Constrained Layer Research Articles

Study of the dynamic electro-mechanical and microstructural behaviour on the elastic wave in FGM/FGPM composite structure: WKB asymptotic approach

This paper presents a theoretical investigation of the horizontally polarized shear wave in a composite structure. The assumed composite is composed of Functionally graded piezoelectric material (FGPM) layer constrained between an FGM (Functionally graded material) layer and a couple stress half-space with size-dependent microstructural effect. The variation in rigidities and densities are considered parabolic and linear in the upper and constrained layers, respectively. An analytical WKB (Wentzel–Kramers–Brillouin) asymptotic approach has been adopted for obtaining the dispersion relation. Also, a finite difference scheme (FDS) has been introduced to calculate the phase velocity and group velocity of the SH-wave. If waves travel in the time domain, it is necessary to check the accuracy and stability requirements. So that FDS has been adopted because of its accuracy, reliability, and flexibility. For the purpose of numerical calculation, three sets of FGPMs are considered namely, PZT−4, PZT−5H ceramic, and ceramic. Graphs have been plotted by means of dimensionless phase velocity against dimensionless wave number to show the effect of various parameters on the propagation of SH-wave. Numerical results demonstrated the accuracy and versatility of the phase and group velocity depending on the stability ratio of the FDS.

Constrained layer damping for mitigating vibration of a rotating disk-drum coupled structure

Rotating disk-drum coupled structures are commonly employed in large rotating machines. They are prone to have vibration issues caused by their decreasing thickness to meet lightweight demands. Constrained layer damping (CLD) is a widely used technique to reduce vibrations, but no studies have yet investigated its application on rotating coupled structures. In this paper, a universal model is proposed and experiments are conducted to investigate the influence of CLD on a rotating cylindrical shell ended by an annular disk. This approach considers the rotating effects, and formulates the equations of motion using the Rayleigh-Ritz method with the help of the Sanders shell theory and Mindlin plate theory. Different sets of artificial springs are applied to model the coupling and boundary conditions. The proposed approach is validated by comparing the numerical results with those obtained from modal and rotor experiments. Then the modal parameters and vibration responses are evaluated for different rotational speeds, and the influences of the location and thickness ratio of the CLD patch and the coupling stiffness on the dynamic characteristics of the system are discussed.

Surface wave dispersion curve inversion using mixture density networks

SUMMARYIn many seismological, environmental and engineering applications a detailed S-wave velocity model of the shallow subsurface is required. This is generally achieved by the inversion of surface wave dispersion curves using various inversion methods. The classical inversion approaches suffer from several shortcomings, such as inaccurate solutions due to local minima or large computation times in case of a wide parameter space. A number of machine learning (ML) approaches have been suggested to tackle these problems, which however do not provide probabilistic solutions and/or constrain layer number and layer thickness to a fixed value. In this study, we develop a novel neural network (NN) approach in order to characterize the shallow velocity structure from Love and Rayleigh wave dispersion curves. The novelty of our method lies in the simultaneous estimation of layer numbers, layer depth and a complete probability distribution of the S-wave velocity structure. This is achieved by a two-step ML approach, where (1) a regular NN classifies the number of layers within the upper 100 m of the subsurface and (2) a mixture density network outputs the depth estimates together with a fully probabilistic solution of the S-wave velocity structure. We show the advantages of our ML approach compared to a conventional neighbourhood inversion and a Markov chain Monte Carlo algorithm. Our ML approach is then applied to dispersion curves extracted from recorded noise data in Munich, Germany. The resulting velocity profile is in accordance with lithologic information at the site, which highlights the potential of our approach.

Laboratory measurements of lightweight floating floor systems on cross-laminated timber (CLT) slabs

Mass timber family of products (including cross-laminated timber - CLT) offer an alternative to fossil fuel-intensive materials for many applications and an opportunity to reduce the carbon footprint of the built environment. However, the use of mass timber in multi-family and commercial buildings presents unique acoustic challenges. Additionally, one of the most desired aspects of mass timber construction is the ability to leave a building's structure exposed as finish, which creates the need for asymmetric assemblies. This means that when speaking about floor/ceiling applications, preferentially any acoustical component should be installed on top of the assembly. To measure airborne sound reduction and impact noise isolation of lightweight floating floor systems and confirm CLT assemblies can provide satisfactory sound insulation, CDM Stravitec launched a testing campaign (done on Belgian Building Research Institute, institution recognized by application of the decree-law of the 30th of January 1947), where measurements were made considering several types of decouplers, such as: discrete bearings with multiple thickness and/or different void depth (filled in totally or partially with insulation material) and mats and strips placed between the CLT slab and different timber, cement and gypsum-based boards with and without use of the well-known constrained layer damping technique. This paper will present the findings of the test campaign.

Experimental study on axial compression of hybrid fiber cement-based composite column with circular cross section

In this study, hybrid fiber cement-based composite materials are used to make the confinement layer of the composite column, and plain concrete is poured inside to form the composite column. Considering the thickness of the confinement layer, the strength of the mixed fiber cement-based composite material of the confinement layer, and the strength of the inner core concrete, two sets of eighteen composite column specimens were designed and fabricated for axial compression tests to study the axial compression performance of the composite columns. The results showed that: The main factor that affects the occurrence time of cracks in composite columns is the strength of the cement-based composite material of the confinement layer. Through the analysis of the load–strain curve, it is found that the influence of the thickness of the confinement layer and the strength of the core concrete on the peak load of the composite column depends on the strength of the confinement layer: When the strength of the confinement layer is greater, the greater the thickness of the confinement layer and the smaller the strength level of the core concrete, the greater the peak load; when the strength of the confinement layer is smaller, the greater the thickness of the confinement layer and the smaller the strength level of the core concrete, the smaller the peak load. The peak strain is mainly related to the thickness of the constrained layer and the strength of the cement-based composite material of the confinement layer; When the strength of the confinement layer is smaller, the greater the thickness of the confinement layer and the smaller the strength of the core concrete, the better the ductility; when the strength of the confinement layer is greater, the specimen with the thickness of the confinement layer of 62.5 mm has better ductility; Based on statistical principles, the bearing capacity prediction formula and peak stress prediction formula of the composite column are established, and the calculated values are in good agreement with the experimental values.

Two-scale concurrent topology optimization method of constrained layer damping structure subjected to non-uniform blast load

Two-scale concurrent topology optimization method of constrained layer damping structure subjected to non-uniform blast load

Viscoelastic damping design – A novel approach for shape optimization of Constrained Layer Damping treatments at different ambient temperatures

Passive damping plays an important role in the vibration mitigation of aeronautic structures. In contrast to active systems, passive damping systems do not require any energy supply. Thus, their readiness is independent, which reduces the failure probability compared to active systems. Constrained Layer Damping (CLD) has become an established treatment for damping bending vibrations. Unlike other passive systems such as shock-mounts, CLD can be compactly integrated into an existing structure as an add-on solution. However, the design scope is limited by mass constraints and the optimal design for maximum damping must be found by optimization. For this purpose, a novel optimization approach is presented. The layer widths of the core and face layers of a CLD structure are treated as design parameters. Compared to the strategy of placing CLD patches on vibration antinodes, the proposed approach provides up to 52 % higher damping. The optimal design of a generic beam structure is determined considering different modes, viscoelastic material stiffnesses and ambient temperatures. Furthermore, the simulated damping is experimentally verified for a shape-optimized beam. The analyses show that the optimal design depends significantly on the viscoelastic material stiffness and is therefore temperature dependent. As a consequence, a generalized design guideline for CLD treatments cannot be derived.

Finite Element Modeling and Vibration Control of Plates with Active Constrained Layer Damping Treatment

An enhanced lightness and thinness is the inevitable trend of modern industrial production, which will also lead to prominent low-frequency vibration problems in the associated structure. To solve the vibration problem of thin plate structures in various engineering fields, the active constrained layer damping (ACLD) thin plate structure is taken as the research object to study vibration control. Based on the FEM method, energy method, and Hamilton principle, the dynamic model of an ACLD thin plate structure is derived, in which the Golla-Hughes-McTavish (GHM) model is used to characterize the damping characteristics of the viscoelastic layer, and the equivalent Rayleigh damping is used to characterize the damping characteristics of the base layer. The order of the model is reduced based on the high-precision physical condensation method and balance reduction method, and the model has good controllability and observability. An LQR controller is designed to actively control the ACLD sheet, and the controller parameters and piezoelectric sheet parameters are optimized. The results show that the finite element model established in this paper is accurate under different boundary conditions, and the model can still accurately and reliably describe the dynamic characteristics of the original system in the time and frequency domain after using the joint reduction method. Under different excitation and boundary conditions, LQR control can effectively suppress structural vibration. Considering the performance and cost balance, the most suitable control parameter for the system is: Q-matrix coefficient is between 1 × 104 and 1 × 105, the R-matrix coefficient is between 1 and 10, and the thickness of the piezoelectric plate is 0.5 mm.

Damping Capabilities of Viscoelastic Composites for Active/Passive Constrained Layer Damping of the Plate Vibration: A Comparative Study

Damping Capabilities of Viscoelastic Composites for Active/Passive Constrained Layer Damping of the Plate Vibration: A Comparative Study

Constrained layer damping concept used on isolated gym floors. Better than Concrete?

As the global fitness trends continues in a post-pandemic world, intra-building disruptions from high-energy fitness create serious acoustical challenges. Solutions from simple roll-out mats and rubber tiles to concrete floating floors supported by spring jack-up isolators are used to achieve acoustical separation for gyms. Understanding the sources of sound and vibration produced in fitness environments and finding effective solutions was a journey that CDM Stravitec began in the 1970s and this area of the acoustics industry has been intensively researched as part of the development of our range of lightweight floating floors. As part of this research, we extensively investigated how the concept of constrained layer damping (CLD) could be employed to mitigate vibration radiation through structures. In the application of fitness flooring, the CLD functions to restrict the physical movement between the rigid board layers decreases the area of influence from the impact, reduces the energy radiation through the composite panel system to its support and subsequently reduces the energy transfer into the structure. Our research has also shown that elastomeric supports balance low-resonant frequency performance to prevent energy build-up at the driving frequencies and can achieve high levels of transmission loss which are comparable to concrete based solutions.

Dynamic behavior of cylindrical shell with partial constrained viscoelastic layer damping under an impact load

Dynamic behavior of cylindrical shell with partial constrained viscoelastic layer damping under an impact load

Dynamical analysis and vibration estimation of a flexible plate with enhanced active constrained layer damping treatment by combinatorial neural networks of surrogates

The effective estimation of the vibration of spacecrafts are frontier issues in the aerospace industry. But the vibration of aerospace components such as space solar panels and flexible manipulators under large overall rotating motion is usually very complex due to strong nonlinearity and often requires a lot of repetitive and burdensome calculations. Artificial neural network (ANN) is composed of interconnected neurons, and a surrogate model can be established to effectively predict the mechanical characteristics. In addition, the computational efficiency will be greatly improved if the object is changed from the model that is established by commercial finite element method (FEM) software or numerical calculations to the surrogates. However, the stochasticity of the estimation by single neural network is inevitable, and some neural networks much rely on the initial weight and threshold. This paper will implement a new combinatorial strategy that relies on multiple neural network models, which have different activation functions and regression feedback processes based on reasonable selection of sample points. To solve the elongated training time led by comparing these neural networks, genetic algorithm (GA) is used to optimize the iteration speed of one neural network when finding the optimal output value. Thus, better estimation accuracy will be achieved by designing an algorithm to combine these combinatorial neural networks of surrogates (CNNS). Based on the proposed method, the vibration estimation of a rotating flexible plate with enhanced active constrained layer damping (EACLD) treatment, and the vibration suppression capacity of the composite structure under various operating conditions will be investigated.

Anomalous impact and vibration damping by liquid crystal elastomers

Anomalous impact and vibration damping by liquid crystal elastomers Liquid Crystal Elastomers (LCE), invented over 30 years ago, have been considered a highly promising material system for soft actuators and artificial muscles ever since. In this second academic piece for Open Access Government, Professor of Polymer Physics, Eugene M. Terentjev explores the anomalous impact and vibration damping by liquid crystal elastomers. There is considerable interest in developing thin conformal coatings of materials that can efficiently dissipate mechanical energy, thus suppressing vibration and noise and protecting from impacts. Traditionally, to create vibration-damping materials one exploits the loss aspect of the viscoelastic response when the energy dissipates as heat in either free or constrained layer configurations.

Designing Structurally Adaptable Multi-mode Products Using Emerging Constrained Layer Pneumatic System Technologies

Designing Structurally Adaptable Multi-mode Products Using Emerging Constrained Layer Pneumatic System Technologies

Lightweight Composite Partitions with High Sound Insulation in Hotel Interior Spaces: Design and Application

Sound insulation performance of partitions is one of the key factors contributing to the comfort of the hotel interior spaces. Based on the theory of constrained layer damping, this study proposed the light-weight composite partition structure with high sound insulation, which was composed of gypsum boards of different thicknesses and an isobutylene isoprene rubber board. The normal incidence sound transmission loss of the structure was evaluated through finite element simulations as well as experiments, which were conducted in a standing wave tube. The results show that the simulation and experimental results of two kinds of lightweight high sound insulation multi-layer composite partition walls are closely aligned; the surface density of the optimized partition wall was less than 42 kg/m2, although the normal incidence STL exceeded 51.8 dB at 200 Hz and at 1/3 octave of 1000 Hz with the maximum value of 58.5 dB. The lightweight composite partition wall with high sound insulation has a huge application potential in enhancing the sound environment quality of hotels.

A smoothed finite element formulation using zig-zag theory for hybrid damping vibration control of laminated functionally graded carbon nanotube reinforced composite plates

The paper presents an efficient numerical approach to deal with the hybrid damping vibration control of laminated functionally graded carbon-nanotube reinforced composite plates (FG-CNTRC) structures. In order to evaluate the damped response, a smoothed finite element model has been derived to simulate the laminated FG-CNTRC plate integrated with active constrained layer damping (ACLD) treatment patches consisting of 1-3 piezoelectric composite (1-3 PZC) layer and a viscoelastic layer. The constrained layer of the ACLD patch is modeled as viscoelastic materials by using the complex modulus. In order to enhance the efficiency of the numerical approach, the proposed framework integrates the zig-zag theory into the cell-based smoothed discrete shear gap method (CS-DSG3) to help increase the accuracy and reduce the computational cost. The accuracy and reliability of the present study are validated by comparing its numerical results to those of other available numerical methods. Moreover, the effect of CNT distribution, nanotube volume fraction, and CNT orientation on the damping behavior of FG-CNTRC plates are investigated. Additionally, the influence of symmetrical and asymmetrical damping treatment configuration for controlling the vibration is also examined in detail. • An efficient numerical approach for the hybrid damping of FG-CNTRC plates is proposed. • Proposed framework helps increase the accuracy and reduce computational cost. • Effects of CNT distribution, volume fraction, and orientation on the damping behavior are examined. • Influence of symmetrical and asymmetrical configuration is examined.

Reviving autoencoder pretraining

The pressing need for pretraining algorithms has been diminished by numerous advances in terms of regularization, architectures, and optimizers. Despite this trend, we re-visit the classic idea of unsupervised autoencoder pretraining and propose a modified variant that relies on a full reverse pass trained in conjunction with a given training task. This yields networks that are as-invertible-as-possible and share mutual information across all constrained layers. We additionally establish links between singular value decomposition and pretraining and show how it can be leveraged for gaining insights about the learned structures. Most importantly, we demonstrate that our approach yields an improved performance for a wide variety of relevant learning and transfer tasks ranging from fully connected networks over residual neural networks to generative adversarial networks. Our results demonstrate that unsupervised pretraining has not lost its practical relevance in today’s deep learning environment.

Augmented active constrained layer damping of beams using graphite reinforced viscoelastic composite material

This paper deals with the use of viscoelastic composite material (VECM) for the constrained layer of an active constrained layer damping (ACLD) treatment for enhanced damping characteristics due to contributions of extensional strains in addition to transverse shear strain. The proposed VECM layer is composed of graphite fibers reinforced in a conventional viscoelastic matrix. The bending analysis of the overall beam is carried out and contributions of extensional and shear strains for damping behavior are found out. The effects of changing various geometric parameters of the present VECM layer on the control performance of the ACLD treatment have also been evaluated and presented.

Experimental Analysis of Constrained Layer Damping Structures for Vibration Isolation in Lightweight Railway Vehicles

Rolling stock manufacturers face the challenge of manufacturing lightweight high-speed trains without deteriorating comfort. One of the difficulties is to mantain or increase structural stiffness and damping as the car bodies become lighter. Leaving aside active solutions, which are expensive and generally complex to implement, increasing structural damping by means of viscoelastic patches (via Constrained Layer Damping) seems to be a viable solution which is in fact already used for acoustic insulation in automotive, aerospace and even railway applications. Although there are works in the literature that try to optimise viscoelastic panels, this work presents an experimental study with two essential contributions: (i) to analyse the influence of a broad set of design parameters such as type of the constraining layer (uniform or honeycomb), thickness of the viscoelastic layer, location, covered area and continuity between patches; and (ii) to consider absolute and specific (per unit mass) damping depending on the design scenario. To locally increase the structural damping of an existing lightweight structure without compromising its weight, partial application of thin viscoelastic and constraining layers turned out to be the best solution. To enhance structural damping from the design stages, disregarding constraining layer mass by incorporating its stiffness into the overall stiffness of the structure, full coverage with thick viscoelastic layer and a honeycomb constraining layer with a high cross-section moment of inertia turned out to be the best option, reaching modal damping ratios up to 22 times higher than structures without viscoelastic materials.

Constrained Layer Assignment for the Protein Burial Folding Code Accounting for Chain Connectivity.

The connection between protein sequences and tertiary structures has intrigued investigators for decades. A plausible hypothesis for the coding scheme postulates that atomic burial information obtainable from the sequence could be sufficient for structural determination when combined to sequence-independent constraints. Accordingly, folding simulations using native burial information expressed by atomic central distances, discretized into a small number L of equiprobable burial layers, have indeed been successful in reaching and distinguishing the native structure of several globular proteins. Attempted predictions of layers from sequence, however, turned out to be insufficiently accurate for most proteins. Here we explore the possibility that a nonuniform assignment of layers, which is intended to account for constraints imposed by chain connectivity, might provide a more efficient burial encoding of tertiary structures. We consider the condition that adjacent Cα-atoms along the sequence cannot occupy nonadjacent layers, in which case the information required to specify sequences of burials would be smaller. It is shown that appropriate folding behavior can still be observed in this explicitly more constrained scenario with a structure-dependent assignment intended to produce the thinnest possible layers still compatible with the imposed burial constraint. This thinnest assignment turns out to be sufficiently restrictive for the observed examples and provides appropriately thinner layers or, equivalently, a larger number of layers, for examples previously observed to indeed require more restrictive constraints when compared to counterparts of similar size, as well as the appropriate increase in number of layers for larger proteins. Implications for the general understanding of the protein folding code are discussed.