Dynamic Loading Situations Research Articles

Investigation of dynamic drivetrain behaviour of a wind turbine during a power converter fault

Damage in electrical components during operation of the drive train of wind turbines can lead to highly dynamic load situations. In particular, power converter components are affected by frequent damage, which leads to highly dynamic torque oscillations. As part of a national project, a research nacelle for a wind turbine was set up at the Center for Wind Power Drives (CWD) and examined with the help of a 4 MW test rig. This test rig allows the drive train of a wind turbine to be intensively investigated so that even the highly dynamic load conditions of a power converter fault could be studied. Among other tests, the fault case of a power converter short circuit was synthetically generated. This paper aims to give an insight into the investigation methodology, test setup and looks into the high speed shaft bearing of the gearbox during this load case in detail.

Abnormal loading of the hip and knee joints in unilateral hip osteoarthritis persists two years after total hip replacement.

A total hip replacement (THR) is a common and routine procedure to reduce pain and restore normal activity. Gait analysis can provide insights into functional characteristics and dynamic joint loading situation not identifiable by clinical examination or static radiographic measures. The present prospective longitudinal study tested whether 2 years after surgery a THR would restore dynamic loading of the knee and hip joints in the frontal plane to normal. Instrumented gait analysis was performed shortly before surgery and approximately 2 years after THR on 15 unilateral hip osteoarthritis (OA) patients. 15 asymptomatic matched individuals were recruited as healthy controls. Results showed that abnormal joint loading persisted 2 years after THR. The 2nd external knee adduction moment in terminal stance in the affected (-34%, p = 0.002, d = 1.22) and non-affected limb (-25%, p = 0.035, d = 0.81) was lower compared to controls and thus indicated a shift in the knee joint load distribution from medial to lateral. A correlation analysis revealed that a smaller hip range of motion explained 46% of 2nd knee adduction moment alterations. In contrast, the 2nd external hip adduction moment in terminal stance was postoperatively higher in the affected (+22%, p = 0.007, d = 1.04) and non-affected limb (+22%, p = 0.005, d = 1.05). Here, 51% of 2nd hip adduction moment alterations can be explained with a greater hip adduction angle. Patients with a THR may therefore be at higher risk for abnormal joint loading and thus for the development of OA in other joints of the lower extremities. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Semi-physical modeling and control of a centrifugal compressor for the air feeding of a PEM fuel cell

Air compressor which is to used to deliver the air (including about 21% oxygen) to the cathode channel for electrochemical reaction is a crucial component for the polymer electrolyte membrane (PEM) fuel cell. The working characteristics of the compressor greatly influences the fuel cell performance as well as the durability. In this paper a semi-physical modeling method is adopted to analyze the operating property of a centrifugal compressor which is more suitable for automotive fuel cells because of its compactness. This model includes many physical and empirical parameters which are very difficult to determine. Interior-point optimization method based on Newton iteration is used to identify those parameters. The result shows that the modeled compressor map has a good agreement with the experimental data. Meanwhile, the compressor efficiency is analyzed and compared with the measurement to further validate the developed model. This compressor is thus adapted to a validated 10 kW fuel cell model. A dynamic feedforward controller is proposed based on the load torque to control the air mass flow, eliminating the disturbance produced by the compressor load in transient. The simulation results show that this compressor could satisfy requirements of the fuel cell under dynamic load situations while keeping both the fuel cell and compressor with high efficiencies.

Investigation of cleavage fracture under dynamic loading conditions: Part II numerical analysis

Part I of this study was an extensive fractographic investigation that covered the topics local crack arrest, and cleavage fracture-inducing mechanisms under dynamic loading situations. Also, it produced data regarding the origin of cleavage fracture. Now, this data is used for the numerical part of this study. First, the development of temperature and strain rate increase at the origin of cleavage fracture is conducted, and linked to discrepancies regarding experiments and the Master Curve concept in a phenomenological way. Then, cleavage fracture controlling mechanical field variables at the origin of fracture are analyzed, whereas very similar conditions regarding crack initiation and propagation are found when compared to quasi-static data. The influence of wave phenomena is examined as well. Finally, micromechanical simulations showed that a local temperature increase at the particle–matrix interface does not influence fracture behavior either, and that conclusively, the actual physical mechanism of cleavage fracture initiation (crack initiation and instability) takes place under the same conditions at elevated loading rates as under quasi-static conditions. Ultimately, the mechanisms responsible for the shortcomings of the Master Curve concept under dynamic loading conditions are identified, and current local approach concepts need to be adjusted to consider local crack arrest to be reliable.

A general concrete model in hydrocodes: Verification and validation of the Riedel–Hiermaier–Thoma model in LS-DYNA

The Riedel–Hiermaier–Thoma model, which is available in ANSYS Autodyn since 2000 as a description of concrete and similar geological materials in highly dynamic loading situations, has recently been implemented in the multi-purpose Finite Element code LS-DYNA. This article gives a brief overview of the physical details and verifies the new implementation by comparing single element test results with the established Autodyn code. Four real cases, ranging from low to very high pressure loading by impact, penetration and blast, are used to demonstrate thereafter the validity of the model in a wide range of applications. Simulation results from both codes are compared to experimental data at several occasions. Although slight differences between the implementations are observed, the overall agreement, both between the codes and with experiments, is very good. The systematic work in this publication demonstrates that the Riedel–Hiermaier–Thoma model is a useful addition to the LS-DYNA material library and shall motivate research to apply the model over a wide range of applications. A comprehensive, physically derived dataset is provided for a C70/85 high-strength concrete used in one validation case.

The turtle carapace as an optimized multi-scale biological composite armor – A review

The turtle carapace, the top dorsal part of the shell, is a remarkable multi-scale dermal armor that has evolved to withstand various types of high-stress events encountered in nature. This keratin-covered boney exoskeleton exhibits a number of structural motifs, including alternating rigid and flexible components, layering and functionally graded elements, designed to protect the reptile during predatory attacks, and smashing events. Here we review the multi-scale structural hierarchy of the turtle carapace and its corresponding mechanical properties. We show how the microscopic features of the carapace govern its various macroscopic mechanical responses relevant to protective functioning, including dynamic (impact and cyclic) compression and bending loading situations. In addition, the effect of hydration, a crucial factor for proper physiological-mechanical behavior of biological materials, is illustrated throughout. We also discuss carapace-inspired designs that could be advantageous over the traditional strategies adopted in impact-resistant materials, and could bring new mechanistic insights.

Optimization of wind turbine towers by using a multivariate stochastic calculation method

In order to improve the structural design of tubular and lattice towers for wind turbines, and in order to allow for detailed structural optimizations, a methodology is desirable which allows for quick and reliable considerations of the complex dynamic load situations. Whereat for the design of details for the machinery and the blade optimization time domain methods using multi-body-simulations are well established, their usage is often to extensive due to the needed level of detail to use them for an iterative tower design. Especially with regard to lattice towers, it is therefore desirable to investigate faster stochastic methods which focus on the overall dynamic behavior based on the probability of structural stresses within the tower construction.Lattice structures are difficult to optimize with respect to their shape and topology by manual methods. Therefore, the lattice has been formulated parametrically in order to allow for an automatic update of the geometrical appearance. Both, the positioning of nodes, bracings, trusses and the overall detailing of the lattice are part of the object oriented algorithm.Using both tools, an automatic structural optimization of the geometry of a lattice structure for an onshore wind turbine has been performed. The gained results of the optimized lattice tower are finally compared to a conventional tubular tower.

Fracture probability modelling of impact-loaded iron ore pellets

Blast furnace iron ore pellets are sintered, centimetre-sized ore spheres with a high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In transporting pellets from pelletizing plants to customers, iron ore pellets are exposed to different static and dynamic loading situations, resulting in strength degradation and, in some cases, fragmentation. This can lead to a reduced gas flow in the blast furnace, which causes reduced quality in steel production. Reliable numerical simulations that can predict the ability of the pellets to endure their handling are important tools for optimizing the design of equipment for iron ore handling. This paper describes the experimental and numerical work performed to investigate the impact fracture behaviour of iron ore pellets at different strain rates. A number of split Hopkinson pressure bar tests with different striker velocities are carried out and analysed to investigate the strain rate dependency of the fracture strength of iron ore pellets. Fracture data for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. A stress based, strain-rate dependent fracture model that takes triaxiality into account is suggested. The fracture model is used and validated with impact tests of iron ore pellets. In the validation experiment, iron ore pellets are fired against a steel plate, and the percentage of fractured pellets at different impact velocities are measured. Finite element simulations of the experiment are carried out and the probability of pellets fracturing during impact are calculated and compared with the experimental results. The agreement between the experiments and numerical simulations shows the validity of the model.

Structural Designs with Consideration of Both Material and Structural Failures

AbstractThis paper provides a simplified formula for modeling the transition between material and structural failures in static and dynamic loading situations. For static situations, the transition equation allows for the calculation of the ultimate capacity between buckling structural failure and compression material failure modes. For dynamic situations, the transition equation allows for the calculation of a smoothed S-N curve between the constant amplitude fatigue limit, namely, the endurance limit, and the low-cycle, high-stress fatigue limit. The simplified formula is based on a quadratic solution that is curve fit to each failure mode and is verified with existing experimental data.

Numerical simulation of concrete confined by transverse reinforcement

The behaviour of concrete confined by transverse reinforcement is a classical topic. Numerous studies have been conducted to establish the stress-strain relationships for concrete under various confining reinforcement arrangements. Many empirical and semi-empirical formulas exist. Simplified analytical models have also been proposed to evaluate the increase in the strength and ductility of confined concrete. However, relatively few studies have been conducted to utilise advanced computational models for a realistic simulation of the behaviour of concrete confined by transverse reinforcement. As a matter of fact, high fidelity simulations using the latest numerical solvers in conjunction with advanced material constitutive models can be a powerful means to investigating the mechanisms underlying the confining effects of different reinforcement schemes. This paper presents a study on the use of high fidelity finite element models for the investigation of the behaviour of concrete confined by stirrups, as well as the interpretation of the numerical results. The development of the models is described in detail, and the essential modelling considerations are discussed. The models are then validated by simulating representative experimental studies on short columns with different confining reinforcement schemes. The development and distribution of the confining stress and the subsequent increase in the axial strength are examined. The models are shown to be capable of reproducing the behaviour of the confined concrete realistically, paving a way for systematic parametric studies and investigation into complicated confinement, load combination, and dynamic loading situations.

Damage prediction of RC containment shell under impact and blast loading

There is world wide concern for safety of nuclear power installations after the terrorist attack on World Trade Center in 2001 and several other civilian structures in the last decade. The nuclear containment structure in many countries is a double shell structure (outer shell a RCC and inner a prestressed concrete). The outer reinforced concrete shell protects the inner shell and is designed for external loading like impact and blast. A comparative study of non-linear response of reinforced concrete nuclear containment cylindrical shell subjected to impact of an aircraft (Phantom) and explosion of different amounts of blast charges have been presented here. A material model which takes into account the strain rate sensitivity in dynamic loading situations, plastic and visco-plastic behavior in three dimensional stress state and cracking in tension has been developed earlier and implemented into a finite element code which has been validated with published literature. The analysis has been made using the developed software. Significant conclusions have been drawn for dissimilarity in response (deflections, stresses, cracks etc.) of the shell for impact and blast loading.

Mechanical behaviour of functionally graded plates under static and dynamic loading

This article presents an analytical solution for the mechanical behaviour of rectangular plates made of functionally graded materials (FGMs) based on the first-order shear deformation theory (FSDT) and the third-order shear deformation theory (TSDT). The FGM plate is assumed to be graded across the thickness. The material properties of the FGM plate are assumed to vary continuously through the thickness of the plate according to a power law distribution of the volume fraction of the constituent materials, except Poisson's ratio, which is assumed to be constant. The plate is subjected to a lateral mechanical load on its upper surface. The equations of motion are written based on displacement fields. The partial differential equations have been solved by the Fourier series expansion. Using the Laplace transform, unknown variables are obtained in the Laplace domain. The resulting formulations enable one to perform the static, dynamic, and free vibration analysis for both FSDT and TSDT plates. Employing the analytical Laplace inversion method and numerical time integration technique based on the Newmark method, time function solution of the problem is obtained and the unknown parameters are derived for a dynamic loading situation. Finally, the natural frequencies of the plate are obtained and dynamic responses are presented in the form of combinations of different frequencies. The results are verified with those reported in the literature.

Dynamic Fracture Simulation of Concrete Using a Virtual Internal Bond Model

A multiscale virtual internal bond (VIB) model for isotropic materials has been recently proposed to describe material deformation and fracture under quasi-static and dynamic loading situations. Fracture simulation using an isotropic VIB model is made possible by incorporating a cohesive type law, inspired by atomistic-level interaction among particles into a hyperelastic framework at the continuum level. Thus, fracture is built directly into the constitutive formulation. The numerical implementation of the material model for brittle materials into a finite-element scheme and the determination of model parameters has been previously researched. In this paper, the VIB model is applied to the dynamic fracture simulation of plain concrete. The experimental study on the dynamic tensile failure of concrete by Gran et al. is used to determine the VIB model material parameters for plain concrete. Simulations and results of comparisons with the concrete — VIB model with the experimental results are presented in this paper.

Strain Rate Model for Dynamic Analysis of Reinforced Concrete Structures

A strain rate dependent material model for concrete has been proposed for analysis of three-dimensional reinforced concrete structures under transient dynamic loading. The model takes into account the pressure sensitivity in three-dimensional loading situations and strain rate sensitivity in dynamic loading situations. The cracking in tension has been modeled using the smeared cracking approach. The strain rate sensitivity has been considered at two levels: the failure surface is made strain rate dependent as is also the fluidity parameter. The tension stiffening effect observed in reinforced concrete structures has also been considered.

Impact Studies in Elastomer, Fly Ash, and Hybrid-filled Epoxy Composites: Part I - Room Temperature Curing

This study involves a system where epoxy as matrix and two reinforcements, namely an elastomer and a less dense oxide known as fly ash, differing in their response to mechanical loading to yield hybrid composite, are used. As rubber particles are known for their resistance to dynamic loading situations, poly(acrylonitrile-co-butadiene), carboxyl terminated, CTBN as the elastomer constitutes the first of the filler. The incorporation of rigid fly ash, as a second filler, has been made to see the change in the behavior in the response to the impact test. Their roles as individual fillers as well as hybrid fillers are studied at various compositions. The directly observed experimental values such as total energy and the derived data like ductility index (DI) are catalogued. While the fly ash-bearing composites show maximum absorption of energy at 3% by weight, the rubber-bearing ones display the same trend at 1%. The values recorded for the hybrid type having 1% were high. The DI showed highest values for the maximum filler bearing compositions in all cases. The scanning electron micrographs of the impact-failed samples helped in understanding the trends seen in the impact data.

Fracture Simulation Using an Elasto-Viscoplastic Virtual Internal Bond Model With Finite Elements

A virtual internal bond (VIB) model for isotropic materials has been recently proposed by Gao (Gao, H., 1997, “Elastic Waves in a Hyperelastic Solid Near its Plane Strain Equibiaxial Cohesive Limit,” Philos. Mag. Lett. 76, pp. 307–314) and Gao and Klein (Gao, H., and Klein, P., 1998, “Numerical Simulation of Crack Growth in an Isotropic Solid With Randomized Internal Cohesive Bonds,” J. Mech. Phys. Solids 46(2), pp. 187–218), in order to describe material deformation and fracture under both static and dynamic loading situations. This is made possible by incorporating a cohesive type law of interaction among particles at the atomistic level into a hyperelastic framework at the continuum level. The finite element implementation of the hyperelastic VIB model in an explicit integration framework has also been successfully described in an earlier work by the authors. This paper extends the isotropic hyperelastic VIB model to ductile materials by incorporating rate effects and hardening behavior of the material into a finite deformation framework. The hyperelastic VIB model is formulated in the intermediate configuration of the multiplicative decomposition of the deformation gradient framework. The results pertaining to the deformation, stress-strain behavior, loading rate effects, and the material hardening behavior are studied for a plate with a hole problem. Comparisons are also made with the corresponding hyperelastic VIB model behavior.

Advanced Manufacturing Technologies Utilising High Density Infrared Radiant Heating

Oak Ridge National Laboratory has developed a unique rapid heating capability utilising a high density infrared (HDI) radiant plasma arc lamp. Power densities ≤3.5 W cm-2 are achievable over an area 35 x 3.175 cm. The power output of the lamp is continuously variable over a range from 1.5% to 100% of available power, and power changes can occur in <20 ms. Processing temperatures ≤3000°C can be obtained in a wide variety of processing environments, making HDI a flexible processing tool. Recently, this newly developed heating method was used to investigate selective softening, i.e. hardness reduction of 6063-T6 aluminium alloy. By changing the incident power and exposure time, the percentage reduction in hardness and softened zone size can be varied. It is shown that computer modelling can be used to predict the thermal history and the resulting heat affected zone during HDI processing. In the present work, a 50% reduction in hardness was achieved and confirmed by mechanical testing and microstructural investigation. Micrographs of softened aluminium show that Mg2Si precipitates had dissolved back into solution. This new approach allows materials to be engineered for a predetermined response to dynamic loading or other environmental situations. SE/S282

Fracture simulation for anisotropic materials using a virtual internal bond model

A virtual internal bond (VIB) model for isotropic materials has been recently proposed to describe material deformation and fracture under static and dynamic loading situations. Fracture simulation using an isotropic VIB model, is made possible by incorporating a cohesive type law, inspired by atomistic-level interaction among particles into a hyper-elastic framework at the continuum level. Thus, fracture is built directly into the constitutive formulation. The numerical implementation of the model into a finite element scheme and the determination of model material parameters was described in detail in [Eng. Fract. Mech. 71 (2004) 401]. In this paper, the isotropic model is extended for the fracture simulation of anisotropic materials. This is done by introducing a bond density function at the atomistic level, that can model a variety of anisotropic materials. The bond density function is modeled by spherical harmonics expansions. The derived anisotropic model is implemented as a material model subroutine in ABAQUS and used to perform fracture simulations in anisotropic materials. Simulations and results of comparisons with the isotropic model are presented in this paper.

A flexible-arm as manipulator position and force detection unit

This paper presents a self-sensory robot arm to two basic sensing problems in control of flexible manipulators: detection of the position and orientation variations due to structural deformation and detection of the contact force of end-effector when manipulator interacts with its environment. Taking advantage of structural flexibility, a flexible robot arm with strain gauges distributed on it acts as a sensing unit. The position and orientation of flexible arm are expressed as a function of curvature of the arm. An interpolation technique gives this continuous curvature function from a finite set of measurements made with strain gauges. A relation between strain measurements and endpoint force of flexible arm is developed and the contact force of end-effector is then determined using a force propagation algorithm. The proposed technique and algorithm were implemented and evaluated in a laboratorial flexible arm. Experimental validations using a vision system and two force sensors have shown that the self-sensory flexible arm can provide accurate endpoint position and force in both static and dynamic loading situations.

Foot type classification: a critical review of current methods

Investigation into the effects of foot structure on foot function, and the risks of injury, has been at the core of many studies, sometimes with conflicting results. Often different methods of foot type classification have been used, making comparison of the results and drawing sound conclusions impossible. This article aims to critically review current methods of foot type classification. It is concluded that if a classification method combines data on structure with information on foot function in dynamic loading situations, it should relate more closely to the functional behaviour of the foot during locomotion.