Search Results (199)

Polyethylene (PE) pipes are extensively used in gas- and water-distribution systems because of their corrosion resistance, toughness, and installation flexibility. However, the field reliability of PE pipeline systems often depends on the quality of butt fusion joints, whose integrity is highly sensitive to welding parameters and thermal history. Among process-induced defects, cold welding and over-welding are particularly critical because they are usually concealed, difficult to identify by visual inspection or short-term pressure testing, and strongly associated with long-term brittle failure. Existing reviews have discussed butt fusion joining or polymer non-destructive testing in a broad sense, yet a defect-oriented synthesis linking process deviation, interfacial evolution, material degradation, and microwave response remains limited. This review therefore focuses specifically on cold welding and over-welding as the two most safety-critical hidden defects in PE butt fusion joints. First, the paper summarises how insufficient heat input, poor wetting, and limited molecular-chain interdiffusion lead to weak interfacial healing and low effective entanglement density, whereas excessive heat input and unfavourable thermal history promote chain scission, thermo-oxidative degradation, abnormal recrystallisation, and microvoid formation. It then compares how these mechanisms influence tensile behaviour, slow crack growth resistance, and long-term service performance. On this basis, conventional radiography and ultrasonics, phased-array ultrasonics, nonlinear acoustics, and microwave non-destructive testing (MNDT) are critically compared. Particular emphasis is placed on the structure–property–signal pathway that links local perturbations in complex permittivity to changes in microwave scattering parameters, including |S11|, |S21|, phase drift, resonance shift, and quality-factor reduction. Finally, a hierarchical evaluation framework is proposed to connect microwave features with defect severity and engineering decisions, and the major barriers to wider engineering adoption—benchmark datasets, quantitative inversion, lift-off robustness, and standardisation—are discussed. By organising the field around a mechanism-based structure–property–signal framework, this review aims to provide a more rigorous basis for defect-oriented quality control and future intelligent inspection of PE butt fusion joints. Full article

Atypical bottom-simulating reflector (BSR)-like responses in structurally complex gas-hydrate provinces are difficult to interpret using morphology alone. This review develops a literature-constrained, physics-guided framework that organizes such responses in the northern South China Sea along three descriptive axes—continuity, geometry/deformation, and multiplicity—retaining six commonly reported end-member expressions as non-mutually exclusive working types. Published observations from the Shenhu area and the Qiongdongnan Basin are examined using a first-order thermo-seismic workflow comprising hydrate phase-equilibrium modeling, acoustic-impedance analysis, and convolutional synthetic seismic modeling. Over the reported GMGS3 drilling-water-depth range and measured geothermal gradients, the model predicts BSR depths of approximately 146–308 mbsf, overlapping the reported 230–400 mbsf interval. At W19, the observed BSR falls within this envelope; at SH-W07-2016, inverse calculations match the shallower interface with a measured-range gradient, while the deeper one requires cooler conditions. An illustrative impedance calculation yields a hydrate-to-gas reflection coefficient of approximately −0.25, consistent with the negative polarity of typical BSRs. The framework supports the interpretation of ambiguous BSR-like responses by testing their physical admissibility, identifying competing geological explanations that a single morphology cannot exclude, and indicating what further seismic or drilling evidence would be needed to discriminate among them; it does not validate morphology–mechanism assignments. Full article

Architectural acoustics and vibration engineering are rapidly evolving through advances in computational modeling, adaptive systems, intelligent sensing, and material design. Current research increasingly integrates acoustic quality and vibration control with structural resilience, occupant well-being, sustainability, and building performance. However, challenges remain in measurement reliability, multifunctional acoustic materials, multidisciplinary design, and real-time monitoring and control. This Special Issue, “Advances in Architectural Acoustics and Vibration”, comprises ten contributions covering room-acoustic measurement, tunable sound absorption, structural vibration control, thermo-acoustic design, bridge monitoring, heritage acoustics, and sustainable and engineered sound-absorbing materials. This editorial synthesizes these advances, identifies key knowledge gaps, and discusses future research directions, with emphasis on adaptive acoustic systems, bio-based materials, multiphysics optimization, artificial intelligence, digital twins, and data-driven structural health monitoring. Full article

In this work, the content of recycled polyethylene (rPE) and pigment (Cp), the antioxidant content (CAO) and ratio (RAO), and the peak internal air temperature (PIAT) of the rotational-molding cycle were optimized. Their combined influence on the mechanical, thermal, acoustic, and surface properties of the composites was studied by the probabilistic–deterministic planning method, which reduced the number of experiments from 3125 to 25. Internal stresses were monitored non-destructively through the third-harmonic amplitude (β) of the ultrasonic signal (mirror-shadow method), supported by mechanical testing, thermogravimetric analysis, infrared spectroscopy, and porosity characterization; weather resistance was assessed by accelerated ultraviolet (UV)-B aging for 333 and 666 h, treated as conditional 5- and 10-year service horizons for Northern Kazakhstan rather than as a literal calendar equivalence. The third-harmonic β was shown to be a sensitive correlational marker of internal stresses (R = 0.81 for the mean failure energy (MFE), Fisher-criterion validated), correlating with the elastic modulus, the impact strength, and the environmental stress cracking resistance (ESCR), and tracking the transition between incomplete (ICS), normal (NS), and thermo-oxidative degradation (TDS) sintering; the correlational nature of this evidence is discussed. For products without UV exposure, the optimal formulation (rPE = 25%, PIAT ≈ 200 °C, Cp = 0.1–0.2%, CAO = 0.25–0.5%, RAO = 0.5–1.0) gave a minimum β (0.076–0.09), MFE ≈ 2.6 J/mm, and 2.5–3% porosity; for sun-exposed products, rPE = 25%, Cp = 0.5%, CAO = 0.5–0.75%, and RAO = 1.0 are recommended. An rPE content of up to 50% did not significantly impair thermal stability or surface hydrophobicity, and a nomogram CAO = f(β,rPE) was developed for rapid formulation selection and quality control. Full article

Difficult-to-machine materials, including titanium alloys, nickel-based superalloys, hardened and high-strength steels, stainless steels, and fiber-reinforced composites, are widely used in advanced manufacturing but impose severe thermo-mechanical–chemical loads on cutting tools, resulting in progressive wear and degradation, localized damage, and, in severe cases, catastrophic failure. This review summarizes recent advances in tool condition monitoring and prognostics following the framework of material characteristics–tool deterioration mechanisms–condition sensing–predictive modeling–manufacturing decision making. The relationships between material properties and tool condition deterioration are first discussed, distinguishing progressive wear mechanisms, such as abrasion, adhesion, diffusion, and oxidation, from thermally induced degradation and localized damage phenomena such as cracking, coating delamination, and edge chipping. Direct tool measurement and indirect process-response monitoring based on force and torque, vibration and acoustic signals, thermal signals, and machine-tool electrical signals are then reviewed, while machining-quality characteristics are treated separately as machining-outcome-based condition indicators. Multisource information fusion is further discussed for integrating complementary tool condition information from these different sources. Tool condition assessment and prognosis are further examined in terms of wear estimation, tool-condition state identification, remaining useful life prediction, and catastrophic-failure risk prediction. Physics-based, data-driven, and hybrid models are compared with respect to accuracy, interpretability, uncertainty, and generalization. Finally, industrial deployment through online inference, edge-cloud collaboration, CNC integration, and digital-twin-supported closed-loop tool health management is discussed, together with key challenges in limited-data learning, cross-condition generalization, multimodal fusion, uncertainty quantification, standardized evaluation, and sustainable manufacturing. Full article

Indoor environmental comfort is essential in performing arts spaces due to its influence on both audience engagement and performers’ experience during live events. This paper primarily investigates the acoustic response of the Goldoni Theatre, with an additional assessment of its thermo-hygrometric and lighting conditions across audience areas. Acoustic measurements were conducted under unoccupied conditions to evaluate the sound field in accordance with standard requirements. The results indicate favourable listening conditions for both music and speech. Complementary surveys were carried out during the summer season to assess thermal comfort while the HVAC system was not in operation, as well as illuminance levels. The findings show that air temperature falls within the optimal comfort range when unconditioned, fluctuating between 24.6 °C and 26.2 °C, whereas illuminance levels remain below the recommended lower limit, specifically between 156 and 190 lux. Overall, this study provides an acoustically focused evaluation of the theatre in Bagnacavallo, complemented by an assessment of its thermal and lighting conditions, which reflects the candlelight practices as typical of similar historical opera houses. Full article

The transition to a low-carbon energy paradigm requires reducing nitrogen oxide NO_x and carbon monoxide CO emissions to 5–9 ppm. This study investigates the impact of the primary zone excess air ratio α and mixing quality on pollutant yields, addressing the “seesaw” trade-off mechanism between NO_x and products of incomplete combustion. Analysis of Lean Premixed and Micromix technologies demonstrates that achieving NO_x levels below 5 ppm requires local α fluctuations to remain within a root-mean-square deviation of 3–4%. An original burner design with an intelligent emission control system is presented, enabling dynamic adjustment of local αin to maintain combustion within a narrow stability window. Experimental results confirm that minimum toxicity, with NO_x concentrations below 20 ppm, is achieved at α_in = 1.7–1.8. The implementation of this technology ensures stable operation across transient and part-load regimes while mitigating thermal NO_x formation and thermoacoustic instabilities. Full article

Wood and wood-based materials represent low-carbon sustainable alternatives to petroleum sound absorbers, yet their baseline sound absorption coefficient varies drastically with wood species, anatomical cutting orientation and pore connectivity due to strong structural anisotropy. This review systematically integrates multiscale structural regulation, porous acoustic theories and data-driven optimization into a unified framework, revealing that broadband high sound absorption relies on the synergistic coordination of impedance matching, thermo-viscous dissipation and low-frequency resonant mechanisms, rather than simply maximizing porosity. We quantitatively compare state-of-the-art wood absorbers: directionally frozen wood aerogels achieve near-perfect absorption (α = 0.95–1.00, NRC = 0.82) across 520–6300 Hz, marking the current performance benchmark, while multifunctional superhydrophobic wood aerogels deliver moderate absorption (α ≈ 0.40) but stand out as all-biomass weather-resistant composites. Rigid-frame JCA/JCAL and poroelastic Biot models are clarified for wood’s distinct stiffness characteristics, and existing data-driven approaches are categorized, highlighting that most neural surrogates rely solely on FEM simulation without physical impedance-tube validation. Critical unresolved challenges including poor moisture/fire durability, insufficient industrial scalability and incomplete material databases are summarized, and targeted research priorities covering gradient manufacturing, hybrid physics–machine learning models and lifecycle environmental evaluation are proposed. Full article

This study quantitatively investigates the coupled effects of curing temperature and slurry density on the early-age acoustic maturation of ultra-low-density Hollow Glass Microsphere (HGM)-modified oil well cement systems, addressing the critical challenge of determining reliable sonic logging timing under lightweight cementing conditions. Longitudinal wave velocity evolution was systematically characterized across a broad thermo–density domain, revealing a consistent three-stage acoustic trajectory comprising percolation-driven acceleration, transition-controlled consolidation, and acoustic stabilization. The results demonstrate that curing temperature primarily regulates the kinetic rate of acoustic maturation through hydration activation, whereas slurry density modulates the initial structural configuration, HGM-induced acoustic impedance heterogeneity, and development of effective solid connectivity. A derivative-based dual-criterion approach was proposed to define the optimal sonic logging time based on intrinsic acoustic stabilization behavior rather than conventional empirical strength-based thresholds. Furthermore, a thermo–density coupled semi-empirical model incorporating Arrhenius-type thermal activation and density-dependent structural effects was developed, providing reliable prediction of sonic logging timing with clear physical interpretability. The model captures the nonlinear interaction between thermal activation and structural constraints, revealing that acoustic maturation is accelerated under elevated-temperature and higher-density conditions but substantially delayed under low-temperature and ultra-low-density scenarios. This study establishes a physics-informed temperature–density–acoustic coupling framework that links hydration-controlled structural evolution with sonic logging optimization, providing a rational basis for improving cement bond evaluation reliability and operational efficiency under challenging wellbore conditions. Full article

A persistent concentration of scale-critical quantities is widely regarded as a necessary precursor to finite-time singularity formation in the three-dimensional incompressible Navier–Stokes equations. This paper develops a conditional structural closure framework for excluding a dynamically sustained persistent concentration within an admissible low-Mach realizable class. A localized amplitude-modulation decomposition of High–High transfer activity is introduced together with a localized Littlewood–Paley bridge linking transfer-amplitude concentration to mechanical concentration. A concentration-representation principle and a low-Mach inheritance mechanism then show that a persistent mechanical concentration necessarily generates a nontrivial thermo-acoustic trace. A central result is a localized structural necessity principle establishing that a persistent concentration necessarily generates a localized transfer-amplitude concentration. Combining the localized Littlewood–Paley bridge, the concentration-representation mechanism, the low-Mach inheritance principle, and a thermo-acoustic ε-regularity framework, we show that the resulting thermo-acoustic concentration scenario is excluded within the admissible low-Mach realizable class. Consequently, a dynamically sustained persistent concentration cannot occur in this class. The result is a conditional structural closure theorem: it excludes a persistent concentration only within the admissible low-Mach realizable class and does not constitute an unconditional regularity theorem for arbitrary solutions of the three-dimensional incompressible Navier–Stokes equations. The sole non-universal assumption is admissible low-Mach realizability, which is shown to follow whenever an admissible entropy-coercive, weakly compressible approximation exists. The principal remaining open problem is the universality of admissible low-Mach realizability. Full article

Accurate monitoring of temperature variations in fluid flow through porous media is important for numerous geophysical, environmental, and chemical processes. Traditional temperature measurement techniques often suffer from limitations such as invasiveness, restricted spatial coverage, or limited capability for real-time subsurface sensing. Thermoacoustic (TA) methods provide a promising alternative by combining electromagnetic excitation with acoustic detection to enable non-contact subsurface monitoring. In this work, thermoacoustic measurements were conducted over a temperature range of 20–60 °C using a water-saturated sand porous medium, and a multiphysics simulation framework incorporating rock physics models, temperature-dependent material properties, acoustic dispersion, and attenuation calibration was developed to reproduce the experimental observations. A clear relationship between temperature and TA signal amplitude was observed, and strong agreement was achieved between the experimentally measured and simulated thermoacoustic responses after applying the proposed calibration procedures. The results demonstrate the feasibility of using thermoacoustic signals to monitor bulk temperature variations in porous media and establish a foundation for future development of spatially resolved thermoacoustic temperature imaging methods. Full article

Non-contact ultrasonic three-dimensional (3D) printing has emerged as a promising alternative to conventional energy-curing manufacturing techniques. However, an insufficient understanding of its underlying curing mechanisms still limits the precise regulation of solidification behavior and stable structural forming. In this context, this work develops a customized ultrasonic printing platform to investigate the thermoacoustic curing behavior of a modified PDMS-based material system. A multiphysics numerical model is established to characterize the focal acoustic pressure, concentrated energy distribution, and transient temperature evolution during printing. Simulated and experimental results collectively indicate that solidification behavior is governed by the balance between localized acoustic energy confinement and thermal diffusion. Systematic experiments are further conducted to quantify the effects of driving power, scanning speed, and line spacing on forming quality. The optimized parameter combination (17.5 W driving power, 0.4 mm/s scanning speed, and 0.2–0.25 mm line spacing) enables stable single-track morphology and favorable interlayer bonding. Additionally, reciprocating scanning trajectories are found to promote localized thermal accumulation, which may introduce dimensional deviations in printed structures. This study provides insights into ultrasonic thermoacoustic curing behavior and offers feasible process guidance for ultrasonic additive manufacturing under the specific material and experimental configurations adopted in this work. Full article

This study proposes a novel approach for performance improvement of an acoustic energy harvester integrated with a flexible polyvinylidene fluoride-based piezoelectric nanogenerator by exploiting the thermoacoustic effect. A prototype of the acoustic energy harvester was first designed and constructed. The influence of the temperature difference across the thermoacoustic stack on the acoustic pressure and open-circuit voltage amplitudes was then experimentally examined. Subsequently, the effects of excitation frequency and driving voltage on the performance of the acoustic energy harvester were systematically analyzed. The results demonstrate that the thermoacoustic effect can be effectively employed to enhance acoustic oscillations and, consequently, improve the electrical output. As the excitation frequency changes, the acoustic oscillations inside the acoustic energy harvester and the open-circuit voltage of the piezoelectric nanogenerator can be either amplified or suppressed depending on the frequency range. In addition, optimal driving voltages exist at which the amplification of acoustic pressure and open-circuit voltage is maximized. Specifically, at an excitation frequency of 85 Hz, a driving voltage of 3.5 V, and a stack temperature difference of 101.5 °C, a maximum pressure amplification factor of 3.73 and a maximum voltage amplification factor of 1.15 are obtained. This study successfully demonstrates the feasibility of utilizing the thermoacoustic effect to amplify acoustic oscillations within a resonator, offering a new pathway for enhancing the performance of acoustic energy harvesters and expanding the application potential of thermoacoustic technology. Full article

In modern precision manufacturing systems, multilayer metal structures are key to achieving high-performance devices. However, during actual processing, they are highly prone to interlayer thermal stress concentration and defects such as interface delamination. To thoroughly elucidate and address this stress evolution issue, this study proposes a two-temperature model based on thermomechanical coupling. A thorough analysis of the thermal–mechanical coupling behavior of copper/aluminum two-layer metal films under femtosecond laser irradiation was conducted, investigating non-equilibrium heat transfer within the two-layer material and the resulting stress evolution. The results indicate that stress waves dynamically modulate the temperature distribution, revealing the critical role of thermo-mechanical coupling in energy transfer. Further studies show that stress waves undergo reflection and transmission at material interfaces, with their phases influenced by the acoustic impedance of the materials. When stress waves propagate from a medium with high acoustic impedance to one with low acoustic impedance, the phase of the transmitted wave remains unchanged, while the phase of the reflected wave reverses. Stress unloading occurs during the phase transition; tensile stress at the interface due to reflection can induce delamination, while horizontal stress tends to initiate cracks. This work contributes to the analysis of stress evolution during laser processing of multilayer metals. Full article

This paper studies the continuation problem for the three-dimensional compressible Navier–Stokes–Fourier system inside an admissible thermo-acoustic regime under periodic boundary conditions. The analysis considers strong solutions in the Sobolev class $H^s\left(\mathrm{\Omega }\right)$, $s>$ 5/2, with positive density and temperature and strict subsonic evolution. Using dyadic Fourier–triadic decomposition together with localized Littlewood–Paley analysis, the nonlinear transfer structure is decomposed into perturbative interaction classes and coherent same-scale High–High interactions. Within the present framework, coherent same-scale High–High persistence is identified as the only currently identified potentially nonperturbative concentration mechanism. A transport–acoustic alternative structure is then derived connecting persistent transport concentration with nonvanishing pressure response. The resulting pressure response is decomposed into thermodynamic and acoustic branches. The transonic acoustic branch is shown to be incompatible with the strict subsonic admissible class. The remaining interaction structure is controlled through entropy-driven thermodynamic dissipation and localized thermo-acoustic regularization. The exclusion of dynamically sustained critical thermo-acoustic concentration yields a localized ε-regularity framework combining thermodynamic dissipation, Campanato decay, and interior parabolic regularization. The resulting estimates provide localized Lipschitz control sufficient for the continuation of admissible strong solutions within the same thermo-acoustic class. The framework further remains compatible with weak–strong stability and irreversible long-time thermodynamic relaxation through the relative entropy structure and free-energy dissipation. Full article