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The harmonic response and acceleration characteristic of drillstring is established to improve borehole quality for the hydrogen underground storage (HUS). The harmonic response laws of drillstring is discussed. Harmonic response analysis includes non-failure case and failure case. Absorber control measure is simulated to lower vibration amplitude of drillstring. The drill string collides violently with the wellbore reduces the wellbore quality and increases the unreliability of the HUS. Lateral harmonic response has the greatest damage to well wall. Torsional harmonic response causes less damage than lateral vibration. High WOB (weight on bit) and high RPM (rotary per minute) are not conducive to the quality of HUS. In course of designing drilling parameter, it is required to avoid or reduce drillstring resonance under low-order inherent frequency as much as possible. The research result is of much significance to improve wellbore quality of hydrogen underground storage. • The dynamic response model of drill string in slim borehole was established. • The harmonic characteristic of drill string during compound drilling were studied. • The acceleration characteristics of drillstring in slim borehole were investigated. • The effects of harmonic and acceleration characteristics on the wellbore quality were studied. [ABSTRACT FROM AUTHOR]

• An ANN based machine learning multiscale modelling strategy is proposed to predict the mechanical properties of PW-CFRP and other types of CFRP with high accuracy and low computational cost based on generated data sets. • A GDQ based computational strategy is established to calculate the random and harmonic frequency-response characteristics for conical-conical shells. • Excitation type, excitation and response points, geometric parameters on the frequency-response characteristics are extensively analyzed. This study analyzes the frequency-response characteristics under non-stationary base random acceleration and harmonic points force excitations of plain woven carbon fiber reinforced polymers (PW-CFRP) conical-conical shells comprehensively. Artificial neural network (ANN) based machine learning multiscale modelling strategy is introduced in the process of predicting the mechanical properties of PW-CFRP. The dataset is generated by randomization, linear fitting and two-step homogenization and then trained to generate an ANN to predict the mechanical properties of PW-CFRP. The governing equations of the conical-conical shell under random acceleration excitation are obtained according to the first order shear deformation theory (FSDT) and Hamilton's principle. After the structure is split along the circumference at the excitation points, the harmonic points force excitations are introduced based on the discontinuity condition between conical segments. Generalized differential quadrature (GDQ) is applied during the solving procedure. After comparison studies focusing on the frequency-response characteristics under two types of excitations, two examples on harmonic and random responses of conical-conical shell and conical-cylindrical shell are carried out separately. In this process, the effects of excitation type, excitation and response points, geometric parameters on the frequency-response characteristics are extensively analyzed, which proves efficiency and accuracy of the ANN based machine learning multiscale modelling strategy and the constructed GDQ based computational strategy. [ABSTRACT FROM AUTHOR]

Abstract In this work, a modified analytical model with closed-form solution is proposed by following the existing framework in the prior works, to analyze the dynamic responses of interfacial shear and peel stresses in adhesively bonded double-lap joints subjected to harmonic axial load. By applying the dynamic equilibrium along the through-thickness direction, the differential equation governing adhesive peel stress is first contained in this model. The dynamic responses of interfacial stresses obtained by finite element simulations under four different loading conditions are used to validate this analytical model. The parametric study based on the proposed model is also implemented to assess the effect of some geometrical parameters on the dynamic response of adhesive interfacial stresses. [ABSTRACT FROM AUTHOR]

Abstract Nanocomposites are preferred over conventional materials because of their superior mechanical properties. Studies need to be carried out, especially on the dynamic response of the composite material. The objective of the present work is to study the dynamic response of Carbon-Nanotube-Reinforced-Polymer (CNRP) material by developing a 3D multiscale finite-element model of the Representative Volume Element (RVE) of the composite material to determine its dynamic properties, in terms of its natural frequencies and damping properties. A computational model consisting of a Single-Walled Carbon Nanotube (SWCN), an interface region and the polymer matrix is constructed for this purpose. The SWCN is modeled as a space frame structure by using the Morse potential and as a thin shell model based on Donnell's Shell Theory. The polymer matrix is modeled with the Mooney-Rivlin strain energy to calculate its non-linear response and the interface region is modeled via van der Waals links based on the Lennard-Jones Potential. The natural frequencies of CNRP are compared with the natural frequencies of the polymer matrix. A relation between damping ratio and natural frequencies is then obtained. Finally, the analysis of harmonic response is conducted to characterize the effects of the SWCN reinforcement in the polymer material. [ABSTRACT FROM AUTHOR]

Abstract The dynamic behavior of counter flow heat exchangers is studied using the harmonic response. To solve the set of partial differential equations the complex notation is used so that these equations become ordinary differential equations. In an appendix it is shown that assuming a uniform temperature in a cross section of the separating wall is correct for the example used as comparison. Experimental results dealing with a double pipe heat exchanger are compared with results obtained by assuming the correlations to be used for the convection heat transfer coefficients. The comparison is satisfactory when the excitation is applied to the inner tube fluid. It is less accurate when the excitation is applied to fluid flowing in the annulus. Finally it is shown that the residence time of the fluids is linked to a peak in the response curves. [ABSTRACT FROM AUTHOR]

Abstract Optimum design and failure prevention against diverse degradation mechanisms of reactor vessel internals(RVIs) are one of safety concerns in nuclear industries. The present study is to investigate effectiveness of current evaluation procedure of the RVIs under pump pulsating conditions as a part of comprehensive vibration assessment program. At first, pressure propagation analyses were performed subjected to typical steady-state and transient conditions to generate pulsating pressure distributions. Subsequently, modal analyses were conducted to examine effect of coolant modeling on dynamic characteristics. Harmonic response analyses were also carried out to examine effect of integrated assembly and numerical analyses data were compared each other and with limited measured data. As a result, it was proven that the integrated assembly with the coolant modeling could predict further realistic behaviors of RVIs instead of the current sub-component models adopting equivalent added-mass assumption. [ABSTRACT FROM AUTHOR]

Highlights • The single variable shear deformation theory (SVSDT) is adopted for dynamic analysis of multi-story frames. • Natural frequencies, mode shapes and harmonic responses are obtained by using dynamic stiffness method (DSM). • The results are presented in comparison with Timoshenko beam theory (TBT). • Harmonic response curves can be used for observation of natural frequencies and anti-resonance frequencies directly. Abstract This study aims to perform free and forced vibration analyses of multi-story frames using the single variable shear deformation theory (SVSDT). The free vibration analysis begins with constructing dynamic stiffness matrices based on analytical solutions to motion equations for frame members according to SVSDT, as well as the Timoshenko beam theory. The natural frequencies are calculated via a global dynamic stiffness matrix of the frame for different column and beam dimensions, and elastic modulus values. The natural frequency results are tabulated with finite element method results to verify the dynamic stiffness method, thereby providing exact values. The mode shapes are plotted, and forced vibration analysis is accomplished using a global dynamic stiffness matrix of the frame for different dynamic lateral load amplitude values. The harmonic response curves are depicted in a logarithmic scale to observe the resonance and anti-resonance frequencies. The numerical examples demonstrate that the SVSDT can be used effectively for the dynamic analysis of frames. [ABSTRACT FROM AUTHOR]

Since the particle damping is highly developed and widely used to suppress the structure vibration and a more efficient and accurate technique for predicting the harmonic responses of particle-damping structure is in need, this paper presents a novel technique to predict the harmonic response of particle-damping structure based on iterative solution method and ANSYS ® secondary development technology. In order to establish the iteration solution method for predicting the harmonic response of particle-damping structure, iteration scheme of particle-damping structure (system) is derived from the mechanical dynamic formulae and particle damping formulae. For single or multiple degree of freedom system, basic solutions of each iteration cycle are solved by mathematical model, while the solutions of continuous systems are solved by ANSYS ® in this paper. To conduct harmonic analysis of highly nonlinear particle-damping system in ANSYS ® , iterative solution method (i.e. iteration scheme) is coded into program by ANSYS ® Parametric Design Language (APDL). Based on the code, module of particle damping is developed and interfaces are created in ANSYS ® using User Interface Design Language (UIDL). To verify the accuracy of the novel technique, two research cases are detailed introduced and frequency response functions (FRFs) of acceleration are obtained by simulations and experiments. It's worthwhile to note that simulation results have excellent consistency with the experiment results. In addition, the simulations conducted by ANSYS ® using iteration solution method developed in this paper is more efficient and consumes less computer resources than previous methods. Consequently, both accuracy and higher efficiency of the novel technique are guaranteed. [ABSTRACT FROM AUTHOR]

This paper presents a new spectral element based on the dynamic stiffness matrix of a prestressed cylindrical shell. The dynamic stiffness matrix is built using first-order shear deformation theory, and natural frequencies are processed easily. Vibration analyses are performed with numerical examples to determine the performance of this approach and the effect of prestressing on frequency response functions. This element has many advantages over the finite element method in terms of accuracy, model size and computing time. [ABSTRACT FROM AUTHOR]

Analyzing hysteretic systems presents a significant challenge due to the memory effect of hysteresis. In this paper we present an incremental harmonic balance (IHB)-based approach to compute the steady-state response of a closed-loop system with hysteresis under a sinusoidal excitation, where the hysteresis element is modeled by the Prandtl–Ishlinskii (PI) operator. While the describing function method (DFM) can be used to obtain an approximate solution for the closed-loop system based on first-order harmonics, the proposed IHB-based approach iteratively calculates the harmonic components of the hysteretic system up to an arbitrary order. The main challenge is the harmonic calculation of the periodic output of the PI operator for a multi-harmonic input. In order to address this problem, an alternative definition of the play operator is utilized as the hysteron for the PI operator. By using the alternative definition, a set of switching time instants, when the play operator enters or exits the boundary region, are determined by a bisection method. The calculation of the incremental harmonic components is finally reformulated as a linear matrix equality that can be solved efficiently. As an illustration, numerical results for a system involving a proportional–integral feedback controller are presented to demonstrate the advantage of the IHB-based approach over the DFM in approximating the harmonic response of the hysteretic system. [ABSTRACT FROM AUTHOR]

Low noise levels are today requested for power transformers in order to comply with customer specifications and environmental legislations. Manufacturers have to improve the acoustic performances of their products and also reduce the costs in the same time. Therefore it is necessary to predict sound levels with a sufficient accuracy for each transformer design. Sound radiation of transformer tanks is influenced by a wide variety of parameters including placement, type, arrangement and dimensions of stiffeners, tank thickness, tank shape and type, insulating fluid or gas (mineral oil, ester or air). The vibration sources in transformers are located within an oil-immersed rib-stiffened transformer tank vessels made of thin and flexible steel plates. The vibrations generate sound pressure waves which are iteratively reflected from structural boundaries and discontinuities. They form standing patterns of vibrations, structural modes of the vessel and standing waves inside the fluid-filled acoustic cavity. If the corresponding natural frequencies of the structures are in the vicinity of the forcing frequencies, unexpectedly high sound levels are regularly observed, [1]. In order to avoid these unexpectedly high sound levels caused by the natural frequencies of the tank, optimization of the tank and tank stiffeners arrangement, dimensions and design has to be carried out. [ABSTRACT FROM AUTHOR]

This paper describes a new analytical solution for adhesively-bonded single-lap and double-lap joints based on an improved shear-lag model. The derived equations assume that all substrates are of the same material. In the case of single-lap joints, the substrates have equal thicknesses. In the case of the double-lap joints, the outer substrates׳ thickness is half the thickness of the inner substrate. The proposed solution takes into account the visco-elastic behavior of the adhesive and substrates. The analytical solutions of aluminum and polymer single-lap joints are compared to finite element solutions. Good agreement is then observed. Subsequently, a parametric study is undertaken and shows that the natural frequencies are sensitive to the material and geometrical properties of the adhesive layer and the substrates. Mainly, it is reported that substrates’ damping attenuates more the resonances heights than the adhesive damping does. [ABSTRACT FROM AUTHOR]

This paper describes a procedure for taking into account distributed loads in the calculation of the harmonic response of a cross-ply laminated circular cylindrical shell using the dynamic stiffness method. This work is a direct continuation of a previous work concerning isotropic materials. Equivalent loads are established on element boundaries to determine the response of the system. Therefore, the vibration analysis is solved with numerical examples in order to determine the performances of this approach. The method allows reducing both the size of the model and computing time, and ensures higher precision compared to the finite element method. [ABSTRACT FROM AUTHOR]

The dynamic behaviour of a micro-cantilever that is transversely excited at its base is investigated in this paper. The base actuation is provided by thermal cycles via taking the advantage of thermal expansion. The Euler–Bernoulli equation along with corresponding boundary conditions is used to model the continuous cantilever beam. The resultant boundary value problem takes into account the thermal expansion and stiffness of the actuator at the base as well as the effect of the surrounding gas or liquid. A closed-form analytical model is developed to compute natural frequencies, mode shapes, and harmonic response of the vibrating cantilever, in addition to an integral function for quality factor. The model is validated via a finite element (FE) analysis using ANSYS commercial package. This validation shows that the proposed model can properly predict the cantilever's vibrating behaviour. [ABSTRACT FROM AUTHOR]

• Rice feeding state prediction by threshing cylinder unbalanced vibration time-frequency signal. • Harmonic response of the threshing drum under undergoing unbalanced vibration was analyzed. • Spectral kurtosis based on short-time Fourier transform was calculated in field threshing state. • Effect of rice stalk winding vibration was analyzed using signal envelope and spectral kurtosis. When the cylinder of rice combine harvester is threshing, the interaction between the fed rice stalk and the threshing teeth makes the cylinder subject to a large vibration shock. Undergoing the influence of this shock, the vibration response of threshing cylinder is non-stationary. In view of the above problems, this paper aims to accurately characterize the harvesting state of the threshing cylinder and extract the impact components caused by the winding of rice stalks. First, the constrained modes and main response harmonics of the threshing cylinder during operation are solved by modal harmonic response analysis. The time-frequency domain analysis was carried out on the threshing cylinder vibration signal undergoing field working conditions. Combined with spectral envelope and spectral kurtosis analysis methods, the main shock frequencies during the threshing process of the cylinder are analyzed. The results show that the main response frequency of the threshing cylinder under no-load state is the response frequency of 14 Hz, but the main frequency component of the threshing cylinder during the harvesting process is 80 Hz. Comparing the results of harmonic response analysis, it can be concluded that the winding of rice stalks will affect the vibration response of the threshing cylinder. Rice threshing state prediction with harmonic response provides a new method for the follow-up threshing cylinder condition monitoring and fault diagnosis. [ABSTRACT FROM AUTHOR]

To study structural seakeeping stability of the marine compound NC machine tool in the ship environment, this research analyses the effects of extreme wave loads including transient slamming and harmonic swings on the machine tool, and the coupling methods of transient reaction, static structural analysis and harmonic response are used to solve the problems. The results show that the major guide pairs of the column are the weakest parts in the machine tool in a ship environment, so the column working deflection angle of the machine tool should be consistent with the ship heading angle to reduce influence of wave loads on dynamic stability of the machine. The data indicate that the minimum safety factor is 3.43 under an extreme surge acceleration of 41.8 m/s 2 , and the normal safety factor of 3.0 shows that the guide pairs are able to endure extreme slamming wave loads of H 1/3 =7.6 m at the maximum velocity of the ship. In addition, the machine tool has a maximum deformation of 0.032 mm and a peak stress of 5.07 MPa under extreme harmonic wave excitation. Importantly, the machine's cutting accuracy was suitable for the rapid manufacturing requirement to maintain a ship's broken components. [ABSTRACT FROM AUTHOR]

A general formulation and solution procedure are proposed for harmonic response of rigid foundation on multilayered half-space. It is suitable for isotropic as well as anisotropic soil medium. The wave motion equation is formulated in frequency wave-number domain in the state space. A hybrid approach is proposed for its solution, where the precise integration algorithm (PIA) is employed to carry out the integration. Very high accuracy can be achieved. The mixed variable form of wave motion equation enables the assembly of layers simple and convenient. The surface Green׳s function is regarded as rigorous, because it is free from approximations and discretization errors. The algorithm is unconditionally stable. The numerical implementation is based on algebraic matrix operation. Numerical examples of vibration of rigid foundation validate the efficiency and accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

Abstract: The main concern of this paper is to establish an analytical solution giving the shear stress profile in a double-lap adhesive joint subjected to harmonic loading. The proposed model is based on the improved “shear-lag” model assuming a linear shear strain distribution in the adherends. The modified shear-lag model is equivalent to the simple shear-lag model when the shear stiffness of the adhesive is insignificant when compared to the shear stiffness of the adherends. We compared the modified and simple shear-lag models to a finite element model when both shear stiffnesses are comparable. It comes out that our modified shear-lag model is closer to the finite element model. Subsequently, we analysed results of our model in terms of newly proposed dimensionless parameters. This study was limited to frequencies lower than a critical defined one and to elastic behaviour of both adherends and adhesive. [Copyright &y& Elsevier]

Abstract: This paper describes a procedure for taking into account distributed loads in the dynamic stiffness matrix formulation, also known as the continuous element method. In that formulation, concentrated or linearly distributed loads are taken into account by considering the necessary number of elements in such a way that these loads are applied on element boundaries. As for distributed loads such as pressure and surface forces, they were not provided for in the formulation. The validation is achieved by comparison of accuracy and computational time of harmonic response calculations performed by the continuous element model and a finite element model. [Copyright &y& Elsevier]

Abstract: A new type of compound multifrequency ultrasonic transducer is analyzed in this paper. The compound multifrequency ultrasonic transducer consists of two sandwiched ultrasonic transducers and a rectangular radiator. In virtue of the coupling between longitudinal vibration of the sandwiched ultrasonic transducers and flexural vibration of the rectangular radiator, the compound multifrequency ultrasonic transducer can produce several resonance frequencies. Some compound multifrequency ultrasonic transducers are designed and simulated by finite element method (ANSYS), and modal shapes and harmonic response are analyzed. The compound multifrequency ultrasonic transducers are designed and manufactured. The resonance frequencies are measured and compared with the numerical results. The effect of the geometrical dimensions of the compound multifrequency ultrasonic transducer and the location of two sandwiched ultrasonic transducers on the compound multifrequency ultrasonic transducer is discussed. It is shown experimentally and numerically that the compound multifrequency ultrasonic transducer has several resonance frequencies. [Copyright &y& Elsevier]

Abstract: The dynamic response of a rigid footing resting on an elastic tensionless Winkler foundation is examined. A parametric investigation, concerning the effect of the main parameters on the response, is performed for harmonic excitation. The parameters examined include the stiffness and the damping of the foundation, the excitation frequency and the superstructure characteristics and loads. The maximum rocking response, the minimum length of contact after uplift, the maximum stress developed at the soil and the factor of safety with respect to the bearing capacity of the soil are used to measure the effect of each dimensionless parameter. An example for earthquake excitation is also given for a plane frame. The results are compared to the ones of a simplified static approach based on the maximum values of the applied loads, similarly to the procedure that is usually applied in practice. The results show that the static approach can predict the response satisfactorily if resonance does not happen, if the stiffness of the foundation is not large compared to the stiffness of the superstructure and if the dynamic part of the axial force of the column is not large; in these cases, it may underestimate or overestimate the response significantly, depending on the sign of the dynamic axial force that is considered. [Copyright &y& Elsevier]

Abstract: This paper describes a procedure for calculating the dynamic stiffness matrix of tubular shells with free edge boundary conditions. Such an analysis forms the basis for the Continuous Element Method. The method is used to formulate a thick axisymmetric shell element which takes into account rotatory inertia, transverse shear deformation and non-axisymmetric loadings. [Copyright &y& Elsevier]

Abstract: Structures are weakened by cracks. When the crack size increases in course of time, the structure becomes weaker than its previous condition. Finally, the structure may breakdown due to a minute crack. Therefore, crack detection and classification is a very important issue. In this study, free and forced vibration analysis of a cracked beam were performed in order to identify the crack in a cantilever beam. Single- and two-edge cracks were evaluated. The study results suggest that free vibration analysis provides suitable information for the detection of single and two cracks, whereas forced vibration can detect only the single crack condition. However, dynamic response of the forced vibration better describes changes in crack depth and location than the free vibration in which the difference between natural frequencies corresponding to a change in crack depth and location only is a minor effect. [Copyright &y& Elsevier]

The oscillations of gas bubbles, without shell, immersed in viscoelastic liquids and driven by an acoustic wave have been the subject of several investigations. They demonstrate that the viscosity coefficient and the spring constant of the liquid have significant influence on the scattering cross section of the gas bubble. For shell-encapsulated gas bubbles, the investigations have been concentrated to bubbles immersed in a pure viscous liquid. This present work computes the ultrasonic scattering cross section, first and second harmonics, of shell-encapsulated gas bubbles immersed in a viscoelastic liquid. The theoretical model of the bubble oscillation is based on the generalized Rayleigh–Plesset equation of motion of a spherical cavity immersed in a viscoelastic liquid represented by a three-parameter linear Oldroyd model. The scattering cross section is computed for Albunex® type of bubble (shell thickness=15 nm, shell shear viscosity=1.77 Pa s, shell modulus of rigidity=88.8 MPa) irradiated by a 3.5 MHz ultrasonic pressure wave with an amplitude of 30 kPa. The results demonstrate that encapsulated bubbles respond independently of the surrounding liquid being pure viscous or viscoelastic as long as the surrounding liquid shear viscosity is as low as 10−3 Pa s. Nevertheless, for higher shear viscosities, the bubble responds differently if the surrounding liquid is pure viscous or viscoelastic. In general, the scattering cross sections of first and second harmonics are larger for the viscoelastic liquid. [Copyright &y& Elsevier]

A novel Lévy series for developing a dynamic stiffness matrix for a completely free orthotropic Kirchhoff plate is presented in this paper. The bending behavior is based on the Kirchhoff–Love thin-plate theory. The dynamic stiffness matrix is derived using the new Lévy series without classical symmetry decomposition, simplifying the building procedure. Harmonic responses obtained by this method and the finite element method are compared to establish the rate of convergence and the degree of precision of the current formulation. [Display omitted] • We present new Lévy series for calculating the dynamic stiffness matrix of free orthotropic plates. • Free boundary conditions are required for plate assemblies. • Modal analysis and harmonic analysis are presented. • The numerical validation is achieved thanks to comparisons with FE results. [ABSTRACT FROM AUTHOR]

• Prestressed concrete sleepers have the disadvantages of resonance and low damping. • Steel-reinforced sleepers are better damping but corrosion and fatigue are a concern. • To eliminate all these disadvantages, CFRP laminate reinforced sleepers developed. • According to modal and harmonic response analysis, they show better damping results. Nowadays high-cost sleeper applications are becoming indispensable because of railway operation conditions and high frequency train loads. For the protection of sleepers and other railway components, "non-prestressed" sleepers have the potential to reduce railway maintenance costs and exhibit a longer service life compared to their prestressed competitors. But the disadvantage of this process is steel reinforcement defects due to corrosion and fatigue. A new type of sleeper with non-pre-stressing process with non-corroding carbon fiber reinforced polymer (CFRP) laminate reinforcements can overcome these disadvantages. Rail seat static positive moment tests have been performed for these new types of sleepers before and it was determined that they can provide the desired static strength parameters even in high speed train lines. In this study, modal and harmonic response analysis has been performed and the results compared with prestressed sleepers with equivalent concrete cross-section dimensions. According to the results this new sleeper model has higher damping advantages and is expected to be beneficial in extending the service life of the railway components, reducing maintenance needs, and harmful effects on the environment. [ABSTRACT FROM AUTHOR]

• A new modelling method for the vertical hydro-hybrid bearing-rotor system is put forward. • Modal analysis of the rotor system has been performed and the first four modes are extracted. • The harmonic responses of the system are simulated for the whole system. • Vibration characteristics at crucial positions of the rotor system are analyzed. This work focuses on the rotor dynamic analysis of the vertical hydro-hybrid bearing-rotor system of a two-circuit main loop liquid Sodium pump system. A new modelling method for the vertical hydro-hybrid bearing-rotor system is put forward. Lubrication parameters are compared with the reference, which verifies correctness of the model. Contours pressure of the bearing are presented. Modal analysis of the rotor system is performed. The first four modes of the system are extracted. Harmonic responses of the system are simulated. Time histories of the displacements, their Fast Fourier transforms (FFT) and axis orbits at different positions of the plain journal bearing, the impeller and the rolling element bearing under different operating conditions are analyzed. Resonance of the rotor system will not be induced under rated operation conditions. Research results are of significance for such vertical hydro-hybrid bearing rotor systems. [ABSTRACT FROM AUTHOR]

This work studies the robust design of structures with minimum dynamic response considering uncertainties in the excitation frequency, using topology optimization. The Monte Carlo Simulation method with stratified sampling is used to model both the expected value and standard deviation of the structural dynamic response, described by a density-weighted norm. Results show that the proposed formulation leads to the design of structures with minimum dynamic response and improved robustness, which is attested by comparison with the deterministic approach. Results also show that the mechanisms used to increase the robustness depend on the target frequency. For low frequencies, a mode separation is preferred, while for higher frequencies, low-energy resonant modes are used. • Robust design of structures with minimum dynamic response with respect to uncertainties in the excitation frequency. • Careful investigation of the formulation by means of symmetric and asymmetric test cases. • Discussion of the mechanisms used to increase the robustness as a function of the target frequency. • Identification of the use of low energy resonances to improve the robustness in harmonic designs. [ABSTRACT FROM AUTHOR]

• We propose a non-modal vibration-based method for material characterization. • The method is developed for estimating the elasticity of thin planar structures. • Our method works based on single frequency harmonic vibration data of whole domain. • The method is robust to noise typical in holography measurements of soft tissue. • Sensitivity of the method to uncertainties and measurement artefacts was studied. We propose a novel material characterization method to estimate the Young's modulus of thin 2-D structures using non-modal noisy single frequency harmonic vibration data measured with holography. The method uses finite-difference discretization to apply the plate equation to all measured pixels inside the boundary of the vibrating structure and then treats the problem as a Bayesian optimization process to find the value of the Young's modulus by minimizing the Euclidian distance between the measured displacement field and repeatedly calculated displacement field using the plate equation. In order to assess the accuracy of the method, ground truth harmonic displacement magnitude fields of different plates were obtained using analytical solutions and the finite-element method and were used to estimate the Young's moduli. We applied Gaussian and non-Gaussian noise with different intensities to assess the robustness and accuracy of the proposed material characterization method in the presence of noise. We demonstrated that for multiple benchmarks for signal to noise ratio of down to 0 dB, our proposed method had errors of less than 5%. We also quantified the effects of uncertainties in the geometrical and material parameters as well as boundary conditions on the estimated Young's modulus. Furthermore, we studied the effects of the mesh size on the runtime and applied the method to experimental holography vibration measurement data of a copper plate. [Display omitted] [ABSTRACT FROM AUTHOR]

Metallic cellular solids are recognized for their high strength to weight ratio, being desirable for applications in the transportation industries to reduce fuel consumption and emissions. Although, there have been significant developments in the manufacturing of these materials and in the prediction of their static mechanical properties, their dynamic behavior (e.g. harmonic response and damping ratio) is still difficult to characterize by direct methods. This is due to the usual complex shape and low damping of metallic cellular solids and the inclusion of external damping by the instrumentation in vibration tests. This study presents an indirect method, based on a numerical inverse engineering approach, to determine the true apparent modulus and damping ratio of metallic cellular solids. For validation purposes, the proposed method was applied to Al-based non-stochastic cellular solids manufactured by investment casting with different architectures, being determined that their dynamic apparent modulus (1.4–217.2 MPa) is significantly different from the static structural results. The damping ratios of these samples were also successfully determined (0.002–0.011) and it is shown that these values are within the expected range for this aluminum based cellular solids. [ABSTRACT FROM AUTHOR]

Bolt-column (BC) joint is an innovative fabricated semi-rigid joint with strong bending stiffness that can meet the need of rapid construction of latticed shell structure. To investigate the dynamic behavior of SLR shells with BC joints subjected to harmonic load and earthquake load, finite element (FE) modeling of SLR shells with BC joint was built taking geometric and material nonlinearity into account, and the simulation method was validated by comparing with the test result on a cylindrical reticulated shell. Based on this model, effect of joint stiffness on the dynamic response was examined and failure modes of SLR shells jointed with BC joint subjected to harmonic load and earthquake load were studied. Two failure modes, dynamic strength failure which results from the extensive plastic deformation and dynamic instability failure which is induced by the geometric nonlinearity of the shell, were defined. Subsequently, the criteria on differentiating the two failure modes were derived based on response characteristics indicators. Furthermore, investigation on damaged factor of SLR shells jointed with BC joint was conducted, and according to numerous numerical examples, the damaged index of SLR shells with BC joint was derived, which can be utilized to conduct fragility analysis. • FE model of SLR shells with BC joints was established and validated by test results. • Tow failure modes, dynamic strength and dynamic instability, were defined. • The criteria on differentiating the two failure modes were derived. • The damaged index of SLR shells with semi-rigid joints was derived. [ABSTRACT FROM AUTHOR]

• Single variable shear deformation theory (SVSDT) • Dynamic stiffness formulations for free vibration and harmonic response analysis. • A multi-storey frame model on flexible foundation. • Effects of soil-structure interaction (SSI) on the dynamic behaviour of frames. • Authors' statement. A single variable shear deformation theory (SVSDT) is applied to free vibrations and harmonic response analysis of a multi-storey frame model considering flexibility of foundation. The column-foundation joints are modelled using three-spring approach instead of fixed support assumption to show the effects of soil-structure interaction (SSI) on the dynamic behaviour of frame model. The dynamic stiffness formulations are used for both free vibration and harmonic response analysis. The results that obtained using SVSDT and Timoshenko beam theory (TBT) are presented comparatively. The calculated natural frequencies are verified by finite element method (FEM). The convergence of FEM for the first three natural frequencies is presented for the fixed supported frame and frame considering SSI. The harmonic response curves are used to reveal the resonant and anti-resonant frequencies directly. It is seen that using a lateral displacement response for harmonic response curves may cause to miss natural frequencies of axial dominant modes of the frame model. However, all required natural frequency values of multi-storey frames considering foundation flexibility can be obtained via harmonic response curves that plotted by using a vertical displacement response of a node of model. Moreover, the proposed approach is validated by experimental data for scaled frame models, which are fixed supported and flexibly supported, respectively. The computation times for harmonic responses are tabulated for frame model on flexible foundation as well as fixed support assumption. [ABSTRACT FROM AUTHOR]