Steady Load Research Articles

Influence of micromorphology and water content on the rheological properties and performance evaluation model of loess mudflow

Evaluation of the rheological characteristics of loess mudflow is of great significance to ecological environment protection (by loess, we mean a wind-blown Quaternary silt deposit), and geological disaster assessment in the Loess Plateau of China. Rheological characteristics of rheology for loess mudflow are highly variable due to heterogeneity in particle micromorphology and water content, and current rheological models struggle to reconcile the structural dynamics with the equilibrium behavior of soil at different concentrations and microstructures. A rheological study of loess mudflow for five regions on the Loess Plateau was carried out in this investigation, and the results showed that loess transformed from a solid-like stage to a liquid-like stage under steady loads and exhibited significant shear thinning characteristics and shear rate dependence, in which the shear rate less than 2 s−1 was the main region of loess strength attenuation and the maximum yield stress is about 1411 Pa. A smaller water content and more complex particle micromorphology led to a higher yield stress, but there was no significant correlation between flow index and particle shape and water content. Additional structural dynamics and particle fractal theory were then introduced, providing an improved model that could reconcile the structural dynamics and particle micromorphology of loess with its equilibrium behavior at different water contents and shear stresses. All the test data were distributed around a dimensionless master curve. Considering the difficulty of obtaining rheological parameters, an evaluation criterion containing three levels (clay-rich, silt-rich, and sand-rich) for the evaluation of the rheological properties of loess mudflow was proposed, which can reconcile the test results and models under different working conditions. Such an evaluation criterion can also be applied to soils of other textures, providing a straightforward manner to determine the relevant rheological parameters. The research results provide a theoretical basis for ecological environmental protection and geological disaster assessment in the Loess Plateau region based on rheological characteristics.

Partially insulated cracks in orthotropic materials under steady state thermo-mechanical loadings

An attempt has been made to investigate the cracked composite medium with thermally conducting multiple cracks at its interface of the dissimilar orthotropic media subjected to thermal and mechanical loadings. The present article examines the governing equations, the associated differential constraints and boundary conditions those govern the temperature field and stress field. Fourier integral transforms, together with their corresponding inverses, have been employed to convert the singular integral equations into a set of linear equations by using the concept of orthogonality and completeness. The numerical technique, namely the Schmidt method, which employs a polynomial expansion of the unknown functions, is used to solve algebraic equations to determine the desired temperature and stress fields. The semi-analytical findings of the expressions for heat flux intensity factor (HFIF), stress intensity factor (SIF), and crack displacements have been mentioned in the article. Both mode-I and II types of cracks have been studied to investigate the effect of thermal conductivity. Detailed graphical representations effectively illustrate the numerical results and the interrelations between crack lengths, bonded strip width, and the partial conductivity coefficient of the crack surface. As the thermal conductivity coefficient increases, the temperature difference tends to zero. The results reveal that an increase in thermal conductivity decreases the SIFs.

Effects of impedance-boundary-controlled casing treatment on the fan performance with eccentric inlet swirl

An eccentric inlet swirl, a source of circumferential non-uniformity in aero-engines, can compromise the stable operational range of the compression system and potentially jeopardize the safety of the entire flight vehicle. This study experimentally examined the additional effects of an eccentric inlet swirl on an axial fan in comparison with a concentric inlet condition. Then, the effectiveness of an impedance-boundary-controlled (IBC) casing treatment (CT) in extending the stable operating range of the fan under eccentric inlets is evaluated. Steady-state loading and prestall disturbance analyses were conducted using a five-hole probe and high-frequency response pressure transducers to elucidate the instability mechanisms of fans exposed to eccentric inlets. The findings indicate that the eccentric swirl generates localized over-loading regions around the circumference, where abnormal prestall disturbances amplify in amplitude across a frequency range of 0.3 to 0.5 times the blade passing frequency. These characteristics were mitigated when IBC CT was applied over the rotor tip, allowing the fan to operate under concentric inlet conditions. The IBC CT enhances the stall margin of the fan by 9.3–19.6% in response to a range of swirl inlet conditions, suggesting its potential to address the irregularity problems in fans/compressors. The mechanisms by which IBC CT extends the stall margin are discussed from the unique perspective of evaluating steady loading and system damping.

Influence of steady aerodynamic loads on hunting stability of high-speed trains

Influence of steady aerodynamic loads on hunting stability of high-speed trains

In Situ Imaging of Parachute Textile Micromechanics Under Tensile Load

Micromechanics of parachute fabrics under tensile loads are studied using in situ x-ray microtomography. Results are presented for two nylon textiles commonly used in parachute systems, MIL-C-7020H Type III and MIL-C-44378(GL) Type II. Textiles are subjected to incremental tension using a custom apparatus that loads the fabric radially, and the microstructure is imaged sequentially at steady load conditions. Microtomography images are processed using learning-aided segmentation and a custom processing pipeline that tracks the locations and morphological properties of individual tows on 3D datasets. Results are used to reconstruct tow microscale properties and meso-scale strains. Our findings reveal a direct relation between the fabric architecture and the meso-scale mechanics. Warp tow pretensioning during manufacturing is found to affect decrimping and the anisotropy of the textile strains. Areal porosity increase with tension is quantified, and a geometric model for pore opening under incremental load is validated.

Diagnostic and prognostic for prescriptive maintenance and control of PEMFC systems in an industrial framework

This paper designed and defined the framework of prescriptive maintenance and its four axes, for hydrogen-energy systems, considering the constraints of actual systems, to improve durability, availability, reliability, performance, safety and operating costs of these systems. Different data-driven approaches for diagnostic and different approaches for prognostic of Remaining Useful Life (RUL) for Proton Exchange Membrane Fuel Cell (PEMFC) systems are discussed. The use of measures always available on actual systems allows to validate the approach in an industrial framework. Several diagnostic algorithms (classification and clustering) are compared to find the best compromise between computation time and accuracy in an online diagnostic framework. For the prognostic part, the data set comes from experimental tests performed under steady load for a PEMFC stack. A degradation trend of PEMFC stack voltage is extracted from these data and two well-known prediction algorithms namely Bidirectional Echo State Network (BiESN) and Bidirectional Long-Short Term Memory network (BiLSTM) are tested and compared to evaluate the robustness of the PEMFC voltage prediction for RUL estimation. The diagnostic and prognostic approaches proposed in this paper are first steps towards future work related to prescriptive maintenance for hydrogen-energy systems (PEMFC, Proton Exchange Membrane Water Electrolyzer and hybridization of the two).

Long-term plasma exposure of ITER-like W/Cu monoblocks with pre-damaged surfaces in EAST experiments

In the ITER and future fusion devices, W/Cu monoblocks will be used as divertor target which are exposed to both steady state heat load and transient heat flux. Especially, the transient heat flux up to 10 GW m−2 during plasma disruption, is expected to induce the shallow surface damages, such as melting, and even boiling of W/Cu monoblocks. Thus, the performance of damaged W/Cu monoblocks under subsequent long-term plasma discharges is a key concern that needs to be verified and tested on existing tokamaks. Since 2022, a new type of main limiter composed of ITER-like W/Cu monoblocks has been installed and tested in EAST. The surface of W/Cu monoblocks of the limiter was damaged by the transient heat flux during the early stages of plasma construction. Subsequently, they were subjected to long-term plasma discharges over 2600 shots in normal plasma discharge conditions. This circumstance conveniently facilitates the discussion of the performance of W/Cu monoblocks with damaged surfaces especially a melting edge with hill structure under prolonged exposure to plasma. In general, the shallow damage resulting from transient heat flux on W/Cu monoblocks appears to have minimal impact on the heat exhaust capacity under steady-state heat loads, as indicated by both experimental monitoring and numerical simulation results. However, shallow melting, leading to a change in surface structure and the formation of hills, could theoretically increase local temperatures, creating potential hot spots. This phenomenon requires further validation through dedicated experiments. Moreover, the brittleness of the near-surface layer may give rise to brittle destructions, such as cracks and even dust particles, posing an additional concern. These findings yield unique qualitative conclusions that can be referenced for ITER and other fusion devices.

Three-phase model of SCIG-based variable speed wind turbine for unbalanced DSLF analysis

Steady state performances of the electric power distribution system are normally assessed or evaluated based on load flow analysis. To properly carry out the analysis, a valid steady state load flow model of each distribution system component, including the wind power plant (WPP), needs to be developed. The present paper proposes a method for modeling and integrating squirrel cage induction generator (SCIG)-based variable speed WPP into a three-phase unbalanced distribution system load flow (DSLF) analysis. The proposed method is based on a single-phase T-circuit model of fixed speed WPP, which has successfully been applied to balanced electric power systems. In the present work, the single-phase T-circuit model is extended and modified to be used in steady state load flow analysis of three-phase unbalanced distribution systems embedded with SCIG-based variable speed WPP. Results of the case studies confirm the validity of the proposed method.

Comparative study on lateral vibration characteristics of the head and tail cars of high-speed trains under unsteady aerodynamic loadings

With the increasing speed of high-speed trains, abnormal vibrations in the tail car pose a threat to its overall stability and running safety. In this study, the aerodynamic and multibody dynamics models for 3-car and 8-car trains are established. The flow field characteristics and dynamic performance around the head and tail cars under both steady and unsteady aerodynamic loadings at a speed of 400 km/h are compared. The results reveal that the surrounding flow field exhibits highly pronounced unsteady characteristics, directly leading to a significant impact of unsteady aerodynamic loadings on the train's dynamic response. Under unsteady loadings, the lateral stability indexes, displacement, velocity, and acceleration of the tail car are all worser compared to those of the head car. Additionally, the larger oscillation amplitudes and frequencies closer to the suspension modal frequencies under unsteady aerodynamic loadings contribute to more pronounced lateral displacements and accelerations, constituting a crucial factor in the observed ‘tail swing' phenomenon for the high-speed train.

Thin-airfoil aerodynamics in a rarefied gas wind tunnel: A theoretical study

We study the steady aerodynamic field and loadings about a thin flat plate placed in a wind tunnel under non-continuum conditions. Considering a two-dimensional straight tunnel configuration, the flow is driven by either density or temperature differences between the inlet and outlet tunnel reservoirs, producing a pressure gradient across the channel. Focusing on highly rarefied conditions, we derive a semi-analytic description for the gas flow field in the free-molecular limit for diffuse- and specular-wall configurations. The solution is valid at arbitrary differences between the inlet and outlet reservoirs as well as plate angles of attack α. The results are compared with direct simulation Monte Carlo calculations, indicating that the free-molecular description is valid through O(1) plate-size-based Knudsen numbers. The aerodynamic lift and drag forces are evaluated and their variations with α, reservoir conditions, and tunnel size are analyzed. At a fixed pressure ratio between the outlet and inlet reservoirs, the density-driven flow generates higher aerodynamic loads compared with its counterpart temperature-driven configuration, in line with the associated larger mass flow rate in the former. The results are discussed in light of the existing rarefied-gas description of the free-stream (non-confined) problem.

Thermal and structural analysis of the DONES target system under steady state and transient loading conditions

One of the crucial steps in the European Roadmap to the realisation of fusion energy is the design and construction of the Demo-orientated NEutron Source (DONES) facility. DONES is a fusion-like neutron source, based on the International Fusion Materials Irradiation Facility (IFMIF) concept, aimed at qualifying and testing the materials to be used in fusion reactors. The Target System (TSY) is a crucial system as it is the component where the interactions between deuterons and a liquid lithium target, flowing on a solid surface (i.e. the Back Plate), take place to produce neutrons for irradiating the testing materials. In this regard, an investigation campaign has been performed to evaluate the thermo-mechanical behaviour of the DONES TSY under selected steady state and transient loading conditions, in light of the most recent design updates (new bellows and connection systems). The first part of the assessment concerned the analysis of the TSY under the normal operation steady state loading scenario. A detailed 3D FEM model has been set up, considering the newest updates of the TSY geometry and of the operational parameters, and a thermo-mechanical analysis has been launched. Results have been mainly checked in terms of TSY global deformation, focusing on the Back Plate and on the connecting bellows displacements, in order to exclude overlapping with the High Flux Test Module and misalignments with the beam footprint. Afterwards, since the lithium inlet temperature has been increased from 250 °C to 300 °C, a transient thermo-mechanical analysis of the TSY under the start-up loading conditions has been performed to check if it is able to withstand the hotter lithium flow according to the RCC-MRx criteria. Therefore, the reference pre-heating strategy has been adopted, assessing the thermal and mechanical behaviour of the TSY, focusing on the Back Plate. The obtained results are presented and critically discussed, suggesting important recommendations for the follow-up of the design.

Mathematical model of discharge and charge in rechargeable polymer based lithium-ion battery

Shepherd’s model is considered as an improved and simple to-apply battery dynamic model. The experimental nominal parameters of five different capacities of Lithium-ion Polymer battery samples are established from the manufacturer’s datasheets. The discharge and charge dynamics of the battery sample with the highest capacity, 3100 mAh are examined and validated. The clarity to derive the dynamic model parameters from the battery datasheet is a fascinating attribute of this model. The experimental database is utilized to study its dynamic feature and subsequently the dynamic battery model, which describes the relationship between the state of charge, the open circuit voltage and ambient temperature. The model is implemented and simulated by using MATLAB/Simulink tools. The current charge-discharge equations describe the optimized electrochemical activities with sustainable long cycle duration. The temperature model brings under control the aging effect, which plays down on the energy capacity of the battery. A steady load of 5 A is linked to the battery and used in a detail simulation of a direct current machine in determination of load effect. The compatibility of these equations and simulations implies that Shepherd’s model is promising to provide guidelines for the analysis of discharge and charge in rechargeable polymer based lithium-ion batteries. The results show that the model can precisely illustrate the dynamic behavior of the batteries.

Calculation Method for the Transient Hot-Spot Temperature Rise of Oil-Immersed Bushing in High-Speed Railway

Traction oil-immersed bushing is the only channel for connecting the high-speed railway system with the external power grid, and its transient hot spot is one of the most important factors reflecting its operation status. Since the traction load of a high-speed railway has obvious impulse characteristics, the existing calculation method for bushing given in IEEE Std C57.19-100™-2012 is incompatible because it is designed for steady electrical loads. Thus, in this paper, the equivalent hot spot temperature rise of the bushing under varying traction loads is calculated by the traction parameters (i.e., operating time <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_ot</i> , interval time <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_it</i> , and per unit transient traction current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_tc</i> ). Then, the difference value of transient hot spot temperature rise is modified by analyzing the change of transient hot spot temperature rise under varying traction loads. Finally, a calculation method is proposed for the transient hot spot temperature rise of the oil-immersed bushing in high-speed railway under different traction loads. A case study of a 110 kV oil-immersed bushing shows that the proposed method is speedy and accurate.

The Steady-State Response Spectrum of Bridge Structures under Statistical Steady Traffic Flow Loads

The Steady-State Response Spectrum of Bridge Structures under Statistical Steady Traffic Flow Loads

Acoustic mechanisms and tonal noise control of contra-rotating ducted fan by rotating speed regulation

The contra-rotating ducted fan (CRDF) involves more tonal noise modes compared with rotor/stator and single-rotor ducted fans. According to the present experiment on small-scale CRDF the dominant tone is concentrated at the harmonics of blade passing frequencies of front-rotor and rear-rotor as the modes of (m,0) and (0,n), as well as the modes (m,m) respectively. To investigate the flow mechanisms and sound propagation characteristics of these three types of tonal noise, unsteady three-dimensional numerical simulation was implemented under different rotational speed matching for CRDF and isolated rotor. Steady load and thickness noise were systematically analyzed using Hanson model. And the generation mechanisms of wake interaction noise and their contribution ratios were analyzed utilizing the duct sound model.It was indicated that tonal noise at the mode of (m,0) (0,n) of CRDF is primarily determined by the blade thickness and steady load. Compared with the single-rotor, the contra-rotating rotors could improve the load allocation between the front and rear rotor, resulting in the forward noise reduction with the constant thrust. Increasing the rear rotor speed enhances the contribution of potential flow interaction noise from the front rotor. Subsequently the front rotor load and wake interference are weakened, leading to noise reduction of approximately 0.3 dB for the rear rotor. However, the potential flow disturbance is intensified which causes noise increase by approximately 3.5 dB on the front rotor. But, increasing the front rotor speed will strengthen both the potential flow interference intensity on the pressure surface of the front rotor blade and the wake disturbance intensity on the leading edge of the rear rotor blade. This generates approximately 3 dB and 3.5 dB noise level increases for the front and rear rotors, respectively. As a result, appropriately raising the rear rotor speed can achieve a reasonable load allocation, and balance the potential flow interaction and wake interaction to realize the whole noise reduction without thrust loss.

Consideration of tungsten recrystallization in plasma facing components design

Tungsten recrystallization leads to a modification of material properties including a reduction in hardness, strength and thermal shock resistance. The recrystallization assisted material degradation compared to the as-received state has made it very undesirable as demonstrated in high heat flux testing. Consequently, tungsten recrystallization temperature has been widely used as the upper limit of material surface temperature under steady state loading conditions. However, this study shows that recrystallization is inevitable where steady state or transient loads are high enough. The efforts to retard recrystallization will only reduce the recrystallized depth but cannot completely avoid it. While it is demonstrated the material will be weakened by recrystallization, the recrystallized depth plays a relatively small role in deciding the fatigue lifetime once it is recrystallized. Therefore, it is recommended that the geometry and fracture toughness of the design is optimised to reduce crack growth into the component. The design criterion against tungsten recrystallization under steady state loading conditions has also been proposed for engineering design stages.

Simplified Control Method for Unified Power Quality Conditioner (UPQC)

Unified Power Quality Conditioner (UPQC) for harmonic elimination and simultaneous compensation of voltage and current, which improves the power quality offered for other harmonic sensitive loads. UPQC consist of combined series active power filter that compensates voltage harmonics of the power supply, and shunt active power filter that compensates harmonic currents of a non-linear load. In this paper a new control algorithm for the UPQC system is optimized and simplified without transformer voltage, load and filter current measurement, so that system performance is improved. The proposed control technique has been evaluated and tested under dynamical and steady state load conditions using PSIM software. The laboratory prototype experimental results for shunt active filter part are given.

On the balance between the tonal and broadband noise of isolated propellers

This study presents a predominantly numerical and theoretical investigation into the balance of tonal and broadband noise due to an isolated propeller in uniform motion. The predicted trends in the balance between tonal and broadband noise radiation with varying blade number and speed of rotation is supported by preliminary experimental measurements. Here, we assume that the dominant noise generation mechanisms are the tones due to steady loading and blade thickness, while the broadband noise is due to boundary layer scattering at the trailing edge. The study also provides a detailed comparison between the tonal and broadband formulations to highlight their similarities and differences. In this paper, we show that the main differences in the behaviour and character of the tonal and broadband spectra and directivities are due to the number of acoustic modes that can be excited. This paper presents a parametric study in which the variation in tonal and broadband noise is investigated as a function of blade tip Mach number ( M t) and blade number ( B) whilst maintaining constant solidity and thrust. This study is repeated for three NACA airfoil profiles. It is found that tonal noise dominates at low blade number and low frequency and/or higher tip speeds, while broadband noise is the major contributor at high-frequencies and at high blade number and low tip speeds. The results show a clear distinction between the combinations of M t and B that are dominated by tonal and by broadband noise. These results are interpreted from fundamental principles relating to modal radiation efficiencies. We confirm this trend of balance between tonal and broadband noise with measured noise at different B and M t. The results of this paper will serve as useful guidelines for preliminary propeller design.

A decision-making model for prediction of a stable disease course in chronic hepatitis B patients

Patients with chronic hepatitis B (CHB) are regularly monitored for HBV DNA and liver enzymes in order to assess disease progression and the need for antiviral therapy. Identifying patients with a stable course of disease can potentially prolong the intervals between visits, withhold unnecessary tests and save money. Accordingly, we aimed to find predictors for a stable disease course in patients with CHB. 579 patients with CHB, who were followed in a tertiary referral center between January 2004–December 2018, were retrospectively analyzed. Patients with low and steady viral load titer (< 2000 IU/ml) and normal ALT levels (< 40 IU/ml) in 6 consecutive clinic encounters were considered to have a stable course of CHB. A stepwise multivariate logistic regression analysis and a decision tree model were used to identify predictors of a stable disease course. Following exclusion of ineligible patients, a total of 220 patients were included in the final analysis. 64/220 patients had a stable disease course. Patients with a stable disease were older (62.99 ± 12.36 Vs. 54.07 ± 13.64, p < 0.001) with a higher percentage of women (53% vs. 38%) and had lower baseline levels of AST, ALT and viral load (VL). In a multivariate analysis, age (OR 0.94, 95% CI 0.91–0.98), baseline ALT (OR 1.06, 95% CI 1.01–1.1) and VL (OR 1.05 95% CI 1.02–1.08), were significantly associated with a stable disease. In a decision tree model, patients 46–67 years old, with baseline VL < 149 IU/mL and ALT < 40 IU/mL had the best probability (91%) for a stable disease course over 4.4 ± 2.2 years. We conclude that integrating patients’ age with baseline VL and ALT can predict a stable disease course in patients with CHB off treatment.

Neutron irradiation effects on the low cycle thermal fatigue performance of first wall mock-ups

For the first wall (FW) of ITER, beryllium will be the plasma facing material and has to sustain high thermal, particle and neutron loads. In order to assess the synergistic effects of thermal and neutron loads in total ten Be-armored FW normal heat flux (NHF) mock-ups were produced consisting of two Be flat tiles each joined via hot isostatic pressing (HIP) to a CuCrZr heat sink and a steel support structure by different manufacturing routes to assess the most promising ones. Five of them were neutron irradiated, two at Centrum Výzkumu Řež in Czech Republic and three in the High Flux Reactor at NRG in the Netherlands. The remaining mock-ups were kept as reference. All flat-tile mock-ups had two Be-tiles and were exposed to cyclic steady state heat loads in the electron beam facilities JUDITH 1 and 2 up to a maximum power density of 3.75 MW/m2, in order to find the damaging threshold. A screening step using 1 MW/m2 was performed after finishing each loading step and after failure for direct comparison and detection of any deterioration caused by the cycling. Despite being still in the early development phase of Be joining, all mock-ups sustained the cycling up to at least 2.75 MW/m2 and clear differences in the performance of irradiated vs. non-irradiated mock-ups were observed.