FEM Analysis on Acoustic Performance of Wall Flow Diesel Particulate Filters

Diesel powered vehicles, in compliance with the more strict exhaust emission standards such as Euro V, is likely to require a diesel particulate filter （DPF）. A DPF used on a vehicle will affect the acoustic emission of the diesel engine, so it is important to investigate the sound propagation rule in DPF and further to propose the optimum DPF design. However, due to the geometrical complexity of the DPF, the traditional analysis method, such as analytical method, can not assess the acoustic performance of DPF accurately in medium and high frequency band. In this paper, a combined approach of finite element analysis and viscosity correction is proposed to predict acoustic performance of DPF. A simplified model of the full DPF is established and is used to analyze the sound propagation characteristic of the DPF. The distribution of the sound pressure and velocity, the transmission matrix of the DPF are obtained using the finite element method. In addition, the method of the viscosity correction is used in the transmission matrix of the DPF to evaluate the acoustic performance of DPF. Based on the FEM computation and the viscosity correction, the transmission losses under the rated load and idle condition of a diesel engine are calculated. The calculation results show that DPF can effectively attenuate exhaust noise, and sound attenuation increase with the rise of the frequency. Sound attenuation is better under rated condition than idle condition of diesel engine, particularly in frequency above 1 000 Hz.

FEM simulation of flexible roll forming based on different material models

Flexible roll forming is a new roll forming process that produces parts with variable cross sections. This forming process is proposed to meet the demand of weight reduction of automobile industry. In order to study the mechanisms and material flow rules in this new forming process,the finite element mothod( FEM) model of a nine-step flexible roll forming of an ultra-high-strength steel bumper is established based on deep understanding and reasonable simplification of the process.Given that the material model is an important factor that influences the simulation accuracy,three material models which consist of different yield criteria and hardening models are adopted in the FEM models. Sheet thickness and springback amount calculated with three material models are studied comparatively. According to sheet thickness reduction and springback amounts,it is found that the MKi( Mises yield criterion and kinematic hardening law) model's result is larger than MI( Mises yield criterion and isotropic hardening law) model and HI( Hill's yield criterion and isotropic hardening law) model. Therefore,it is concluded that material models do have influences on the flexible roll forming simulation and need to be determined carefully.

Stochastic analysis of excavation-induced wall deflection and box culvert settlement considering spatial variability of soil stiffness

In this study, a three-dimensional (3D) finite element modelling (FEM) analysis is carried out to investigate the effects of soil spatial variability on the response of retaining walls and an adjacent box culvert due to a braced excavation. The spatial variability of soil stiffness is modelled using a variogram and calibrated by high-quality experimental data. Multiple random field samples (RFSs) of soil stiffness are generated using geostatistical analysis and mapped onto a finite element mesh for stochastic analysis of excavation-induced structural responses by Monte Carlo simulation. It is found that the spatial variability of soil stiffness can be described by an exponential variogram, and the associated vertical correlation length is varied from 1.3 m to 1.6 m. It also reveals that the spatial variability of soil stiffness has a significant effect on the variations of retaining wall deflections and box culvert settlements. The ignorance of spatial variability in 3D FEM can result in an underestimation of lateral wall deflections and culvert settlements. Thus, the stochastic structural responses obtained from the 3D analysis could serve as an effective aid for probabilistic design and analysis of excavations.

基于三维精细化动力学模型的局部模态获取技术

Structural dynamic problems encountered within launch vehicles are sometimes related to entire dynamic characteristics of the vehicle,and sometimes related to local dynamic characteristics of some parts of vehicles.To acquire local dynamic characteristics,it usually requires the building of a three-dimensional detailed FEM model.It is important that the simulation of mass and stiffness of local part is accurate.The local mode acquisition of a gas tank and its bracket installed in the inter-tank section is taken as an example in this paper.It can be seen that the local modes are consistent with the section modal test results.Finally,the verified three-dimensional detailed FEM model of the inter-tank section is assembled within the entire launch vehicle,and the local modes of the gas tank and its bracket under flight conditions are predicted.

双头单螺杆泵定子衬套力学行为分析

为研究双头单螺杆泵定子衬套的受力状态及内轮廓线的变形规律,分析了内压、压差、材料非线性、橡胶泊松比等多种因素对定子衬套应力、应变及内轮廓线变形规律的影响,并拟合出双头单螺杆泵定子衬套在均匀内压作用下内轮廓线位移的方程式及非均匀内压下内轮廓线最大位移公式。分析结果表明:均匀压力下,衬套应力、应变呈周期性变化,内轮廓线位移呈正弦规律变化,位移与内压成线性关系;压差作用下,衬套应力、应变最大值向压差作用处转移,内轮廓线变形规律发生改变,位移及其变形幅度均增大;衬套橡胶泊松比微小的变化即会对衬套变形产生非常大的影响。因此,实际生产中应注意注胶工艺及泊松比的变化。研究结果为定子、转子过盈量的选取及线型的优化设计提供了理论基础,对提高双头单螺杆泵工作效率和使用寿命具有重要工程实际意义。

Evaluating rockfalls at a historical settlement in the Ihlara Valley(Cappadocia, Turkey) using kinematic, numerical, 2D trajectory, and risk rating methods

Rockfalls are one of the most dangerous natural events in hilly terrains, and they substantially threaten residential areas and transport corridors in these environments. This study is aimed to analyze the risk of rockfall from a slope to nearby houses in a historical settlement with past rockfall histories. It contains numerous applications to study rockfall danger from different points of view(e.g., kinematics,numerical stability analysis, risk assessment, 2D trajectory). The rockfall kinematics revealed the statistics for different structurally controlled failure modes among the surveyed slope discontinuities,especially wedge type and block toppling were the most significant ones. Finite element analysis showed that the slope was stable under the natural condition with a safety factor of 2.19. The rockfall risk rating system calculated a medium risk for the houses downstream. Based on the field measurements, a possible rockfall profile was determined and located as an input in the 2D rockfall trajectory program. The rigid-body impact model runs utilized various shapes and sizes of blocks to simulate the rockfall events realistically. According to the 2D trajectory model results, there was no rockfall danger for the investigated downslope houses. The study showed the importance of using different analysis techniques to solve rockfall risk in protected areas based on scientific and rational approaches.

Cavity effect on Rayleigh wave dispersion and P-wave refraction

Sinkholes and cavities can represent serious hazards to human safety and urban infrastructures,cause roadbed subsidence,and so on.It is therefore essential to evaluate various sinkholes in different depths and sizes to assess the risk of collapse.This paper evaluates the effect of different cavities on Rayleigh-wave propagation and body(P)wave refraction.Rayleigh(R)wave propagation is analyzed according to the classical multi-channel analysis of surface waves(MASW)method also considering the R-wave backscattering.Synthetic seismic traces are computed by means of finite element modeling(FEM)for cavity and intrusion at different depths and sizes.Furthermore,field acquisition data is used to verify the detection effect of a cavity on R-and P-waves.The results show that the presence of backscattered R-waves and the changes in the R-wave velocity spectrum can help in cavity identification.Additional possible evidence is represented by significant changes in the refraction travel times over the cavity location.It can be concluded that the field data are in good agreement with the synthetic,and it could be effective to consider the results of both R-and P-wave analysis in order to efficiently identify the cavities.

Development and application of an interface constitutive model for fully grouted rock-bolts and cable-bolts

This paper proposes a new interface constitutive model for fully grouted rock-bolts and cable-bolts based on pull-out test results.A database was created combining published experimental data with in-house tests.By means of a comprehensive framework,a Coulomb-type failure criterion accounting for friction mobilization was defined.During the elastic phase,in which the interface joint is not yet created,the proposed model provides zero radial displacement,and once the interface joint is created,interface dilatancy is modeled using a non-associated plastic potential inspired from the behavior of rock joints.The results predicted by the proposed model are in good agreement with experimental results.The model has been implemented in a finite element method(FEM)code and numerical simulations have been performed at the elementary and the structural scales.The results obtained provide confidence in the ability of the new model to assist in the design and optimization of bolting patterns.

Effects of cross-anisotropy and stress-dependency of pavement layers on pavement responses under dynamic truck loading

Previous studies by the authors have determined pavement responses under dynamic loading consid- ering cross-anisotropy in one layer only, either the cross-anisotropic viscoelastic asphalt concrete （AC） layer or the cross-anisotropic stress-dependent base layer, but not both. This study evaluates pavement stress-strain responses considering cross-anisotropy in all layers, i.e. AC, base and subbase, using finite element modeling （FEM） technique. An instrumented pavement section on Interstate 1-40 near Albuquerque, New Mexico was used in ABAQUS framework as model geometry. Field asphalt cores were collected and tested in the laboratory to determine the cross-anisotropy （n-values） defined by horizontal to vertical modulus ratio, and other viscoelastic parameters as inputs of the model incorporated through user defined material interface （UMAT） functionality in ABAQUS. Field base and subbase materials were also collected and tested in the laboratory to determine stress-dependent nonlinear elastic model parameters, as inputs of the model, again incorporated through UMAT. The model validation task was carried out using field-measured deflections and strain values under falling weight deflectometer （FWD） loads at the instrumented section. The validated model was then subjected to an actual truck loading for studying cross-anisotropic effects. It was observed that horizontal tensile strain at the bottom of the AC layer and vertical strains in all layers decreased with an increase in n-value of the asphalt layer, from n （ 1 （anisotropy） to n - 1 （isotropy）. This indicates that the increase in horizontal modulus caused the decrease in layer strains. It was also observed that if the base and subbase layers were considered stressdependent instead of linear elastic unbound layers, the horizontal tensile strain at the bottom of the asphalt layer increased and vertical strains on top of the base and subbase also increased.

Behavior and design method of square-tubed reinforced concrete short columns under axial compression

The behavior of square-tubed reinforced concrete (STRC) short columns subjected to axial compression was studied in detail with an accurate nonlinear finite element model (FEM) . Different width to thickness ratios (D/t = 50 150) of the steel tube and the compressive strength of concrete (C80 and C50) were adopted in this research. The axial load strength,steel tube strain and load-shortening response were determined from FEM and the analysis results from FEM were compared with those from experiment. The analysis and test results indicate that the concrete strength little affectes the confinement of the steel tube on the concrete. The transverse stress of the tube at the axial load point increases with the increment in the width to thickness ratio. Based on the results from FEM and experiment,a formula for the prediction of the axial load strength was proposed in this paper.

Hybrid graded element model for transient heat conduction in functionally graded materials

This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials （FGMs）. First, a Laplace transform approach is used to handle the time variable. Then, a fundamental solution in Laplace space for FGMs is constructed. Next, a hybrid graded element is formulated based on the obtained fundamental solution and a frame field. As a result, the graded properties of FGMs are naturally reflected by using the fundamental solution to interpolate the intra-element field. Further, Stefest＇s algorithm is employed to convert the results in Laplace space back into the time-space domain. Finally, the performance of the proposed method is assessed by several benchmark examples. The results demonstrate well the efficiency and accuracy of the proposed method.

Thermo-hydro-mechanical-air coupling finite element method and its application to multi-phase problems

In this paper, a finite element method （FEM）-based multi-phase problem based on a newly proposed thermal elastoplastic constitutive model for saturated/unsaturated geomaterial is discussed. A program of FEM named as SOFT, adopting unified field equations for thermo-hydro-mechanical-air （THMA） behavior of geomaterial and using finite element-finite difference （FE-FD） scheme for so/l-water-air three-phase coupling problem, is used in the numerical simulation. As an application of the newly proposed numerical method, two engineering problems, one for slope failure in unsaturated model ground and another for in situ heating test related to deep geological repository of high-level radioactive waste （HLRW）, are simulated. The model tests on slope failure in unsaturated Shirasu ground, carried out by Kitamura et al. （2007）, is simulated in the framework of soil-water-air three-phase coupling under the condition of constant temperature. While the in situ heating test reported by Munoz （2006） is simulated in the same framework under the conditions of variable temperature hut constant air pressure.

Active tectonics in Taiwan:insights from a 3-D viscous finite element model

Taiwan is a young orogenic belt with complex spatial distributions of deformation and earthquakes. We have constructed a three-dimensional finite element model to explore how the interplays between lithospheric struc- ture and plate boundary processes control the distribution of stress and strain rates in the Taiwan region. The model assumes a liberalized power-law rheology and incorporates main lithospheric structures; the model domain is loaded by the present-day crustal velocity applied at its bound- aries. The model successfully reproduces the main features of the GPS-measured strain rate patterns and the earth- quake-indicated stress states in the Taiwan region. The best fitting model requires the viscosity of the lower crust to be two orders of magnitude lower than that of the upper crust and lithospheric mantle. The calculated deviatoric stress is high in regions of thrust faulting and low in regions of extensional and strike-slip faulting, consistent with the spatial pattern of seismic intensity in Taiwan.

Dynamic Characteristics of Inflated Torus Using Finite Element Analysis

In recent years, inflatable structures have been a subject of interest for space applications such as communication antenna, solar thermal propulsion and entry/landing systems. The inflatable structures characterized by high strength-to-mass ratios, minimal stowage volume, which makes them suitable for cost-effective large space structures. A typical example for the inflatable structure is the inflated torus which often used in order to provide structure support. In this study, our main focus is to understand the dynamic characteristics of an inflated torus in order to formulate an accurate mathematical model suitable for active vibration control applications. A commercial finite element package, ANSYS, is used to model the inflated torus. To verify the model the obtained frequencies and mode shapes are compared with the published results, which are derived using analytical approach, the verification shows a good agreement between the FEM and the analytical results. Based on the verified model, parametric study was investigated; the material thickness increase causes the natural frequencies decrease, while the increase of the inflation pressure simply results in stiffening the ring, which means that the natural frequency increased. The FEM analysis gives an easy and fast way for the vibration analysis of the structures compared with the complicated analytical solutions.

Mechanical Behavior of Plastic Pipe Reinforced by Cross-Winding Steel Wire Subject to Foundation Settlement

Plastic pipe reinforced by cross helically wound steel wires(PSP)is a new plastic-matrix steel composite pipe developed in China.To investigate the stress of PSP under foundation settlement,a finite element model(FEM)is proposed.The stresses and strains of PSP are obtained by the FEM analysis.The mechanic behavior of PSP subject to a foundation settlement is analyzed.Finally,the influence factor analysis of settlement deformation,such as settlement depth,overlying soil depth,diameter of PSP and inner pressure of PSP,are discussed.

Free vibration characteristics of sectioned unidirectional/bidirectional functionally graded material cantilever beams based on finite element analysis

Advancements in manufacturing technology,including the rapid development of additive manufacturing(AM),allow the fabrication of complex functionally graded material(FGM)sectioned beams.Portions of these beams may be made from different materials with possibly different gradients of material properties.The present work proposes models to investigate the free vibration of FGM sectioned beams based on onedimensional(1D)finite element analysis.For this purpose,a sample beam is divided into discrete elements,and the total energy stored in each element during vibration is computed by considering either the Timoshenko or Euler-Bernoulli beam theory.Then,Hamilton’s principle is used to derive the equations of motion for the beam.The effects of material properties and dimensions of FGM sections on the beam’s natural frequencies and their corresponding mode shapes are then investigated based on a dynamic Timoshenko model(TM).The presented model is validated by comparison with three-dimensional(3D)finite element simulations of the first three mode shapes of the beam.

State of the art in finite element approaches for milling process:a review

Over a century,metal cutting has been observed as a vital process in the domain of manufacturing.Among the numerous available metal-cutting processes,milling has been considered as one of the most employable processes to machine a variety of engineering materials productively.In the milling process,material removal occurs when the workpiece is fed against a rotating tool with multiple cutting edges.In order to maximize the profitability of metal cutting operations,it is essential that the various input and output variable relationships are analyzed and optimized.The experimental method of studying milling processes is costly and time demanding,particularly when a large variety of elements such as cutting tool shape,materials,cutting conditions,and so on,are included.Due to these issues,other alternatives emerged in the form of mathematical simulations that employ numerical methods.The finite element approaches have well-proven to be the most practical and commonly utilized numerical methods.The finite element model(FEM)can be used to determine the various physical interactions occurring during the machining process along with the prediction of various milling characteristics,such as cutting forces,cutting temperature,stresses,etc.,with the help of milling inputs.In the present article,various research studies in the broad milling process domain practiced with numerous finite element approaches have been critically reviewed and reported.It further highlights the several experimental and finite element approaches-based research studies that attempted to analyze and optimize the overall performance of the different milling processes.In recent years,various investigators have explored numerous ways to enhance milling performance by probing the different factors that influence the quality attributes.Some of the studies have also been found to be focused on the economic impacts of milling and various process inputs that affect milling performance.Furthermore,various milling factors’impact on the performance characteristics are presented and critically discussed.The issues related to the recent improvements in tool-work interaction modeling,experimental techniques for acquiring various milling performance measures,and the aspects of turn and micro-milling with finite element-based modeling have been further highlighted.Among the various available classifications in the milling process as employed in industries,face milling is more strongly established compared to other versions such as end milling,helical milling,gear milling,etc.The final section of this research article explores the various research aspects and outlines future research directions.

Numerical Investigation of the Thermal Distortion in Multi-Laser Powder Bed Fusion(ML-PBF)Additive Manufacturing of Inconel 625

Metal additive manufacturing,especially laser powder bed fusion(L-PBF),is increasingly being used to fabricate complex parts with fine features.Emerging L-PBF systems have large build volumes and several lasers that op-erate simultaneously.Hence,they can produce large and complex parts at reduced costs and short build times.However,the thermal distortion remains a critical challenge.Hence,a thorough understanding of the impact of multiple lasers on part distortion in multi-laser PBF(ML-PBF)is imperative.Although experimental investigation is possible,a more conducive approach is to design and create suitable predictive models to understand the impact of multiple lasers consolidating a part into layers.To fulfill this goal,in this study,a commercially available and widely used thermo-mechanical model,Netfabb,was used to investigate the effects of multiple lasers for com-plex scan patterns such as raster,spiral,and Hilbert on the temperature distribution and thermal distortion.The results show that the thermal distortion is minimal for the spiral scan pattern.Additionally,multiple lasers were found to decrease the build time(as expected)while maintaining or reducing the thermal distortion compared with their single-laser counterparts for all scan patterns(except Hilbert).Therefore,the newly developed ML-PBF predictive model is capable of providing critical insights into the effects of using multiple lasers,thereby opening new possibilities for the faster production of complex parts.In the future,small-scale computational models will be expanded to include large-scale parts,and probabilistic models will be developed to establish correlations.

Numerical Simulation and Sensitivity Analysis of Parameters for Multistand Roll Forming of Channel Section With Outer Edge

Cold roll forming is a high production but complex metal forming process under the conditions of coupled effects with multi-factor. A new booting finite element method （FEM） model using the updated Lagrangian （IAL） method for multistand roll forming process is developed and validated. Compared with most of the literatures related to roll forming simulation, the new model can take the roll rotation into account and is well suited for simulating multistand roll forming. Based on the model, the process of a channel section with outer edge formed with twelve passes is simulated and the sensitivity analysis of parameters is conducted with orthogonal design combined FEM model. It is found that the multistand roll forming process can be efficiently analyzed by the new booting model, and sensitivity analysis shows that the yield strength plays an important role in controlling the quality of the products.

Accurate 3D Reconstruction of Subject-Specific Knee Finite Element Model to Simulate the Articular Cartilage Defects

The biomechanical relationship between the articular cartilage defect and knee osteoarthritis (OA) has not been clearly defined. This study presents a 3D knee finite element model (FEM) to determine the effect of cartilage defects on the stress distribution around the defect rim. The complete knee FEM, which includes bones, articular cartilages, menisci and ligaments, is developed from computed tomography and magnetic resonance images. This FEM then is validated and used to simulate femoral cartilage defects. Based on the obtained results, it is confirmed that the 3D knee FEM is reconstructed with high-fidelity level and can faithfully predict the knee contact behavior. Cartilage defects drastically affect the stress distribution on articular cartilages. When the defect size was smaller than 1.00cm2, the stress elevation and redistribution were found undistinguishable. However, significant stress elevation and redistribution were detected due to the large defect sizes ( 1.00cm2). This alteration of stress distribution has important implications relating to the progression of cartilage defect to OA in the human knee joint.