PROTRACED COUNTERINSURGENCY: CHINESE COIN STRATEGY IN XINJIANG by MAJ J. Scott LaRonde, USA, 95 pages. In 1949, following the conclusion of its revolutionary war against the Chinese Nationalist forces, the People’s Liberation Army (PLA) peacefully occupied China’s western most province of Xinjiang. For nearly sixty years, the PLA has conducted a counterinsurgency against several, mostly Uyghur-led, separatist movements. Despite periods of significant violence, particularly in the early 1950s and again in the 1990s, the separatist forces have not gained momentum and remained at a level one insurgency. Mao ZeDeng is revered as a master insurgent and the father of Fourth Generation Warfare. Strategists in armies worldwide study his writings on revolutionary and guerilla warfare. This monograph concludes that Mao, as well as the communist leaders who followed him, was also successful at waging protracted counterinsurgency. For nearly sixty years, separatist movements in Xinjiang, Tibet, and Taiwan have all failed. This monograph analyzes the conflict in Xinjiang and concludes that the Chinese continue to defeat the separatist movement in Xinjiang through a strategy that counters Mao’s seven fundamentals of revolutionary warfare.

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Approved for Public Release; Distribution is Unlimited

In this paper, the concept of characteristic length introduced in the definition of the dynamic tortuosity by Johnson, Koplik, and Dashen [J. Fluid Mech. 176, 379 (1987)] is extended to express the frequency dependence of the bulk modulus of the saturating fluid at high frequencies. A general phenomenological frequency dependence for this dynamic bulk modulus is obtained using the expression for the dynamic tortuosity. The theoretical predictions for dynamic tortuosity and bulk modulus are compared with experimental results obtained from acoustic measurements on a rigid‐frame porous material saturated with air.

Dynamic tortuosity and bulk modulus in air‐saturated porous media

One major cause of elastic wave attenuation in heterogeneous porous media is wave-induced flow of the pore fluid between heterogeneities of various scales. It is believed that for frequencies below 1 kHz, the most important cause is the wave-induced flow between mesoscopic inhomogeneities, which are large compared with the typical individual pore size but small compared to the wavelength. Various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter-scale mesoscopic heterogeneities. Laboratory and field measurements of seismic attenuation in fluid-saturated rocks provide indications of the role of the wave-induced flow. Signatures of wave-induced flow include the frequency and saturation dependence of P-wave attenuation and its associated velocity dispersion, frequency-dependent shear-wave splitting, and attenuation anisotropy. During the last four decades, numerous models for attenuation and velocity dispersion from wave-induced flow have been developed with varying degrees of rigor and complexity. These models can be categorized roughly into three groups according to their underlying theoretical framework. The first group of models is based on Biot’s theory of poroelasticity. The second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation. Another group of models is derived using the theory of viscoelasticity. Though all models predict attenuation and velocity dispersion typical for a relaxation process, there exist differences that can be related to the type of disorder periodic, random, space dimension and to the way the local flow is incorporated. The differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies. In recent years, some theoretical models of wave-induced fluid flow have been validated numerically, using finite-difference, finite-element, and reflectivity algorithms applied to Biot’s equations of poroelasticity. Application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data.

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Seismic wave attenuation and dispersion resulting from wave-induced flow in porous rocks — A review

Measurements of dynamic compressibility of air-filled porous sound-absorbing materials are compared with predictions involving two parameters, the static thermal permeability k0′ and the thermal characteristic dimension Λ′. Emphasis on the notion of dynamic and static thermal permeability—the latter being a geometrical parameter equal to the inverse trapping constant of the solid frame—is apparently new. The static thermal permeability plays, in the description of the thermal exchanges between frame and saturating fluid, a role similar to the viscous permeability in the description of the viscous forces. Using both parameters, a simple model is constructed for the dynamic thermal permeability k′(ω), which is completely analogous to the Johnson et al. [J. Fluid Mech. 176, 379 (1987)] model of dynamic viscous permeability k(ω). The resultant modeling of dynamic compressibility provides predictions which are closer to the experimental results than the previously used simpler model where the compressibility i...

/pdf/dynamic-compressibility-of-air-in-porous-structures-at-2iyuu4x9mx.pdf

Dynamic compressibility of air in porous structures at audible frequencies

https://www.win.tue.nl/~sjoerdr/papers/boek.pdf

An introduction to acoustics

Preface to the second edition. 1 Plane waves in isotropic fluids and solids. 1.1 Introduction. 1.2 Notation - vector operators. 1.3 Strain in a deformable medium. 1.4 Stress in a deformable medium. 1.5 Stress-strain relations for an isotropic elastic medium. 1.6 Equations of motion. 1.7 Wave equation in a fluid. 1.8 Wave equations in an elastic solid. References. 2 Acoustic impedance at normal incidence of fluids. Substitution of a fluid layer for a porous layer. 2.1 Introduction. 2.2 Plane waves in unbounded fluids. 2.3 Main properties of impedance at normal incidence. 2.4 Reflection coefficient and absorption coefficient at normal incidence. 2.5 Fluids equivalent to porous materials: the laws of Delany and Bazley. 2.6 Examples. 2.7 The complex exponential representation. References. 3 Acoustic impedance at oblique incidence in fluids. Substitution of a fluid layer for a porous layer. 3.1 Introduction. 3.2 Inhomogeneous plane waves in isotropic fluids. 3.3 Reflection and refraction at oblique incidence. 3.4 Impedance at oblique incidence in isotropic fluids. 3.5 Reflection coefficient and absorption coefficient at oblique incidence. 3.6 Examples. 3.7 Plane waves in fluids equivalent to transversely isotropic porous media. 3.8 Impedance at oblique incidence at the surface of a fluid equivalent to an anisotropic porous material. 3.9 Example. References. 4 Sound propagation in cylindrical tubes and porous materials having cylindrical pores. 4.1 Introduction. 4.2 Viscosity effects. 4.3 Thermal effects. 4.4 Effective density and bulk modulus for cylindrical tubes having triangular, rectangular and hexagonal cross-sections. 4.5 High- and low-frequency approximation. 4.6 Evaluation of the effective density and the bulk modulus of the air in layers of porous materials with identical pores perpendicular to the surface. 4.7 The biot model for rigid framed materials. 4.8 Impedance of a layer with identical pores perpendicular to the surface. 4.9 Tortuosity and flow resistivity in a simple anisotropic material. 4.10 Impedance at normal incidence and sound propagation in oblique pores. Appendix 4.A Important expressions. Description on the microscopic scale. Effective density and bulk modulus. References. 5 Sound propagation in porous materials having a rigid frame. 5.1 Introduction. 5.2 Viscous and thermal dynamic and static permeability. 5.3 Classical tortuosity, characteristic dimensions, quasi-static tortuosity. 5.4 Models for the effective density and the bulk modulus of the saturating fluid. 5.5 Simpler models. 5.6 Prediction of the effective density and the bulk modulus of open cell foams and fibrous materials with the different models. 5.7 Fluid layer equivalent to a porous layer. 5.8 Summary of the semi-phenomenological models. 5.9 Homogenization. 5.10 Double porosity media. Appendix 5.A: Simplified calculation of the tortuosity for a porous material having pores made up of an alternating sequence of cylinders. Appendix 5.B: Calculation of the characteristic length LAMBDA'. Appendix 5.C: Calculation of the characteristic length LAMBDA for a cylinder perpendicular to the direction of propagation. References. 6 Biot theory of sound propagation in porous materials having an elastic frame. 6.1 Introduction. 6.2 Stress and strain in porous materials. 6.3 Inertial forces in the biot theory. 6.4 Wave equations. 6.5 The two compressional waves and the shear wave. 6.6 Prediction of surface impedance at normal incidence for a layer of porous material backed by an impervious rigid wall. Appendix 6.A: Other representations of the Biot theory. References. 7 Point source above rigid framed porous layers. 7.1 Introduction. 7.2 Sommerfeld representation of the monopole field over a plane reflecting surface. 7.3 The complex sin theta plane. 7.4 The method of steepest descent (passage path method). 7.5 Poles of the reflection coefficient. 7.6 The pole subtraction method. 7.7 Pole localization. 7.8 The modified version of the Chien and Soroka model. Appendix 7.A Evaluation of N. Appendix 7.B Evaluation of p r by the pole subtraction method. Appendix 7.C From the pole subtraction to the passage path: Locally reacting surface. References. 8 Porous frame excitation by point sources in air and by stress circular and line sources - modes of air saturated porous frames. 8.1 Introduction. 8.2 Prediction of the frame displacement. 8.3 Semi-infinite layer - Rayleigh wave. 8.4 Layer of finite thickness - modified Rayleigh wave. 8.5 Layer of finite thickness - modes and resonances. Appendix 8.A Coefficients r ij and M i,j. Appendix 8.B Double Fourier transform and Hankel transform. Appendix 8.B Appendix .C Rayleigh pole contribution. References. 9 Porous materials with perforated facings. 9.1 Introduction. 9.2 Inertial effect and flow resistance. 9.3 Impedance at normal incidence of a layered porous material covered by a perforated facing - Helmoltz resonator. 9.4 Impedance at oblique incidence of a layered porous material covered by a facing having cirular perforations. References. 10 Transversally isotropic poroelastic media. 10.1 Introduction. 10.2 Frame in vacuum. 10.3 Transversally isotropic poroelastic layer. 10.4 Waves with a given slowness component in the symmetry plane. 10.5 Sound source in air above a layer of finite thickness. 10.6 Mechanical excitation at the surface of the porous layer. 10.7 Symmetry axis different from the normal to the surface. 10.8 Rayleigh poles and Rayleigh waves. 10.9 Transfer matrix representation of transversally isotropic poroelastic media. Appendix 10.A: Coefficients T i in Equation (10.46). Appendix 10.B: Coefficients A i in Equation (10.97). References. 11 Modelling multilayered systems with porous materials using the transfer matrix method. 11.1 Introduction. 11.2 Transfer matrix method. 11.3 Matrix representation of classical media. 11.4 Coupling transfer matrices. 11.5 Assembling the global transfer matrix. 11.6 Calculation of the acoustic indicators. 11.7 Applications. Appendix 11.A The elements T ij of the Transfer Matrix T ]. References. 12 Extensions to the transfer matrix method. 12.1 Introduction. 12.2 Finite size correction for the transmission problem. 12.3 Finite size correction for the absorption problem. 12.4 Point load excitation. 12.5 Point source excitation. 12.6 Other applications. Appendix 12.A: An algorithm to evaluate the geometrical radiation impedance. References. 13 Finite element modelling of poroelastic materials. 13.1 Introduction. 13.2 Displacement based formulations. 13.3 The mixed displacement-pressure formulation. 13.4 Coupling conditions. 13.5 Other formulations in terms of mixed variables. 13.6 Numerical implementation. 13.7 Dissipated power within a porous medium. 13.8 Radiation conditions. 13.9 Examples. References. Index.

Propagation of Sound in Porous Media: Modeling Sound Absorbing Materials

Measurements of the acoustical properties of some porous road pavements are presented here and an acoustical method for monitoring the performance of these surfaces is presented. Porous road pavements have been used previously because of their driving qualities and drainage capacities during rainy days (i.e., the elimination of water splash and spray) but they have also been found to reduce traffic noise substantially. Reductions in A-weighted sound levels of 3–5 dB, compared to a dense pavement structure, have been measured. To study further their acoustical performance, measurements over real road surfaces have been carried out and the results compared to theoretical predictions based upon models describing the surface impedance and sound propagation. For the impedance characterization, both a phenomenological and a microstructural model were used. Both approaches introduce a viscous and a thermal dependence to account for the different phenomena inside the porous structure. By incorporating these models into the theoretical propagation predictions, it is possible to evaluate the impact of porous asphalt on highway noise levels. A nondestructive testing technique has been designed for determining in situ the noise reduction performance of porous road pavements.

Porous road pavements: Acoustical characterization and propagation effects

The computational tools available for prediction of sound propagation through the atmosphere have increased dramatically during the past decade. The numerical techniques include analytical solutions for selected index of refraction profiles, ray trace techniques which include interaction with a complex impedance boundary, a Gaussian beam ray trace algorithm, and more sophisticated approximate solutions to the full wave equation; the fast field program (FFP) and the parabolic equation (PE) solutions. This large aray of computational approaches raises questions concerning under what conditions the various approaches are reliable and concerns about possible errors in specific implementations. This paper presents comparisons of predictions from the several models assuming a complex impedance ground and four atmospheric conditions. For the cases studied, it was found that the FFP and PE algorithms agree to within numerical accuracy over the full range of conditions and agree with the analytical solutions where available. Comparisons to ray solutions define regimes where ray approaches can be used. There is no attempt to compare calculated transmission losses to measurements,

Benchmark cases for outdoor sound propagation models

An experimental system for the measurement of porosity, the volume fraction of air contained in a material, is described. Porosity is important as one of several parameters required by acoustical theory to characterize a porous material. As with the technique described by Beranek [J. Acoust. Soc. Am. 13, 248–260 (1942)], the isothermal pressure change in a closed volume containing a sample material is measured for a known change in the volume. The volume of air contained in the sample, and hence the porosity, is inferred from these two quantities. The new system, though, avoids the use of liquids, either directly in the technique or for temperature stabilization. Instead, a piston of accurately known diameter is used to produce the change in volume, and the change in pressure is measured with an electronic pressure transducer. Model calculations and measurements on real materials confirm that porosity can be measured rapidly and conveniently with this apparatus, with an accuracy of better than 1% over a broad range of sample volumes and porosities.

Air‐based system for the measurement of porosity

A measurement system has been developed that can determine flow resistances quickly and accurately and can be used to complement acoustical measurements on the same samples. The use of electronic components permits measurements to be made 20–50 times faster than with the commonly used Leonard apparatus. Variable‐capacitance pressure transducers are used to measure pressure differences across both the test sample and a laminar flow element with known flow resistance (these two in series): For steady nonpulsating flow, the ratio of flow resistances equals the ratio of measured pressure differences. The rate of air flow through the sample is adjusted using a mass flow controller; flows of 10−3–1 cm3 s−1 can be controlled to better than 1%. Flow resistances between 1 and 105 g cm−4 s−1 can be determined with an accuracy of better than 1.6%. The corresponding range of flow resistivities of porous materials that can be determined with the present sample holder is 1–106 cgs‐rayl cm−1. Initial measurements have b...

Gilles A. Daigle

Papers

Propagation of Sound in Porous Media: Modeling Sound Absorbing Materials

Porous road pavements: Acoustical characterization and propagation effects

Benchmark cases for outdoor sound propagation models

Air‐based system for the measurement of porosity

Electronic system for the measurement of flow resistance