Instantaneous Load Research Articles

A Novel VSG Control Strategy for UPS Voltage Source Inverter with Impulsive Load

This paper proposes a novel control strategy to alleviate the impulsive current for Uninterruptible Power Supply (UPS), which is designed based on the theory of virtual synchronous generator (VSG) and dynamic switching method. The power quality of UPS will become distortion when the instantaneous impulsive load is imposed on UPS. Especially, the output current of UPS will increase quickly in short time. In order to maintain the uninterrupted output voltage and reduce the distortion of output voltage of UPS under the action of instantaneous impulse load, Dynamic switching method is proposed to resist impulse load with large scale impulse current, Meanwhile, the VSG control strategy is adopted to deal with the slow power switching and provide virtual inertia for the system, so that the output voltage of UPS can remain uninterrupted and stable. Finally, simulation and experimental results show that this method can effectively suppress the impulse current, reduce the output voltage distortion of UPS inverter, and ensure the good performance of On-line UPS under impulse load.

Analysis of wind-induced responses of landing assembled Chinese solar greenhouses

The wind-induced responses of a landing assembled Chinese solar greenhouse (CSG) were investigated by considering fluctuating wind speeds. Fluctuating wind speeds were simulated using the harmony superposition method. The dynamic properties of the CSG were extracted using modal analysis. The displacement and bending stress of the CSG under mean and instantaneous wind loads were compared. The results showed that both the displacement and bending stress under the south wind (0° direction) were lower than those under the north wind (180° direction). When the wind direction was 0°, the maximum displacement and bending stress under instantaneous wind loads were 1.926 and 1.673 times those under mean wind loads, respectively. When the wind direction was 180°, the maximum displacement and bending stress under instantaneous wind loads were 2.054 and 2.003 times those under mean wind loads, respectively. To estimate the nodal displacement wind vibration coefficients and quantify the amplification effects of instantaneous wind loads, the effects of the structural damping ratios, sectional dimensions, and simulated wind speed samples on the wind-induced responses of the CSG were investigated. Finally, a global nodal displacement wind vibration coefficient of 2.0 is recommended for the case study. These results can provide a reference for the wind-resistance design of landing assembled CSG. • Fluctuating wind speeds were simulated using the harmony superposition method. • The wind-induced responses of a landing assembled CSG were investigated. • The dynamic properties of the CSG were extracted using modal analysis. • The nodal displacement wind vibration coefficients were obtained.

Lubrication Properties of Textured CSS-42L Bearing Steel Filled With Sn-Ag-Cu-Ti3C2 Under Harsh Environmental Conditions

Abstract To study tribological enhancements of MXene-Ti3C2 under harsh environmental conditions (acidification, emulsification, and high-temperature oxidation), the textured CSS-42L bearing steel surfaces filled with Sn-Ag-Cu-Ti3C2 (TSs-SACT) were prepared. Under harsh conditions, lubrication properties of TSs-SACT were investigated. The results showed that the vibrations of frictional forces and loads of TSs-SACT with the best antifriction performance were suppressed. The curves of instantaneous frictional forces of TSs-SACT were the smoothest, and the amplitudes of instantaneous loads were reduced. Sn-Ag-Cu-Ti3C2 with good adsorption could inhibit the oil film ruptures, which improves the lubrication. TSs-SACT induced the tribochemical reactions to produce the intermetallic compounds and oxides with good tribological properties, resulting in the uniform profiles with excellent antifriction performance and wear resistance.

Experimental investigation and micromechanics-based damage modeling of the stress relaxation mechanical properties in gray sandstone

The geomechanical behaviors of the gray sandstones under dry and fully saturated conditions are investigated by both of experimental and numerical studies in this paper. Conventional triaxial compression tests and single-stage stress relaxation tests are performed on cylindrical specimens under these two different states. The experimental results show that both peak strength and elastic modulus are reduced due to the presentence of the pore water which is contributed the weakening. While the typical incomplete attenuation characteristics of the two states are only having slight difference, the final stress relaxation extent under the statured condition is larger than the dry condition when the strain ratio is the same. Based on the pioneering work, a new micromechanical damage–friction coupling constitutive model with containing fewer parameters and each being physically meaningful for the stress relaxation is proposed here. Its chief novelty lies in considering both the instantaneous plastic internal variables and relaxation load to build the relationship between model’s parameter and experimental data. The single-stage relaxation tests of the sandstones are well-benchmarked with this model, which indicates that the proposed new model can capture the incomplete attenuation features of stress relaxation behavior of gray sandstones.

Biomechanical Comparison of Six Different Root-Analog Implants and the Conventional Morse Taper Implant by Finite Element Analysis.

Taper implants differ greatly from anatomical teeth in shape. In this study, seven three-dimensional finite element models were established, including a conventional taper implant and six root-analog implants with different root numbers and shapes. Vertical, horizontal, and oblique instantaneous loads of 100 N were applied to the models to obtain stress distribution in the implant, mucosa, cortical bone, and cancellous bone. ANSYS was used to perform the analysis under hypothetical experimental conditions. We find the stresses in all the implants and surrounding tissues varied by loading direction, the sequence of stress magnitude is vertical load, oblique load, and then horizontal load. The maximum stress values in root-analog implants were significantly less than in the taper implant. Moreover, stress distribution in the former was equalized contrary to the concentrated stress in the latter. Root-analog implants with different root geometry also revealed a pattern: stresses in multiple-root implant models were lower than those in single-root implants under the same load. The implant with a long and rounded root distributed the stress more uniformly, and it was mainly concentrated on the implant itself and cancellous bone. However, the opposite effect was observed in the short implant on mucosa and cortical bone. The root geometry of anatomical teeth can modify their functions. A uniform-shaped implant can hardly meet their functional requirements. Thus, the root-analog implant could be a possible solution.

Multimodal Fibrous Static and Dynamic Tactile Sensor.

A highly versatile, low-cost, and robust tactile sensor capable of acquiring load measurements under static and dynamic modes employing a poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] micronanofiber element is presented. The sensor is comprised of three essential layers, a fibrous core P(VDF-TrFE) layer and two Ni/Cu conductive fabric electrode layers, with a total thickness of less than 300 μm. Using an in situ electrospinning process, the core fibers are deposited directly to a soft poly(dimethylsiloxane) (PDMS) fingertip. The core layer conforms to the surface and requires no additional processing, exhibiting the capability of the in situ electrospinning fabrication method to alleviate poor surface contacts and resolve issues associated with adhesion. The fabricated tactile sensor displayed a reliable and consistent measurement performance of static and instantaneous dynamic loads over a total of 30 000 test cycles. The capabilities and implications of the presented tactile sensor design for multimodal sensing in robot tactile sensing applications is further discussed and elucidated.

ISO 13909 compliant contractual payment station coal sampling plant: process design and equipment selection for chemical, physical and moisture sampling

The paper discusses the process design and mass balance highlights to illustrate the ISO 13909 compliance of a 4-year-running contractual payment station sampling plant. The plant is used to sample -60mm coal supply to a coal fired power station infrastructure belonging to the South African National Power Utility. Payment parameters are proximate analysis (Calorific Value, Ash-, Sulphur content), physical (size and abrasion index) and moisture content. Over and above ergonomic physical samples and timeous moisture samples, the plant also delivers the crushed chemical sample in triplicate for buyer-, seller- and referee analysis. The lot period was defined as 24 hours production while the system compliance was designed around mass-based sampling. Production varies over a wide range of throughout tonnages from 800-3600 ton/h as dictated by complex boiler and silo operational requirements. The plant required a unique operational philosophy to adapt the number of primary increments (and corresponding time interval) per sublot size to the varying production rates which over a fix lot period results in varying lot size. Furthermore, a contractual grade, calibrated, 6-idler belt scale is used to measure the instantaneous conveyor load which in turn controls the cutter speed via a programmable logic controller (PLC) prompted variable speed drive (VSD) setpoint to sample fixed increment mass to represent fixed production mass interval. The primary belt end crosscut sampler boasts a unique articulated joint design sample chute to fit down the high sample tract; eliminating the delineation errors associated with the previous competitor design.

Development of a Benchmarking Energy Performance Indicator (BEPI) monitor for existing traction lift systems

Energy consumption of lift systems is one key issue in modern high-rise buildings, drawing property owners’ attention and accounting for 6% of total electricity consumption by end-use in Hong Kong. A Benchmarking Energy Performance Indicator (BEPI), <J/kg-m>, measured in J.kg−1.m−1 and proposed by the first author of this paper for lift installations is mentioned in the Technical Guidelines of the Building Energy Code, as one emerging good engineering practice. BEPI is a fair parameter for comparing energy performance of lifts irrespective of their brand, model, travel, speed, capacity and control. It considers energy performance due to both the motor drive efficiency and traffic control intelligence. However, one main obstacle to make it statutory is the lacking of a generic monitor able to retrieve three sets of real time data (normally unavailable on an existing lift) to compute the BEPI, namely energy consumption, instantaneous car load and traveling distance, and to collect ample data statistically reliable enough to determine an acceptable threshold value. This paper describes the development of a proof-of-concept prototype BEPI monitor by giving full technical details on the rationale and history of development, the hardware components, software framework, and updated numerical results of one implementation inside the headquarters of Electrical & Mechanical Services Department (EMSD) of HKSAR. Experiences in installing and calibrating those external sensors that make the whole system non-disturbing to normal lift operation, as well as the procedures in computing the BEPI, are discussed in greater details. It has been shown that the BEPI is traffic dependent but the weekly average of it is relatively stable, confirming it may be robust enough for benchmarking purpose. The solution described in this paper may help roll out the monitoring of BEPI for all lifts inside and outside Hong Kong.

Analysis of the Dynamic Characteristics of the Top Flange Pile Driving Process of a Novel Monopile Foundation without a Transition Section

As the most widely used foundation type, the pile-driving capacity of large-diameter monopile foundations and the hammer force of pile top flanges is increasing, as are the stress and strain of traditional flange structures under the resistance to the cyclic impact load of pile hammers. This paper conducts an empirical study on the Rudong 150 MW offshore wind farm project in Longyuan, Jiangsu Province. The numerical simulation and calculation method of large-diameter pile fatigue damage is mastered and proposed, and a simulation analysis and comparison is conducted, as is an analysis of the sensitivity and feedback of the key software parameters. Based on the results of the above analysis, a pile simulation analysis of the offshore wind power projects under construction and those that are about to be started is performed. The pile hammer stroke energy and pile top hammer stroke process curve are extracted. According to the time range curve of limit and hammer stroke forces, the flange limit stress and distribution of the pile roof are simulated. Combined with the process characteristics of large-diameter pile sinking and analysis in the case of high hammer energy and high acceleration, the effect of the impact on the sensor is discussed. The results show that the instantaneous loading analysis could load at the flange of the pile, the maximum instantaneous stress was above 500 MPa, and the final maximum stress was approximately 307 MPa. Different loading methods vary greatly in the calculation results of the structure, so choosing the appropriate loading simulation method is key to pile sinking analysis.

Accuracy of the adaptive friction clutch operation with variable gain

Shown that an increase in the external load leads to a decrease in the potential torque of an adaptive friction clutch with a variable gain, i.e., the instantaneous limit load that the clutch is able to transmit without slipping with an instantaneous increase in the external load. The clutch actuation occurs when the value of the increasing external load becomes equal to the decreasing potential torque of the clutch.

General Approximate Analytical Solutions for One-Dimensional Nonlinear Consolidation of Soft Soils under Time-Dependent Loading

A surcharge preloading method with time-dependent loading is widely used for accelerating the consolidation process of soft soils, and different loading patterns have a great effect on the consolidation characteristics. For one-dimensional nonlinear consolidation of soft soils considering the variable compressibility and permeability, the general approximate analytical solutions for one-dimensional nonlinear consolidation under time-dependent loading are derived. Moreover, two forms of boundary conditions are considered according to engineering practice. With reference to the general analytical solutions presented, the expressions for the solutions under several common loading patterns, such as the multistage instantaneous loading pattern, multistage linear loading pattern, and cyclic loading pattern, are given. The accuracy and correctness of the approximate analytical solutions are proven by comparing the approximate analytical solutions with the finite-difference solutions and two experimental results with different boundary conditions. Based on the approximate analytical solutions proposed, the consolidation behaviors of soft soils under different loading patterns are analyzed. In conclusion, the proposed approximate analytical solutions have a simple and clear form, which is convenient for calculations in engineering applications.

Reliability and fatigue life analysis of key parts of shearer

The poor reliability of shearer restricts the development and production efficiency of thin coal seam. The dynamic characteristics of the key parts have a great influence on the reliability and fatigue life of the thin seam shearer. In order to achieve high-yield and high-efficiency production of thin coal seams, the instantaneous load on the spiral drum was calculated based on the mechanical model of the spiral drum during the cutting process and the coal sample properties. According to the structure of the shearer and the material of key parts, a rigid-flexible coupling model of the shearer was established, and the stress information of the rocker arm shell, planetary carrier and planetary shaft was obtained by dynamic simulations. The membership function between material stress and structural reliability was constructed by Gaussian membership function, the main factors affecting the reliability of shearer were analyzed by orthogonal simulation test and PSO-BP neural network. The fatigue life of rocker arm shell, planetary carrier and planetary shaft were predicted by counting the rain flow of the stress information. Measures to improve the reliability and fatigue life of the shearer were proposed based on the analysis results, and effectiveness of the method proposed in this paper was verified by the practical application.

General analytical solutions for one‐dimensional nonlinear consolidation of saturated clay under non‐isothermal distribution condition

AbstractThe fluctuation of temperature leads to the changes of physical‐mechanical properties of clayey soils. In some practical projects such as landfills, the compacted clay liner is usually subjected to a non‐isothermal distribution state. For one‐dimensional nonlinear consolidation process of saturated clay under non‐isothermal distribution condition, the general analytical solutions considering time‐dependent loading are derived for the first time, where the methods of algebraic transformation and separation variable are used. Moreover, two forms of boundary conditions are included according to engineering practice. Referring to the proposed general analytical solutions, the expressions for the analytical solutions under instantaneous loading pattern and single‐stage linear loading pattern are developed. Besides, the correctness of the presented analytical solutions is validated by comparing with the existing analytical solutions and finite difference solutions. Based on the proposed analytical solutions, the influence of temperature gradient, final loading and loading time on the consolidation behaviors is analyzed. It is found that the increase in temperature gradient accelerates the consolidation rate, and the average volume compressibility coefficient decreases by 65.4% when final loading increases from 50 to 500 kPa. In conclusion, the analytical solutions proposed in this study are more comprehensive and can be applied in different engineering cases.

Biomechanical adaptations following a music‐based biofeedback gait retraining program to reduce peak tibial accelerations

The present study aimed to determine whether runners can reduce impact measures after a six-session in-the-field gait retraining program with real-time musical biofeedback on axial peak tibial acceleration (PTAa ) and identify the associated biomechanical adaptations. Twenty trained high-impact runners were assigned to either the biofeedback or the music-only condition. The biofeedback group received real-time feedback on the PTAa during the gait retraining program, whereas the music-only condition received a sham treatment. Three-dimensional gait analysis was conducted in the laboratory before (PRE) and within one week after completing the gait retraining program (POST). Subjects were instructed to replicate the running style from the last gait retraining session without receiving feedback while running overground at a constant speed of 2.9m∙s-1 . Only the biofeedback group showed significant reductions in both PTAa (∆x̅=-26.9%, p=0.006) and vertical instantaneous loading rate (∆x̅=-29.2%, p=0.003) from PRE to POST. In terms of biomechanical adaptations, two strategies were identified. Two subjects transitioned toward a more forefoot strike. The remaining eight subjects used a pronounced rearfoot strike and posteriorly inclined shank at initial contact combined with less knee extension at toe-off while reducing vertical excursion of the center of mass. After completing a music-based biofeedback gait retraining program, runners can reduce impact while running overground in a laboratory. We identified two distinct self-selected strategies used by the participants to achieve reductions in impact.

Horizontal impact loads and torsional moment induced by partial cargo shifts

Previous studies demonstrate that significant cargo shifts occurred in all cargo holds of vessels in carriage of nickel ores may lead to catastrophic consequences of ship capsizing and sinking. Nevertheless, partial cargo shifts, despite its seldom occurrence in other types of vessels, are not unusual in bulk carriers, specifically for those with nickel ores which tend to liquefy as vessels experience long-time engine vibrations or unfavorable oblique waves. Regrettably, it has not been well described in previous literatures, therefore overlooked by ship operators and naval architects in ship structural design. The instantaneous impact loads to vessel's structures induced by partial cargo shifts, thus, remain unclear. Despite partial cargo shifts being unlikely to lead to life lost or ship capsizing, critical damage to cargo holds, shell plates and precise apparatuses in the wheelhouse can be identified frequently, sometimes even causing ship a hazardous list of 6–15°. Unfortunately, a number of similar accidents occurred in S.E. Asia waters have been found without reporting these accidents to IMO due to various reasons. The instantaneous impact loads, involving the torsional moments and horizontal sectional loads, initially overlooked by plenty of naval architects but subsequently estimated by our research team, are really huge, usually giving rise to a dangerous list of vessels as well as apparent or underlying damage to vessel's configurations. Conventional approaches, such as potential flow theory, volume of fluid method, moving particle semi-implicit method, smoothed particle hydrodynamics, etc., are significantly limited by their unsatisfactory precision in predicting and calculating those extraordinary loads. Here we estimate the torsional moments and horizontal sectional loads in oblique waves at various exciting rolling frequencies using improved Finite Element approach. The final results yielded from the model tests are strikingly in line with that from the numerical approach, manifesting that the modified numerical method behaves in a reasonable manner in tracking and capturing the complicated surface of large viscous fluid.

Acute effects of footwear on running impact loading in the preschool years

ABSTRACT The aim of this study was to assess acute effects of footwear conditions (barefoot, minimalist and standard running shoes) on running impact loading in the preschool years. Fourty-eight habitually shod preschool children (26 males and 22 females) were divided into four age groups (3-, 4-, 5- and 6-year-old). Children performed a simple running game in three different conditions. Three-dimensional biomechanical analysis was carried out during overground running. Statistical parametric mapping was performed on the vertical ground reaction force profiles during the stance phase and one-way repeated measures ANOVA on the vertical instantaneous loading rate. Three-year-old children displayed significantly lower vertical ground reaction force values in the barefoot condition compared to minimalist (3-7% stance) and standard running shoes (7-11% stance). There were also differences in vertical instantaneous loading rate, where 3-year-olds had lower loading when barefoot than in minimalist (p = 0.010, d = 1.19) or running shoes (p = 0.045, d = 0.98), despite no differences in the footstrike pattern (mostly rearfoot-midfoot strike). No differences were found for the older children. Running in minimalist shoes did not imitate barefoot running in 3-year-old children. On the contrary, increased loading was observed in minimalist shoes in early running developmental stages.

Flexural Behavior of Reinforced Concrete Beams under Instantaneous Loading: Effects of Recycled Ceramic as Cement and Aggregates Replacement

The flexural behavior of five reinforced concrete beams containing recycled ceramic as cement and aggregate replacement subjected to a monotonic static load up to failure was studied. A full-scale, four-point load test was conducted on these beams for 28 days. The experimental results were compared with the conventional concrete as a control specimen. The cross-section and effective span of these beams were (160 × 200 mm) and 2200 mm, respectively. The data recorded during the tests were the ultimate load at failure, steel-reinforcement bar strain, the strain of concrete, cracking history, and mode of failure. The beam containing 100% recycled aggregates displayed an ultimate load of up to 99% of the control beam specimen. In addition, the first crack load was almost similar for both specimens (about 14 kN). The deflection of the beam composed of 100% of the recycled aggregates was reduced by 43% compared to the control specimen. Regardless of the recycled ceramic aggregates ratio, quantities such as service, yield, and ultimate load of the proposed beams exhibited a comparable trend. It was asserted that the ceramic wastes might be of potential use in producing high-performance concrete needed by the structural industry. It might be an effective strategy to decrease the pressure on the environment, thus reducing the amount of natural resources usage.

Dynamic response analysis of a whole steel frame solar greenhouse under wind loads

In recent years, whole steel frame steel greenhouses have become increasingly prevalent. With the characteristics of large flexibility and small mass, whole steel frame steel greenhouses are sensitive to wind loads. However, studies on the safety of whole steel frame steel greenhouses under wind loads are still limited. In this study, a 10 m span whole steel frame solar greenhouse was taken as the research objective. Taking the Davenport spectrum as the target spectrum, the time history of the wind speed was simulated by the harmonic superposition method. The finite element model of the greenhouse structure was established using ANSYS software. The simulated wind pressure was applied on the greenhouse structure for dynamic response analysis. The dynamic response results were compared with the static analysis results under average wind load. The results showed that the greenhouse structure mainly bears bending stress under wind load. The bending stress, axial stress and displacement of the greenhouse skeleton under average wind loads are lower than those under instantaneous wind loads. It is necessary to consider the dynamic characteristics of wind loads in the design of solar greenhouses. A wind-induced vibration coefficient is obtained, which can be used to convert the dynamic load into the equivalent static load and improve its design efficiency.

Modeling and evaluation of SOC-based coordinated EV charging for powermanagement in a distribution system

The importance of using clean energy in electrical energy generation and transportation network planning has recently increased due to carbon footprint rising. In this direction, the use of electric vehicles (EV), known as ultra-low carbon emission vehicles, has become widespread in addition to renewable energy sources (RES) such as wind and photovoltaic (PV) power generations. The trend of EVs to be preferred the primary means of transport has revealed the effects of charging an additional load on the grid. There is a need to create coordinated charging methods by considering the approaches for real-time charging models of EVs. In this paper, SOC-based EV coordinated charging was proposed for power management to prevent adverse effects including transformer overload, instantaneous peak loading and line overload in the existing distribution network. The proposed coordinated EV charging method was tested on the modified Roy Billinton test system (RBTS) Bus 2 network. AC 11 kW uncoordinated charging units have been respectively 123.76% distribution transformer and 115.16% distribution line overloading for 500 EVs on the grid with 13,9% diversity factor. However, these values that are 72.05% of distribution transformer and 67.01% of distribution grid overloading according to permittable level were decreased by the proposed coordinated charging method. Also, the state of charge (SOC) based coordinated method can increase 3.5% rate the diversity factor of charging capacity at the charging station with PV and battery energy system (BES) while ensured grid stability and energy efficiency.

Impact of Parasitic and Load Current on the Attenuation of Motor Terminal Overvoltage in SiC-Based Drives

In SiC-based adjustable speed drives, the high voltage slew rate ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dv\!/\!dt$</tex-math></inline-formula> ) of the switching transitions results in excessive overvoltage at the motor terminals due to the reflected voltages across the drive power cables. Besides the cable length, the switching rise/fall times of the voltage pulses are a key parameter to quantify the motor overvoltage in pulsewidth modulation (PWM) inverter-fed drives. These times are varying depending on the load current and parasitic elements of SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s, that is, a standard two-level converter typically results in a nonuniform overvoltage envelop at the motor terminals. This article analyses the switching mechanism of the two-level converter considering the impact of SiC parasitic elements and load current showing how they affect the motor overvoltage in cable-fed drives. The analysis is then extended to the mitigation of the motor overvoltage using quasi-three-level (Q3L) modulation as a candidate filter-less approach with a T-type converter. The theoretical analysis is validated through experimental tests by using the Q3L T-type converter. The analysis and results show that the instantaneous load current value critically determines the peak motor overvoltage, while it allows either a full or partial overvoltage mitigation when the Q3L modulation is adopted.