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A wind turbine load analysis featuring both fatigue and extreme loads for a full range Linear Parameter Varying (LPV) controller is presented in this paper. The National Renewable Energy Laboratory (NREL) 5 MW reference wind turbine is simulated with realistic profiles of turbulent wind, according to the IEC 61400-1 regulation, using several NREL's tools, with a total of 354 numerical simulations. Classical techniques has been applied, like the Rain-flow counting (RFC) algorithm, and the Palmgren-Miner Rule with Goodman's correction to estimate the wind turbine components damage rate. The mechanical loads under consideration are the tower and blades main moments. The results show a lifetime equivalent load reduction with the LPV controller in comparison with the classical Gain Scheduling Proportional Integral (GSPI), for all analyzed loads, similar to those achieved by other publications in the literature. This improvement is achieved using the same online measurements and information as the used by the GSPI controller. • A full range LPV controller which reduces mechanical loads of a wind turbine is evaluated. • The AEP comparison shows no significant reduction. • All the analyzed loads presented an improvement, particularly, the blade root out of plane bending moment. • Both fatigue and extreme loads are considered under the IEC 61400-1 regulation. • The improvements are achieved with a classical control topology without extra sensors or actuators. [ABSTRACT FROM AUTHOR]

Highlights • A quasi-static compression test and the numerical simulation on the bow model was carried out. The static stiffness characteristic of the ship bow was compared with the dynamic ones. • The impact force and the dynamic response of piers due to collision at different impact velocities with ships with different bow stiffnesses were experimentally studied. • Three concrete materials were considered in modelling the pier to find the influence of different material model assumptions on the collision simulation. • Finite element analysis of the full-scale ship-pier collision was conducted to examine the reasonability of the scaled model tests. A parametric analysis method was used to study the effects of the dynamic parameters and impact velocity on the impact force and ship bow crush depth. Abstract Ship collision with bridge piers is one of the most frequent types of accidents that may lead to a bridge failure. The collision characteristic of bow structure is significant to the study ship-pier collision process. In this paper, the quasi-static compression test and numerical simulation of a simplified bow model were carried out to study the static stiffness characteristic of the ship bow for further comparison with the dynamic ones. To evaluate the performance of reinforced concrete (RC) piers against ship collision, and to guide the design of the bridge piers and anti-collision, scaled model tests of ship-pier collision and finite element simulations based on the main pier no. 217 of the Shijiu Lake Bridge were carried out. The damage process and failure mode of the pier were analysed. Instead of rigid or elastic materials in most of the previous works of numerical simulation of ship collision with bridge piers, the bridge pier is modelled with nonlinear materials to simulate the pier characteristics more accurately. To examine the reasonability of the scaled model tests, finite element analysis of the full-scale ship-pier collision was conducted. In the light of the numerical results, the design impact loads prescribed by Eurocode and AASHTO LRFD Bridge Design Specifications were evaluated. Parametric studies were carried out to investigate the effects of the dynamic parameters and impact velocity on the impact force and ship bow crush depth. [ABSTRACT FROM AUTHOR]

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

Highlights • Application of Markov Chain in availability calculation in a redundant system with load sharing was considered. • Multi-objective optimization of cost and availability through NSGA2 was accomplished. • Allocation of redundancies and maintenance investments for a series-parallel system. • Impact of load sharing modeling in reliability allocation problem is verified • Simulation for a real industrial system is presented. Abstract Reliability allocation problem (RAP) deals with the dilemma between reliability (or availability) increase and some undesirable consequences, as an increase in cost. Therefore, new installations or maintenance investments should be optimally allocated to maximize the reliability (or availability), considering all restrictions. This paper proposes a solution for the RAP problem, taking into account failure dependency among redundant components. Because of that, a stochastic approach, based on Markov Chain, is applied. The multi-objective problem is solved with NSGA-II (Non-Dominated Sorting Genetic Algorithm II), assuming availability and overall costs as objective functions. Two examples are tested with the proposed approach. The first case is a hypothetical system with 5 subsystems in series. The second example is a real industrial application. In both cases, a Pareto front is obtained, allowing an analysis of viable solutions to be adopted. Additionally, the failure dependency effect is also present in the optimization results. Therefore, it is possible to investigate the influence on the system availability and final cost. [ABSTRACT FROM AUTHOR]

Abstract This paper reports on the energy absorption characteristics of four types of innovative foam-filled multi-cell composite panels (FMCPs) composed of glass fiber reinforced polymer (GFRP) face sheets, GFRP lattice webs, and polyurethane (PU) foam. Quasi-static compression experiments on the FMCPs manufactured by a vacuum assisted resin infusion process (VARIP) were performed to demonstrate the feasibility of the proposed panels. Compared with the traditional FMCP with double-layer orthogonal foam cells, a maximum decrease in the peak crushing force (PCF) of approximately 148% was obtained for the FMCP with trapezoidal cells. Moreover, the enormous decrease in bearing load has been overcome by the proposed FMCPs. Among the four proposed FMCPs, the FMCP with double-layer dislocation cells exhibited the greatest specific energy absorption (SEA) capacity and the highest mean crushing load (MCL). Several numerical simulations using ANSYS/LS-DYNA were conducted on the FMCP with double-layer dislocation cells to parametrically investigate the effects of the face-sheet and lattice-web thickness, the foam-cell height, the foam-cell width, and the foam density. The effectiveness and feasibility of the numerical model were verified by the experimental results. The numerical results demonstrated that thicker face sheets and lattice webs, higher foam densities, and narrower foam cells can significantly increase the PCF and bearing load decrease. Moreover, the PCF and bearing load decrease were hardly affected by the foam-cell height. [ABSTRACT FROM AUTHOR]

Abstract Foam core sandwich structure has excellent insulation and specific strength and is widely used in the aerospace, aviation, navigation and military fields. The hemispherical shell of this kind sandwich structure is often used as energy and load carrying component due to its energy absorption ability. Some foam core sandwich hemispherical structures work in particular ultra-low temperature environments which undergo both temperature and mechanical loads. The research on the load carrying capacity of such structures in ultra-low temperature environment is essential for design and verify its properties. In this paper, the low-temperature mechanical properties of the face sheet and core materials were tested. The thermo-mechanical coupling numerical model was established and verified by comparison with the experimental results. Through the numerical simulation, the compressive behavior of the foam core hemispherical shells with different sizes was obtained under three different low-temperature loading situations. The effect of temperature loading on the deformation mode, load carrying capacity and deformation accumulation is further studied. It is suggested that the cooling of the out sheet is a relatively preferred low-temperature loading method. It also provides advice and ideas for the use of such structures. [ABSTRACT FROM AUTHOR]

Abstract The rock breaking mechanism is significantly affected by the joints in the rock mass. With the purpose to study the influence of joint characteristic parameters on cutting force and penetration, experimental explorations that contain miniature cutter head with double cutters are conducted in this paper on the basis of Rolling Indentation Abrasion Test (RIAT). In the present research, prefabricated joints of different forms are made in the rock samples. The experimental conclusions indicate that the optimal angle between horizontal and joint plane is equal to 30° for rock breaking process. In detail, the minimum thrust and the maximum penetration, which are related to the rock chipping angle for different joint orientations, are obtained at the optimal angle. Meanwhile, the improved theoretical formulas which are suitable for both intact and jointed rock are proposed. Besides, the change of thrust with penetration can be divided into four stages, which are the loading, starting, boring and stripping stages. Through simulating the rock breaking process by the rock rolling boring experimental method, this study measures the thrust, torque, penetration on the disc cutter, and reveals the influences of joint orientation and spacing on cutting forces and penetration. Furthermore, the penetration variation is summarized and the results are in good agreement with the field observation and numerical simulation results. [ABSTRACT FROM AUTHOR]

The paper presents a simplified analytical method to examine the crushing resistance of web girders subjected to local static or dynamic in-plane loads. A new theoretical model, inspired by existing simplified approaches, is developed to describe the progressive plastic deformation behaviour of web girders. It is of considerable practical importance to estimate the extent of structural deformation within ship web girders during collision and grounding accidents. In this paper, new formulae to evaluate this crushing force are proposed on the basis of a new folding deformation mode. The folding deformation of web girders is divided into two parts, plastic deformation and elastic buckling zones, which are not taken into account for in the existing models. Thus, the proposed formulae can well express the crushing deformation behaviour of the first and subsequent folds. They are validated with experimental results of web girder found in literature and actual numerical simulations performed by the explicit LS-DYNA finite element solver. The elastic buckling zone, which absorbs almost zero energy, is captured and confirmed by the numerical results. In addition, the analytical method derives expressions to estimate the average strain rate of the web girders during the impact process and evaluates the material strain rate sensitivity with the Cowper-Symonds constitutive model. These adopted formulae, validated with an existing drop weight impact test, can well capture the dynamic effect of web girders. [ABSTRACT FROM AUTHOR]

Obtaining an accurate simulation of the boundary conditions is very challenging but it is essential in order to represent the true behaviour of the whole structure in fire. In recent years, hybrid simulation has been emerging as an efficient and economical method for simulating realistic boundary conditions in the field of earthquake engineering. This technique can be used to study the load redistribution that may occur in a structural system as a result of locally elevated temperatures. In this paper, the fire-exposed element will be modelled in one analysis (a 3D model) and the rest of the structure in another analysis (a 2D model). This kind of sub-structuring enables the behaviour of the structural system as a whole to be studied. A hybrid simulation (HS) approach is presented and successfully implemented using the OpenFresco and OpenSees software. This approach enables the simulation of the correct restraint provided by the cold structure to the fire affected structural element. The HS analysis of a composite beam is compared with an unrestrained or simply supported version to highlight the difference in behaviour. Finally, the Cardington restrained beam test is modelled to demonstrate the potential of HS technique. Good agreement with the test results highlights that HS approach can be an effective method for studying the behaviour of the whole structural system. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of construction method (e.g. false skew, helicoidal and logarithmic method) on the mechanical behaviour and load carrying capacity of single span skew masonry arches. Simulations were performed with the three dimensional computational software, based on the Discrete Element Method of analysis. Each stone/brick of the masonry skew arch was represented by a distinct block. Mortar joints were modelled as zero thickness interfaces which can open and close depending on the magnitude and direction of the stresses applied to them. The variables investigated were the construction method, the angle of skew, the size of masonry blocks and the critical location of the live load along the span of the arch. At each skew arch, a full width vertical line load was applied incrementally until collapse. From the results analysis, it was found that for a skew masonry arch constructed using the false skew method, as the angle of skew increase, sliding between voussoirs in the arch increases and failure load decreases. However, for skew masonry arches constructed using the helicoidal and logarithmic method, as the angle of skew increases, the failure load increases. Three different characteristic failure modes were identified depending on the contact friction angle and the method of construction. These observations provide new insight into the behaviour and lead to suggestions for understanding the load carrying capacity and failure mode of skew arches. [ABSTRACT FROM AUTHOR]

An analysis model of the dynamic properties of 2–2 multi-layered cement-based piezoelectric composite under impact load and its definite problems are investigated based on the theory of piezo-elasticity in this paper. The theoretical solutions are obtained according to the Duhamel integral and variable separation method. After analyzing the physical meaning and the convergence of the theoretical solutions, the numerical simulations of the composite are presented by utilizing the various loads including the transient step, the transient haversine wave and the transient isosceles triangle loads. The theoretical solutions are compared with the numerical simulations, as well as reported results. Excellent agreements among these results are found. In addition, the influences of the number of layers of the composite and the piezoelectric parameters on the response of dynamic properties are discussed. The work could benefit the design and preparation of the 2–2 multi-layered cement-based piezoelectric composite in engineering practice. [ABSTRACT FROM AUTHOR]

Pin-connections have wide applications in civil structures, such as bridges. Health monitoring of the pin connection plays a significant role to ensure the safety and longevity of these structures. In this paper, a contact model for the pin connection and the normal applied force on the connection was first built based on the Hertzian contact theory, and the validity of the model was verified by the simulation results from a 3D finite element model of a pin connection. The contact model indicates that the contact area between the pin and the pin support increases with the applied force on the connection. Based on this contact model, the authors then present a feasibility study on the load monitoring of pin-connected structures using Lead Zirconate Titanate (PZT) transducers. A tension-controllable structure with a pin connection was fabricated and investigated to verify the effectiveness of the proposed method. Two PZT patches are mounted on the pin and the connected structural surface, respectively. One PZT patch, acting as an actuator, generates a swept sine wave that propagates through the contact area of the pin joint interface and the other one, acting as a sensor, detected the response signal. In the experiment, wavelet packet analysis was employed to quantitatively analyze the transmitted signal between two PZTs when different load levels were applied on the connection. Experimental results demonstrate that energy of the transmitted signal monotonously increases with the load on the pin connection, which is consistent with the simulation result of the contact model. The proposed method has the potential to be employed in real-time monitoring of the loading status of pin connections in practical applications. [ABSTRACT FROM AUTHOR]

Concrete permeability is usually determined by testing unstressed, non-damaged specimens in laboratories as a constant. In reality, however, concrete is subjected to various operational loads in the time span of its service life. Therefore, the permeability of stressed concrete can be time-variant and completely different from that of unstressed conditions. This paper intends to develop a new methodology to determine the permeability of stressed concrete over time, based on the damage mechanics of concrete meso-structure in conjunction with Monte Carlo simulation and finite element analysis. It is found in this study that the permeability of concrete starts to increase when the applied stress in concrete reaches a certain threshold value for the given aggregate fraction. It is also found that the aggregate fraction is the most influential factor for permeability degradation of concrete. The significance of the developed methodology is that it can determine the permeability degradation of concrete with different mechanical properties and geometries of constituent materials under various applied loads over time, which would be otherwise impractical experimentally. [ABSTRACT FROM AUTHOR]

Single rigid body models are often used for fast simulation of tracked vehicle dynamics on soft soils. Modeling of soil-track interaction forces is the key modeling aspect here. Accuracy of the soil-track interaction model depends on calculation of soil deformation in track contact patch and modeling of soil resistive response to this deformation. An algorithmic method to calculate soft soil deformation at points in track contact patch, during spatial motion simulation using single body models of tracked vehicles, is discussed here. Improved calculations of shear displacement distribution in the track contact patch compared to existing methods, and realistically modeling plastically deformable nature of soil in the sinkage direction in single body modeling of tracked vehicle, are the novel contributions of this paper. Results of spatial motion simulation from a single body model using the proposed method and from a higher degree of freedom multibody model are compared for motion over flat and uneven terrains. Single body modeling of tracked vehicle using the proposed method affords quicker results with sufficient accuracy when compared to those obtained from the multibody model. [ABSTRACT FROM AUTHOR]

In this paper, a method to simulate ductile crack growth under very low-cycle fatigue loading condition is given and simulation results are compared with published test data of compact tension specimens and circumferential through-wall cracked pipes. The damage model in simulation is based on the multi-axial fracture strain energy. Two parameters in the damage model are determined from tensile and fracture toughness data under the monotonic loading condition. The determined damage model is then used to simulate ductile crack growth in compact tension specimens subjected to cyclic loading with large-amplitudes and in full-scale through-wall cracked pipes subjected to monotonic and cyclic loading with two different load ratios. Predicted results show a good agreement with experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive test database of concentric compression experiments on pultruded fiber-reinforced polymer (PFRP) specimens that failed in a global flexural buckling mode published in literature between 1969 and 2016. A new closed-form equation to determine the reduction factor for global flexural buckling of PFRP structural struts under axial compression is developed on the basis of the Ayrton-Perry formula and observed initial out-of-straightness of PFRP members measured by other researchers. Recognizing that data on initial imperfections may be unavailable, a second new empirical closed-form equation is derived based upon the experimental database. Validation of the two explicit expressions is performed by both comparison to experimental data and comparison with validated numerical simulations. In addition, the accuracies of the two proposed equations are compared with those of five closed-form solutions available in the literature; both results in more accurate predictions than the extant equations. Both new proposed equations can be conveniently used by structural engineers at the preliminary engineering design stage for accurately assessing the reliability and safety of composite structures under concentric compressive loading. [ABSTRACT FROM AUTHOR]

In this paper, we present a possible application of memristive switches for implementation of main-line mounted loaded-line phase shifters. The underlining idea is to replace PIN diodes, acting as RF/microwave switches, with memristors in order to reduce power consumption. As a proof-of-concept, circuit-level simulations are performed to validate the expected functionality. Parasitic effects caused by the memristor programming circuitry, which might be relevant at RF/microwave frequencies, are taken into consideration. Pi's model is used to represent memristors at RF/microwave frequencies and Biolek's model is used for exploring the memristance setting issues. Our simulation results make memristors the promising candidates for the phase shifters. [ABSTRACT FROM AUTHOR]

When hit by a high-velocity projectile, a fluid-filled container might suffer from Hydrodynamic Ram. The entire tank structure can possibly rupture due to the loads from primary shock wave and a cavity developed in the liquid. In this paper, a countermeasure, of which the rubber layer is inserted on the walls of the tank, is proposed to alleviate the dynamic response of fluid-filled container under the impact of high-velocity projectile. The applicability of the numerical method in simulating the process of high speed projectile penetrates the fluid-filled container is validated by comparing the numerical results with the experimental data in the literature. Then, numerical simulations were conducted to investigate the process of projectile penetrates the fluid-filled container with rubber layer insertion between the walls of container and fluid, with the velocities of 450 m/s, 600 m/s, 750 m/s, 900 m/s and 1050 m/s, respectively. The influence of rubber layer on the dynamic responses of tank walls, the change of pressure of shock wave in water and the energy absorption of structural walls and rubber layers were analyzed. The results indicate that the rubber layer has a significant effect on shock wave acting on container walls. The dynamic response of liquid tank under the loading of the shock wave and local pressure, which is caused by the high speed fragments traveling in the fluid, decreases remarkably. [ABSTRACT FROM AUTHOR]

In this paper, collapse properties of the capped-end cone tubes made from steel alloy 430 with circular holes under quasi-static axial loading have been studied experimentally and numerically. Simulations were performed using finite element LS-Dyna software and 11 types of cone with various number of holes (3, 4 and 5) and heights (20,40 and 60 mm relative to bottom base of cone) in four different thicknesses (0.2, 0.4, 0.6 and 1 mm), so, 44 different states were totally simulated and the collapse properties of them were extracted. The samples with the thickness of 0.2 mm were tested on an experimental basis in order to ensure the accuracy of the simulation results. Comparing the obtained results indicates good agreement between the experimental and numerical data. According to the obtained results, it was found that open end absorbers are more efficient compared to similar capped-end structures. Also, it was revealed that creating holes in the capped-end cone decreases the maximum force and increases crush force efficiency. In addition, it was found that creating hole farther away from the underlying base is more effective for improving the collapse properties. In the final section, the effects of thickness on the collapse properties were evaluated. The obtained results in this study can be a good guidance for investigation on the effect of discontinuity on collapse properties. [ABSTRACT FROM AUTHOR]

In this paper, the recent development of extended consecutive-interpolation 4-node quadrilateral element (XCQ4), which goes beyond certain limitations of conventional methods, is further employed to study dynamic and static thermoelastic fracture problems. In particular, static stress intensity factors (SIFs) and transient dynamic responses of two-dimensional (2-D) stationary cracks in elastic solids under thermal and thermal-mechanical loadings are investigated. In addition, simulation of quasi-static crack propagation under thermal-mechanical loading condition is also performed. To precisely capture the singularity and discontinuity of temperature, heat flux, and displacements due to the presence of crack, the unknown field variables of mechanical displacements and temperature are approximated in terms of the XCQ4 framework by different enrichment strategies, which include either the use of the conventional branch functions or the new ramp function associated with Heaviside function. Only adiabatic condition is considered on the crack surfaces. For quasi-static crack growth analysis, the maximum hoop stress criterion, which is also valid for thermo-elastic fracture mechanics, is adopted. For transient crack analyses, the inertial effect is taken into account for the interaction integral in the consideration of DSIFs. Through eight numerical examples for thermoelastic fracture problems, the validity of the XCQ4 is confirmed by a comparison of the obtained results to those derived from different approaches in previous studies. In addition, the accuracy, performance, and superior advantages of the XCQ4 over standard extended finite element approach are also demonstrated. [ABSTRACT FROM AUTHOR]

In terms of the interaction between buckling and snap-through for shallow structures affected by geometrical imperfections results have shown that, after the nonlinear bifurcation, load reductions occurs accompanied with a predictable tendency. In order to do it, the tracing of interaction domains and interaction curves presented in recent papers by the same Authors, has been proposed. In this study, every simple structural arrangement has been analyzed with regards to different shallowness ratios, slenderness, restraining conditions and imperfection patterns. It has been observed how the driving parameters could be led back to two original interaction ( Δ ) and form ( Ω ) factors. This procedure could shed new light on the application of the more burdensome imperfection pattern for the instability of geometrically nonlinear structures. Possible implications of these results have been presented, with a special attention to sensors and structural identification. The study accomplished numerous numerical simulations and showed good agreement with the theoretical expected results. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the development and application of numerical methods to structural hydrodynamic loading. Fluid-structure interaction is complex, as the ideal code must be able to handle non-linearities, predict thin walled structural collapse (accumulation of plasticity, damage and failure), in addition to capturing the physical response of water (cavitation, suction, and aeration). No single numerical method is able to do all efficiently. Originally developed for aerospace problems, the Crashworthiness, Impacts and Structural Mechanics Group (CISM) at Cranfield University has applied its coupled FE-SPH capability to both Aerospace and Offshore engineering problems. This paper is split into several parts. First, an overview of previous analytical, experimental and numerical studies into water impact research will be provided to understand the different structural collapse mechanisms between hard and water surfaces. This research provided the framework for a coupled Finite Element-Smooth Particle Hydrodynamic (FE-SPH) approach, where key principles will be reviewed and functionally demonstrated through progressively complex offshore examples, including tethered buoys and green water loading on ship superstructures. Limitations of a coupled FE-SPH code will be presented by considering aircraft ditching through a Cranfield co-ordinated European FP7 project, SMAES ( SM art A ircraft in E mergency S ituations). For ditching certification, allowances are made for “probable” structural damage, which is where developments in numerical methods are required. Equally applicable to Offshore, ditching places considerable demands on water modelling due to deficiencies in modelling flow phenomena such as air cushioning, cavitation, suction and ventilation effects. These issues will be explored in order to provide a roadmap for future methods development, which will benefit both Aerospace and Offshore communities. [Copyright &y& Elsevier]

Recent studies at the Center for Infrastructure Protection and Physical Security (CIPPS) have focused on both active and passive protection, the definition and characterization of combined blast and fragment loads on structural elements, the influence of Ultra High Performance Concrete (UHPC) on the behavior of structural elements, and evaluating analysis approaches for progressive collapse assessment. Those studies have highlighted important issues that have not been sufficiently addressed previously, and this paper is aimed at describing the observations from the CIPPS studies that could be used to treat such difficult issues. [ABSTRACT FROM AUTHOR]

This paper analyzes the long-term offshore foundation that undergoes numerous mechanical cycles. The numerical approach follows the hybrid scheme that incorporates a mechanical constitutive model to extract stress into strains at the first cycle into polynomial-type strain accumulation functions to track the progressive plastic deformation. In particular, the strain function contains the fundamental features that require simulating the long-term response of geomaterials: volumetric strain (terminal void ratio) and shear strain (shakedown or ratcheting), the strain accumulation rate, and stress obliquity. A model is calibrated under zero-lateral strain boundary condition by relaxing model parameters. The semi-empirical numerical scheme is used to simulate two offshore foundations subjected to repetitive loads (i.e., monopile and shallow foundation). Numerical results show that the most pronounced displacements occur during early cycles (N < 100), yet their incremental rate approaches toward an asymptotic value. With stress redistribution around the foundations, vertical and horizontal displacements increase with the number of cycles and the asymptotic displacement increases with higher load amplitude. [ABSTRACT FROM AUTHOR]

In this paper, the gas tungsten-arc welding (GTAW) process of a thin cylinder made of Al6061-T6 alloy was simulated using 3-D finite element model in the ABAQUS code and the induced distribution of residual stress was obtained. Temperature dependent thermo-mechanical properties were considered for the aluminum alloy and for simulating the heat source of tungsten arc welding; Goldak's double ellipsoid model was employed. The numerical simulation method employed for the GTAW process of investigated aluminum material was validated experimentally using the hole drilling method as well. High residual stresses were found around the weld line and HAZ area which can increase the risk of crack initiation and propagation in this region of welded aluminum cylinder. Hence in the second part of this research, a longitudinal semi-elliptical crack was considered in the wall of aluminum cylinder subjected to combined internal pressure and torsional loads and its mixed mode I/II fracture parameters (i.e. K I , K II and T ) were determined numerically along the crack front and for different crack geometries. Finally the influence of obtained residual stress field on the computed fracture parameters was reanalyzed using the coupled residual stress/mechanical loading applied to the cylinder. The residual stress field had no effect on the mode II fracture component but the most influence of this factor was observed for mode I stress intensity factor ( K I ) and the deepest point of 3D elliptical crack. [ABSTRACT FROM AUTHOR]

For sake of striking a balance between the need of drilling efficiency and the constrains of power budget on the moon, the penetrations per revolution of drill bit are generally limited in the range around 0.1 mm, and besides the geometric angle of the cutting blade need to be well designed. This paper introduces a simulation approach based on PFC 3D (particle flow code 3 dimensions) for analyzing the cutting load feature on lunar rock simulant, which is derived from different geometric-angle blades with a small cutting depth. The mean values of the cutting force of five blades in the survey region (four on the boundary points and one on the center point) are selected as the macroscopic responses of model. The method of experimental design which includes Plackett-Burman (PB) design and central composite design (CCD) method is adopted in the matching procedure of microparameters in PFC model. Using the optimization method of enumeration, the optimum set of microparameters is acquired. Then, the experimental validation is implemented by using other twenty-five blades with different geometric angles, and the results from both simulations and laboratory tests give fair agreements. Additionally, the rock breaking process cut by different blades are quantified from simulation analysis. This research provides the theoretical support for the refinement of the rock cutting load prediction and the geometric design of cutting blade on the drill bit. [ABSTRACT FROM AUTHOR]

In this paper, an innovative mathematic model dealing with the hysteresis effect of evaporation of pore solution and the nonlinear relationship between diffusivity of moisture and saturation degree of pores solution is established to describe the sulfate attack to reinforced concrete with drying-wetting cycles. The coupling effects of sulfate attack and external loading condition are investigated using a four-point-bending experiment on a reinforced concrete beam and compared with the model predictions. In the experiments, ultrasonic array method is employed to detect the change of the field of modulus of elasticity due to the damage in concrete under sulfate attack coupled with loading condition. The external loading, resulting in tensile strain inside concrete matrix, accelerates the degradation process of concrete subjected to sulfate attack. The modulus variation of concrete under sulfate attack with loading exhibits two apparent stages: (1) the enhancing stage of ettringite crystallization and (2) weakening stage due to overexpansion. The experimental results verified the rationality and validity of the diffusion model proposed in this study, considering the coupling effects of external sulfate attack and loading condition. [ABSTRACT FROM AUTHOR]

The present paper quantifies the adverse effects that can generate rebar section loss, induced by corrosion, especially on the bearing capacity of nuclear power plant cooling towers under extreme wind conditions. Numerical simulations, taking into account, appearance of concrete cracks and their evolution via an appropriate material concrete law and rebar’s yielding, are conducted. Different levels of corrosion are considered which are approximated by rebar section loss. Finally, to restore the integrity of these structures, composite material such as a carbon fiber reinforced plastic (CFRP) layer is modelled. The enhancement of the bearing capacity of the damaged structure compared to the undamaged structure is evaluated in the pre- and post-cracking regime. The main conclusion drawn from the numerical results is that the CFRP reinforcement is very effective for improving the integrity of RC cooling tower shells even when the latter present an advanced corrosion rate. [ABSTRACT FROM AUTHOR]

Abstract: Previous studies of pounding responses of bridge structures to seismic loadings are usually based on the point to point pounding assumption by using the simplified lumped mass model or beam–column element model. It has been found these simplified models can be used to calculate bridge pounding response with consideration of only the longitudinal excitation. In a real bridge structure under seismic loading, pounding could take place along the entire or part of surfaces of the adjacent segments. Moreover, torsional response of the adjacent decks owing to the asymmetric deck or induced by spatially varying transverse ground motions at multiple bridge supports may result in eccentric poundings between adjacent bridge decks. A detailed 3D finite element model is necessary to consider the surface to surface and torsional response induced eccentric poundings and the corresponding damage. This paper performs numerical simulations of pounding damage between bridge girders and between bridge girder and the corresponding abutment of a two-span simply-supported bridge to spatially varying ground motions based on a detailed 3D finite element model by using the explicit finite element code LS-DYNA. The dislocation and unseating potentials of the bridge are also modelled. The bridge components including the bridge girders, abutments, pier, bearings, longitudinal reinforcement bars and stirrups are included in the model. The non-linear material behaviour including the strain rate effects of concrete and steel rebar are considered. The spatially varying ground motions are stochastically simulated. The damage mechanism of the bridge under spatially varying seismic loadings is examined. Numerical results show that the method adopted in the present paper can realistically capture the seismic induced damage of bridge structures. [Copyright &y& Elsevier]

A microgrid optimal scheduling model is developed in this paper to demonstrate microgrid's capability in offering ancillary services to the utility grid. The application of localized ancillary services is of significant importance to grid operators as the growing proliferation of distributed renewable energy resources, mainly solar generation, is causing major technical challenges in supply-load balance. The proposed microgrid optimal scheduling model coordinates the microgrid net load with the aggregated consumers/prosumers net load in its connected distribution feeder to capture both inter-hour and intra-hour net load variations. In particular, net load variations for three various time resolutions are considered, including hourly ramping, 10-min based load following, and 1-min based frequency regulation. Numerical simulations on a test distribution feeder with one microgrid and several consumers/prosumers indicate the effectiveness of the proposed model and the viability of the microgrid application in supporting grid operation. [ABSTRACT FROM AUTHOR]

This paper deals with the investigation of a numerical simulation method to appropriately represent relevant failure mechanisms of carbon fiber reinforced plastic (CFRP) components subjected to dynamic crash loads. The presented work considers the stacked shell approach, using a stack of continuum shell elements and cohesive elements, and focuses on the calibration of simulation input parameters. Furthermore, modeling aspects are discussed to reduce mesh-dependencies for the simulation of progressive crushing. The validation of the numerical approach is performed on the basis of an extensive test program of CFRP crush absorbers on the structural level. The capability of current state-of-the-art technologies for the simulation of progressive crushing is identified. The simulations capture general failure effects and force-displacement characteristics for different designs and loading conditions. Drawbacks are identified in the definition of cohesive input parameters to obtain numerical stability for complex loading conditions. The numerical simulations were performed using the commercial finite element software Abaqus/Explicit. [ABSTRACT FROM AUTHOR]

This paper presents a detailed investigation about the geometric non-linear stiffness behavior of corrugated laminates in six different load cases. The considered tensile, bending, and shear load cases allow the modeling with a unit-cell approach assuming a generalized plane strain state. The torsional load case is more complex. There the mechanical response depends on the number of unit-cells and the width of the samples in case of geometric non-linearities. We first identify the load cases that show a non-linear stiffness response under large deformation. Then the non-linear behavior is analyzed in detail using numerical simulation and we aim for mechanical explanations to describe the non-linear behavior. The FE simulations of the torsional load case are validated using experiments with 3D printed samples. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate ductile failure under shear-dominated loadings using a model of plastic porous solids incorporating void shape effects. We use the model proposed by (Madou and Leblond, 2012a,b; Madou et al., 2013; Madou and Leblond, 2013) to study the fracture of butterfly specimens subjected to combined tension and shear. This model is able to reproduce, for various loading conditions, the macroscopic softening behavior and the location of cracks observed in experiments performed by Dunand and Mohr (2011a,b). Void shape effects appear to have a very significant influence on ductile damage at low stress triaxiality. [ABSTRACT FROM AUTHOR]

Cluster supply chain network is a typical complex network and easily suffers cascading failures under disruption events, which is caused by the under-load of enterprises. Improving network resilience can increase the ability of recovery from cascading failures. Social resilience is found in ant colony and comes from ant’s spatial fidelity zones (SFZ). Starting from the under-load failures, this paper proposes a resilience method to cascading failures in cluster supply chain network by leveraging on social resilience of ant colony. First, the mapping between ant colony SFZ and cluster supply chain network SFZ is presented. Second, a new cascading model for cluster supply chain network is constructed based on under-load failures. Then, the SFZ-based resilience method and index to cascading failures are developed according to ant colony’s social resilience. Finally, a numerical simulation and a case study are used to verify the validity of the cascading model and the resilience method. Experimental results show that, the cluster supply chain network becomes resilient to cascading failures under the SFZ-based resilience method, and the cluster supply chain network resilience can be enhanced by improving the ability of enterprises to recover and adjust. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the development of a new methodology predicting residual stresses induced in finish turning of a AISI304L stainless steel. A hybrid approach combining experimental results and a numerical model is applied. The model simulates the residual stresses generation by applying equivalent thermo-mechanical loadings onto the machined surface without modeling the chip removal process, which enables rapid calculation. The shape and the intensity of equivalent thermo-mechanical loadings are identified through experimental measurements. Friction tests enable to model the thermal and mechanical loadings along the tool–workmaterial interface. Orthogonal cutting tests provide thermal and mechanical loadings below the primary and third shear zone. This model has already been presented in several papers, but only in a 2D configuration. The objective of this paper is to transfer this hybrid approach into a 3D configuration, which is closer to a concrete longitudinal turning operation. Based on this new model, the paper aims at investigating the interactions between each revolution. It is shown that around five revolutions are necessary to reach a steady state. Finally numerical results are compared with experimental measurements obtained by X-Ray diffraction. It is shown that residual stresses cannot be considered as homogeneous over the surface due to tool''s feed. Additionally, the X-Ray beam is much too large to be able to quantify this heterogeneity. Based on average numerical values coherent with average values obtained by X-Ray diffraction, it is shown that the numerical model provides consistent results compared to experimental measurements for a large range of cutting speed and feed. [Copyright &y& Elsevier]

Abstract: A numerical model is introduced in this paper to investigate both global and local ice loads on ship hulls. This model is partly based on empirical data, by which the observed phenomena of continuous icebreaking can be well reproduced. In the simulation of a full-scale icebreaking trial, the interdependence between the ice load and the ship’s motion is considered, and the three degree-of-freedom rigid body equations of surge, sway and yaw are solved by numerical integration. The variations in the level ice thickness and in the strength properties of ice can also be taken into account. The simulated ice loads on ship hulls are discussed through two case studies, in which the ship’s performance, the statistics of ice-induced frame loads, and the spatial distribution of ice loads around the hull are analyzed and compared with field measurements. As far as we know the present paper is the first to integrate all the features above. It is hoped that further studies on this numerical model can supplement the field and laboratory measurements in establishing a design basis for the ice-going ships especially for ships navigating in the first-year ice. [Copyright &y& Elsevier]

Abstract: One of the key components in a mining dump truck is the drive axle housing. Failure of this component during normal use is unacceptable. Recently, early fatigue fracture became a problem during the normal working process of these machines. However, it is difficult to calculate exactly the fatigue failure life of the drive axle housing based on bench testing or pure computer simulation due to the differences between practical road conditions (such as slope and roughness) and simplified boundary conditions. To increase the reliability of analysis results a new analysis method based on dynamic strain measurement from practical mine road surface conditions combined with finite element analysis is proposed in this paper. The dynamic strain and stress on the drive axle housing is obtained by strain measurements while the truck travels over normal mine road surface conditions. The dynamic stress was analyzed using the rain-flow counting method, which can determine the amplitudes and mean values of counted cycles. The influence of the stress mean value was taken into consideration with the Morrow’s model. According to the assumption of a linear Palmgren–Miner hypothesis of damage accumulation and using typical fatigue characteristics of the material, the fatigue failure life was calculated. Analysis of the measurements showed that the dynamic stress experienced by the axle housing was far greater than expected. In order to find the factors affecting the dynamic stress of the drive axle housing, the slope of the road surface, any uneven loading and eccentricities were analyzed using the finite element method. This paper shows that the new analysis methods described are valuable tools for analyzing the reasons behind the failure of these truck axle housings. [Copyright &y& Elsevier]

Abstract: There is relatively little experimental and numerical research on the fundamental behavior of high strength circular concrete-filled steel tubular (CFST) slender beam–columns. In a companion paper, a new numerical model for predicting the nonlinear inelastic behavior of high strength circular CFST slender beam–columns under axial load and bending was presented. The numerical model developed accounts for confinement effects on the strength and ductility of the concrete core and on circular steel tubes as well as initial geometric imperfections of beam–columns. This paper presents the verification of the numerical model and extensive parametric studies on the fundamental behavior of high strength circular CFST slender beam–columns. The ultimate strengths and axial load–deflection responses of circular CFST slender beam–columns under eccentric loading predicted by the numerical model are verified by corresponding experimental results. The computer program implementing the numerical model is used to investigate the fundamental behavior of high strength circular CFST slender beam–columns in terms of load–deflection responses, ultimate strengths, axial load–moment interaction diagrams, and strength increase due to concrete confinement. Parameters examined include column slenderness ratio, eccentricity ratio, concrete compressive strengths, steel yield strengths, steel ratio and concrete confinement. It is demonstrated that the numerical model developed is an efficient computer simulation and design tool for high strength circular CFST slender beam–columns. Benchmark numerical results presented in this paper are valuable in the development of composite design codes for high strength circular CFST slender beam–columns. [ABSTRACT FROM AUTHOR]

Abstract: Extensive research focused on the structural behavior of hybrid steel plate girders is nowadays available in the literature. Furthermore, extensive research devoted to the resistance of homogeneous girders to patch loading has been performed in the last decades. Investigations dealing simultaneously with both fields are, however, rather scarce. The driving force behind developing the present research work has been the aim of completing the knowledge of the patch loading field for the particular structural alternative of hybrid steel plate girder. In the current paper, experimental results found in the literature as well as additional numerical simulations developed by the authors are summarized. The results presented can be used for assessing the resistance of hybrid steel plate girders subjected to patch loading. An in-depth exploit of such results is presented in a companion paper. [Copyright &y& Elsevier]

Abstract: This paper describes a method to analyze for the large deflections of curved prismatic cantilever beams with uniform curvature subjected to a follower load at the tip. The large deflection, the deflection dependent follower load and the initial curved geometry are the important features of the beam considered in this work. Shear force formulation proposed by Lee [Large deflections of cantilever beams of non-linear elastic material under a combined loading. Int J Non-Linear Mech 2002;37(3)] is used for deriving the governing equations. Using this approach, the resulting two point boundary value problem (TPBVP) can be reduced to an initial value problem (IVP). Fourth order Runge–Kutta method along with one parameter reverse shooting method is applied to the numerical solution to the problem. A novel approach presented in this paper of integrating from the free end to the fixed end of the cantilever beam simply replaces the two parameter shooting with a single parameter shooting yielding several advantages. This solution technique is demonstrated for various types of follower tip loads on curved and straight cantilever beams and is validated with existing solutions in the literature. [Copyright &y& Elsevier]

Abstract: Railway organizations are facing continuous increase in train frequency, running speed and axle load with ever limited financial resources. This is why methods broadening knowledge of external loads and internal rail stresses are of higher importance to address rail design or maintenance process. The following paper explains how the development and application of such methods has been conducted by a european partnership (called NOVUM) between railway organizations (SNCF, DB AG, RATP) and rail producer (CORUS) sharing their specific own competences, experience and material resources. Research institutes and universities (BAM, GKSS, INRETS, INSA, LMS) have been in charge of building sound numerical simulations or experimental tests and tools. Theoretical aspects of the method are described in independent paper “A global approach for modelling fatigue and fracture of rails”. A first task group of the program is dedicated to the determination of external forces coming from wheel/rail and from rail/support interactions. The second and third task groups are about material properties and internal stresses inside rail section. Laboratory and track validations are undertaken in the fourth task group. Two characteristic cases are then chosen to check the developed models. [Copyright &y& Elsevier]

The paper discusses a high velocity impact scenario where representative fuselage composite plates are statically preloaded and then impacted with a blunt impactor at velocities in the range 70–105 m/s. Compression and tension preloads that represent design limit load were considered as well as lower preloads that a structure would carry more frequently. Gas gun impact tests were performed to generate a validation database for comparison with results from numerical simulation. A modelling methodology to simulate preloads and transient impact events was documented. The numerical model captures intra- and inter-ply damage by using layers of shell elements connected with cohesive interface layers. Both test and simulation results indicate an influence of static preloads on the impact damage response. The numerical model was especially used to better understand the interaction between preloads and dynamic impact loads which are complex especially for impact on buckled plates. [ABSTRACT FROM AUTHOR]

Long-span bridge traffic loading is governed by congestion. Although congestion can take various forms, most previous studies consider only a queue of vehicles. In this paper, traffic micro-simulation is used to generate several congested traffic scenarios on a two-lane same-direction roadway passing over two long-span bridges. To this end, an acknowledged car-following model is coupled with a lane-changing model. Different traffic compositions and several congestion patterns are analysed in relation to their traffic features and influence on bridge loading. It is found that: (a) slow-moving traffic may be as critical as the full-stop condition, depending on the span length; (b) critical long in-lane truck platoons form mainly at moderate inflows, typically occurring outside of rush hours; (c) the truck distribution between lanes has a limited effect on the total loading; (d) the presence of cars has a strong indirect influence on loading through their interaction with trucks. The methodology and the findings have relevance for computing a more accurate traffic loading for long-span bridges. [ABSTRACT FROM AUTHOR]

The existence of macroscopic flaws in geomaterial structures profoundly influences their load-carrying capacity and failure patterns. This paper is devoted to the numerical investigation of mixed–mode fracture propagation in a cracked Brazilian disk (CBD) specimen by means of the embedded strong discontinuity approach (SDA). A recently modified nonassociated, three-invariant cap plasticity model with mixed isotropic/kinematic hardening is used to predict the continuum response for the intact part of the specimen. In addition, this constitutive model adopts bifurcation analysis to track the inception of new localization and crack path propagation. For the post-localization regime, a cohesive-law fracture model, able to address mixed-model failure condition, is implemented to characterize the constitutive softening behavior on the surface of discontinuity. To capture propagating fracture, the Assumed Enhanced Strain (AES) method is employed. Furthermore, particular mathematical treatments are incorporated into the simulation concerning numerical efficiency and robustness issues. Finally, the results obtained from the enhanced FE simulations are analyzed and critically compared with experimental results available in the literature. [ABSTRACT FROM AUTHOR]

Ground overload is one of the most important factors that threaten the safe operations of oil and gas pipelines. The mechanical behaviour of a buried pipeline under ground overload was investigated using the finite element method in this paper. The effects of the overload parameters, pipeline parameters and surrounding soil parameters on the stress–strain response of the buried pipeline were discussed. The results show that the maximum von Mises stress appears on the top of the buried pipeline under the loading area when the ground load is small, and the stress distribution is oval. As the ground load increases, the maximum stress increases, and the high stress area extends. The von Mises stress, plastic strain, plastic area size, settlement and ovality of the buried pipeline increase as the ground load and loading area increase. The buckling phenomenon of the no-pressure buried pipeline is more serious than the pressure pipeline. As the internal pressure increases, the high stress area and the maximum plastic strain of the buried pipeline first decrease and then increase, the settlement of the buried pipeline increases, and the ovality decreases. The von Mises stress, maximum plastic strain, settlement and ovality of the buried pipeline decrease with increasing buried depth, the surrounding soil's elasticity modulus, Poisson's ratio and cohesion. The maximum von Mises stress, high stress area, the maximum plastic strain, plastic area and ovality increase as the diameter–thickness ratio increases. The critical diameter–thickness ratio is 60, and the settlement of the buried pipeline first increases and then decreases as the diameter–thickness ratio increases. Finally, a protective device of the buried pipeline is designed for preventing ground overload. It can be repaired in a timely manner without stopping the transmission of oil and gas and widely used in different locations because of its simple structure and convenient installation. [ABSTRACT FROM AUTHOR]

Cast iron columns were used in many 19th century structures. Many such structures are still in use today and it is important that they fulfill the current requirements on fire resistance. This paper presents the results of a comprehensive study of the behavior and fire resistance of cast iron columns based on extensive numerical simulations using ABAQUS. The ABAQUS simulation model was validated against six fire tests performed in the USA in 1917. The validated model was then used to investigate the effects of several parameters (column slenderness, load factor, load eccentricity, imperfections of column and cross section, axial restraint) on the behaviour of cast iron columns in fire. The parametric study results indicate that the fire resistance is governed by the applied load and these columns are sensitive to load eccentricity. Based on a comparison between the numerical simulation results and predictions of the EN 1993-1-2 method which is for modern steel structures, it has been found that the EN 1993-1-2 method can give safe and reasonably accurate estimate of the strength and fire resistance of cast iron columns. [ABSTRACT FROM AUTHOR]

In this paper, the shear behaviour and mechanisms of asperity degradation of rock joints under direct shear tests were studied using numerical and experimental approaches. PFC2D was used for numerical simulations, in which the intact material is simulated by a dense packing of circular particles bonded together at their contact points and by breakage of these bonds under loading regimes, the damage process is simulated. The joint interfaces were simulated by a newly developed modified smooth joint model in which micro-scale slip surfaces are applied at contacts between particles of upper and lower blocks of the shear box. In order to study the ability of this numerical approach in reproducing the shearing mechanisms and asperity degradation of rock joints in direct shear tests, a comparative study was carried out against the physical experiments. Experimental and numerical direct shear tests were carried out on saw-tooth triangular joints with the base angles of 20° and 30° under different normal stresses. Three shearing mechanisms of sliding, surface wear and asperity shearing off were observed in these experiments. The comparison of the shear behaviour and mechanisms of asperity degradation of physical and numerical experiments showed that the results of numerical models are in good agreement with physical experiments and this numerical approach can reproduce the shear behaviour of rock joints under different loading conditions. [ABSTRACT FROM AUTHOR]

Design and operation of high-speed planing craft is ruled by the hydrodynamic impact loads and the related craft responses occurring at violent wave encounters. Simulation, measurement and characterization of these loads and responses is however far from trivial. Hereby the general knowledge about these processes is actually rather limited and it is common to rely on simple semi-empirical formulas when designing and analyzing high-speed craft. This paper presents a unique set of impact acceleration data for a high-speed craft in waves, generated based on non-linear strip simulations. Methods and measures for statistical characterization of the acceleration process are established and evaluated, and by application of these methods on the simulation data a number of issues are clarified, for example: slamming time scales and selection of appropriate sampling rates and filtering levels; identification of peak values in acceleration signals; statistical distributions and convergence; and the relation between the statistical peak fraction averages that are commonly used as design parameters and the actual extreme values. The established methods and generated results form a valuable basis for setting up and analyzing high-speed craft experiments and simulations, and for validating and updating the prevailing semi-empirical methods. [ABSTRACT FROM AUTHOR]

This paper presents a solution to the ship–ice interaction problem solved in the time domain by a combined method involving numerical simulations and semi-empirical formula. The breaking process of an intact level ice by an advancing ice breaker has been investigated by a 2D numerical method. An interaction detection technique has been introduced. In order to compute the ice load, a pressure-area relationship for the ice was applied, and a flexural ice plate model was developed. A 3-degree-of-freedom (3DOF) model was adopted to simulate ship maneuvering in level ice. The proposed numerical method has been validated by using the experimental results of an 1:20 scaled CCG R-Class icebreaker model and the full-scale turning circle results. [ABSTRACT FROM AUTHOR]