Loading Method Research Articles

Hydroxyapatite and pore former effects on the microstructure and mechanical strength of porous pellets loaded with Lactobacillus

Porous hydroxyapatite (HAP) pellets were prepared by extrusion/spheronization/sintering and loaded with Lactobacillus (La-5). Micronized (PFm) or coarse size (PFc) microcrystalline cellulose were the pore formers, while HAP grades from Budenheim (Tri-cafos®) and Sigma-Aldrich with different specific surface (Sw) were the substrates. Green pellets were heated to sublime microcrystalline cellulose, followed by sintering to form porous pellets. These were characterized by electron/optical microscopy/image analysis, porosimetry, nitrogen sorption and mechanically. Stronger pellets resulted from the high Sw HAP and PFm, and larger pores from the low Sw HAP and PFc. HAP origin impacted on pellet strength. Two loading methods were applied: (i) immersion of pellets in La-5 suspension and (ii) injection of suspension into pellets under vacuum. The latter gave 3-x higher loading, which was maximum for the Tri-cafos® 250 HAP/PFc pellets with larger pores that allowed entrance of bacteria, but adequate strength to resist disintegration during loading. La-5 viability in 250 HAP/PFc pellets was 1.2 × 108 CFU/g.

Effect of external prestressing on the special shear lag behavior of precast box girder bridges

The shear lag behavior exhibited by precast segmental box girders (PSBGs) under concentrated external prestressing differs significantly from that observed in box girders subjected to vertical loads. To study the special shear lag behavior of PSBGs under external prestressing, a theoretical analytical method was developed based on the classical energy variational principle. In this analysis, the effect of external prestressing was decomposed into axial compression and bending effects through the equivalent load method. For each of these effects, appropriate longitudinal warping displacement modes were assumed, and the total energy functional expressions of the system under these two effects were further established. The governing differential equations for the two effects were derived using the principle of energy variation. Analytical solutions for the normal stress of the beam section under axial compression and bending effects were deduced, and corresponding boundary conditions were obtained. Subsequently, the normal stress of the section under the two effects was superimposed to obtain the comprehensive normal stress distribution curve of the beam section under external prestressing. The reliability of the theoretical analysis method was validated through a comparison of the theoretical analysis results with experimental and numerical analysis results.

Backbone curves of subgrade silty filler under intermittent train-induced loading

The loading intermittence duo to the time interval between adjacent passing trains is conducive to improving the dynamic stability of railway subgrade, but this intermittence effect is always ignored in existing experimental studies on the dynamic characteristics of subgrade fillers in which a continuous cyclic loading method was adopted to simulate the long-term train-induced loading on subgrade. This paper aims to study the backbone curves of subgrade silty filler under intermittent train-induced loading, considering the time interval between adjacent passing trains. By conducting a series of intermittent cyclic triaxial tests on silty filler, the backbone curves of each loading stage were constructed, and the effects of loading intermittence on the backbone curves were elaborated. The experiment results indicate that the loading intermittence enhances the resistance of subgrade silty filler to the dynamic loading and is conducive to the upward deviation of the backbone curves. The loading intermittence could effectively increase the ultimate value of dynamic stress amplitude that the silty filler could bear under cyclic loading, but has little effect on the maximum/initial resilient modulus. The backbone curves increase approximately linear under the states of plastic shakedown and plastic creep, but show significant nonlinearity after including the incremental collapse samples. Hyperbolic models for backbone curves such as H-D model and its improvement model could be adopted to characterize the backbone curves of silty filler under intermittent loading, and the normalization of H-D model was also discussed to integrate the influencing factors (i.e., moisture content and confining pressure) of the backbone curves.

Aerodynamic fatigue evaluation of the equipment cabin of high‐speed trains based on sub‐zone loading method

AbstractThe equipment cabins of high‐speed trains encountered alternating pressure loads during operation. A fatigue evaluation methodology based on sub‐zone aerodynamic loading was proposed. Theoretical model was given between pressure load at each zone and the accompanying six structural stress components. Stress recovery matrix was formulated by finite element analysis (FEA) in sub‐zone loading cases to relate the stress to the measured pressure loads. Vehicle test gathered the pressure time‐history data of cabin sub‐zones at the head car in different ambient conditions, from which the two‐dimensional stress spectrum was derived by rain‐flow counting. The fatigue damage of welds was then assessed utilizing the Miner's and Corten Dolan's rules, yielding maximum equivalent damages of 0.72 and 0.23, respectively. The structural fatigue damage under high environmental wind conditions was 1–3 times greater than in calm weather. Nonetheless, the fatigue damage incurred by the metal matrix was significantly lower, demonstrating a substantial safety margin.

Utilizing ASCE/SEI 7 to Estimate Wind Speeds for Forensic Investigations

The American Society of Civil Engineers/Structural Engineering Institute (ASCE/SEI) 7 standard is utilized to determine design wind loading on buildings and other structures. However, it can also be utilized in a forensic capacity to approximate a wind speed that would cause specific conditions to occur, such as the overturning of a structure. This paper provides a brief overview of the ASCE/SEI 7 method for wind loading and discusses the use of various adjustment factors used to determine the wind on structures, including wind directionality factor, velocity pressure coefficient, topographic factor, and the ground elevation factor. A clear understanding of these factors — and how to apply them — is crucial to estimating a wind speed and resulting force to cause a particular event or condition to occur.

A multi-core fiber coupler without a central core

An efficient method for fabricating multi-core fiber couplers based on the thermal diffusion technique is proposed to realize the connection of single-mode fibers to multi-core fibers without a central core. The fabrication efficiency of the multi-core fiber coupler is improved by fiber-loaded hydrogen. The simulation results show that the single-mode fiber and the multi-core fiber can be coupled stably and efficiently by using the designed double-clad fiber to connect the single-mode fiber and the multi-core fiber. Double-clad fiber and multi-core fiber were loaded with hydrogen to enhance the dopant diffusion rate. Three-dimensional refractive index measurements of the multi-core fiber coupler show that the dopant diffusion rate and the diffusion zone length of the hydrogen-loaded fiber are significantly increased compared to the original fiber. These enhancements contributed to the shorter fabrication time of multi-core fiber couplers. The multi-core fiber couplers fabricated by thermal diffusion technology have the advantages of high coupling efficiency, high integration, simple manufacture, and high mechanical strength. Enhancing the diffusion rate of optical fibers by using the hydrogen loading method will increase the application potential of multi-core optical fiber couplers prepared by thermal diffusion technology, and accelerate the translation of multi-core fibers toward optical communication and optical fiber sensing.

Novel framework for predicting constraint effects on fracture toughness using an elastic–plastic phase field model and modified boundary layer formulations

Fracture toughness is dependent on geometry according to a phenomenon known as the constraint effect on fracture toughness. In this paper, we propose a framework to predict constraint effects on fracture toughness using an elastic–plastic phase field model and modified boundary layer formulations. An elastic–plastic material was adopted because constraint effects are typically related to plastic deformation at the crack tip. Modified boundary layer formulations were used as loading methods to control phase field evolution at the crack tip. Numerical results indicate that fracture toughness increases with negative T-stress. The effects of yield stress and the linear hardening coefficient on constraint effects were also investigated. The results revealed that the variation in fracture toughness was greater in materials with low-strain hardening and yield stress compared to that in materials with high-strain hardening and yield stress. Finally, the variation in cleavage fracture toughness as predicted by our framework with a limited set of available experimental data was evaluated. The trend of the predicted results is consistent with that of the experimental results.

Direct tensile damage process of calcite vein shale based on 3D CT reconstruction

AbstractFrom core observations of shales of the Niutitang formation in the northern part of Guizhou Province, China, calcite was often found to act as a natural fracture filler and affect the extension of fractures in hydraulic fracturing. Therefore, it is crucial to understand the tensile mechanical behavior of shales by calcite veins. In this paper, by computed tomography scanning of shales containing calcite veins of different dip angles from the Niutitang formation, a three‐dimensional numerical model reflecting the internal fine structure of the shale was constructed. Direct tensile numerical simulations were carried out to investigate the effect of calcite veins at different angles on the fine‐scale damage process and mechanical properties of shale. The experimental results show that the tensile capacity of the shale increases with the increase in calcite veins. Depending on the dip angle of the calcite vein, the damage pattern of the shale is divided into three types of damage: pull‐off damage along the calcite vein, jagged damage, and horizontal damage perpendicular to the loading method. At high dip angles, the shale damage is more intense and the fracture network more complex. The temporal and spatial characteristics of the acoustic emissions provide a good indication of the microscopic behavior of the shale specimens during the damage process. The box dimension method was used to calculate the fractal dimension of the shale specimens at the final damage, and it was found that the damage was more intense and the fracture network was more complex at high dip angles, and there was an angular threshold.

An ultra-short-term forecasting method for multivariate loads of user-level integrated energy systems in a microscopic perspective: based on multi-energy spatio-temporal coupling and dual-attention mechanism

An ultra-short-term multivariate load forecasting method under a microscopic perspective is proposed to address the characteristics of user-level integrated energy systems (UIES), which are small in scale and have large load fluctuations. Firstly, the spatio-temporal correlation of users’ energy use behavior within the UIES is analyzed, and a multivariate load input feature set in the form of a class image is constructed based on the various types of load units. Secondly, in order to maintain the feature independence and temporal integrity of each load during the feature extraction process, a deep neural network architecture with spatio-temporal coupling characteristics is designed. Among them, the multi-channel parallel convolutional neural network (MCNN) performs independent spatial feature extraction of the 2D load component pixel images at each moment in time, and feature fusion of various types of load features in high dimensional space. A bidirectional long short-term memory network (BiLSTM) is used as a feature sharing layer to perform temporal feature extraction on the fused load sequences. In addition, a spatial attention layer and a temporal attention layer are designed in this paper for the original input load pixel images and the fused load sequences, respectively, so that the model can better capture the important information. Finally, a multi-task learning approach based on the hard sharing mechanism achieves joint prediction of each load. The measured load data of a UIES is analyzed as an example to verify the superiority of the method proposed in this paper.

Anisotropic thermal expansion based on a novel metamaterial

Metamaterials exhibiting exceptional thermoelastic properties are emerging as promising candidates for scientific and engineering applications. Previous studies on mechanical metamaterials with negative thermal expansion (NTE) have primarily focused on enhancing isotropic NTE, often resulting in a high coefficient of thermal expansion (CTE) but low stiffness that characterizes bending-dominated NTE metamaterials. In this study, we proposed a novel mechanical metamaterial with significant anisotropic thermal expansion behavior and substantial stiffness based on the cross structure, re-entrant structure, and triangular structure with NTE. The programmable CTE and effective elastic modulus were analytically derived using the unit load method and stiffness matrix method, respectively, which were validated by numerical results obtained from finite element analysis (FEA). Drawing inspiration from the body-centered cubic and face-centered cubic strategies, two types of extended three-dimensional metamaterials can be obtained. The results demonstrate that a larger length ratio λ and angle θ3 can enhance the NTE effect, while reducing the Young's modulus. The maximum magnitudes of NTE and positive thermal expansion (PTE) are achieved at approximately θ2 = 90°, resulting in a decreased stiffness and slight negative Poisson's ratio (NPR). By adjusting the angles θ2 of re-entrant structures, six distinct anisotropic thermal expansion behaviors can be obtained in this planar metamaterial. Furthermore, a wider range of isotropic CTE as well as an extended range of anisotropic CTE can be achieved in the present metamaterial compared to its original metamaterials. The proposed metamaterial can be combined with traditional triangle metamaterials to enhance thermoelastic properties. The analysis also provides valuable insights into designing metamaterials with large CTE, optimal stiffness, and lightweight properties simultaneously for engineering applications.

I-V Characteristics Measuring System for PV Generator based on PDM Inverter

This paper presents a new method to characterize photovoltaic panels. The power electronic converter used is a Pulse Density Modulation (PDM) inverter. In this method, the inverter plays two roles: First, it is a DC inductor emulator. Second, it allows assembly between inductive and capacitive load methods. The PDM inverter is adapted to operate at very high switching frequency. In this application, it avoids the difficulties of making DC inductors with high DC current and its control remains very simple. This is an asset for increasing the power, power density and rapidity of tracers based on this method. The main disadvantage of this method, compared to methods based on DC-DC converter, is the use of twice as many semiconductor components. But this disadvantage can be compensated by a gain on reactive components. The simulations and experimental results of the proposed system are shown.

Improvements in Frequency Control of an AC Microgrid by Means of Micro-Hydropower Combined Flow-Reduced Dump Load Control Method

Load Frequency Control (LFC) is an issue of top importance to ensure microgrids (MGs) safe and reliable operation in AC MGs. Primary frequency control of each energy source can be guaranteed in AC MGs in order to integrate other energy sources. This paper proposes a micro-hydro frequency control scheme, combining the control of a reduced dump load and the nozzle flow control of Pelton turbines operating in isolated from electricity grid. Some researchs have reported the integration of dump load and flow control methods, but they did not reduce the dump load value and adjust the nozzle flow linearly to the power value demanded by users, causing the inefficient use of water. Simulation results were obtained in Matlab®/Simulink® using models obtained from previous research and proven by means of experimental studies. The simulation of the proposed scheme shows that instantaneous frequency variation is about 2 % even for perturbations magnitude up to 12 %. The validation result shows a 60 % reduction in overshoot and settling time of frequency temporal behaviour operating the micro-hydro autonomously.

Insight into the liposomal encapsulation of mono and bis-naphthalimides.

Mitonafide-loaded liposomes are a promising strategy to overcome the neurotoxicity observed in clinical trials for this drug. This study investigates the influence of loaded mitonafide or a dimer analogue on different liposomal formulations and their therapeutic efficacy in vitro. Physicochemical properties of the liposomes were manipulated using different loading methods (namely bilayer or core loading) and varying the rigidity of the bilayer using distinct phospholipid compositions. Our results demonstrated that the mitonafide dimer analogue had a comparable encapsulation efficiency (EE%) into the liposomes when loaded into rigid or flexible bilayers in contrast to the low mitonafide monomer EE%. A pH gradient core loading method resulted in a more efficient mechanism to load the monomer into the liposomes. DOSY NMR and spectrofluorometric studies revealed key differences in the structure of the vesicles and the arrangement of the monomer or the dimer in the bilayer or the core of the liposomes. The in vitro assessment of the formulations using MDA-MB-231 and RT-112 cells revealed that a flexible lipid bilayer allows a faster drug release, which correlated well with the spectroscopy studies. This study investigated for the first time that the characteristics of the lipid bilayer and the loading method influence the encapsulation efficacy, colloidal properties, photoactivity and stability of mono and bis-naphthalimides loaded in a liposomal carrier, essential factors that will impact the performance of the formulation in a biological scenario.

ШЕСТНАДЦАТИУЗЛОВОЙ ЭЛЕМЕНТ ОБОЛОЧКИ С МАТРИЧНОЙ СХЕМОЙ СТАБИЛИЗАЦИИ

A sixteen-node finite element of a thin-walled shell is designed using a matrix stabilization scheme based on the introduction of the Hellinger-Reisner functional with independent deformation. Initially, the assumed independent deformation is divided into a lower order part and a higher order part. The stiffness matrix corresponding to the lower order assumed deformation is equivalent to the finite element stiffness matrix of the assumed displacement model with a reduced integration scheme. Spurious kinematic modes of the finite element are suppressed by introducing a stabilization matrix associated with a correctly selected set of assumed higher order deformation fields. As an example, a cylindrical shell with given geometric parameters and elasticity characteristics (elastic modulus, Poisson's ratio), loaded with concentrated forces at two opposite points, was considered. The problem considered fixed boundary conditions. Due to the symmetry of the geometry and load, only one octant of the shell was modeled with various finite element meshes, including irregular ones. The table showed the dimensionless deflections of the shell with fixed ends at the point where the concentrated force is applied. Good convergence is observed when the mesh of the finite element model is refined. There is no rigorous analytical solution for the presented case with fixed ends. The computational results show that this finite element can be used to provide reliable solutions for calculating the stress state of thin plates and shells irrespective of the curved geometry of the element, loading method and pinched boundary conditions. The presented element can be used to solve various modelling problems, as well as to test the performance of other shell elements.

Dynamic load altering attack detection based on adaptive fading Kalman filter in smart grid

AbstractThis paper mainly studies a detection method of dynamic load altering attacks (D‐LAAs) in smart grids. First, communication factors are considered, and a smart grid discrete system model under D‐LAA attack is established. Second, for closed‐loop D‐LAAs, an adaptive fading Kalman filter (AFKF) is designed to estimate the states of smart grids with Gaussian noise in real time, and a Euclidean distance ratio detection algorithm based on AFKF is proposed to detect D‐LAAs. Moreover, the proposed detection algorithm can identify D‐LAAs even in the presence of noise in the measurement data, significantly enhancing the speed of attack detection. Finally, take a smart grid with three generators and six buses as an example. Its feasibility and effectiveness of the Euclidean distance ratio detection algorithm are verified by simulations. The simulations are carried out through the real‐time hardware‐in‐the‐loop simulation platform, which is mainly composed of StarSim and multi‐tasking devices.

End-to-End Steady-State Adaptive Slicing Method for Dynamic Network State and Load

End-to-End Steady-State Adaptive Slicing Method for Dynamic Network State and Load

Numerical analysis of influencing factors on wave load for an amphibious aircraft

Numerical method of wave load for an amphibious aircraft is carried out in this paper, and its effectiveness is verified by comparing with towing tank model test. It shows that at the same wavelength and speed, the aircraft’s wave load is positively correlated with the change of wave height, but with the increase of wavelength, the difference shows a gradually decrease. And wave load is positively correlated with the speed, the greater the speed, the greater the wave load is. The wave load decreases with the increase of the wavelength. The peak load generally occurs in the short wave state of 1.2 times the length of the fuselage. With the increase of the wavelength, the aircraft load gradually decreases.

Математическая модель электротехнического комплекса с накопителем электрической энергии для испытания асинхронных двигателей

The research highlights the problem of developing repair infrastructure for new rolling stock, including those with asynchronous traction motors. Therefore, an electrical engineering complex for testing asynchronous motors was chosen as the object of research. The scheme of testing a pair of asynchronous machines using the method of mutual loading is considered. To smooth out current surges in transient modes, an electric energy storage device is used in this scheme. As a result of the research, a mathematical model of the test circuit in question was obtained, which considered an energy storage device connected to a DC link of the test circuit. The solution of the test problem to verify the operability of the considered circuit showed its high efficiency in smoothing current surges in transient modes in the mutual load circuit.

Net load forecasting method in distribution grid planning based on LSTM network

Distribution grid planning involves multiple nodes, lines, equipment, and other elements. Due to the large scale of the system, there are complex interactions in space. The net load is affected by the load changes of different nodes. If this spatial complexity is not fully considered, the net load prediction results may be inaccurate. Therefore, in order to ensure the effect of net load forecasting, a method of net load forecasting in distribution grid planning based on the Long Short-Term Memory (LSTM) network is proposed. This method fully considers the characteristics of distribution grid planning and constructs a net load forecasting model for distribution grid planning based on the LSTM network. This model selects the 3σ criterion detects and corrects the singular values in the historical load data, and obtains the reasonable maximum time series results of each day; The adaptive noise complete set empirical mode decomposition method is used to decompose the sequence results and generates Intrinsic Mode Function (IMF) components of each time series; According to the component results, a load forecasting model based on LSTM network is constructed, and the initial learning rate and cell number parameters of LSTM network are optimized by improving the Pelican optimization algorithm to improve the precision of load forecasting of LSTM network. The test results show that the method can detect singular values in the data and weaken the impact of grid planning on netload forecasting; It can effectively complete the decomposition of historical load data, and each component after decomposition will not be aliased; The prediction error of net load is less than 1.25%, which can provide a reliable basis for grid planning of distribution network.

Daily Load Forecasting and Data-Driven Strategies for Steel Industry Based on Random Forest Modeling

Abstract As a large power consumer, the iron and steel industry urgently needs to improve productivity, reduce energy consumption, and save costs by revolutionizing energy management. In this study, we design a power demand management system for the iron and steel industry, and around the load management module, we propose a data-driven strategy based on daily load situational awareness and introduce the random forest model into daily load forecasting in the iron and steel industry. At the same time, the projection principle is applied to improve the traditional gray correlation similar day selection algorithm, and a combination method of daily load forecasting based on the gray projection improved random forest algorithm is proposed. The electric load data of the iron and steel industry in a specific region is utilized as an experimental sample to investigate the model’s forecasting performance and the impact of the data-driven strategy. The model for daily load forecasting in this paper has an average relative error of 1.18%, which is better than other models. The application of the data-driven strategy brought about 6.99% and 6.69% reductions in load demand and basic electricity cost. The data-driven strategy for the steel industry based on the Random Forest model can predict electric loads more accurately and reduce energy costs, as shown by the results.