Actual Loading Conditions Research Articles

Multi-DoF Force Characterization of Soft Actuators

Soft actuators provide highly adaptable actuator options for applications in wearable devices, grippers, and mobile robots due to their inherent compliance. However, this compliance causes soft actuators to have virtually infinite degrees of freedom (DoF) of motion and challenges the accurate prediction of their displacement and interaction forces. While several studies have characterized soft actuators either in blocked condition or in a specific range of motion, the testing conditions often do not match actual loading conditions, which leads to discrepancies between expected and observed mechanical behaviour. Here, we propose a novel multi-DoF experimental protocol for characterizing soft actuator interaction forces by considering three critical aspects-anchoring conditions, displacement boundary conditions, and actuation power. In order to conduct this multi-DoF characterization, we designed a novel reconfigurable robotic test platform for enforcing anchoring conditions and planar displacement boundary conditions, and measuring forces at multiple contact locations. Using this experimental protocol and setup, we dictated three loading conditions-pulling force, tip loading, and three-point bending-and analyzed the interaction forces of a soft bending actuator. Our results show that the three loading conditions produce distinct actuator behaviors. This validates the importance of loading conditions on soft actuator performance.

Engine Speed Control System for Improving the Fuel Efficiency of Agricultural Tractors for Plowing Operations

This study was conducted to develop a load-sensitive engine speed control system to maximize the fuel efficiency of an agricultural tractor. The engine speed controller was developed through a model-based design approach using a tractor simulation model. The simulated engine speed and torque values were measured with an average error range of 1.4–4.9% compared to results obtained from field experiments. Using the tractor model, the gain parameters of the proportional–integral (PI) controller were optimized under the step, ramp, and actual load conditions. The simulation results using the actual load showed that the engine speed could be adjusted to within 2–3% of the desired value using the proposed engine speed controller. The throttle control system was constructed using four parts of a tractor engine, a microprocessor with an engine speed control algorithm, a throttle actuator, and a data acquisition system. Using the developed system, the operating engine speed values showed an average 1.17 % error compared to the desired engine speed. Three fuel efficiency parameters were used for evaluating the fuel-saving performance of the control system: specific volumetric fuel consumption (SVFC), fuel consumption per tilled area (FCA), and fuel consumption per work hour (FC). The values for SVFC, FCA, and FC obtained from the engine speed control system during plowing operations were 23.03–57.87%, 4.11–42.06%, and −7.24–38.48%, respectively, showing an improvement over the same operations without the control system.

Non-steady state electro-thermally coupled weather-dependent power flow technique for a geographically-traversed overhead-line capacity improvement

Overhead lines rated under conventional line rating techniques have limited power transfer capacity to avoid congestion and line overloading. Rating and operating them under actual weather and loading conditions with electro-thermally coupled parameters can significantly increase line loadability. As a result, line congestion and overloading can be minimized, thus avoiding load shedding. This paper presents an electro-thermally coupled (ETC) line rating technique for an overhead line passing through a large geographical area and exposed to multiple weather conditions. The presented technique, using a dynamic weather scenario, was found to enable efficient and reliable transfer of excess electricity to avoid load shedding. Because the line passed through a large geographical area, regions exposed to the worst weather exhibited the lowest thermal and current loadability with regard to electricity transmission. This paper therefore focuses on these spans to find the line temperature, temperature-dependent line AC resistance, branch active power flow and bus voltage magnitude based on time- and space-dependent weather conditions in comparison to time- and space-independent weather conditions, using the newly developed weather-integrated power flow tool. The paper also addresses the sensitivity between weather-dependent line temperature and associated weather across critical spans, where weather affecting critical spans is used to determine the line temperature.

Multiscale Toughening Mechanisms in Biological Materials and Bioinspired Designs.

Biological materials found in Nature such as nacre and bone are well recognized as light-weight, strong, and tough structural materials. The remarkable toughness and damage tolerance of such biological materials are conferred through hierarchical assembly of their multiscale (i.e., atomic- to macroscale) architectures and components. Herein, the toughening mechanisms of different organisms at multilength scales are identified and summarized: macromolecular deformation, chemical bond breakage, and biomineral crystal imperfections at the atomic scale; biopolymer fibril reconfiguration/deformation and biomineral nanoparticle/nanoplatelet/nanorod translation, and crack reorientation at the nanoscale; crack deflection and twisting by characteristic features such as tubules and lamellae at the microscale; and structure and morphology optimization at the macroscale. In addition, the actual loading conditions of the natural organisms are different, leading to energy dissipation occurring at different time scales. These toughening mechanisms are further illustrated by comparing the experimental results with computational modeling. Modeling methods at different length and time scales are reviewed. Examples of biomimetic designs that realize the multiscale toughening mechanisms in engineering materials are introduced. Indeed, there is still plenty of room mimicking the strong and tough biological designs at the multilength and time scale in Nature.

Evaluation of remaining fatigue life of concrete sleeper based on field loading conditions

The main functions of the sleepers in ballasted tracks include transferring loads, securing rail gauge and maintaining railway track geometry. Sleepers can be manufactured using timber, concrete, steel or other engineered materials, but concrete is most commonly used around the world. There are a number of researches on the impact load characteristics and the ultimate load carrying capacity of prestressed concrete sleepers, but research on the fatigue life of prestressed concrete sleepers is very limited. A prestressed concrete sleeper's fatigue damage is mainly due to the repeated loads derived from dynamic wheel-rail interactions, especially when either wheel or rail irregularity is present. Fatigue failure is thus a time-dependent limited state where a concrete sleeper accumulates damage to a failure point over its service life. Concrete sleepers could usually suffer from the dynamic fatigue loading spectra throughout their whole lives, and simultaneously, both static and dynamic load-carrying capacities of concrete sleepers degrades over time. Therefore, a fatigue life assessment is an important and complicated research frontier. Field loading conditions, material time-dependent and dynamic properties, and the dynamic bending moments of prestressed concrete sleepers are quantitatively analysed in this study. This paper also presents an updated fatigue life assessment method for concrete sleepers, and provides a case study based on actual field loading conditions and the time-dependent behaviour of materials. The new insights obtained from this study will improve concrete sleeper maintenance and inspection criteria, and provide a new reference for a rational dynamic design principle of railway concrete sleepers and bearers.

Analisa Performa Pembangkit Berdasarkan Tingkat Kevakuman Kondensor Pada PLTU Barru Unit 2

Vacuum condenser is one of the parameters that affect the performance of the plant. To keep the plant's performance remains stable then it takes a good degree of vacuum in the condenser. This final project aims to determine the performance of plants based on the level of vacuum condenser different. The method used is collecting data on the actual load conditions 50%, 75% and 100% and then perform data analysis. The results will be presented in tables and graphs then be deduced. Based on data and analysis that has been carried out, the results obtained are better condenser vacuum pressure, the specific steam consumption, specific fuel consumption and turbine heat rate (heat rate) will decrease, while the efficiency of the turbine will increase

Effect of overload on fatigue crack growth behavior of thin copper foil

Smart stress-memory patch (SSMP) which consists of electrodeposited copper foil has been proposed as a sensor to measure fatigue loading for structural health monitoring in previous researches. In this study, the fatigue crack growth behavior of the copper foil was examined under constant amplitude loading with single overload and variable amplitude loading in order to evaluate the applicability of SSMP to the actual loading conditions. Under the overload condition, the fatigue crack growth rate gradually decreased after the overload and reached a minimum value, and then recovered to the baseline. Since the retardation behavior was different from one of thick specimen, a new model to quantify the crack growth in the thin specimen was proposed based on a modified Wheeler model. The proposed model successfully reproduced the fatigue crack growth curve under the single overload condition. Additionally, the proposed model was extended to the variable amplitude loading conditions by including cycle-by-cycle calculation procedure. The results showed that the fatigue crack growth behavior can be represented by the proposed model under the variable amplitude loading condition. Therefore, the feasibility of applying SSMP to actual loading conditions was demonstrated.

Harvesting kinetic energy from roadway pavement through an electromagnetic speed bump

Roadway pavements are repeatedly subjected to two different types of energy sources—solar radiation and kinetic energy from passing vehicles. Therefore, they have great potential to be utilized as sustainable energy sources. In this study, an electromagnetic speed bump energy harvester (ESE) prototype was developed to harvest energy from the kinetic energy of passing vehicles and to simultaneously control vehicles’ speed. The ESE absorbs the deflection generated by a passing vehicle and converts it to a rotating shaft that triggers an embedded generator. A set of laboratory tests were conducted to simulate traffic conditions and evaluate the performance of the prototype in generating electrical power. These tests investigated the effect of load magnitude, time of loading, time of unloading, and ratio of loading time to unloading time on the power output generated by the ESE. The experimental results had a maximum average power of 3.21 mW, which shows that the proposed prototype promises to generate substantial power under actual traffic loading conditions. The effect of load magnitude was negligible, while a shorter time of loading led to a higher power output, implying that the optimum vehicle speed for maximizing the power output is the speed limit in the ESE location. Four sets of linear static analyses were performed in order to evaluate the response of the prototype fabrication. The top component of the ESE was modeled using material properties of steel, aluminum, or composites of heavy-duty rubber, and the bottom frames were given steel or aluminum properties.

Structural failure test of a 52.5 m wind turbine blade under combined loading

Blade is one of the basic and key components in wind turbines. To get closer to the actual loading condition of blade under complex and extreme wind conditions to more accurately analyse the structural failure characteristics of large wind turbine blades. The structural collapse test of a 52.5 m wind turbine blade under combined loading was carried out. The entire process of damage under ultimate load was recorded and analysed in detail. The joint analysis of the failure region after the blade collapse and the failure mode during the test process were performed. The research shows that the geometrical nonlinear buckling of spar cap and shear web, the delamination result from non-uniform stress distribution and further fracture of Aft panel cause catastrophic failure of the blade. The torsional moment cause oblique cracks and oblique bulges, aggravates the expansion of the internal and external composite cracks of blade, affects the final failure mode after blade collapses (critical failure mode), and make the spar cap at suction side to clockwise twist from blade tip to root. The research results lay a theoretical foundation for subsequent model establishment and simulation analysis of large wind turbine blades under combined loading.

Forensic investigation of a slender high-rise structure subject to dynamic wind conditions

The forensic engineering of a collapsed reinforced concrete fin wall structure is presented in this paper. The investigative process considers the assessment between the actual wind load conditions structure during the time of collapse against the actual structural capacity of the structure. Three design conditions are considered in this study; in-situ wind speed during the time of incident, wind speed used by the design consultant and wind speed recommended by Jabatan Meterologi Malaysia (JMM) in 1995, which was the time of design. The structure is both analyzed from a static analysis and dynamic time history analysis standpoint. It was found that the amplification factor due to the near resonance of wind energies between 0.25-0.30 Hz and the natural frequency of the structure, 0.27Hz. This resulted in a amplification of 1.8 over quasi-static loading conditions as governed by CP3 design code. It was further found that the dynamic wind loading imposed against the structure was 10% less from the actual capacity of the structure determined via nonlinear pushover analysis. This result is at best marginal considering the inelastic performance of the structure and the actual as-built condition of the structure; giving strong indication to the role of resonance in the collapse. The technical interpretation of the design codes leading to the responsibilities of the design consultant are not discussed in this paper.

Load-Dependent Rotating Performance of Motorized Spindles: Measurement and Evaluation Using Multi-Zones Error Map

The rotating performance of motorized spindles is critical to the dimensional accuracy and surface quality of the parts to be machined. This paper proposes a novel measurement strategy and an evaluation method of spindle's rotating performance, considering the loads imposed on the spindle. To be specific, cutting loads are simplified as a unified function to guide the load simulation, and the load-induced error is eliminated using a position adjustment procedure. In a certain speed-load combination, the spindle's rotating performance under the unified load function is measured using a data envelope method. To extend the assessment to all typical work conditions, an evaluation scheme for different speed and load combinations is proposed based on a visual ideal of Multi-Zones Error Map (MZE Map). The necessity of considering the load-dependent rotating performance is demonstrated via several tests conducted on proposed load simulation platform. Besides, the procedures for developing the MZE Map are performed, and the results express an overview relationship between rotating performance and different speed-load conditions. The proposed method provides a new approach to evaluate the rotating performance considering the actual load conditions. This load-dependent oriented evaluating strategy contributes to a more precise health evaluation and management method for motorized spindles in actual machining process.

Structural optimization of the transport bracket for large tonnage round bar

Reducing the deformation of the transport bracket was the basic means to improve the mate precision between the large tonnage round bar and the bracket. The finite element model of the bracket was established and the actual loading conditions of the bracket for transporting the large tonnage round bar were analyzed by ABAQUS. The deformation and the weak areas of the bracket were investigated by the finite element analysis. The optimization model was obtained by the methods of replacing the type of the channel steel, improving the bracket structure and arranging fulcrums. These methods were adopted selectively to optimize the bracket structure based on the bracket’s maximum deformation demand. The finite element analysis not only shortened the design cycle, reduced the design cost, but also provided technical support for the bracket structure design.

Investigation of unbound granular material behavior using precision unbound material analyzer and repeated load triaxial test

Abstract This study aims to investigate the mechanical behavior of unbound granular materials (UGM) the using precision unbound material analyzer (PUMA) and repeated load triaxial test (RLTT). Both single-size and mixed-size aggregate and two graded materials were used for multi-stage loading tests in this study. The confining stress, resilient modulus, and permanent strains of six granular materials were analyzed considering the effect of particle size on the performance of UGM. The results of PUMA tests showed that the confining stress became smaller with more large-size particles and denser structure. Resilient modulus was found to be sensitive to particle size when the axial load stress was greater than 40 kPa. The resilient modulus of high-density materials calculated from the variable confining pressure (VCP) model was greater than that from the constant confining pressure (CCP) model. The results suggested that axial load, material type, and the largest particle size needed to be considered for analysis of confining stress and resilient modulus. Without considering confining stress, resilient modulus might be underestimated for high-density materials but overestimated for low-density materials using the CCP model. The resilient modulus and permanent strains measured using the PUMA were similar to those measured using the RLTT in the range of 10 kPa to 20 kPa confining stress. The predicted permanent strains from the CCP model and RLTT had greater error than the predictions from the VCP model and PUMA tests compared to experimental measurements. The dynamic confining stress in PUMA tests was found effectively to simulate the actual loading condition of UGM in a pavement. Although RLTT and PUMA tests present consistent results for characterizing the behavior of UGM, the PUMA can provide more reasonable results for simulating confining stress and measuring resilient modulus.

Power maximization from resonant electromagnetic vibration harvesters feeding bridge rectifiers

SummaryIn this paper, it is shown that, for resonant electromagnetic vibration energy harvesters (REVEH) feeding diode bridge rectifiers, it is possible to quantify how close the ideal load condition is to the actual load condition. For this purpose, a new figure of merit, the REVEH exploitation factor (REF), is introduced. The higher the REF, the higher the REVEH exploitation. Moreover, by using the REF, a suitable technique for increasing the extracted power in a frequency region of interest is investigated. This is the frequency region where a significant energy content of the input vibrations is present. The investigated technique is based on the proper insertion of additional non‐dissipative components (capacitors or inductors) between the REVEH coil and the bridge rectifier. Experimental results confirm the validity of the theoretical analysis.

Compilation of NC lathe dynamic cutting force spectrum based on two-dimensional mixture models

The load spectrum of numerical control machine tool (NCMT) is the basis data of reliability design, life prediction, and reliability bench test with simulated actual load conditions. Static cutting force spectrum, which can be compiled by empirical formula, cannot accurately reflect the real load conditions. Hence, a method for compiling the spectrum of dynamic turning force is proposed by using two-dimensional mixture models. Dynamic turning force is measured in the laboratory based on a large amount of cutting process data collected in the user field. Mean–frequency and amplitude–frequency matrices of dynamic turning force are obtained by the rainflow counting method. The probability distributions of mean and amplitude are established by using Weibull mixture models (WMM) according to the characteristics of the dynamic turning force, and the two main problems of this method are the determination of the number of mixture components and the estimation of parameters. Gray relation analysis is used to quantify the multi-objective evaluation matrix, and thus the number of mixture components is determined. Parameters are estimated using the improved expectation maximization (EM) algorithm, where the initial values of parameters are obtained by the K-means++ and Bayesian random classification. Finally, the joint probability distribution function between the mean and amplitude is established by the Copula function. Thus, the dynamic cutting force spectrum is compiled. Case analysis results show that the mean and amplitude distribution models with high fitting precision can be obtained using the proposed method. Furthermore, the precision of the load spectrum of NCMT is improved.

Development of Permanent Deformation Master Curves of Asphalt Mixtures by Load-Temperature Superposition

AbstractThe optional multiple repeated load (OMRL) test, which involves multiple load levels, is a more promising test method to simulate actual traffic load conditions on pavements. The presented ...

Hardened raceway calculation analysis of a three-row roller slewing bearing

Three-row roller slewing bearings are large and often exposed to quite complex loads. The raceway surface is hardened to improve its carrying capacity. An inadequate hardened raceway depth can cause the raceway to be crushed. In contrast, an excessively large hardened raceway depth can increase the overall vibration, processing difficulty, and cost. Thus, it is critical to determine the optimal hardening depth. We propose a quick method to analyze this depth. The use of non-linear springs instead of a solid roller provides the maximum contact load between the roller and raceway according to the actual load conditions. A finite element model for the local roller and raceway contact is established. The depth thickness under the raceway is divided into a hardened layer, a transition layer, and a core layer. Each layer has distinct elastic–plastic material parameters. The results of a roller and raceway compression experiment validate the roller and raceway finite element model. The accuracy of the raceway as described by the model with different layers is verified by an indentation test of heat-treated 42CrMo. The results show the following: 1) both the value and depth position of the maximum stress increase under normal loads, and 2) the choice of algorithm has a strong influence on the calculated value of the fatigue life.

Numerical Investigation of Timber Log‐Haus Walls with Steel Dovetail Reinforcements under In‐Plane Seismic Loads

The paper investigates the structural response and vulnerability of timber log‐haus walls under in‐plane seismic loads. Careful consideration is given, in particular, to the structural efficiency of additional metal fasteners introduced within the thickness of traditional timber log‐walls. Log‐haus systems are in fact typically obtained by stacking multiple logs and generally used for residential or commercial buildings up to two levels. Their seismic characterization, however, still requires further investigations and studies, since current standards for timber structures (i.e., Eurocode 5 and Eurocode 8) do not provide specific recommendations for their seismic design. In this regard, the so‐called “steel dovetail profiles” investigated in this paper are aimed to improve the in‐plane stiffness and ultimate resistance of traditional log‐walls. In particular, taking advantage of past experiments carried out on small‐scale joint specimens, as well as past 3D numerical efforts for the same structural typology (unreinforced assemblies), full 3D solid models are described in ABAQUS to assess the potential of steel dovetail profiles, as well as to capture possible issues. Numerical simulations are proposed both for small‐scale specimens and full log‐haus assemblies, being representative of the actual loading and boundary conditions for log‐haus walls as part of a real building. As such, the effects of key input parameters and main influencing aspects are emphasized. In conclusion, it is shown that the examined reinforcing technique can offer rather stable initial stiffness and ultimate resistance increase, compared to unreinforced assemblies. At the same time, several aspects should be taken into account to properly optimize their benefits.

Classification and Calculation of Drive Loads

To permit calculation of the fatigue strength of drive components, drives are classified in terms of their loading conditions. Formulas are presented for the equivalence factors used in converting the actual variable loading conditions to conventional constant conditions. The overload coefficients required in calculating the static strength of drive components at the peak load are also determined.

Development of a 1.5 kV, 1.2 kA Pulsed-Power Supply for Light Sintering

This paper presents the design and experimental results of the 36-kW pulsed-power supply for the xenon flash lamp. The continuous conduction mode series-parallel resonant converter is modified. This means that not only the few hundred kilohertz of high switching frequency is introduced to replace the resonant inductor with the leakage inductor of transformer but also the high output current is accomplished by using three-phase delta-connected transformers. In addition, the snubber capacitor of the inverter switches and the power factor correction module is both omitted in the compact structure. Although these main components have changed, the efficiency and power factor of the rated dummy load reach 96% and 0.96%, respectively. Within 36-kW average power, the proposed pulsed-power supply can generate as versatile combination of output pulse. For example, it can generate 20-ms pulse with 1-Hz repetition rate or generate 1-ms pulse with 20-Hz repetition rate. The used insulated gate bipolar transistor is protected from the turn-OFF peak voltage by the snubber circuit, and the effect of the snubber circuit is shown at the actual load condition.