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This paper provides a comparison between the conventional Electromagnetic Forming (EMF) technique and the novel Electromagnetic Hydraulic Forming (EMHF) approach. The EMHF involves the use of finite element analysis coupled with the EM and arbitrary Lagrangian–Eulerian techniques analyzed through LS-DYNA. In the free-bulge configuration, EMF is influenced by the forming coil, resulting in a dead zone and uneven forming. Additionally, EMF can only be used to shape materials with high electrical conductivity. In contrast, EMHF, driven by induced hydraulic pressure from the electromagnetic field-affected drive sheet, is independent of the electrical conductivity of the material and produces dome-shaped workpieces. For rectangular die shapes, EMF is prone to collision owing to the acceleration of the blank, which results in a reduced quality owing to bouncing. However, EMHF exhibits no bouncing effect and successfully achieves the target shape in most cases. The two techniques differ in the strain rate, with EMF at 4850/s, whereas EMHF operates at approximately 1250/s. Despite being slower, EMHF is still a high-speed forming technique. In conclusion, EMHF is a promising technique capable of addressing the shortcomings of conventional EMF and achieving improvements in forming processes. [ABSTRACT FROM AUTHOR]

The split Hopkinson pressure bar (SHPB) is a machine used for obtaining dynamic material properties at high strain rates of 102–104 s−1. In the SHPB test, the material properties obtained vary depending on the shape of the specimen. In other words, it is important to understand the behavior of the specimen when selecting the specimen dimensions. However, specific standards, such as the size of specimens and bars for the SHPB, have not yet been established. This study investigates the effect of changing the specimen diameter on strain and stress results. Comparison and verification with experimental results were performed using the LS-DYNA program. Specimens are cylindrical titanium grade 1. The specifications of bars and length ( L ) of the specimens were not changed. The results revealed that the reflected ratio increased, and the transmitted ratio decreased as the area of the specimen decreased. The ratios of these strains are affected by impedance ( Z = ρ A C ). The area reduction of specimens under the same conditions made it possible to obtain dynamic properties at a higher strain rate. It was shown that the impedance relationship and strain rate can be altered by varying the diameter of the specimen without changing the dimensions or material of the bar itself. [ABSTRACT FROM AUTHOR]

This study presents a fatigue analysis procedure for inclined structures operated in level ice fields. Three methods for calculating the local ice load causing fatigue damage, namely the direct method, simplified method, and semi-analytical method, were introduced and compared. The direct method uses finite element analysis to simulate the continuous breaking of ice, while the simplified method and the semi-analytical method estimate the probability distribution of local ice loads based on theoretical equations and empirical data. The fatigue damage ratio at the target location was calculated by applying the ice load calculated by each method to a deformable finite element model of the structure. The results obtained from each method indicate that they provide a reasonable estimation of the local ice load causing fatigue damage in level ice fields. The direct method offers high accuracy but requires significant computational time, while the simplified method and semi-analytical method offer a faster analysis time and are more suitable for long-term time domain analysis. The semi-analytical method requires empirical data to supplement theoretical formulas due to the complex natural phenomena involving various environmental conditions that must be modeled. The findings of this study provide valuable insights into the prediction of fatigue damage in ice-going ships due to long-term ice impacts. The methods proposed in this study can aid in the design of Arctic ships exposed to various conditions and provide a more cost-effective and time-efficient approach to evaluating fatigue damage compared to field measurement. Future research in this field could investigate the application of these methods to other types of structures and further refine the methodology to improve accuracy and reduce computational costs. [ABSTRACT FROM AUTHOR]

Electricity generation from renewable energy sources is emerging as a result of global carbon emission reduction policies. However, most renewable energy sources are non-dispatchable and cannot be adjusted to meet the fluctuating electricity demands of society. A flexible operation process has been proposed as an effective solution to compensate for the unstable nature of renewable energy sources. Thermal load fluctuations during flexible operation may cause creep–fatigue damage to the high-temperature components of thermal power plants, as they are designed with a focus on creep damage under a constant power level. This study investigated the residual life of high-temperature components, such as a superheater tube and a reheater header, to failure under flexible operation conditions using finite element analysis and empirical models. First, we determined an analytical solution for the straightened superheater tube under thermal conditions and compared it with the numerical solution to verify the numerical models. Through the verified finite element model, the creep–fatigue life of the reheater header was estimated by considering flexible operation factors and employing the Coffin–Manson and Larson–Miller models. Although fatigue damage increases with decreasing minimum load and ramp rate, we confirmed that creep damage significantly affects the residual life during flexible operation. In addition, a surrogate model was proposed to evaluate the residual life of the reheater as a function of the flexible operation factors using the machine learning methodology, based on the results of finite element methods. It can be used to predict its residual life without performing complex thermo-structural analysis and relying on empirical models for fatigue and creep life. We expect our findings to contribute to the efficient operation of thermal power plants by optimizing the flexible operation factors. [ABSTRACT FROM AUTHOR]

This study presented experimental and numerical research to investigate the effect of cryogenic leakage on a plate structure of AH36-grade steel containing welded joints. To simulate the cryogenic leakage conditions, the welded plate was exposed to a temperature of −196 °C by supplying liquid nitrogen (LN2) to the center of the steel plate. The time-dependent temperature history and strain variation were measured by using thermocouples and strain gauges attached to the plate surface. Additionally, the residual stress of the middle surface section before and after the cryogenic leakage process was measured by X-ray diffraction analysis (XRD). A three-dimensional finite element model was created with the use of a commercial finite element analysis (FEA) program to simulate the flux-cored arc welding process and cryogenic leakage process. The steel surface temperature dropped sharply and reached approximately −196 °C at 160 s after LN2 supplement. After the first 650 s of the LN2 leakage experiment, the outside of the trough reached approximately −75 °C and −25 °C, depending on the location of the thermal couples. Although there was a relative difference in the results, the experiment and numerical simulation results for temperature and stress distribution showed good agreement. The results could be utilized in the ship design stage adopting welded structures as a basic database. [ABSTRACT FROM AUTHOR]

Various regulations are being devised and implemented to prevent the environmental pollution that is threatening mankind. The International Maritime Organization has strengthened regulations on sulfur, a notorious pollutant, to prevent sea pollution. In addition, the production of LNG fueled ships is increasing. Among various metals, 9% nickel steel is widely used in the shipbuilding industry because it is advantageous in terms of material strength and cryogenic impact toughness. Various studies are being carried out to predict and prevent its distortion, caused by welding, in the design. To predict welding distortion during flux core arc welding, this study found a way to refine the parameters constituting the Goldak welding heat source. The optimal heat source parameters were derived by using BOP experiments, cross-sectional analysis, finite element analysis and global optimization algorithm. When re-analyzed and verified based on the values, an error of up to 6.3% was found between simulation results and experimental values. The process was improved by clarifying the objective function and reducing the range of candidate welding efficiencies during global optimization and the process efficiency was also improved by reducing analysis time with a simplified model. Therefore, it is thought that this study can contribute to the productivity improvement of LNG storage containers, helping engineers apply it immediately in the industrial field. [ABSTRACT FROM AUTHOR]

Due to environmental regulations, vehicle weight reduction technology has recently emerged as a key factor influencing market competitiveness in the automobile industry. Although the demand for aluminum alloy for vehicle weight reduction is increasing, its application in the automobile industry is limited due to its low formability. Electromagnetic forming (EMF) technology has been proposed as a method to improve the low formability of aluminum alloys. EMF is a technology of forming a metal workpiece at high speed without physical contact by applying a strong electromagnetic field to the workpiece to be formed. In this study, we performed an analytical study on the characteristics of electromagnetic forming. Finite element analysis was performed with the same model as in the general drawing process, and the results of the forming process, formability, and finite element analysis were compared. Through the results of finite element analysis, it was confirmed that the EMF process showed significant deformation at the die shoulder and center. Furthermore, EMF has an advantage in formability due to having a smaller amount of sheet inflow than the drawing process; however, its forming accuracy is low. [ABSTRACT FROM AUTHOR]

Ships and offshore structures are subjected to impact loads, such as slamming and sloshing. High impact pressures can cause permanent hull deformation by a single impact event. In addition, significant fatigue damage can be accumulated via repeated impact pressures. In this study, the plastic deformation behavior of flat plates under slamming impact is numerically investigated using a coupled Eulerian–Lagrangian method. The dynamic impact pressure of the flat plates by weight and drop height is investigated under the assumption of viscous and compressible fluids. To evaluate the plastic deformation of the plate, contact between water and the plate is removed after a certain duration after dropping, and then the remaining deformation is measured. Optimized finite element models for drop simulations are selected via a mesh sensitivity study, and the simulation results are calibrated and compared with experimental data. Results of the simulation and the experiment show good agreement in general in terms of deflection range. However, because the initial condition of the plate is not reflected in the simulation, some discrepancy is observed in maximum deflections. Finally, a discussion is presented for a more accurate fluid impact analysis model based on the comparison results with the experimental data. [ABSTRACT FROM AUTHOR]

As the world's hydrocarbon supplies are gradually being depleted, the search for alternative energy sources with acceptably low emissions of environmentally harmful pollutants is a growing concern. Hydrogen has been proposed by numerous researchers as a fuel source for ships. Liquid hydrogen (LH2) has been shown to be particularly attractive as a ship fuel with respect to its ability to reduce pollution, density, high performance in engines, and high caloric value per unit mass. However, working with hydrogen in the liquid phase requires very low (i.e., cryogenic) temperatures. The design of a cryogenic LH2 pipeline is very different from the design of a normal fluid pipe due to the change between the liquid and gas states involved and the effect of thermal and structural characteristics on the cryogenic temperature during LH2 transportation through the transfer pipeline. This study investigated the material and thermal-structural characteristics of a multi-layer vacuum-insulated pipeline system through experiments and finite element analysis. The experimental and numerical results can be used as a database of material parameters for thermal-structural analysis when designing applications such as LH2 pipeline systems for hydrogen carriers and hydrogen-fuelled ships. [ABSTRACT FROM AUTHOR]

Transcranial focused ultrasound (FUS) is a noninvasive treatment for brain tumors and neuromodulation. Based on normal incidence, conventional FUS techniques use a focused or an array of ultrasonic transducers to overcome the attenuation and absorption of ultrasound in the skull; however, this remains the main limitation of using FUS. A dual-mode conversion technique based on Lamb waves is proposed to achieve high transmission efficiency. This concept was validated using the finite element analysis (FEA) and experiments based on changes in the incident angle. Aluminum, plexiglass, and a human skull were used as materials with different attenuations. The transmission loss was calculated for each material, and the results were compared with the reflectance function of the Lamb waves. Oblique incidence based on dual-mode conversion exhibited a better transmission efficiency than that of a normal incidence for all of the specimens. The total transmission losses for the materials were 13.7, 15.46, and 3.91 dB less than those associated with the normal incidence. A wedge transducer was designed and fabricated to implement the proposed method. The results demonstrated the potential applicability of the dual-mode conversion technique for the human skull. [ABSTRACT FROM AUTHOR]

The most important technical issue in the shipbuilding industry regarding liquefied natural gas (LNG) carrier cargo containment systems (CCS) is securing the structural reliability of the primary barrier, which is in direct contact with the LNG. Fracture of the primary barrier by the hydrodynamic load of the LNG CCS may lead to disasters because it is difficult to implement immediate safety measures in the marine environment, unlike on land. Hence, structural reliability of the LNG membrane is the most critical issue in LNG carrier CCSs, where thin and corrugated 304L stainless steel is often used as the primary barrier to prevent repeated thermal deformation from the temperature difference during loading (−163 °C) and unloading (20 °C) of the LNG. However, plastic deformation of the 1.2 mm-thick corrugated membrane of the LNG CCS has been reported continuously owing to its vulnerability to cryogenic hydrodynamic loads. In the present study, we conducted a parametric analysis to investigate the effects of the corrugation shape as a preliminary study of the primary barrier. Finite element analysis was conducted with a simplified plate to focus on the effects of corrugation. Furthermore, a two-step validation was conducted using the above experimental results to ensure reliability of the structural analysis. The results show that optimizing the corrugation shape could ensure better structural safety than the conventional design. [ABSTRACT FROM AUTHOR]

We present an elastic damage constitutive model for polymeric foam based on thermodynamics framework to consider the effects of anisotropy and the growth and coalescence of cavities. The evolution equation of the proposed model describes the material behavior sustaining anisotropic and unilateral damage. To carry out finite element analysis, the material properties for various polymeric foams are applied to the proposed damage model; we thus implement the proposed damage model in the commercial finite element program as a user-defined material subroutine. In order to validate the proposed anisotropic damage model, the numerical results are compared to the results of a series of tensile and compressive tests on various polymeric foams. Additionally, we propose the failure criterion for this damage model as based on the mass-dependent energy per unit mass at failure. The developed damage model can be used for further research on damage mechanics and finite element analysis of polymeric foams in continuum mechanics. [ABSTRACT FROM AUTHOR]

The curved plate has been extensively used as a structural member in many industrial fields, especially the shipbuilding industry. The present study investigated the ultimate strength and collapse behavior of the simply supported curved plate under a longitudinal compressive load. To do this, experimental apparatuses for evaluating the buckling collapse test of the curved plates was developed. Then, a series of buckling collapse experiments was carried out by considering the flank angle, slenderness ratio, and aspect ratio of plates. To examine the fundamental buckling and collapse behavior of the curved plate, elastoplastic large deflection analysis was performed using the commercial finite element analysis program. On the basis of both the experimental and FE analysis, the effects of the flank angle, slenderness ratio, and aspect ratio on the characteristics of the buckling and collapse behavior of the curved plates are discussed. Finally, the empirical design formula for predicting the ultimate strength of curved plates was derived. The proposed empirical formula is a good indicator for estimating the behavior of the curved plate. [ABSTRACT FROM AUTHOR]

Summary: An important issue in impedance‐based damage monitoring is to deploy sensors in proper positions in which damage‐sensitive impedance responses can be captured effectively. In this study, a full‐scale multi‐strand anchorage is analyzed to determine optimal locations of piezoelectric sensors for impedance‐based monitoring of locally damaged strands. First, stress variations of the multi‐strand anchorage are experimentally measured to estimate the anchorage behavior under the effect of locally damaged strands. Strain signals are examined for axial, circumferential, and radial stress components under the variation of prestress forces. Second, a finite element analysis is made on the multi‐strand anchorage to back up the experimental findings. Third, a damage‐sensitive structural model is interpreted for the local strand breakage. Finally, impedance responses sensitive to local strand breakage are experimentally examined for a few scenarios simulated in the anchorage system. PZT (lead zirconate titanate) sensors deployed on the anchor head and the bearing plate are evaluated to comparatively determine ideal regions of interest for impedance monitoring. The results show that the greater stress variation yields the greater variations in impedance responses and the near‐top and near‐anchor heads are ideal regions of interest for damage‐sensitive impedance monitoring. [ABSTRACT FROM AUTHOR]

• A free-interface based dynamic condensation method is newly developed. • In the formulation, substructural FE models are fully decoupled. • Non-matching mesh and complicated substructural interfaces can be modeled. • Accuracy, computational efficiency and modeling ability are demonstrated. In this paper, a novel dynamic condensation method is proposed with free interface substructuring, in which the substructures are completely decoupled. The substructures are independently defined and the substructural finite element (FE) models are individually reduced by adopting the improved reduced system (IRS) method. The reduced mass and stiffness matrices of substructures are assembled using a Lagrange multiplier vector, leading to the final reduced model. Using the proposed method, each of the substructural FE models can be reduced in parallel without coupling among the neighboring substructures. Thus, the method can be applied with ease to substructures connected through non-matching meshes. Moreover, complicated substructural interfaces can be accommodated when employing this method. The formulation of the proposed method is presented in detail, and its accuracy, computational efficiency, and modeling ability are investigated using several demonstrative engineering problems. [ABSTRACT FROM AUTHOR]

Ice loads should be considered in the design stage of the ice-going ships. The loads will be determined by the ice features present given the location, the time of year and the environmental conditions. Normally, a ship follows a sea path covered with ice broken by an ice breaker. Therefore, it is important to estimate its performance in broken ice fields. In this study, a numerical simulation of an ice going ship navigating through broken ice field was carried out using the finite element method. Ice floes with random distributions of size, thickness and shape were modeled, and an efficient numerical simulation method for ice-sea, ice-structure, and ice-ice interactions was proposed for rapid computation. Important parameters, such as the drag force coefficient and the pressure-penetration relationship in interaction modeling were obtained based on the results of detailed analysis using the coupled Eulerian-Lagrangian method. The simulations were conducted under the same conditions as tests carried out in an ice model basin, and the results were compared. • Numerically efficient ice-fluid interaction model was built up using Morison type formula. • Numerically efficient ice-structure interaction model was built up using pressure-penetration relation. • Simulation results were compared with model basin test and good correspondence was achieved. [ABSTRACT FROM AUTHOR]

Recently, as the use of the induction range has increased rapidly, many studies have been studied. However, most of them are research on inverters, and the effect of the ferrite cores is insufficient in the induction range. Therefore, in this paper, the effect of the ferrite core in the induction range was analyzed, and the ferrite structure for improving the efficiency was proposed by using 3-D finite-element method (FEM). In order to verify the simulation results, the efficiency improvement was verified through experiments with three inputs of 1.2, 1.8, and 3.0 kW. [ABSTRACT FROM AUTHOR]

Highlights • The most efficient element/FE formulation couple for numerical simulation of the flexibly-reconfigurable roll forming process is identified. • Several shell and solid elements from Serendipity and Lagrangian families with various interpolation degrees in rolling, transverse, and thickness directions are studied. • Irreducible and mixed FE approaches are coupled with the elements and their performances are compared. • The element/formulation couples are compared after a surrogate-based Pareto optimization of their performance with respect to the FE input parameters. • The sensitivity of the flexibly-reconfigurable roll forming process to various parameters including thickness, width, initial transverse radius, roll gap distribution, and material properties is investigated. Graphical abstract Abstract Flexibly-reconfigurable roll forming (FRRF) process is suggested in recent years as a response to the needs of modern manufacturing industries for small-lot or even single-lot production of doubly-curved sheet metal surfaces with reduced costs. In FRRF, a sheet metal is deformed by the use of two bent rollers with non-constant roll gap where the rolling and roll-bending mechanisms are imposed together. Thanks to FRRF process, the costs due to the manufacturing of dies are reduced; however, the computational cost for process design becomes significant as each design may be used for a few or even a single production. Hence, the net production rate is controlled by computational time that can be several times longer than the forming time. Considering the deformation mechanism in FRRF, this study tries to specialize an analysis method to FRRF that is accurate and efficient. This is accomplished by an in-house Matlab implementation of an efficient finite element approach and testing various combinations of elements and variational formulations (mixed and irreducible) to find the best combination of them for numerical simulation of FRRF. For this purpose, first a set of preliminary comparisons are made to select: (1) the best integration method for the elements with irreducible formulation, (2) the best stress components to be included in the nodal parameters for the elements with mixed formulation, and (3) the best elemental class (Serendipity or Lagrangian) for the elements with nonlinear interpolation in at least two directions. Then, the best variational formulation is decided for each elemental family by comparing the simulation results in a range of numerical model parameters. Finally, the FE model parameters are optimized for each candidate by a surrogate-based Pareto optimization method, and the best element/formulation couple is selected among all the candidates by the technique for order of preference by similarity to ideal solution (TOPSIS). Moreover, in order to identify the most decisive parameters in the analysis and design of FRRF process, the response of FRRF to variation of several process parameters including thickness, width, rollers' curvature radius, roll gap distribution, and material properties is investigated and the results are compared with those reported by the other studies. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Multi roll-dies drawing (MRD) process was suggested to reduce the drawing force. • The drawing forces of multi dies drawing (MDD) and MRD processes were predicted. • The effects of the force reduction and additional reduction area were evaluated. Abstract In the past decades, drawing processes have been applied to industries worldwide by employing several new solutions. In the case of drawing using conventional dies in tandem, it is widely-known that the deliberate application of back-pull can contribute to the improvement of die life and reduction in die load. To a certain extent, back-pull is present in the drawing process because the drawing force in the preceding stand tends to act as a back-pull in the next drawing stand. In the case of drawing by using a non-driven roll-die, deformation occurs between the roller pairs without the driven rolls. The drawing process using a non-driven roll-die can lead to a decrease in friction. The drawing process using a roll-die consumes lower power in comparison with other processes, owing to the decrease of friction. In this study, a multi-roll-die drawing (MRD) process, which is a new tandem drawing process through a non-driven four roll-die and converging die, is proposed to reduce the drawing force. The MRD was evaluated by being compared with the multi-die drawing process (MDD). First, a prediction model of the drawing force based on Geleji’s equations and the cross-sectional method was used. Additionally, the contact areas of the converging die and roll-die were modified for the shape-drawing process. The drawing force of the process through two dies in tandem was evaluated by being compared with the drawing force of a conventional drawing process. Subsequently, finite element (FE) simulations were performed to predict the drawing force in each process. They were used to verify the calculated drawing forces of the MDD and MRD processes. Moreover, experiments with regard to the MDD and MRD processes were performed to verify the predicted drawing forces. The predicted results were compared with the experimental results. Thereby, it was found that the predicted drawing force was in good agreement with the experimentally measured force. The drawing force reduction in the MRD process was evaluated by being compared with that of the MDD process. To investigate the effect of each process, numerical simulations, and Vickers micro-hardness tests were conducted, and their results were compared. [ABSTRACT FROM AUTHOR]

The roll profile in the multi-stage profile rolling process for manufacturing shaped wires influences product quality and dimensional accuracy significantly. Because the multi-stage profile rolling process is affected by many variables, such as elongation, rolling reduction, and width spread in a complex manner, many difficulties are involved in roll design. The roll profile design is predominantly conducted using finite element analysis (FEA). In this paper, a design method using virtual flow line, which is a roll profile design method in the multi-stage profile rolling process, is proposed. This design method employs a cross-section of the three-dimensional (3D) profile as the roll profile with a virtual flow line, thereby enabling roll profile design without performing FEA. To validate the design method, roll profiles were designed by applying the design method to the profiles of 12 products typically manufactured industrially using the profile rolling process, and FEA was conducted. The results indicate that the proposed method not only ensures higher dimensional accuracy than the conventional method but also assigns a higher strain rate. [ABSTRACT FROM AUTHOR]

Flexibly-reconfigurable roll forming (FRRF) process is recently introduced for the production of doubly-curved sheet metal surfaces with convenient change of the curvatures for each part. In FRRF, the sheet metal is deformed by a pair of small-diameter bent rollers with non-constant roll gap distribution from center to edge locations; the resulted part has two curvatures in transverse and in longitudinal directions. In this process, the sheet experiences a bending deformation before rolling, a plane strain compression during rolling, and another bending deformation after rolling. The previous finite element (FE) simulations of FRRF have been performed using 3D solid elements. In the present study, in order to increase the efficiency and accuracy of shape prediction process, the domain is decomposed into three subdomains of pre-rolling, rolling, and post-rolling deformation steps; each subdomain is solved separately by hiring an appropriate method for it. The pre-rolling and rolling deformation steps are solved only one time as the deformation is steady-state in these subdomains. For the post-rolling deformation step in which the sheet undergoes unknown curvature changes, an elastoplastic FEM with curvilinear shell elements is used with an initial stress state and accumulative plastic strain fields recorded from the other subdomains. The mathematical foundation of the method, the numerical computation procedure, and the sensitivity analysis of the method to different parameters are presented. In order to validate the numerical method with experimental data, several specimens with various dimensions are processed by FRRF and the results are compared to the numerical data. [ABSTRACT FROM AUTHOR]

The objective of the work reported in this paper is to improve the well-known dual Craig-Bampton (DCB) method. The original transformation matrix of the DCB method is enhanced by considering the higher-order effect of residual substructural modes through residual flexibility. Using the new transformation matrix, original finite element models can be more accurately approximated in the reduced models. Herein, additional generalized coordinates are newly defined for considering the 2nd order residual flexibility. Additional coordinates related to the interface boundary can be eliminated by applying the concept of SEREP (the system equivalent reduction expansion process). The formulation of the improved DCB method is presented in detail, and its accuracy is investigated through numerical examples. [ABSTRACT FROM AUTHOR]

A technique is developed to clearly establish the shear resistance of a cellular structure, retaining wall composed of a steel frame and fill materials with both continuous and discontinuous characteristics. To overcome the limitation of the existing analysis approach based on continuum mechanics, in which the shear behavior and interaction between the frames and fill material of this type of structure are difficult to describe, this paper introduces displacement incremental analysis into the distinct element method. The results obtained by using the proposed approach are compared with experimental results to verify its accuracy. The results show an internal friction angle of fill materials and overburdening load are major factor determining the shear resistance of a retaining wall with a cellular structure type. From the results of the parametric study on the shear behavior of this type of structure, this paper also proposes a shear resistance moment-shear displacement formula for designing a retaining wall with a cellular structure type. [ABSTRACT FROM AUTHOR]

For most ice – sloping structure interactions, the incoming ice floes' failures are determined by the formation of circumferential cracks. This physical process can be simplified as analyzing the bending failure of an ice wedges resting on a fluid foundation. In history, closed-form analytical/empirical solutions have been developed for the static bending problem; and numerical solutions have been attempted for the dynamic scenarios. This paper revisits this classic problem and conducts extensive Finite Element Method (FEM) – based simulations on the dynamic bending of an ice wedge resting on a Winkler-type elastic foundation. The simulations are based on inputs (i.e., ice wedge geometry, loading radius and loading rate) within ranges that are typical for engineering applications. Based on the simulation, a database of 'ice breaking load' and 'ice breaking length' is constructed. Then we applied the Artificial Neural Network (ANN) method to establish the general relationship between the varying inputs (i.e., ice wedge angle, loading radius and rate) with the target outputs (i.e., breaking load and length). Such relationship is expressed in simple closed-form (i.e., Eq. (13)) allowing for easy, efficient and wide engineering applications. In the process of developing the ANN model, based on extensive FEM-simulations, we managed to extend Nevel's (1972) analytical solution. We also quantitatively demonstrated many well-known dynamic effects in this classic problem, e.g., a faster loading rate leads to a larger ice breaking load and a shorter ice breaking length. In addition, we also uncovered the failure pattern transition of an ice wedge, i.e., when an ice wedge's angle is below 100°, the circumferential crack will develop first; however, when the ice wedge gets wider than around 100°, depending on the loading radius and interaction velocity, the radial crack is more prone to develop first. • Extensive finite element method – based simulations on the dynamic bending of an ice wedge resting on a Winkler-type elastic foundation are conducted based on inputs (i.e., ice wedge geometry, loading radius and loading rate) within ranges that are typical for engineering applications. • Based on the simulation, a database of 'ice breaking load' and 'ice breaking length' is constructed. Then we applied the artificial neural network method to establish the general relationship between the varying inputs with the target outputs. • Such relationship is expressed in simple closed-form allowing for easy, efficient and wide engineering applications. [ABSTRACT FROM AUTHOR]

• The formation mechanism of DBs observed in AA1100 after PF and R-PF during MADF was unraveled by microtexture analysis. • Calculation of the lattice rotation rate and the d i v g ˙ was used to evaluate the kinematic stability of deformed grains under the R-PF. • The heterogeneity of the orientation stability was used to explain the development of the DBs in the R-PF specimen. • CPFEM successfully simulated the development of DBs within deformed grains during the R-PF. • The heterogeneity of orientation stability occurring within the blurry bands enhanced the formation of DBs in the deformed grains during the R-PF. In this study, the formation mechanism of deformation bands (DBs) observed in AA1100 after plane forging (PF) and return-plane forging (R-PF) during multi-axis diagonal forging (MADF) was unraveled via microtexture analysis using a rate-sensitive model and crystal plasticity finite element method (CPFEM). Blurry bands with an orientation relationship of mainly LAGBs were developed in the deformed grains in the PF specimen. The heterogeneity of the orientation stability (Q) that occurred within the blurry bands and their surrounding regions contributed to the development of the DBs in the deformed grains in the R-PF specimen. Microstructure-based CPFEM successfully simulated the development of DBs within deformed grains during R-PF. CPFEM revealed that heterogeneity of the crystallographic orientation that occurred within the blurry bands and their surrounding regions inside the PF specimen was the main cause of the formation of DBs in the deformed grains during R-PF. Graphical Abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

Various wave energy converters (WECs) have been developed to utilize ocean wave energy resources. Among them, an oscillating water column (OWC) device is a promising wave energy converter that has undergone several pilot tests in the ocean with various prototype devices. Recently, a breakwater-integrated OWC-WEC system was proposed to improve the economic feasibility by reducing the construction and installation costs of the OWC chamber structure. In this study, a numerical investigation was conducted to simulate the hydrodynamic energy conversion problem for a breakwater-integrated OWC-WEC. The boundary value problem with the Laplace equation was solved directly by using a three-dimensional numerical wave tank based on a finite element method in the time domain. In the present numerical method, an efficient numerical model for the tetrapod (TTP), which is used to protect a rubble mound breakwater, was introduced using multiple blocks and numerical damping zone. Further, numerical investigations were performed on the effects of breakwater integration, TTP layer modeling, and the application of the numerical damping zone, and their features in terms of the wavefield and the OWC chamber responses were analyzed. Finally, the validity of the present numerical method was examined by comparing it with the experimental data. • Hydrodynamics of a breakwater-integrated OWC-WEC is numerically investigated. • Multiple blocks are applied to the breakwater and TTP model to consider wave scattering. • Numerical damping is applied to the TTP layer to consider wave energy dissipation. • Validity of numerical method is examined by comparing with the model test data. [ABSTRACT FROM AUTHOR]

This paper introduces a newly constructed type-N coaxial microcalorimeter that will serve as a primary power standard in Korea Research Institute of Standards and Science. The detailed design scheme of the microcalorimeter is presented, and its characteristics are evaluated. The performance of an adiabatic line was simulated with a finite-element-method-based tool and predicted. The measured insertion loss of the assembled adiabatic line was less than 0.15 dB. Frequency and power sweep measurements were performed on a reference standard to find a substituted power level that minimized the dual-element error. We also propose evaluation standards that can be used for the measurement of radio frequency loss. The correction factor for the effective efficiency of the reference standard was experimentally evaluated. We also present an uncertainty evaluation process and the corrected effective efficiency of a type-N coaxial reference standard. [ABSTRACT FROM PUBLISHER]

This study has been motivated to numerically evaluate the performance of the mountable PZT-interface for impedance monitoring in tendon-anchorage. Firstly, electromechanical impedance monitoring and feature classification methods are outlined. Secondly, a structural model of tendon-anchorage subsystem with mountable PZT-interface is designed for impedance monitoring. Finally, the feasibility of the mountable PZT-interface is numerically examined. A finite element (FE) model is designed for the lab-scaled tendon-anchorage. The FE model of the PZT-interface is tuned as its impedance signatures meet the experimental test results at the same frequency ranges and also with identical patterns. Equivalent model properties of the FE model corresponding to prestress forces inflicted on the lab-tested structure are identified from the fine-tuning practice. [ABSTRACT FROM AUTHOR]

In the present study, an evaluation method for the initial and progressive failure of composite laminates was proposed based on the Puck failure criterion and damage mechanics, respectively. In other words, the initial failure (crack initiation in the fiber and/or matrix) and progressive failure (crack growth in the fiber and/or matrix) were evaluated using the Puck failure criterion, and fiber- and matrix-dependent damage variables, respectively. In addition, the ABAQUS user-defined subroutine UMAT was developed based on coupling theories for the failure criterion and damage mechanics in order to efficiently analyze the progressive failure phenomenon in glass/carbon fiber-reinforced composite laminates. The developed subroutine was applied to the failure of industrial composite laminates, and the analysis results were compared to the experimental/numerical results previously reported in the literature. This comparative study confirmed that the simulation results were in good agreement with the reported composite failure results. [ABSTRACT FROM AUTHOR]

Cutouts are widely used in ships and offshore structures. These cutouts are used mainly for inspection, and they may be fitted for various purposes, including passing pipes and weight reduction. In general, plates with cutouts (perforated plates) are given high importance at the structural design stage because they can reduce the structural strength. In this regard, local reinforced perforated plates are used in shipyards to satisfy buckling and ultimate strength requirements, but quantitative evaluations of the reinforced perforated plates have not yet been carried out. To mitigate the decrease in the strength of perforated plates, the Carling, face-plating, and doubling stiffening methods have been adopted with the goal of increasing both the buckling and ultimate strengths. In particular, the Carling stiffener has been partially adopted at holes typically found in shipyards (e.g., access holes, lightening holes), but no standard methodologies or recommendations are available for the use of this stiffener. In the present study, a series of numerical studies were undertaken to analyze the buckling and ultimate strengths for various stiffening methods (Carling, face-plating, and doubling) and loading conditions (axial compression and in-plane edge shear loading). An optimal reinforcement method was determined by comparing stiffened weights and ultimate strengths of the three methods. Finally, a design formula for calculating the ultimate strength of a perforated plate was developed on the basis of over 144 cases of finite element analysis. [ABSTRACT FROM AUTHOR]

This paper presents the characteristic analysis and experiment of surface-mounted type variable-flux permanent-magnet machines considering magnetization and demagnetization based on electromagnetic transfer relations. For this purpose, we derive the analytical solutions for the magnetic fields generated by the magnetization level of AlNiCo magnets and currents on the basis of the transfer relations in terms of a 2-D polar coordinate system. The magnetization levels of the AlNiCo magnets are determined by the magnetic fields generated by the armature reaction field. A 2-D permeance function is also introduced to consider slotting effects. The analytical results of the magnetic field are validated extensively with finite-element (FE) analyses. On the basis of these solutions, the induced voltage is also determined analytically. Finally, the predictions are compared with FE analyses and measured data to confirm the validity of the analysis methods presented in this paper. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the behavioral characteristics of the lateral deflection of a simply supported perforated steel plate subjected to axial compression. Investigating the lateral deflection of the perforated plate is of great significance because the buckling limit of structural members can be predicted not only by strength but also by displacement (or deflection). For this purpose, we conducted buckling experiments by considering various variables of the perforated plate, such as opening size, thickness, and aspect ratio. In addition, a series of elastoplastic large deflection analyses were performed using the commercial finite element analysis program, and the calculated results were compared along with the experimental results. Finally, practical curves, which can predict lateral deflection with an increase in axial displacement, and the occurrence point of ultimate strength are reported in this study. The results showed that there was a distinct difference in the behavior of lateral deflection between perforated plates with different opening ratios. The local buckling occurred mainly around the opening and was more dominant with an increase in the opening ratio. In addition, the ultimate strength of the perforated plate was determined at the end of the local buckling phase. [ABSTRACT FROM AUTHOR]

Because environmentally-friendly fuels such as natural gas and hydrogen are primarily stored in the form of cryogenic liquids to enable efficient transportation, the demand for cryogenic fuel (LNG, LH) ships has been increasing as the primary carriers of environmentally-friendly fuels. In such ships, insulation systems must be used to prevent heat inflow to the tank to suppress the generation of boil-off gas (BOG). The presence of BOG can lead to an increased internal pressure, and thus, its control and prediction are key aspects in the design of fuel tanks. In this regard, although the thermal analysis of the phase change through a finite element analysis requires less computational time than that implemented through computational fluid dynamics, the former is relatively more error-prone. Therefore, in this study, a cryogenic fuel tank to be incorporated in ships was established, and the boil-off rate (BOR), measured considering liquid nitrogen, was compared with that obtained using the finite element method. Insulation material with a cubic structure was applied to the cylindrical tank to increase the insulation performance and space efficiency. To predict the BOR through finite element analysis, the effective thermal conductivity was calculated through an empirical correlation and applied to the designed fuel tank. The calculation was predicted to within 1% of the minimum error, and the internal fluid behavior was evaluated by analyzing the vertical temperature profile according to the filling ratio. [ABSTRACT FROM AUTHOR]

Abstract: Two-dimensional images of solid oxide fuel cell (SOFC) cathode microstructures (50:50 wt.% LSM:YSZ) are used to generate three-dimensional finite element (FE) models. An approximate, heuristic scheme is developed to derive a microstructure of 30:70 wt.% LSM:YSZ composition from the original, real microstructures. The derived model is validated by calculating three-phase boundary (TPB) and phase surface area densities by comparing with data available in the literature. Construction of such derived microstructures will provide insights on the effects of phase compositions on the mechanics of electrode structures. The heuristic scheme is not proposed as a replacement for rigorous approaches such as the random packing model, but rather as a simplified approach for deriving reasonably realistic microstructures of different compositions within a limited range of validity. The models are analyzed using finite elements to estimate thermal stresses and probability of failure using Weibull analysis. The effects of temperature-dependent material properties and phase volume fractions on probability of failure of the cathode are discussed. [Copyright &y& Elsevier]

In this study, the useful application of an instrumented structural health monitoring (SHM) system is proposed for the reliable seismic performance evaluation based on measured response data. A seismic fragility is chosen as a key index for probabilistic seismic performance assessment on an infrastructure. The seismic performance evaluation procedure consists of the following five main steps; (1) measuring ambient vibration of a bridge under general traveling vehicles; (2) identifying modal parameters including natural frequencies and mode shapes from the measured acceleration data by output-only modal identification method; (3) updating linear structural parameters in a preliminary finite element (FE) model using the identified modal parameters; (4) analyzing nonlinear response time histories of the structure using nonlinear seismic analysis program; and finally (5) evaluating the probabilistic seismic performance in terms of seismic fragility. In the present study, the seismic fragility curves are represented by a log-normal distribution function. An instrumented highway bridge is utilized to demonstrate the proposed evaluation procedure and it is found that the seismic fragility of a highway bridge can be reliably evaluated by combining the modal information obtained from the instrumented SHM system and FE model updating by using the information. [ABSTRACT FROM AUTHOR]

In this study, we formulate the effective temperature-dependent thermal conductivity of laminated composites. The studied laminated composites consist of laminas (plies) made of unidirectional fiber-reinforced matrix with various fiber orientations. The effective thermal conductivity is obtained through a two-scale homogenization scheme. A simplified micromechanical model of a unidirectional fiber-reinforced lamina is formulated at the lower scale. Thermal conductivities of fiber and matrix constituents are allowed to change with temperature. The upper scale uses a sublaminate model to homogenize temperature-dependent thermal conductivities of only a representative lamina stacking sequence in laminated composites. The effective thermal conductivity of each lamina, in the sublaminate model, is obtained using the simplified micromechanical model. The thermal conductivities from the micromechanical and sublaminate models represent average nonlinear properties of fictitiously homogeneous composite media. Interface conditions between fiber and matrix constituents and within laminas are assumed to be perfect. Experimental data available in the literature are used to verify the proposed multi-scale framework. We then analyze transient heat conduction in the homogenized composites. Temperature profiles, during transient heat conduction, in the homogenized composites are compared to the ones in heterogeneous composites. The heterogeneous composites, having different fiber arrangements and sizes, are modeled using finite element (FE) method. [ABSTRACT FROM AUTHOR]

Abstract: Modal behavior of a three-dimensional (3D) homogeneous and functionally graded (FG) cantilever beam is studied using the Rayleigh–Ritz (RR) method and the finite element method (FEM). The effect of Poisson’s ratio and material sampling point on the natural frequencies is further addressed using the FEM. The natural frequencies (first three) obtained using the RR method converge as the number of admissible shape functions increase. The natural frequencies (first 15) obtained using the FEM vary considerably with the material gradation, more so for the lower modes than for the higher modes. Poisson’s ratio significantly changes the torsional natural frequencies of the homogeneous and graded beams. Considerable change in the natural frequencies is seen for the linear graded beams whose material properties are sampled at the element centroid rather than at Gaussian integration points. This difference is easily observed for beams modeled using a coarse mesh rather than a fine mesh. The natural frequencies of the y direction hyperbolic tangent beam with material nonhomogeneity parameter matches well with those of the y direction bi-material beam. The natural frequencies of the power-law graded 3D cantilever beam obtained using the FEM matches closely with the 2D reference (Qian and Ching, 2004 ) solution obtained using the meshless local Petrov–Galerkin method. [Copyright &y& Elsevier]

Abstract: This study formulates a micromechanical model for predicting effective viscoelastic–viscoplastic responses of composites. The studied composites consist of solid spherical particle reinforcements dispersed in a homogeneous matrix. The particle constituent is assumed linear elastic, while the matrix exhibits combined viscoelastic–viscoplastic responses. The Schapery integral model is used for the 3D isotropic non-linear viscoelastic responses. Two viscoplastic models are considered: the Perzyna model, having a rate-independent yield surface and an overstress function, and the Valanis endochronic model based on an irreversible thermodynamics without a yield surface. The Valanis model is suitable for materials when viscoplastic responses occur at early loadings (small stress levels). A unit-cell model with four particle and polymer sub-cells is generated to obtain homogenized responses of the particle-reinforced composites. Available micromechanical models and experimental data in the literature are used to verify the proposed micromechanical model in predicting effective time-dependent and inelastic responses of composites. Field variables in the homogenized composites are compared to the ones in heterogeneous composites. The heterogeneous composites, having detailed particle geometries, are modeled using finite element (FE) method. [Copyright &y& Elsevier]

Abstract: An experimental study is conducted to simulate the thermal stresses generated in mass concrete. Accurate prediction of the thermal stresses by analysis is quite difficult particularly at early ages, due to uncertain age-dependent properties of concrete. A series of tests was conducted in which the amount of restraint in a thermal stress device (TSD) was varied. The effect of aging and the amount of restraint on stress development that can occur in realistic structures was evaluated. The influence of the uncertain early-age properties of concrete (i.e., elastic modulus, thermal dilation, autogenous deformation and transitional thermal creep), on the generation of thermal stresses was incorporated using a TSD due to the simultaneous development of temperature and the corresponding stress in a restrained specimen from the very beginning of the process. The effect of various amounts of restraint on the generation of thermal stress was pronounced. Numerical simulations of the thermal stress setup were also performed using the finite element code DIANA to verify and extend the experimental interpretation and to determine the maximum value of restrained stress which would occur under highest level of restraint. Adopting this methodology may simplify the complexity of thermal stress analyses (i.e., more precise 3-D thermal stress analysis can be performed using material properties achieved from 1-D uniaxial tests) due to the difficulty of accurately determining the early-age properties of concrete. [Copyright &y& Elsevier]

Metal forming processes such as hydroforming and sheet metal forming using tubular material and thin sheet metal have been widely used in lots of industrial fields for manufacturing of various parts that could be equipped with mechanical products. However, it is not easy to design sequential processes properly because there are various design variables that affect formability of the parts. Therefore preliminary evaluation of formability for the given process should be carried out to minimize time consumption and development cost. With the advances in finite element analysis technique over the decades, the formability evaluation using numerical simulation has been conducted in view of strain distribution and final shape. In this paper, the application of forming limit criteria is carried out for the tube hydroforming and sheet metal forming processes using theoretical background based on plastic instability conditions. Consequently, it is confirmed that the local necking and diffuse necking criteria of sheet are suitable for formability evaluation of both hydroforming and sheet metal forming processes. [ABSTRACT FROM AUTHOR]

Fiber metal laminates as one of new hybrid materials with the bonded structure of thin metal sheets and fiber/epoxy layers have been developed for the last three decades. These kinds of materials can provide the characteristics of the excellent fatigue, impact and damage tolerance with a relatively low density. Because metal sheets and fiber/epoxy layers are bonded each other, the bonding between two materials is critical. In this study, the bonding strength is investigated experimentally with respect to surface roughness of metal sheets. The equivalent material properties of carbon reinforced aluminum laminates as the input data in the numerical simulation are also investigated and compared with the experimental result. The application of the equivalent material property to the numerical simulation can provide the high degree of efficiency in the build-up of the finite element model and the numerical simulation. [ABSTRACT FROM AUTHOR]