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核磁共振测井仪探头的优化设计能够增强仪器的探测特性,提高仪器的信噪比, 而探头设计中的数值方法对设计结果至关重要.本文利用电磁场有限元方法对贴井壁型核磁共振测井仪探头静磁场和射频场进行了2D和3D的数值模拟,深入分析了数值模型形状、模型尺寸、 单元形状对数值模拟结果的影响,并将有限元数值模拟结果与实测数据做了对比. 结果显示:数值模拟结果与实测数据符合.在设计核磁共振测井仪探头结构时, 选取与井眼形状一致的圆形模型,模型尺寸范围在10—15倍探头外径, 并采用三角形单元可以有效提高数值模拟方法精度,增强优化设计结果的可靠性. 相似文献
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基于SPH方法的瞬态粘弹性流体的数值模拟 总被引:2,自引:1,他引:1
运用SPH(Smoothed Particle Hydrodynamics)方法模拟基于Oldroyd-B模型的平面突然起动Couette流,通过数值解与解析解的比较,验证SPH方法模拟瞬态粘弹性流动的准确性;且对基于Oldroyd-B模型的方腔驱动流进行SPH模拟.采用一种新的固壁边界处理方法,有效地防止了粒子穿透,提高数值计算的准确性.用数值算例验证SPH方法对粘弹性流体模拟的有效性和稳定性. 相似文献
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从层流动能出发提出数值模拟原则;综合考虑自然、旁路和分离流转捩的因素构建实用的层流动能湍流模型,结合预处理和基本求解技术发展出适于转捩流动的数值模拟方法和程序.针对预处理技术,以Weiss-Smith矩阵为基础,考虑湍流粘性的影响;针对基本离散格式和边界条件,结合模型方程进行对角占优强化等特殊处理.最后通过平板边界层和典型翼型,特别是低雷诺数翼型的数值模拟,验证数值方法的有效性和鲁棒性.算例表明本文的方法能够为求解更复杂的流动提供参考. 相似文献
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根据零压力梯度平板的实验数据对B-C转捩模型中的经验关联式进行标定.标定后的B-C转捩模型在进口湍流度较低的平板算例上可以提供更合理的转捩预测结果.但受限于RANS方法自身特性,B-C转捩模型对转捩后出现的大分离流动计算可靠性较差.结合延迟分离涡模拟SA-DDES方法和B-C转捩模型,发展了转捩-延迟分离涡模拟BC-DDES方法.三维S-K平板的数值模拟表明,BC-DDES方法能得到与B-C转捩模型一致的转捩结果.三维圆柱绕流的数值模拟表明,BC-DDES方法得到与实验符合的平均阻力系数和表面压力分布,并且计算花费比tHRLES方法少. 相似文献
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提出一种求解BN非守恒型两相流模型的方法.从微观角度出发,构造与BN模型相匹配的Gas-kineticscheme(GKS),通过对粒子速度分布函数积分求矩得到通量,把非守恒项直接包含到数值通量的演化和构造中,较好地处理了方程中包含的非守恒项.数值试验说明本方法的有效性. 相似文献
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Richard Valenta 《Czechoslovak Journal of Physics》1996,46(9):817-823
Formal solution of coupled equations for pressure and temperature that are generated in a viscous gas closed in a finite, simply connected region is explained. One different from the other, homogeneous, given in frequency domain boundary conditions for the pressure and temperature are taken into account. 相似文献
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A closed system of surface elasticity equations was derived in terms of surface quantities defined as integrals of respective excess bulk quantities normal to the interface. The equations were consistently linearized for the case of small strains. It is shown that these equations are more general than the Shuttleworth equations. Equations of this type were also derived for the particular case of an interface formed by a thin layer with constant properties. The derived equations were used to consider bending of a plate under pressure applied to both sides. 相似文献
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H.-B. Valentini 《等离子体物理论文集》1980,20(1):39-59
Starting from the Boltzmann equation the moment equations up to the third order for a non-quasineutral plasma are derived. It is shown that for a non-quasineutral plasma, in the distinction from the second order set of moment equations, the systems of the first order and of the third order can be closed in a physically reasonable manner by a relatively simple method when near the walls the ion gas has a high drift velocity caused by an electric field. From this follows that in non-quasineutral plasmas the ion pressure must be neglected in the first order set of equations consisting of the equations of continuity and of momentum transfer. Terms of the first order in the ion pressure related to the electron pressure are taken into consideration for the third order system. In this way one obtains a unified set of differential equations to treat both the quasineutral plasma core and the space charge sheath at the walls jointly taking into account a non-vanishing ion temperature. This set of equations is applied to the positive column in the free-fall regime. 相似文献
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Acoustic signature of a submarine hull under harmonic excitation 总被引:2,自引:0,他引:2
The structural and acoustic responses of a submarine under harmonic force excitation are presented. The submarine hull is modelled as a cylindrical shell with internal bulkheads and ring stiffeners. The cylindrical shell is closed by truncated conical shells, which in turn are closed at each end using circular plates. The entire structure is submerged in a heavy fluid medium. The structural responses of the submerged vessel are calculated by solving the cylindrical shell equations of motion using a wave approach and the conical shell equations with a power series solution. The far-field radiated sound pressure is then calculated by means of the Helmholtz integral. The contribution of the conical end closures on the radiated sound pressure for the lowest circumferential mode numbers is clearly observed. Results from the analytical model are compared with computational results from a fully coupled finite element/boundary element model. 相似文献
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V. N. Strel'tsov 《Foundations of Physics》1977,7(5-6):325-330
The relativistic transformation equations for the pressure, volume, energy, and momentum of a gas in a closed container are discussed. Considerations are given in support of pressure noninvariance, volume dilatation, and the fact that the energy and momentum of a gas form a four-vector. It is shown that the relativistic transformation formula for temperature resulting from the Lorentz invariance requirement of the equation of state of an ideal gas coincides with the Ott formula. 相似文献
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I. V. Chermyaninov V. G. Chernyak 《Journal of Experimental and Theoretical Physics》2013,117(1):11-20
The cross transport processes that occur in a single-component gas in a capillary and are caused by resonance laser radiation and pressure and temperature gradients are studied. An expression for entropy production is derived using a system of kinetic Boltzmann equations in a linear approximation. The kinetic coefficients that determine the transport processes are shown to satisfy the Onsager reciprocal relations at any Knudsen numbers and any character of the elastic interaction of gas particles with the capillary surface. The light-induced baro- and thermoeffects that take place in a closed heat-insulated system in the field of resonance laser radiation are considered. Analytical expressions are obtained for the Onsager coefficients in an almost free-molecular regime. The light-induced pressure and temperature gradients that appear in a closed heat-insulated capillary under typical experimental conditions are numerically estimated. 相似文献
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J. G. Williams 《General Relativity and Gravitation》1998,30(1):27-33
A new family of solutions is presented for the (2+1)-dimensional Einstein equations with a rotating perfect fluid source. The mass density and pressure are everywhere positive. Features of the spacetime include closed timelike curves and Finkelstein-Misner metrical kinks. 相似文献
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de Vries MP Schutte HK Veldman AE Verkerke GJ 《The Journal of the Acoustical Society of America》2002,111(4):1847-1853
A new numerical model of the vocal folds is presented based on the well-known two-mass models of the vocal folds. The two-mass model is coupled to a model of glottal airflow based on the incompressible Navier-Stokes equations. Glottal waves are produced using different initial glottal gaps and different subglottal pressures. Fundamental frequency, glottal peak flow, and closed phase of the glottal waves have been compared with values known from the literature. The phonation threshold pressure was determined for different initial glottal gaps. The phonation threshold pressure obtained using the flow model with Navier-Stokes equations corresponds better to values determined in normal phonation than the phonation threshold pressure obtained using the flow model based on the Bernoulli equation. Using the Navier-Stokes equations, an increase of the subglottal pressure causes the fundamental frequency and the glottal peak flow to increase, whereas the fundamental frequency in the Bernoulli-based model does not change with increasing pressure. 相似文献
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采用SINDA/FLUINT软件建立了具有盲支管的低温加注管路模型,仿真计算得到了不同阀门关闭时间、盲支管长度、阀门关闭顺序、管径下的水击压力变化情况。结果显示,阀门关闭时间越短,造成盲支管内的压力变化越剧烈,形成较大的压力峰值,容易对管路造成损坏;在低温管路处于冷态的情况下,盲支管长度对盲支管内压力峰值影响不大;某一支路阀门关闭使得该阀前压力出现变化,对另一支路压力影响不大,在整个管路形成封闭腔后,阀门关闭造成系统压力急剧变化,影响较大;管径越大,阀门关闭时的水击压力峰值越大。 相似文献