Damping Measures Research Articles

Structural Stability Analysis of Bridge Structure Using FEA

In the current research, the dynamic analysis of bridge structure is conducted to determine the natural frequency and mode shape. The dynamic analysis is conducted using ANSYS FEA simulation package. The critical regions of high deformation and energy states are determined. The analysis revealed the presence of several dominant vibration modes, each associated with distinct deformation patterns and nodal patterns. These findings shed light on potential vulnerability zones and areas of concern that may be susceptible to resonance and excessive vibrations during bridge operation. Understanding these critical modes is vital for designing appropriate damping and vibration control measures to ensure the bridge's long-term stability and safety.

Analysis of ground motion measurement data under engineering blasting condition

To ensure that large precision instruments and equipment are in the best working condition, it is necessary to provide a suitable working environment for them. At this time, there is a high requirement for the vibration of the foundation at the location. Measuring the foundation vibration parameters, analyzing the foundation vibration state, and taking necessary damping measures during the construction process to provide basis are the premise of equipment installation and normal work. Combined with an application example, this paper briefly introduces the general situation of a project blasting, and obtains the basic characteristic parameters such as the peak velocity of ground motion and the time of arrival during the blasting operation; Based on the basic principle of regression analysis, the relationship between the peak velocity and the distance between the detonation centers and the charge weight is obtained by fitting the Sadovsky formula.

Power system wideband oscillation estimation, localization, and mitigation

AbstractWith the development of the energy structure of the power system, the characterization of the observed oscillation in the power system has steadily evolved. With the increasingly high penetration of distributed energy sources and power electronic devices, such as the photovoltaic, wind power and charging pile, the basic mechanism, frequency ranges and propagation of oscillation would become more dynamic and complex. Therefore, the traditional parameter estimation, as well as the suppression methods would also suffer from dynamic oscillations. To this end, this paper first investigates the oscillation propagation and typical events caused by the oscillations. Next, the oscillation model estimation method including the model‐based and data‐driven based methods is discussed. The benefits and difficulties of various parameter estimate techniques are highlighted. Under this context, the validity and limitations of the current power system stability are summarized. Furthermore, the different oscillation damping and mitigation measures are compared, and the major adaptability and limitations are listed for the specific application scenarios. Conclusions are drawn, and the wideband oscillation becomes the future research objective where the future work is presented at the end of the paper.

Friction-induced noise in drum brakes: finite-element modeling and experiments with special focus on damping

Brake squeal in friction brakes is a typical audible noise phenomenon in vehicles leading to high development and sometimes warranty costs for the suppliers. The friction forces generated during braking are responsible for self-excited vibrations in the audible frequency range starting from 1hbox { kHz}. In the past countermeasures against friction-induced vibrations are mostly investigated for disk brakes while the present study focuses on drum brakes. Damping is in the context of self-excited vibrations often one of the key measures. Nowadays recuperative braking in electric vehicles relieves the conventional friction brake. Due to safety reasons, electric vehicles need to possess at least a second independent brake system. Therefore, simpler drum brakes are on the rise again when developing brake systems. Compared to brake disks, where damping elements can hardly be implemented, the freely accessible drum surface and the brake shoes offer so far unused potential for applying passive damping measures. The present paper focuses on how damping measures influence the noise behavior of drum brakes. Industrial and non-industrial brake components are investigated in detail. Experimental as well as numerical procedures are used to assess damping and noise characteristics.

Study on model reduction for position optimization of acoustic black holes

AbstractNoise radiation of plate structures is a common problem with the design of machines in mechanical engineering. Noise can be reduced by designing passive damping measures. One of these measures can be the application of an ‘acoustic black hole’ (ABH). It is a targeted adaptation of the thickness of plate‐like structures to direct the acoustically critical bending waves to a certain region – the ABH. There, an applied damping material can dissipate the vibration energy very efficiently. A major challenge in design of this measure is to find an optimal position of the ABH with respect to low vibrations. Optimization can be a tedious task, especially for complex industrial geometries where the dicretized equations of motion can have millions DoF.This contribution shows on the example of a study on a rectangular plate how model reduction can help to reduce the computational costs for this position optimization. Three different reduction methods are shown: First, a condensation of internal state variables from the viscoelastic evolution equations via Schur complement. Second, modal truncation applied to the condensed equations from the first method and third, moment matching applied to the full order model. Computed mean squared‐admittance levels are compared to show the accuracy of the methods. Speed‐up and accuracy results show that Schur complement and moment matching are promising approaches while a naive modal truncation can lead to wrong results.

Study on Seismic Response and Damping Measures of Surrounding Rock and Secondary Lining of Deep Tunnel

Tunnel construction is gradually developing to areas with high in situ stress; the deeper the tunnel construction, the more intense the earthquake disturbance. Under the background of frequent earthquakes, the seismic characteristics of tunnels become an important content related to the safety and stability of engineering structures. In view of the key problems of seismic response and vibration reduction measures for complex deep buried tunnels, the methods of advanced grouting and foam concrete aseismic are studied in this paper. Firstly, through geological survey, the in situ stress and geological conditions of the study area are analyzed. The structural characteristics of surrounding rock and related rock mechanics parameters are analyzed. The failure criterion of concrete lining under dynamic load is studied theoretically, and the relevant numerical calculation parameters are modified. A numerical model based on viscous boundary conditions is established. Through numerical calculation, the seismic response of tunnel surrounding rock and lining under different damping measures is analyzed. The research results have theoretical research value and social and economic benefits for ensuring the safety and stability of tunnel structure and improving the seismic fortification level.

Transient dynamics, damping, and mode coupling of nonlinear systems with internal resonances

The study of both linear and nonlinear structural vibrations routinely circles the concise yet complex problem of choosing a set of coordinates which yield simple equations of motion. In both experimental and mathematical methods, that choice is a difficult one because of measurement, computational, and interpretation difficulties. Often times, researchers choose to solve their problems in terms of linear, undamped mode shapes because they are easy to obtain; however, this is known to give rise to complicated phenomena such as mode coupling and internal resonance. This work considers the nature of mode coupling and internal resonance in systems containing non-proportional damping, linear detuning, and cubic nonlinearities through the method of multiple scales as well as instantaneous measures of effective damping. The energy decay observed in the structural modes is well approximated by the slow-flow equations in terms of the modal amplitudes, and it is shown how mode coupling enhances the damping observed in the system. Moreover, in the presence of a 3:1 internal resonance between two modes, the nonlinearities not only enhance the dissipation, but can allow for the exchange and transfer of energy between the resonant modes. However, this exchange depends on the resonant phase between the modes and is proportional to the energy in the lowest mode. The results of the analysis tie together interpretations used by both experimentalists and theoreticians to study such systems and provide a more concrete way to interpret these phenomena.

Development of a Series Capable Production Process for Fiber‐Reinforced Composites with Thermoplastic Matrices and Material‐Integrated Piezoceramic Modules

Fiber‐reinforced thermoplastic composites are widely used in technical applications, for example, in machine, automotive, and equipment industries. Reasons for this are the excellent and adaptable mechanical properties and the high potential of the associated manufacturing processes for a very efficient and resource‐efficient production with larger volumes. However, these lightweight structures often show high vibration amplitudes and high resulting sound radiation due to their reduced weight and moments of inertia, which results in a decreased vibro‐acoustic performance especially for dynamically loaded applications. Besides passive damping measures, active vibration control using piezoelectric transducers is a suitable option. The layer‐wise built‐up of the fiber‐reinforced composites enables the integration of additional elements, such as flat sensors and actuators into this layup. This offers the possibility to embed piezoceramic modules to create function‐integrative components, which are able to sense or generate vibrations. A main challenge for a successfully transfer of this technology into industrial applications is the development of appropriate series‐capable manufacturing processes for integrating piezoceramic modules into composite structures. This contribution is intended to show a possibility to realize such a process. Here, the basic idea is to use thermoplastic polymers as matrix and raw materials in order to enable very efficient and fast production processes. But the major advantages of this new material concept, short cycle times, and relatively simple processing tools can only be facilitated, if some challenges, especially in regard to press processes, are overcome. The processing temperatures of thermoplastic based composites are higher than those for thermoset matric based composites. Integrating the piezoceramic modules, the Curie temperature may be exceeded, which will cause the depolarization of the piezoceramic elements. The presented newly developed manufacturing technology pays special attention to this fact. For the first time, this technology allows to realize a one shot technology for fiber‐reinforced composites with thermoplastic matrices and integrated piezoceramic elements. Thereby, the focus is on the conception and analysis of the manufacturing process and experimental investigations to determine suitable material and processing parameters.

Structural and functional evidence for the scaffolding effect of alveolar blood vessels

ABSTRACT A contribution of pulmonary blood distension to alveolar opening was first proposed more than 100 years ago. To investigate the contribution of blood distension to lung mechanics, we studied control mice (normal perfusion), mice after exsanguination (absent perfusion) and mice after varying degrees of parenchymal resection (supra-normal perfusion). On inflation, mean tracheal pressures were higher in the bloodless mouse (4.0 ± 2.5 cm H2O); however, there was minimal difference between conditions on deflation (0.7 ± 0.9 cm H2O). To separate the peripheral and central mechanical effects of blood volume, multi-frequency lung impedance data was fitted to the constant-phase model. The presence or absence of blood had no effect on central airway resistance (p > .05). In contrast, measures of tissue damping (G), tissue elastance (H) and hysteresivity (η) demonstrated a significant increase in bloodless mice relative to control mice (p < .001). After varying amount of surgical resection and associated supra-normal perfusion of the remaining lung, there was an increase in G and H. Although the absolute difference in G and H increased with the amount of parenchymal resection, the proportional contribution of blood was identical in all conditions. The presence of blood in the pulmonary vasculature resulted in a constant 64 ± 5% reduction in tissue damping (G) and a 55 ± 4% reduction in tissue elastance (H). This nearly-constant contribution of blood to lung hysteresivity was only reduced by positive end-expiratory pressure (PEEP). To identify a distinct structural subset of vessels in the lung potentially contributing to these observations, vascular casting and scanning electron microscopy of the lung demonstrated morphologically distinct vascular rings at the alveolar opening. Our results suggest that intravascular blood distension, likely attributable to a subset of vessels in the alveolar entrance ring, contributes a measurable scaffolding effect to the functional recruitment of the peripheral lung.

Novel analysis of 4DCT imaging quantifies progressive increases in anatomic dead space during mechanical ventilation in mice.

Increased dead space is an important prognostic marker in early acute respiratory distress syndrome (ARDS) that correlates with mortality. The cause of increased dead space in ARDS has largely been attributed to increased alveolar dead space due to ventilation/perfusion mismatching and shunt. We sought to determine whether anatomic dead space also increases in response to mechanical ventilation. Mice received intratracheal lipopolysaccharide (LPS) or saline and mechanical ventilation (MV). Four-dimensional computed tomography (4DCT) scans were performed at onset of MV and after 5 h of MV. Detailed measurements of airway volumes and lung tidal volumes were performed using image analysis software. The forced oscillation technique was used to obtain measures of airway resistance, tissue damping, and tissue elastance. The ratio of airway volumes to total tidal volume increased significantly in response to 5 h of mechanical ventilation, regardless of LPS exposure, and airways demonstrated significant variation in volumes over the respiratory cycle. These findings were associated with an increase in tissue elastance (decreased lung compliance) but without changes in tidal volumes. Airway volumes increased over time with exposure to mechanical ventilation without a concomitant increase in tidal volumes. These findings suggest that anatomic dead space fraction increases progressively with exposure to positive pressure ventilation and may represent a pathological process.NEW & NOTEWORTHY We demonstrate that anatomic dead space ventilation increases significantly over time in mice in response to mechanical ventilation. The novel functional lung-imaging techniques applied here yield sensitive measures of airway volumes that may have wide applications.

Correlation of ISO 16840-2:2007 impact damping and hysteresis measures for a sample of wheelchair seating cushions

ABSTRACTHysteresis and impact damping measures were made on 37 wheelchair seating cushions according to ISO 16840-2:2007 Wheelchair seating—Part 2: Determination of physical and mechanical characteristics of devices intended to manage tissue integrity—seat cushions. These measures were then correlated using Spearman and Pearson correlations to investigate the relationship between them. Correlations were also conducted on the subset of cushions comprising only those with planar foam construction. Correlation between the hysteresis measures (h250 and h500) and the mean number of rebounds greater in amplitude than 10% of the peak acceleration amplitude (R10%) were weak, as were the correlations between the hysteresis measures and the mean peak first rebound acceleration (aa). Correlations between hysteresis and the mean peak second rebound acceleration (a2), and also hysteresis and the ratio of first and second peak (a2:aa) however were moderate. Results demonstrate that the relationship between these two measures is complex. The assertion implicit in ISO 16840-2:2007 is that the two measures are related, but this study shows that these should not be assumed to be equivalent or used interchangeably.

Experimental investigation and finite element modelling of a new high damping metallic material

The properties of a high damping metallic material are investigated experimentally and a plausible finite element (FE) representation based on the results is deduced. The material consists of hollow, bonded aluminium spheres filled with ceramic particles. The damping mainly occurs due to dissipation via particle interaction. Consequently, one has to model the damping in such a way that shearing contributes only a little to the energy dissipation and the damping properties are orthotropic while the material stiffness is isotropic. Using the model of constant hysteresis for frequency‐domain calculations, the complex stiffness matrix is constructed from the real‐valued isotropic stiffness matrix, and the complex‐valued orthotropic damping matrix. Since the finite element code used only offers the possibility of the damping matrix of an element being proportional to its stiffness, two superimposed finite element models are utilized, one representing the material's stiffness the other it's damping properties. The material parameters are obtained from an experimental modal analysis (EMA) on three samples of the material. The modelling approach is verified on a single hexahedral element and a simulation of the experimental modal analysis. Finally, a sandwich frame structure consisting of the damping material sandwiched between two aluminium frames is investigated by means of an EMA and a respective finite element modal analysis which makes use of the aforementioned modelling approach. A comparison of the results is given in terms of eigenfrequencies and the corresponding modal damping measures.

Study on Damping Measures of Pump Piping Vibration Isolation Device

The problem about pump piping system vibration isolation that is hard to be solved at the present stage in the practice engineering was studied in this paper. Damping measures which is the necessary measure is proposed in this study. Theoretical analysis is given to the main parameter (thickness) of the influences of the damping. Based on the free damping measure, constrained damping measures was proposed and verified by the experiments. The results show that the damping effect was improved with the increasing of the thickness. Under the same conditions, the effect of the constrained damping measures was better than the free damping measures. The results have significant guidance in the isolation vibration of the pump system.

Microstructural design studies for locally dissipative acoustic metamaterials

Stress wave attenuation performance of locally dissipative acoustic metamaterials with various damped oscillator microstructures is studied using mechanical lattice models. The presence of damping is represented by a complex effective mass. Analytical solutions and numerical verifications of transmissibility are obtained for Kelvin-Voigt-type (KVO), Maxwell-type, and Zener-type (ZO) oscillators with viscous damping. Although peak attenuation at resonance is diminished, dissipative microstructures can provide broad spectrum attenuation without increasing mass ratio, obviating the bandgap width limitation of locally resonant microstructures. KVO gives the best broad spectrum performance akin to a low-pass filter for excitation frequencies above a cut-off value for a prescribed transmissibility criterion. For ZO, by tailoring the damping and stiffness, the frequency range of appreciable attenuation can at least span the bandgap widths of two limiting locally resonant cases. Static and frequency-dependent measures of optimal damping that maximize the attenuation characteristics are proposed. A transitional value for the excitation frequency is identified within the locally resonant bandgap, above which there always exists an optimal amount of damping that renders the attenuation for the dissipative metamaterial greater than that for the locally resonant case. Further microstructures with hysteretic damping depict a frequency-independent scaling in the effective mass and attenuation factor, but the bandgap width remains nearly the same as that for the corresponding viscously damped microstructures. This study demonstrates that dissipative microstructures, which are to some extent unavoidable in practical designs, when tuned, provide a means to substantially enhance the attenuation bandwidth of locally resonant acoustic metamaterials while also enabling the removal of the energy sequestered by the oscillators from the system.

Prediction of underwater noise and far field propagation due to pile driving for offshore wind farms

Wind energy plays a key role toward a greener and more sustainable energy generation. Due to limited onshore areas and possible negative effects on human living space, offshore wind parks become increasingly popular. During construction by pile driving, however, high levels of underwater sound emission are observed. To avoid negative effects on marine mammals and other sea life, different approaches, like, e.g., bubble curtains or cofferdams, are currently investigated to cut down the sound pressure levels. In order to predict the expected underwater noise, both with and without sound damping measures, numerical simulation models are needed to avoid complex and costly offshore tests. Within this contribution, possible modeling strategies for the prediction of underwater noise due to pile driving are discussed. Different approaches are shown for the direct adjacencies of the pile and for the far field sound propagation. The effectivity of potential noise mitigation measures is investigated using a detailed finite element model of the surroundings of the pile. The far field propagation in the kilohertz range at distances of several kilometer from the pile, on the other hand, is computed by a model based on wavenumber integration. Finally, the model validation with corresponding offshore tests is addressed.

Dynamic Testing of Single- and Double-Story Steel-Sheathed Cold-Formed Steel-Framed Shear Walls

AbstractThis paper describes an experimental investigation of steel-sheathed cold-formed steel-framed shear walls by means of dynamic shake table tests. The objective was to evaluate the seismic performance and to identify whether the shear-wall behavior was consistent with past static tests, to obtain measures of damping and natural period of vibration, to investigate the influence of a second story, and to validate and improve the accuracy of the numerically predicted force-deformation response. The scope of study comprised five single-story and five double-story walls of the platform framing technique. Each wall was subjected to a suite of excitations: impact test to measure the linear-viscous damping ratio, harmonic excitation to estimate the natural period of vibration, and ground motions representative of the seismic hazard in Canada. An overview is presented of the test setup and dynamic loading protocols, as well as the test results and numerical model.

Numerical and experimental investigation of a highly effective single-sided vibro-impact non-linear energy sink for shock mitigation

In this paper a highly asymmetric, lightweight, vibro-impact non-linear energy sink (NES) leading to very efficient passive non-linear targeted energy transfer (TET) is investigated. To this end, a two degree-of-freedom linear system (the primary structure) is coupled to a single-sided vibro-impact (VI) attachment with highly asymmetric impact non-linearity (the VI NES). The proposed NES passively absorbs and rapidly dissipates a considerable amount of the impulse energy induced into the linear structure, leading to very effective shock mitigation compared to a double-sided (symmetric) VI NES. We find that appropriate selection of the weak linear stiffness that couples the non-linear VI attachment to the linear structure plays a significant role in the proposed design. Moreover, in contrast to the double-sided VI NES which has optimal performance for a narrow range of input energies, the proposed single-sided asymmetric VI NES maintains a high level of performance over a broad range of high input energies. Hence, the proposed design is especially suitable for severe shock mitigation in infrastructure. To quantify the enhanced shock mitigation performance of the asymmetric VI NES we employ measures of effective damping and stiffness developed in previous works to demonstrate that the primary structure with attached NES possesses drastically increased effective damping and stiffness compared to its nominal properties when no NES is attached. A series of experimental results fully validates the theoretical predictions.

Seismic Analysis and Design of Minpu Double-Deck Cable-Stayed Bridge

The Minpu Bridge for the Pudong Airport Expressway is a large double-deck cable-stayed bridge over the Huangpu River, Shanghai. It is also an important structure to link the local road system. The bridge has two towers, double cable planes and composite truss stiffening girder. Its substructure includes piers on drilled piles. Its spans are arranged as: 4×63+708+4×63m,with a total length of 1212m. It becomes the longest double-deck highway cablestayed bridge in the world on its completion. The basic seismic fortification intensity at bridge site is 7 degrees, and there are no specific seismic design codes for such special bridge in China. Therefore, it is very important to carry out the seismic performance study of the Minpu Bridge to ensure the seismic safety. In this paper, the dynamic response simulations of the entire bridge are undertaken on the procedure as following: The first stage is to establish a threedimensional dynamic finite element analytical model to analyze the dynamic characters and seismic response of structure by the methods of response spectrum and nonlinear time-history analysis, then to identify the vulnerable parts of the bridge and to check its seismic capacity according to the seismic performance requirements assigned by owner. Next, to propose the design revision or to develop seismic damping and isolation measures such as viscous dampers parameters and girder-pier lateral restraints to improve the structural seismic performance. At last, according to the results of the dynamic analysis, the suggestions of the bridge design and the seismic safety evaluation of the structure are presented. Application of research results shows that seismic damping and isolation measures described in the paper is feasible, effective and applicable.

Damping and induced damping of a lightweight sandwich panel with simple and complex attachments

Accurately estimating a structure's broadband response is highly dependent on a proper characterization of the system's internal damping as well as induced (or effective) damping when coupled systems are considered. In many aerospace and related applications a primary or master structure is loaded with equipment or substructures. The effects of these attachments on the master structure are often poorly understood and frequently overlooked, but in many cases can dominate the master structure's response. In this work various measures of damping of a lightweight aerospace panel (aluminum sandwich honeycomb core panel) with simple (lumped mass) and complex (electronic equipment) attachments are investigated using experimental techniques and simple statistical energy analysis models. The panel's various measures of damping in steady-state conditions are defined and explored. The panels with simple and complex attachments are experimentally evaluated using power injection methods. The results show that at different frequencies the simple panel's response is controlled by internal and then acoustic radiation damping. The complex attachment's induced damping effects, however, can far exceed both the structure internal and acoustic radiation components. A range of complex attachment configurations are evaluated and general design assessment procedures developed for use by designers. Future work is planned to explore the systems transient response and derived parameters, as well as investigate the effects when the attachment mass varies over a greater range of values, a realistic condition applicable to many aerospace systems.

Acoustic waves in transversely excited atmospheric &lt;inline-formula&gt;&lt;math display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;CO&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; laser discharges: effect on performance and reduction techniques

Results are presented on the influence of acoustic waves on the performance of high-repetition-rate TEA CO2 lasers. It is shown that acoustic waves generated inside the laser cavity lead to nonuniform discharges, resulting in a deterioration of the laser beam quality, decreased output energy, and an increase in pulse-to-pulse energy variation. The effect of the gas mix on the acoustic behavior is investigated, and experimental results on laser performance across a range of gas mixtures are presented. Methods to reduce the effects of acoustic waves are presented together with experimental results. The influence of acoustic damping measures on laser gain are demonstrated, showing a significant improvement in gain and output power at high pulse repetition rates.