Numerical investigation of cavitation generated by an ultrasonic dental scaler tip vibrating in a compressible liquid

Bacterial biofilm accumulation around dental implants is a significant problem leading to peri-implant diseases and implant failure. Cavitation occurring in the cooling water around ultrasonic scaler tips can be used as a novel solution to remove debris without any surface damage. However, current clinically available instruments provide insufficient cavitation around the activated tip surface. To solve this problem a critical understanding of the vibro-acoustic behaviour of the scaler tip and the associated cavitation dynamics is necessary. In this research, we carried out a numerical study for an ultrasound dental scaler with a curved shape tip vibrating in water, using ABAQUS based on the finite element method. We simulated the three-dimensional, nonlinear and transient interaction between the vibration and deformation of the scaler tip, the water flow around the scaler and the cavitation formation and dynamics. The numerical model was well validated with the experiments and there was excellent agreement for displacement at the free end of the scaler. A systematic parametric study has been carried out for the cavitation volume around the scaler tip in terms of the frequency, amplitude and power of the tip vibration. The numerical results indicate that the amount of cavitation around the scaler tip increases with the frequency and amplitude of the vibration. However, if the frequency is far from the natural frequency, the cavitation volume around the free end decreases due to reduced free end vibration amplitude.     

涡旋板弹簧的有限元分析及实验

板弹簧支承技术是线性压缩机的关键技术之一,在为活塞提供轴向回复力的同时,还用来支承压缩活塞、保证密封间隙。在优化分析的基础上,文中设计制造了一款三臂涡旋板弹簧。利用ANSYS有限元软件分析了该款板弹簧的轴向刚度、径向刚度、应力分布以及固有频率特性,并对板弹簧的轴向刚度和固有频率进行了实验研究。实验结果表明,采用有限元分析方法分析板弹簧性能是有效的。     

Determining directional emissivity: Numerical estimation and experimental validation by using infrared thermography

Little research has examined that inaccurate estimations of directional emissivity form a major challenge during both passive and active thermographic measurements. Especially with the increasing use of complex curved shapes and the growing precision of thermal cameras, these errors limit the accuracy of the thermal measurements. In this work we developed a technique to estimate the directional emissivity using updated numerical simulations. The reradiation on concave surfaces is examined by thermal imaging of a homogeneous heated curved metal and nylon test sample. We used finite element modelling to predict the reradiation of concave structures in order to calculate the parameters of an approximating formula for the emissivity dependent on the angle to the normal vector on each element. The differences between experimental and numerical results of the steel test sample are explained using electron microscopy imaging and the validation on different materials. The results suggest that it is possible to determine the errors of thermal imaging testing of complex shapes using a numerical model.     

An evaluation of solution algorithms and numerical approximation methods for modeling an ion exchange process

The focus of this work is on the modeling of an ion exchange process that occurs in drinking water treatment applications. The model formulation consists of a two-scale model in which a set of microscale diffusion equations representing ion exchange resin particles that vary in size and age are coupled through a boundary condition with a macroscopic ordinary differential equation (ODE), which represents the concentration of a species in a well-mixed reactor. We introduce a new age-averaged model (AAM) that averages all ion exchange particle ages for a given size particle to avoid the expensive Monte-Carlo simulation associated with previous modeling applications. We discuss two different numerical schemes to approximate both the original Monte-Carlo algorithm and the new AAM for this two-scale problem. The first scheme is based on the finite element formulation in space coupled with an existing backward difference formula-based ODE solver in time. The second scheme uses an integral equation based Krylov deferred correction (KDC) method and a fast elliptic solver (FES) for the resulting elliptic equations. Numerical results are presented to validate the new AAM algorithm, which is also shown to be more computationally efficient than the original Monte-Carlo algorithm. We also demonstrate that the higher order KDC scheme is more efficient than the traditional finite element solution approach and this advantage becomes increasingly important as the desired accuracy of the solution increases. We also discuss issues of smoothness, which affect the efficiency of the KDC–FES approach, and outline additional algorithmic changes that would further improve the efficiency of these developing methods for a wide range of applications.     

A prediction of the acoustic field of a vibrating box by FEM-BEM

I.Mathematicalmodelofacousticfie1dByapplyingtheSommerfeldradiationcondihonThus,anacousticfic1disdescribcdbyHelmholtzformula.Byconsideringaficldpointinthearea,Helmholtzformulaisgivenbythefollowingthreeintegra1equations:(1)Theexternalintcgra1fOrmu1a'(2)Thcintcrnalintegralformu1af(3)Thesurfaceintegralformu1afwhcreP.isthesoundpressureonthcSsurface;rthedistancefrompointqtothee1ementsurfacedSiqtheficldpoint,tuthefrcqucncyoftheacousticradiation;pthedensityofthesurroundingmedium,vsthenormalvibrati…     

On the experimental validation of combustion simulations in turbulent non-premixed jets

A Reynolds averaged Navier–Stokes (RANS) based combustion model, which incorporated the conditional source-term estimation (CSE) method for the closure of the chemical source term and the trajectory generated low-dimensional manifold (TGLDM) method for the reduction of detailed chemistry, was applied to predict the OH radical distribution in a combusting non-premixed methane jet. The results of the numerical prediction were compared with the results of a complementary experimental study in which the OH radical fields of combusting non-premixed methane jets were visualized using planar laser induced fluorescence (PLIF). It is well known within the modelling community that RANS based models are unable to capture the stochastic nature of turbulent combustion and autoignition, and are therefore unable to predict individual realizations of the flame. In this study, the agreement between the predicted OH field and a well-converged ensemble average of the experimental results was also shown to be poor. The lack of agreement between the numerical results and the ensemble averaged experimental results expose the potential significance of the known weakness in the RANS method. A statistical analysis of the experimental results was also performed. The results of the analysis showed that a minimum of 100 individual realizations was required to provide a well-converged average OH field for the combusting non-premixed jet under investigation. The significance of this result with respect to the validation of large-eddy simulations (LES) of combusting jets is discussed.     

能动反射镜低频像差补偿能力分析

 采用Algor软件包并利用有限元法对37单元能动反射镜低频误差补偿能力进行了分析计算，确定了镜面厚度8mm，驱动器间距46mm，极头直径12mm等能动反射镜制造的关键参数。通过计算机仿真分析证明，基于这些参数所设计的能动反射镜可以对低频误差进行有效校正，校正精度的均方根值小于等于λ／８，从而可以为能动反射镜的制造提供理论依据。     

A review of analytical methods, based on the wave approach, to compute partitions transmission loss

In this paper, various methods for calculating partition transparency are investigated. These methods are all based on the wave approach, yet they differ in the way of considering the incident field, partition leaf dimensions and the absorbing material, or absorbent, incorporated between the partition leaves. The method verification has been done through comparison with the experimental data available in the literature. Results are very convincing and the wave approach proves to be highly accurate. The basic wave approach is well suited for modeling of infinite single or double-leaf partitions, although the diffuse incident field requires spatial windowing to achieve agreement with experimental data. When porous material is incorporated inside double-leaf partitions, the model needs to be enhanced, based on the Biot theory, to ensure coincidence with experimental data. In the case of partitions, which cannot be considered infinite, spatial windowing is applied to the transparency to correct for the dimensional effect, especially in the low-frequency range. The final model turns out to be highly accurate, as long as spatial windowing is limited to the first coincidence frequency. The wave approach therefore proves to be a suitable method and calculation times are moreover acceptable.     

Theoretical prediction and experimental validation of the angle-of-arrival probability density of a laser beam in a strong plane-flame turbulence

The propagation of a laser beam through a plane turbulent flame is studied using geometrical optics approximation. The random fluctuations of the refractive index caused by a strong thermal turbulence in the flame create random perturbations of the laser beam direction. From the Markovian process model applied along the whole random path of the beam, the theoretical probability density of the laser beam angle-of-arrival is derived from the analytical solution of the Einstein-Fokker-Kolmogorov equation, which we have determined in terms of a series expansion of spherical harmonics. An experimental setup and a method for measuring this probability density are described. The experimental results obtained are shown to agree with the theoretical predictions.     

Hybridizable discontinuous Galerkin methods for the time-harmonic Maxwell’s equations

We present two hybridizable discontinuous Galerkin (HDG) methods for the numerical solution of the time-harmonic Maxwell’s equations. The first HDG method explicitly enforces the divergence-free condition and thus necessitates the introduction of a Lagrange multiplier. It produces a linear system for the degrees of freedom of the approximate traces of both the tangential component of the vector field and the Lagrange multiplier. The second HDG method does not explicitly enforce the divergence-free condition and thus results in a linear system for the degrees of freedom of the approximate trace of the tangential component of the vector field only. For both HDG methods, the approximate vector field converges with the optimal order of k + 1 in the L²-norm, when polynomials of degree k are used to represent all the approximate variables. We propose elementwise postprocessing to obtain a new H^curl-conforming approximate vector field which converges with order k + 1 in the H^curl-norm. We present extensive numerical examples to demonstrate and compare the performance of the HDG methods.     

Theory of phononic gaps induced by inertial amplification in finite structures

The characteristics of inertial amplification induced gaps are derived and compared with those of local resonance and Bragg gaps in finite lattices. Deep inertial amplification gaps at low frequencies are obtained without using a multitude of unit cells. These gaps remain deep regardless of boundary conditions, excitation direction or mode.     

Numerical and experimental studies on housing optimization for noise reduction of an axial piston pump

This paper presents a methodology to reduce the noise of an axial piston pump through modification of the housing structure, combined with both numerical and experimental methods. The finite element models of the housing and cover are established, and are assembled together. The finite element models are validated and updated using experimental modal analysis. The frequency response function of the assembly is calculated, and the shell element in the inner surfaces of the housing is added. The effects of the thickness of the shell element on the frequency response function are identified. A topology optimization is conducted for the purpose of reducing the frequency response function and the increase of mass. The prototype pump is manufactured and assembled. Different experimental measurements are carried out, including the measurement of the vibration and the distributions of the sound pressure levels around the pump. Results show that the vibration and noise are reduced by using the optimized housing. In particular, the average sound pressure level is reduced by about 2 dB(A) at the discharge pressure of 250 bar, and the sound pressure level at the second harmonic is reduced significantly. The method proposed here can also be used for other kinds of displacement pumps.     

Low frequency vibroacoustic investigation of wooden T-junctions

In this paper, an experimental investigation on the influence of glue on the low frequency vibroacoustic performance (up to 200 Hz) of wooden T-junctions is presented along with a discussion of modelling issues related to the junctions. The mock-ups studied represent cut-outs of full size timber floor assemblies typically used in Sweden. Their dynamic performance was first studied experimentally by means of modal analysis. Moreover, finite element (FE) simulations of the T-junctions were carried out to establish reliable prediction tools, using the measurement data as calibration input. Modelling issues were addressed to investigate the influence of different features that must be taken into account when simulating the connections as part of larger structures. Guidelines for modelling these type of connections, when developing low frequency FE predictive tools, are presented here.     

Comparison and implementation of the various numerical methods used for calculating transmission loss in silencer systems

Issues concerning the design and use of large-scale silencers are more prevalent today then ever before. With the increased use of large industrial machinery (such as gas turbines) and the increase in public awareness and concern for noise control, the desire to be able to properly design silencers for specific applications is increasing. Even today, most silencer design is performed by simply modifying existing designs without full confidence of the new performance characteristics. Due to the size and expense of these silencers, it would be beneficial to have means to predict the insertion loss (IL) or transmission loss (TL) characteristics at the design stage. To properly accomplish this, many factors such as geometry, absorptive material properties, flow effects, break out noise, and self-generated noise must be considered. The use of the finite element method (FEM) and the boundary element method (BEM) can aid in the prediction and design. This paper examines three of the different methods used in calculation of TL values; namely the “traditional” laboratory method, the 4-pole transfer matrix method and the 3-point method. A comparison of these methods based on such criteria as accuracy, computation time, and ease of use was conducted. In addition, the idiosyncrasies and problems encountered during implementation are presented. The conclusions were that the FEM is better suited for this kind of application and that the 3-point method was the fastest method and was easier to use than the 4-pole method.     

An assessment of the high frequency boundary element and Rayleigh integral approximations

This paper revisits the popular Rayleigh integral approximation and also considers a second approximation, the high frequency boundary element method, which is similar to the Rayleigh integral. The Rayleigh integral approximation under consideration is enhanced so that only the elements visible to a particular point in the field are used to calculate the sound pressure at that point. It is demonstrated how both the Rayleigh integral and high frequency boundary element method are approximations to the boundary integral equation so that similarities between the two methods are recognized. Several test cases were conducted in order to assess and compare both methods. The first set of test cases was the pulsating and oscillating sphere. Both methods were then compared on more applied examples including a running engine, construction cab, and transmission housing. It was concluded that though both methods can reliably predict the sound power for some problems, the high frequency boundary element method is the more robust.     

A reagent-based strategy for the design of large combinatorial libraries: A preliminary experimental validation

Combinatorial library design can be carried out at either the reagent or the product level. Various reports in the literature have come to conflicting conclusions in favor of one over the other. In this paper a reagent-based screening library design strategy is presented. The method relies on analysis of scaffolds and building blocks separately to define the overall diversity in a compound file. The primary diversity selection by properties relevant for molecular recognition and by redundancy is followed by the application of filters for molecular properties known to be relevant for drug-likeness. Filter properties are rapidly estimated at the product level using a fragmental estimation approach. Initial experimental data suggest that high diversity in vast screening libraries can be achieved by carefully applied reagent level analysis. A potential role of diverse screening libraries in chemical genomics (pharmacological knockouts) is also discussed.     

重频应用下等离子体电光开关热退偏损耗分析

 基于有限元数值方法,给出电光晶体KDP在高平均功率激光负载下温度场分布和应力场分布。在此基础上得到了折射率随温度变化、电光系数随温度变化、及应力双折射引入的退偏损耗。数值模拟显示：电光系数随温度变化和应力双折射是引起开关退偏损耗的主要因素。当入射激光平均功率为40 W、辐照时间为420 s时,KDP晶体最高温度为38.43 ℃,电光系数随温度变化及应力双折射引入的最大退偏损耗分别为2.38%和4.04%。实验测量了应力双折射导致的退偏损耗,实验结果和理论结果符合较好。     

Transmission loss prediction on a single-inlet/double-outlet cylindrical expansion-chamber muffler by using the modal meshing approach

This work formulates the acoustical performance prediction on a single-inlet/double-outlet cylindrical expansion-chamber muffler. Expressions for the transmission loss (TL) of the muffler are formulated by using the modal meshing approach and the plane wave theory, respectively. The parametric influence upon the values of TL for this kind of muffler is numerically analyzed for various cases of length-diameter ratio, and the computed results of TL are compared to present the higher order mode effects. The results by the modal meshing approach are also compared with the finite element method to verify its accuracy.     

FAIR收集环二极超导实验磁体的研究

为验证国际反质子和离子加速器(Facility for Antiproton and Ion Research-FAIR)收集环(Collector Ring-CR)二极超导磁体工程设计的可靠性,设计并制造了用于导体性能测试的实验磁体,借助基于有限元的ANSYS软件对其进行了分析,达到了实验磁体的强度要求,实验结果表明导体在低温下性能稳定。进行的研究为收集环二极超导磁体的研发提供了有益的参考。     

The experimental validation of a numerical model for the prediction of the vibrations in the free field produced by road traffic

The objective of the present paper is the experimental validation of a numerical model for the prediction of traffic-induced vibrations. The vibrations in the free field, generated by the passage of a vehicle on an uneven road, are predicted in two stages. First, the equations of motion of the vehicle are solved to determine the dynamic axle loads. Next, these axle loads are applied to the road and the free field vibrations are computed. An elaborate measurement campaign has been set up to validate this model. The response of a Volvo FL6 truck and the response in the free field have been measured simultaneously during the passage of the truck over an artificial road unevenness. The parameters related to the vehicle, the road and the soil have been determined experimentally. A comparison of the predicted and the measured response demonstrates the predictive qualities of the numerical model. Furthermore, the results provide a clear insight in the influence of the vehicle speed on the vehicle's and the free field response.