Rigid Plate Research Articles

Sound attenuation performance at high sound pressure level of micro-perforated panel sound absorber with embedded resistive screen

In this paper, a composite sound absorber made of a micro-perforated panel (MPP), an air cavity with embedded resistive screen and a rigid back plate is investigated at high sound pressure level (SPL). The sound absorption coefficient predicted theoretically is compared with the experimental measurement at 150 dB and a good agreement is obtained. It is demonstrated that the incorporation of resistive screen within the air cavity improves significantly the sound absorption that presents a large frequency band and remains almost identical with respect to the SPL compared to a classical MPP absorber whose sound absorption peak varies with the SPL. The MPP absorber with the resistive screen glued on the MPP is studied and different resistive screens are compared at 150 dB and it is observed that the sound absorption coefficient increases with a large frequency band, which depends on the airflow resistivity of the screen. A sensitivity analysis shows that the resistance per unit area of the screen affects the acoustic properties of the absorber at low SPL while at high SPL, the acoustic properties are mainly controlled by the perforation ratio of the MPP and the acoustic orifice Mach number.

Vortex synchronization-enabled heat-transfer enhancement in a channel with backward- and forward-facing steps

A channel with one backward-facing step and one forward-facing step is a typical configuration in engineering applications. In the channel, good heat transfer performance is often required, and the enhancement is usually achieved by employing different passive control methods, such as modification of geometric configuration or application of nanofluid. However, the other control method, i.e., active flow control (AFC), which is likely more effective, has been rarely applied in such a scenario. This study aims to bridge this gap by exploring how a rigid plate affects the heat transfer of the channel. The plate either is stationary or actively rotates, corresponding to passive flow control or AFC. The influences of the horizontal position of the plate (S) and its orientation angle (θ) on the heat transfer performance are studied when the plate is stationary to provide a baseline. Compared to the baseline, the effects of S, θ, and the rotation frequency (fr) are revealed when the plate undergoes a sinusoidal rotation. Such a thermo-fluid dynamic problem is numerically simulated by the immersed-boundary lattice Boltzmann method. The results show that the plate can improve the heat transfer performance no matter whether it rotates or not, compared to the case without a plate. The rotating plate outperforms the stationary one when θ and fr are properly chosen at each S. Substantial improvement can be achieved when vortex synchronization or resonance occurs in the channel, i.e., when the natural vortex shedding frequency is close or equal to fr.

Optimizing non-Newtonian fluids for impact protection of laminates

Non-Newtonian fluids can be used for the protection of flexible laminates. Understanding the coupling between the flow of the protecting fluid and the deformation of the protected solids is necessary in order to optimize this functionality. We present a scaling analysis of the problem based on a single coupling variable, the effective width of a squeeze flow between flat rigid plates, and predict that impact protection for laminates is optimized by using shear-thinning, and not shear-thickening, fluids. The prediction is verified experimentally by measuring the velocity and pressure in impact experiments. Our scaling analysis should be generically applicable for non-Newtonian fluid-solid interactions in diverse applications.

Experimental study on the flow-induced vibrations of a circular cylinder with a rear flexibly hinged splitter plate

The flow around a circular cylinder is a canonical configuration that may be encountered in many engineering applications, as for instance, civil engineering, architecture, or marine structures. In particular, when bluff bodies are slender and feature low mass-damping characteristics, they may undergo flow-induced vibrations (FIVs), which may result in severe structural fatigue and damage. Here, we present an experimental study on the effect of flexibly hinged splitter plates in the FIV of a flexibly mounted circular cylinder (of diameter D) subject to an uniform cross-flow of velocity u∞. The dynamic response and forcing of the low mass-damping system is characterized for plates of different lengths Lp and different values of the torsional stiffness of the hinge kp. Reductions of the dynamic response of more than 90% can be generally reached at the upper branch, especially when a plate of length l*=Lp/D=2 with intermediate degree of torsional stiffness is attached, which is shown to represent the best solution as it mitigates the oscillations of the system (cylinder and plate) for the whole range investigated of reduced velocity U*=u∞/fnD=[3.9,9.8], where fn is the natural frequency of oscillation. In general, the hinged plates are able to attenuate the vortex-induced vibration system response by increasing shedding frequency, until the ratio f*=f/fn>1 is reached. At high values of U*, a general transition to galloping-like dynamics, characterized by f*<1, occurs. The tested hinged plates modify the transition between regimes, which is associated with shifts in the phase difference between the forcing and response, combining features of the dynamics of both flexible and static rigid plates already reported in the literature. The use of hinged plates has been proven to provide with a significant attenuation of the system response and its associated drag, a feature that can be considered of practical relevance in many engineering applications. In addition, the key aspects for designing these elements as the torsional stiffness and plate length have been analyzed here.

Flexible structures enhance fluid mixing in a channel flow

Early fluid mixing in channel flows without incurring much drop in the pressure head is desired in industrial applications. This study explores wall-mounted flexible plates as obstacles to enhance mixing in channel flows. Using fluid–structure-scalar interaction simulations, we investigate the oscillations of the flexible plates under the flow, which serve as a vortex generator and help increase the mixing. The channel flow involves a scalar field with distinct concentrations initially separated across the channel, gradually intermixing due to vortical structures of varying scales. We have used the “mixing index” and “head loss” metrics along the channel length to assess the mixing quality when plates with different flexibility (characterized by the Cauchy number, Ca) are used. This study introduces a comprehensive criterion, the “coefficient of performance,” derived by comparing mixing and head loss in the presence and absence of obstacles. Aggregating results across various Ca values reveal that flexible plates substantially improve fluid mixing compared to rigid plates. We have also investigated the effect of the pulsatile fluid inlet (quantified by Strouhal number, Stf) and found that lower inlet flow pulsation (Stf<32) adversely impacts mixing performance, recommending a steady inlet flow. However, at high Stf, specifically in the configuration with Ca = 0.06 and Stf = 32, the best mixing performance is achieved in the channel, which marginally outperforms the steady inlet case. The conclusive takeaways from this study are that the plates with increased flexibility result in better mixing, and high inlet pulsation can be employed to fine-tune the mixing performance for further enhancement.

Correlating mantle cooling with tectonic transitions on early Earth

Abstract The dominant tectonic mode operating on early Earth (before ca. 2.5 Ga) remains elusive, with an increasing body of evidence suggesting that non-plate tectonic modes were likely more prevalent at that time. Thus, how plate tectonics evolved after that remains contentious. We performed two-dimensional numerical modeling of mantle convection at temperatures appropriate for the Hadean–Archean eons and show that subduction and rift systems may have spontaneously emerged on Earth from an earlier drip-and-rift–dominated tectonic mode in response to the secular cooling of the mantle. This cooling of the mantle was mediated by repeated events of rifting and dripping that likely occurred over a few hundred million years. As the mantle cooled, its effective viscosity and the thickness and strength of the lithosphere increased, which helped establish rigid plates and initiate plate tectonics on Earth.

Constitutive models for confined elastomeric layers: Effects of nonlinearity and compressibility

Elastomers tend to undergo large deformations accompanied by small volumetric changes. For elastomeric layers sandwiched between rigid plates, large deformations can be significantly limited by the constraints imposed by the plates. Further, those constraints can be enhanced by material’s inability to undergo large volumetric changes. From this perspective, it is appropriate to examine the validity of constitutive models, in which an elastomer is treated as incompressible, for analysis of the confined layers. Here, this issue is addressed by considering the mechanical response of sandwiched elastomeric layers using three constitutive models. The first one, referred to as compressible neo-Hookean, is regarded as exact. The other two models are regarded as approximations. Of those two, the first one neglects nonlinearity and the second one neglects compressibility. Accordingly, the modeling errors associated with the former are treated as measures of importance of nonlinearity, and the modeling errors associated with the latter are treated as measures of importance of compressibility. The modeling errors are evaluated using the force–displacement curve and the mean stress at the layer center as the quantities of interest. Numerical results are presented for rubber and polydimethylsiloxane (PDMS), characterized by Poisson’s ratios ν=0.4999 and ν=0.49, respectively. It is shown that, even when the forces applied to the plates are large, considering nonlinearity is important for thick but not for thin layers. In contrast, considering compressibility is important for thin layers. The need for considering compressibility is further assessed by introducing a competition parameter, which reinforces the notion that compressibility is important for modeling PDMS layers and thin rubber layers.

An experimental investigation of the flow control of a circular cylinder in near wake with parallel plates at Re = 7500

The vortex street suppression in the near wake region of the cylinder with parallel plates was investigated using particle image velocimetry (PIV) at Reynolds number of Re = 7500. The rigid plates are designed as flat, parallel with the free-stream direction, and located on both sides of the cylinder. Two different plate lengths (0.5D and 1D based on the cylinder diameter, D) were examined at gap ratios of g/D = 0.1, 0.3, 0.5, 0.7, and 0.9, respectively. Proper Orthogonal Decomposition (POD) analyses were also employed to reveal vortex mechanism in the near wake region. The gap ratio significantly influences the interaction of the vortices. At low gap ratios, the plates directly affect the development of shear layers on both side of the cylinder. The shear layers elongate downstream with a reduction of the vortex shedding frequency. Moreover, Reynolds shear stress, vortex shedding instabilities and vortex street are suppressed in the near wake region with the help of using parallel plates. On the other hand, vortex shedding reinforces instabilities at higher gap ratios. Besides, the most effective gap ratio is different for each the plate lengths to suppress instabilities.

Analysis of a Wind-Driven Power Generation System with Root Slapping Mechanism

This study introduces a groundbreaking slap-type Vibration Energy Harvesting (VEH) system, leveraging a rotating shaft with magnets to induce vibrations in an adjacent elastic steel sheet through magnetic repulsion. This unique design causes the elastic sheet to vibrate, initiating the oscillation of a seesaw-type rigid plate lever. The lever then slaps a piezoelectric patch (PZT) at the elastic steel sheet’s root, converting vibrations into electrical energy. Notably, the design enables the PZT to withstand deformation and flapping forces simultaneously, enhancing power conversion efficiency. The driving force for the rotating shaft is harnessed from the downstream flow field generated by moving objects like rotorcraft, fixed-wing aircraft, motorcycles, and bicycles. Beyond conventional vibration energy harvesting, this design taps into additional electric energy generated by the PZT’s slapping force. This study includes mathematical modeling of nonlinear elastic beams, utilizing the Method of Multiple Scales (MOMS) for in-depth vibration mode analysis. Experimental validation ensures the convergence of theory and practice, confirming the feasibility and superior voltage generation efficiency of this slap-type VEH concept compared to traditional VEH systems.

Flow control using hot splitter plates in the wake of a circular cylinder: A hybrid strategy

A novel and effective hybrid technique, which involves active surface heating strategies in conjunction with the use of passive splitter plates in the wake of the cylinder, is proposed. In this report, we present the results of a numerical investigation on the two-dimensional, laminar mixed convection flow over a circular cylinder with a hot rigid splitter plate attached to it on the wake side. A projection algorithm-based finite volume method is employed to obtain the solution of the coupled, nonlinear governing partial differential equations subjected to Courant–Friedrichs–Lewy conditions. The isothermal heating of the splitter plate under the influence of the gravity field generates an upward buoyancy force in the wake of the cylinder. For different length-to-diameter (L/D) ratios, the effect of heating on aerodynamic, wake, and heat transfer characteristics has been studied for a wide range of parameters; 75 ≤Re≤ 150, 0 ≤Ri≤ 1, and 0.5 ≤L/D≤ 1 at Pr = 0.7. It is observed that the hot splitter plate would bring about conspicuous changes such as asymmetry in the vortex shedding behind the cylinder at low Reynolds numbers. The outcomes demonstrate a notable improvement in convective heat transfer and drag, with gains of up to 7% and 15%, respectively. It is found that the rate of heat transfer and vortex shedding frequency decrease with an increase in L/D ratio. Correlations for the estimation of Strouhal number and Nusselt number have also been proposed which helps provide a more thorough understanding of thermal and aerodynamic features of the hybrid approach.

Testing and Analysis of Frictional Performance of Carbon Fiber/Metal Composite Materials

In order to enhance the friction and wear performance of carbon fiber/steel composite structures, experiments were conducted to adjust the ratio of thermosetting epoxy resin and C12-C14 glycol ether. A modified liquid was developed that could fully fill the gaps in the carbon fiber and enhance the adhesion characteristics between the fiber surface and 18CrMnTiH round steel material. The effects of self-made modified epoxy adhesive and single-component epoxy adhesive on the mechanical properties of composite materials were compared using ISO814-86 determination of the bond strength of sulfur-cured rubber to metal—two-plate method and international standard ISO1747-1976 determination of the shear strength of sulfur-cured rubber bonded to rigid metal plates—four-plate shear method. The friction and wear performance test analyzed the friction coefficient of composite materials under different pretreatment times. The results showed that the pretreatment treatment effectively reduced the friction coefficient of carbon fiber and effectively extended the service life of the material. This study has certain reference significance for extending the friction and wear resistance performance of carbon fiber-reinforced relative motion metal parts.

Heat transport and flow structure in thermal convection with two liquid layers

We report an experimental investigation of the heat transport and flow field in a rectangular Rayleigh–Bénard convection (RBC) cell with two immiscible fluids: silicone oil and glycerol. The global heat transport of the system is divided into three ranges corresponding to the different flow structures formed in the glycerol layer. In range I, the glycerol layer is dominated by conduction, and no plume is formed over the interface. In range II, cellular rolls are formed in the glycerol layer and the horizontal motion of rolls causes an oscillation of temperature in the interface. In range III, the cellular pattern is time-independent, and the interface forms a group of wavelets with wave numbers consistent with the mode of the cellular pattern. In lower-thin glycerol, the Nusselt (Nu) grows from conduction to convection through an oscillating subcritical bifurcation at critical Rayleigh number $Ra_c$ . The value of $Ra_c$ in the present work is smaller than the theoretical prediction of both-rigid boundaries and greater than the prediction of one-rigid and one-free boundaries. In the upper-thick silicone oil layer, $Nu$ increases with increasing $Ra$ , but it is smaller than that of traditional RBC. For the silicone oil layer in two-layer RBC, the hot plumes emitting over the liquid–liquid interface showed different shape and different velocity from cold plumes emitting from the top rigid plate. This implies that the velocity boundary condition strongly influences the flow structure in turbulent convection.

Failure mechanisms of anisotropic pentamode-based bridge bearings: A dynamic analysis

Pentamodes are known for their almost zero shear modulus while providing high compression stiffness; a characteristic, which renders pentamodes suitable for application in seismic isolation. The current study focuses on bearings composed of alternating layers of pentamode crystals of an elastoplastic material with rigid steel plates. Pushover analyses are conducted, and plastic inges are gradually created. The failure mechanisms of the bearing are discussed and compared to those without stiffening plates. The influence of the directionality of an induced earthquake is also investigated. Since pentamode unit cells and pentamode modules are only symmetrical with respect to a vertical level, their structural response is anisotropic. Consequently, a bearing symmetric with respect to its diagonal is not expected to have an isotropic response. Depending on the formulation the ability to withstand the induced shear loading can be increased up to 30–50%. The cells, modules and bearings are proven to feature a weak direction defined by their lowest nodes, which specify how they are connected to the ground. It is proposed that a bearing composed of rotated instead of justified layers would be more isotropic. Positive and negative aspects of such a structure are discussed. The dynamic behavior of layered pentamode bearings is also discussed. Eigenfrequency and dynamic analyses of real-life bridge bearings under harmonic and real time histories showed that stiffening plates may improve a bearing’s response up to 115%.

Development of a Restraint System for Rear-Facing Car Seats

In self-driving vehicles, passengers can set their seats in an unconventional seating position, such as rear-facing. Sitting in such an orientation can increase the risk of whiplash in the head-and-neck system in a frontal impact, as frontal crashes usually have higher severities compared with rear-end crashes. This paper shows that a forward-facing front seat optimised for rear-impact protection needs to be redesigned to be used as a rear-facing seat. In the second and main part of this paper, a restraint system for rear-facing car seats is developed, and frontal impact simulations with 64 km/h of delta-V are used to evaluate its performance. The designed seating system comprises two rigid torso plates, a fixed recliner and an energy absorber under the seat pan. Without using the developed restraint system, the 50th percentile male human model is exposed to neck shear forces exceeding 600 N. With the developed restraint system, neck shear forces are less than 350 N in frontal impacts with 64 km/h of delta-V. Apart from whiplash, the risk of head, chest, lower extremity and lower back injuries are also evaluated. The results confirm that the developed restraint system successfully protects the occupant since all assessment criteria values are lower than the injury assessment reference values.

Vibration-control mechanism and damping performance of the eccentric connected structure-control system

Installing energy-dissipation devices in connected structures can greatly enhance their seismic performance. Currently, two-dimensional models are extensively studied, but they fail to fully capture the effects of eccentricities on the control efficiency of connected structures. To address this limitation, this study proposes a series-parallel rigid plate model that can simulate an eccentric connected structure-control system (ECSCS), enabling a comprehensive investigation. The study begins by deriving the equations of motion for the simplified model. It then analyzes the effects of energy-dissipation story (EDS) eccentricities, translational frequency ratio, and translational damping ratio on the torsional direction factor and torsional energy ratio at each mode frequency, specifically considering x-direction eccentricity. The subsequent exploration reveals the vibration-control mechanism and optimizes the EDS parameters using a multi-objective particle swarm optimization (MOPSO) algorithm. Additionally, the control effects for various eccentricity ratios are compared. The findings demonstrate that modifying the parameters of the EDS can effectively reduce translational-torsional coupling effects and torsional energy ratios in each substructure. While the addition of EDS may increase the top rotation acceleration and inter-story drift ratio in some cases, the peak values of other dynamic responses decrease. Moreover, adjusting the span of the EDS significantly increases the translational-torsional frequency ratio and enhances the torsional resistance of the structure. The study also emphasizes the importance of considering the impact of an asymmetric lower tower on the control effect of ECSCS. In most cases, lower towers with the same eccentricity demonstrate superior control due to the contribution of EDS.

Numerical simulations of Phan-Thien-Tanner viscoelastic fluid flows based on the SPH method

Numerical simulations of viscoelastic fluid flows are always a hot issue in the field of computational fluid dynamics and the study of their complex rheological properties has important academic and engineering application value. In the present work, we develop a smoothed particle hydrodynamics (SPH) method for simulating transient viscoelastic fluid flows governed by the Phan-Thien-Tanner (PTT) constitutive equation. To improve the computational accuracy of the SPH method, the mixed symmetric correction algorithm of kernel gradient is implemented. To remove the particle clustering and unphysical fracture in fluid stretching which is named as the tensile instability, the artificial stress model is added into the momentum equation. We firstly apply the proposed SPH method to solve the plane Poiseuille flow of a PTT viscoelastic fluid, in which the effectiveness and advantage of the method are verified by comparing the SPH solution with those obtained by the finite volume method (FVM) and analyzing the l2 norm error of different SPH solutions to the FVM solution. Then, the method is employed to simulate the impact behavior of a PTT viscoelastic droplet with a rigid plate. In particular, we not only investigate the spreading behavior of PTT viscoelastic droplet after impacting the rigid plate, but also for the first time capture and analyze the bouncing behavior of droplet by decreasing the Reynolds number. The influences of the Reynolds number, the Weissenberg number, the solvent viscosity ratio, and the PTT elongational parameter on the droplet dynamics behavior are further deeply studied. Numerical results demonstrate that the SPH method proposed in this paper is a powerful computation tool for simulating PTT viscoelastic fluid flows and is capable of effectively describing their complex rheological properties and free surface variation characteristics.

3D stack-up assembly tolerance analysis for sealing optimization of PEMFCs

As elastic rubber seals are in contact with rigid metal bipolar plates (BPPs), multi-layer stack seals are critical to PEMFC safety. The precision of rigid-flexible seals is significantly affected by assembly errors. To reveal the transformation mechanism from BPPs manufacturing tolerances to PEMFC sealing, this study adopted semi-analytical modeling and numerical simulation. A deviation transfer model with three parameters (deviation size |r→|, deviation direction φr, rotation angle θr) was constructed on the basis of manufacturing tolerances to evaluate BPPs deviation. Numerical simulations were further conducted to obtain rubber-metal contact status. The effect of varying deviations on leakage was also investigated. It is found that: 1) φr causes various sealing behaviors in various sealing zones; 2) θr slightly affects leakage rates; 3) |r→| is crucial for optimizing the BPPs tolerance. The proposed method investigates the effect of 3D stack-up assembly errors on sealing performance and provides a theoretical foundation for the tolerance design and optimization of PEMFCs.

Self-deployable hinges for monolithic space structures using multi-material additive manufacturing

Deployable structures inspired by origami have gained significant prominence in space applications, including solar arrays, reflector arrays, and satellite antennas. Traditionally, these structures consist of separate components that are folded during launch and later deployed in space using springs or actuator mechanisms. However, recent advancements in multi-material additive manufacturing have opened new possibilities for the fabrication of monolithic structures, integrating deployable mechanisms into a single entity. In this paper, we present a novel framework for designing unidirectional (UD) and bidirectional (BD) hinges utilizing viscoelastic materials, incorporated into rigid plates, forming deployable structures. These hinges exhibit the unique ability to store strain energy upon deformation and self-deploy to a flat configuration when released. The experimental results presented here demonstrate the effectiveness and feasibility of our hinge designs in real-world applications. To demonstrate the practical applicability of these hinge designs, we construct a Repeating Unit Cell (RUC) of a large origami-inspired deployable structure, showcasing their compatibility with popular deployable structure patterns.

The Effect of the Layout of a Rigid Splitter Plate on the Flow-Induced Vibration of a Downstream Cylinder Subjected to Wake Flow

In this study, the effect of additional positions of rigid splitter plates on the response characteristics of tandem cylinders at a Reynolds number of 150 and a fixed distance ratio of 5.0 was numerically investigated via the computational fluid dynamics (CFD) method. Four layouts for the cylinder–plate body, including a downstream cylinder (DC), a downstream cylinder–plate body with a wake side plate (DCP), a downstream plate–cylinder body with an incoming flow side plate (DPC), and a downstream plate–cylinder–plate body with a double-sided plate (DPCP), are considered. The results show that the splitter plate attached to the incoming flow side or the wake side can suppress the vibration of the downstream cylinder in a specific reduced velocity range (4.0 < Ur ≤ 10.0). Compared with the DC, the maximum response amplitude of the DPC and DCP in the lock-in region is reduced by 30.8% and 47.4%, and the lock-in bandwidth is also significantly narrower. The layer separation point of the upstream cylinder moves downstream upon adding splitter plates to both the incoming flow and wake sides, and the resulting splitter shear layer of the DPCP is completely parallel to the free flow, while the maximum response amplitude is reduced by 93.6%, which realizes the best effect of stream-induced vibration suppression.

Asymptotic analysis of thin linear elastic layers constrained by two rigid plates

Two asymptotic solutions are presented for linear elastic thin, not necessarily circular, cylindrical layers fully constrained by two rigid plates. Other than being small, the plate displacements and rotations are not restricted, and therefore, in general, a constrained layer is subjected to combined stretching, bending, shearing, and twisting. The first solution is restricted to layers formed by compressible solids, whose Poisson’s ratio is not too close to one half. This solution is a superposition of a polynomial displacement field, valid in the bulk of the layer, and a corrective displacement field, which decays exponentially fast away from the cylindrical surface and becomes negligible at distances comparable to the layer thickness. The second solution is not restricted in terms Poisson’s ratio but it is correct only to a leading order. This solution unifies leading-order solutions for layers formed by compressible, nearly incompressible, and incompressible solids. The unification involves a parameter characterizing the competition between compressibility and thinness.