Current Loading Conditions Research Articles

Biomechanical Modelling for Tooth Survival Studies: Mechanical Properties, Loads and Boundary Conditions-A Narrative Review.

Recent biomechanical studies have focused on studying the response of teeth before and after different treatments under functional and parafunctional loads. These studies often involve experimental and/or finite element analysis (FEA). Current loading and boundary conditions may not entirely represent the real condition of the tooth in clinical situations. The importance of homogenizing both sample characterization and boundary conditions definition for future dental biomechanical studies is highlighted. The mechanical properties of dental structural tissues are presented, along with the effect of functional and parafunctional loads and other environmental and biological parameters that may influence tooth survival. A range of values for Young's modulus, Poisson ratio, compressive strength, threshold stress intensity factor and fracture toughness are provided for enamel and dentin; as well as Young's modulus and Poisson ratio for the PDL, trabecular and cortical bone. Angles, loading magnitude and frequency are provided for functional and parafunctional loads. The environmental and physiological conditions (age, gender, tooth, humidity, etc.), that may influence tooth survival are also discussed. Oversimplifications of biomechanical models could end up in results that divert from the natural behavior of teeth. Experimental validation models with close-to-reality boundary conditions should be developed to compare the validity of simplified models.

A Fully Integrated Low-Dropout Regulator with Improved Load Regulation and Transient Responses.

A fully integrated low-dropout (LDO) regulator with improved load regulation and transient responses in 40 nm technology is presented in this paper. Combining adjustable threshold push–pull stage (ATPS) and master–slave power transistors topology, the proposed LDO maintains a three-stage structure within the full load range. The proposed structure ensures the steady-state performance of LDO and achieves 0.017 mV/mA load regulation. The ATPS consumes little quiescent current at light load current condition, and the turn-on threshold of the ATPS can be adjusted by a current source. Once the value of current source is set, the turn-on threshold is also determined. A benefit of the proposed structure is that the LDO can be stable from 0 to 100 mA load current with a maximum 100 pF parasitic load capacitance and a 0.7 pF compensation capacitor. It also shows good figure of merit (FOM) without an extra transient enhanced circuit. For the maximum 100 mA load transient with 100 ns edge time, the undershoot and overshoot are less than 33 mV. The dropout voltage of the regulator is 200 mV with input voltage of 1.1 V. The total current consumption of the LDO was 24.6 μA at no load.

Critical issues in existing RC deck stiffened arch bridges under seismic actions

Existing Reinforced Concrete arch bridges represent still today an important part of transportation network. The peculiarities of such bridges make particularly complex the assessment of their behaviour under both static and dynamic actions and, therefore, their safety. This work concentrates on a specific arch bridge typology known as the “Maillart –Type Arch Bridges” or “Deck-Stiffened Arch Bridges”, characterized by a very stiff deck beam and a slender and wide vault. As well as for the RC structures designed during 50s of the last century, where some important details for concrete elements were not considered, RC Deck-Stiffened Arch Bridges could be subjected to similar structural deficiencies. Moreover, the current loading conditions provide actions that were not considered in the original design or have changed over the time, such as the seismic actions or the moving loads due to the vehicular traffic.For the evaluation of the main critical issues related to the current performance of the “Maillart–Type Arch Bridges”, this study, starting from a “simulated design” according to the design rules and the mandatory codes in force at the construction time, defines a large building inventory of simulated bridges (3000 samples) characterized by different values of the most significant geometrical parameters. Firstly, each bridge of the inventory is modelled and studied by means of a linear Response Spectrum Analysis (RSA) implemented in the software SAP2000. The large number of structural analyses allowed to investigate the seismic behaviour of such a bridge typology, assess and localize the most frequent failure modes. The results of the RSA allowed developing preliminary fragility functions at the Ultimate Limit State, based on shear or flexural failure of single elements of the bridges. Lastly, Non-Linear Time History Analyses (NLTHA) were carried out on two representative case studies extracted from the simulated inventory and the results were examined in terms of fragility curves obtained according to the Cloud methodology for four Damage States. Despite the different approaches (RSA on large scale and NLTHA on two prototypes), a comparison of the fragility curves for equivalent Damage States was also proposed and a good agreement was found. These fragility curves are a first step for the assessment of the seismic vulnerability of “Maillart–Type Arch Bridges” and can be useful for planning seismic risk mitigation interventions for such a bridge typology.

Experimental and numerical study of the hydrodynamic features of a cylindrical FPSO considering current-induced motion

Hydrodynamic features of a cylindrical FPSO in the wave, current and coupled wave and current load conditions were experimentally and numerically studied in high sea states. In the wave condition, a large low frequency IL (inline, along the environmental load's direction) motion is observed which is mainly dominated by the 2nd order difference frequency wave loads but no CF (crossflow, perpendicular to the environmental load's direction) motion, and the heave motion is excited by the 1st order wave force. In the current condition, obvious motions are observed in the IL and CF directions, and the dominant frequency of the inline motion is about twice of that of the crossflow motion. Vortex-induced forces are supposed as the main reason. The motion amplitudes in the coupled load condition are larger than those in pure wave condition in 6 DOFs, especially for an obvious CF motion, and the mean offset is about the sum of those in the wave and current conditions. Numerical simulation is then conduced with the identified damping coefficients (from model test) and considering the current-induced motion. The wave motions can be correctly revealed in the numerical simulation by a modified panel model (including an additional damping). For the coupled-load condition, by a simplified time-domain VIM prediction method, the IL and CF motions can be revealed but the amplitude is a little overestimated. The experimental findings and numerical results reveal hydrodynamic features of a cylindrical FPSO, which also provide a reference for the design of it.

Mechanical behavior of bolted steel laminated bamboo lumber connections loaded perpendicular to grain

Laminated bamboo lumber (LBL) is increasingly used in structural applications for its superior mechanical properties. Connections always play a significant role in structural application and this paper presents test results on the mechanical behavior of typical bolted connections in LBL that are often subjected to loading in perpendicular to the grain direction. This paper presents a pilot test program to provide useful experimental evidence of the behavior of bolted connections in LBL. 45 specimens in 9 groups were considered in the current study to investigate the effects of LBL thickness, the edge distance of the joint and the failure characteristics when loading was applied perpendicular to the grain. Obtained results showed that the connections predominantly underwent splitting failure perpendicular to grain and was brittle in nature. The edge distance showed pronounced effect on the ultimate capacity of connections compared to the thickness. Typical splitting failure of LBL under the current loading conditions showed mixed mode fractures i.e., combination type I and II fracture modes. Existing analytical techniques for timber were used to predict the observed connection capacities but they all produced significantly conservative results. A semi-empirical formula based on Vander Put model has been proposed to capture the behavior of LBL bolted connections under perpendicular to the grain loading.

Load Sharing and Voltage Restoration Improvement in DC Microgrids with Adaptive Droop Control Strategy

DC microgrid is a connecting network between distributed DC generators. The converter control on DCMG is used to obtain proportional load sharing and voltage restoration of DC bus. The traditional droop control is a common control technique in DC microgrid networks with multiple unit converters. However, this technique has limited performance when the difference of the line resistance is considered. In this paper, the intelligent adaptive droop control is proposed to improve the accuracy of load sharing, while the distributed secondary loop is utilized to minimize the DC bus voltage deviation. The droop resistance is tuned using fuzzy logic controller so that the load power sharing error compensation is obtained, while the DC bus voltage deviation is reduced by the PI controller. The exchange of output currents between converter units through communication lines is considered to obtain the actual load current conditions. The proposed droop control strategy can guarantee the load power sharing balance between three sources with a ratio close to 1:1:1. The results of the comparison analysis between the proposed technique and the traditional droop control are simulated completely using Matlab/Simulink, even under fluctuating loads and the line resistance changes.

Highly Flexible Stencil Printed Alkaline Ag2O-Zn Battery for Wearable Electronics

Flexible power sources such as batteries are essential to realize wearable and conformable electronic devices. The mechanical stability of the electrodes plays an important role in determining the overall flexibility of the battery. Styrene block copolymers-based elastomers have the potential to be used as binder materials in the electrodes for retaining their structural integrity under flexing during regular use. In this work, we demonstrate a stencil-printed flexible primary Ag2O-Zn battery on a nonconductive nylon mesh substrate that uses styrene-butadiene rubber as the anodic binder. A polyacrylic acid-based alkaline polymer gel is used as an electrolyte. The flexible alkaline battery achieved discharge capacities of 2.5 mAh and 1.6 mAh without and with a bend radius of 0.8 cm, respectively, under a constant current load condition of 0.1 mA.

Lanthanum Strontium Manganite Oxygen Electrode Reaction Mechanism in High-Temperature Solid Oxide Water Electrolysis

High-temperature solid oxide water electrolysis cells have become the center of attention of the research community owing to several advantages over traditional water electrolysis technologies. Among others, solid oxide water electrolysis represents highly efficient technology with the possibility to operate in a reversible regime (fuel cell/steam electrolysis). Despite the fast reaction kinetics due to the high operating temperature (600-900 °C). A more detailed understanding of the reaction mechanism is of critical importance to further develop this technology.Lanthanum-strontium-manganite La1-xSrxMnO3-δ is still considered a viable material for an oxygen electrode due to its high electrical conductivity, good chemical stability, and thermomechanical compatibility with various solid electrolytes. However, its negligible ionic conductivity is frequently reported in the literature. Although, La1-xSrxMnO3-δ is utilized as an oxygen electrode for several decades and its properties are reported in the literature, the reaction mechanism occurring on this oxygen electrode is insufficiently described, with multiple discrepancies occurring between the individual authors. The open literature almost exclusively considers the oxygen reduction reaction. Here La1-xSrxMnO3-δ is described exclusively as a pure electron conductor. In the case of the oxygen evolution reaction, only the mechanism reversed to the oxygen reduction is considered, which is clearly an oversimplification.Recent articles tend to connect the defect chemistry of La1-xSrxMnO3-δ and electrochemistry to disapprove the generally accepted description of reaction mechanisms, owing to the rather low agreement between theory and experimental data. In the framework of this study, a series of experiments was conducted, both under current-less as well as current-load conditions using laboratory button cells. Oxygen electrodes based on various mixtures of La0.8Sr0.2MnO3-δ-ZrO2:Y2O3 were tested to prove that La1-xSrxMnO3-δ may become a mixed ionic-electron conductor under specific conditions.The obtained data showed that conditions, such as oxygen partial pressure, temperature and, in particular, the polarization history, could result in a partial reduction of Mn4+ to Mn2+ in the crystal lattice of La1-xSrxMnO3-δ. The change of valence is of a great importance because it creates oxygen vacancies through which oxide ions can be transported. Therefore, under such conditions La1-xSrxMnO3-δ becomes a partial mixed ionic-electron conductor, significantly increasing the number of active reaction sites in the three-dimensional structure of the electrode. The most recent articles reported this behavior; however, only during the oxygen reduction reaction owing to the most suitable conditions for the Mn oxidation state transition. Within the framework of this study, the aim is to expand this concept also to the conditions of the oxygen evolution reaction, which has been completely omitted in the literature. The presented results significantly contribute to the understanding of solid oxide cells and represent a solid base for further modelling of the electrolysis cell, and optimization of its construction as well as operational conditions.This work was supported by the Technology Agency of the Czech Republic under project no. TK04030143.

Analysis of cascaded H-bridge multilevel inverter with current control methods

A detailed model and analysis of a five-level cascaded H-bridge (CHB) multilevel inverter with different current control methods are presented. Simulation models of the CHB inverter with hysteresis current controller, PI current controller using SPWM technique and predictive current controller have been built to demonstrate the CHB inverter system performance with regard to load current THD and reference current tracking. In controlling the load current, the hysteresis and the PI current controllers have the problem of current ripple and phase lag, respectively. The proposed predictive current control method effectively addresses these issues. The current control methods are analyzed for varying reference current and unbalanced load conditions. The simulation results are observed and analyzed using the MATLAB Simulink software to validate the current control methods.

Effect of stress-relief heat treatments on the microstructure and mechanical response of additively manufactured IN625 thin-walled elements

Metallic structures fabricated with laser powder-bed fusion (LPBF) often have elemental segregations that are far from equilibrium and high levels of residual stresses due to the localized melting and rapid solidification that occur during printing. These unique characteristics result in mechanical property debits that make it difficult to employ such printed parts in critical applications. However, post-processing heat treatments can minimize the negative effects of residual stresses and reduce segregation. In this study, we measure the effect of two stress-relief heat treatments, 870°C for 1 h (industry-recommended) and 800°C for 1 h (potential alternative), on the microstructure and room temperature, monotonic quasi-static mechanical response of LPBF-processed thin-walled Inconel 625 T-elements. Electron backscatter diffraction analysis revealed an overall columnar microstructure with a strong <001> texture that is closely aligned with the build direction. The well-developed dislocation cell walls in both stress-relieved cases were found to be decorated with two types of blocky precipitates, namely, (Nb, N)-rich MX and (Nb, Mo, Si, N)-rich -M6X with scant evidence of the deleterious δ phase. The slightly larger size and higher volume fraction of precipitates in the 870°C case was found to have a small effect on the mechanical response of the T-elements under the current loading conditions and the difference in mechanical response of the two heat treatments was only significant at the very later stages of deformation. These findings make 800°C for 1 h a viable stress-relief alternative for our IN625 samples under the loading conditions studied here.

High-Speed Searching of Optimum Switching Pattern for Digital Active Gate Drive to Adapt to Various Load Conditions

Digital active gate driving has been shown to effectively manage the switching performance for power devices with the adjustable driving waveforms. However, most of the studies are based on a dedicated test circuit rather than a practical inverter with the sinusoidal output current. In fact, it is the dependence on the load current that makes the design of the gate driving profiles a critical issue. To investigate the digital active gate driver in an inverter application, this article has applied optimal patterns adapting to time-varying output load current. Prior to the search of optimal patterns, the proper design of time slot is discussed with three different time resolutions. With the proper resolution determined for patterns, multiple optimizations are carried out for different current conditions. In this way, the search for optimal patterns can be completed in an efficient time. Next, a lookup table of optimal switching pattern in correspondence with each certain load current condition was built in advance. According to the output load current, the optimal pattern is selected based on the lookup table. Compared to conventional constant driving waveform, the power loss has been reduced by 7% with full optimal lookup table applied.

Twin Inverter-Fed Induction Machines Artificial Loading Without Mechanical Coupling

This article presents an artificial loading method for induction machines using industrial static frequency converters (VFCs), low cost programmable logic controllers (PLCs) for command and control and standardized communication protocols. Different approaches of artificial loading method are presented in this paper. Induction machine full load testing is difficult, especially at high power and almost impossible for vertical axis machines. Mechanized IM start/stop procedure and closed-loop loading method, here presented, reduce overall testing time. The overall manpower cost is reduced thanks to the lack of IMs mechanical coupling. Moreover, thermal test at rated IM current and power losses equivalation are presented in this paper. Bidirectional VFC utilization for a single motor can't always be a solution for artificial loading because of high variations of grid power (voltage). Two identical IMs without mechanical coupling driven by two identical dc bus interconnected VFCs artificial loading method is presented in this paper. The power circulation between the machines is performed via the common dc link. This opens the possibility to test machines with rated power larger than the lab power source rating. The rated current artificial loading conditions are achieved without mechanical coupling, without VFC oversizing and using standard equipment.

A Novel Approach to Predict Transformer Temperature Rise under Harmonic Load Current Conditions

In South Africa, distribution transformers (DTs) facilitating solar photovoltaic applications represent the highest percentage of total ownership cost investment for independent power producers (IPPs). One of the most indispensable variables that regulate DTs’ operational life span is the hotspot temperature. The prevailing analytical approaches designated to guesstimate the transformer thermal necessities were fathered in accordance with the conservative foundation that an electrical transformer is prone to uniform mean daily and monthly peak loads. In order to appropriately puzzle out the transformer thermal necessities, the formation of a more detailed thermal model that operates with real-time contorted cyclic loading, ambient air temperature, and the intrinsic characteristics of the transformer in-service losses is required. In the current work, various regression models are proposed for the modification of the top-oil formula and the hotspot temperature formula in the IEEE loading guide standard to replicate the real harmonic load currents (HLCs) and the fluctuating ambient air temperature (AT) on an hourly and daily basis. The proposed thermal model is examined in various transformers case studies, in which the computed outcomes produce an error margin of no more than 3% throughout all test cases when compared to the measured data.

Stray Load Loss Valuation in Electrical Transformers: A Review

The electricity production opus in South Africa has transformed over the last few years from predominantly coal power generation to a blend of renewable energy generation. The necessity emerges to ascertain whether electrical transformer design philosophies in local manufacturers are contemporary in reference to customer specifications, under increasing penetration of harmonics and distortion as a result of increasing deployment of decentralized power systems. Accurate computation of transformer stray load loss is imperative in localizing the hotspot regions and design of adequate insulation system and consequently cooling system. This loss must also be met by manufacturers based on the customer specifications to avoid penalties. The review of current scientific works affirms the ongoing interest in utilizing the advancement of computational power for painstaking evaluation and management of stray load loss in electric transformers. This article confers overview research, evolution and application of diverse computer-based tools for analyzing the stray load loss based on over 60 published scientific works. Mathematical formulations that can be practically employed by transformer designers during the design phase under normal and harmonic load current conditions are discussed.

A Synchronous Auxiliary Resonant Commutated Pole Soft-Switching Inverter With Improved Load Adaptability

To realize a soft-switching inverter with small volume and high efficiency, a synchronous auxiliary resonant commutated pole (SARCP) soft-switching inverter with improved load adaptability is proposed, which only contains two auxiliary inductors. In one switching cycle, all commutation processes can be synchronously assisted by an auxiliary inductor. Soft switching is achievable for all switches of the SARCP inverter. Compared with the auxiliary resonant commutated pole (ARCP) inverter, the SARCP inverter has improved load adaptability, especially in the light load current condition, which is beneficial to reduce the total power loss and the dc-link capacitance. The equivalent circuits of the SARCP inverter are given under different operation modes. The operation principle, soft-switching implementation conditions, parameter optimization design methods, and the characteristics of the SARCP inverter are analyzed. Finally, simulation and experimental results verify the effectiveness of the SARCP inverter.

A 15-V Output Highly-Efficient Charge Pump IC for Biomedical Applications

This work proposes a highly efficient charge-pump IC for biomedical applications. The charge pump IC consists of a four-stage complementary charge transfer switch core which is used to generate a high output voltage of 15 V from an input of 3.2 V. The circuit also utilizes the input voltage modulation technique to regulate the output voltage while supporting a maximum load current up to 5 mA. The implemented circuit achieves a measured power efficiency of 88.3% and output voltage ripple of 1% at maximum current load condition. The overall circuit is implemented using 180 nm CMOS technology and occupies an area of 0.98 mm².

Sensor-Reduction Control for Dual Active Bridge Converter Under Dual-Phase-Shift Modulation

This paper proposes a sensor-reduction control in order to control the output voltage of the dual active bridge (DAB) converter under dual-phase-shift (DPS) modulation. The deadbeat control-based Lagrange multiplier method (LMM) is adopted to achieve current stress optimization (CSO). A first-order extended state observer (ESO) is established to observe the load current based on the basis of the dynamic equation of the output capacitor. Compared to the existing ESO for the DAB converter, the proposed observer is able to reject disturbances even when output capacitor mismatches occur, resulting in better observer performance. Besides, the proposed method exhibits good steady-state performance without using any compensating controller. Consequently, the proposed method enables current sensorless control and significantly decreases the number of control parameters, resulting in increased simplicity and cost-saving. The simulation and experimental results obtained with a 300 W prototype demonstrate that the proposed method outperforms the existing methods under changing load current and input voltage conditions.

A Robustness Temperature Inversion Method for Cable Straight Joints Based on Improved Sparrow Search Algorithm Optimized BPNN

The temperature of cable conductor is of great significance to improve the current carrying capacity, asset utilization and safe operation of cable lines. Aiming at the problems of slow calculation speed, low accuracy and weak anti-interference ability of the current temperature calculation methods, this paper proposes an inversion method based on improved sparrow search algorithm (ISSA) optimized back propagation neural network (BPNN). Tent mapping was used to increase the initial population diversity of sparrow. Modified sparrow optimization formula to improve convergence speed. Chaotic perturbation is applied to the optimal individual to improve the global and local search ability of SSA. The multi-physics simulation model of 110kv straight connector was established, and the temperature distribution data under three different working conditions were obtained. According to the simulation data and CEC2017 standard test experiments, the optimization ability of the improved model is compared with particle swarm optimization (PSO), whale optimization algorithm (WOA), SSA and MSWOA. To verify the generalization performance and migration ability of the proposed method, the thermal cycle test and inversion calculation of the 10kV cable straight-through joint were carried out. The results show that ISSA-BPNN has high accuracy, fast convergence speed, good robustness, and is less affected by cable joint type, load current and cable environment conditions. It has good engineering practicability.

Pure mode II dynamic fracture characteristics and failure mechanism of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass

Due to the amorphous nature of bulk metallic glasses (BMGs), the fracture mechanism of such materials is quite different from that of their crystalline counterparts. By far, how to obtain mode II dynamic fracture properties and reveal failure mechanism of BMGs remains an important issue to resolve. In this work, a novel experimental technique is adopted to determine pure mode II dynamic fracture toughness (DFT) of Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG under high loading rates. The variations of fracture toughness, failure modes, and micromechanism of the material are investigated under different loading rates. The results show that under the current loading conditions, the loading rate is precisely controlled between 2.03 × 106 MPa ⋅ m1/2/s and 7.17 × 106 MPa ⋅ m1/2/s. The fracture initiation time tf decreases with the increase of loading rates, but the mode II DFT is insensitive to the change of loading rates. According to different failure morphologies and fracture modes, the fracture surface exhibits three characteristic regions, where the corresponding micromechanism is analyzed in detail. From zone A to zone B, there exists an evolution of the fracture modes from brittle to ductile, and then to thermal-softening controlled fracture type. In zone C, due to the influence of the stress state at the crack tip, the component of mode I fracture set in, and the fracture path shows deflections from the main shear plane.

Static and modal analysis of a crankshaft reciprocating driver for reciprocating-airfoil (RA) driven VTOL aircraft

New modes of transportation systems are under intensive development because traditional systems fail to become mass transportation means due to their technological limitations. To meet the growing demand for VTOL vehicles, a novel VTOL technology, reciprocating-airfoil (RA) driven VTOL aircraft, had been introduced. The objective of this study is to model a crankshaft to structurally determine the feasibility of using a crankshaft structure as the reciprocating driver of this novel VTOL technology. Unlike the conventional crankshaft IC engines or compressors, the crankshaft system herein is a reciprocating driver to generate long-stroke reciprocating motion of the wings for VTOL vehicle operations. The unique challenges of this study are the exceedingly long crank arms and stringent weight minimizations that require the use of high-strength carbon fiber materials. The crankshaft model is geometrically designed by using SOLIDWORKS design software, and the commercial Ansys Mechanical Solver has been selected for the FEM structural analysis. Based on the nonlinear static analysis results, the maximum stress is developed at the junctions between the main shaft and the middle crank web. However, all of the determined deformation, stress, and strain under the current loading conditions as well as weight requirement is acceptable. Also, according to the modal analysis result, the possible resonance chance is low. In conclusion, this study provides a pathway for the final development of the novel reciprocating airfoil VTOL technology.