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In Part I of this paper, quasi-static fracture toughness tests were reported which were carried out on two carbon fiber reinforced polymer materials. One laminate was unidirectional and the second was composed of plies fabricated from a twill fabric. In Part II, which is presented here, micro-computerized tomography was performed providing a relationship between the observed experimental behavior and the micromechanical structure of the materials. This was carried out for the double cantilever beam (DCB), mixed mode bending (MMB) and end-notched flexure (ENF) specimens. Load–displacement curves were simulated numerically by means of a cohesive zone model and the finite element method to obtain better insight into the failure mechanisms observed for DCB and ENF specimens. [Display omitted] • Quasi-static fracture toughness testing was reported on in Part I of this paper. • Micro-computerized tomography was carried out on many of the specimens. • Damage mechanisms on the micro-scale were assessed. • Numerical simulations were carried out by means of a cohesive zone model. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present the results of the prediction of the properties of PVD/CVD coatings with the use of finite element method (FEM) analysis. The possibility of employing the FEM in the evaluation of stress distribution in multilayer Ti/Ti(C,N)/CrN, Ti/Ti(C,N)/(Ti,Al)N, Ti/(Ti,Si)N/(Ti,Si)N, and Ti/DLC/DLC coatings by taking into account their deposition conditions on magnesium alloys has been discussed in the paper. The difference in internal stresses in the zone between the coating and the substrate is caused by, first of all, the difference between the mechanical and thermal properties of the substrate and the coating, and also by the structural changes that occur in these materials during the fabrication process, especially during the cooling process following PVD and CVD treatment. The experimental values of stresses were determined based on X-ray diffraction patterns that correspond to the modelled values, which in turn can be used to confirm the correctness of the accepted mathematical model for testing the problem. An FEM model was established for the purpose of building a computer simulation of the internal stresses in the coatings. The accuracy of the FEM model was verified by comparing the results of the computer simulation of the stresses with experimental results. A computer simulation of the stresses was carried out in the ANSYS environment using the FEM method. Structure observations, chemical composition measurements, and mechanical property characterisations of the investigated materials has been carried out to give a background for the discussion of the results that were recorded during the modelling process. [ABSTRACT FROM AUTHOR]

Piezoresistive pressure sensors with excellent performance are widely used in the field of biomedical engineering for measuring pressure, however, residual stress will be introduced in the process of repackaging and effect the performance of the sensor. The effect of residual stress on the repackaged pressure sensor is often neglected, but it will cause errors in measuring physiological signals. In this paper, effect of residual stress on the performance of a self-packaging pressure sensor (SPS) is analyzed by finite element analysis (FEA) and experiments. Through analysis of simulation results and experimental data, the material and structure of SPS are optimized. A reinforced plate is used in the self-packaging structure, which can solve the problem of stress induced by the self-packaging structure. Compared with the ordinary SPS, the effect of the self-packaging structure proposed in this paper is reduced by more than 80%; measurement accuracy of SPS in weak signal detection is significantly improved. [ABSTRACT FROM AUTHOR]

A numerical method is employed to investigate the fluid flowing dynamics in fractured reservoirs in this paper. Owing to the multi-scales and strong heterogeneity, description of fracture network systems plays a significant role for a successful fractured reservoir simulation model. Comparing to previous works, this paper proposes a combination of dual continuum and discrete fracture network (DFN) model, which is used to simulate the flow in reservoirs with multi-scale fractures and proved feasible. In the first part of the paper, implicit flow equations of oil and water phase in fractured reservoirs are established to consider the nonlinearity properties. And then the control volume finite element method based on the unstructured grid system and N-R iteration are used to obtain the numerical solution. Moreover, the accuracy of this simulator is proved to be reasonable by field data; Sensitivity analysis shows that the existences of complex multi-scale fracture networks have great impacts on water flooding. Compared with the homogeneous reservoir, natural fracture (micro and large scale) networks can change the direction and velocity of the waterfront, which finally leads to the more serious water breakthrough, higher water cut and less recovery. The research and the numerical results obtained in this paper can provide theoretical guidance for efficient and scale development of natural fractured reservoirs. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic explicit finite element (FE) simulation method to predict the highly nonlinear response of axially and rotationally restrained reinforced concrete (RC) beams at ambient temperature and in fire condition. Catenary action, developed during the large deflection behaviour of RC beams, is an important mechanism of resisting progressive collapse. This paper explains the numerical simulation challenges, including temporary instabilities, local failure of materials, non-convergence and long simulation time, and proposes methods to resolve these challenges. The effectiveness of the proposed simulation model is checked by comparison of the simulation results against relevant test results of restrained RC beams at ambient temperature and in fire. It has been found that using the explicit simulation method can follow the whole range behaviour of restrained RC beams until complete structural failure. Either load factoring or mass scaling may be used to speed up the simulation process. Damping can be applied to minimise significant dynamic effects following beam bending failure. This paper will give guidance on how to select the appropriate load factoring, mass scaling and damping values. [ABSTRACT FROM AUTHOR]

• A numerical simulation method for the multifactor coupling of stress field and temperature field is developed. • The numerical simulation method is in good agreement with the experiment results at elevated temperatures. • The numerical simulative description of the grout material failure and fracture of a steel bar. • Prediction of the yield point and the ultimate point of FGSC from 25 °C to 1000 °C. Fire is one of the main objects of study at the cutting edge of the research on disaster prevention and mitigation in structures. In the event of a fire, the mechanical properties of the structural material will be significantly reduced, resulting in serious consequences. This paper simulates the tensile properties of sleeve grouting members at five different temperatures, to contribute to the research here. The simulated member stress-strain curves fit well with the corresponding experimental results. The paper introduces constitutive models of concrete, steel, and sleeve. Beyond that, a feasible finite element model of the grouted sleeve is proposed. Two special points' (yield point, ultimate point) coordinate formulas which are related to different temperatures (25–1000 °C) are presented. It indicates the regularity of fully-grouted sleeve tensile force-displacement curves in various temperatures. Meanwhile, the research content provides the basis for further research on reinforcing bars spliced by grout-filled coupling sleeves. [ABSTRACT FROM AUTHOR]

• The lattice structure construction method based on finite element mesh is proposed. • The optimization design method of heterogeneous lattice structure for additive manufacturing based on MIST method is proposed. • The lattice structure construction and optimization problem realized by using parametric language APDL. With the improvement of lightweight demand and the development of additive manufacturing technology, the manufacturing of complex lattice structure is made possible, and the construction of complex lattice structure is became more and more important. However, the existing commercial software will have the phenomenon of boundary cell damaged when realizing lattice structure for curve and surface graphics. Being aimed at the problem of boundary unit cell damage in the construction of large-scale lattice structure, this paper proposes a lattice structure construction method based on finite element mesh. Through the description of the parameterization, implementation principle and specific process of lattice structure, and finally compared with the existing commercial software inspire, the result is shown that this method is better than the lattice structure construction problem of commercial software, It also is solved the problem of boundary cell damage in the construction of large-scale lattice structure. In addition, many studies show that the optimized heterogeneous lattice structure is had better mechanical performance. In this paper, a method for optimizing the cross-sectional area of lattice members is proposed based on the mist method. In two-dimensional and three-dimensional numerical examples, the total volume strain energy of the lattice structure has been improved by more than 60% in theory. [ABSTRACT FROM AUTHOR]

• A finite element model was built for simulating the leaf wrapping around the roller. • The deviation value was used as the indicator of wrapping degree in the simulation. • The leaf wrapping around the rotating roller composed of four stages. • The wrapping characteristics was analyzed based on finite element method and orthogonal method. In order to solve the problem of wrapping between sugarcane leaves and rotating roller of returning the machine, the length of rotating rollers (A), the number of bulges (B), and the leaf quantity (C) were taken as influence factors in this paper. A finite element model was built to simulate the process of the leaf wrapping around the rotating roller. Through the simulation analysis of the deviation value and the wrapping time, the results showed that: (1) these factors all had an influence on the wrapping degree by comparing the average deviation value; (2) there were four stages in the wrapping process; (3) the longer the roller length, the more the number of bulges, and the less the leaf quantity, causing the less the wrapping time. In addition, a test system was designed and constructed, and the model was validated using single-factor tests compared with simulation results. The results of the experiment using the orthogonal test method, range method, variance method, and comprehensive balance method showed that: (1) the priority order of these factors was B > C > A; (2) the effects of these factors were all significant; (3) the best wrapping combination was A 1 B 2 C 4 ; and the best anti-wrapping combination was A 4 B 4 C 1. This paper not only provides a reliable finite element model of the leaf wrapping around the rotating roller, but also provide a foundation for the optimization and improvement of the rotating roller's anti-wrapping characteristics. [ABSTRACT FROM AUTHOR]

Aluminium alloy has recently become popular in New Zealand's construction sector as a sustainable building material. However, in roll-formed aluminium alloy (RFA) channel beams, particularly those having web holes, cripples at points of concentrated or localised loading. In this paper, end-two-flange (ETF) web crippling behaviour of RFA unlipped channels having web holes was investigated using experimental tests, numerical simulations and a deep learning model referred as deep belief network (DBN). A total of 1080 data points was generated to train the DBN, using a finite element (FE) model that was validated using 30 new experimental results reported in this paper. Compared to the test data, the DBN predictions were conservative by around 6%. Using the DBN predictions, a comprehensive parametric study was undertaken which used the validated FE model in order to explore the effects of hole size, hole location, section thickness, and bearing plate on the web crippling strength of RFA channels having web holes. Web crippling strengths obtained from the DBN, tests and finite element analysis (FEA) were utilised to evaluate the performance of current design specifications from the American Iron and Steel Institute (AISI), Australian/New Zealand Standards (AS/NZS 1664; AS/NZS 4600:2018) and Eurocode (CEN 2006, 2007). It is shown that the current design rules are not reliable to predict the web crippling strength of RFA unlipped channels with web holes. As a consequence of the parametric analysis, new web crippling strength and web crippling strength reduction factor formulae for perforated RFA unlipped channels were proposed. A reliability analysis was then conducted, which confirmed that the proposed equations are capable of predicting the ETF web crippling strength of perforated RFA unlipped channels. • ETF web crippling behaviour of roll-formed aluminium alloy channels was studied experimentally and numerically. • Finite element analysis was conducted and validated against test results. • A deep-learning model was developed to predict the web crippling strength. • A parametric study was conducted to investigate the effects of different parameters. • New design equations were proposed for web crippling strength of roll-formed aluminium alloy channels. [ABSTRACT FROM AUTHOR]

Highlights • Integrated thermal protection structures, inspired by Norway spruce, were designed. • Thermal behaviors of those structures were investigated by finite element method. • The thermal conductivity of SLM-processed Ti6Al4V ITP structures was measured. • The simulation results were consistent with the measured thermal conductivity. Abstract With the development of hypersonic vehicles and reusable launch vehicles, the design of integrated thermal protection (ITP) structures needs to meet the demanding requirement of thermal protection. More complex geometries, such as lattice structures and bio-inspired structures, have been introduced into the design of ITP structures, aiming to enhance the thermal protection performance. Additive manufacturing holds high flexibility in processing and enables more complex designs, which is suitable for the fabrication of complex ITP structures. In this paper, inspired by the structures of Norway spruce stem, a series of ITP structures with different gradient hollow designs was proposed and manufactured by selective laser melting (SLM). The steady-state and transient thermal behavior of those bio-inspired ITP structures were investigated by finite element method (FEM). To verify the accuracy of the FEM simulation results, Ti6Al4V components with different bio-inspired ITP structures were fabricated by SLM and thermal conductivities of those SLM-processed components were experimentally measured. The FEM thermal simulation revealed that the gradient-structure with larger hollow tubes near the top and bottom plates and smaller hollow tubes in the center possessed the lowest bottom surface temperature of 262.8 °C, which was 21.4 °C lower than the structure with the highest bottom surface temperature. The thermal conductivity measurement revealed that the gradient-structure, with the lowest bottom surface temperature obtained by FEM thermal simulation, had the lowest thermal conductivity of 2.321 W/(m⋅K), which was about 29% lower than that of the structure possessing the highest thermal conductivity. [ABSTRACT FROM AUTHOR]

• A new test specimen for simulating rock pipe jacking has been designed. • The frictional law under seven complex contact condition has been analyzed. • A three-dimensional simulation method for pipe jacking has been studied in ADINA. • The causes of the sudden drastic increase in jacking force have been verified in the study area. In ultra-long-distance rock micro-shield pipe jacking, the pipe wall friction resistance is a key factor that determines the magnitude of the jacking force and the layout of the intermediate jacking stations (IJSs), whereas the pipe-rock contact condition is the critical factor controlling the pipe string wall friction resistance. This paper aims to reveal the variation law of the friction resistance between the outer wall of a large-section of concrete pipe string and the surrounding rock during construction via ultra-long-distance rock micro-shield pipe jacking. To that end, the shear friction behaviour and mechanical mechanism was investigated between sandstone and concrete pipe string walls under seven different complex contact conditions (primarily considering various combinations of the three substances, namely, extra-pipe in situ debris, bentonite slurry and sand-laden waste mud at the pipe-rock contact surface) through direct rock shear tests based on the actual pipe-rock contact condition at the Guanjingkou Water Conservancy Project in Chongqing. The average friction coefficient (AFC) of the residual phase of the contact surface under 7 contact conditions was obtained by friction testing. Combined with the contact situation between the surrounding rock and pipe strings at the stage of a rapidly increasing jacking force, a three-dimensional finite element model was established, and the displacement control method was used to simulate the jacking. The comparison with the field monitoring results shows that the numerical model can accurately predict the jacking force and verify the reliability of the AFC parameters in the numerical calculation. Therefore, the combination of indoor testing and the finite element method can be applied to study the jacking force for other ultra-long rock micro-shield pipe jacking applications. [ABSTRACT FROM AUTHOR]

• Two benchmarks are presented, for the validation of modelling/simulation aspects of stiffened panels subjected to buckling effects. • Different numerical strategies are presented to properly model the unstable behavior of the panels, including path-following approaches, geometric and material nonlinear effects. • The models account for initial geometric imperfections coming from friction stir welding joining operations. • Modelling and simulation guidelines are presented for subsequent researchers involved in the design process of stiffened panels for aeronautic applications. This work deals with the effective modelling and simulation of the behavior of stiffened panels, when subjected to compressive (buckling) loads. Within the Finite Element Method, two numerical strategies are compared, namely the Riks method and the displacement incremental control method, including damping effects. The capabilities and limitations of both approaches are explored for two distinct benchmarks: a panel with a blade stiffener, and a panel with a T shaped stiffener. In both cases, material (plasticity) and geometrical (large displacements) nonlinearities are considered, together with a modelling strategy based on shell elements. Following previous works of the authors, each panel accounts for initial geometric imperfections coming from friction stir welding joining operations. The paper shows a number of considerations that must be undertaken when choosing between one of the two modelling strategies. Both benchmarks involve a number of challenges from the point of view of modelling unstable structural behaviors, and therefore the proposed benchmarks can represent a valid set of case studies in the understanding of the capabilities of current numerical simulation codes. [ABSTRACT FROM AUTHOR]

• A FEM model is established based on modified Boussinesq equations to simulate wave propagation and breaking. • The incident wave heights increase for different periods to catch different kinds of wave breaking. • Oblique regular and irregular incident waves and multidirectional waves are considered. • The initial breaking threshold parameter should take different values for oblique and multidirectional waves. Creating a representative numerical simulation of the propagation and breaking of waves along slopes is an important problem in engineering design. Most studies on wave breaking have focused on the propagation of normal incident waves on gentle slopes. In practice, however, waves on steep slopes are obliquely incident or multidirectional irregular waves. In this paper, the eddy viscosity term is introduced to the momentum equation of the improved Boussinesq equations to model wave dissipation caused by breaking and friction, and a numerical model based on an unstructured finite element method (FEM) is established based on the governing equations. It is applied to simulate wave propagation on a steep slope of 1:5. Parallel physical experiments are conducted for comparative analysis that considered a large number of cases, including those featuring of normal and oblique incident regular and irregular waves, and multidirectional waves. The heights of the incident wave increase for different periods to represent different kinds of waves breaking. Based on examination, the effectiveness and accuracy of the numerical model is verified through a comprehensive comparison between the numerical and the experimental results, including in terms of variation in wave height, wave spectrum, and nonlinear parameters. Satisfactory agreement between the numerical and experimental values shows that the proposed model is effective in representing the breaking of oblique incident regular waves, irregular waves, and multidirectional incident irregular waves. However, the initial threshold of the breaking parameter η t (I) takes different values for oblique and multidirectional waves. This needs to be paid attention when the breaking of waves is simulated using the Boussinesq equations. [ABSTRACT FROM AUTHOR]

In this paper, the chemotaxis partial differential equations models which describe the movement by one community in reaction to one chemical or biological signal are given and solved numerically on surfaces. The models and the numerical method concerned are in terms of a generic form of chemotaxis models. We develop a new semi-implicit finite element scheme based on the gradient and Laplacian recoveries to linearize the equations. Meanwhile, we modify the proposed semi-implicit scheme as a characteristic form and present a novel strategy for the discretization of characteristic derivative on surface. The lumped mass modification is employed for positivity preservation. And the related analysis results are provided. We investigate the accuracy and convergence of the proposed method by numerical tests. And the simulations of blowing-up solution, pattern formulations and aggregations of bacteria demonstrate the applicability of the proposed methods. [ABSTRACT FROM AUTHOR]

Highlights • Ballistic impact tests on 4 mm thick Weldox 700 E steel plates struck by blunt rigid projectiles were conducted and a failure mode of shear plugging was identified in the tests. • The strength and fracture models of the steel were calibrated using a hybrid experimental-numerical method. • FE simulations were carried out by using either a modified version of the Johnson-Cook (MJC) fracture criterion or the Lode dependent Modified Mohr–Coulomb (MMC) fracture criterion. • FE simulations using the MJC and MMC fracture criteria predicted almost the same ballistic performance of the targets. • For targets of Lode dependent fracture, FE simulations showed that the Lode dependent fracture criterion would predict a much lower ballistic limit for less ductile targets. However, for targets with high ductility, introducing the Lode angle into the fracture criterion would not obviously alter the ballistic limit prediction. Abstract The necessity of incorporating the Lode angle into a fracture criterion in predicting ballistic resistance of ductile metal plates has not been well elucidated so far although the ductility of a metal may be Lode dependent. In this paper, 4.0 mm thick Weldox 700 E steel plates were fired by 5.95 mm diameter blunt rigid projectiles in a one-stage gas gun in the impact velocity range of 141.2 m/s∼275.7 m/s. A failure mode of shear plugging was observed in the test and the ballistic limit was obtained by fitting the initial-residual velocity data. An axisymmetric finite element (FE) model corresponding to the test was built in ABAQUS and then was utilized to predict the ballistic resistance and fracture behavior of the targets. In the FE model, a slightly modified Johnson-Cook constitutive relation was companied by either a Lode independent modified Johnson-Cook (MJC) or the Lode dependent modified Mohr–Coulomb (MMC) fracture criterion. The plasticity and fracture of the metal were fully calibrated by a series of mechanical tests under varying stress states, strain rates and temperatures. According to the tests and parallel FE simulations, it was found that the fracture of Weldox 700 E is obviously Lode dependent. However, ballistic simulations using the MMC and MJC fracture criterion predicted very close ballistic limit velocity and similar shear plugging failure mode when compared with the test results. The dominant stress state of the material failed in the process of shear plugging was revealed by detailed FE analysis and it was found that the ductility of the metal is quite different on the dominant stress state according to the two fracture criteria. To interpret the current simulation results, further FE simulations were carried out on fictitious metals and it was found that for less ductile metallic plates the MMC fracture criterion predicts a much lower ballistic limit velocity (as much as 22%) when compared with the simulation result from the MJC fracture criterion. In contrast, for metal plates with high ductility, the simulations from the two different fracture criteria would produce quite close ballistic limit velocity predictions. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a type of wide band micro-perforated panel (MPP) absorber with an array of parallel arranged sub-cavities at different depths based on the quadratic residue sequence (QRS). An analytical prediction model is proposed for evaluating the normal incidence sound absorption coefficients of this type of MPP absorber in its design stage. Next, simulations with a finite element procedure and experimental measurements were conducted to provide cross-validations of the proposed analytical model and to facilitate the discussions on the sound absorption performance of this type of MPP absorber. The results show that the analytical model provides simple yet accurate prediction on the sound absorption performance of this MPP absorber; the absorption bandwidth of this type of MPP absorber can be significantly enhanced through the fine design on the sub-cavity depth sequence. It is also shown that the normal incidence absorption coefficient of this type of MPP absorber can remain beyond 0.5 in the frequency range of 450–3500 Hz, with the maximum value of 0.98. [ABSTRACT FROM AUTHOR]

Abstract The scaled boundary finite element method (SBFEM) coupled with the finite element method (FEM) for the simulation of the interaction problem between the elastic plate structure and the multi-layered unbounded elastic soil is first developed in this paper. First, the whole system is subdivided into three sub-domains, including the semi-infinite far-field system, the near-field sub-domain, and the plate structure. The far field of the soil is modeled by utilizing the modified scaled boundary finite element method with a scaling line instead of the scaling center used in the traditional SBFEM. In the traditional SBFEM, only the boundary is discretized with surface elements, so the spatial dimension is reduced by one, and the final governing equation can be solved analytically in the radial direction of the scaled coordinate system, and it can exactly meet the infinite domain problem. The stiffness matrix of the three-dimensional (3D) near field is obtained using the standard FEM. The SBFEM is also applied in order to simulate the deformation characteristics of the plate structure based on the 3D elastic equation without introducing any assumption of the thin plate theory, and the high-order spectral element is introduced in order to discretize the middle surface of plate so that the complicated curved boundaries can be better represented. Then, according to the principle of the degree of freedom matching at the same node, the global stiffness matrix of the plate-soil system can be obtained by coupling the stiffness matrices of the sub-domains at the far-field/near-field interface, as well as at the plate/near-field interface. Thus, the response of the whole system under the external load can be solved naturally. Four numerical examples, consisting of a square plate resting on an isotropic soil, multi-layered soil with weak and thin interlayer, a plate with a different geometrical shape and a square plate with a hole, are provided in order to validate the accuracy and versatility of the proposed formulations. [ABSTRACT FROM AUTHOR]

Abstract This paper deals with the link between the acoustic activity due to damage in wound composite structures and the simulated evolution of damage variables. A damage model able to accurately capture the different degradation modes which may occur in this type of material is first selected. A parallel is drawn between the continuous evolution of the damage variables and the discrete acoustic events. The mechanical behaviour of notched samples made of two different wound composite lay-ups and involving complex damage combinations are simulated and compared to acoustic emission. The satisfactory correlation confirms the physical meaning of the damage variables and validates the model assumptions. The association of experimental acoustic signals and a damage model is a tool to understand the degradation scenario of wound composite structures and the meaning of the recorded acoustic events. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an on-line variable-fidelity surrogate-assisted harmony search algorithm (VFS-HS) for expensive engineering design optimization problems. VFS-HS employs a novel model-management strategy that uses a multi-level screening mechanism based on non-dominated sorting to strictly control the numbers of low-fidelity and high-fidelity evaluations and to keep a balance between exploration and exploitation. The performance of VFS-HS is validated through comparison not only to those of four single-fidelity surrogate-assisted optimization methods (i.e. the particle swarm optimization algorithm with radial basis function-based surrogate (OPUS-RBF), the two-layer surrogate-assisted particle swarm optimization algorithm (TLSAPSO), the surrogate-assisted hierarchical particle swarm optimization (SHPSO) and the hybrid surrogate-based optimization using space reduction (HSOSR)) but also to that a multi-fidelity surrogate-assisted optimization method (the multi-fidelity Gaussian process and radial basis function-model-assisted memetic differential evolution (MGPMDE)) on the CEC2014 expensive optimization test suite. A real-world problem of the optimal design for a long cylindrical gas-pressure vessel is also investigated. The results show that VFS-HS outperforms all the compared methods. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a new polymorphic element modelling approach for multi-scale simulation, with an application to fracture in composite structures. We propose the concept of polymorphic elements; these are elements that exist as an evolving superposition of various states, each representing the relevant physics with the required level of fidelity. During a numerical simulation, polymorphic elements can change their formulation to more effectively represent the structural state or to improve computational efficiency. This change is achieved by transitioning progressively between states and by repartitioning each state on-the-fly as required at any given instant during the analysis. In this way, polymorphic elements offer the possibility to carry out a multiscale simulation without having to define a priori where the local model should be located. Polymorphic elements can be implemented as simple user-defined elements which can be readily integrated in a Finite Element code. Each individual user-defined polymorphic element contains all the relevant superposed states (and their coupling), as well as the ability to self-refine. We implemented a polymorphic element with continuum (plain strain) and structural (beam) states for the multiscale simulation of crack propagation. To verify the formulation, we applied it to the multiscale simulation of known mode I, mode II andmixed-mode I and II crack propagation scenarios, obtaining good accuracy and up to 70% reduction in computational time —the reduction in computational time can potentially be even more significant for large engineering structures where the local model is a small portion of the total. We further applied our polymorphic element formulation to the multiscale simulation of a more complex problem involving interaction between cracks (delamination migration), thereby demonstrating the potential impact of the proposed multiscale modelling approach for realistic engineering problems. Highlights • New polymorphic Floating Node Method for multiscale analysis. • Element-level management of coupling between scales. • Location and extent of high-fidelity scale able to evolve during analysis. • Implementation of VCCT and CZM within polymorphic elements for multi-scale failure analysis of composite structures. [ABSTRACT FROM AUTHOR]

Highlights • An intrinsic cohesive zone approach is proposed for the impact failure of automotive windshield laminated glass. • Gradual energy dissipation process of glass-PVB debonding can be modeled by means of the cohesive zone model. • A windshield finite element model is developed to account for the two failure patterns, including glass fracture and glass-PVB debonding. • The effectiveness of the proposed model is validated by comparing simulation results under center and corner impact with experimental ones. • Parametric studies are conducted to investigate the effects of adhesion parameters, PVB material parameters, and impact velocities and angles on the impact fracture behavior and energy absorption performance of the windshield. Abstract Though windshield laminated glass is a simple sandwiched composite structure, it is of vital importance to investigate its damage and energy absorption behavior for the purpose of pedestrian safety protection. This paper proposes an intrinsic cohesive zone approach to achieve this end. A finite element windshield glazing model is established by inserting cohesive elements into the common surfaces between glass elements, and the interfaces between glass and PVB prior to simulations. The appeal of this model is that both of the two main failure patterns and their energy absorptions, i.e. glass fracture and glass-PVB debonding, of the windshield can be captured by means of the intrinsic cohesive zone approach. The effectiveness of the proposed model is validated by comparing the simulation results under center and corner impact with the corresponding experimental outcomes. Finally, the effects of adhesion parameters, PVB material parameters, and impact velocities and angles on the impact fracture behavior and energy absorption performance of the windshield are thoroughly investigated. [ABSTRACT FROM AUTHOR]

Highlights • Definition of different techniques to simulate the shock environment measured during a qualification test by mechanical impact of a space instrument. The simulations are performed with the finite element method (FEM). • Some of the proposed FEM techniques take into account complex aspects in the definition of the input levels such as the non-uniformity in the acceleration field at the mechanical interface of the tested instrument and the non-negligible cross input levels found during the shock test. • Comparison of the simulations results obtained from each proposed technique with shock test data to determine the accuracy. Abstract Space instruments must be structurally verified to confirm their capability to withstand the severe vibrations and shock environments during the launch phase. The shock loads are caused by the pyrotechnic devices employed for the separation between the launcher stages and for the release of the fairing and the spacecraft. The most recommended verification method for shocks is by testing, which can be performed by different test methods such as electrodynamic shakers, mechanical impact shock machines or pyrotechnic devices. Recently, numerical shock simulations have been incorporated as a part of the structural verification of the space instruments with the aim of providing additional information that cannot be easily obtained from test data. One of most determining aspects to simulate the same environment measured during a shock test by mechanical impact is the definition of the input acceleration, which may be non-uniform and with non-negligible cross levels. The objective of this paper is to propose new techniques that define with precision the input acceleration field measured in the shock test considering the mentioned aspects for the shock simulations by the finite element method. The analyses are performed with the finite element (FE) model of the space instrument STEP of the Solar Orbiter mission and the results are compared with the shock test data to evaluate the improvement of the accuracy achieved from the shock simulations with the different proposed methods. [ABSTRACT FROM AUTHOR]

Highlights • The radial impact test is simulated, for a number of different aluminium wheels, by means of a finite element model. The model includes tyre, wheel, striker and supporting structure. The actual structure of the tyre is modelled. • A wheel instrumented with strain gauges has been used to validate the finite element model. An additional set of four families of different wheel types, equipped with different tyres, has been considered to enlarge the validation activity. • The modelling approach has proved to be effective in reproducing the final plastic deformation of the wheel and thus to predict the compliance of the wheel design with the requirements coming from standards. Abstract Safety is a crucial issue for automotive wheels, normally subject to severe dynamic working conditions. Severe indoor tests have been conceived and standardised to guarantee the required safety standards of vehicle wheels. This paper is devoted to the analysis and virtual simulation of the radial impact test of aluminium wheels, one of the most severe tests the wheel has to pass before production. The radial impact test is simulated, for a number of different aluminium wheels, by means of a finite element model. The model includes tyre, wheel, striker and supporting structure. The actual structure of the tyre is modelled. Tyre damping is included through a Rayleigh model, whose parameters are experimentally identified. The wheel material inhomogeneity is taken into account by assigning different stress/strain curves to wheel rim and spokes. A wheel instrumented with strain gauges has been used to validate the finite element model. An additional set of four families of different wheel types, equipped with different tyres, has been considered to asses the experimental variability and to compare the outputs of the corresponding impact models realized by the same procedure. The finite element model of the radial impact test has proven to be effective in reproducing the final plastic deformation of the wheel and thus to predict the compliance of the wheel design with the requirements coming from standards. [ABSTRACT FROM AUTHOR]

Highlights • Numerical simulation to describe the aqueous humor flow in the anterior chamber. • Numerical simulation to describe the aqueous humor flow in Schlemms canal. • Influence of position of the collector channels on the pressure in Schlemms canal. • Relation between intraocular pressure and the number of closed collector channels. Abstract Glaucoma is a progressive and a degenerative eye disease that gradually deteriorates the vision. The origin of glaucoma is still under debate. Recent studies report that 50% of the aqueous humor outflow resistance resides on collector channels and Schlemm's canal (SC). This paper provides a descriptive analysis of the aqueous humor outflow through the anterior chamber, the trabecular meshwork (TM) and the SC. The aim of this work is to determine the influence of the collector channels position on the intraocular pressure (IOP) and its contribution to the development of glaucoma. Pressure and wall shear stress distributions are presented for four cases. The first case has an arrangement of collector channels according to micro CT (Gong and Francis, 2014). The remaining cases have an symmetrical distribution; case 2 has all open quadrants (AOQ), cases 3 have three quadrants completely open and just one quadrant semi closed (SCQ), and finally cases 4 consider that a quadrant is completely closed (CQ). Symmetrical and micro CT cases have 29 collector channels. The results show that the position and the opening of the collector channels have a strong influence on the IOP. [ABSTRACT FROM AUTHOR]

Abstract In the literature, the plane-strain assumption usually forms the basis of inverse analyses of excavations, mainly due to the high computational cost of 3D analyses. In this paper, a procedure that quantifies three-dimensional effects of excavation is proposed. Such three-dimensional effects are represented as an uncertainty term that corrects plane-strain-based predictions, thereby offering an alternative approach to perform 3D inverse analysis without excessive computations. The results of an inverse analysis performed on an excavation case history show that (i) the procedure is able to quantify three-dimensional effects reasonably well and (ii) improved predictions of excavation field responses can be obtained. [ABSTRACT FROM AUTHOR]

Abstract It is important to account for inherent variability in the material properties in the design and analysis of engineering structures. These properties are typically not homogeneous, but vary across the spatial coordinates within a structure, as well as from specimen to specimen. This form of uncertainty is commonly modelled using random fields within the Stochastic Finite Element Method. Simulation within this framework can be complicated by the dependence of a random field's correlation function upon the geometry of the domain over which it is defined. In this paper, a new method is proposed for simulating random fields over a general two-dimension curved surface, represented as a finite element mesh. The covariance function is parametrised using the geodesic distance, evaluated using the solution to the 'discrete geodesic problem,' and a point discretisation approach is subsequently applied in order to sample the random field at the nodes of the model. The major contribution of the present work is the development of a methodology for simulating random fields over curved surfaces of arbitrary geometry, with a focus upon non-intrusive application to industrial finite element models using 'off the shelf' commercial software. In order to demonstrate the potential impact of the proposed approach, the algorithm is applied in an uncertainty quantification case study concerning vibration and buckling of an industrial composite aircraft wing model. [ABSTRACT FROM AUTHOR]

Abstract In this work, we present and analyze a new weak Galerkin (WG) finite element method for the Brinkman equations. The finite element spaces which are made up of piecewise polynomials are easy to be constructed. Especially, the variational form considered in this work is based on two gradient operators. The stability, priori error estimates and L 2 error estimates for velocity are proved in this paper. In addition, we prove that the new method also yields globally divergence-free velocity approximations. The convergence rates are independent of the Reynolds number, thus the new WG finite element method is efficient for both the Stokes and Darcy equations dominated. Finally, numerical results illustrate the performance of the method and support the theoretical properties of the estimator. [ABSTRACT FROM AUTHOR]

Abstract This paper describes the dynamic behaviour of a composite beam rotating at a constant angular velocity excited by an MFC (Macro Fiber Composite) actuator. The beam has a rectangular cross-section and is made of six plies of a unidirectional glass-epoxy laminate. The laminate has ply orientation of [45/−45/90]s. The MFC (Macro Fiber Composite) active element and a resistance strain gauge were fixed on the opposite sides of the beam surface. The role of piezoelectric actuators is to generate an additional effect to excite the system. The problem was solved by the finite element method, and selected cases were verified experimentally. The numerical solution is obtained with an implicit method. A numerical model of the rotating beam excited by the MFC activator was developed. To this end, a commercial Abaqus software package was used. This model consisted of a non-deformable hub and a laminated beam with an actuator whose complex structure was replaced with a substitute model verified in previous static and dynamic studies. Two cases are considered in detail: (a) the MFC actuator is powered with harmonic voltage and (b) the source of excitation is a harmonic transverse force at the free end of the beam. Both variants were examined with a constant rotational speed modelled as a centrifugal force acting on the blades. In all numerical simulations, the system response at a selected point on the blade was measured. As a result, resonance curves were obtained for selected variants of excitation. After that, we conducted our own experimental tests of the beam excited by the MFC activator powered by variable harmonic voltage. The dynamic response of the system, i.e. displacement, was recorded in real time with a laser sensor. The experimental results were plotted as amplitude-frequency characteristics for different amplitude of the activator voltage. The results of experimental tests and numerical simulations show very high agreement. [ABSTRACT FROM AUTHOR]

Abstract This paper was dealt with buckling and post-buckling behavior of short thin-walled Z-columns made of a carbon-epoxy laminate, subjected to eccentric compressive load. The buckling mode and the buckling load of real structures versus load eccentricity were discussed. The study involved both experimental tests were carried out on real laminated structures and numerical simulations by the finite element method. The buckling load of real structures was determined by approximation methods on the basis of experimental and numerical post-buckling equilibrium paths of the structure. Additionally, in numerical simulations, the bifurcation load value was determined by solving an eigen problem. In all cases, experimental findings and numerical results show high agreement. The study determined the quantitative influence of the direction and value of compressive load eccentricity on the buckling load and rigidity of the structure in the post-buckling state. [ABSTRACT FROM AUTHOR]

Abstract Convective seepage flow plays a key role not only in naturally forming mineral deposits and oil reservoirs, but also in the carbon-dioxide sequestration in fluid-saturated rocks. This paper presents a steady-state numerical solver, which is based on the finite element method (FEM) and progressive asymptotic approach procedure (PAAP), to solve steady-state convective seepage flow problems in fluid-saturated heterogeneous rocks. Although this kind of flow problem is commonly solved by using transient-state numerical solvers, the use of the proposed steady-state numerical solver, which is the main characteristic of this study, can have certain advantages. After the proposed steady-state numerical solver is verified by a benchmark testing problem, for which analytical solutions are available for comparison, it is further applied to simulate steady-state convective seepage flow in the Australia North West Shelf basin, which is composed of naturally-formed heterogeneous porous rocks. Through the simulated numerical results, it can be found that: (1) compared with the analytical solutions of the benchmark testing problem, the use of the steady-state numerical solver can produce correct and accurate numerical simulation results for dealing with convective seepage flow problems in fluid-saturated heterogeneous rocks. (2) The main advantage of using the steady-state numerical solver is to avoid the need of considering initial conditions of the problem, which are commonly difficult to be determined because the convective seepage flow within the upper crust is a past event in geology. (3) In the Australia North West Shelf basin, the convective seepage flow and temperature distribution patterns depend strongly on both the permeability contrast of the faults and the basin geometry (including the layer structures and fault locations) in the computational model. Highlights • To present and verify the numerical method for modeling large-scale convective seepage flow in heterogeneous rocks. • To simulate large-scale convective seepage flow in the Australia North West Shelf basin. • Rock permeability heterogeneity can affect large-scale convective seepage flow and temperature patterns. • Basin geometry can also affect large-scale convective seepage flow and temperature patterns. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a novel triangular closed-chain soft rolling robot. The proposed robot uses the least number of soft actuators (i.e. three) among current closed-chain soft rolling robots and can achieve faster rolling locomotion. To verify its feasibility in theory, we build a state-space model for simulating its rolling locomotion based on the continuum deformation and the rolling dynamics. Different from previous pseudo-rigid and finite element models, this model is fully analytical and continuous. To validate this model, we conduct experiments of rolling locomotion with a prototype constructed by three Curl Pneumatic Artificial Muscles (CPAMs). The results show that the proposed robot can roll forward with an average velocity of 20–21 mm/s on level ground and 12–13 mm/s on 8° inclined ground. The error of the mass center trajectories and average velocities between the simulation and experiment is within 10%. The proposed soft robot can be expanded into parallel or tetrahedron morphology to enable the steering movement, and it has potential applications in the space exploration and medical operation. [ABSTRACT FROM AUTHOR]

Abstract In this paper we propose a new, purely algebraic, Petrov–Galerkin reduced basis (RB) method to solve the parametrized Stokes equations, where parameters serve to identify the (variable) domain geometry. Our method is obtained as an algebraic least squares reduced basis (aLS-RB) method, and improves the existing RB methods for Stokes equations in several directions. First of all, it does not require to enrich the velocity space, as often done when dealing with a velocity–pressure formulation, relying on a Petrov–Galerkin RB method rather than on a Galerkin RB (G-RB) method. Then, it exploits a suitable approximation of the matrix-norm in the definition of the (global) supremizing operator. The proposed method also provides a fully automated procedure to assemble and solve the RB problem, able to treat any kind of parametrization, and we rigorously prove the stability of the resulting aLS-RB problem (in the sense of a suitable inf–supcondition). Next, we introduce a coarse aLSRB (caLSRB) method, which is obtained by employing an approximated RB test space, and further improves the efficiency of the aLSRB method both offline and online. We provide numerical comparisons between the proposed methods and the current state-of-art G-RB methods. The new approach results in a more convenient option both during the offline and the online stage of computation, as shown by the numerical results. [ABSTRACT FROM AUTHOR]

Abstract Remote handling of heavy in-vessel components inside nuclear fusion reactors requires the use of large robotic mechanisms, whose numerical analysis is highly complex. As a matter of fact, these robots are subject to large deformations, either induced by the geometric configuration of their mechanical structure or by the heavy payloads they usually transport. This work was motivated by the need of deriving physical-based predictive models able to simulate the mechanical behavior of such large robotic mechanisms, while performing dynamic tasks. The method formulates the dynamics of robotic manipulators on a Lie group, and uses a finite element procedure to discretize the flexible bodies. The method is applied to a complex mechanism, the serial/parallel flexible manipulator which has been recently selected for DEMO blanket remote handling. The case studies investigated in this paper involve the simulations of this manipulator while handling the inboard and outboard blanket segments according to the sequence of maneuvers planned for their removal processes from the vessel. The results show that such dynamic simulations could give useful information for design, analysis and control of remote handling equipment. The generality of the method makes this approach prone to be easily used in simulating the dynamics of other flexible manipulators for remote handling of large in-vessel components inside nuclear fusion reactors. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a simulation technique to predict the material removal profile is developed for a disc-shaped compliant polishing tool which is commonly used in robotic polishing. The methodology is based on the Archard wear model implemented with adaptive meshing technique in the commercial finite element ABAQUS® software. Initially, the effect of tool compliance on the static contact pressure distribution is investigated experimentally using pressure films. Numerical 3D finite element model is developed for the same in order to predict the contact pressure distribution which in turn influences the material removal profile prediction. The material removal study is carried out with a robotic arm, and the polished surface is later scanned for the material removal profile. In order to predict the material removal profile, the finite element simulation in ABAQUS® is carried out using 'dynamic-implicit', followed by executing the umeshmotion FORTRAN subroutine in the 'general-static', where the nodes are displaced based on the wear model and using Arbitrary Lagrangian-Eulerian (ALE). The results are again imported in dynamic implicit and the simulation is restarted. The cycle continues till the experimental polishing time is reached. The experimental and simulation results of contact pressure are in good agreement with each other and bring out the effect of tool compliance on dynamic pressure which in turns affects the overall three-dimensional material removal profile. Highlights • Polishing tool's compliance on the pressure distribution is investigated experimentally and numerically. • Arbitrary Lagrangian-Eulerian methodology was implemented in finite element code to predict the material removal. • The numerical simulations of MRR agrees well with the experimental measurements within 10% margin. [ABSTRACT FROM AUTHOR]

Abstract The paper presents a numerical investigation of the ship collision response for a floating pontoon. High fidelity finite element models of a container ship bow and a prestressed concrete pontoon wall are established. The effect of prestressing on the collision resistance of the pontoon is discussed. Integrated numerical simulations are conducted to study the structural deformation and energy absorption of the striking ship and the struck pontoon. The results are compared with the structural responses when a rigid ship collides with a deformable pontoon and a deformable ship collides against a rigid pontoon. Parametric studies are also carried out to investigate the effect of the pontoon wall thickness and the strength and dimension of the ship bulb. A dynamic punching shear check procedure that can be used in the preliminary design phase is proposed. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a grid-independent numerical methodology that couples the strip theory based discrete vortex method (SDVM) with the finite element method (FEM) to simulate the vortex-induced vibration (VIV) of a long flexible vertical riser. Based on the strip theory, a three-dimensional flow filed is approximately simulated by a series of computational 'flow strips'. A Lagrangian discrete vortex method is employed to numerically solve the unsteady vorticity transport equations of each 'flow strip'. The flexible riser is modelled as a tensioned Bernoulli-Euler beam with the dynamical equation solved by the finite element method in time domain. The two-dimensional DVM code is firstly validated for the VIV simulation of a rigid cylinder that was experimentally studied by Khalak and Williamson (1996). Referring to two typical experimental configurations of Lehn (2003) and Chaplin et al. (2005), the VIV of a long flexible riser immersed in a uniform and stepped incoming flow are numerically simulated, respectively. A good agreement was achieved through detailed comparisons between the present numerical prediction and the experimental data, including the structural in-line and cross-flow VIV response modes, root mean square amplitudes and the dominant frequency. The occurrence of standing and travelling wave responses, dual resonance between in-line and cross-flow motions and figure-eight trajectory are reported. The wake patterns corresponding to two response waves are also presented and investigated. Related to structural local vibration amplitude, two principle vortex patterns resembling the '2S' and '2P' modes are identified in the wake. The standing wave component of structural response determines the vortex shedding pattern. The travelling wave component affects the spanwise vortices shedding at different phases. Highlights • A SDVM-FEM coupled numerical methodology is developed to simulate the VIV of long flexible risers. • Simulation has been carried on two typical experimental configurations to validate the numerical model. • The occurrence of standing and travelling wave responses are reported. • The wake patterns corresponding to two response waves are presented and investigated. [ABSTRACT FROM AUTHOR]

Abstract Multi-scale finite element (FE) modeling is an effective method to balance the computational efficiency and accuracy using different elements to simulate different parts of structures considering the demands of engineering practice. In order to analyze the earthquake-induced damage and collapse of Gaoyuan bridge in Wenchuan earthquake, the simplified rigid surface coupling method is developed to achieve the coupling between solid element and beam element based on LS-DYNA program at this study. The numerical results have shown that the failure of A2 abutment and strong pounding force cause the bridge superstructure lost longitudinal constraints, and the girders of the third span and forth span fell down due to oversize longitudinal displacement. Obviously, the multi-scale FE modeling is a high-efficiently analytical method for simulating local damage and even collapse of bridges structures under strong earthquake excitations. The inclined degree of bridge bents and the damage of concrete in different bridge piers using the multi-scale FE modeling method improved in this paper agrees well with actual earthquake damage of Gaoyuan highway bridge. Highlights • Simplified coupling method of rigid surface and the formula of displacement coordination were developed. • Collapse modes and local damage mechanisms of Gaoyuan bridge collapsed during the Wenchuan earthquake were simulated. • Compared results of numerical simulation with the actual collapse process in global level and damage details. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we present an inverse problem of identifying the reaction coefficient for time fractional diffusion equations in two dimensional spaces by using boundary Neumann data. It is proved that the forward operator is continuous with respect to the unknown parameter. Because the inverse problem is often ill-posed, regularization strategies are imposed on the least fit-to-data functional to overcome the stability issue. There may exist various kinds of functions to reconstruct. It is crucial to choose a suitable regularization method. We present a multi-parameter regularization L 2 + B V method for the inverse problem. This can extend the applicability for reconstructing the unknown functions. Rigorous analysis is carried out for the inverse problem. In particular, we analyze the existence and stability of regularized variational problem and the convergence. To reduce the dimension in the inversion for numerical simulation, the unknown coefficient is represented by a suitable set of basis functions based on a priori information. A few numerical examples are presented for the inverse problem in time fractional diffusion equations to confirm the theoretic analysis and the efficacy of the different regularization methods. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an analysis of the trajectories of tribocharged ABS and PVC particles in a free fall electrostatic separator. The installation that is the subject of this study is equipped with four vertical cylindrical electrodes. The behavior of the particles in this installation is compared with the one in a conventional configuration represented by two plate electrodes. The trajectory of the particles in both configurations is obtained by the numerical resolution of Newton's equation, which takes into account the magnitude and the direction of the electrostatic, gravitational and aerodynamic forces applied to the particles in the electrostatic separation zone. The calculation of the electrostatic force applied to the particles in this zone is performed using a numerical model of the electrostatic field obtained by finite element method implemented by means of the PDE-tool library of MATLAB software. The results of this study show that the use of a four-electrode configuration improves the quality of recovered products as it reduces the nuisible effect of the impacts between particles and electrodes observed in conventional plate-electrode installation. The use of the new configuration requires the development of a collector the shape of which should be adapted to the spatial distribution of the particles recovered at the outlet of the installation. Highlights • Comparative analysis of PVC/ABS particle trajectories in two electrostatic separators. • The trajectories are obtained by the numerical resolution of Newton's equation. • The use of a four-electrode configuration improves the quality of recovered products. • Diminution of the hazardous effect of the impacts between particles and electrodes. [ABSTRACT FROM AUTHOR]

Abstract Closed-form expressions to estimate the energy absorption and damage extent for severe ship collision damages were initially developed in 1999 [1, 2], and further validated with experimental data in 2016 [3]. To gain further confidence for applications within design using the proposed analytical procedure, it is evident that more detailed and comprehensive comparisons and validations with experiments and numerical simulations are necessary. The purpose of the present paper is to use the analytical approach and finite element analyses to study in depth model-scale and full-scale collision tests so that to further quantify key calculation parameters and to verify the capability and accuracy of the proposed analytical method. In total 18 experimental tests and one full-scale collision accident are evaluated. The 18 experimental energy absorption-penetration and collision force-penetration curves, and the associated finite element simulations, are compared with results obtained from the analytical calculations. It can be concluded that the analytical method gives consistently good agreement with all experiments analysed here. Finally, an application of the analytical method is demonstrated by an example where speed restrictions are determined in a port to avoid LNG cargo leakage in an event of an LNG carrier being struck by another ship. Highlights • An analytical method for ship collision damage assessments is validated with 18 experiments and one full-scale collision accident data. • It is demonstrated that a consistent good agreement with the experiments is achieved when using a common criterion for the assessment. • Comparisons of energy-penetration and collision force-penetration curves between the experimental results, the analytical calculations and the finite element simulations are also provided. • An application example for managing collision risks at busy ports to avoid potential cargo leakage in an event of an LNG carrier struck by other ships is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract Downburst produces strong winds near the ground and causes severe damage to buildings and people. The non-stationarity of downburst is characterized by moving downdraft and pulsed jet to the ground. In practice, both characteristics have often been observed simultaneously. These characteristics significantly affect the wind loads on buildings, particularly on low-rise buildings. However, the previous experimental studies of downbursts focused on each of these characteristics separately. No study has been made of their coupled effect. Therefore, we have developed a downburst simulator, which can generate a pulsed jet and a moving downdraft either separately or simultaneously. In the present paper, we have experimentally investigated the effects of non-stationary characteristics of downbursts on the wind field and wind loads on a flat-roofed low-rise building using this downburst simulator. The results may become a useful database for validating numerical simulation models of downbursts. Highlights • Effects of movement and impinging jet on the flow field of downburst is investigated. • Non-stationary flow fields of moving and pulsed jet are experimentally reproduced. • Downburst-induced pressure on a building is measured with a downburst simulator. • Downburst-induced wind forces are different from those by turbulent boundary layers. [ABSTRACT FROM AUTHOR]

Abstract Finite element (FE) analysis in geotechnical engineering often involves entities which can be represented as one-dimensional elements in three-dimensions (e.g. structural components, drains, heat exchanger pipes). Although structural components require an FE formulation accounting only for their mechanical behaviour, for the latter two examples, a coupled approach is necessary. This paper presents the first complete coupled thermo-hydro-mechanical FE formulation for one-dimensional beam elements for three-dimensional analysis. The possibility of deactivating each of the systems enables simulation of both coupled and uncoupled behaviour, and hence a range of engineering problems. The performance of these elements is demonstrated through various numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract This paper presents experimental and numerical studies on the behaviour of components and composite floor system under column removal scenarios. Shear connectors, double angle-cleat connections and flush end plate connections were extracted from a three-dimensional composite floor system and tested under different loading conditions. The load-displacement curves of these components were compared with the results predicted from existing models. A simplified numerical model was developed to simulate the behaviour of composite floor systems subject to progressive collapse, in which the properties of springs were determined from component tests. The model was then validated against experimental results in terms of load-displacement relationship and failure mode. Finally, parametric studies were conducted to investigate the effects of slab thickness, aspect ratio and reinforcement. Numerical results suggested that the aspect ratio of slabs has the most significant effect on the load capacity of composite floor systems under progressive collapse scenarios. Highlights • Experimental tests were carried out on various components in composite floor systems. • Numerical model was developed for a composite floor system under a column removal scenario. • Parametric studies were conducted on the effects of slab thickness, aspect ratio and reinforcement. [ABSTRACT FROM AUTHOR]

Highlights • A novel model and measurement method for contact analysis of TWUSM are proposed. • The proposed measurement method make it possible to determine motor parameters in running TWUSM. • Vibration parameters in our model are identified based on measured force and feedback voltage rather than theoretical assumption. • The simultaneous effects of the preload force on the resonance frequencies and vibration amplitudes were validated rather than one effect. • Some phenomena, such as the variations of starting-up voltages and working ranges can be predicted and analyzed. • Very useful and convenient for the motor design, performance prediction, working range choice and control of TWUSM. Abstract In previous studies, contact models of traveling-wave ultrasonic motor (TWUSM) only considered the effect of the preload on the resonance frequency, and were based on theoretical calculations or assumptions because vibration parameters in working conditions are hard to measure. In this paper, a novel model and measurement method for contact analysis of TWUSM are proposed. The proposed measurement method enables the determination of vibration parameters during motor operation. Our model differs from previous reported models in three aspects: vibration parameters are identified based on measured force and feedback voltage rather than theoretical assumptions; the simultaneous effects of the preload force on the resonance frequency and vibration amplitude were analyzed and validated; some phenomena in working conditions, such as the starting-up voltages and working ranges under different preload forces, can be predicted and analyzed. The feasibility and effectiveness of this model was verified by the good agreement between the measured and calculated results. Our work provides a very useful and convenient way for performance prediction, working range choice and control of TWUSM. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The analysis of an entangled cross-linked fibrous material at low deformation is explored as way of predicting the shear behaviour, especially the shear hysteresis. This paper presents a 3D finite element model to characterize the carbon fibre network rigidified by epoxy cross-links. The morphology of the representative volume element (RVE) is studied to guarantee that it is representative of the actual material that was characterized experimentally. Two steps are simulated, namely the initial compression during the shaping and before the polymerization of the epoxy resin and the cyclic shear testing of the material with its rigidified network of fibres. A numerical simulation of an RVE is used to present a description of the measured hysteresis loop that is decomposed of linear and nonlinear parts. A comparison between the numerical prediction and the experiment data is discussed. Even if the 3D numerical model under-predict the average shear stiffness of the material, it can capture the complex shapes of the measured hysteresis loops at different strain amplitudes. [ABSTRACT FROM AUTHOR]

Abstract In the paper, the finite element method and the finite volume method are used in parallel for the simulation of a pulse propagation in periodically layered composites beyond the validity of homogenization methods. The direct numerical integration of a pulse propagation demonstrates dispersion effects and dynamic stress redistribution in physical space on the example of a one-dimensional layered bar. Results of numerical simulations are compared with the analytical solution constructed specifically for the considered problem. The analytical solution as well as numerical computations show the strong influence of the composition of constituents on the dispersion of a pulse in a heterogeneous bar and the equivalence of results obtained by two numerical methods. [ABSTRACT FROM AUTHOR]

Abstract Dyneema® fibres and fabrics are widely used for ballistic protection due to its lightweight and super mechanical properties against high strain rate impact, and finite element (FE) simulation and analysis are used to study the response to the impact in parallel to the experimental-based research methods. However, elastic constants of the yarn except the Young's modulus were difficult to obtain and were basically assigned based on assumptions and approximations in the FE modelling, which caused some inaccuracies. This paper reports a study on the influence of each elastic constant of Dyneema® yarn model in modelling a single layer Dyneema® woven fabric against ballistic impact using the orthogonal experiment method. Orthogonal table L25 (56) was employed to analyse six factors (i.e. E 11 , E 33 , ν, G 13 , G 23 , and their interactions) with each having five levels. The ballistic modelling results were validated against the experimental results, viz. energy absorption, failure time of the first yarn broken and number of failed yarns. According to the orthogonal analysis, G 13 was shown as the most significant in influencing the simulated results, with a confidence level of more than 95%, and ν was the least significant. Through the orthogonal study, the combination of levels of the elastic constants that led to a significant agreement between the FE and practical results was identified. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a fractal hierarchical hexagon structure inspired by bionic structures, such as spider webs, as a novel lightweight energy absorber. Experimental testing and computational modeling are carried out to characterize the effects of fractal order and geometrical shapes on the crashworthiness of this new structure compared to a simple hierarchical structure. The computational results reveal that both simple hierarchical and fractal structures can present significant improvement in energy absorption over single wall nonhierarchical structure. Furthermore, fractal configuration, geometrical parameters and order have important effect on the energy absorption efficiency of fractal hierarchical structures, with the 2nd order design being the optimal for a given mass. The findings of this research offer a new route for designing novel lightweight energy absorbers with improved crash protection against impact. Graphical abstract Unlabelled Image Highlights • Thin-walled structures with hierarchical and fractal cross section present great potential to improve energy absorption. • The high order fractal designs outperform the corresponding simple hierarchical designs with the same mass. • Fractal configurations and geometry have remarkable influence on the energy absorption of fractal structure. [ABSTRACT FROM AUTHOR]

Recently, the market promotion of wireless power transfer (WPT) products has generated great expectations for systematic design and optimization of practical WPT system (especially the coupler). The existing optimization methods usually employ the Finite Element Analysis (FEA) to simulate the magnetic field, where the effects and requirements of overall circuit are neglected. To address this issue, an optimization approach for the coupler based on circuit simulation is proposed in this paper, and the secondary compensation capacitor is further optimized to improve the system performance. The simulation model is embedded into Simulink and the calculation part is embedded into MATLAB, where the objective is to achieve the maximum efficiency by searching three variables under adequate constraints. The numerical results imply that the proposed method is more effective and accurate than the traditional trial-and-error way, and that it suits the practical WPT system design excellently. [ABSTRACT FROM AUTHOR]

This paper presents a robust, efficient, and strongly scalable solution methodology for simulation of complex turbulent flows on unstructured grids. The compressible Reynolds averaged Navier–Stokes (RANS) equations and the negative Spalart–Allmaras (SA) turbulence model are discretized, in coupled form, using a Streamline Upwind Petrov–Galerkin (SUPG) scheme. The time integration is fully implicit, and the discretized equations are advanced towards a steady-state solution using a pseudo-transient continuation (PTC). For solution of the linearized systems, a preconditioned Krylov solver is used. Seeking robustness, Krylov solvers are commonly preconditioned using incomplete factorization methods such as ILU(k). However, these methods are neither memory efficient, nor strongly scalable. To provide a better alternative, the implicit line solution method, which has been traditionally used in finite-volume methods, is revised and enhanced to solve stiffer linear systems. In the developed method, the lines are generated using a matrix-based approach, which connects the strongly-coupled unknowns. In addition, to improve the robustness of the line solver for high-CFL systems, a dual-CFL strategy, with a lower CFL number in the preconditioner matrix, is developed. Also, it is shown that for high-order continuous finite-element discretizations, the interconnections of the degrees of freedom on a line form a banded matrix which is wider than tridiagonal, but still can be factorized completely without generating any fill-ins. The developed line preconditioner is strongly scalable and, in contrast to the ILU factorization, its convergence behavior does not depend on the number of partitions. Two three-dimensional numerical examples are presented in which the performance of the line preconditioner is compared with that of the ILU(k) preconditioner. This comparison shows that, in addition to robustness improvements, the line preconditioner offers significant benefits in terms of memory efficiency. [ABSTRACT FROM AUTHOR]