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In this paper, time fractional reaction–diffusion equations with the Caputo fractional derivative are solved by using the classical L 1 -formula and the finite volume element (FVE) methods on triangular grids. The existence and uniqueness for the fully discrete FVE scheme are given. The stability results and optimal a priori error estimate in L 2 (Ω) -norm are derived, but it is difficult to obtain the corresponding results in H 1 (Ω) -norm, so another analysis technique is introduced and used to achieve our goal. Finally, some numerical results are given to verify the feasibility and effectiveness. [ABSTRACT FROM AUTHOR]

Although fiber reinforced polymers (FRPs) have become the most widely used material to strengthened existing concrete structures in shear, premature debonding of externally bonded FRP remains a significant cause of material under-utilisation. In an effort to suppress debonding failure, research has shown that the use of ±45° bidirectional fabric patch anchors can delay the occurrence of FRP debonding. However, most research to date on patch anchors has been based on joint-level tests and the data available on full-scale beam applications has been very limited. One means by which additional data can be generated on the performance of patch anchors when applied to full-scale beams is using finite element simulations. This paper presents a 2D and 3D non-linear finite element model calibrated using available data on prestressed T-beams strengthened in shear with FRP laminates and patch anchors. The models captured the failure modes, strains in the FRP and crack patterns of the specimens very well and predicted the failure load for the control, strengthened and anchored specimens within a margin of difference of 6–9%, 4–13% and 1–2%, respectively. Parametric studies involving variation of concrete strength and FRP thickness were conducted to generate additional data and the research findings are presented. [ABSTRACT FROM AUTHOR]

In eddy current (EC) nondestructive testing, coil is usually wound on core or covered by shield to improve the sensitivity of defect detection and ability of anti-interference of the probe. However, when core or shield is used, the magnetic field will be redistributed, resulting in a change in the speed of EC attenuation in the depth direction. The purpose of this paper is to reveal the influence of core and shield on skin depth of EC. The results of the finite element analysis show that applying core or shield on coil results in smaller skin depth and the skin depth decreases as the core or shield approaches the test sample. In addition, when both core and shield are used, the reduction of skin depth is minimal if both core and shield are ferromagnetic. The simulation results are verified by experiment. [ABSTRACT FROM AUTHOR]

ACL reconstruction is the recommended surgery for young, physically active persons with complete ACL rupture. This study has MAHE, Manipal ethics committee clearance. This research is a case study on AMP and TT techniques of ACL reconstruction. The two techniques of Reconstruction of ACL undertaken on different subjects are compared with the healthy knee joint and Reconstructed-ACL (R–ACL) which have undergone simulation, based on the stress induced. This research paper is based on a retrospective study that utilizes image data from previously carried–out surgery on patients and does not cause any harm to the living condition of the patients. Computer Tomography (CT) image of the human knee joint of a person who had undergone ACL reconstruction by Anteromedial Portal (AMP) technique and another person who had undergone ACL reconstruction by Traditional Transtibial (TT) technique were considered for this study. A 3-dimensional (3D) geometry of the reconstructed ACL is generated from the CT images of human knee joints of both persons. A Magnetic Resonance Image (MRI) of a healthy human knee joint is considered. A 3-D geometric image of this healthy human knee joint is considered. It is discretized into a finite element model. The healthy ACL was replaced by a reconstructed ACL in the healthy human knee joint. The loads and boundary conditions corresponding to the Lachman test were applied to the human knee joint. In this study, equivalent stress (Von-Mises) in the ACL reconstructed by the AMP technique was found to be 16.07 MPa, whereas the equivalent stress in the ACL which has undergone TT technique of ACL reconstruc- tion was 36.73 MPa. The equivalent stress distribution in the model was assessed and compared with earlier studies. Based on the analysis, it was found that the AMP technique is better than the TT technique of ACL reconstruction. [ABSTRACT FROM AUTHOR]

This paper proposes a method of describing a global failure in geomechanics problems using the finite element method. When considering a quasi-static approach, a limit state cannot be described properly before a numerical divergence of the computation is reached. The main idea is to use a dynamic approach to catch the failure state of a quasi-static problem. However, the events that occur after the failure state are not taken into consideration, because after such a state, the response of a geostructure is not physically and mathematically unique. The second point developed in this paper is the definition of a proper safety factor, which can be useful for engineers. The second-order work criterion under local (homogeneous problems) and global (boundary value problems) forms is reviewed to determine the physical and mathematical interests of using it. Selected finite element simulations are presented. The best way of defining a safety factor using such numerical methods is proposed. [ABSTRACT FROM AUTHOR]

As the permanent submarine support structures for subsea wells, pipeline manifolds and pipeline terminations, the mudmat foundation works under obviously complex, nonlinear and uncertain loading, which makes a great challenge for the research of the stability of mudmat foundation. In this paper, finite element method is utilised to investigate the behaviour of square mudmat foundation without embedment in NC clay to fully 3D loading conditions: V-H-M and V-H-T. According to the analysis results, the relevant failure envelop surfaces and formulas are proposed to predict the capacity of mudmat foundation. These results could be treated as reference for the design work of the mudmat foundation. [ABSTRACT FROM AUTHOR]

The variable cross-section structure (comprising a riser, surface casing and cementing cement ring) of an oil well associated with an offshore oil platform is similar to that of a steel pipe pile foundation. If a well structure with variable cross-section characteristics can be used to provide bearing capacity, the construction cost of platforms will be reduced. In this paper, the finite element analysis method is used to study the vertical bearing mechanism of composite piles composed of a riser and a surface casing in saturated clay and sand. Based on the theory of spherical cavity expansion, the calculation methods of end resistance and skin friction resistance of composite pile are established. Finally, based on a field test of the bearing capacity of composite piles, the accuracy of the proposed calculation method is verified. [ABSTRACT FROM AUTHOR]

Scarf patching is the preferred technique for repairing physically damaged aircraft composite structures. The commonly used patch design is a circular conical frustum with a 3°optimized scarf angle. However, for this repair patch design the volume of material removed from the repaired composite panel can be quite large. This paper examines the effects of the different parameters on the stress state in the patch adhesive, such as ply orientation, stacking sequence, ply thickness and scarf angle. It explores an adaptive design of the repair patch for orthotropic materials and composite laminates, using 3D Finite Element Analysis. The design optimization approach is based on the evaluation of a Failure Criterion Index (FCI) and the minimization of its Relative Standard Deviation (RSD). An optimized scarf shape, which takes into account biaxial tensile loading conditions, fiber direction, and stacking sequence, is an elliptical conical frustum that induces a variable scarf angle along the sweeping angle. This design showed that less parent material is removed than that of the circular shape (decreased by up to 41%) and that the shear stress dispersion in the adhesive was significantly reduced (RSD decreased by up to 18%). The optimization method and the improved shapes are presented and discussed with respect to the influencing parameters. [ABSTRACT FROM AUTHOR]

Friction characteristics have great influence on forming quality and formability during single point incremental forming. At the same time, the friction coefficient has a significant influence on the finite element model of forming process. In this paper, the friction coefficient of forming process was studied deeply through the combination of theoretical research and experimental research. Firstly, a single point incremental forming mechanical model considering friction was established, and a method to solve the friction coefficient of forming process was obtained. On this basis, the direct relationship between forming parameters and friction coefficient was established by response surface method, and the influence law of forming parameters on friction coefficient was analyzed. The results provided theoretical and technical support for the improvement of friction mechanism and forming quality in single point incremental forming. [ABSTRACT FROM AUTHOR]

In this paper, a new combination of time and spatial discretization is proposed for a partial integro-differential equation (PIDE) arising in the valuation of European options under Merton's model. We first present a high-order compact (HOC) difference scheme in space based on a uniform mesh to obtain a highly accurate result, and the discontinuous Galerkin (DG) finite element method in time is introduced that can deal with the loss of the time analyticity. A penalty method is proposed for a partial integro-differential complementarity problem arising in the valuation of the American put option. Numerical experiments are performed to verify the accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

Vehicle safety performance is important to reduce occupant injuries during accidents. In general, vehicle manufacturers are utilizing analytical models to predict the vehicle passive safety performance during the early design stage. The two popular methods are the Occupant Limit Criterion (OLC) and Vehicle Pulse Index (VPI). In this paper, new VPI parameters are proposed to predict the driver 3 ms chest acceleration of Hybrid III 50th percentile (H350) in B-segment vehicle subjected to generic crash load cases. A good correlation between the newly optimized VPI parameters with the measured 3 ms chest acceleration is observed in this work. More refinement can be further included to improve the robustness of the new proposed parameters by adding more sampling data. [ABSTRACT FROM AUTHOR]

Finite element analysis of double tubes under axial and oblique loads are presented in this paper. This study tested double tubes which consisted of an outer tube and an inner tube. The inner tube used varied, in terms of shape, including the form of a triangle, square, hexagon, and octagonal. The crash behavior of the four types of tubes are first investigated by nonlinear finite element analysis through ABAQUS. It is found that the octagonal tube has the best crashworthiness performance under axial impact regarding both specific energy absorption (SEA) and peak crushing force (PCF). Then, the variations in the loading angle were analyzed in the oblique test category for octagonal tubes with angular variations of 10°, 20°, and 30°. In addition, optimization design of the octagonal tube is performed by adopting multiobjective nueral network algorithm to achieve maximum SEA capacity and minimum TEA with and without considering load angle effect. It is found that the optimal designs of the octagonal tubes under different load angles. [ABSTRACT FROM AUTHOR]

This paper examines a finite element method for the chemotaxis-growth model with indirect attractant production and logistic source. To begin, we propose a regularized problem of the truncated problem. We then obtain some a priori estimates of regularized solutions that are independent of the regularization parameter using a well-defined entropy inequality for the regularized problem. Additionally, we offer an efficient fully discrete finite element approximation of the regularized problem. A fixed point theorem is then used to prove that the approximate solutions exist. A discrete entropy inequality is also proposed for fully discrete finite element problems, as well as some stability bounds. We also investigate the convergence of the fully discrete problem. [ABSTRACT FROM AUTHOR]

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This paper investigates the challenges and opportunities emerging from the application of finite element method-based open-source software in ship structural analysis. Application of general procedure for development and assessment of FEA software used for ship structures is presented and demonstrated on the new upgrade of open-source FEA software OOFEM (Object-Oriented Finite Element Method). Properties of new quadrilateral shell FEs implemented in OOFEM are presented. The new FEs comply with relevant class requirements and are suitable for the usage in the analysis of real-world ship structures. The implemented software upgrade is validated on a series of test problems ranging from simple engineering structures to a real-world model of one part of megayacht's superstructure. The benefits of validation tests and challenges encountered in the process of selecting the tests and interpreting their results are also discussed. [ABSTRACT FROM AUTHOR]

This paper exhibits a numerical simulation study of the 1s→2p ISB-related linear and nonlinear optical absorption in single, double, and triple QWs considering the effects of the compositions, temperature, and QW's number. Our calculations were performed numerically as part of the effective mass approximation using finite element analysis. Our results reveal that for different nanostructures, optical absorption in quantum wells strongly depends on geometry, compositions, and temperature. Furthermore, we have found that optical absorption is greater and more sensitive to compositions and temperature variations in single QW than in double and triple QWs. In addition, a red-shift (blue-shift) associated with an enhancement (fall) of the resonance peaks of the optical absorption spectrum was obtained under the variation of composition, temperature, and number of QW per structure. However, we noticed that adding a QW causes a dramatic decrease in optical absorption due to the high loss rate due to oblique tunnelling and non-radiative optical transitions in double and multiple QWs compared to a single QW. We hope that this study will make a modest contribution to the field of theoretical and computational condensed matter physics. [ABSTRACT FROM AUTHOR]

This paper analyses free vibration of interacting length-scales of 3D-thin-walled structures by combination of Finite Elements Method and analytical calculation of strain and kinetic energies. Equivalent single layer elements with structurally homogenized mass and stiffness enable significantly reduced computational cost. Analytical equations are used to re-introduce effects of inertia-induced deformations of the local length-scale that are restrained by the kinematic of homogenized equivalent single layer elements. The method is validated against fine mesh Finite Element Analysis in a case study representing typical 3D-structure seen in cruise ships. The method achieves excellent accuracy for the 10 first natural modes. [ABSTRACT FROM AUTHOR]

This study performs a substantial statistical analysis on the effects of damage characteristics, such as position and severity, on a specific damage metric composed of coefficients obtained from the discrete wavelet transform. The results of the analysis serve as the basis for developing more sophisticated and optimized damage-identifying methods in structural health monitoring. For the methodological procedure, a carbon fiber reinforced polymer beam was numerically modeled using the finite element method where the damage was induced considering a local reduction of stiffness in different positions and levels of severity. The numerical methodology was validated with modal experimental tests. Results obtained through analysis of variance and design of experiments indicated the sensitivity of each factor and the response surface provided the best combination of factors for each response. Knowing the sensitivity and interaction of these parameters is essential for the correct formulation of damage indexes or other techniques in damage identification. The results obtained in this paper can be used as a guideline for engineers when developing new wavelet transform-based strategies for structural health monitoring. [ABSTRACT FROM AUTHOR]

The majority of the existing historical brick masonry buildings and monuments in Iran were built adopting a structural system made of modularly connected Persian arched walls; two piers connected by an arc-shaped spandrel. Previous earthquakes revealed that these structures are highly vulnerable and seismic rehabilitation of them is of great significance. However, architectural character and cultural value of these monumental structures significantly rely on the appearance of the building and its decorative finishing. Thus, any retrofitting method modifying the appearance of the building is unacceptable. During the last decades, centercore strengthening method has been developed for seismic rehabilitation of these structures. This paper presents an experimental and numerical investigation on the in-plane behavior of Persian arched walls, before and after retrofitting by centercore method. For this purpose, using fired clay bricks and gypsum-clay mortar, three arched walls were built and tested under reversed cyclic in-plane loading. The results showed a significant increase in the ultimate lateral resistance and improvement of seismic performance indices including ductility and energy dissipation. Moreover, a three-dimensional nonlinear finite element model using a combined approach of smeared cracks and discrete elements was adopted to investigate the monotonic in-plane behavior of the retrofitted arched walls. [ABSTRACT FROM AUTHOR]

In this paper, the required limiting pressure to be offered by the lining of circular tunnels formed in clay overlain by another clay layer under undrained condition has been computed. Both the layers are anisotropic in nature from the shear strength point of view. The upper layer is considered relatively either weaker or stronger than the lower layer i.e. undrained anisotropic shear strength of upper layer is relatively either smaller or greater than that of lower layer. Lower bound limit analysis coupled with finite element formulation and second order cone programming has been employed to perform the analysis. For different thickness of upper layer above crown of tunnel, the limiting lining pressure to maintain stability of tunnel has been obtained by varying thickness of lower clay layer, anisotropic parameters, normalised overburden pressure, undrained cohesion and unit weight of upper layer relative to lower layer. The solutions obtained from this analysis reveal that anisotropy in shear strength has significant effect on the required lining pressure to keep tunnel in stable condition. [ABSTRACT FROM AUTHOR]

Piezoelectric-structure interaction (PSI) and fluid-structure interaction (FSI) are multi-physics coupled systems. These interactions affect the vibration characteristics of coupled systems and thus such complex coupled systems must be controlled. This paper proposes computational control based on the finite element method for strongly coupled multi-physics analysis of the PSI of a thin flexible piezoelectric bimorph actuator. The vibration characteristics and the effect of direct velocity and displacement feedback (DVDFB) control in coupled systems are investigated. The displacement and velocity feedback gains are used together as well as separately. DVDFB control is extended to the FSI of stiff and soft structures to study vibration characteristics using active control and compare the stability of the two types of structure. The results of PSI show a reduction in actuator displacement amplitude and a shift in the resonance frequency due to DVDFB control. For FSI, the results for a stiff material show a reduction in displacement. The velocity feedback gain has no effect for a stiff material and leads to instability due to a large control force. The results for a soft material show a reduction in displacement and amplitude and more stability compared to the case for the stiff material. [ABSTRACT FROM AUTHOR]

This paper reviews research reported over the last three decades on enhancing the torque density of a switched reluctance machine (SRM) through improved magnetic structure of the machine. To this effect, various pole configurations, modifications to pole geometry such as introduction of teeth in stator poles, tapering of stator and rotor poles, non-uniform airgap, introduction of flux barriers in the poles, and segmental rotor are studied. All salient points in the review are supported by comparative analyses based on finite element analysis (FEA) of candidate machine designs. Increasing the number of rotor poles and introduction of teeth in stator poles enhance the torque density at low current density, while increasing multiplicity is beneficial at high current densities. Quantum of electromechanical energy conversion per individual stroke can be increased by tapering of poles, non-uniform airgap and by introduction of flux barrier in the poles. A segmental rotor can increase the stator winding flux-linkage for a given excitation, and thereby, the torque output of the machine. [ABSTRACT FROM AUTHOR]

This paper proposes a three-layered co-running track model for predicting and analysing the dynamic behaviour of railway turnouts during the passage of trains. It is a multi-body dynamic model with space-dependent track parameters. The method is demonstrated by applying a UIC60-760-1:15 turnout (with curve radius 760 m and turnout angle 1:15). Equivalent track properties are introduced, based on the turnout track flexibility, and the rail receptance and impact force results are compared with the results from a finite element (FE) model. The validation results show a good agreement with those of the FE model, but with far less computational expense in terms of power and time. The new model is found to capture the dominant dynamic behaviour of the turnout across all frequencies up to 2000 Hz. The results have drawn that consideration of higher frequencies is important due to the nature of dynamic forces affecting the crossing region and high-speed cases. [ABSTRACT FROM AUTHOR]

There are many uncertainties related to existing bridges that are approaching or have exceeded their original design life. Lifetime extension analysis of bridges should be based on validated numerical models that can be effectively established. This paper presents a new procedure to obtain an optimal solution from sensitivity-based model updating with respect to an improvement in the modal properties, such as the natural frequencies and mode shapes, based on realistic parameter values. The procedure combines variations in the ratios of overdetermined systems with different definitions of local parameter bounds in a structured approach using a sensitivity analysis. The feasibility of the procedure is demonstrated in an experimental case study. Model updating is performed on a full-scale steel bridge using the natural frequencies and modal assurance criterion (MAC) numbers, where the numerical model is established by considering general uncertainties and model simplifications to reduce the model complexity. From the optimal solution for the case study considered, an improvement in modal parameters is obtained with highly reliable parameter values. The proposed procedure can be applied to similar case studies, irrespective of the structure under consideration and the corresponding parameterisation to be made, to effectively obtain a validated numerical model. [ABSTRACT FROM AUTHOR]

In order to study the influence of internal heat source of ball screw feed transmission system on the thermal error of ball screw, the theoretical modeling and experimental research are carried out on the temperature field and temperature rise characteristics of ball screw in this paper. Firstly, on the basis of analyzing heat generation mechanism and heat transfer of ball screw, the positive temperature field of ideal heat transfer of heat source and the negative temperature field caused by heat transfer are derived. In addition, the mathematical model of dynamic temperature field of ball screw feed system about time and position is established according to the superposition principle of temperature field, and the temperature field and thermal error of x-axis ball screw in horizontal machining center are measured. Secondly based on the experimental temperature field data, a complete finite element model of the temperature field of the ball screw feeding system is constructed, and temperature at any point of the system and the undetermined coefficient of the numerical model of temperature field under this working condition are determined by the finite element model. Finally, the thermal error distribution of the ball screw is calculated by the numerical model, the theoretical and experimental error distributions are compared, and the correctness of the theoretical model of the temperature field under this working condition is verified. [ABSTRACT FROM AUTHOR]

The residual displacement of column has significant effect on the post-earthquake functionality of bridge. In this paper, the nonlinear finite element model of a simply supported beam bridge was built. The seismic performance of reinforced concrete column, unbonded prestressed reinforced concrete (UBPRC) column, and fully prestressed column was compared. Quasi-static residual displacement was adopted in the fragility analysis. The result showed that the quasi-static residual displacement affects the vulnerability of bridge system only for the collapse damage limit state. UBPRC column is a good balance between the vulnerability arising from peak displacement and residual displacement. [ABSTRACT FROM AUTHOR]

Minimally invasive surgery (MIS) is a viable alternative to general surgery with distinct advantages. Robotically assisted MIS, has been demonstrated to achieve higher accuracy and repeatability in comparison with those of manual procedures. Despite these advantages, owing to the nature of some surgical procedures in which dexterous tissue manipulations in deep narrow areas of the human body are necessary, there is a need for further miniaturized tools with smaller bending radii. To cater to this requirement, this study proposes a new compliant mechanism based surgical robotic forceps. It can generate four degrees of freedom at the tip of the forceps including two bending motions in two perpendicular axes, grasping and rotation. A better combination of the stress distribution through the elastic material, grasping force, and range of motion was determined based on a series of finite element analyses. In addition, the manufactured prototype underwent a series of laboratory experiments to evaluate its effectiveness. Details of the mechanism, finite element analysis, prototype implementation, and evaluations are presented in this paper. [ABSTRACT FROM AUTHOR]

Present-day commercial tactile sensors for motion monitoring show poor water-absorbency, air-permeability, dynamic and flexibility, thus, prohibitive in wearable tech. To compensate for this restriction, this paper is concerned with the development and modeling of a stretchy arch-like tactile sensor for detecting signals in motion of a contact tissue. The main objective of this study is to design and model a piezoelectric sensor capable of measuring both obvious and weak movement state of contact tissue. The prototype sensor consists of three elastic layers and a combined arch. The cylindrical layer is made of micromachined resilient rubber can be used in noise reduction and shape-preserving property. The middle layer with a U-like structure that is built by high elasticity silica gel. The bottom layer is made of hyperelastomer with fence-like structure serving as a substrate and possessing hypo-allergenic and breathability function. Detecting the sensed objects athletic qualities is based on the relative deformation of contact object on the stretchy arch-like element. The PVDF film is embedded on the arched base plate and then sandwiched between the two electrodes to measure the force applied on the sensor. Mathematical algorithms and three-dimensional finite element modeling are used to analyze the performance of the designed system. The experimental results are very promising and proving the capability of the stretchy tactile sensor for haptic sensing and dynamic motion detection. [ABSTRACT FROM AUTHOR]

Cultural heritage buildings are valued in contemporary societies as they reflect the lifestyles and creative achievements our predecessors. For this reason, many countries have introduced regulations to ensure conservation of their historic buildings for the future, permitting minimal changes only to their original structure and characteristics. The key question addressed in this study is: how best can we assess the current structural behavior of a historical building, in particular wooden structures which may have survived for several centuries despite the deleterious consequences of decay, ageing and earthquakes? This paper focuses on a structural behavior assessment under current conditions (i.e. before restoration) of the Velipaşa Han Building, an impressive "caravanserai" or han (inn) building dating from the 19th century, in the central Anatolian region of Turkey. This assessment includes non-destructive tests to obtain the resistance of the timber structural elements and to determine the modal response of the building. In addition, a finite element model was developed, based on an on-site investigation and the proposed restoration project, and validated by consideration of in situ experimental measurements. The model also used a condition assessment of the building after proposed restoration. Through in situ inspection, experimental measurement and numerical investigation, the current structural behavior of the building was evaluated and, based on this, recommendations for intervention are presented in the study. [ABSTRACT FROM AUTHOR]

In this paper, the crashworthiness characteristics of tapered structures with the uniform cells in cross-section subjected to oblique impacts are theoretically and numerically investigated. Benefiting from tapered structure simplifications into the corner, crisscross and T-shape parts in non-tapered structures, an engineering formula is proposed to estimate the mean crush load during structure deformations. In order to represent the behavior of the structures subjected to oblique impacts with regard to energy absorption, an oblique impact coefficient extracted from a comprehensive parametric study on the responses of the structures is considered in the formulation. In order to conduct the parametric study, a finite element model for the crumpling processes of different tapered and non-tapered structures with the uniform cells in the cross-section under axial and oblique impacts is prepared. The contributions of cell-number in the cross-section, taper angle, wall thickness, aspect ratio and impact angel on the peak crush load, mean crush load, specific energy absorption, crush force efficiency, transition thickness and transition impact angle in the crushing processes of the tapered structures with uniform cells in cross-section subjected to oblique impacts are presented and discussed. In particular case, the predicted structural energy absorption by the numerical model is compared with those experimental results that are available in the literature, indicating a good agreement. [ABSTRACT FROM AUTHOR]

Field evidence revealed that buried cast iron water pipes can deteriorate through large localized corrosion patches with lengths greater than 1 m, formed by a cluster of small pits. This study investigated the effect of large corrosion patches on the performance of large-diameter cast iron pipes. Although large corrosion patches are highly irregular in nature, they were idealized as semi-ellipsoids. To validate the approximation of corrosion patch geometries with semi-ellipsoids, comparison of finite element models of scanned corroded pipe geometries with the approximated semi-ellipsoidal patches on the same pipes were conducted. Following this validation, parametric studies were performed, which covered a wide range of the pipe and patch dimensions. Based on the finite element analysis, an equation for stress concentration factors was derived and is presented in this paper. This development will significantly assist the pipe engineers and asset managers in the condition assessment of corroded cast iron pipelines. [ABSTRACT FROM AUTHOR]

In this paper, the energy absorption capacity of continuous fiber-reinforced thermoplastic auxetic structures is examined experimentally and the results compared with both numerical and analytical methods. To this extent, a 3 D printing technology of Fused Deposition Modeling (FDM) is implemented for fabricating the auxetic honeycombs and quasi-static compression test is conducted to extract the load-displacement behavior of the structure. Both hollow and foam filled lattice structures are tested, and the results revealed that the absorbed energy increased by 20% for PLA and 70% for PA specimens, when using foam. Finite element analysis is also performed using the explicit solver. The onset of failure is determined using the maximum stress criterion and VUSDFLD subroutine and the damage growth is modeled by decreasing the mechanical properties of the elements. The obtained results are in relatively good agreement with the experimental analysis. In addition, a theoretical formulation is developed and the probabilistic analysis is performed to draw the honeycomb failure design envelope, which is a practical tool for designing of various honeycomb configurations. The failure envelope shows that decreasing the strut angle increases the honeycomb failure load, however, the auxetic property of the structure decreases. [ABSTRACT FROM AUTHOR]

Titanium and stainless steel are widely used in industries due to their advantages of high strength and good corrosion resistance. Such materials have common electromagnetic features – with a relatively low conductivity ～105 − 106 S/m and a relative permeability of 1. In terms of structure health monitoring, conductivity is an important physical parameter of metal materials, which is closely related to its purity, heat treatment state, internal stress state, hardness and temperature. Therefore, accurate and efficient conductivity estimation of such metals is extremely important to ensure product quality and normal operation of equipment. This paper presents an efficient conductivity estimation method of metals based on eddy current testing. The sensors used are with two coaxially cylindrical coils acting as transmitting coil and receiving coil respectively. According to the characteristics of low-conductivity and sensor configuration, a simplified theoretical model derived from the classic Dodd–Deeds theory is proposed. Moreover, the finite element method (FEM) simulation and experiments are carried out to verify the proposed model. The experiments are carried out on stainless steel 316 and different Titanium alloys with a commercial impedance analyzer, and the results indicate that the average relative measurement error is less than 2.8%. [ABSTRACT FROM AUTHOR]

AbstractIn this paper, the Gyroid triply periodic minimal surface is prepared by liquid crystal display photopolymerization technology, and 10 models of the periodic parameter T in [1/5, 2] are designed. Using the method of finite element method and experimental verification, when T = 1/3, there are fewer stress concentration areas on the Gyroid surface, the number of grids is moderate, the compression crush rate is the smallest, and the porosity error is reasonable. Through the microscopic morphology, it is found that the surface, after printing, forms gear shape and resin residue so that the actual volume is larger than the theoretical volume, and the porosity is minor. Keeping periodic parameter T = 1/3 and porosity of 50%, four kinds of Gyroid surface structures were designed by changing the parameter surface offset, wall thickness, offset thickness, and gradient arrangement. The effects of different loading directions on its mechanical properties, deformation behavior, and energy absorption were discussed through compression experiments. The results show that the vertical load is applied to form a fault zone from the upper left angle to the lower right angle of 45°, and the parallel load is applied to create a fault zone from the upper right angle to the lower left grade of 45°. When the load is used in the vertical direction, the energy absorption and energy efficiency of the surface offset Gyroid surface are the largest. When the load is applied in the parallel order, the energy absorption curves of the four structures change similarly, and the deformation amplitude of the wall thickness Gyroid surface during the compression process is relatively stable. The energy efficiency of gradient arrangement Gyroid surface increases fastest in the compaction stage. [ABSTRACT FROM AUTHOR]

In this paper, a numerical axisymmetric elastic stress wave propagation analysis of the 2D-FGM hollow thick finite cylinder has been performed. The new accurate material distribution model based on Mori-Tanaka scheme and third-order transition function for 2D-FGMs has been implemented in the graded finite element method with higher-order quadrilateral elements. A non-uniform impulsive pressure has been applied on the one-third of the top inner cylinder wall. Consequently, different wave velocities and reflections from the boundaries have been observed due to the graded distribution of material along with two directions. Moreover, the effects of two-dimensional material property distributions on the stress wave propagations and displacements through the cylindrical wall at different locations have been studied systematically. Normalized effective stresses based on von-Mises criteria has been performed in comparison with the internal impulsive pressure amplitude to provide a measure of the cylinder wall response to the mechanical impact loading, the effective stresses are nearly 2.5 times the internal pressure loading amplitude, closed to the impact location. According to the results, 2D material property gradations has effected the stresses significantly. Alternatively, desired stress values can be achieved through optimal design and appropriate choice of property distribution. [ABSTRACT FROM AUTHOR]

An implicit limit state function is predicted with a support vector machine (SVM) for reliability analysis of engineering structures to reduce the number of finite element analyses. The accuracy and predictability of the SVM method are reduced considerably by noise in data. In this paper, density-based spatial clustering of applications with noise (DBSCAN) is applied to reduce the noise in training samples for SVM regression. Then, the SVM model is linked with Monte Carlo simulation (MCS) to find out the reliability of the engineering structures. Four different examples of static and dynamic problems are solved to show acceptability and efficiency of the proposed method. It is observed that the proposed method is suitable for a smaller number of performance function calls. Direct MCS, artificial neural network-based MCS and response surface methods have been used to examine the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

A novel high-temperature resistant carbon fiber/bismaleimide resin composite shell is proposed and its bistable characteristics are studied in megathermal environment. Bistable structures are prepared with epoxy resin composites conventionally, which prone to undergone glass transition at high temperature. The study of high-temperature resistant bistable structure become necessary to suit aerospace field. In this work, the effect of elevated temperatures and different ply angles were investigated on curvatures and snap behaviors of carbon fiber/bismaleimide resin composite bistable shells through experiment and finite element analysis. These results provided significant understanding of morphing behaviors for the carbon fiber/bismaleimide bistable structure in megathermal environment. A novel high-temperature resistant carbon fiber/bismaleimide resin composite shell is proposed and its bistable characteristics in megathermal environment are studied in this paper. Bistable structures are prepared with epoxy resin composites conventionally, which prone to undergone glass transition at high temperature. The study of high-temperature resistant composite bistable structure become necessary to suit the actual working conditions. In this work, the anti-symmetric bistable shells with different ply angles (40°, 45°, 50°) are fabricated using T700/QY8911 prepreg. The effect of elevated temperatures and different ply angles were investigated on the principal curvatures and twisting curvatures of carbon fiber/bismaleimide resin composite bistable shells through experiment and finite element analysis. The snap behaviors of the bistable shells with different ply angles at different temperatures were obtained. Furthermore, a novel two-point tensile loading method was applied to the snap-back processes of carbon fiber/bismaleimide resin composite bistable shells with the subtended angles greater than 180°. It is noticed that the bistable shells have better high-temperature stability than carbon fiber/epoxy bistable shells. These results provided significant understanding of morphing behaviors for the carbon fiber/bismaleimide bistable structure in megathermal environment. [ABSTRACT FROM AUTHOR]

Helical piles have lately emerged as a viable alternative foundation solution in offshore geotechnical applications. The helical piles are typically installed in groups to resist large loads from the structures and may encounter combined loading due to some factor such as the waves from the water surrounding it. Recent research works on group helical piles focused mostly on piles embedded in sand and their response to individual loading regimes. This research has been carried out to examine the behaviour of the helical pile groups embedded in soft clay subjected to combined uplift and lateral loading considering three different configurations (rectangular, triangular, and square) and different spacings between the helical piles (2 to 5 times the helix diameter). A three-dimensional finite element model is developed to predict the load-displacement response of the group and is validated against the 1 g laboratory scale model test results. The findings from the analyses reveal that the influence of combined loading reduces the lateral capacity of the group helical pile. The spacing between the helical piles also has a substantial impact on the response to combined loading. The role of critical spacing ratio for various configurations has also been discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper presents the demonstration of underwater thermoacoustic (TA) sound generation using three-dimensional graphene (3D-C). 3D-C is able to interface with water as the immediate acoustic medium, resulting in reduced attenuation across solid packaging encapsulation due to favorable acoustic impedance matching. This is shown using array configurations of 2*2 and 4*4 individual 3D-C elements prepared onto printed circuit boards and secured within a watertight cuboid Delrin container with deionized water. Comparisons of underwater acoustic performance between internal medium of water and air shows significant improvement in measured sound pressure level (SPL) with internal water medium, in contrast with internal air medium where SPL were below noise floor. This demonstration opens up new possibilities of 3D-C for underwater acoustic applications. Simulations are conducted using 3D finite element model generated with COMSOL Multiphysics and validated with experimental results. A revised formulation of transmission voltage response (TVR) specific to TA sound generation is proposed due to the difference in power scaling of TA sound generation and subsequently validated using simulation. [ABSTRACT FROM AUTHOR]

Few investigations have considered comprehensive deformation constraints when calculating thermal stress of concrete slab. In this paper, the comprehensive and refined non-linear deformation constraints model of concrete slab is firstly proposed by setting non-linear spring elements at bottom and side of the slab and the capacity of shear load transfer across joints is considered as well. The results show that thermal stresses calculated by refined non-linear deformation constraints model are in good consistent with experimental results. The foundation reaction modulus has little effect on thermal stresses, but has a significant effect on gap between slab and its foundation. The stiffer base results in higher curling stresses at bottom of slab, and the types of base have an important effect on frictional resistance in horizontal direction at bottom of slab. The larger shear stiffness of joints will increase thermal stresses and shear force along joints but decrease deflections of slab. [ABSTRACT FROM AUTHOR]

A reaction–diffusion problem with discontinuous source term and Dirichlet's boundary conditions on the unit square is considered in this paper. The proposed problem has been discretized using a combination of standard Galerkin finite element method (FEM) and non-symmetric discontinuous Galerkin finite element method with an interior penalty (NIPG) with bilinear elements. Layer adapted mesh of Shishkin type has been utilized to discretize the domain. Standard Galerkin FEM is applied on the layer part of the domain where the domain is dense enough and NIPG is applied to the outside layer part. By means of special choice of discontinuity-penalization parameters, the scheme is proved to be uniformly convergent of order $ \mathcal {O}(\varepsilon ^{1/4}N^{-1} + N^{-1} \ln N) $ O (ε 1 / 4 N − 1 + N − 1 ln ⁡ N). Numerical tests are carried out in support of theoretical findings. [ABSTRACT FROM AUTHOR]

Due to improvements in diesel engine power and performance, the piston in the combustion chamber is subjected increasingly higher thermal and mechanical loads. The cyclic changes in thermal and mechanical stresses seriously affect the piston fatigue life. Therefore, it is necessary to analyze the strength of the piston in the design process. In this paper, the finite element analysis of piston under thermal, mechanical and thermo-mechanical loads coupling is carried out by using the ANSYS software. By analyzing the heat and force distributions on the piston, the stress and strain distributions on the piston can be obtained, so as to determine the maximum stress concentration areas and check whether the piston strength meets the requirements. Results indicate that the highest temperature on the piston appears at the top of the combustion chamber bulge, where the deformations of the piston and combustion chamber are the most serious. There is a large stress concentration in the contact between the piston pin seat, the piston pin hole and the piston. The minimum number of piston cycles is 1.2×106 times, which meets the piston cycle number from starting, running, and to stopping process. Thus the strength of the diesel engine piston meets the requirements. [ABSTRACT FROM AUTHOR]

This paper aims to study the effect of stress corrosion on the electrochemical behavior and corrosion mechanism of epoxy zinc-rich coating/steel substrate. The electrochemical impedance spectroscopy (EIS) was applied to characterize the corrosion behavior of the system under different stress conditions (σ1 = 0MPa; σ2 = 120MPa; σ3 = 180MPa and σ4 = 240 MPa), and appropriate equivalent circuits were established. Additionally, the von Mises stress distribution and potential distribution around the pitting pit at the coating-substrate interface were quantified by means of finite element analysis. The approach used different tensile strains and the depths of the pitting pit to relate the corrosion current density and corrosion rate to the corrosion process. The EIS results demonstrate that, given the same time, the failure time of the epoxy zinc-rich coating/steel substrate system with 240 MPa is shortened by 27.8% compared to the system without stress. Meanwhile, the finite element model confirms that the uneven potential distribution around the pitting pit is responsible for coating failure. In-depth profile of the corrosion rate shows an increasing trend over the distance from the opening. Then this local corrosion acceleration will cause further stress concentration, which in turn accelerates the corrosion process of the system. [ABSTRACT FROM AUTHOR]

This paper presents a constitutive model for the behavior of steel fiber reinforced concrete (SFRC) under mixed mode cracking taking into account the fiber orientation effect by using a micromechanical approach. Firstly, the resistant mechanisms of an inclined fiber are modeled by a closed-form analytical function. The bridging force is calculated by integrating on the cracked surface, the product of the fiber extraction force by its orientation probability. A modified model of the aggregate interlock mechanism is combined with the fiber bridging stresses to obtain the cohesive stresses. This mesoscale model is then extended using an elastic damage model and a fixed smeared cracking concept to assess the structural behavior. The model is finally implemented in a Finite Element Analysis (FEA) software, its performance is tested with some experimental results collected in the literature. The model successfully integrates the fiber orientation effect and shows a good prediction of stress transmission. [ABSTRACT FROM AUTHOR]

This paper presents static modelling and simulation of a spherically-shaped hyperelastic balloon actuator subjected to an angular rotation with an internally applied air pressure. These actuators are extensively used in soft robotics because its safe and flexible nature. The balloon actuator is a pneumatic-type actuator made of a polymeric material. A continuum mechanics-based analytical modelling and Finite element method-based simulation are performed to predict the response of the actuator for a given angular rotation with internally applied air pressure. The proposed modelling framework is subsequently utilised to perform the parametric studies for varying pressure, thickness, and rotational speed of the actuator. Various elastic instability curves are also obtained to examine the critical inflation of the rubber balloon actuator. The analytical findings agree well with the FEM simulations. [ABSTRACT FROM AUTHOR]

This paper explores the aero-thermo-elastic properties of variable stiffness composite laminates (VSCLs) with fibers steered along curved trajectories using a refined 1 D model. High-order solutions are generated by the p-version finite element method in conjunction with the Carrera Unified Formulation (CUF), which is applied to structural modeling by employing the improved hierarchical Legendre expansion (IHLE) in particular. The merit of using such a kind of expansion lies in that both the Equivalent Single Layer (ESL) and Layer-Wise (LW) theories can be formulated in a compact and straightforward manner. The linear piston theory is utilized to model the aerodynamic force, whereas the steady-state temperature field is applied during the flutter analysis. The weak-form governing equations are derived by taking a perturbation of the equilibrium configuration, and divergence and flutter instabilities are determined by solving the related eigenvalue problem. The accuracy of the proposed model has been verified through several test cases involving flutter, thermal buckling, and vibration of symmetric and antisymmetric VSCLs. The obtained results were compared to those obtained using the ABAQUS software and the available literature. Finally, the effect of the kinematic order, shear coefficient, and temperature variation on the critical dynamic pressure of VSCLs is thoroughly investigated. [ABSTRACT FROM AUTHOR]

Earthen levees are critical civil infrastructure of coastal regions for flood protection. Earthquakes can cause significant deformation and damage to earthen levees. Seismic performance of such levees under the earthquake hazards is a major concern in their safety evaluation. However, there are significant uncertainties in assessing the seismic behavior of earthen levees and geotechnical uncertainties play a critical role in the probabilistic assessment of earthquake-induced deformation and failures. This paper presents a simplified probabilistic framework for assessing the seismic performance of earthen levees with dynamic analysis and finite element modeling. In this framework, the effects of geotechnical uncertainties are explicitly considered in the uncertainty propagation for probabilistic evaluation of seismic deformations of earthen levees under earthquake hazards. The probability curves are developed to describe the correlations among the probability of exceedance, limiting deformation value, and input peak ground acceleration. The derived probability curves can provide valuable information for risk assessment and risk-informed decision-making of earthen levee infrastructure. The effectiveness of the proposed probabilistic framework is demonstrated through a case study of earthen levee example. [ABSTRACT FROM AUTHOR]

A new hybrid finite-element model was developed for heat flux and temperature analyses in porous material. The model in this paper was based on an assumed heat flux hybrid finite-element method, which is a twofield functional. An independent heat flux field that meets a priori inner thermal equilibrium was assumed inside the element, and a temperature field was assumed on the cell boundary. Temperature was used as the Lagrange multiplier to introduce the continuous condition of heat flux at the hole edge into the functional, and a modified complementary energy functional was obtained. The element flux field that was built up of polynomial terms and reciprocal terms from the stream function and that can consider the shape of pores in location coordinates was raised for the first time. Several numerical examples are discussed and compared with conventional finite-element methods to validate the accuracy and efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

Clinically, skin flap transplantation was often used to repair skin wounds. However, the flap design process with sample cloth is rough and easy to cause infection and necrosis. So an accurate and individual shape design of preoperative flap should be solved. Therefore, a 3D wound flattening method for mapping skin mechanical properties based on finite element method was proposed. Firstly, the 3D point cloud of skin wound was obtained by 3D scanner, and the hierarchical structure of wound model was established. Then a geometric flattening method of wound surface was proposed based on the existing surface flattening theory. The concept of deformed point was introduced according to the special shape of wound surface, and the corresponding modification was given to the original flattening process. Secondly, the mechanical properties of pig skin samples with different orientations were measured by static tensile test. Finally, based on the morphological flattening of wound model and the mechanical parameters of pig skin, a unit material model based on material deformation energy was established. The unit deformation was attributed to the equivalent load acting on the node, and a finite element optimization method of wound unfolding shape based on material deformation energy was proposed. In order to optimize the overall deformation energy, the flap shape was optimized and adjusted to achieve the preoperative design. Clinical examples were selected for verification and analysis. The results show that the proposed method can provide a reasonable and reliable preliminary guide for preoperative flap shape design in clinical wound repair. [ABSTRACT FROM AUTHOR]

This paper presents development of a frequency up conversion piezoelectric energy harvesting system that takes cattle movement vibrations and convert it into electrical energy. The harvested power can be used to power some devices relating to cattle precision farming operations. The design should get excitation from cattle motion frequency in the range of 5-8 Hz and upconverts it to a much high resonant frequency of 47.2-76.05 Hz. A Finite Element Analysis (FEA) is modeled and studied using COMSOL Multiphysics. The model is expected to generate power sufficient enough to operate devices like pedometers which consume on average 1.8 V. [ABSTRACT FROM AUTHOR]