Transient Loading Research Articles

An equivalent spring-based model to couple the motion of visco-hyperelastic dielectric elastomer with the confined compressible fluid/air mass

Soft materials exhibiting large voltage-induced deformation under external stimuli have gained increasing attention in the recent past owing to their potential applications in soft transducers. Dielectric elastomer actuators (DEAs) coupled with a fluid/air mass have proved to undergo considerable voltage-induced deformation. This article presents a framework to couple the motion of an inflated Dielectric elastomer (DE) membrane with a confined compressible fluid/air mass and develops a nonlinear dynamic analytical model to predict the polar region deflection of an inflated DE membrane attached to an airtight chamber (namely bulging actuators) stimulated by an electric field. In order to derive the differential equations which determine the dynamic behavior of the membrane coupled to an airtight chamber, the Euler–Lagrange equation is employed, which takes into account the effects of membrane pre-stretch, initial inflation pressure, membrane viscoelastic behavior, and transient electric loading. A hypothesis of pseudo-air-spring is incorporated to consider the effect of the volume of the confined fluid/air mass. The experimental investigation conducted for various geometrical and loading conditions in both depressurized and pressurized states of actuation shows that the developed nonlinear model satisfactorily predicts the influence of fluid/air mass on the dynamic response of the considered DE membrane undergoing small voltage-induced deformation. Finally, the proposed framework is incorporated for building insights on several effecting parameters such as inflation pressure, quality, and quantity of the confined fluid mass, etc., on the electrodynamic behavior of the actuator. The results reveal that the volume of the air column appreciably alters the nonlinear dynamic behavior of the bulging actuator. Poincaré plots along with phase diagrams are presented for analyzing the periodicity of the nonlinear oscillations of the actuator. The underlying theoretical framework and the obtained inferences of the present article can be implemented effectively in the design of a futuristic class of structures whose motion is coupled with compressible fluid/ air mass subjected to time-dependent actuation.

Advanced proof testing for structural ceramics

AbstractProof testing is used to remove weak ceramic components from a manufactured batch in turn truncating the lower end of the strength‐failure probability distribution. With proof testing, components are subjected to stresses comparable to those observed during service load histories resulting in the remaining ones having assured minimum reliabilities. The degree to which the reliability of the remaining parts is assured depends on the proof test protocol, which includes multiple variables such as stress level, realistic sampling of flaws, complex geometries, multiaxial stresses, transient loading histories, time‐dependent damage due to slow crack growth and/or fatigue, and change in material behavior due to temperature and/or environmental conditions. This paper advances the early work done on proof test theory, which was limited to simple stress states, to include general stress and material states. The theory introduced in this paper takes into account practical conditions often encountered in industrial applications. This advanced proof test theory was coded into the CARES/Life code (Ceramics Analysis and Reliability Evaluation of Structures/Life). Examples are provided to demonstrate the theory.

Demonstrating tungsten fiber-reinforced porous-matrix tungsten composites for future fusion application

Tungsten fiber-reinforced tungsten (Wf/W) has been developed to improve the fracture toughness of W materials, as demonstrated in previous studies (2019 Nucl. Fusion 59 086034; 2021 Mater. Sci. Eng. A 817 141361). In the present study, we focus on the performance of the developed Wf/W materials under fusion-relevant test conditions and further demonstrate their use as plasma facing materials in future fusion reactors. Specifically, one set of Wf/W samples was exposed to Ne plasma to investigate the erosion resistance against plasma sputtering, in comparison to the reference ITER-grade W sample. In addition, deuterium (D) retention in the plasma-exposed Wf/W samples was studied via thermal desorption spectroscopy. Furthermore, laser thermal shock tests were performed on Wf/W to simulate the transient heat load condition and to investigate the material performance under extreme heat flux. With increasing porosity, Wf/W exhibits lower mass loss (net erosion) after Ne plasma exposure. Though porous, Wf/W composites unexpectedly show a comparable D retention to the reference bulk W, which is attributed to the openness of the pores in the matrix. Thermal shock testing results indicate a similar cracking threshold (0.38 GW m−2, 1 ms) as compared with that of ITER-grade W materials. However, due to the lower thermal conductivity of porous matrix Wf/W, under extremely high loading conditions (1.6 GW m−2, 2 ms) surface melting was observed. The present work demonstrates the great potential of the porous matrix Wf/W for future fusion application.

Decompression Load Analysis in Large Passenger Planes with Windshield Cracked

To prevent the possible accident of a large passenger plane due to rapid decompression, transient load analysis is of vital importance in the assessment of structure strength and also an important clause of airworthiness standard. A 0-D isentropic model and a 1-D model based on the characteristic line are developed to simulate the rapid decompression process of the cockpit-cabin model due to a cracked windshield. The accuracy of these models is presented by comparing them with experiments and 3-D CFD simulations. Then, the 1-D model is applied to study the influence of cabin and cockpit volume, windshield and decompression panel area, compartments, and environment pressure on the decompression load. The non-dimensional decompression time and the non-dimensional decompression load are developed to evaluate the decompression characteristics, and the correlation equations are established. The relative deviation between the results of the correlation equation fit and the results of the one-dimensional simulation is less than 3%. This work provides a new engineering method for structure strength design and decompression load analysis with high accuracy and low resource consumption.

Feature Extraction of V–I Trajectory Using 2-D Fourier Series for Electrical Load Classification

Nonintrusive load monitoring (NILM) techniques allow the individual consumption of devices in an installation to be reported to the user, collaborating in the awareness and managing consumers’ energy use. One of the most critical steps in NILM procedures is feature extraction, which involves the quantitative description of the load signature. Most state-of-the-art methods, particularly those involving voltage–current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V–I</i> ) trajectories, are based on features that specialists design when manually analyzing signals—the so-called hand-crafted features. On the other hand, this work presents a mathematical method that describes the transient and steady-state (SS) load signature using a 2-D Fourier series, avoiding hand-crafted descriptors. The proposed approach evaluates load identification results with different classifiers and publicly available datasets. In addition to the evaluation of the proposed method’s computational resources, such as execution time and memory footprint in an embedded system, their robustness to noise insertion is also assessed. The results of the proposed approach indicate an average per-class accuracy higher than 90%, equivalent or superior to hand-crafted <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V–I</i> trajectory-based methods in most cases and even deep learning approaches recently presented in the literature. Such results reinforce the main contributions of this work: 1) a mathematical method to extract interpretable features; 2) results comparable or superior to other state-of-the-art methods; and 3) promising results in computational resources in an embedded system.

Short-term stress of quaternary ammonium compounds on intracellular and extracellular resistance genes in denitrification systems

The wastewater containing high quaternary ammonium compounds (QACs) concentrations from hospitals and other sources may cause the transient shock loads on the wastewater treatment plants (WWTPs). Denitrification is the key part of nitrogen removal from wastewater, however, the effects of QACs on the denitrification and the spread patterns of intracellular and extracellular resistance genes were still unknown. The short-term stress of three frequently detected QACs on denitrification were systematically investigated in this study. The inhibitory effect on nitrate removal had the following rules: BAC C12 > ATMAC C12 > DADMAC C12. The inhibition of QACs on denitrification performance was correlated with the reduction of Thauera abundance, and a higher QACs concentration made stronger inhibitory effect. Moreover, high concentrations of QACs could cause a significant decrease in reactive oxygen species, inhibit cell activity and extracellular polymeric substances secretion. Furthermore, QACs stimulated an overall increase of intracellular and extracellular QACs resistance genes in denitrification systems, both in sludge and in water. And co-selection among resistance genes occurred under shock loads of QACs, especially a high BAC C12 concentration caused a substantial raise in abundances of resistance genes in water. It was worth noting that resistance genes in sludge and water were mainly contributed by different bacteria. Rhizobium and Pseudomonas may be the potential hosts contributed to resistance genes in sludge while Thauera mainly contributed to that in water.

Influence of Class-8 Truck Passing Oncoming Truck Using CFD Simulation

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The commercial vehicle development process needs to consider the vehicle aerodynamics not only in ideal flow conditions, but also in the turbulent real world environment. The turbulent real world environment includes not only atmospheric turbulence, but also the vehicle to vehicle interactions that happen when driving around other vehicles or into and out of the wake of in/on coming vehicles.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;A vehicle driving into the wake of an oncoming vehicle not only experiences an increase in the total aerodynamic forces, it also experiences unsteady transient loads over the vehicle components such as windshield, mirror, sunvisor, door and side fairing. To properly design specific components, designers need to understand the magnitude of unsteady forces on various vehicle components, otherwise these components may fail which imposes warranty and safety risks.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;In this paper, we attempt to understand the various forces acting on the primary vehicle during a passing maneuver. The main purpose is to understand the incremental unsteady forces acting on the major components such as windshield, side door, sunvisor and mirror.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;Result from this study shows, very large swings in side-force magnitude, which could lead to vehicle stability issues for empty trailers that are subjected to large forces acting on little inertial mass. Local forces on isolated components show very high frequency unsteady load that could lead to component fatigue and failure if these loading conditions are not incorporated as part of the vehicle component design.&lt;/div&gt;&lt;/div&gt;

Electric fields control water-gated proton transfer in cytochrome c oxidase

Aerobic life is powered by membrane-bound enzymes that catalyze the transfer of electrons to oxygen and protons across a biological membrane. Cytochrome c oxidase (CcO) functions as a terminal electron acceptor in mitochondrial and bacterial respiratory chains, driving cellular respiration and transducing the free energy from O2 reduction into proton pumping. Here we show that CcO creates orientated electric fields around a nonpolar cavity next to the active site, establishing a molecular switch that directs the protons along distinct pathways. By combining large-scale quantum chemical density functional theory (DFT) calculations with hybrid quantum mechanics/molecular mechanics (QM/MM) simulations and atomistic molecular dynamics (MD) explorations, we find that reduction of the electron donor, heme a, leads to dissociation of an arginine (Arg438)-heme a3 D-propionate ion-pair. This ion-pair dissociation creates a strong electric field of up to 1 V Å-1 along a water-mediated proton array leading to a transient proton loading site (PLS) near the active site. Protonation of the PLS triggers the reduction of the active site, which in turn aligns the electric field vectors along a second, "chemical," proton pathway. We find a linear energy relationship of the proton transfer barrier with the electric field strength that explains the effectivity of the gating process. Our mechanism shows distinct similarities to principles also found in other energy-converting enzymes, suggesting that orientated electric fields generally control enzyme catalysis.

Study on the time-varying extreme value characteristic of the transient loads on a 5:1 rectangular cylinder subjected to a thunderstorm-like wind

A reasonable extreme probability model to estimate the transient loads is essential for structural wind resistance design. The transient aerodynamic characteristics of a 5:1 rectangular cylinder under thunderstorm-like wind are experimentally studied based on the multiple-fan active wind tunnel technique. In this paper, the non-Gaussian characteristics of the transient pressures are analyzed with emphasis on the time-varying skewness and time-varying kurtosis. A generalized time-varying extreme value model for uniformly modulated nonstationary stochastic processes is proposed, which is adopted to study the extreme value of transient loads on a 5:1 rectangular cylinder under a thunderstorm-like wind. Compared with the stationary flow condition, the results show that the non-Gaussian features of the transient pressures is noticeable, which is determined by the time-varying turbulence intensity. The greater the time-varying turbulence intensity, the stronger the non-Gaussian characteristic of the transient loads is, which is consistent with the stationary wind case. Notably, the presented work confirms that the conventional mean extreme value model may seriously underestimate the extreme value of transient loads. Moreover, the extreme values under stationary flow are slightly higher than those under transient wind pressures. The results show that the peak factors in the suction region are significantly greater than that in the reattachment region, and the time-varying peak factors under transient wind pressures are slightly less than in the stationary flow case.

Emission Characteristics and Formation Pathways of Intermediate Volatile Organic Compounds from Ocean-Going Vessels: Comparison of Engine Conditions and Fuel Types.

The lack of emission data for ocean-going vessels (OGVs) and the recent fuel switching make it urgent to enhance the onboard measurement of ship emissions, especially for intermediate volatile organic compounds (IVOCs). This study focused on the IVOC emission characteristics and formation pathways of three OGVs under various engine conditions (power and load) and fuel oils (heavy fuel oil (HFO) versus marine gas oil (MGO)). The results showed that the (1) IVOC emission factors (EFIVOC) of the three OGVs increased with engine power and were higher for MGO (1494.4 ± 421.7 mg/kg) than HFO (1830.5 ± 534.5 mg/kg) and engine load is an important parameter. (2) Engine load and oil type affect the composition and volatility distribution of IVOCs. The proportion of polycyclic aromatic hydrocarbons in IVOCs increased with a higher load, and using MGO shifted IVOC components to a higher volatility in contrast to HFO. (3) The compositions of IVOCs were more like those in fuel oils under low loads than under high loads, indicating that different formation pathways of IVOCs exist for different engine loads. (4) A higher EFIVOC was observed nearshore than in open sea owing to the lower and transient engine load, which indicates the necessity of paying attention to the IVOC emissions for ships.

AC Losses in JT-60SA TF Magnet During Commissioning: Experimental Analysis and Modeling

During the integrated commissioning of JT-60SA tokamak, the Toroidal Field (TF) magnet has experienced fast current discharges which have induced AC losses in its winding packs (WP) and in its casings. Using the thermo-hydraulic sensors network installed at the inlet and outlet of the TF coils, we have performed enthalpy balances to estimate the transient heat loads generated by AC losses. In parallel, we have modeled the hysteresis and coupling losses produced in the WP and the eddy currents losses produced in the casings by such events. We then assess and discuss the consistency between these experimental and first theoretical analyses from the energy balance point of view.

Analysis of slope fracturing under transient earthquake loading by random discrete element method

Earthquake can cause significant rock fracturing in either the short or long terms. A comprehensive analysis of the fracturing mechanism is critical for assessing the risks of potential slope failures, landslides and rock avalanches in seismic prone areas. This study employed 2D discrete element method (DEM) to investigate the fracturing of an intact rock slope of 600 m in base length and 300 m in height, with explicit considerations of material heterogeneity by random field theory. A total of 5400 DEM simulations were performed, and the characteristics of slope fracturing were statistically analysed. The dynamic loading by earthquake has triggered significant amplifications of ground motion and slope damage at the slope crest, resulting in densely spaced and interconnect fractures. These fractures split the slope into a collection of rock fragments with varied shapes, and the fragment size followed the Weibull's cumulative distribution. More than 70% of generated fragments were finer than 0.1 times the initial slope size, while only few large fragments existed at the slope base. The fragment size distribution pattern could quantitatively agree with field observations. The distributions of final slope damage index and cumulated fragmentation energy all followed the normal distribution pattern. The overall bulk seismic energy input into the slope was dissipated mainly at discontinuities and decreased with the increase of slope inclination. • Differential ground displacements exist widely within the slope, which is critical for earthquake induced fractures. • The sizes of the generated rock fragments follow well the Weibull's cumulative distribution. • Statistically, the slope damage index and fragmentation energy all follow the normal distribution pattern. • The slope damage intensity decreases with the increase of slope inclination angle.

Static and transient thermal conductions and associated thermal stresses in an elastic strip with a rigid line inclusion

The problem of a rigid inclusion in an elastic strip under steady or transient thermal loading is studied. The inclusion is assumed to be extremely thin and thermally insulated so that it does not disturb the heat conduction in the strip. The thermal strain and stress fields are obtained by using the singular integral equation technique. The inclusion tip strain and stress are found to be singular. The near tip stresses are expressed in terms of the thermal strain intensity factor. Case studies include the influence of temperature boundary condition, inclusion location and strip width on the thermal strain intensity factor. The highest and lowest values (upper and lower bounds) of the intensity of the thermal strain are identified.

Development of a unified constitutive model coupled with a continuum damage model for design and evaluation of high-temperature components

A unified constitutive model (UCM) coupled with a continuum damage model (CDM) is developed to design and evaluate high-temperature components in the energy, aerospace, and petrochemical industries. While different constitutive models can predict certain aspects of thermomechanical creep-fatigue responses, a generally applicable model for both short and long-term responses, including stress relaxation and tertiary creep/damage, and strain softening has not been available. Hence, this study unifies strain-focused viscoplastic and creep-rupture-focused damage models to predict fatigue, creep, and creep-fatigue interactions using a single set of model parameters. Two CDMs, Kachanov and isotropic damage, are evaluated by coupling these with a modified Chaboche UCM. The strengths and limitations of the original Kachanov and isotropic damage models in predicting a broad set of low-cycle fatigue and creep responses for a commercially important material, modified Grade 91 steel, are determined. Based on the evaluations, a modified isotropic damage model is proposed. The proposed UCM-CDM is experimentally validated against a large set of modified Grade 91 steel responses, including cyclic softening, rate-dependence, short-term stress relaxation, long-term creep, thermomechanical fatigue, and creep-fatigue interaction at temperatures 400 to 625 °C. The UCM is further validated by simulating a set of modified Grade 91 steel notch specimen creep responses. The modified UCM is demonstrated to simulate the influence of stress triaxiality and prior fatigue on creep rupture life. Finally, the proposed UCM is evaluated by analyzing a thick cylinder under thermal transient loading to demonstrate the modified UCM’s applicability for the design and evaluation of high-temperature components.

Determination of extreme responses of USFG's equilibrium glide path hovering in ocean current

The UiS subsea-freight glider (USFG) is a state-of-the-art autonomous vessel designed to be an alternative to existing transportation technologies and serve the demands of small-scale fields for CO2 transportation. Generally, these smaller fields cannot economically justify the costs of large tankers, cargo ships, or underwater pipelines on the seabed, as the transport volume is nominal compared to larger fields. The USFG can travel underwater at an operational depth of 200 m, allowing the glider to carry freight operations without considering ideal weather windows. It can manoeuvre itself underwater by monitoring the flow between the ballast tanks aboard. During the entire mission of the USFG, from capturing to injection locations, it follows a pre-laid saw-tooth path while experiencing transient loads from the ocean current. The extreme surge and heave responses of the USFG are vital for its design. Extreme motion along the surge direction affects the range of the glider (vital for battery design) and the dynamic controller parameters concerning manoeuvrability. For this paper, the averaged conditional exceedance rate (ACER) is employed to scrutinize the extreme motion (surge direction) of the USFG while gliding to a defined depth. This is done when the glider is exposed to an average current velocity of 0.5 m/s and 1.0 m/s. The data used for analysis in this study is obtained from the time-domain simulations carried out on a two-dimensional mathematical model developed in Simulink. The presented ACER method efficiently uses the available data points and accurately predicts the extreme surge responses precisely and accurately. This study can effectively promote the design improvement of the USFG; thus, the safety and economic benefits can be essentially enhanced.

An integrated smart thermo-chemical energy network

Managing the intermittency of renewable sources together with transient (hourly to daily to seasonal) energy demands is one of the principal challenges of delivering a net-zero energy system. Smart multifunctional thermo-chemical energy networks represent an alternative energy network and storage system, a solution based on the distribution of energy via thermo-chemical material rather than thermal energy, gas, fuels or electricity– an option that has scope for integrated short- and long-term energy storage. This is the first research work to realise such a system and demonstrate how it might operate using smart control strategies and how thermo-chemical fluids (TCFs) can be used as a medium for timely energy storage and distribution. The experimental study also describes the effect of steady and variable heat sources on TCF regeneration performance and estimates the potential of thermo-chemical energy networks, which would be particularly beneficial in buildings with high energy consumption for humidity control. This research proves the practicality of the design idea for such a network, which would be governed by centralised control, regenerated by steady or transient heat loads and capable of supplying a variety of demands in an experimental setting. The energy and economic potential of the network were also assessed, identifying temperature and humidity control application scenarios with energy savings of more than 60% compared to conventional operation and payback periods of 6.6–9.7 years.

Weight function procedure for reduced order fracture analysis of arbitrary flaws in cylindrical pressure vessels

Fracture mechanics calculations using the finite element method can be computationally expensive, which makes them challenging to use in engineering evaluations of flaws in pressure vessels. The weight function (WF) technique is a reduced order fracture modeling method that is widely used to greatly reduce these computational costs. Its computational efficiency is essential for use in probabilistic fracture mechanics evaluations of embrittled nuclear reactor pressure vessels (RPVs), due to the large number of sampled flaws that must be evaluated. Although the WF technique is general, it is typically used only for axis-aligned flaws. Recent discoveries of off-axis flaws in operating nuclear reactors have necessitated detailed simulations of such flaws and the interactions between neighboring flaws. This paper presents a generalized WF approach applicable for analyzing arbitrary flaw geometries in thick-walled cylindrical vessels, including surface-breaking and subsurface flaws, which can either axis-aligned or off-axis, and can account for interactions with other flaws. This approach is demonstrated on representative simulations of multiple flaw geometries in a RPV subjected to transient loading conditions. In all cases, the WF technique gives good comparison with benchmark results from direct simulation with greatly reduced computational effort.

Physical-based variable geometry turbines predictive control to enhance new hybrid powertrains’ transient response

Nowadays, internal combustion engine (ICE) concerns regarding fuel consumption motivate engine developers to research new technologies, including turbocharging, downsizing and hybridization. Variable geometry turbines (VGT) have been specifically developed for spark-ignited (SI) ICE in recent years. The transient response of such engines, critical for the new certification cycles and drivability, is mainly governed by the VGT management. This work proposes a physically-based control strategy to govern the VGT position to improve the overall system response. The control system evaluates at each considered time step the VGT position providing the maximum feasible turbocharger acceleration through the energy balance along the turbocharger, considering inertia and physical constraints. Once developed, the strategy is evaluated on a fully-validated one-dimensional engine model under heavy transient load demand operation. The model results are compared with experimental data based on a proportional–integral–derivative controller calibrated for the same transient manoeuvre. The new approach showed equivalent or faster transient dynamics with a substantial reduction in calibration time, reducing the time for implementing new turbocharger technologies for future powertrains. Furthermore, the proposed control’s highly physical basis allows for its application to any other fuelled thermodynamic system, including a variable geometry turbine.

A Strong Form Meshless Method for the Solution of FGM Plates

Laminated composite structures suffer from failure because of concentrations of gradient fields on interfaces due to discontinuity of material properties. The rapid development of material science enables designers to replace classical laminated plate elements in aerospace structures with more advanced ones made of functionally graded materials (FGM), which are microscopic composite materials with continuous variation of material coefficients according to the contents of their micro-constituents. Utilization of FGM eliminates the inconvenience of laminated structures but gives rise to substantial changes in structural design This paper deals with the presentation of a strong formulation meshless method for the solution of FGM composite plates. Recall that the fourth-order derivatives of deflections are involved in the governing equations for plate structures. However, the high-order derivatives of field variables in partial differential equations (PDE) lead to increasing inaccuracy of approximations. For that reason, the decomposition of the high-order governing equations into the second-order PDE is proposed. For the spatial approximation of field variables, the meshless moving least square (MLS) approximation technique is employed. The reliability (numerical stability, convergence, and accuracy) as well as computational efficiency of the developed method is illustrated by several numerical investigations of the response of FGM plates with the transversal gradation of material coefficients under stationary and/or transient mechanical and thermal loadings.

The dynamic stall dilemma for vertical-axis wind turbines

Vertical-axis wind turbines (VAWT) are excellent candidates to complement traditional wind turbines and increase the total wind energy capacity. Development of VAWT has been hampered by their low efficiency and structural unreliability, which are related to the occurrence of dynamic stall. Dynamic stall consists of the formation, growth, and shedding of large-scale vortices, followed by massive flow separation. The vortex shedding is detrimental to the turbine's efficiency and causes significant load fluctuations that jeopardise the turbine's structural integrity. We present a comprehensive experimental characterisation of dynamic stall on a VAWT blade including time-resolved load and velocity field measurements. Particular attention is dedicated to the dilemma faced by VAWT to either operate at lower tip-speed ratios to maximise their peak aerodynamic performance but experience dynamic stall, or to avoid dynamic stall at the cost of reducing their peak performance. Based on the results, we map turbine operating conditions to one of three regimes: deep stall, light stall, and no stall. The light stall regime offers VAWT the best compromise in the dynamic stall dilemma as it yields positive tangential forces during the upwind and downwind rotation and reduces load transients by 75% compared to the deep stall regime.