Full Range Of Loading Conditions Research Articles

Stability enhancement of bi‐directional voltage source converters in modern power systems

AbstractIn future modern power systems, reliability and resilience could be an extreme challenge caused by the stability issues of the bidirectional power converters (BPCs). The non‐linear dynamics of DC link voltage (DCLV) of BPCs in interaction with the existing linear control schemes may decrease the stability margin and cause operating‐point‐dependent instability issues. Existing approaches may solve this issue by reducing the DCLV control loop bandwidth, which considerably degrades the system performance. To tackle this issue, first, the root cause of the instability challenge is analytically investigated, and then, a non‐linear stabilizer control scheme based on Lyapunov theorem is proposed. Considering the non‐linear dynamic of the BPCs and the interaction between dynamics of DC link voltage and AC currents in the proposed stabilizer, it guarantees the stability of the converter in both directions of power flow and the full range of loading conditions. The performance of the proposed scheme is verified through simulation of the system under various operating conditions, considering uncertainties, disturbances, and short‐circuit events, and comparing it with that of prevalent controllers.

The finite element method-based pattern recognition approach for the classification of patient-specific gunshot injury.

Violence related injuries and deaths mostly caused by firearms are a major problem throughout the world. Understanding the factors that control the extent of hard-soft tissue wound patterns using computer imaging techniques, numerical methods, and machine learning algorithms may help physicians to diagnose and treat those injuries more properly. Here, we investigate the use of computational results coupled with the pattern recognition algorithms to develop an approach for forensic applications. Initially, computer tomography (CT) images of the patient whose leg was shot by a 9 × 19 parabellum bullet are used to construct the FE models of that patient's femoral bone and the surrounding soft tissues. Then, Hounsfield units-based material properties are assigned to elements of the bone. To simulate the full range of loading conditions encountered in ballistic events, a constitutive model that captures the strain-rate dependent response is implemented. The entrance pathway vector of the bullet is directed in accordance with the patient's wound and the simulations are deployed for the cases having various inlet velocities such as 150, 200, 250, 300, and 350 m/s. Once the FE results for each case are obtained, they are processed with supervised machine learning algorithms to classify the wound and inlet velocity correspondence. The results demonstrate that they can be diagnosed with a percent accuracy of 97.3, 97.5, and 98.3 for the decision tree (DT), k-nearest neighbors (kNN) and support vector machine (SVM) classifier, respectively. This approach may provide a useful framework in classifying the wound type, predicting the bullet impact velocity and its firing distance.

Experimental study on the effect of eccentric compressive load on the stability and load-carrying capacity of thin-walled composite profiles

This paper relates to an experimental study on the compression of thin-walled composite profiles with open cross-sectional shapes and a symmetric layup. The primary objective of the study was to determine the effect of eccentric compressive load on the stability and load-carrying capacity of the analysed profiles. The study investigated the effect of laminate layup and cross-sectional shape on the buckling load, postbuckling equilibrium path and failure load of the structures under compression. The experiments were performed on samples of short columns made of CFRP by autoclaving. Real composite structures were subjected to compression until failure; test parameters were measured in order to determine post-buckling equilibrium paths for the full range of loading conditions. The initiation of composite material damage was assessed by acoustic emission. The employed research methods made it possible to examine the problems of nonlinear stability and load-carrying capacity of the compressed structures.

An Integrated Boost Active Bridge Based Secondary Inductive Power Transfer Converter

Due to its inherent safety, robustness, and high efficiency, inductive power transfer (IPT) technology is highly suitable for the implementation of wireless electric vehicle (EV) chargers. In addition, IPT-based EV chargers can provide consistent vehicle-to-grid services, opportunistic charging, and in-motion/dynamic charging. However, designing such systems to adhere to applicable standards, while ensuring constant power transfer, and high efficiency, remains a challenge. For example, to meet the requirements outlined by SAE J2954, a wireless charger should tolerate a coupling change from 10% to 30% and a battery voltage variation from 280 to 420 V. A boost active bridge (BAB) converter presented in previous work was shown as a suitable solution; however, this system utilized two additional dc inductors. As such, this article presents a BAB converter, which integrates the current splitting functionality previously achieved using two dc inductors into a Double D magnetic coupler. This achieves a reduction in the magnetic volume of approximately 70%. Analysis of the proposed converter together with detailed design guidelines to maximize power transfer efficiency for a system designed to meet the SAEJ2954 specifications is also presented. Experimentally obtained efficiencies from a 7-kW prototype system showed minimal variation over the full range of loading conditions, ranging between 94.2% and 92%.

Gradual degradation of a thin-walled aluminum adhesive joint with omega cross section under bending

The aim of the study was to examine deformation and degradation of a longeron fragment or a crossbeam in aircraft fuselage. The study included: (1) performing new laboratory investigations and (2) developing a corresponding numerical model of the structural element's behavior. Laboratory tests, i.e. controlled deformation by 3 PB (3-point bending) until bending collapse, were performed on specimens with a thin-walled omega cross section consisting of 2 aluminum parts: a roll-formed omega shape and a flat strip. Both parts were continuously bonded with 4 different types of structural adhesives, Fig. 1.Results of the laboratory tests and numerical analysis provided comprehensive knowledge of the structural element's behavior over the full range of loading conditions, starting from the elastic response, through the initialization of bending collapse and degradation processes, local folding and cracking, up to the final phase of bending collapse. A Finite Element Analysis (FEA) model of the structural element's deformation including adhesive layer damage and ductile damage in the aluminum parts of the test specimen was elaborated. The model allowed for the description of the longeron's gradual degradation until the final failure including: (1) plastic collapse mechanisms with cracking inside the aluminum parts and (2) delamination of the adhesive layers under 3 PB deformation.The agreement between the experimental and FEA results confirms that the numerical model of the investigated structural element was designed based on correct assumptions.

Kinematic Differences in Posterior Stabilized Total Knees Determined by a Holistic Experimental Evaluation Method

Posterior stabilized (PS) total knees are regarded as one classification, although there are considerable differences in condylar and cam-post geometries which may affect their kinematic outputs. Evaluation methods for kinematics have included Oxford type machines [1], robots [2], knee simulators [3,4], computer models [5], and loading rigs specifically designed to measure laxity in line with the ASTM standard on constraint [6].We developed a desktop machine for kinematic evaluation of total knee models under a full range of loading conditions and flexion angles, and proposed that the data from the anatomic knee be used as the benchmark [7].Our hypotheses were that current PS designs will show a large variation in kinematic output, that these would differ from anatomic characteristics, and that an asymmetric guided motion design could potentially restore anatomic kinematics.The test machine applied combinations of compressive loads, shear forces and torques, at a full range of flexion angles, representing a spectrum of functional activities. Forces of 1,000 N compression, 200 N shear, and 5 Nm torque were applied by computer controlled pneumatic actuators.Springs of the correct stiffness represented soft tissue restraints [8]. The five loading conditions were applied sequentially at incremental flexion angles specified in Fig. 1 ranging from 0 – 120 degrees. Fig. 1 shows a schematic of loading and constraint parameters of the machine.The sequence of loading conditions was: Compression load only, compression and anterior shear, compression and posterior shear, compression and internal torque, and compression and external torque.By digitization of fiducial points on the femoral and tibial components at each test condition, and subsequent computer modeling, the femoral-tibial and kinematic data were determined. The test parts were metal-poly components, and for a new asymmetric guided motion design, a stereo-lithographic model in a hard, low-friction plastic was used, with a Krytox AT fluoro ether grease used for lubrication. All TKR components used were left knee components. Three current PS designs were tested together with a Guided Motion PS design intended to reproduce characteristics of anatomic motion.Both qualitative (Fig. 2) and quantitative (Figs. 3 and 4) data were acquired from 3D computer analysis.The first design (PS1) showed uniform posterior displacement of the contact points after 90 deg flexion. The anterior and posterior (AP) shear contacts showed moderate AP sliding which could allow some paradoxical motion. There was restricted internal-external rotation after 90 deg flexion due to restraint of the cam-post and the posterior plastic lip.PS2 showed a progressive posterior displacement with flexion, but the possibility of large AP sliding due to shear forces. There was adequate internal-external rotation at all flexion angles. PS3 showed contact points which were posterior, even on the posterior edges, under most test conditions. The square post showed corner contacts and restraint of rotation. The three designs showed symmetric lateral and medial motion.The fourth design was a Guided Motion with high medial conformity, low lateral conformity, and a rounded cam-post to reproduce the characteristics of the normal knee. There was progressive lateral rollback with flexion, 3–4 mm posterior medial rollback in high flexion, as with the anatomic knee, small AP medial sliding with shear forces, and adequate internal-external rotation.The test method proved to be simple and convenient to use and provided data which would evaluate any TKR design compared with an anatomic benchmark. The method is also an effective tool for comparing designs of varying constraint against one another to evaluate the performance characteristics of a specific PS as compared to known clinical designs.Current PS designs showed variable geometric characteristics which would impact function: an asymmetric Guided Motion design could better reproduce the motion characteristics of the normal anatomic knee. In a previous study using a similar method, kinematic characteristics of the normal anatomic knee were determined, to be applied as a benchmark for TKA design [7]. These anatomic characteristics for our specific loading conditions were: for the neutral path of motion during flexion, small AP displacements on the medial side, and continuous posterior displacement on the lateral side; small AP laxities medially and 3–8 mm laxity laterally; internal - external rotational laxities of 13–25 degrees with instant centers of rotation on the medial side.

A viscoelastic, viscoplastic model of cortical bone valid at low and high strain rates

The stress-strain behavior of cortical bone is well known to be strain-rate dependent, exhibiting both viscoelastic and viscoplastic behavior. Viscoelasticity has been demonstrated in literature data with initial modulus increasing by more than a factor of 2 as applied strain rate is increased from 0.001 to 1500 s(-1). A strong dependence of yield on strain rate has also been reported in the literature, with the yield stress at 250 s(-1) having been observed to be more than twice that at 0.001 s(-1), demonstrating the material viscoplasticity. Constitutive models which capture this rate-dependent behavior from very low to very high strain rates are required in order to model and simulate the full range of loading conditions which may be experienced in vivo; particularly those involving impact, ballistic and blast events. This paper proposes a new viscoelastic, viscoplastic constitutive model which has been developed to meet these requirements. The model is fitted to three sets of stress-strain measurements from the literature and shown to be valid at strain rates ranging over seven orders of magnitude.

A non-quadratic yield function for polymeric foams

The yield behavior of a closed cell polymeric foam is investigated under multiaxial loadings. A phenomenological yield function is developed to characterize the initial yield behavior of the closed cell polymeric foam under a full range of loading conditions. The principal stresses of a relative stress tensor and the second invariant of the deviatoric stress tensor are the main parameters in the yield function. The yield function is a linear combination of non-quadratic functions of the relative principal stresses and the second invariant of the deviatoric stress tensor. The convexity of the yield surface based on the non-quadratic yield function is proved. The non-quadratic yield function is shown to well characterize the yield behavior of a closed cell polymeric foam in [Deshpande, V.S., Fleck, N.A., 2001. Multi-axial yield behavior of polymer foams. Acta Materialia 49, 1859–1866] under a full range of loading conditions. Finally, a comparison of different phenomenological yield functions to characterize the yield behavior of the foam is presented.

Probabilistic design analysis of the influence of material property on the human cervical spine.

Studies reported previously in the literature have described the importance of material variation on the cervical responses and have examined some effects by varying the material properties, but there is no systematic approach using statistical methods to understand the influence of material variation on a cervical spine model under a full range of loading conditions, especially under compression and anterior and posterior shear. A probabilistic design system based on Monte Carlo simulation methods using Latin hypercube sampling techniques is used to analyze the material sensitivity of a C4-C6 cervical spine model involving 13 uncertain input parameters on the biomechanical responses and disc annulus stresses under compression, anterior shear, posterior shear, flexion, extension, lateral bending, and axial rotation. The loading types and range of values were as follows: compression, 0-1 mm; anterior shear, 0-2 mm; posterior shear, 0-3.5 mm; flexion, extension, lateral bending, and axial rotation. 0-1.8 Nm with 73.6-N preload. For each case, the load-deflection and key stress values at various spinal components were captured after each load step. The model was also validated under the same conditions. The minimum and maximum predicted responses were within the range of the experimental data. Ignoring compression loading, the combined effects on the biomechanical responses of the cervical ligaments under the remaining loads are enormous. Their total impacts are almost equal to or slightly less than the influence of disc annulus. Results show that the fiber mechanical properties did not have a significant effect on the compressive stiffness. This study reveals important features that help us identify the critical input parameters and enable us to reduce the development time of a patient-specific biomechanical model.

Fully Coupled Analysis of Failure and Remediation of Lower San Fernando Dam

The extent of flow deformation in an embankment dam is determined by the driving forces and the residual strength of the soil, as well as by the kinematic constraints. The soil conditions of berm and buttress, as well as of foundation, are also critical factors affecting seismic performance of an embankment dam. A careful examination of these factors is necessary when proposing remedial measures to a seismically deficient dam. This paper presents a set of fully coupled finite element analyses of the response of the well-known lower San Fernando Dam during the 1971 earthquake. A critical state model incorporating the concept of state-dependent dilatancy was employed to describe soil behavior over the full range of loading conditions encountered. The results show clearly that a flow slide occurred on the upstream side, and indicate that a downstream flow slide would occur, too, if the downstream berm had not been constructed before the event. The analyses show also that the addition of an upstream berm could effectively prevent the upstream flow slide.

NON-LINEAR MODELLING OF HYDRAULIC MOUNTS: THEORY AND EXPERIMENT

This paper focuses on the development of a complete non-linear model of a hydraulic engine mount and the evaluation of the model using a unique experimental apparatus. The model is capable of capturing both the low- and high-frequency behavior of hydraulic mounts. The results presented here provide a significant improvement over existing models by considering all non-linear aspects of a hydraulic engine mount. Enhancements to already published non-linear models include a continuous function that follows a simplistic yet effective approach to capture the switching effect and leakage through the decoupler, and upper chamber bulge damping. It is shown that the model developed here provides the appropriate system response over the full range of loading conditions (frequency and amplitude) encountered in practice. In order to obtain the parameter values for the non-linear model, a unique test apparatus is introduced. Using the experimental set-up, it is possible to verify the model of individual components of the mount, and later on test the behavior of the whole assembly. These data also establish the relative importance of several damping, inertia and stiffness terms. In addition, the measured responses of the mounts to loading at various frequencies and amplitudes are compared to the predictions of the mathematical model. The comparisons generally show a very good agreement (better than 10%), which corroborate the non-linear model of the mount. It is felt that this work will help engineers in reducing mount design time, by providing insight into the effects of various parameters within the mount.

Analysis of Laterally Loaded Shafts in Rock

The behavior of both flexible and rigid shafts socketed into rock and subjected to lateral loads and moments is studied. Parametric solutions for the load‐displacement relations are generated using the finite element technique. Based on these solutions, simple, approximate, closed‐form equations are developed to describe the response for the full range of loading conditions, material parameters, and socket‐rock mass stiffnesses encountered in practice. These results are in close agreement with available solutions for the limiting cases of flexible and rigid shafts. The solutions give horizontal groundline displacements and rotations and can incorporate an overlying soil layer. The problem of assessing the lateral load capacity of rock‐socketed foundations is also addressed, and a method of analysis to predict this capacity is suggested. The application of the theory, in the form of back‐analysis, to a single case involving the field loading of a pair of rock‐socketed shafts is also described.