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The study investigated the fretting fatigue behavior of a bridge‐flat component, utilizing a flat specimen with two bridge‐type pads tested under cyclic loading. Numerical simulations were also carried out using the finite element method. Firstly, precise calculations of contact stress were performed with the material's elastoplastic model. Secondly, the stress distribution on the maximum stress cross‐section was extracted, and the stress gradient was computed. Finally, a stress fatigue life prediction model considering the stress gradient was proposed, and the predicted life was compared with the test life. The results of the study revealed that the specimens exhibited high stress gradients at the edges of the contact region during the bridge‐flat tests. In comparison with plain fatigue, fretting fatigue life was significantly reduced. The life prediction model proposed in this paper demonstrated good accuracy for predicting fretting fatigue. [ABSTRACT FROM AUTHOR]

As urban population increases, integrated underground–aboveground complexes are being constructed at growing paces in major cities. The seismic analysis of such complexes is crucial for the safety and functionality in the threat of potential earthquake disasters. However, fine‐grained numerical modeling and analysis of such large and complex structures are still inefficient due to the consideration of the soil–structure interaction (SSI). To address this challenge, an efficient approach for numerical modeling of large‐scale seismic SSI analysis is presented in this paper to overcome the limitations of existing finite element analysis (FEA) software. Moreover, a multi‐graphic processing unit (GPU) parallel explicit algorithm is implemented for the nonlinear dynamic SSI problems to further increase the computational efficiency. A large underground–aboveground complex project in China is used as an example to demonstrate the capability of the integrated method. The accuracy and reliability of the multi‐GPU parallel explicit finite element algorithm for SSI analysis (GFEA‐SSIA) are verified through a comparative analysis of the linear‐elastic and nonlinear dynamic response of the building calculated by GFEA‐SSIA and common FEA software. Finally, the structural response and structural damage of the underground–aboveground complex are analyzed under multidirectional seismic motions, and the damage distributions of the structures are provided. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis, electromagnetic evaluation, and prototyping of a novel motor structure called the sinusoidal rotor switched reluctance motor. In this innovative design, a significant departure from the conventional switched reluctance motor is observed, as modifications are made to the rotor with the goal of reduction torque ripple and radial force characteristics. Importantly, despite these advancements, the proposed motor retains the weight and volume characteristics of the traditional, type. The key attributes of these motors have been thoroughly assessed using the three‐dimensional finite element method, complemented by a sensitivity analysis aimed at identifying the most optimal configuration within the proposed design. The findings reveal that the suggested structure successfully achieves a notable reduction in torque ripple and radial force when compared to the traditional counterpart, albeit with an expected reduction in average torque. These features render the new topology particularly well‐suited for applications that prioritise noise and vibration reduction. Furthermore, the effectiveness of the proposed topology is corroborated through experimental tests, providing empirical evidence of its advantages and potential for practical applications. [ABSTRACT FROM AUTHOR]

In this paper, the effect of non‐relaxing torsion loadings on the fatigue lifetime reinforcement of carbon black filled natural rubber is fully addressed. Torsion fatigue tests with different loading ratios have been performed with highly notched axisymmetric‐shaped specimens. Finite element analysis is used to predict the mechanical state at any point in the specimens. The prediction is significantly improved by taking into account the heterogeneous accommodation. The first Haigh diagram under fatigue torsion is built and analyzed by calculating the minimum loading in terms of the Cauchy stress as the normal stress to the crack for the minimum angle prescribed during the cycle. A strong lifetime reinforcement has been observed, which is found to be of the same amplitude to the one obtained under uniaxial tension with the same material. This has been confirmed by specific tests that combined non‐relaxing torsion and non‐relaxing tension loadings. Post‐mortem analysis carried out at the macroscopic and the microscopic scales enabled us to identify damage mechanisms, especially in the cases where the lifetime reinforcement was observed. [ABSTRACT FROM AUTHOR]

Surface integrity influences the material fatigue performance significantly, but most micromechanical models based on crystal plasticity only consider the microstructure of the matrix. In this paper, a crystal plastic finite element modeling method was proposed, which simultaneously considered surface roughness, residual stress, and gradual microstructure. It was verified through multiaxial fatigue experiments of materials processed by different multistage machining processes. The results show that larger axial residual compressive stress and smaller grain size can lead to higher multiaxial fatigue life. The existence of residual compressive stress causes the location of material crack initiation to decrease from the surface layer to the subsurface layer. The proposed model can predict the multiaxial fatigue life of materials within a 50% error band. Highlights: A crystal plasticity model considering surface integrity was established.The multiaxial fatigue life of turning specimens is higher than that of grinding.The residual compressive stress cause crack initiation at the subsurface layer.A fatigue life prediction method was proposed within a 50% error band. [ABSTRACT FROM AUTHOR]

In this paper, counter rotating dual rotor wound field flux switching wind power generator is revisited to study the generating characteristics of the AC output power curves based on finite element analysis (FEA) and experimental study. Analysis are performed under dynamic conditions, such as variable resistance, field excitation and speed. Also, electromagnetic performance is studied under variation of the field and armature currents. Analysis reveals that outer port machines with higher power capability and better electromagnetic performance compared to the inner port counterparts, although with higher fluctuations exhibited on the torque profiles of the former due to higher slotting effects. From the power generation characteristics curves, it is clear that the developed wind generator is able to produce reliable performance over a wide operating range. The accuracy of the FEA predicted results are validated, experimentally. The cover image is based on the Research Article Generating characteristics and experimentation of counter rotating dual rotor wound field flux switching wind generator by Wasiq Ullah et al., https://doi.org/10.1049/elp2.12374. [ABSTRACT FROM AUTHOR]

Harmonic magnetic gears (HMGs) have the advantage of lubrication‐free, high speed ratio and high torque density, which make it an attractive solution for safety critical applications. Due to eccentricity caused by machining and assembly, HMG suffers from dynamic eccentricity (DE) in operation, however, its effect on HMG performance is still unknown. Transmission characteristic of HMG under DE is studied. First, a magnetic equivalent circuit (MEC) model of HMG is proposed to build the magnetic coupling torque analytically, and the geometry of air gap is analysed parametrically to derive its equivalent reluctances. Flux density and coupling torque can be acquired by solving MEC equations. The accuracy of the MEC model is verified by finite element method. To study the transmission characteristic, an electromechanical coupling simulation framework for HMG is constructed, motion trajectories of rotors are investigated in case of DE, the output torque in locked‐rotor condition and speed response in continuous operation can be derived by simulation. It is found that torque ripples that have the same frequency with input rotor are induced by DE; the results are then verified in the experiment. This paper provides a theoretical guidance for the design and condition monitoring of HMG. [ABSTRACT FROM AUTHOR]

This paper introduces a technique aimed at improving the performance of an interior permanent magnet synchronous machine (IPMSM) by reducing torque ripple and radial force harmonics. Unlike conventional IPMSMs, the proposed method employs a variable airgap length that is defined by a mathematical function. Two distinct rotor shapes are investigated to determine the most efficient design. Finite Element Analysis is employed to assess both the electromagnetic and mechanical attributes of the proposed motors. It compares the results for three operating points of the shaped motor with those of a conventional one. The investigation delves into the influence of rotor geometry on key output parameters, including Back Electromotive Force (back‐EMF) harmonics, average torque, cogging torque, torque ripple, efficiency, power factor, and radial force harmonics. The findings indicate that optimising rotor shape can significantly enhance IPMSM performance by reducing torque ripples and radial force harmonics, while simultaneously increasing average torque and efficiency at different operating points. [ABSTRACT FROM AUTHOR]

This paper evaluates the influence of contact pressure on the surface contact state, fretting damage degradation mechanism, crack initiation and propagation characteristics, and fretting fatigue life of A319‐T6 cast aluminum alloy in fretting fatigue test using bridge‐type fretting pad. For a certain range of contact pressure, the fretting fatigue life exhibits a trend of increasing and subsequently decreasing with increasing contact pressure. With finite element analysis, the fretting contact region can be divided into two characteristic zones according to the dynamic evolution of the contact status within one fatigue cycle. The contact pressure affects both the distribution of the two characteristic zones as well as the relative slip range, which results in distinct fretting damage mechanisms. The nucleation characteristics and propagation paths of fatigue cracks under three typical contact pressures were analyzed considering the effects of fretting damage and heterogeneous microstructures of the alloy, accounting for the contact pressure dependency of the fretting fatigue life. Highlights: The dynamic evolution of the contact status affected by contact pressure is considered.The fretting damage evolution with the variation of contact pressure is evaluated.The nucleation characteristics and propagation paths of fatigue cracks are elaborated.The contact pressure dependency of the fretting fatigue life is summarized. [ABSTRACT FROM AUTHOR]

Background: This paper compares experimental findings and simulation outcomes of single and multiple protein models moving through a nanopipette biosensor. It provides insights into the factors influencing the process and explores their relevance to proteomics. Methods: Nanopipette biosensors were produced by pulling borosilicate glass tubes and treating them with an electron beam. A scanning electron microscope was used to characterize the nanopipettes. The study measured and modeled ionic currents for the elastase‐specific inhibitor protein. Simulation models were developed using the finite element method and Poisson–Boltzmann formalism, considering different protein configurations and translocation scenarios. Results: The results showed that the pore current of a nanopipette decreases as the protein approaches the nanopipette. The minimum pore current occurs at the widest part of the protein, and the current increases as the protein progresses through the nanopipette. For multiple protein translocations, the pore current decreases between the widest parts of the first and second proteins, and the lowest current is observed at the broadest part of the second protein. After the third protein, the pore current remains constant. It is also found that the fractional blockade difference, translocation speed, fluctuation in pore current, and dwell time are all affected by the number of proteins translocating through the nanopipette. The fractional blockade difference, the decrease in pore current caused by the protein, increases with the number of proteins while the translocation speed decreases. The fluctuation in pore current and dwell time is also longer for three‐protein translocations than for single‐protein translocations. Conclusion: This study offers valuable insights into biomolecule transport through nanopipettes, enhances our understanding of protein dynamics in restricted environments, and significantly contributes to single‐protein sequencing studies, drug screening, and proteomics. [ABSTRACT FROM AUTHOR]

To solve the problems mechanically caused by parallel direct‐drive permanent magnet motors (DD‐PMSM). This paper proposes a concave‐core stator direct‐drive permanent magnet motor (CCSDD‐PMSM) structure. In this study, an auxiliary yoke structure is proposed to optimise the magnetic circuit and analyse the cogging torque to achieve the minimum detent force. Based on the unit motor and combined with the magnetomotive force to analyse the symmetry of different winding distributions, the stability characteristics of the motor are studied. The magnetic field distribution of the motor load air gap is calculated using the finite element method. The contribution of different spatial order harmonics to the motor output torque is calculated using the Maxwell tensor method. The torque calculation expression of the CCSDD‐PMSM is given. Finally, an experimental prototype is made to verify the accuracy of the analysis in this paper. [ABSTRACT FROM AUTHOR]

During the multistage fracturing of shale gas horizontal wells, casing damage frequently occurs, making it essential to evaluate casing stress and deformation. This paper establishes a mathematical model of thermo‐hydro‐mechanical coupling and a finite element model of casing‐cement sheath‐formation (CCF). This paper examines the effects of temperature, casing thickness, nonuniform in situ stress, mechanical properties of cement sheath, and treating pressure on the stress and deformation of CCF. Finally, the study investigates the variation of local in situ stress at the heel and casing stress from toe to heel. The results show that the low temperature of CCF, high elastic modulus of cement sheath, small casing thickness, high treating pressure, and large nonuniform in situ stress can exacerbate casing stress. After pumping off, the local in situ stress and its nonuniformity near heel gradually increased, and the effective stress of casing increases compared with the pumping on the process. As the fracturing stages increase, the effective stress of casing at heel increases, and the casing at heel preferentially damages. The results provide a theoretical basis and guidance for maintaining wellbore integrity and preventing casing damage in the multistage fracturing of shale gas horizontal wells. [ABSTRACT FROM AUTHOR]

This paper presents the mixed mode I/II stress intensity factors (SIFs) of slanted cracks/notches under tension loading. A two‐dimensional finite element analysis (FEA) was employed using the ABAQUS program. Based on the literature survey, there is a lack of solutions for SIFs of slanted cracks in plane stress plates. The strain energy approach (SEA) was adopted to analyze the notched cases. Mode I and II SIFs are derived via the SEA method from the strain energy computed using the FEA technique. The results show excellent agreement with other researchers' work. The key contribution of the present paper is the presentation of the effect of the crack/notch length to plate width ratio on the mode I and II SIFs of a slant‐edge‐cracked/notched plate under different boundary conditions. Sets of new data of mode I and II SIFs are provided herein in tabular and graphical formats. Highlights: Stress intensity factors (SIFs) of single edge‐cracked/notched plates under mode I/II loading computed.Parametric and comparative analysis of SIFs of pinned/clamped boundary conditions (BCs).SIFs derived from finite element analysis (FEA) computed elemental energies by strain energy approach.Effects of pinned and clamped BCs on mode I/II SIFs of cracked/notched plates shown. [ABSTRACT FROM AUTHOR]

This paper proposes the upscaling of conventional individual bridge health monitoring problems into urban regions and transportation networks via mobile and smart sensing techniques together with an innovative reconnaissance procedure. The paper associates structural failure probabilities with systemic features and proposes decision criteria to optimize postdisaster actions. Twenty bridges constituting transportation network infrastructure compose the testbed region and utilize smartphone accelerometers for dynamics characterization in a vibration‐based framework. In this framework, reconnaissance output serves for model development, and mobile sensor data enable finite element model updating. Structural reliability analyses merged in a chain setting generate the systemic behavior of cascaded bridge performance. Combining systemic reliability with transportation and health services demand, one can optimize the response strategies of the bridge population and strategize disaster‐related decisions in a postevent assessment setting. Based on a testbed region with remote access to nearby vicinities, 18 earthquake scenarios are conducted to visualize the optimal evacuation strategies on the network, taking systemic bridge performance into consideration. Cost‐free mobile sensing support adds one more fundamental information source for reducing the uncertainty of the models and, therefore, improves associated mitigation actions. [ABSTRACT FROM AUTHOR]

Fractional slot concentrated winding (FSCW) permanent magnet (PM) machines are gaining more attention for low‐speed applications because of their great advantages. This paper proposes a new structure for an FSCW double rotor axial flux PM synchronous machine (DRAFPMSM) with counter‐rotating rotors. In addition, an analytical formula for the Back EMF waveform of the proposed structure is presented. The accuracy of the formula is investigated by designing a 40 W sample machine. The rotors of this machine rotate with speeds of 600 and 428 rpm in opposite directions. The Back EMF of the sample machine is calculated using the suggested formula. In addition, the finite element method (FEM) is used to determine the Back EMF waveform. Comparison of the obtained results confirms that the new formula yields the Back EMF precisely such that the results well match to those of FEM. The effect of the relative position of two rotors on the Back EMF waveform is investigated using the proposed formula. In addition, the optimum relative position of two rotors for minimizing the Back EMF THD of the case study machine is determined. [ABSTRACT FROM AUTHOR]

Deformable superstructures are man‐made materials with large deformation properties that surpass those of natural materials. However, traditional deformable superstructures generally use conventional materials as substrates, limiting their applications in multi‐mode reconfigurable robots and space‐expandable morphing structures. In this work, amine‐acrylate‐based liquid crystal elastomers (LCEs) are used as deformable superstructures substrate to provide high driving stress and strain. By changing the molar ratio of amine to acrylate, the thermal and mechanical properties of the LCEs are modified. The LCE with a ratio of 0.9 exhibited improved polymerization degree, elongation at break, and toughness. Besides an anisotropic finite deformation model based on hyperelastic theory is developed for the LCEs to capture the configuration variation under temperature activation. Built upon these findings, an LCE‐based paper‐cutting structure with negative Poisson's ratio and a 2D lattice superstructure model are combined, processed, and molded by laser cutting. The developed superstructure is pre‐programmed to the configuration required for service conditions, and the deformation processes are analyzed using both experimental and finite element methods. This study is expected to advance the application of deformable superstructures and LCEs in the fields of defense and military, aerospace, and bionic robotics. [ABSTRACT FROM AUTHOR]

In vitro reconstruction of highly mature engineered heart tissues (EHTs) is attempted for the selection of cardiotoxic drugs suitable for individual patients before administration. Mechanical contractile force generated in the EHTs is known to be a critical indicator for evaluating the EHT response. However, measuring contractile force requires anchoring the EHT in a tailored force‐sensing cell culture chamber, causing technical difficulties in the stable evaluation of contractile force in long‐term culture. This paper proposes a hydrogel‐sheathed human induced pluripotent stem cell (hiPSC)‐derived heart microtissue (H3M) that can provide an anchor‐free contractile force measurement platform in commonly used multi‐well plates. The contractile force associated with tissue formation and drug response is calculated by motion tracking and finite element analysis on the bending angle of the hydrogel sheath. From the experiment of the drug response, H3M is an excellent drug screening platform with high sensitivity and early testing capability compared to conventionally anchored EHT. This unique platform would be useful and versatile for regenerative therapy and drug discovery research in EHT. [ABSTRACT FROM AUTHOR]

The main bearing assembly structure is one of the most important main load‐bearing structures of a diesel engine. The working loads of this structure increases dramatically with the increase of the power density of diesel engines, resulting in the problem of unsatisfactory reliability coordination design in restricted design space, while the mechanisms for coordinated design are still at the blank stage. Aiming at the problem, a multilevel multiobjective coordination matching design technique is innovatively proposed in this paper. This technique is characterized by a multilevel multiobjective coordination evaluation system for the assembly structure and its components based on the improved analytic hierarchy process. The finite element model and mathematical model of the main bearing assembly structure are established to realize the joint of finite element technology and optimization technology for coordination matching design. By carrying out verification experiments, the strength coordination, deformation coordination and contact strength coordination of the assembly structure increase by 13.91%, 14.96%, and 2.63%, respectively, after matching design, while the mass coordination remains almost constant meeting the lightweight design requirements. The overall coordination of the main bearing assembly structure is improved by 11.10%, achieving the goal of matching design of the main bearing assembly structure. The results show that the coordination evaluation system can quantitatively characterize the coordination relationship of the assembly structure and the multi‐reliability of components, and it is a feasible coordination evaluation method. The demonstrated coordination evaluation system and coordination matching design modeling approach provide important theoretical guidance for the matching design of complex assembly structures. [ABSTRACT FROM AUTHOR]

An improved moment of load path model for rolling contact fatigue life prediction is proposed in this paper. First, the complex multiaxial stress variation of the subsurface materials under rolling contact conditions was analyzed by the finite element method. Next, the equivalent stress parameter was presented to characterize the complex stress state based on the improved moment of load path method. The key concept of the proposed method is building a new coordinate system for analyzing the load path of the complex multiaxial stress state. The efficiency of the proposed model was validated with different kinds of fatigue test results in the existing literature. The model results show a good agreement with the test data. Finally, the model was used to obtain the relationship of the Hertz stress versus fatigue life under rolling contact conditions according to the fatigue life data. Highlights: The proposed multiaxial life prediction model considers the hydrostatic stress.The correlation of the multiaxial test data is built using a defined stress parameter.Rolling contact fatigue life is predicted by the proposed multiaxial model. [ABSTRACT FROM AUTHOR]

Sanding production of the underground gas storage (UGS) in the depleted reservoir will cause the decline of effective storage capacity, and the erosion of well string and auxiliary equipment, and other engineering problems. A deep understanding of the sanding production contributes to maintaining the injection and production capacity of gas storage and the long‐term safety of the UGS. In this paper, core samples of five main sedimentary microfacies were drilled from the UGS in middle China. The mechanical properties with different conditions of the moisture content in multi‐cycling injection–production process were tested. The critical drawdown pressure (CDP) calculation methods for the UGS were established based on the stress analysis near the wellbore and the Mogi–Coulomb criterion. Adopting the finite element method simulation on the geological model of the target UGS, the geo‐stress of the formation was calculated by inversed analysis and validated based on the Kaiser effect of rock. Then, the CDP of two target wells of the UGS were investigated. The effects of the water moisture and the cycling times of the injection–production process on the CDP were also analyzed. The geo‐stress distribution shows that the horizontal maximum principal stress ranges from 53 to 68 MPa, and the horizontal minimum principal stress is 46–58 MPa in the target reservoir section, and the vertical minimum principal stress is 69–77 MPa in the target reservoir. The calculated CDP changed with the types of the sedimentary microfacies in the range of [6.27, 8.77] MPa, in which the CDP of the mixed mud and sand flat sedimentary facies was the lowest. The weakness of the CDP with the increasing of the moisture content and the cycling times were analyzed quantitively. [ABSTRACT FROM AUTHOR]

Calibration of unknown model parameters is a common task in many ocean model applications. We present an adjoint‐based optimization of an unstructured mesh shallow water model for the Baltic Sea. Spatially varying bottom friction parameter is tuned to minimize the misfit with respect to tide gauge sea surface height (SSH) observations. A key benefit of adjoint‐based optimization is that computational cost does not depend on the number of unknown variables. Adjoint models are, however, typically very laborious to implement. In this work, we leverage a domain specific language framework in which the discrete adjoint model can be obtained automatically. The adjoint model is both exactly compatible with the discrete forward model and computationally efficient. A gradient‐based quasi‐Newton method is used to minimize the misfit. Optimizing spatially‐variable parameters is typically an under‐determined problem and can lead to over‐fitting. We employ Hessian‐based regularization to penalize the spatial curvature of the friction field to overcome this problem. The SSH dynamics in the Baltic Sea are simulated for a 3‐month period. Optimization of the bottom friction parameter results in significant improvement of the model performance. The results are especially encouraging in the complex Danish Straits region, highlighting the benefit of unstructured meshes. Domain specific language frameworks enable automated model analysis and provide easy access to adjoint modeling. Our application shows that this capability can be enabled with few efforts, and the optimization procedure is robust and computationally efficient. Plain Language Summary: Ocean circulation models have several unknown parameters that must be tuned for each application in order to produce physically meaningful results. The tuning process can be a very laborious and time consuming task. In this paper, we investigate an automated way to tune the model's friction at the sea bed to minimize the model's error in predicted sea surface height (SSH). The method is based on a novel way of defining the model's equations which enables solving such optimization problems automatically. The methodology is tested in the Baltic Sea. The modeled SSH is compared against observations at several tide gauges. We show that by optimizing the bottom friction, the model's capability to predict SSH improves significantly. Moreover, we show that the optimization process is robust and computationally efficient. Key Points: Adjoint‐based optimization is used to optimize bottom friction coefficient in 2D water elevation model for the Baltic SeaThe discrete adjoint model is automatically generated by leveraging a symbolic representation of the discrete forward model equationsThe optimization method is robust and results in significant improvement in the sea surface height performance at tide gauge locations [ABSTRACT FROM AUTHOR]

The traditional extended finite element method (XFEM) is suitable for simulating crack growth, but the crack‐tip stress field analysis still depends on the enriched function. In this paper, based on the numerical eigensolution of the singular displacement and stress field together with the Hellinger–Reissner (H–R) variational principle, a novel crack‐tip singular element is established to replace the enriched element in the crack‐tip region in the traditional XFEM. The stress field inside the element adopts a series expression instead of only including the leading‐order terms. The element only requires Gaussian integration at the element boundary and avoids mesh refinement in the crack‐tip region. The element can be used to analyze cracks in anisotropic materials, interface cracks, and cracks terminating at the bimaterial interface. The numerical solutions of the singular stress field in various crack forms are presented through numerical examples, which proves the effectiveness and versatility of the novel crack‐tip singular element. Highlights: An extended finite element method with a novel crack‐tip singular element is proposed.The convergence speed of the present extended finite element method is satisfactory.The compatibility between the singular element and other elements is good.The singular element has the feature of multifunction. [ABSTRACT FROM AUTHOR]

In this paper, the two‐dimensional (2D) (0°/90°) plain‐woven Amosic‐3 SiC/SiC turbine guide vane (TGV) was fabricated using the chemical vapor infiltration method. Thermal and stress analysis of the TGV was conducted using the finite element method analysis. Multiple thermal shock tests at T = 1250, 1350, 1400, 1420, 1450, 1470, and 1480°C were conducted for N = 100, 100, 400, 300, 200, 200, and 700 cycles. After thermal shock tests, the surface damage of the TGV was observed visually, and the micro damage mechanism was analyzed using the scanning electronic microscopy. Micro X‐ray computed tomography was adopted to characterize the internal damages in the SiC/SiC guide vanes. The delamination occurred at the positions approaching internal hollow, due to the weak binding force along the thickness direction and the high thermal shock stress caused by the temperature change. The diameter, area, volume, and sphericity distributions of the pores inside of the guide vanes were also obtained. [ABSTRACT FROM AUTHOR]

Conformal contact is a commonly presented contact form in assemblies. Non‐proportional loading is the main characteristics of conformal contact, which leads to prominent difficulty in revealing fretting crack behavior. In this paper, a finite element prediction model for Ti‐6Al‐4V pin‐hole contact fretting fatigue crack initiation was developed, which simultaneously considered the effect of fretting wear, surface roughness, surface skewness, surface kurtosis, and residual stress. The results show that phase differences of stress component, change in direction of principal stress, and high stress gradient are the main reasons for the initiation of fretting fatigue under conformal contact condition. The model based on the Fatemi–Socie (FS) parameter successfully predicted the location, orientation, and fatigue life of crack initiation, which agrees well with the experimental results. Additionally, machining‐induced residual stress can effectively inhibit mode I crack initiation at valleys. Moreover, ignoring the surface microgeometry characteristics reduces the prediction accuracy of the crack behavior. Highlights: Surface microgeometry characteristics and residual stress were considered.Residual stress has less effect than roughness on conformal contact fretting fatigue.Consideration of surface geometry significantly improves the prediction accuracy.The predicted results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The mismatching constraint effect on crack propagation through the heat‐affected zone (HAZ) in a welded joint is presented in this paper. It is shown that due to this effect, the fracture behavior of an overmatched welded joint depends on the mechanical properties and the size of the region of the crack tip location, as well as on the properties and the size of surrounding regions. The finite element analysis of high‐strength low‐alloyed (HSLA) steel welded joints with crack tips in the heat‐affected zone is performed based on previous experimental work. Two locations of the crack tip are analyzed: fine‐grained HAZ (FGHAZ) and coarse‐grained HAZ (CGHAZ). In both cases, after the initial propagation of the crack in FGHAZ or CGHAZ, its propagation is directed toward more ductile base metal, thus increasing the fracture resistance of a welded joint. Some new observations about the reasons for such behavior due to crack tip strain fields are presented as well. Highlights: The behavior of the crack with the tip located in fine‐grained heat‐affected zone (FGHAZ) is under the significant influence of adjacent coarse‐grained HAZ (CGHAZ) and WM.Strain at the crack tip in CGHAZ is absorbed by more ductile regions, causing more favorable stress conditions.In both cases, overmatching changed the crack propagating direction toward weaker and more ductile base metal (BM). [ABSTRACT FROM AUTHOR]

Due to its simple construction, the linear induction motor (LIM) provides a linear driving force without any intermediate motion translation system. LIMs are widely used in various industrial applications, including maglev rail transit and the national defense industry. However, LIMs are affected by the end effect and suffer from problems such as low efficiencies and low power factors. To make improvements, in this paper, an ensemble multi‐objective optimal design method for a short primary double‐sided linear induction motor (SP‐DLIM) is proposed. First, a simplified Quasi‐3D equivalent circuit model (ECM) for an SP‐DLIM applicable to the model in this paper is derived. The 3‐D transient finite element method and an experimental prototype are utilised to prove that the derived ECM is accurate enough to solve the SP‐DLIM optimisation problem. Second, an ensemble multi‐objective optimal design method of SP‐DLIM is presented, with proposed design constraints and four different optimisation problems. Then, an improved differential evolutionary (IDE) algorithm is proposed to optimise the efficiency, power factor, and tooth weight of the motor. The three‐dimensional time‐stepping finite element method is utilised to verify the validity of the optimisation method. Further, a comparison of the results suggests that the IDE yields the best performance to those of other advanced heuristic algorithms. [ABSTRACT FROM AUTHOR]

This article has conducted a comprehensive study on the stator and rotor vibration characteristics of the doubly‐fed induction generator (DFIG) in the case of radial air gap eccentricity (RAGE). Differently from other previous studies, this paper not only investigates the vibration characteristics of stator and rotor in radial static air gap eccentricity (RSAGE) and radial dynamic air‐gap eccentricity (RDAGE) fault but also takes the radial hybrid air gap eccentricity (RHAGE) into account. Through theoretical derivation, the detailed expressions of stator magnetic pull per unit area (MPPUA) and rotor unbalanced magnetic pull (UMP) are obtained. The finite element analysis (FEA) and experiment based on a two pairs of poles DFIG, and the results are consistent with theoretical calculations. It is shown that RAGE will enlarge the magnitude of stator MPPUA/vibration and rotor UMP/vibration. Specifically, RSAGE will not change the frequency components of stator MPPUA/vibration but will bring new frequency components to rotor UMP/vibration. However, both stator MPPUA/vibration and rotor UMP/vibration will generate new frequency components during RDAGE fault. In addition, the effect of RHAGE is the superposition of RSAGE and RDAGE. The research conclusions obtained in this paper can be used as a supplementary criterion for diagnosing the eccentricity of DFIG. [ABSTRACT FROM AUTHOR]

In this paper, a novel variable‐leakage‐flux interior permanent magnet (VLF‐IPM) motor is proposed, which is a kind of mechanical flux‐adjusting PM motor. The VLF‐IPM motor can obtain the advantages of the IPM motor and overcome the difficulty to adjust PM airgap flux by locating a self‐activating device that is introduced in this paper on the rotor. The effect of the flux barriers on the flux leakage circuit is analysed by establishing a rotor parametric model to clarify the influence of flux barriers of the VLF‐IPM motor on flux‐adjusting performance. Then, the electromagnetic performance of VLF‐IPM motors with different volume ratios of cylindrical permanent magnets (CPMs) and rectangular permanent magnets (RPMs) are compared by using the finite element analysis (FEA) method, and the experiment results show that VLF‐IPM motor with characteristics of 0 < κrc < 1 has more advantages comprehensively. Moreover, a multi‐objective optimization process is adopted based on sensitivity analysis which can reflect the influences of geometric parameters on the optimization objectives including average torque, torque ripple and cogging torque. Then, the Non‐dominated Sorting Genetic Algorithm II(NSGA‐II) is utilised to determine the optimal model. Finally, a prototype is manufactured and tested, and the effectiveness of the novel VLF‐IPM motor and the self‐activating device are verified by the simulation and experiments. [ABSTRACT FROM AUTHOR]

Agricultural rims are highly loaded components which affect the functionality and safety of tractors significantly. For this reason, it is essential to prevent a damage of the rims. However, fatigue‐initiated cracks along the bolt circle arise at any time during application. Until now, the determining load for the crack initiation is unclear. The paper investigates this fatigue problem by experimental, analytical, and numerical methods. Therefore, a test rig using hydraulic actuators is designed to load the rim by rotating bending in combination with a lateral force. The loads are deduced by an analytical model of the tractor under different driving situations like cornering. The finite element model shows the critical locations by performing a fatigue analysis of the driving situation. The experimental and numerical results verify the assumption that the rotating bending in combination with a lateral force leads to the fatigue cracks also found by tractors in reality. Highlights: The paper shows the fatigue testing of 42″ tractor rims under rotating bendingAn analytical model for forces at the wheels for various driving situations is presentedA finite element analysis of this non‐proportional load situation is presentedComparison of experimental and numerical fatigue investigation is shown [ABSTRACT FROM AUTHOR]

Structural damage identification technology based on modal parameters is an extremely effective monitoring method. Because of the structural characteristics of the conductor, with its small diameter and long span, it is not easy to obtain the modal parameters by manual excitation. Here, a method for structural health monitoring of the conductor under wind load excitation is proposed. Firstly, the natural frequency change law of the conductor after broken strand damage is obtained by analyzing the conductor modal parameters calculation formula and IEEE standards. Then, the vibration characteristics are calculated by vibration experiments and finite element methods. Finally, through the broken strand experiment, this paper demonstrates how to determine the damage degree of the conductor using the modal parameters. And it is applied to online monitoring in the field. The results show that this method is convenient, fast, and accurate. [ABSTRACT FROM AUTHOR]

The influences of slot/pole number combinations on electromagnetic performances, including flux linkage, inductance, and torque ripple harmonic components etc., resulting from unbalanced characteristics between north and south poles in concentrated winding permanent magnet (PM) machines with symmetrical and asymmetric rotor pole shaping methods are theoretically analysed and experimentally validated in this paper. It shows that for the PM machines with odd number of coils per phase per submachine, including consequent pole (CP) and surface‐mounted PM (SPM) machines, the influences of unbalanced pole characteristics can lead to additional torque ripple harmonics due to additive effects in windings, but can be cancelled in other machines. Compared with symmetrical pole shaping method, asymmetric pole shaping method can result in lower torque ripple for CPPM machines with odd number of coils per phase per submachine, while symmetrical and asymmetric pole shapes have similar effects on torque ripple reduction for other CPPM machines and all the SPM machines. The findings have been validated by finite element analyses on 12‐slot/8‐pole, 12‐slot/10‐pole, 9‐slot/6‐pole, and 12‐slot/14‐pole machines, and by experiments with 12‐slot/8‐pole and 12‐slot/10‐pole CPPM prototypes. [ABSTRACT FROM AUTHOR]

Compared with the single‐stator permanent magnet synchronous motor(SS‐PMSM), the double‐stator permanent magnet synchronous motor(DS‐PMSM) can make full use of the space in the motor cavity to make it have higher torque density, so it is more suitable for direct‐drive occasions with low‐speed and high‐torque. This paper aims to design and compare the parameters and performances of DS‐PMSMs with four different rotor structures: 1)Series magnetic circuit of radial magnetised single‐layer permanent magnet(type Ⅰ), 2)Series magnetic circuit of radial magnetised double‐layer permanent magnet(type Ⅱ), 3)Parallel magnetic circuit of radial magnetised double‐layer permanent magnet(type Ⅲ), 4)Parallel magnetic circuit of tangential magnetised permanent magnet(type Ⅳ). Firstly, the equivalent magnetic circuit method is used to analyse the magnetic circuits of the four DS‐PMSMs. Next, the finite element analysis tool is used to compare the performances of the four DS‐PMSMs with the same volume. Their air‐gap flux density, no‐load back‐EMF, cogging torque, torque characteristics, moment of inertia, rotor loss and efficiency are quantitatively analysed and compared. Finally, this paper provides guidance and suggestions for the selection of the rotor structure of DS‐PMSM. [ABSTRACT FROM AUTHOR]

The high‐frequency power transformer (HFPT) has become a vital component of the power system. For HFPT insulations, surface discharge is a serious problem. Polyimide (PI) is a widely used insulating material for HFPT's. A needle‐plate electrode structure‐based experimental setup was developed to produce and measure the surface discharge. This paper first time used the fluid‐kinetic model by adopting the finite element simulation method to address the micro‐level study of surface discharge. This paper aimed at the discharge phenomenon of the PI under the direct action of high‐frequency sinusoidal voltage and has not considered the overvoltage phenomenon caused by the waveform parameters that is the actual high‐frequency action on the PI material. The development of surface discharge at various stages was analysed. Particle densities and electric field distributions versus discharge time were determined. Frequency, temperature, and air pressure have a significant effect on surface discharge behaviour. As a result, the applied voltage reaches its peak value at high‐frequency, so the flashover time of surface discharge is reduced under the high frequency. The electron density of the streamer development increases as the temperature rises, and the time to flashover the channel becomes shorter. The higher the electron density and the longer the discharge channel develops while the gas pressure is lower. The simulation results have high accuracy and good agreement with experimental data. [ABSTRACT FROM AUTHOR]

It is difficult to separate Luer lock adapters during the external ventricular drainage (EVD) since they are often connected by a threaded connection, and the infusion needle put into the patient's body gets pulled out when extubation occurs unexpectedly. The paper described a new magnetic connection assembly made up of ring magnetic permanents and a Hall sensor that could be used to replace Luer lock adapters for quicker disconnection and reconnection of the drainage catheter. For the design and analysis of the device, the finite element method magnetics (FEMM) was used to estimate the size of magnetic permanents and the best detection site of the Hall sensor for detecting whether the magnetic permanents were closely attracted and/or pulled apart. Then an experiment was conducted to confirm our findings. Both simulation and experiment revealed that a pair of hollow cylindrical magnetic permanents, each with height 10 mm, outer diameter 8 mm, and inner diameter 4 mm, could achieve the same force as the Luer lock adapters held, and that the best Hall sensor detection position was in the middle of the permanent magnets, with a radial distance of about 2 mm. [ABSTRACT FROM AUTHOR]

Permanent magnet eddy current couplers have been widely used in large fan and pump loads to achieve the purpose of speed regulation and energy saving. In order to reduce the coupler axial volume and simplify the actuator, a novel flux adjustable axial flux permanent magnet eddy current coupler (FAAF‐PMECC) is proposed in this paper. The permanent magnet rotor is divided into three parts: the inner, middle and outer parts, where the permanent magnets are embedded in the core and the adjacent poles are magnetised in opposite directions. The middle part is the adjusting permanent magnet ring (AR), which can rotate around the shaft. The inner part and outer part are fixed permanent magnet rings (FR) that are fixed with the shaft, and the output torque can be controlled by adjusting the relative angle of AR and FR. The structure and working principle of FAAF‐PMECC are described in detail, and the output torque analytical model of the whole regulating process is established based on the magnetic equivalent circuit method. The AR regulation process is simulated by the variable reluctance model. The validation results show that the proposed structure can achieve a good speed regulation effect, and the output torque calculated by the analytical model in a certain slip speed range matches well with the output torque obtained using the 3D finite element method and experimental measurements. The sensitivity analysis of the structure parameters is also carried out. The analysis shows that the proposed coupler can achieve a wide speed range. [ABSTRACT FROM AUTHOR]

In this paper, the analytical relationship among supply voltage, current, and structure parameters of the permanent magnet (PM) motor is cleverly deduced by using an intermediate‐flux linkage. After further consideration of boundary conditions, the direct field‐circuit coupled analytical model in integrated matrix form is subsequently constructed. Using this model, the vector potentials and currents of the motor can be calculated simultaneously, and the electromagnetic performance, such as the output torque, winding flux linkage, and so on can be further calculated by the vector potentials. Because the control parameters and motor structure parameters are both considered in the derivation process, the proposed analytical model can be used to analyse the motor operation performance under different control strategies. Its validity is finally verified on a 10‐pole/12‐slot PM motor. The results of the proposed direct field‐circuit coupled analytical model are compared with those of field‐circuit coupled time‐stepping finite element model and experiment under speed‐current double closed‐loop and current closed‐loop control strategies, respectively. The results of the proposed model are proved well with finite element simulation and experimental results. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the optimal design of a 120 W outer‐rotor permanent magnet synchronous machine for air‐conditioning applications to reduce the electricity consumption and machine costs. To this end, a 2‐D analytical magnetic model, combined with a teaching–learning based optimisation algorithm is employed. The objectives are to simultaneously maximise the machine efficiency and minimise the material cost. Constraints such as the required output torque, predefined machine volume, maximum allowable torque ripple and unbalanced magnetic force and limitations to avoid iron core magnetic saturation are imposed simultaneously. To find the flux density in iron parts, a new method based on the subdomain technique has been presented. To evaluate the analytical model in terms of accuracy and speed, the results of the 2‐D analytical approach are compared with those of the 2‐D and 3‐D linear/non‐linear finite element method. Finally, a prototype of the optimised machine is fabricated and the superiority of the presented approach is demonstrated. [ABSTRACT FROM AUTHOR]

A novel DC‐Excited Flux‐Switching Linear Motor (DC‐FSLM) is investigated in this paper, where a simple secondary is used as the machine stator. The phases and excitation windings are placed on the primary, which contributes to a low‐cost and simple structure linear motor with acceptable dynamic performance. The motor operation under dynamic load is analysed by a parametric Magnetic Equivalent Circuit (MEC), and the core saturation is modelled by the non‐linear reluctance of the flux tubes. Moreover, the end‐effect is considered by virtual zones at both entrance and exit ends of the primary. In the considered MEC, the model accuracy can be selected as desired as well as different DC‐FSLMs with various properties can be modelled. Finally, the machine capabilities and performance characteristics are discussed by simulation results, and validation is performed by the Finite Element Method (FEM). [ABSTRACT FROM AUTHOR]

There are still many gaps in the research on the multiaxial fatigue failure mechanism of the gear shaft. In this paper, cyclic stress–strain response and biaxial fatigue damage characteristics of gear steel AISI 9310 were investigated. The specimens showed obvious cyclic softening characteristics at all phase angles, and the softening rate was directly associated with the initiation and propagation of cracks. The fractographies at different phase angles revealed that the specimens under out‐of‐phase loading suffered fatigue failure caused by a single crack source on the surface, while the fatigue crack under in‐phase loading was gathered together by the propagation of different crack sources. Finally, the established crystal plastic finite element model showed a good prediction of the plastic strain energy density at different phase angles, and the maximum error was 13.03%. Furthermore, a biaxial fatigue life prediction method was proposed, with a maximum error of 39.5%. Highlights: Plastic strain energy density shows logarithmic relationship with the number of cycles.The OP loading fatigue crack propagation failure was caused by a single crack source.The established crystal plastic model could effectively simulate plastic strain energy density.A fatigue life prediction method was proposed, with a maximum error of 39.5%. [ABSTRACT FROM AUTHOR]

The humidity role in the partial discharge (PD) inception mechanism is quite challenging, especially when considering the environmental temperature. Indeed, there is no general rule to explain the humidity effect on the PD phenomenon. In this paper, the PD activity in inter‐turn insulation is experimentally investigated for different relative humidity (RH) conditions at three different ambient temperatures, that is, 30°C, 60°C, and 90°C. Partial discharge inception voltage (PDIV) is directly measured through a photomultiplier tube (PMT), whereas the tip‐up tests are performed aiming at monitoring both dissipation factor (tanδ) and insulation capacitance (IC). These extra measurements (diagnostic dielectric markers) allow better assessing the insulation status. The adoption of the tip‐up test enables the insulation properties measurement. Based on the tip‐up tests' findings, the interfacial polarization process starts at 75% RH under 60°C, while the high conductivity area is already formed at 75% RH when the ambient temperature is 90°C. The water film formation deduced from the tip‐up test is then used to explain the trend of PDIV, and the validity is further proved by finite element analysis (FEA). [ABSTRACT FROM AUTHOR]

The efficiency, power density, and torque of axial flux generators are higher than those of radial flux generators. In this paper, a new axial flux switching generator with a coreless stator is designed for micro wind turbine applications. Generator parts are designed based on nominal values, and their dimensions are determined. Cogging torque is an undesired torque ripple intrinsic in the design of a permanent magnet generator, which should be minimized due to its effects: vibration and noise. In addition, since aerodynamic power is low during start‐up at low wind speeds, the cogging torque must be as low as possible to achieve a low cut‐in speed. The design, optimization, and fabrication of a new coreless axial flux‐switching generator for micro‐wind turbine application are investigated and compared with the conventional one. The prototype machine is an axial‐field flux‐switching permanent magnet generator with a two‐rotor‐one‐stators configuration. The stator of the proposed generator is made up of coils and magnets and has no iron core. First, the generator's design to reduce cogging torque is investigated using nominal values, and the dimensions of the various parts of the generator are calculated according to these values. Then the designed generator was simulated three‐dimensionally using the FEM. Finally, a prototype of the desired generator is built. Comparing the results obtained from the finite element method and laboratory testing shows that these results are broadly consistent. [ABSTRACT FROM AUTHOR]

Electrical machine design optimization is an expensive procedure as it contains numerous variables and multiple objectives. Therefore, it might require hundreds of time‐consuming finite element analyses (FEA). Surrogate models are one of the superior alternatives that can overcome the computational burden of FEA. However, in optimization problems with sensitive input‐output relationships, surrogate models can lack accuracy or suffer from unreasonable initial FE‐computational cost. To tackle this problem, this work presents a novel strategy called Waveform‐Targeted Surrogate Modeling (WTSM) that improves the computational efficiency of surrogate‐based design optimization of electrical machines by modifying the model construction process. In this paper, an Interior Permanent Magnet Machine (IPMSM) is studied to evaluate the proposed strategy's performance compared to the conventional Black Box Modeling (BBM) method. A two‐step assessment procedure consisting of multiple scenarios has been developed to analyse the reliability of the WTSM concerning different training‐validation datasets. Meanwhile, the Kriging model and Latin‐Hypercube‐Sampling (LHS) method are employed for surrogate model construction purposes. From the discussion and the results, it can be found that the proposed WTSM strategy can significantly increase the accuracy of the surrogate modelling procedure while the required computational cost can be reduced. [ABSTRACT FROM AUTHOR]

The impulse impedance of the tower is the core parameter to evaluate the lightning protection performance of the transmission line. The high soil resistivity and the underground rock layers in the mountainous areas will induce large impulse impedance and further lead to frequent lightning striking accidents. Therefore, this paper proposes a circuit‐finite element model (CFEM) and investigates the corresponding impedance‐reduction optimization method of the grounding device in mountainous areas. The model takes into account the nonlinear characteristics of the soil. Based on the parallel‐plate electrode and the concentric hemispheric test device, the nonlinear curves of the soil resistivity of five typical kinds of soils with the electric field intensity are obtained. To justify the CFEM, the field experiment of a single horizontal conductor is performed, with an average relative error of 4.67%. Based on the CFEM, this paper presents an impedance‐reduction optimization method for the grounding device in the mountainous areas, while proposing the best design method and the optimal layout of the grounding device in the rocky zone. The research results can provide a reference for the design transformation and protection optimization of the transmission tower grounding device in mountainous areas. [ABSTRACT FROM AUTHOR]

Time‐domain reflectometry applied for power cable diagnostics employs transmission line parameters to determine signal shape and delay. This paper proposes to utilize pulse reflection measurement to evaluate the symmetry of a three‐core power cable as part of production quality assessment. For a rotation‐symmetric three‐core power cable, transmission line parameters can be obtained analytically, and with modal analysis propagation channels can be decoupled. Asymmetry caused by inaccurate core positioning complicates the decoupling process. This paper utilizes the "field‐circuit" approach for the analysis. The finite element method is used to obtain the electromagnetic field distribution for two types of asymmetry introduced in a cable design. Modal analysis results are validated by considering asymmetry as a perturbation of the symmetric cable design. The influence of asymmetry on the time‐domain pulse response is simulated. Deviation from a symmetric configuration is observable, in particular in terms of propagation velocity, which can be employed to assess cable manufacturing accuracy. [ABSTRACT FROM AUTHOR]

With the railway advancement of speed and load capacity, new high‐power diesel locomotives occupy a prominent position. Due to the susceptibility of onboard signal equipment comprised of microelectronic devices, the diesel locomotive's traction motor (TM) may produce serious disturbance to cab signalling, possibly distorting the signal pattern via receiving coils, even resulting in mutation and decoding error of cab signals. However, the existing research studies pay little attention to this electromagnetic interference problem. This paper studies the radiated alternating magnetic field of the TM and interference coupling path to onboard equipment. It first analyses the cab signalling working principle and clarifies the interference mechanism, focussing on the quantitative analysis of the radiated magnetic field and interference electromotive force. Then, based on the ANSYS platform, the finite element method is used to complete modelling, simulation, and verification. Finally, combined with the railway field data, a typical interference case is analysed, verifying that the distorted signal pulses under the radiated magnetic field are the primary cause of decoding failures. This research establishes the quantitative relationship between the traction radiation intensity and the interference amplitude on signals, helping explore the countermeasures, improve the cab signal decoding accuracy, and ensure transportation efficiency. [ABSTRACT FROM AUTHOR]

The doubly fed induction generator is commonly used in commercial wind turbines because of its simplicity and robustness; it is a wound rotor induction machine. It has a relatively small airgap which makes it more vulnerable to unbalanced magnetic pull. This paper presents a simulation model to investigate the ability of extra stator windings with pm ± 1 pole‐pairs to control the unbalanced magnetic pull (UMP). These auxiliary windings are inserted in the stator slots and they are used to produce counteracting flux that reduces the UMP. In the theory section, an UMP control matrix is fully developed that involves additional winding currents for obtaining active UMP control. The algorithm for controlling the UMP is then introduced. This uses vector control with stator flux orientation. Several simulations are carried out using MATLAB and Altair Flux 2D finite element analysis. These show a good reduction of UMP under open circuit and locked rotor tests. These models allow the study of the combined effects of radial forces with changes in the machine design. It was found that the average power absorbed by the auxiliary windings equals 13% of the total power losses in normal operation conditions. [ABSTRACT FROM AUTHOR]

In this paper, a Random‐XFEM technology was employed to simulate hydraulic fracture interaction with the natural void in a random field of Young's modulus. The random distribution of Young's modulus is characterized by random field theory, while the stress and pressure fields fracturing were solved by the extended finite element method. And a Random‐XFEM iteration algorithm was proposed to solve the hydraulic fracture propagation problem. Then the proposed model was verified against the KGD model and numerical study. A series of numerical examples were presented to analyze the interaction mechanism of hydraulic fracture and void in a random field. The numerical results show that the random field of Young's modulus has a great impact on the hydraulic fracture propagation path. Under the random distribution of Young's modulus, the hydraulic fracture would deviate from the direction of maximum horizontal principal stress. And the random field parameters (Young's modulus mean and point variance) have different effects on the hydraulic fracture propagation path. Also, the interaction patterns of hydraulic fracture and void are greatly affected by random fields. [ABSTRACT FROM AUTHOR]

Building a complex fracture network in a deep shale gas reservoir during multicluster hydraulic fracturing is challenging. On the one hand, hydraulic fractures tend to propagate along shale bedding planes, thus leading to a limited hydraulic fracture height; on the other hand, under the effect of high in situ stress and weak plane of fractures, multihydraulic fractures can hardly initiate and propagate uniformly. All of these will jeopardize the performance of hydraulic fracturing. This paper considers the influence of natural fracture network, shale beddings, fracturing‐fluid leakage, and high in situ stresses, and builds a numerical model to simulate multifracture propagations along vertical direction during hydraulic fracturing in deep shale reservoirs. The model is developed based on the theory of solid–fluid coupling and finite element method with pore pressure cohesive element technique are used to simulate multicluster fracture initiation and propagation. Moreover, the model is verified by published experiment data, and a good agreement between model and experiment results is observed. The influences of pump rate and fracturing‐fluid viscosity on fracture geometry are discussed, and the flow dynamics around each perforation cluster under different perforation parameters are also studied. Finally, suggestions to improve overall outcome of multicluster hydraulic fracturing are also provided. [ABSTRACT FROM AUTHOR]

For the first time, this paper proposes a multiscale computational approach to investigate mixed‐mode I/II fracture in two‐dimensional lattices containing material anisotropies which find their applications in additive manufacturing of cellular structures. The layer‐by‐layer fabrication of lattices produced by the additive manufacturing techniques causes material anisotropies corresponding to the build orientation. Such material anisotropies, together with the cell topology, affect the fracture behavior of lattice components under various mechanical loading. The effective macroscopic elastic properties of periodic lattices obtained via numerical homogenization are fed into a continuum‐based fracture criterion to obtain crack path and onset of fracture under mixed‐mode I/II conditions. Different cell topologies are considered, and the predictions are compared with the results obtained directly by the finite element analysis. The results of this work can pave the way toward further understanding, and eventually, optimizing fracture toughness of additively manufactured lattices against various loading profiles. [ABSTRACT FROM AUTHOR]

This paper presents a reluctance-based model considering the frequency-dependent loss nature of the windings for the analysis of three-phase five-leg transformers under grid voltages with direct current (DC) bias. This is very important especially for proper determination of their harmonic current distortion and maximum loading capability (MLC) under DC-biased grid voltage conditions. To figure out the developed model's validity under sinusoidal and DC-biased grid voltage cases, it is comparatively analyzed with the model based on 2D finite element method (FEM). Thus, for the considered transformer type operated under DC bias, the excitation current's harmonic pollution, losses, and reactive power demand parameters are analyzed by using the developed model. Additionally, by regarding these performance parameters, the DC susceptibilities of the considered-type transformer and the single-phase shell-type transformer are comparatively evaluated. Finally, for the studied grid voltage conditions, the effects of two important design considerations as (i) magnetic core material selection and (ii) legs' cross-sectional area sizing on the MLC are investigated. It is concluded from these investigations that under saturation conditions, the transformers, which have the core material with higher permeability or lower reluctance, draw higher excitation current, and have lower MLC ratio when compared to ones having the core material with lower permeability or higher reluctance. However, for unsaturated transformers, which work under DC bias, the case is the opposite to that in saturation conditions. On the other hand, under DC bias conditions, the effect of cross-sectional area sizing on the MLC ratio is much more for the transformer with high permeable magnetic core material with regards to ones with low permeable magnetic core material. [ABSTRACT FROM AUTHOR]