Finite Element Numerical Simulation Method Research Articles

An Applicable Time Reversal Analysis of Guided Waves in Al-Plate with Ultrasonic Immersion Testing

Ultrasonic guided waves are capable of propagating relatively long distances in plate-like structures generates leaky lamb waves from the metal surface, a key phenomenon to characterize the surface defects of metal structures. The general technique of time reversing guided plate waves is advantageous to investigate various kinds of defects. The present research has been focused on the adopted time reversal technique for ultrasonic immersion testing. System’s electromechanical irreversibility effect is a barrier for the time reversal analysis of lamb waves in water medium based immersion testing which cannot be avoided experimentally. In this study, this critical time reversal signal reconstruction problem has been solved using the correction factor calculated from the reference experiment and finite element method (FEM) numerical simulation in a water medium. Two kinds of experiments were conducted, first one is a through-transmission system without the use of specimen for the calculation of correction factor and another experiment is pitch-catch system performed on the aluminum specimen, using two 1 MHz center frequency transducers with a diameter of 12.7 mm. Basically, this paper is intended to investigate a methodical approach applicable to analyze guided plate wave signal reconstruction using time reversal technique in water medium ultrasonic immersion testing. The proposed approach can be applied in any time reversal inspection of a plate and pipe-like structures in ultrasonic immersion system.

DEMO Breeding Blanket Helium Cooled First Wall design investigation to cope high heat loads

In the framework of the European “HORIZON 2020” program, EURO fusion develops a fusion power demonstrator (DEMO). According to a recent study about plasma heat loads, it appeared that the First Wall, which is the first part of the Breeding Blanket in front of the plasma, will face some high heat fluxes on some poloidal locations of the Breeding Blanket.In order to cope such high heat fluxes, this paper presents the investigation on different Helium cooled First Wall design integrated to the Breeding Blanket on the basis of standard square and circular smooth channels and with different options for the Tungsten armor surrounding the channels, taking advantages to the different material properties. The performances of the different concepts have been assessed with thermal and mechanical Finite Element Method numerical simulation based on a slice of the Helium Cooled Lithium Lead concept. Results are compared with the RCC-MRx design rules to prevent failure during normal and accidental condition. The results show that the options with channels surrounded by Tungsten could meet some plasma heat loads requirements from design point of view. However, the concept is still at an early stage of development and open issues are discussed.

Investigation of gas flow through soils and granular fill materials for the optimisation of radon soil depressurisation systems

The purpose of this study is to investigate gas flow through different types of granular fill materials and soil by means of a series of experimental laboratory tests, in relation to soil depressurisation systems for radon reduction under buildings and the soil surrounding the foundation. Gas permeability characterisation of materials used as granular fill material beneath the slab in buildings is a key parameter for the optimum performance of soil depressurisation systems to mitigate radon. A test apparatus was developed, adapted from previous studies, to measure the gas permeability of the samples and Finite Element Method numerical simulations were validated to simulate the flow behaviour through them. Theoretical expressions for permeability were discussed based on the analysis of experimental results and numerical simulations, finding that Darcy-Forchheimer equation provides the best match to the experimental results. Darcy's law also proved to be suitable for low gas velocities, whereas Ergun's equation resulted in a poor fit of the experimental data. Benchmark analysis of the granular fill materials under study and other European standards (Spanish, Irish and British) is also presented.

Three-Dimensional Wave-Field Characteristics of Earth-Rock Dams with Different Hidden Hazards

The three-dimensional wave-field characteristics of dangerous earth-rock dams are the premise and foundation to identify the hidden hazards of the earth-rock dams via wave test method. Based on the equivalent elastic wave theory in isotropic mediums, the three-dimensional wave field of earth-rock dams with different defects was calculated using the finite element numerical simulation method. The characteristic and regularity of the three-dimensional wave field was explored. The result of the analysis shows that the size and position of the defects are closely related with the wave-field information received on the dam surface. The elasticity modulus and density of the defects have great effect on the wave field, and alternately, Poisson’s ratio of the defects has little effect on the wave field. The greater the difference between the wave velocity of the hazardous materials and the dam body is, the stronger the energy of the scattered wave will be, which in turn will produce clearer lineups of the scattered wave on the time-history profile. For a single wave movement signal, the dominant frequency amplitude is exponentially correlated with the longitudinal wave velocity of the hazardous materials. Therefore, in the process of wave detection for earth-rock dam hazards, the effect of the elasticity modulus, density, and wave velocity on the test signal should be taken into account. The dominant frequency amplitude can serve as one of the control parameters for interpretation of dam hazards by the analysis of the wave test signal.

Ultracompact low-pass modal filters based on shortcuts to adiabaticity

A versatile approach to the design of photonic ultracompact low-pass modal filters is proposed. The idea stems from the shortcut to adiabaticity protocol, originally developed for quantum-mechanical systems and recently introduced in full-wave optics. This method allows one to achieve efficient rejection of higher order modes in a broad wavelength range for any two-dimensional multimode optical waveguide in an ultracompact configuration of the filter. A study case, corroborated by finite-element method numerical simulations, is reported for slab waveguides.

Study on stability of bucket foundation under backfill

Bucket foundation is a new type of port hydraulic structure that has emerged in recent years. Currently, it is used more and more in coastal engineering. However, due to its complicated structure, the stability of the bucket foundation structure has not been solved. This sinking bucket foundation relies on its own weight and soil mass to resist external force to maintain its stability. In this paper, the finite element numerical simulation method is used to study the more reasonable arrangement of bucket foundation through the analysis of slippage resistance, capsizing ability and instability form of bucket foundation under different diameter-height ratio and different rear backfill. It provides reference for stability analysis and research of bucket foundation.

Evaluation method of highway slope stability based on deep displacement curve characteristics

Taking the slope of Yunnan Wuyi Expressway as a case study, the typical geologic generalization models of three kinds of slopes were established by means of statistical analysis. The limit equilibrium method, finite element numerical simulation method, and deep displacement curve type analysis are combined to evaluate the slope stability under various working conditions in a comprehensive way. The relationship between the deep displacement characteristic curve and slope stability, and a slope stability criterion is established based on the characteristics of deep displacement curve. This method is a supplement to the current Chinese standards on slope stability evaluation. According to the analysis to typical slope projects in central Yunnan, this evaluation method is simple and feasible, which is suitable to evaluate the stability of various types of highway slopes in central Yunnan in China.

Simulation of stress fields and quantitative prediction of fractures distribution in upper Ordovician biological limestone formation within Hetianhe field, Tarim Basin, NW China

The carbonate is the main gas producing system in the Hetian River gas field of Tarim Basin, within which structural fractures serve as the main seepage channel and accumulation spaces. The development process of carbonate gas field in the Hetianhe area shows that the enrichment of gas is closely related to the development of fracture parameters. On the basis of core data and imaging logging data, the characteristics of tectonic fractures parameters were determined. Combining three dimensional finite element numerical simulation method, we simulated paleo tectonic stress field of two key fracture periods(late Hercynian and Himalayan period) and current stress field in Hetian river gas field. The fracture linear density and aperture formulas were established to calculate the distribution of tectonic fractures in different periods. Then the impacts of faulting and folding on the development of fractures could be analyzed. The simulation results showed that the value of maximum principal stress during the Late Hercynian period in the Hetianhe area is 300–320 MPa with a direction of NW-SE(310-130°), and the direction of maximum principal stress is NE-SW(40–220°), with a 500–520 MPa value. The folding play the primary role, and the faults paly the secondary control in the generation of fractures during the late Hercynian and Himalayan periods. The 3-D finite element geo-mechanical numerical modelling and fracture density, aperture calculation methods are not only for carbonate fractures in the Hetianhe area, but also for the development of other reservoir fractures.

Mode coupling and competition in square-racetrack hybrid-cavity semiconductor lasers

We propose and demonstrate square-racetrack hybrid-cavity semiconductor lasers to achieve lasing mode control. Strong mode coupling between the modes of the square and racetrack cavities is predicted by finite element method numerical simulation and confirmed by experimental lasing spectra. Mode coupling leads to anti-crossing of the mode wavelengths, crossing of the mode quality factors, and hybrid modes with the field distributing in both square and racetrack cavities, and will affect the competition of lasing modes together with gain distribution induced by separately injected current of the two cavities. Single-mode lasing with a side-mode suppression ratio up to 38 dB and dual-mode lasing with an intensity ratio down to 1 dB are realized by tuning the injection current. Furthermore, increasing racetrack cavity size affects the mode competition process and results in racetrack-mode-dominated lasing for square-racetrack hybrid-cavity semiconductor lasers.

The differences between the measured heat flow and BSR heat flow in the Shenhu gas hydrate drilling area, northern South China Sea

Temperature is an important factor that affects the stability of a gas hydrate. To investigate the geothermal characteristics in the gas hydrate drilling area, heat flow measurements were performed in the surrounding area of the SH2 well. The measured heat flow was compared with the bottom simulating reflector heat flow, which was calculated by using the depth of the bottom simulating reflector in the seismic data. Combined with the geological background of the Shenhu drilling area, we analyzed the reasons for the differences between the measured heat flow and the bottom simulating reflector heat flow. In addition to analyzing the differences caused by the calculation parameters, we calculated the 3-D topographic effects on the measured heat flow by using the finite element numerical simulation method. The results show that the measured heat flow was seriously affected by the topography and produced a −50–30% error in the study area. After terrain correction of the measured heat flow, we found that the data were greater than the bottom simulating reflector heat flow at almost all sites. Therefore, we considered the impact of fluid activity and calculated the relationship among the thickness of the gas hydrate stability zone, the fluid flux and the heat flow. The results show that when the base of the bottom simulating reflector was at a certain depth, the geothermal gradient increased with the increasing upward migration of the fluid flux. Therefore, when upward fluid migration is present, the measured heat flow in the seafloor sediments is greater than the heat flow in the deep layers. In general, we showed that the influences of the topography and fluid activity are the main factors leading to the inconsistency between the bottom simulating reflector heat flow and the measured heat flow in the Shenhu gas hydrate drilling area.

A CMOS Pixelated Nanocapacitor Biosensor Platform for High-Frequency Impedance Spectroscopy and Imaging.

We describe the realization of a fully electronic label-free temperature-controlled biosensing platform aimed to overcome the Debye screening limit over a wide range of electrolyte salt concentrations. It is based on an improved version of a 90-nm CMOS-integrated circuit featuring a nanocapacitor array, readout and A/D conversion circuitry, and a field programmable gate array (FPGA)-based interface board with NIOS II soft processor. We describe chip's processing, mounting, microfluidics, temperature control system, as well as the calibration and compensation procedures to reduce systematic errors, which altogether make up a complete quantitative sensor platform. Capacitance spectra recorded up to 70MHz are shown and successfully compared to predictions by finite element method (FEM) numerical simulations in the Poisson-Drift-Diffusion formalism. They demonstrate the ability of the chip to reach high upper frequency of operation, thus overcoming the low-frequency Debye screening limit at nearly physiological salt concentrations in the electrolyte, and allowing for detection of events occurring beyond the extent of the electrical double layer. Furthermore, calibrated multifrequency measurements enable quantitative recording of capacitance spectra, whose features can reveal new properties of the analytes. The scalability of the electrode dimensions, interelectrode pitch, and size of the array make this sensing approach of quite general applicability, even in a non-bio context (e.g., gas sensing).

Effects of coarse aggregates on chloride diffusion coefficients of concrete and interfacial transition zone under experimental drying-wetting cycles

Chloride ions diffusion into concrete is one of the most significant factors for reinforced concrete (RC) structures exposed to marine environment, and this can deteriorate reinforcing steel in concrete and cause steel corrosion, ultimately, shorten the durability and serviceability of RC structures. In this paper, the in-door physical experiment method was adopted to explore the effects of natural coarse aggregate on chloride concentration profiles and diffusion behaviors for concrete specimens under man-made exposure condition of drying-wetting cycles. All investigations were based on 10 concrete mixture designs containing variable volume fractions and maximum sizes of natural coarse aggregate for maximum exposure period of 170 days. The chloride profiles versus exposure time, coarse aggregate volume fraction and maximum size were discussed in this paper. The time-dependent model of surface chloride concentration, and the multifactor model of chloride diffusion coefficient of concrete specimens included exposure time, volume fraction, and maximum size of coarse aggregate were developed based on the experimental measurements. In addition, an empirical prediction model for estimating the chloride diffusion coefficient of interfacial transition zone (ITZ) by the consideration of coarse aggregate was determined. Finally, the accuracy and reasonability of the two models of chloride diffusion coefficients for concrete and ITZ considering the effects of coarse aggregate were validated in terms of the meso-scopic finite element numerical simulation method for chloride diffusion into concrete.

Discussion on the Application of LS-DYNA in Superfine Grinding of Wheat Bran

Superfine grinding, involving the fragmentation mechanism of wheat bran cell tissue, is being employed by milling industry. In order to determine the effect of wheat bran cell tissue on the fragmentation mechanism when using superfine grinding, a technical scheme of the nonlinear finite element numerical simulation method based on LS-DYNA is proposed in this paper. The physiological characteristics of wheat bran structural layers including outer pericarp, intermediate layer and aleurone layer are examined first, and then the mechanical properties of wheat bran structural layers and their effects on the super fine grinding process are analyzed. Secondly, the explicit time integration algorithm of LS-DYNA is introduced, and the application feasibility of LS-DYNA in the analysis of wheat bran superfine grinding mechanism is discussed. Finally, the specific application of LS-DYNA in the determination of grinding form and load, the selection and design of the grinding media and the selection of grinding temperature are discussed in detail in the process of superfine grinding for wheat bran cell tissue. The above research provides a theoretical basis for selecting and developing the equipment and technology suitable for wheat bran superfine grinding, and lays a theoretical foundation for enhancing the quality and efficiency of wheat bran superfine grinding.Supported by National Natural Science Foundation - Henan Joint Fund Key Support Project (No. U1604254) and Open Subject of National Engineering Laboratory of Wheat & Corn Further Processing (No. NL2017010).

Ultrafast Anisotropic Exciton Dynamics in Nanopatterned MoS2 Sheets

We study the optical properties of an anisotropic ripple-shaped two-dimensional molybdenum disulfide (MoS2) nanosheet deposited by chemical vapor deposition onto a nanopatterned silica (SiO2) substrate. We unveil a giant anisotropic optical response in the linear and nonlinear regime by a combination of optical extinction measurements, ultrafast broadband transient absorption experiments, and finite element method numerical simulations. In steady state optical measurements, such anisotropy appears as a polarization-dependent extinction in correspondence with the characteristic excitonic peaks (A, B, C, and D) of MoS2. Along with spectral changes, ultrafast measurements strikingly exhibit the onset of an anisotropic relaxation dynamic in the region of the C exciton. Numerical simulations indicate that the observed polarization-dependent optical response is dictated by the nanopattering of MoS2, with peculiar features belonging to the out-of-plane component of the dielectric tensor of MoS2 that is made effective through the rippled configuration. Our findings give a rationale to the anisotropic exciton response and show that morphology manipulation represents a valuable option for the tuning of optical and electronic properties in transition-metal dichalcogenides.

Reliability Analysis of Sealing Structure of Electromechanical System Based on Kriging Model

The sealing performance of aircraft electromechanical system has a great influence on flight safety, and the reliability of its typical seal structure is analyzed by researcher. In this paper, we regard reciprocating seal structure as a research object to study structural reliability. Having been based on the finite element numerical simulation method, the contact stress between the rubber sealing ring and the cylinder wall is calculated, and the relationship between the contact stress and the pressure of the hydraulic medium is built, and the friction force on different working conditions are compared. Through the co-simulation, the adaptive Kriging model obtained by EFF learning mechanism is used to describe the failure probability of the seal ring, so as to evaluate the reliability of the sealing structure. This article proposes a new idea of numerical evaluation for the reliability analysis of sealing structure, and also provides a theoretical basis for the optimal design of sealing structure.

Research on the Anti-Cracking Performance of High Viscoelastic Tar Sands

The principle of fracture energy was put forward to evaluate the anti-cracking performance of high viscoelastic tar sands. To effectively reconstruct the anti-cracking performance of high viscoelastic tar sands, a semi-circular bending test was performed to measure the maximum load and fracture energy. The test results show that when the test temperature remains constant, the maximum failure load of the specimen increases along with loading rate, while the fracture energy of the specimen decreases along with increasing loading rate. Meanwhile, when the loading rate remains constant, the maximum failure load of the specimen decreases along with increasing temperature, while the fracture energy increases along with temperature. The test device is simple and cheap, while the test specimen is easy to manufacture. Therefore, the semi-circular bending test can be used as a standard method for testing the crack resistance design of asphalt mixture. A parameter sensitivity analysis is also conducted by using the ABAQUS finite element numerical simulation method. The experiment and numerical simulation results are compared to verify whether fracture energy can be used to evaluate the anti-cracking performance of high viscoelastic tar sands.

Programmable Multistable Mechanisms: Synthesis and Modeling

Compliant mechanisms can be classified according to the number of their stable states and are called multistable mechanisms if they have more than one stable state. We introduce a new family of mechanisms for which the number of stable states is modified by programming inputs. We call such mechanisms programmable multistable mechanisms (PMM). A complete qualitative analysis of a PMM, the T-mechanism, is provided including a description of its multistability as a function of the programming inputs. We give an exhaustive set of diagrams illustrating equilibrium states and their stiffness as one programming input varies while the other is fixed. Constant force behavior is also characterized. Our results use polynomial expressions for the reaction force derived from Euler–Bernoulli beam theory. Qualitative behavior follows from the evaluation of the zeros of the polynomial and its discriminant. These analytical results are validated by numerical finite element method simulations.

Tapered microelectrode array system for dielectrophoretically filtration: fabrication, characterization, and simulation study

This paper presents the fabrication, characterization, and simulation of microelectrode arrays system with tapered profile having an aluminum surface for dielectrophoresis (DEP)-based manipulation of particles. The proposed structure demonstrates more effective electric field gradient compared with its counterpart with untapered profile. Therefore, according to the asymmetric distribution of the electric field in the active region of microelectrode, it produces more effective particle manipulation. The tapered aluminum microelectrode array (TAMA) fabrication process uses a state-of-the-art technique in the formation of the resist’s taper profile. The performance of TAMA with various sidewall profile angles (5 deg to 90 deg) was analyzed through finite-element method numerical simulations to offer a better understanding of the origin of the sidewall profile effect. The ability of capturing and manipulating of the device was examined through modification of the Clausius–Mossotti factor and cross-over frequency (fx0). The fabricated system has been particularly implemented for filtration of particles with a desired diameter from a mixture of particles with three different diameters in an aqueous medium. The microelectrode system with tapered side wall profile offers a more efficient platform for particle manipulation and sensing applications compared with the conventional microelectrode systems.

On the mechanical properties of particle reinforced metallic glass matrix composites

In the present manuscript a modified coupled thermo-mechanical constitutive model is employed to describe the mechanical property of metallic glass (MG) matrix, and the geometrical models of particle reinforced MG matrix composites are established based on the inner structures. Then finite element method (FEM) numerical simulations on the mechanical properties of composites are conducted systemically by integrating with related experimental investigations, and the effects of different factors, including the volume fraction of particle (which determines the amount of particle and the interspace between particles), the mechanical property of particle material and the strain rate, on the deformation and failure characteristics of composites are analyzed. Related analysis demonstrates that the composite mainly displays as a shear manner, however, the reinforced particles can lead to an improvement for its plasticity. Furthermore, several internal and external factors have significant influences on the deformation and failure characteristics of composites. The corresponding mechanical properties depend firmly on the initiation and propagation of shear band and shear crack within the composite.

Studies on Pounding Response Considering Structure-Soil-Structure Interaction under Seismic Loads

Pounding phenomena considering structure–soil–structure interaction (SSSI) under seismic loads are investigated in this paper. Based on a practical engineering project, this work presents a three-dimensional finite element numerical simulation method using ANSYS software. According to Chinese design code, the models of adjacent shear wall structures on Shanghai soft soil with the rigid foundation, box foundation and pile foundation are built respectively. In the simulation, the Davidenkov model of the soil skeleton curve is assumed for soil behavior, and the contact elements with Kelvin model are adopted to simulate pounding phenomena between adjacent structures. Finally, the dynamic responses of adjacent structures considering the pounding and SSSI effects are analyzed. The results show that pounding phenomena may occur, indicating that the seismic separation requirement for adjacent buildings of Chinese design code may not be enough to avoid pounding effect. Pounding and SSSI effects worsen the adjacent buildings’ conditions because their acceleration and shear responses are amplified after pounding considering SSSI. These results are significant for studying the effect of pounding and SSSI phenomena on seismic responses of structures and national sustainable development, especially in earthquake prevention and disaster reduction.