Metastructures made of spring-mass resonators present a band gap at the natural frequency of the resonator. This rule cannot be generalized for more complex resonators. This work analyses the case of a metastructure composed by a periodic arrangement of vertical beams rigidly joined to a horizontal beam. The vertical beams work as resonators, and their natural frequencies play a strong role on the band structure of the whole system, however, different to the case with spring-mass resonators. Since this metastructure can be considered as a lattice, Bloch's theorem is applied to the unit cell and a numerical procedure based on the Finite Element Method permits to obtain the dispersion curves. Illustrative results show the influence of the natural frequencies of the horizontal and vertical beams on the band structure.

Despite widespread use of aft-fuselage mounted twin-engine aircraft in the business jet industry, a thorough investigation into the vibro-acoustic properties of this aircraft type has yet to be undertaken. Additionally, the effect of bulkhead pressurization on the vibro-acoustic properties of this aircraft fuselage has yet to be investigated in isolation. This work investigates the effect of bulkhead pressurization on two different designs of an aft-fuselage twin-engine mounted aircraft: a single, and a double bulkhead design. A modal analysis, a harmonic frequency response analysis, and an acoustic response analysis were performed. A split bulkhead pressurization methodology was introduced as a means of improving structural performance without impacting passenger comfort levels in double bulkhead aircraft. Modal coupling between components was seen to be the primary cause of increased cabin noise, peaking above 80 Hz. The bulkhead frequency response was highly dependent upon bulkhead pressurization, as the modal participation factors were significantly impacted by bulkhead pressurization. Therefore, the importance of understanding all bulkhead natural frequencies was highlighted, as the response changed as a function of bulkhead pressurization. Bulkhead resonance conditions generated a tone in the acoustic frequency response inside the passenger cabin, highlighting the importance of this component to passenger comfort levels.

This paper discusses the dynamic characteristics of plastic plates with bolted joints. The effects of tightening torque on the modal properties of the plates are investigated. Experimental and numerical modal analyses have been conducted on the plates made of acrylonitrile butadiene styrene (ABS), that are clamped by bolted joints. First, the effect of tightening torque on the vibration mode of the plates is investigated by experimental modal analyses. Modal testing has been conducted for various tightening torque values and the relationships between the modal parameters and the tightening torques are discussed. Second, the effects of tightening torque on the vibration mode are studied by using analytical models for the bolted joints based on finite element method (FEM). Based on the comparisons between the experimental and the numerical results, a modeling strategy for the boundary conditions between the plates is introduced, and its validity is discussed. From both experimental and numerical studies, it is shown that the natural frequencies of the structures with bolted joints tend to converge to specific values as tightening torque increases. Moreover, it is also shown that when modeling the bolted plates by FEM, the inter-plate motion should be constrained by a boundary condition to properly suppress the out-of-phase motion of the plates.

A pendulum-type tuned mass damper (TMD) - tuned sloshing damper (TSD) system is proposed as a cost effective device to reduce wind-induced structural motion. Lagrange's principle is employed to develop an equivalent mechanical model for the system. The sloshing liquid provides additional gravitational restoring force to the pendulum TMD, but does not provide a corresponding increase to its inertia. As a result, the natural frequency of the pendulum TMD is increased due to the TSD degree of freedom. Shake table testing is conducted on several pendulum TMD-TSD systems that are subjected to harmonic base excitation at discrete frequencies near the natural frequency of the pendulum TMD. The modelled and experimental results are in reasonable agreement when the liquid is not shallow, or the response amplitude is not large. The pendulum TMD-TSD is coupled to a linear structure and it is demonstrated through an analytical study that the device provides performance that is comparable to a traditional TMD. The proposed system is advantageous because it does not require a viscous damping system that is often one of the most costly components of traditional TMDs.

This paper presents a shape memory alloy actuator design using a bimorph structure capable of high-speed actuation and low power consumption. Two active layers of shape memory alloy wires are separated by a passive layer of thermoplastic polyurethane. This structure results in a bending actuator when current is alternated between the two active shape memory alloy layers. Actuators of lengths 20, 25, 30, 35 and 40 mm were tested at peak current input of 110, 120, 130 and 140 mA. The 40 mm actuator was shown to have a natural frequency of 11.4 Hz with a bending displacement of 26.4 mm perpendicular to the neutral position and a power input of 0.78 watts (140 mA peak current input). A relationship between the input current and the resulting vibratory characteristics was found. As the current increases, the natural frequency decreases and the damping ratio increases. The experimental results are compared with an FEM vibration analysis and an Euler-Bernoulli cantilever beam equations.

The proper thermal diagnostics of the pipeline insulation is an important problem. The heat losses from the pipelines depend distinctly on a quality of this insulation. Changes of weather conditions cause transient accumulation of heat in the pipeline insulation and may cause difficulties during evaluation of the quality of the pipeline thermal insulation. Generally, the goal of this investigation was to identify the heat exchange processes on the external shell of the pipelines and the scale of heat accumulation inside the thermal insulation. This is important because during the calculations of heat losses from the thermal pipelines on the basis of infrared camera measurement results usually a steady thermal state is assumed. In order to determine the distributions of the temperature inside the thermal insulation the calculations of the temperature changes inside the pipeline insulation for real changeable meteorological conditions with use of software Ansys-Fluent and others have been carried out. Both the heat transfer between the inner pipeline tube and outer pipeline shell and heat accumulation inside the pipeline elements were considered. For the pipeline insulation evaluation purpose different coefficients for the analysis of heat accumulation scale were defined and used. The measurement results of the temperature of inner pipeline tube and outer pipeline shell gathered during the operation of the special experimental rig were used as input data for aforementioned numerical simulations. The conclusions resulting from this work may be useful for specialists involved in the examination and technical evaluation of the thermal insulation of pipelines.

Despite the rapid growth and widespread recognition of Additive Manufacturing (AM) technologies, the geometrical inaccuracy of the manufactured products remains a challenging issue and effective prediction of the geometric deviations in AM is critical for the solution of this issue. The layerwise characteristic of the AM process has motivated the investigation of deviation from in-plane and out-of-plane perspectives, the latter of which has been seldom studied and will be the focus of this paper. In this paper, an out-of-plane deviation modeling method will be proposed based on statistical modal analysis. Owing to the convenience in data acquisition, AM simulation is conducted to obtain the layer-level out-of-plane deviation on parts manufactured by the Selective Laser Melting process. Discrete Cosine Transform is adopted to identify the major deviation modes from the data. The statistical relationship between mode coefficients and related part and process parameters is studied based on the Gaussian Process model. To gain data for model training, experimental design is conducted to sample parameter combinations as simulation input. A case study is presented to demonstrate the proposed method and the effectiveness is validated on test data. The method can be applied in multiple domains of AM, such as quality control and tolerancing, to provide high-fidelity prediction of geometric deviations.

The motivation and objective of the present study are to propose a hybrid control system for offshore jacket platforms to mitigate the vibrations induced by multiple hazards, namely, the earthquakes and regular and irregular waves. State-of-the-art indicates that not much work is reported on hybrid control of offshore jacket platforms for multiple hazards using a control algorithm, which is robust against uncertainties. A decentralized sliding mode control algorithm using magneto-rheological (MR) dampers is employed for the semi-active controller because of its robustness against parametric uncertainties and reliability. Passive shape memory alloy rubber bearings (SMARBs) are selected as passive isolators because of their high damping capacities, high fatigue resistance, and super elastic behavior, which are highly desirable for offshore applications. The scope of the present study is to demonstrate the efficiency of the proposed controller and investigate the effects of different influencing parameters. A jacket platform, reported in the literature, is taken as an illustrative example. A significant reduction in the top deck displacement is observed. The position and number of MR dampers affect the performance of the controller significantly. Limitations of the controller imposed due to the greater weightage or penalty imposed on displacements by the semi-active control algorithm as well as due to the magnetic saturation of MR dampers are overcome by the high energy dissipation of the passive SMARBs, thus making the hybrid controller highly efficient. The effectiveness of the controller is more for the earthquakes and random waves than for the regular waves.

A new reduction method is proposed to investigate the behavior stability of rotor-bearing systems subject to a multifrequency rotational motion of their base. Combining the modal analysis and the construction of specific dynamic Ritz vectors, this method is able to deal with complex rotordynamics characteristics such as nonproportional damping, nonself-adjoint matrices, or time-varying parametric coefficients. This paper focuses first on assessing the accuracy and efficiency of the reduction method by computing time history and spectral responses of full and reduced models due to multifrequency base excitations. Its main potential is then highlighted in the parametric stability analysis through Floquet theory. The proposed numerical examples are composed with academic and industrial rotors, both modeled with one-dimensional Timoshenko beam finite element and supported by hydrodynamic journal bearings.

In this paper, we report the bending spectrum measured experimentally on oscillating beams with free extremes in a frequency range below and above the cutoff or critical frequency. The experimental setup used to obtain the bending spectrum consisted of a novel and selective method to excite mainly bending modes, as well as an identification process in which oscillation modes other than bending were discarded. For the first time, we identified bending modes above the cutoff frequency for square and circular cross-sectional beams and a good agreement is obtained when the measured frequencies are compared with the predictions of the Timoshenko beam theory (TBT) and those numerically obtained from the elasticity theory by using a three-dimensional finite element method (FEM) calculation. Higher frequency values at which TBT should cease to be valid were not achieved in the experiments. Instead, our experimental results show that TBT remains valid above the cutoff frequency, with an error smaller than 6%.

This paper evaluates the effects of uncertainties on the load capacity of a four-pad tilting-pad journal bearing, in which the pad radius, oil viscosity, and radial clearance are considered as uncertain information. The hydrodynamic supporting forces at the bearing pads are obtained by solving the Reynolds equation. In this case, the uncertain parameters are modeled as fuzzy type-2 variables. Fuzzy type-2 sets have been widely used due to their ability to model higher orders of uncertainties as compared with the fuzzy type-1 approach. They allow for inaccurate knowledge to be included in the membership functions used to describe the uncertain parameters. In the present contribution, the so-called α-level optimization was associated with the fuzzy type-2 technique for uncertainty analysis purposes. A sensitivity analysis was also carried out as an additional assessment of the considered uncertain parameters. The numerical results allowed to understand how the uncertain parameters affect the bearing supporting forces for three shaft speeds, namely, 3000, 9000, and 15,000 rpm. It was demonstrated that the effect of the uncertain parameters on the supporting forces increases according to the shaft speed. Additionally, the load capacity revealed to be more sensitive to variations on the oil viscosity and radial clearance than to the pad radius concerning the adopted uncertain interval. Consequently, the obtained results can provide suitable information for the design, manufacturing, and maintenance of tilting-pad journal bearings.

In this paper, the idea of an axially moving time-dependent beam model is briefly introduced. The nonlinear response of an axially moving beam is investigated. The effects of a time and spatial dependent tension depending on the external forces at the boundary and a tension dependent speed are highlighted, which gives a new model to study the parametric vibration of axially moving structures. This paper focuses on simultaneous resonant cases that are the principal parametric resonance of first mode and internal resonance of the first two modes. In general, the method of multiple scales can study nonlinear vibration of axially moving structures with homogeneous boundary conditions. Taking Kelvin viscoelastic constitutive relation into account, the inhomogeneous boundary conditions make the solvability conditions fail, which is also one of the highlights of this paper. In order to resolve this problem, the technique of the modified solvability conditions is employed. The influence of some parameters, such as material’s viscoelastic coefficients, viscous damping coefficients, and the axial tension fluctuation amplitudes, on the steady-state vibration responses is demonstrated by some numerical examples. Furthermore, the approximate analytical results are verified by using the differential quadrature method (DQM).

The objective of this study is to develop a novel methodology to assess the energy flow between a nonlinear energy sink (NES) and the primary system it is attached to in terms of energy orientation, which is directly related to the sign of the power present on the primary system. To extend the work done in previous studies, which have focused primarily on the analytical treatment, characterization, and performance evaluation of NES as passive nonlinear dampers for structures under different types of excitations, this study incorporates a methodology for determining whether energy is entering or leaving a primary oscillator when interacting with an NES, by means of considering the power flow of the primary oscillator. Several current measures for evaluating the effectiveness of the NES at extracting and dissipating energy irreversibly are considered through numerical simulations of systems with different damping cases of the NES. Each case provides a different dissipation scenario in the combined system, which is subjected to different types of base excitation signals such as impulse and seismic records. The methodology is further validated experimentally using a two degrees-of-freedom system with an NES attached to the second mass. Comparisons of the modeled responses versus the measured responses are provided for several physical damping realization scenarios in the NES.

An operational modal response method for application to the structure health and integrity of pipelines is investigated. The modal response characteristics of externally supported pipe structures are quantified through flow Reynolds number (Re d ) variation. Pipe flow turbulence and the resulting hydrodynamic pressure fluctuations on the interior pipe wall provide the structural forcing mechanism, and signals from wall-mounted accelerometers provide the system response. During experiments, the Reynolds number is varied from 51,000 to 154,000. Over this Reynolds number range, the pipe flow turbulence was found sufficient enough to excite the structure at frequencies up to 400 Hz. Modal response characteristics obtained through Reynolds number variation were found to be in agreement with results from impact hammer modal testing. The in-situ modal response method developed was applied to two different structural health monitoring investigations, one involving loss-of-material and the other involving loss-of-fluid. The loss-of-material scenario simulated the process of external pipe wall corrosion, and the developed method was able to detect material loss as small as 1.4%. The loss-of-fluid scenario simulated a small leak. Despite the low operating pressure of 0.024 MPa, the methodology was able to detect fluid loss as low as 0.1% of the bulk flow rate. The developed method has the potential to offer in-situ continuous pipeline health monitoring that relies on the continuous changes (flow rate, product viscosity, product density) that are inherent to an operational pipeline system.

In this paper, the single-sided vibro-impact track nonlinear energy sink (SSVI track NES) is studied. The SSVI track NES, which is attached to a primary structure, has nonlinear behavior caused by the NES mass moving on a fixed track and impacting on the primary structure at an impact surface. Unlike previous studies of the SSVI track NES, both the horizontal and vertical dynamics of the primary structure are considered. A numerical study is carried out to investigate the way in which energy is dissipated in this system. Assuming a track shape with a quartic polynomial, an optimization procedure that considers the total energy dissipated during a time period is carried out, to determine the optimum NES mass and track parameter. It is found that there is dynamic coupling between the horizontal and vertical directions caused by the SSVI track NES motion. The vibrational energy, originally in the structure in the horizontal direction, is transferred to the vertical motion of the structure where it is dissipated. Considering that many civil and mechanical systems are particularly vulnerable to extreme loads in the horizontal direction, this energy transformation can be beneficial to prevent or limit damage to the structure. The effect on energy dissipation of the position of the impact surface in the SSVI track NES and the ratio of the vertical to horizontal stiffness in the primary structure are discussed. Numerical results demonstrate a robust and stable performance of the SSVI track NES over a wide range of stiffness ratios.

Under excitation due to the environment or traffic load, cable vibration never ceases; thus, fatigue cycles generated by vibration-induced additional cable tension (VACT) owing to the change of the cable configuration from static to dynamic are significantly frequent. Therefore, VACT is a non-negligible cable-fatigue load. To investigate the cable dynamic stability and fatigue, it is necessary to determine VACT in a dynamic environment. Herein, a method for estimating VACT in the frequency-domain by using acceleration data is proposed. In this method, according to the cable vibration control equation, the frequency-domain relationship between the VACT and the vibration response of the measuring point is established based on the dynamic stiffness. Parameter analysis simplifies the proposed model to estimate VACT using only acceleration data. The proposed method is verified with cable acceleration data.

Built-up structures, such as airplanes, ships, and even refrigeration systems, which have many components, can be substructured to speed up and facilitate the process of calculating the vibratory response of the complete system. In many structures, there are rubber isolators that connect component parts, and these connections can each occur over a finite distributed area. It is often convenient and intuitive to substructure the system at the isolators. However, in previous work, it has been shown that the frequency response of the complete system does not always agree with the frequency response of the system calculated from the mobilities of the subsystems. It was thought that this was due to the distributed area connection of the isolators, and this motivated the study reported in this article. An investigation into some issues that occur when substructuring a system that contains soft distributed isolators is described. Using finite element models, it is shown that if a system is substructured, such that the interface between the substructures occurs at a soft rubber isolator, then there is a limited frequency range over which the frequency response function of the assembled system is accurate. It is further shown that it is far better to substructure the system, at stiff, discrete connections, if possible. The frequency range over which the frequency response of the assembled system should then be more accurate over a much wider frequency range.

The electromagnetic acoustic resonance (EMAR) method with shear wave is sensitive to boundary conditions and plate thickness. In this paper, a new noncontact ultrasonic testing method based on the electromagnetic acoustic transducer (EMAT) in the resonant mode is proposed for the bonding strength evaluation in metal-based adhesive structures. Different from the conventional pulse-echo method using short-burst excitation for bonding inspection, the attenuation coefficient feature of the resonant ultrasonic signal with long-burst excitation is applied to increase the signal-to-noise ratio (SNR) and detecting sensitivity of the EMAT for adhesive bonding strength evaluation. A theoretical model for adhesive bonding testing with EMAT signals in the resonant mode is established. To extract the signal feature representing the reflection coefficient, the time-domain signal was processed by Hilbert transformation and exponential curve fitting. Through the simulation on the received signal, the correlation between the attenuation coefficient of the exponent fitted curve and the strength on the adhesive imperfect interface were confirmed. Finally, the proposed correlation is verified by an experiment on stainless steel plates bonded with polymethyl methacrylate plates by epoxy adhesion via a permanent magnetic EMAT.

Non-engine order rotor blade vibration is an aeroelastic phenomenon of major interest for compressor designers resulting from an excitation of rotor blade modes through aerodynamic instabilities. Indicators for a comparable type of instability, caused by propagating acoustic modes have been observed in an experimental multistage high-speed compressor by Safran Helicopter Engines. It is intended to understand the cause for these instabilities by combining experimental data and numerical simulations. Unsteady pressure measurements were carried out by case-mounted and stator-mounted transducers. Rotor tip timing and magnet-coil sensor systems were installed to measure the blade vibrations. Experimental results show non-engine order signatures in the unsteady pressure signal coherent to the shifted frequency of blade vibrations. In the present paper the waveform of these oscillations is analysed in detail, showing a dominant propagating acoustic mode interacting with vibrations of Rotor-2. The root cause for the non-synchronous oscillations is identified as an acoustic mode that is cut-off downstream of Rotor-3. During the test, the mode changes its frequency and circumferential order, affecting the amplitude of associated blade vibrations.

By monitoring the structural vibration and analyzing the modal parameter, hidden damage can be identified at an early stage, preventing abrupt failures for important structural components. However, the modal parameter has exhibited a low sensitivity to the interfacial damage, such as the delamination in the composite beam. In this paper, a signal processing method is developed to increase the sensitivity of the modal parameter to the delamination. Both the first- and high-order modal parameters are transformed to an approximate waveform capacity dimension (AWCD). Based on the wave peaks of the modal parameters in the AWCD, the start and end of the delamination can be accurately pinpointed. Since the AWCD method can highlight the delamination-related waveform features of the modal parameters, the delamination can be identified without referring to the baselines. Both analytical and experimental investigations demonstrate that the AWCD method can modify the waveforms of the modal parameters and lead to an accurate identification of the delamination in composite cantilever beams.