Quasi-static Simulations Research Articles

Microscale Schottky superlubric generator with high direct-current density and ultralong life

Miniaturized or microscale generators that can effectively convert weak and random mechanical energy into electricity have significant potential to provide solutions for the power supply problem of distributed devices. However, owing to the common occurrence of friction and wear, all such generators developed so far have failed to simultaneously achieve sufficiently high current density and sufficiently long lifetime, which are crucial for real-world applications. To address this issue, we invent a microscale Schottky superlubric generator (S-SLG), such that the sliding contact between microsized graphite flakes and n-type silicon is in a structural superlubric state (an ultra-low friction and wearless state). The S-SLG not only generates high current (~210 Am−2) and power (~7 Wm−2) densities, but also achieves a long lifetime of at least 5,000 cycles, while maintaining stable high electrical current density (~119 Am−2). No current decay and wear are observed during the experiment, indicating that the actual persistence of the S-SLG is enduring or virtually unlimited. By excluding the mechanism of friction-induced excitation in the S-SLG, we further demonstrate an electronic drift process during relative sliding using a quasi-static semiconductor finite element simulation. Our work may guide and accelerate the future use of S-SLGs in real-world applications.

The role of annealing in determining the yielding behavior of glasses under cyclic shear deformation

Yielding behavior in amorphous solids has been investigated in computer simulations using uniform and cyclic shear deformation. Recent results characterize yielding as a discontinuous transition, with the degree of annealing of glasses being a significant parameter. Under uniform shear, discontinuous changes in stresses at yielding occur in the high annealing regime, separated from the poor annealing regime in which yielding is gradual. In cyclic shear simulations, relatively poorly annealed glasses become progressively better annealed as the yielding point is approached, with a relatively modest but clear discontinuous change at yielding. To understand better the role of annealing on yielding characteristics, we perform athermal quasistatic cyclic shear simulations of glasses prepared with a wide range of annealing in two qualitatively different systems-a model of silica (a network glass) and an atomic binary mixture glass. Two strikingly different regimes of behavior emerge. Energies of poorly annealed samples evolve toward a unique threshold energy as the strain amplitude increases, before yielding takes place. Well-annealed samples, in contrast, show no significant energy change with strain amplitude until they yield, accompanied by discontinuous energy changes that increase with the degree of annealing. Significantly, the threshold energy for both systems corresponds to dynamical cross-over temperatures associated with changes in the character of the energy landscape sampled by glass-forming liquids.

Effect of metal and polymer mating gears on the bending fatigue performance of asymmetric polymer gears

The material of the mating gear influences the fatigue life of polymer gears. The bending fatigue characteristics of polyamide 66 asymmetric gears (34°/20° and 20°/34°) corresponding to steel–polymer and polymer–polymer material combinations were investigated. The performance of symmetric gear pairs (20°/20°) was determined to serve as a comparison. Quasi-static numerical simulations were performed in a finite element analysis tool to predict root bending stress, load sharing ratio, and tooth deflection. The bending fatigue strength of steel–polymer and polymer–polymer pairs of each test configuration was determined using bending fatigue tests. The load sharing ratio and root bending stress of polymer–polymer pairs decreased substantially compared to steel–polymer pairs. The extent of deflection-induced load sharing was greater in polymer–polymer pairs. The bending fatigue life of polymer–polymer pairs was lower than that of steel–polymer pairs owing to the higher operating temperature. In polymer–polymer pairs, polymer driving and driven gears increased the heat generated and diminished the heat dissipation to the environment. In steel–polymer and polymer–polymer pairs, the configuration with the highest bending fatigue strength was 34°/20° and 20°/34°, respectively. This divergence was caused by the increase in temperature difference between the two configurations for polymer–polymer pairs. Analysis of hysteresis loops indicated that the loop area was higher for polymer–polymer pairs, signifying the increased amount of dissipated energy. No noticeable variation was observed between the failure modes of steel–polymer and polymer–polymer pairs despite the significant difference in the operating temperatures. The bending stress and operating temperature were the dominant factors affecting the performance of steel–polymer and polymer–polymer gear pairs, respectively.

Control of an Electric Vehicle Hybrid Energy Storage System

Abstract In electric vehicles battery life can be prolonged by using hybrid energy storage systems (HESS ), which combine high energy density batteries with supercapacitors, characterized by high power density. This paper deals with the control of electronic power converters from an active parallel HESS. The load of the HESS is the electrical motor drive of an electric vehicle. The interfaces between the DC-link and the power sources are four-phase bidirectional DC-DC converters driven in current control mode, based on the current references supplied by an active parallel HESS power distribution algorithm. We present a rule-based fuzzy energy management algorithm for a HESS powered electric vehicle and its simulation in MATLAB/Simulink® environment using the Quasi-Static Simulation (QSS ) and Fuzzy Logic toolboxes. Also, simulation results in driving and regenerative braking operation modes of the electric vehicle are presented.

Effect of mass distribution on curving performance for a loaded wagon

The location of wagon gravity center for a loaded wagon is underestimated in a vehicle–track coupled system. The asymmetric wheel load distribution due to loading offset significantly affects the wheel-rail contact state and seriously deteriorates the curving performance in conjunction with the height of gravity center and cant deficiency. Optimizing the location of gravity center and cruising velocity, therefore, is of interest to prevent the derailment and promote the transport capacity of railway wagons. This study aims to reveal the three-dimensional influencing mechanism of mass distribution on vehicle curving performance under different velocities. The wheel unloading ratio is regarded as the evaluation index. A simplified quasi-static model is established considering essential assumptions to highlight the influence of lateral and vertical offset on curving performance. For a more accurate description, the MBS models with various locations of wagon gravity center are built and then negotiate curves in different simulation cases. The simulation results reveal that the distribution of wheel unloading ratio determined by loading offset is like contour lines of ‘basin’. Based on the conclusions of quasi-static analysis and dynamics simulations, the regression equation is proposed and the fitting parameters are calculated for each simulation case. This paper demonstrates the necessity of optimizing the location of wagon gravity center according to the running condition and offers a novel strategy to load and transport the cargo by railway wagons.

Enhancing PV Hosting Capacity Using Smart Inverters and Time of Use Tariffs

Optimizing the Photovoltaic (PV) hosting capacity (HC) considering the irradiance's variability properly and the load during the day represents a critical matter. Typically, the high PV HC results in overvoltage and high voltage fluctuations at the point of common coupling (PCC) with the utility. In this paper, a new algorithm is proposed for enhancing PV HC by considering the smart inverter functions to overcome key PCC issues. The Volt-Var and dynamic reactive current functions of the smart inverter are suggested to increase the PV HC. Furthermore, the time of use tariff is utilized for mitigating the duck curve issue at the utility by reducing the peak to valley difference of the substation net load curve. Quasi-static time-series simulations are performed using the OpenDSS program to prove the effectiveness of the proposed algorithm. The proposed algorithm is validated by extensive numerical analysis on the standard IEEE 123 node test feeder. Deduced outcomes are very encouraging in mitigating the overvoltage, reducing the energy losses, limiting the considerable number of on-load tap changes, and alleviating the high voltage fluctuations.

Evaluating the Curtailment Risk of Non-Firm Utility-Scale Solar Photovoltaic Plants under a Novel Last-In First-Out Principle of Access Interconnection Agreement

With the increasing share of distributed energy resources on the electric grid, utility companies are facing significant decisions about infrastructure upgrades. An alternative to extensive and capital-intensive upgrades is to offer non-firm interconnection opportunities to distributed generators, via a coordinated operation of utility scale resources. This paper introduces a novel flexible interconnection option based on the last-in, first-out principles of access aimed at minimizing the unnecessary non-firm generation energy curtailment by balancing access rights and contribution to thermal overloads. Although we focus on solar photovoltaic (PV) plants in this work, the introduced flexible interconnection option applies to any distributed generation technology. The curtailment risk of individual non-firm PV units is evaluated across a range of PV penetration levels in a yearlong quasi-static time-series simulation on a real-world feeder. The results show the importance of the size of the curtailment zone in the curtailment risk distribution among flexible generation units as well as that of the “access right” defined by the order in which PV units connect to the grid. Case study results reveal that, with a proper selection of curtailment radius, utilities can reduce the total curtailment of flexible PV resources by up to more than 45%. Findings show that non-firm PV generators can effectively avoid all thermal limit-related upgrade costs.

An exploratory investigation of patellofemoral joint loadings during directional lunges in badminton

Anterior knee pain is a commonly documented musculoskeletal disorder among badminton players. However, current biomechanical studies of badminton lunges mainly report kinetic profiles in the lower extremity with few investigations of in-vivo loadings. The objective of this study was to evaluate tissue loadings in the patellofemoral joint via musculoskeletal modelling and Finite Element simulation. The collected marker trajectories, ground reaction force and muscle activation data were used for musculoskeletal modelling to compute knee joint angles and quadricep muscle forces. These parameters were then set as boundary conditions and loads for a quasistatic simulation using the Abaqus Explicit solver. Simulations revealed that the left-forward (LF) and backward lunges showed greater contact pressure (14.98–29.61%) and von Mises stress (14.17–32.02%) than the right-forward and backward lunges; while, loadings in the left-backward lunge were greater than the left-forward lunge by 13–14%. Specifically, the stress in the chondral layer was greater than the contact interface, particularly in the patellar cartilage. These findings suggest that right-side dominant badminton players load higher in the right patellofemoral joint during left-side (backhand) lunges. Knowledge of these tissue loadings may provide implications for the training of badminton footwork, such as musculature development, to reduce cartilage loading accumulation, and prevent anterior knee pain.

Studying the structures of modal filter with circular reflection symmetry

The paper considers the protection of radio-electronic equipment (REE) against ultrashort pulses (USPs) by using the symmetry to decompose a USP into a doubled number of pulses with half as small amplitude. For the first time, we performed a quasistatic simulation of the time response of a 4-conductor and 8-conductor MFs with circular reflection symmetry. It is shown that these MFs are able to decompose the USP into a sequence of pulses of smaller amplitude. However, in order to obtain the required attenuation level, additional optimization by several criteria is required.

Designing a low-mass, high-current modal filter for the spacecraft power bus

The paper presents the results of a quasi-static simulation of a modal filter with a reduced cross-section of conductors that are conducting a significant current. Time characteristics in differential and common modes are considered. The dependence of the attenuation coefficient on the thickness of the conductors is shown.

Quasi-static analysis of a two-conductor modal filter with a thin passive conductor

The paper presents the results of the quasi-static analysis of a two-conductor modal filter with a thin passive conductor. The geometrical parameters of the structure under investigation were optimized using a genetic algorithm. The authors performed the quasi-static simulation in the time domain with and without losses. It revealed that with a significant reduction in the thickness of the passive conductor it is possible to preserve or improve the electromechanical properties of the modal filter. The authors showed that in the proposed configuration the difference of per-unit-length delays increased from 0.43 to 0.93 ns, and the maximum output voltage decreased from 501 to 498 mV.

Low-Frequency Elastic Properties of a Polymineralic Carbonate: Laboratory Measurement and Digital Rock Physics

We demonstrate that the static elastic properties of a carbonate sample, comprised of dolomite and calcite, could be accurately predicted by Digital Rock Physics (DRP), a non-invasive testing method for simulating laboratory measurements. We present a state-of-the-art algorithm that uses X-ray Computed Tomography (CT) imagery to compute the elastic properties of a lacustrine rudstone sample. The high-resolution CT-images provide a digital sample that is used for analyzing microstructures and performing quasi-static compression numerical simulations. Here, we present the modified Segmentation-Less method withOut Targets method: a combination of segmentation-based and segmentation-less DRP. This new method assigns the spatial distribution of elastic properties of the sample based on homogenization theory and overcomes the monomineralic limitation of the previous work, allowing the algorithm to be used on polymineralic rocks. The method starts by partitioning CT-images of the sample into smaller sub-images, each of which contains only two phases: a mineral (calcite or dolomite) and air. Then, each sub-image is converted into elastic property arrays. Finally, the elastic property arrays from the sub-images are combined and fed into a finite element algorithm to compute the effective elastic properties of the sample. We compared the numerical results to the laboratory measurements of low-frequency elastic properties. We find that the Young’s moduli of both the dry and the fully saturated sample fall within 10% of the laboratory measurements. Our analysis also shows that segmentation-based DRP should be used cautiously to compute elastic properties of carbonate rocks similar to our sample.

A basic design for automotive crash boxes using an efficient corrugated conical tube

Frontal vehicle structure is of high importance through crash energy managements and crash boxes are the fundamental structural component for vehicle safety as well as after sales issues. Similar to many other vehicle components, the detail design of crash box is usually part of manufacture knowhow. However, some guide lines are always available. In this article a general procedure is introduced for designing of crash box with the aid of novel thin walled structures and according to conventional crash scenarios. The problem is followed through some basic steps. Firstly, the crash box idea is selected through a wide range of previous investigated elements and is packaged in a real bench vehicle. Then thanks to the protection provided by the new crash box on the other more expensive components (e.g. headlamp, cooling pack, etc.), the effectiveness of this element are acknowledged through the low speed offset crash. Further on the robustness of new proposed crash box is approved by high speed crash simulations. The quasi-static simulations implemented during the analyses are carried out by finite element explicit code (Abaqus) and the FE modeling and dynamic simulation through the next steps are also performed in ANSA and PAM CRASH respectively. Finally in addition to the general crash box design proposed procedure, the achieved results demonstrated that the corrugated conical thin walled tubes deforms in regular and rather stable shape under both axial and oblique loadings. They also produced a reasonable reaction force versus deformations which leads to stiff and crashworthy energy absorber in comparison to traditional rectangular and even some special models like as origami shapes, and so they could be a valuable selection for crash box implementations in passenger cars.

Strong and Tough Bioinspired Additive-Manufactured Dual-Phase Mechanical Metamaterial Composites

Nature's materials are generally hybrid composites with superior mechanical properties achieved through delicate architectural designs. Inspired by the precipitation hardening mechanisms observed in biological materials as well as engineering alloys, we develop here dual-phase mechanical metamaterial composites by employing architected lattice materials as the constituent matrix and reinforcement phases. The composite metamaterials made from austenitic stainless steel are simply fabricated using selected laser melting based additive manufacturing. Using quasi-static compression tests and simulation studies, we find that strength and toughness can be simultaneously enhanced with the addition of reinforcement phase grains. Effects of reinforcement phase patterning and connectivity are examined. By fully utilizing the energy dissipation from phase-boundary slip, an optimized dual-phase metamaterial is designed with the maximum slip area, where every truss unit in the matrix phase is completely surrounded by reinforcement phase lattices; this material exhibits a specific energy absorption capability that is ~2.5 times that of the constituent matrix phase lattices. The design rationale for dissipative dual-phase metamaterials is analyzed and summarized with a focus on phase pattering. The present digital multi-phase mechanical metamaterials can emulate almost any of nature's architectures and toughening mechanisms, offering a novel pathway to manipulate mechanical properties through arbitrary phase-material selection and patterning. We believe that this could markedly expand the design space for the development of future materials.

An axisymmetric ordinary state-based peridynamic model for thermal cracking of linear elastic solids

This paper proposes an axisymmetric ordinary state-based peridynamic model considering the thermal expansion effect for temperature-induced cracking of linear elastic solids. Both the force state and bond failure criterion of the model are built in axisymmetric domain. The direct calculation for peridynamic bond energy density of the axisymmetric model considering thermal terms is given. The adaptive dynamic relaxation method is adopted for the quasi-static peridynamic simulations. Validity and reliability of the proposed axisymmetric model are illustrated by numerical examples of cold-induced fracture in a pipe with an inner crack. It is shown that the displacement predicted by the proposed peridynamic model is in good agreement with the corresponding finite element method. The critical bond energy density criterion for thermal cracking is verified via comparisons with the critical fracture temperature loads computed from the virtual crack closure technique and released energy based on Griffith’s theory. The sensitivity of the present model on the peridynamic discretization is investigated and discussed in both the continuous deformation and cracking cases. The performance of the peridynamic model is further demonstrated for cold-induced fracture of double-layered pipes with inner cracks, and the cracking behaviors influenced by the interfacial toughness and number of inner cracks are captured, respectively. The present model is capable of solving axisymmetric thermal cracking problems of linear elastic solids effectively, and it can be applied in more advanced axisymmetric structures which involve more complicated cracking issues.

Effect of gravity on the orientation and detachment of cubic particles adsorbed at soap film or liquid interfaces.

We investigate the interaction that occurs between a light solid cube falling under gravity and a horizontal soap film that is pinned to a circular ring. We observe in both experiments and quasi-static simulations that the final orientation of a cube that becomes entrapped by a soap film is strongly dependent on the Bond number. A cube is rotated by a soap film into one of three main orientations in a process that is driven by energy minimisation. The likelihood of observing each of these final orientations is shown to depend on the Bond number, and the most energetically favourable orientation depends on the terminal height reached by the cube. We also find a critical value for the Bond number, above which a cube is no longer supported by a soap film and detachment occurs, to be less than one.

Sensitivity analysis of factors affecting for the engraving of rifle projectile

In order to study the primary and secondary relationship between the factors affecting the engraving resistance of one small-caliber rifle projectile, quasi-static push tests were carried out for jacket material by H90 copper and copper clad steel projectile in three kinds of gun barrels with different structures and the corresponding changes of the engraving resistance were obtained and analyzed. At the same time, numerical simulations were carried out for constant high-speed extrusion. Quasi-static test and dynamic simulation results were analyzed, the order of the factors affecting the peak of engraving resistance under quasi-static is the yield strength of jacket>free stroke> engraving length>rifle number> lead, and the factors affecting the peak of extrusion force under high-speed is engraving velocity>yield strength of jacket>free stroke> engraving length >rifle number>lead. It is also found that the relative steady engraving resistance value is close 60% of its peak value under quasi-static, while the same value under high-speed is between 1/8 and 1/6 of the peak value, the results of force peak are basically quite.

The Influence of Axial Compression Ratio on the Seismic Behavior of RC Frame Column

In order to analyze the quantitative influence of the axial compression ratio on the seismic performance of reinforced concrete (RC) frame column, this paper carried out the numerical analysis of the quasi-static simulation of a RC frame column and analyzed its hysteresis performance, bearing capacity, stiffness degradation, energy consumption capacity and ductility capacity under different axial compression ratios, based on OpenSees finite element software, considering the buckling and fatigue damage model. The results show that the smaller the axial compression ratio, the fuller the hysteresis curve and the slower the stiffness degradation of the column. The ultimate bearing capacity of the column increases by 24.6% when the axial compression ratio increases from 0.3 to 0.8, but bearing capacity decreasing and stiffness degradation is faster and faster. When the deformation does not exceed the ultimate displacement, the equivalent viscous damping at each displacement level of high axial compression ratio column is greater than that of the low axial compression ratio, but the total hysteretic energy decreases about 64.2% at maximum amplitude. The ultimate displacement gradually decreases with the increase in the axial compression ratio, and the ductility factor decreases about 55.9% at maximum amplitude. The results can be referenced by the seismic design and analysis of RC frame.

Methodology for the Techno-Economic Assessment of Medium-Voltage Photovoltaic Prosumers Under Net-Metering Policy

Net-metering has been introduced as an alternative to the feed-in tariff scheme to encourage consumers to act as prosumers by installing photovoltaics. Originally, net-metering referred mainly to household photovoltaic systems, however, larger prosumers connected to medium-voltage networks are also considered. Scope of this paper is to present a techno-economic assessment methodology to evaluate the viability of net-metering policy in medium-voltage prosumers. Unlike most relevant methods, the proposed methodology combines techno-economic analysis with a quasi-static simulation model incorporating the real-world operational properties of the distribution network, where the medium-voltage prosumers are connected. The analysis focuses on nine university campuses operating under net-metering policy. The impact of several important parameters on the viability of the investment as well as on the optimal size of the system is investigated; among them special emphasis is given on the applicability of the decentralized voltage regulation techniques applied to the prosumer’s photovoltaic system.

In-situ monitoring for liquid metal jetting using a millimeter-wave impedance diagnostic

This article presents a millimeter-wave diagnostic for the in-situ monitoring of liquid metal jetting additive manufacturing systems. The diagnostic leverages a T-junction waveguide device to monitor impedance changes due to jetted metal droplets in real time. An analytical formulation for the time-domain T-junction operation is presented and supported with a quasi-static full-wave electromagnetic simulation model. The approach is evaluated experimentally with metallic spheres of known diameters ranging from 0.79 to 3.18 mm. It is then demonstrated in a custom drop-on-demand liquid metal jetting system where effective droplet diameters ranging from 0.8 to 1.6 mm are detected. Experimental results demonstrate that this approach can provide information about droplet size, timing, and motion by monitoring a single parameter, the reflection coefficient amplitude at the input port. These results show the promise of the impedance diagnostic as a reliable in-situ characterization method for metal droplets in an advanced manufacturing system.