Research on the Generation Mechanism and Suppression Method of Aerodynamic Noise in Expansion Cavity Based on Hybrid Method

The expansion chamber serves as the primary silencing structure within the exhaust pipeline.However,it can also act as a sound-emitting structure when subjected to airflow.This article presents a hybrid method for numerically simulating and analyzing the unsteady flow and aerodynamic noise in an expansion chamber under the influence of airflow.A fluid simulation model is established,utilizing the Large Eddy Simulation(LES)method to calculate the unsteady flow within the expansion chamber.The simulation results effectively capture the development and changes of the unsteady flow and vorticity inside the cavity,exhibiting a high level of consistency with experimental observations.To calculate the aerodynamic noise sources within the cavity,the flow field results are integrated using the method of integral interpolation and inserted into the acoustic grid.The acoustic analogy method is then employed to determine the aerodynamic noise sources.An acoustic simulation model is established,and the flow noise source is imported into the sound field grid to calculate the sound pressure at the far-field response point.The calculated sound pressure levels and resonance frequencies show good agreement with the experimental results.To address the issue of airflow regeneration noise within the cavity,perforated tubes are selected as a means of noise suppression.An experimental platformfor airflow regeneration noise is constructed,and experimental samples are processed to analyze and verify the noise suppression effect of perforated tube expansion cavities under different airflow velocities.The research findings indicate that the perforated tube expansion cavity can effectively suppress low-frequency aerodynamic noise within the cavity by impeding the formation of strong shear layers.Moreover,the semi-perforated tube expansion cavity demonstrates the most effective suppression of aerodynamic noise.

Dynamic Spherical Cavity Expansion in Concrete *L

Aim To determine the stress on wall of the spherical cavity while the spherical cavity expanding in concrete. Methods In Eulerian coordinate, the dimensionless radial stress equations were derived for the spherically symmetric, cavity expansion problem in plastic and elastic region of concrete by means of the similarity transformation. In the equations, Mohr Coulomb yield criterion was used.Results The dimensionless radial stress profiles were obtained. The relation between the dimensionless radial stress and the locked volumetric strain was analysed.Conclusion The test results show that the relative error between the model, which is applied in the closed form penetration equations that are developed, and the test data is less than 15.8%.

Semi-analytical solution for drained expansion analysis of a hollow cylinder of critical state soils

The expansion of a thick-walled hollow cylinder in soil is of non-self-similar nature that the stress/deformation paths are not the same for different soil material points.As a result,this problem cannot be solved by the common self-similar-based similarity techniques.This paper proposes a novel,exact solution for rigorous drained expansion analysis of a hollow cylinder of critical state soils.Considering stress-dependent elastic moduli of soils,new analytical stress and displacement solutions for the nonself-similar problem are developed taking the small strain assumption in the elastic zone.In the plastic zone,the cavity expansion response is formulated into a set of first-order partial differential equations(PDEs)with the combination use of Eulerian and Lagrangian descriptions,and a novel solution algorithm is developed to efficiently solve this complex boundary value problem.The solution is presented in a general form and thus can be useful for a wide range of soils.With the new solution,the non-self-similar nature induced by the finite outer boundary is clearly demonstrated and highlighted,which is found to be greatly different to the behaviour of cavity expansion in infinite soil mass.The present solution may serve as a benchmark for verifying the performance of advanced numerical techniques with critical state soil models and be used to capture the finite boundary effect for pressuremeter tests in small-sized calibration chambers.

A spherical cavity expansion model for penetration of ogival-nosed projectiles into concrete targets with shear-dilatancy

A dynamic spherical cavity-expansion penetration model is suggested herein to predict the penetration and perforation of concrete targets struck normally by ogivalnosed projectiles.Shear dilatancy as well as compressibility of the material in comminuted region are considered in the paper by introducing a dilatant-kinematic relation.A procedure is first presented to compute the radial stress at the cavity surface and then a numerical method is used to calculate the results of penetration and perforation with friction being taken into account.The influences of various target parameters such as shear strength,bulk modulus,density,Poisson＇s ratio and tensile strength on the depth of penetration are delineated.It is shown that the model predictions are in good agreement with available experimental data.It is also shown that the shear strength plays a dominant role in the target resistance to penetration.

ANALYTICAL SOLUTIONS TO EXPANSION OF CYLINDRICAL CAVITY IN LINEAR SOFTENING SOIL

Based on the results of conventional triaxial compression tests for a soil, a trilinear elasto-plastic model is proposed to simulate the stress-strain softening curve. According to this curve, the constitutive relation between the bulk strain and two principal strains is established. By using Mohr-Coulomb’s yield criterion as the initial yield function with plastic ?ow phases stage and constructing the rational yield function for the strain softening phase stage, the analytical solutions to the stress, strain, and displacement ?elds for the expansion of cylindrical cavity are presented. Finally, a computational example is used to show the radii of di?erent stress zones and the corresponding internal pressure.

Influence of particle contact models on soil response of poorly graded sand during cavity expansion in discrete element simulation

The discrete element method(DEM) has been extensively adopted to investigate many complex geotechnical related problems due to its capability to incorporate the discontinuous nature of granular materials. In particular, when simulating large deformations or distortion of soil(e.g. cavity expansion),DEM can be very effective as other numerical solutions may experience convergence problems. Cavity expansion theory has widespread applications in geotechnical engineering, particularly to the problems concerning in situ testing, pile installation and so forth. In addition, the behaviour of geomaterials in a macro-level is utterly determined by microscopic properties, highlighting the importance of contact models. Despite the fact that there are numerous contact models proposed to mimic the realistic behaviour of granular materials, there are lack of studies on the effects of these contact models on the soil response.Hence, in this study, a series of three-dimensional numerical simulations with different contact constitutive models was conducted to simulate the response of sandy soils during cylindrical cavity expansion. In this numerical investigation, three contact models, i.e. linear contact model, rolling resistance contact model,and Hertz contact model, are considered. It should be noted that the former two models are linear based models, providing linearly elastic and frictional plasticity behaviours, whereas the latter one consists of nonlinear formulation based on an approximation of the theory of Mindlin and Deresiewicz. To examine the effects of these contact models, several cylindrical cavities were created and expanded gradually from an initial radius of 0.055 m to a final radius of 0.1 m. The numerical predictions confirm that the calibrated contact models produced similar results regarding the variations of cavity pressure, radial stress, deviatoric stress, volumetric strain, as well as the soil radial displacement. However, the linear contact model may result in inaccurate predictions when highly angular soil particles are involved. In addition, considering the excessive soil displacement induced by the pile installation(i.e. cavity expansion), a minimum distance of11 a(a is the cavity radius) is recommend for practicing engineers to avoid the potential damages to the existing piles and adjacent structures.

Analytical solutions for finite cylindrical dynamic cavity expansion in compressible elastic-plastic materials

Analytical solutions for the dynamic cylindrical cavity expansion in a com-pressible elastic-plastic cylinder with a finite radius are developed by taking into account of the effect of lateral free boundary, which are different from the traditional cavity expan-sion models for targets with infinite dimensions. The finite cylindrical cavity expansion process begins with an elastic-plastic stage followed by a plastic stage. The elastic-plastic stage ends and the plastic stage starts when the plastic wave front reaches the lateral free boundary. Approximate solutions of radial stress on cavity wall are derived by using the Von-Mise yield criterion and Forrestal’s similarity transformation method. The effects of the lateral free boundary and finite radius on the radial stress on the cavity wall are discussed, and comparisons are also conducted with the finite cylindrical cavity expansion in incompressible elastic-plastic materials. Numerical results show that the lateral free boundary has significant influence on the cavity expansion process and the radial stress on the cavity wall of metal cylinder with a finite radius.

Energy dissipation of cavity expansion based on generalized non-linear failure criterion under high stresses

Based on the compression mechanism for analyzing the cavity expansion problem in soil under high stresses,generalized non-linear failure criterion and large strain and energy conservation in plastic region during the cavity expanding were adopted.The energy conservation equation was established and the limited pressure of cavity expansion under high stresses was given based on the energy dissipation analysis method,in which the energy generated from cavity expansion is absorbed by the volume change and shear strain caused in soil.The factors of large strain and dilatation were considered by the proposed method.The analysis shows that the limited pressure is determined by failure criterion,stress state,large deformation characteristic,dilatation and strength of soil.It is shown from the comparison that the results with the proposed method approximate to those of the in-situ method.The cavity expansion pressure first decreases and then increases nonlinearly with both of shear modulus and dilatation increasing.

Severe plastic deformation of commercially pure aluminum using novel equal channel angular expansion extrusion with spherical cavity

Equal channel angular expansion extrusion with spherical cavity(ECAEE-SC)was introduced as a novel severe plastic deformation(SPD)technique,which is capable of imposing large plastic strain and intrinsic back-pressure on the processed billet.The plastic deformation behaviors of commercially pure aluminum during ECAEE-SC process were investigated using finite element analysis DEFORM-3D simulation software.The material flow,the load history,the distribution of effective strain and mean stress in the billet were analyzed in comparison with conventional equal channel angular extrusion(ECAE)process.In addition,single-pass ECAEE-SC was experimentally conducted on commercially pure aluminum at room temperature for validation,and the evolution of microstructure and microhardness of as-processed material was discussed.It was shown that during the process,the material is in the ideal hydrostatic stress state and the load requirement for ECAEE-SC is much more than that for ECAE.After a single-pass ECAEE-SC,an average strain of 3.51 was accumulated in the billet with homogeneous distribution.Moreover,the microstructure was significantly refined and composed of equiaxed ultrafine grains with sub-micron size.Considerable improvement in the average microhardness of aluminum was also found,which was homogenized and increased from HV 36.61 to HV 70.20,denoting 91.75%improvement compared with that of the as-cast billet.

Expansion of spherical cavity of strain-softening materials with different elastic moduli of tension and compression

An expansion theory of spherical cavities in strain-softening materials with different moduli of tension and com-pression was presented. For geomaterials,two controlling parameters were introduced to take into account the different moduli and strain-softening properties. By means of elastic theory with different moduli and stress-softening models,general solutions cal-culating Tresca and Mohr-Coulomb materials' stress and displacement fields of expansion of spherical cavity were derived. The effects caused by different elastic moduli in tensile and compression and strain-softening rates on stress and displacement fields and development of plastic zone of expansion of cavity were analyzed. The results show that the ultimate expansion pressure,stress and displacement fields and development of plastic zone vary with the different elastic moduli and strain-softening prop-erties. If classical elastic theory is adopted and strain-softening properties are neglected,rather large errors may be the result.

An undrained expansion solution of cylindrical cavity in SANICLAY for K_(0)-consolidated clays

This paper proposes a rigorous undrained solution for cylindrical cavity expansion problems in K_(0)-consolidated clays,adopting a simple non-associated and anisotropic model,SANICLAY.The cavity expansion theory is well extended to consider non-associativity,K_(0)-consolidation and stress-induced anisotropy with combined rotational and distortional hardening of yield surface and plastic potential in the multiaxial stress space.The developed solution can be recovered for validation against the modified Cam-clay(MCC)solution by simply setting model constants,avoiding non-associativity and anisotropy.The source code is provided to facilitate the use for extensions.After investigating the effects of overconsolidation ratio on the cavity pressure curves,stress distributions,evolutions of anisotropic parameters and stress paths,the variations with three-dimensional(3D)evolutions of yield surface and plastic potential during undrained cavity expansion are shown for various K_(0)-consolidated clays.A parametric study on the model constants is presented to depict the influences on the stress distributions and paths,critical state surfaces and Lode’s angles at failure.The proposed solution also provides a general framework for formulating equations for undrained expansion of cylindrical cavities under an initial cross anisotropic condition using sophisticated anisotropic soil models.It serves as a precise benchmark for extensions of analytical solutions,numerical simulations of cavity expansion,and backcalculations of geotechnical problems.

Static solution on four-region spherial cavity expansion model in a pressure sensitive medium

Spherical cavity expansion model is often used to study the mechanic characteristics of pressure sensitive mediums. The most important one we do in the paper is that we construct a four-region model with σθ≠0 in damage region,which is different from what Satapathy did before and is more reasonable. By adopting this model,different constitutive equations were constructed by different method-elastic mechanics in elastic region,damage mechanics and fracture mechanics in damage region,and macro-micro mechanics theory in plastic region. Then using Durban's self-similarity assumption,the control differential equations with boundary conditions were established,and the static numerical solution of stress field and displacement field in the three different regions of elastic,damage and plastic area were discussed respectively. Results showed that this four-region model can describe precisely the mechanic characteristics of pressure sensitive mediums under initial pressure.

Undrained semi-analytical solution for cylindrical cavity expansion in anisotropic soils under biaxial stress conditions

This paper presents an undrained semi-analytical elastoplastic solution for cylindrical cavity expansion in anisotropic soil under the biaxial stress conditions.The advanced simplified SANICLAY model is used to simulate the elastoplastic behavior of soil.The cavity expansion is treated as an initial value problem and solved as a system of eight first-order ordinary differential equations including four stress components and four anisotropic parameters.The results are validated by comparing the new solutions with existing ones.The distributions of stress components and anisotropic parameters around the cavity wall,the expansion process,the stress yield trajectory of a soil element and the shape and size of elastoplastic boundary are further investigated to explore the cavity expansion response of soils under biaxial in situ stresses.The results of extensive parameters analysis demonstrate that the circumferential position of the soil element and the anisotropy of the soils have noticeable impacts on the expansion response under biaxial in situ stresses.Since the present solution not only considers the anisotropy and anisotropy evolution of natural soil,but also eliminates the conventional assumption of uniform radial pressure,the solution is better than other theoretical solutions to explain the pressure test and pile installation effect of shallow saturated soil.

Anti-plane (SH) waves diffraction by an underground semi-circular cavity:analytical solution

Diffraction of a two-dimensional （2D） semi-circular cavity in a half-space under incident SH-waves is studied using the classic wave function expansion method with a new de-coupling technique. This so-called ＂improved cosine half- range expansion＂ algorithm exhibits an excellent performance in reducing displacement residual errors at two rim points of concern. The governing equations are developed in a manner that minimizes the residues of the boundary conditions. Detailed derivation and analysis procedures as well as truncation of infinite linear governing equations are presented. The semi-circular cavity model presented in this paper, due to its simple profile, is expected to be used in seismic wave propagation studies as a benchmark for examining the accuracies of various analytical or numerical methods for mixed-boundary wave propagation problems.

Diffraction of plane SH waves by a semi-circular cavity in half-space

This paper presents a closed-form solution for diffraction of plane SH waves by a semi-circular cavity in half-space by using wave function expansion method. Accuracy of the solution is checked by the displacement residual and stress residual along the boundaries. Numerical results show that there are notable differences for response amplitudes between a semi-circular cavity and a whole-circular cavity in a half-space.

Complete eigenmode analysis of a ladder-type multiple-gap resonant cavity

A theoretical model is developed for calculating the eigenmodes of the multi-gap resonant cavity. The structure of concern is a kind of ladder-type circuit, offering the advantages of easy fabrication, high characteristic impedance （R/Q）, and thermal capacity in the millimeter wave to THz regime. The eigenfunction expansion method is used to establish the field expressions for the gaps and the coupling region. Then, the match conditions at the interface are employed, which leads to a group of complicate boundary equations in the form of an infinite series. To facilitate the mathematical treatments and perform a highly efficient calculation, these boundary equations are transformed into the algebraic forms through the matrix representations. Finally, the concise dispersion equation is obtained. The roots of the dispersion equation include both the axial modes in the gaps, which include the fundamental and the high-order modes, and the cavity modes in the coupling region. Extensive numerical results are presented and the behaviors of the multi-gap resonant cavity are examined.

砂土中能量桩单桩水平承载特性模型试验研究

为探究能量桩单桩水平承载特性,针对砂土中能量桩在水平荷载下的承载特性进行研究,基于模型试验,分析了水平荷载作用下能量桩在制冷和加热过程中的桩顶位移、桩前土压力以及桩身弯矩等的变化规律。研究结果表明:制冷会引起能量桩桩顶水平位移略微增大,增量为0.48%D(D为桩体直径),而加热会引起较大的桩顶水平位移,达到了2.38%D;制冷和加热在初始阶段会引起桩前土压力增大,初始增长阶段结束后,土压力变化较小,多为缓慢增长或基本不变。相较于初始土压力,制冷和加热结束时的土压力基本呈增长趋势,仅个别埋深处土压力减小。制冷过程中,埋深0%L~40%L(L为有效桩长)范围内的弯矩增大,埋深40%L~100%L位置处的弯矩变化较小;加热过程中,埋深0%L~60%L范围内的弯矩均有所增大,0%L~40%L位置处的弯矩增大最为明显。制冷和加热过程中均在20%L处产生了最大弯矩,最大弯矩的增加量分别为9.93%和10.32%。进一步基于圆孔扩张理论提出了弯矩计算的理论解,并与试验结果进行对比分析,理论计算值与实测值较为吻合。

鼻腔扩容术联合腭咽成形术治疗伴鼻塞症状阻塞性睡眠呼吸暂停低通气综合征的疗效

目的:探讨鼻腔扩容术联合腭咽成形术治疗伴鼻塞症状阻塞性睡眠呼吸暂停低通气综合征(OSAHS)的疗效。方法:选取80例伴鼻塞症状OSAHS患者为研究对象,根据手术方式不同分为对照组和观察组,每组各40例。对照组患者实施单纯腭咽成形术治疗;观察组患者实施鼻腔扩容术联合腭咽成形术治疗,术后随访6个月。比较两组患者临床疗效、鼻腔通气功能[鼻腔阻力、鼾声指数及鼻呼吸总量]、睡眠呼吸指标[呼吸暂停低通气指数(AHI)、最低动脉血氧饱和度(LSaO_(2))、血氧饱和度(SpO_(2))、深睡眠比例及觉醒指数、Epwoeth嗜睡量表(ESS)评分]及生活质量[魁北克睡眠问卷(QSQ)评分]。结果:观察组患者临床总有效率高于对照组(92.50%vs.75.00%,P<0.05)。治疗后6个月,两组患者鼻腔阻力、鼾声指数、AHI、觉醒指数及ESS评分均降低(P<0.05),且观察组低于对照组(P<0.05);鼻呼吸总量、LSaO_(2)、SpO_(2)、深睡眠比例、QSQ各维度评分及总分均升高(P<0.05),且观察组高于对照组(P<0.05)。结论:鼻腔扩容术联合腭咽成形术是一种治疗伴鼻塞症状OSAHS的有效方式,可改善患者鼻腔通气功能及睡眠呼吸参数,提升生活质量。

一种考虑球体变形的钨球侵彻低碳钢深度计算模型

为了研究钨球在高速撞击下的变形行为对侵彻效果的影响,对钨球侵彻半无限低碳钢靶进行试验研究,得到<1600 m/s冲击速度下钨球变形特征和靶板侵彻深度随冲击速度的变化规律。在此基础上构建钨球侵彻塑性变形模型。将钨球变形模型和球形空腔膨胀阻力模型相结合,建立钨球变形侵彻深度计算模型。对比不同撞击速度下钨球变形侵彻模型、刚性侵彻模型的计算结果。对比结果表明,变形侵彻模型能够更加准确地计算钨球对半无限靶的侵彻深度,计算结果与试验相比最大误差20%(正误差15%,负误差5%),精度较刚性侵彻模型提升42.86%。

小孔扩张理论在原位测试中的应用研究进展

小孔扩张理论在原位测试理论分析方面具有显著的适用性和重要性。本文主要总结和阐述了小孔扩张理论在原位测试领域如静力触探(cone penetration test,CPT)、孔压静力触探(piezocone penetration test,CPTU)、旁压试验(pressuremeter test,PMT)等近年来的相关研究成果,具体包括锥贯阻力、孔隙水压力和基于CPT/PMT法的桩基承载力预测,以及相关土性参数(强度参数,如不排水抗剪强度、内摩擦角;状态参数,如超固结比与相对密度等)解译方面的应用。最后结合室内及现场试验的应用实例分析,对基于孔扩张理论在原位测试应用中所存在的局限性和不足作了相应的总结,并指出该理论未来还需进一步完善。