipelines with leaks. A global optimized nonlinear curve fitting method is then employed to identify both viscoelastic parameters and potential leaks by knowing/measuring other system and flow conditions. Extensive experimental validations and numerical applications of both single and branched pipe systems demonstrate the very good efficiency and accuracy of the developed method for leak detection in different viscoelastic pipe systems. Furthermore, the mechanism of transient wave-leak-viscoelasticity is analysed based on these application results and theoretical evidence. Finally, a sensitivity analysis is performed to quantify and discuss the advantages and potential limitations of the developed method in the paper. [ABSTRACT FROM AUTHOR]

• A fast ITA method for pipe condition assessment is proposed via surrogate modeling. • A sampling strategy is proposed for multiple parameters with sparse feature. • The Kriging method needs <100 numerical simulations for pipe problems. • The method is applied for viscoelastic parameters estimation and leak identification. Inverse transient analysis (ITA) is a powerful tool for pipeline condition assessment, where the concerned parameters are decided by matching the measured transient signal with its physical model. This scheme is computationally expensive because, in the optimization procedure, the model has to be evaluated many times via time-domain full-wave numerical simulations. To address this problem, a fast algorithm of ITA is proposed, where the role of the numerical model is replaced by an easy-to-evaluate surrogate model. The Kriging method is employed to build the surrogate model of transient wave, given a series of samples of concerned parameters and the associated numerical model outputs. Considering the sparse nature of the high-dimensional pipe condition parameters, a sparse sampling strategy is proposed to optimize the samples of parameters. Two application examples, i.e., pipe viscoelastic parameter estimation and leakage identification, are introduced to demonstrate that the proposed method is as accurate as the traditional ITA but has a much lower computational cost. [ABSTRACT FROM AUTHOR]