Hard Wall Research Articles

Analysis of vibration and sound characteristics of fluid conveying pipeline considering the effect of acoustic-solid coupling

Objectives In order to accurately grasp the vibration and sound characteristics of pipelines, a numerical simulation is carried out. Methods Based on the theory of acoustic-solid coupling, a numerical model of a pipeline is established. The dispersion curve of the vibration and acoustic modes of the pipeline is solved by parametric scanning. The dispersion characteristics of the elastic wall pipeline with air, water and crude oil, as well as the absolute pressure stress distribution in the pipeline, are analyzed, and the effects of wall thickness, elastic wall and hard sound field wall on the dispersion characteristics of the pipeline are studied. Results The results show that wall thickness has little effect on the propagation mode of elastic waves in the pipeline, and the dispersion curve is shifted to high frequency with the increase in wall thickness, mainly influencing the cut-off frequency. Due to the effects of acoustic-solid coupling, the number of modes of the elastic pipeline increases, and the increased mode number is mainly the deformation mode of the pipeline wall. The absolute sound pressure distribution in the elastic wall is basically the same as that in the hard sound field wall. The dispersion characteristics of liquid or gas inside are different, while the dispersion characteristics of water or oil inside are similar, but the direct modes of the two are different. Conclusions The results of this study can provide a theoretical basis for the pipeline acoustic detection of ships.

Ergodic and nonergodic many-body dynamics in strongly nonlinear lattices.

The study of nonlinear oscillator chains in classical many-body dynamics has a storied history going back to the seminal work of Fermi etal. [Los Alamos Scientific Laboratory Report No. LA-1940, 1955 (unpublished)]. We introduce a family of such systems which consist of chains of N harmonically coupled particles with the nonlinearity introduced by confining the motion of each individual particle to a box or stadium with hard walls. The stadia are arranged on a one-dimensional lattice but they individually do not have to be one dimensional, thus permitting the introduction of chaos already at the lattice scale. For the most part we study the case where the motion is entirely one dimensional. We find that the system exhibits a mixed phase space for any finite value of N. Computations of Lyapunov spectra at randomly picked phase space locations and a direct comparison between Hamiltonian evolution and phase space averages indicate that the regular regions of phase space are not significant at large system sizes. While the continuum limit of our model is itself a singular limit of the integrable sinh Gordon theory, we do not see any evidence for the kind of nonergodicity famously seen in the work of Fermi etal. Finally, we examine the chain with particles confined to two-dimensional stadia where the individual stadium is already chaotic and find a much more chaotic phase space at small system sizes.

Performance enhancement of an automotive silencer using acoustic metamaterial baffles

The potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date acoustic metamaterials have not been experimentally tested in an automotive silencer for performance enhancement. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. These results are then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of the acoustic labyrinthine DENORMS cylinder proved to be the most significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. It was also found that the traditional hard wall internal baffle silencer performance can be improved by replacing it with a DENORMS internal baffle. Acoustic metamaterials have potential as a novel method for automotive companies to attenuate sound of specific frequencies.

Multiscale Approaches for Confined Ring Polymer Solutions.

We apply a hierarchy of multiscale modeling approaches to investigate the structure of ring polymer solutions under planar confinement. In particular, we employ both monomer-resolved (MR-DFT) and a coarse-grained (CG-DFT) density functional theories for fully flexible ring polymers, with the former based on a flexible tangent hard-sphere model and the latter based on an effective soft-colloid representation, to elucidate the ring polymer organization within slits of variable width in different concentration regimes. The predicted monomer and polymer center-of-mass densities in confinement, as well as the surface tension at the solution-wall interface, are compared to explicit molecular dynamics (MD) simulations. The approaches yield quantitative (MR-DFT) or semiquantitative (CG-DFT) agreement with MD. In addition, we provide a systematic comparison between confined linear and ring polymer solutions. When compared to their linear counterparts, the rings are found to feature a higher propensity to structure in confinement that translates into a distinct shape of the depletion potentials between two walls immersed into a polymer solution. The depletion potentials that we extract from CG-DFT and MR-DFT are in semiquantitative agreement with each other. Overall, we find consistency among all approaches as regards the shapes, trends, and qualitative characteristics of density profiles and depletion potentials induced on hard walls by linear and cyclic polymers.

Effects of domain walls in bilayer graphene in an external magnetic field

We investigate bilayer graphene systems with layer switching domain walls separating the two energetically equivalent Bernal stackings in the presence of an external magnetic field. To this end we calculate quantum transport and local densities of three microscopic models for a single domain wall: a hard wall, a defect due to shear, and a defect due to tension. The quantum transport calculations are performed with a recursive Green's function method. Technically, we discuss an explicit algorithm for the separation of a system into subsystems for the recursion and we present an optimization of the well known iteration scheme for lead self-energies for sparse chain couplings. We find strong physical differences for the three different types of domain walls in the integer quantum Hall regime. For a domain wall due to shearing of the upper graphene layer there is a plateau formation in the magnetoconductance for sufficiently wide defect regions. For wide domain walls due to tension in the upper graphene layer there is only an approximate plateau formation with fluctuations of the order of the elementary conuctance quantum $\sigma_0$. A direct transition between stacking regions like for the hard wall domain wall shows no plateau formation and is therefore not a good model for either of the previously mentioned extended domain walls.

Entropy-Driven Heterogeneous Crystallization of Hard-Sphere Chains under Unidimensional Confinement.

We investigate, through Monte Carlo simulations, the heterogeneous crystallization of linear chains of tangent hard spheres under confinement in one dimension. Confinement is realized through flat, impenetrable, and parallel walls. A wide range of systems is studied with respect to their average chain lengths (N = 12 to 100) and packing densities (φ = 0.50 to 0.61). The local structure is quantified through the Characteristic Crystallographic Element (CCE) norm descriptor. Here, we split the phenomenon into the bulk crystallization, far from the walls, and the projected surface crystallization in layers adjacent to the confining surfaces. Once a critical volume fraction is met, the chains show a phase transition, starting from regions near the hard walls. The established crystal morphologies consist of alternating hexagonal close-packed or face-centered cubic layers with a stacking direction perpendicular to the confining walls. Crystal layer perfection is observed with an increasing concentration. As in the case of the unconstrained phase transition of athermal polymers at high densities, crystal nucleation and growth compete with the formation of sites of a fivefold local symmetry. While surface crystallites show perfection with a predominantly triangular character, the morphologies of square crystals or of a mixed type are also formed. The simulation results show that the rate of perfection of the surface crystallization is not significantly faster than that of the bulk crystallization.

The Effect of Higher Dimensional QCD Operators on the Spectroscopy of Bottom-Up Holographic Models

Within the bottom-up holographic approach to QCD, the highly excited hadrons are identified with the bulk normal modes in the fifth “holographic” dimension. We show that additional states in the same mass range can appear also from taking into consideration the 5D fields dual to higher dimensional QCD operators. The possible effects of these operators have not been taken into account in virtually any phenomenological applications. Using the scalar case as the simplest example, we demonstrate that the additional higher dimensional operators lead to a large degeneracy of highly excited states in the soft wall holographic model, and in the hard wall holographic model, they result in a proliferation of excited states. The considered model can be viewed as the first analytical toy model predicting a one-to-one mapping of the excited meson states to definite QCD operators, to which they prefer to couple.

Functional packaging of seeds.

SummaryThe encapsulation of seeds in hard coats and fruit walls (pericarp layers) fulfils protective and dispersal functions in many plant families. In angiosperms, packaging structures possess a remarkable range of different morphologies and functionalities, as illustrated by thermo and hygro‐responsive seed pods and appendages, as well as mechanically strong and water‐impermeable shells. Key to these different functionalities are characteristic structural arrangements and chemical modifications of the underlying sclerenchymatous tissues. Although many ecological aspects of hard seed encapsulation have been well documented, a detailed understanding of the relationship between tissue structure and function only recently started to emerge, especially in the context of environmentally driven fruit opening and seed dispersal (responsive encapsulations) and the outstanding durability of some seed coats and indehiscent fruits (static encapsulations). In this review, we focus on the tissue properties of these two systems, with particular consideration of water interactions, mechanical resistance, and force generation. Common principles, as well as unique adaptations, are discussed in different plant species. Understanding how plants integrate a broad range of functions and properties for seed protection during storage and dispersal plays a central role for seed conservation, population dynamics, and plant‐based material developments.

Shannon information entropy sum of the confined hydrogenic atom under the influence of an electric field

In this work, we present the effects of an external electric field on the Shannon entropy sum of a spherically confined hydrogenic atom. The confinement considered is of the impenetrable hard wall type. The electric field modifies the spectrum of the confined hydrogenic system, which results in avoided crossings among the energy levels of the system, with strong competition between the Coulombic and hard wall potential. The results presented indicate that the electric field is a strong candidate to modify information theoretic measures. In addition, we examine the effects of field strength, nuclear charge and hard walls on the minima/maxima structure of the entropic sum. Shannon entropy sum, $$S_t$$ , versus confinement radius, $$R_c$$ , of the 2p level of confined hydrogenic atoms, with field strength $$\epsilon = 0$$ (black), $$\epsilon = 0.001$$ (red), $$\epsilon = 0.01$$ (green) and $$\epsilon = 0.05$$ (blue). The intensity of the field modifies the structure in $$S_t$$ .

Anisotropy-independent packing of confined hard ellipses

We have examined the close-packed structure and ordering properties of hard ellipses between two parallel hard walls by using geometrical conjectures and Monte Carlo simulations. Starting from closely packed hard disk structures, we discover two competing densest packings of ellipses with the stretching of hard disks into different directions. We find that parallel and tilted close-packed structures alternate with widening pore width up to the two-dimensional bulk limit, where both structures produce the same close packing value (η=π/12). Our results highlight that the densest packing does not depend on the aspect ratio of the ellipse. This universal behavior is confirmed for three different aspect ratios (κ=2, 3, and 4) using replica exchange Monte Carlo simulation. Our simulation results show that even the global phase diagram is universal, where layering transitions between parallel structures and tilted-parallel structural changes are present.

Experimental validation and uncertainty quantification in wave-based computational room acoustics

It is well known that input data uncertainty has a major influence on the correctness of room acoustic simulations. This paper proposes a comprehensive framework for experimental validation and uncertainty quantification in room acoustic simulations. The sources of uncertainty in room acoustic simulations are many, but especially the boundary conditions present significant uncertainty. The input data uncertainty is propagated through the simulation model, which in this work is a wave-based time-domain discontinuous Galerkin finite element method (DGFEM) simulation scheme, and is then presented as a ‘probability box’ (p-box), expressing both aleatory and epistemic input data uncertainties and model form uncertainties. The p-box can then be compared against the perceptual limits of the human auditory system to gauge the severity of the uncertainty. The framework is applied on a small room with an absorbing wall for the experimental validation of the simulation results and the uncertainty quantification of three boundary parameters: the flow resistivity of the porous absorber, the thickness of the porous absorber, and the absorption characteristics of the remaining hard walls. It is found that the input data uncertainty and the model form uncertainty are too high for the model to be able to predict several room acoustic parameters within just noticeable thresholds.

Constrained non-crossing Brownian motions, fermions and the Ferrari–Spohn distribution

A conditioned stochastic process can display a very different behavior from the unconditioned process. In particular, a conditioned process can exhibit non-Gaussian fluctuations even if the unconditioned process is Gaussian. In this work, we revisit the Ferrari–Spohn model of a Brownian bridge conditioned to avoid a moving wall, which pushes the system into a large-deviation regime. We extend this model to an arbitrary number N of non-crossing Brownian bridges. We obtain the joint distribution of the distances of the Brownian particles from the wall at an intermediate time in the form of the determinant of an N × N matrix whose entries are given in terms of the Airy function. We show that this distribution coincides with that of the positions of N spinless noninteracting fermions trapped by a linear potential with a hard wall. We then explore the N ≫ 1 behavior of the system. For simplicity we focus on the case where the wall’s position is given by a semicircle as a function of time, but we expect our results to be valid for any concave wall function.

Wall slip and bulk yielding in soft particle suspensions

We simulate a dense athermal suspension of soft particles sheared between hard walls of a prescribed roughness profile, using a method that fully accounts for the fluid mechanics of the solvent between the particles, and between the particles and the walls, as well as for the solid mechanics of changes in the particle shapes. We thus capture the widely observed phenomenon of elastohydrodynamic wall slip, in which the soft particles become deformed in shear and lift away from the wall slightly, leaving behind a thin lubricating solvent layer of high shear. For imposed stresses below the material's bulk yield stress, we show the observed wall slip to be dominated by this thin solvent layer. At higher stresses, it is augmented by an additional contribution arising from a fluidisation of the first few layers of particles near the wall. By systematically varying the roughness of the walls, we quantify a suppression of slip with increasing wall roughness. For smooth walls, slip radically changes the steady state bulk flow curve of shear stress as a function of shear rate, by conferring a branch of apparent (slip-induced) flow even for $\sigma<\sigma_y$, as seen experimentally. We also elucidate the effects of slip on the dynamics of yielding following the imposition of a constant shear stress, characterising the timescales at which bulk yielding arises, and at which slip first sets in.

A 2D Optimal Path Planning Algorithm for Autonomous Underwater Vehicle Driving in Unknown Underwater Canyons

This research aims to solve the safe navigation problem of autonomous underwater vehicles (AUVs) in deep ocean, which is a complex and changeable environment with various mountains. When an AUV reaches the deep sea navigation, it encounters many underwater canyons, and the hard valley walls threaten its safety seriously. To solve the problem on the safe driving of AUV in underwater canyons and address the potential of AUV autonomous obstacle avoidance in uncertain environments, an improved AUV path planning algorithm based on the deep deterministic policy gradient (DDPG) algorithm is proposed in this work. This method refers to an end-to-end path planning algorithm that optimizes the strategy directly. It takes sensor information as input and driving speed and yaw angle as outputs. The path planning algorithm can reach the predetermined target point while avoiding large-scale static obstacles, such as valley walls in the simulated underwater canyon environment, as well as sudden small-scale dynamic obstacles, such as marine life and other vehicles. In addition, this research aims at the multi-objective structure of the obstacle avoidance of path planning, modularized reward function design, and combined artificial potential field method to set continuous rewards. This research also proposes a new algorithm called deep SumTree-deterministic policy gradient algorithm (SumTree-DDPG), which improves the random storage and extraction strategy of DDPG algorithm experience samples. According to the importance of the experience samples, the samples are classified and stored in combination with the SumTree structure, high-quality samples are extracted continuously, and SumTree-DDPG algorithm finally improves the speed of the convergence model. Finally, this research uses Python language to write an underwater canyon simulation environment and builds a deep reinforcement learning simulation platform on a high-performance computer to conduct simulation learning training for AUV. Data simulation verified that the proposed path planning method can guide the under-actuated underwater robot to navigate to the target without colliding with any obstacles. In comparison with the DDPG algorithm, the stability, training’s total reward, and robustness of the improved Sumtree-DDPG algorithm planner in this study are better.

Nonlocal Hydrodynamic Models for the Optical Response of Plasmonic Nanostructures

In order to model the interaction between light and plasmonic structures at deep-nanometer scale, which is governed by non-classical effects, a nonlocal hydrodynamic approach has been extensively studied. Several hydrodynamic models have been proposed, solving the coupled equations: the linearized hydrodynamic equation of motion and the electrodynamic Maxwell’s equations, by employing additional boundary conditions. This work compares four hydrodynamic models: the hard wall hydrodynamic model (HW-HDM), the curl-free hydrodynamic model (CF-HDM), the shear forces hydrodynamic model (SF-HDM), and the quantum hydrodynamic model (Q-HDM). The analysis is conducted for a metallic spherical nanoparticle, as an example. The above hydrodynamic models are also compared with experiments available in literature. It is demonstrated that HW-HDM and QHDM outperform the other two hydrodynamic models.

Strong gravity effects of charged Q-clouds and inflating black holes

In this paper, we re-examine charged Q-clouds around spherically symmetric, static black holes. In particular, we demonstrate that for fixed coupling constants two different branches of charged scalar clouds exist around Schwarzschild black holes. This had not been noticed previously. We find that the new solutions possess a ‛hard wall’ at maximal possible gauge coupling. This wall separates the interior (containing the black hole horizon), in which the scalar field is trapped in the ‛false vacuum’, from the ‛true vacuum’ exterior. When taking back-reaction onto the space-time into account, we find that at maximal possible back-reaction, the black hole solutions corresponding to these two branches either become extremal black holes with diverging scalar field derivative on the horizon or inflating black holes with a second, ‛cosmological’ horizon which—outside this second horizon—correspond to extremal Reissner–Nordström black holes.

Configuration entropy and confinement/deconfinement transiton in holographic QCD

In the holographic AdS/QCD approach, the confinement/deconfinement transition is associated with the Hawking-Page transition of a thermal anti-de Sitter (AdS) space to an AdS black hole. In the case of the hard wall model, the thermal transition takes place in the planar AdS thanks to the introduction of an infrared cut-off in the geometry. The corresponding thermodynamic entropy of the SU(N) gauge theory jumps from proportional to N0 in the confined hadronic phase to proportional to N2 in the plasma phase, corresponding to the presence of the color degrees of freedom. The Hawking-Page transition is understood by considering a semiclassical picture of a system consisting of two different geometries that are asymptotically AdS. One is the AdS black hole and the other the thermal AdS space. The relative stability between these competing geometries varies with the temperature. So, the transition is essentially a problem of stability. An interesting tool to study stability of physical systems is the configuration entropy (CE), inspired in the Shannon informational entropy. In this work we investigate the CE for the case of the AdS/QCD hard wall model at finite temperature. We propose a regularized form for the energy densities of the black hole (BH) and of the thermal AdS geometries that makes it possible to calculate their CEs as a function of the temperature. We find a relation between stability and the value of the CE for the system of asymptotically AdS geometries. Remarkably, it is found that the CE is proportional to log⁡(T), where T is the temperature. This result makes it possible to write out a simple relation between the configuration and the thermodynamic entropies.

Hydrothermal formation of iron-oxyhydroxide chimney mounds in a shallow semi-enclosed bay at Satsuma Iwo-Jima Island, Kagoshima, Japan

Abstract Hydrothermal iron-oxyhydroxide chimney mounds (iron mounds) have been discovered in a fishing port in Nagahama Bay, located on the southwest coast of Satsuma Iwo-Jima Island, south of Kyushu Island, Japan. In the fishing port, uncovered ∼1.0-m-high iron mounds in shallow waters formed under relatively calm conditions. Typically, the fishing port has orange-colored turbid waters that mix with outer ocean waters during high tide. Colloidal iron-oxyhydroxides form due to the oxidation of ferrous iron in hydrothermal waters (pH = 5.5; temperature = 55 °C) as they mix with seawater. The mounds are made of two types of material: hard, dark brown–orange, high-density material; and soft, brownish orange–yellow, low-density material. Computed tomography scans of the harder iron mound material revealed a cabbage-like structure consisting of micropipe structures with diameters of 2–5 mm. These micropipes have relatively hard walls made of iron oxyhydroxides (FeOH) and are identified as discharge pipes. Nucleic acid staining genetic sequencing and scanning electron microscope observations suggest that the mounds formed mainly from bacterial stalks with high concentrations of FeOH colloidal matter. In the harder parts of the mounds, these “fat stalks,” which contain oxyhydroxide colloidal aggregates, are entwined and concentrated. The softer material contains twisted stalk-like structures, which are coated with FeOH colloidal particles. Deoxyribonucleic acid (DNA) examination of the iron mounds revealed the presence of iron-oxidizing bacteria, especially at the mound surface. We estimate that the iron mounds accumulated at a rate of ∼1700 tons/1000 m2/yr. This is an order of magnitude higher than the rate of FeOH sedimentation via chemical precipitation of FeOH colloids within the fishing port. This suggests that biogenic activity, resulting in the production of entwined FeOH stalks, leads to the rapid accumulation of FeOH beds and that biogenic activity within the water mass rich in FeOH colloids is an efficient means of generating thick iron-rich sedimentary sequences. As such, we propose that some ancient iron formations may have also formed through the biogenic production of FeOH stalks rather than solely through chemical sedimentation in a water mass rich in FeOH colloids. It appears that these rapidly forming biogenic FeOH iron mounds, distributed over a wide area of ocean floor, are also relatively protected from erosion and diagenetic alteration (reduction). Previous studies have reported that ancient iron formations were commonly deposited in deeper environments via direct iron oxidation from the water column in a ferruginous ocean. However, there are several hydrothermal vent inflows preserved with FeOH that would have formed appropriate redox boundary conditions in an otherwise anoxic ocean. Under these conditions, iron mound mat-type sedimentary deposits might have formed and been well preserved and affected by early diagenesis where higher heat flow occurred in the Archean ocean. The FeOH mounds in Nagahama Bay provide an example of the iron formation sedimentary environment and important information for estimating the past depositional state of iron formations.

Improved multimodal formulation of the wave propagation in a 3D waveguide with varying cross-section and curvature.

An efficient method is proposed to solve the multimodal wave propagation within a three-dimensional waveguide bounded by a hard wall with varying cross section and curvature. This is achieved by first turning the original problem, in a complex-shaped waveguide, into a cylindrical waveguide with unit radius, by means of an adapted and flexible geometrical transformation. Then supplementary modes are defined to enrich the standard modal basis that is usually considered in such methods and to help restore the right boundary condition. It is shown through various numerical applications that the introduction of these supplementary modes, whatever the complexity of the waveguide geometry, significantly enhances the multimodal method, notably by increasing its convergence rate, whether one's aim is to solve the wavefield or the scattering problem.

Acoustic radiation force and torque on spheroidal particles in an ideal cylindrical chamber.

In this article, the acoustic radiation force and torque exerted on a small spheroidal particle immersed in a nonviscous fluid inside an ideal cylindrical chamber is theoretically investigated. The ideal chamber comprises a hard top and bottom (rigid boundary condition) and a soft or hard lateral wall. By assuming that the particle is much smaller than the acoustic wavelength, analytical expressions of the radiation force and torque caused by an acoustic wave of arbitrary shape are presented. Unlike previous results, these expressions are given relative to a fixed laboratory frame. The model is showcased for analyzing the behavior of an elongated metallic microspheroid (with a 10:1 aspect ratio) in a half-wavelength acoustofluidic chamber with a diameter of a few millimeters. The results show that the radiation torque aligns the microspheroid along the nodal plane, and the radiation force causes a translational motion with a speed of up to one body length per second. Finally, the implications of this study on propelled nanorods by ultrasound are discussed.