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Showing records 26 to 50 of 263. [First] Page: 1 2 3 4 5 6 Last
Improved Time-Varying BLF-Based Tracking Control of a Position-Constrained Robot
Tan Zhang, Jinzhong Zhang
February 10, 2024 (v1)
Keywords: adaptive control, barrier Lyapunov function, constraint control, robot, tracking control
In this work, one improved symmetric time-variant logarithmic barrier, Lyapunov function (BLF), is developed for the first time to handle the state constraint problem of nonlinear systems. It is universal in the sense that the improved barrier function is a general one that can be used not only in systems with constrained requirements but also in systems without constrained requirements, without altering the designed controller. First of all, the n-link robotic system is transformed into a kind of multi-input and multi-output (MIMO) system. Then, a trajectory tracking control scheme is designed by combining the improved time-variant logarithmic BLF with the disturbance observer to solve the problems of model uncertainty and position constraint for the robotic system. We give that under the proposed controller, all the robotic system’s error vectors can trend to the equilibrium point asymptotically while the constraint conditions on the position are always met. Finally, the effectivenes... [more]
Discrete Meta-Simulation of Silage Based on RSM and GA-BP-GA Optimization Parameter Calibration
Gonghao Li, Juan Ma, Xiang Tian, Chao Zhao, Shiguan An, Rui Guo, Bin Feng, Jie Zhang
February 10, 2024 (v1)
Keywords: BP neural network, discrete element method, Genetic Algorithm, parameter calibration, response surface method, silage
The EDEM software (Altair EDEM 2022.0 professional version 8.0.0) was used to create a discrete element model of silage to address the lack of silage evidence parameters and contact parameters between silage and conveying equipment when using the discrete element method to simulate and analyze crucial aspects of silage conveying and feeding. Physical tests and simulations were used to calibrate the significant parameters, and the silage stacking angle obtained from simulation and tests was then validated. The response value of the stacking angle (38.65°) obtained from the physical examination was used as the response value. The response surface (RSM) finding and the GA finding based on the genetic algorithm (GA) artificial neural network (BP) model were used to compare the significance parameters. The PB and steepest climb tests were used to screen the significant factors. Results indicate that the static friction coefficient between silage and silage, the rolling friction coefficient... [more]
Stick−Slip Characteristics of Drill Strings and the Related Drilling Parameters Optimization
Chao Wang, Wenbo Chen, Zhe Wu, Jun Li, Gonghui Liu
February 10, 2024 (v1)
Subject: Optimization
Keywords: drill string, drilling parameter, Optimization, stick–slip vibration
To eliminate or reduce stick−slip vibration in torsional vibration of the drilling string and improve the rate of penetration (ROP), a stick−slip vibration model of the drilling string considering the ROP was established based on the multidimensional torsional vibration model of the drilling string. The model was verified by simulation analysis. The characteristics of the drilling string stick−slip vibration in the three stages of stationary, slip, and stick were analyzed. This paper investigated the influence of rotary torque, rotary speed, and weight on bit (WOB) on stick−slip vibrations in the drill string. Based on this, the relationship between the drilling parameters and ROP was established. Drilling parameter optimization was completed for soft, medium-hard, and hard formations. Results showed that appropriately increasing torque and decreasing WOB can reduce or even eliminate stick−slip vibrations in the drill string and increase the ROP. The parameter optimization increased th... [more]
Anomaly Recognition, Diagnosis and Prediction of Massive Data Flow Based on Time-GAN and DBSCAN for Power Dispatching Automation System
Wenjie Liu, Pengfei Lei, Dong Xu, Xiaorong Zhu
February 10, 2024 (v1)
Keywords: DBSCAN, fault diagnosis, fault prediction, supervised learning, Time-GAN
Existing power anomaly detection is mainly based on analyzing static offline data. But this method takes a long time and has low identification accuracy when detecting timing and frequency anomalies, since this method requires offline screening, classification and preprocessing of the collected data, which is very laborious. Anomaly detection with supervised learning requires a large amount of abnormal data and cannot detect unknown anomalies. So, this paper innovatively proposes the idea of applying Time-series Generative Adversarial Networks (Time-GAN) in a dispatching automation system for the identification, diagnosis and prediction of massive data flow anomalies. First of all, regarding the problem of insufficient abnormal data, we use Time-GAN to generate a large number of reliable datasets for training fault diagnosis models. In addition, Time-GAN can ameliorate the imbalance between various types of data. Secondly, unsupervised learning methods such as Density-Based Spatial Clu... [more]
Response of Nitrogen Removal Performance and Microbial Distribution to Seasonal Shock Nutrients Load in a Lakeshore Multicell Constructed Wetland
Jing Yuan, Bin Wang, Zeying Hou, Jiayu Peng, Dan Li, Zhaosheng Chu
February 10, 2024 (v1)
Subject: Biosystems
Keywords: hydraulic characters, lakeshore wetlands, microbial community, nitrogen removal, nonpoint source pollution, spatial and temporal regulation
Multicell constructed wetlands (MCWs) on lakeshores are a prospective treatment technique. However, the factors affecting the nutrient removal performance of lakeshore MCWs at the field scale are unclear. This study chose a field-scale lakeshore MCW with the highest mass removal efficiency (approximately 49,175.12 mg m−2 day−1) for total nitrogen removal in the wet season to investigate the response of nitrogen removal and microbial distribution to seasonal shock nutrients load. The mass loading rates in the wet season were as high as 43~72 times over those in the dry season. Hence, a storage pond (SP), as a forebay retention cell, was necessary to mitigate the shock loads of the influent, which is beneficial to nitrogen removal of the MCW system. The two major genera in the sediments are heterotrophic nitrification−aerobic denitrification bacteria, and the abundance and species of the nitrogen-related functional genera were higher in the wet season than the dry season. According to th... [more]
A Lightweight Identification Method for Complex Power Industry Tasks Based on Knowledge Distillation and Network Pruning
Wendi Wang, Xiangling Zhou, Chengling Jiang, Hong Zhu, Hao Yu, Shufan Wang
February 10, 2024 (v1)
Keywords: knowledge distillation, network pruning, power industry, service identification
Lightweight service identification models are very important for resource-constrained distribution grid systems. To address the increasingly larger deep learning models, we provide a method for the lightweight identification of complex power services based on knowledge distillation and network pruning. Specifically, a pruning method based on Taylor expansion is first used to rank the importance of the parameters of the small-scale network and delete some of the parameters, compressing the model parameters and reducing the amount of operation and complexity. Then, knowledge distillation is used to migrate the knowledge from the large-scale network ResNet50 to the small-scale network so that the small-scale network can fit the soft-label information output from the large-scale neural network through the loss function to complete the knowledge migration of the large-scale neural network. Experimental results show that this method can compress the model size of the small network and improv... [more]
Study on Process Parameters in Hydrothermal Liquefaction of Rice Straw and Cow Dung: Product Distribution and Application of Biochar in Wastewater Treatment
Asiful H. Seikh, Hamad F. Alharbi, Ibrahim A. Alnaser, Mohammad R. Karim, Jabair A. Mohammed, Muhammad Omer Aijaz, Ahmed Hassan, Hany S. Abdo
February 10, 2024 (v1)
Keywords: bio-char, bio-oil, colorants, cow dung, hydrothermal liquefaction, rice straw
In this study, rice straw (RS) and cow dung (CD) waste were hydrothermally processed for the recovery of bio-oil and biochar. The hydrothermal experiments were performed in a 5 L capacity reactor under the following process conditions: temperature (240−340 °C), solvent to biomass ratios of 1:1, 1:2, 2:1, 1:3 and 3:1, a time of 1 h and a pressure of 15 bar. The HTL products were characterized via FTIR, SEM and GC−MS (gas chromatography mass spectrometry). It was seen that the maximum bio-oil yield was 32.5 wt% and the biochar yield was 18.5 wt% for the 2:1 RS:CD mixture at a temperature of 320 °C. The bio-oil contained hexadecane, heptadecane, octadecane and other hydrocarbons, and their presence was confirmed by GC−MS. The biochar was analyzed, and it was used in wastewater treatment to remove the colorants. The biochar also showed some promising results in the colorants removal study, with an efficiency of more than 76%.
Non-Classical Circularly Polarized Luminescence Control of Peptide Luminophore Based on Precise Chiral Space Control
Yoshitane Imai, Mizuki Kitamatsu
February 10, 2024 (v1)
Subject: Biosystems
Keywords: chiral molecule, circularly polarized luminescence (CPL), peptide, pyrene
Light that rotates in a circular spiral when viewed from the front is known as circularly polarized luminescence (CPL), and can be divided into two types, namely, left- and right-rotating light. To emit both left- and right-rotating CPLs, two types of optically active luminophores, namely, enantiomer D- and L-bodies, are generally required. This mini-review mainly discusses our latest study on CPL properties via the control of the pyrene ring as the luminescent unit incorporated into chiral peptides. In this study, optically active peptide−pyrene organoluminescent materials that emit CPL were synthesized by combining a peptide as a frame and two pyrene rings as a luminescent unit. By adjusting the interpyrene distance, external conditions, and absolute chiral configuration (D- or L-configuration), the chiral spatial configuration of the luminescent pyrene ring was precisely controlled. Consequently, the direction of CPL rotation from pyrenylalanine-containing peptides with the same con... [more]
Mathematical Modeling of Prediction of Horizontal Wells with Gravel Pack Combined with ICD in Bottom-Water Reservoirs
Shili Qin, Ning Zhang, Bobo Cao, Yongsheng An, Runshi Huo
February 10, 2024 (v1)
Keywords: bottom-water reservoir, gravel pack, horizontal wells, inflow control device
During the development of horizontal wells in bottom-water reservoirs, the strong heterogeneity of reservoir permeability leads to premature bottom-water breakthroughs at locations with high permeability in the horizontal wellbore, and the water content rises rapidly, which seriously affects production. To cope with this problem, a new technology has emerged in recent years that utilizes gravel filling to block the flow in the annulus between the horizontal well and the borehole and utilizes the Inflow Control Device (ICD) completion tool to carry out segmental water control in horizontal wells. Unlike conventional horizontal well ICD completions that use packers for segmentation, gravel packs combined with ICD completions break the original segmentation routine and increase the complexity of the production dynamic simulation. In this paper, the flow in different spatial dimensions, such as reservoirs, gravel-packed layers, ICD completion sections, and horizontal wellbores, is modeled... [more]
Atomic Orbital Search Algorithm for Efficient Maximum Power Point Tracking in Partially Shaded Solar PV Systems
Md Tahmid Hussain, Mohd Tariq, Adil Sarwar, Shabana Urooj, Amal BaQais, Md. Alamgir Hossain
February 10, 2024 (v1)
Keywords: atomic orbital search (AOS), maximum power point tracking (MPPT), metaheuristic algorithms, partial shading condition (PSC), photovoltaic (PV)
The efficient extraction of solar PV power is crucial to maximize utilization, even in rapidly changing environmental conditions. The increasing energy demands highlight the importance of solar photovoltaic (PV) systems for cost-effective energy production. However, traditional PV systems with bypass diodes at their output terminals often produce multiple power peaks, leading to significant power losses if the optimal combination of voltage and current is not achieved. To address this issue, algorithms capable of finding the highest value of a function are employed. Since the PV power output is a complex function with multiple local maximum power points (LMPPs), conventional algorithms struggle to handle partial shading conditions (PSC). As a result, nature-inspired algorithms, also known as metaheuristic algorithms, are used to maximize the power output of solar PV arrays. In this study, we introduced a novel metaheuristic algorithm called atomic orbital search for maximum power point... [more]
Adsorption of Multi-Collector on Long-Flame Coal Surface via Density Functional Theory Calculation and Molecular Dynamics Simulation
Gan Cheng, Yujie Peng, Yang Lu, Mengni Zhang
February 10, 2024 (v1)
Keywords: Adsorption, collector, long-flame coal, molecular dynamics, quantum chemistry
The quantum chemical properties of long-flame coal (LFC) and collectors (kerosene, diesel, diethyl phthalate (DEP), biodiesel collector (BDC), and emulsified biodiesel collector (EBDC)) were analyzed via the density functional theory (DFT). The molecular dynamics (MD) of the coal−collector−water system and the adsorption of collectors on LFC were conducted based on the first principles. The results showed that the frontier molecular orbitals of kerosene, diesel, DEP, and BDC were 0.38 eV, 0.28 eV, 0.27 eV, and 0.20 eV, respectively. The chemical reactivity order of the above mentioned collectors was BDC > DEP > diesel > kerosene. Kerosene, diesel, and DEP adsorbed with carbonyl, hydroxyl, and carboxyl groups in LFC, respectively. Carboxyl groups in BDC and carboxyl groups in LFC bilaterally adsorbed, while BDC repelled water molecules via hydrogen bonds on the LFC surface. In the systems of BDC and EBDC, the diffusion coefficients of a water molecule were 2.83 × 10−4 cm2/s and 3.73 × 1... [more]
Biochemical Characterization and Fuel Properties of Endemic Taurus Flowering Ash (Fraxinus ornus subsp. cilicica) Bark from Turkey
Ali Umut Şen, Rita Simões, Cengiz Yücedağ, Isabel Miranda, Ângela Fernandes, Helena Pereira
February 10, 2024 (v1)
Keywords: antioxidant, calcium, ignition temperature, suberin, ω-hydroxy acids
Taurus flowering ash (Fraxinus ornus subsp. cilicica) is an endemic tree species in Turkey. The bark of the species was characterized for summative chemical composition, the monomeric composition of polysaccharides, phenolic content, in vitro and ex vivo antioxidant properties of hydrophilic extracts, the composition of lipophilic extractives and suberin, and thermal degradation. The bark has an elevated ash content (17%), primarily composed of calcium, and a noteworthy extractive content (38.9%), predominantly of hydrophilic compounds. The antioxidant activity of the bark extracts is moderate, with an IC50 value of 40 μg/mL and an EC50 value of 230 μg/mL by DPPH and TBARS methods. The lipophilic extractives principally contain fatty acids and diterpenoids. The suberin content is low (1%) and composed primarily of ω-hydroxy acids with 9,10,18 trihydroxyoctadecanoic acid as the major suberin monomer. The lignin content is low (9.8%), and polysaccharides represent 33%. The ignition tempe... [more]
Advancing Fault Prediction: A Comparative Study between LSTM and Spiking Neural Networks
Rute Souza de Abreu, Ivanovitch Silva, Yuri Thomas Nunes, Renan C. Moioli, Luiz Affonso Guedes
February 10, 2024 (v1)
Keywords: generalized stochastic Petri net (GSPN), industrial processes, LSTM networks, spiking neural networks (SNNs), system fault prediction
Predicting system faults is critical to improving productivity, reducing costs, and enforcing safety in industrial processes. Yet, traditional methodologies frequently falter due to the intricate nature of the task. This research presents a novel use of spiking neural networks (SNNs) in anticipating faults in syntactical time series, utilizing the generalized stochastic Petri net (GSPN) model. The inherent ability of SNNs to process both time and space aspects of data positions them as a prime instrument for this endeavor. A comparative evaluation with long short-term memory (LSTM) networks suggests that SNNs offer comparable robustness and performance.
Effect of Hot Filament Chemical Vapor Deposition Filament Distribution on Coated Tools Performance in Milling of Zirconia Ceramics
Louis Luo Fan, Wai Sze Yip, Zhanwan Sun, Baolong Zhang, Suet To
February 10, 2024 (v1)
Subject: Materials
Keywords: diamond-coated tools, hot filament chemical vapor deposition, micro-milling, surface integrity, zirconia
Zirconia ceramics (ZrO2) have been used for a variety of applications due to their superior physical properties, including in machining tools and dentures. Nonetheless, due to its extreme hardness and brittleness in both sintered and half-sintered forms, zirconia is difficult to machine. In this study, half-sintered zirconia blocks are milled with tungsten carbide milling tools which arecoated with diamond film using hot filament chemical vapor deposition (HFCVD) at various substrate-to-filament distances. The objective was to determine the effect of substrate-to-filament distances on the coating thickness, diamond purity, coating grain size, and ZrO2 machining performance during HFCVD. The experimental results show that, in HFCVD, the grain size and coating thickness of the diamond film on milling tools tend to decrease when the substrate-to-filament distances decrease. Tool failure happened at a cutting time of 200 min for all coated tools. However, the machining quality in terms of... [more]
A Review of Nano and Microscale Heat Transfer: An Experimental and Molecular Dynamics Perspective
Samyabrata Chatterjee, Paras, Han Hu, Monojit Chakraborty
February 10, 2024 (v1)
Keywords: force-fields, liquid thin-film, microelectronic devices, molecular dynamics, thermal transportation
Significant progress in the development of micro and nanoscale devices has been observed for the past three decades. The thermal transportation in these small-length scales varies significantly, and it is difficult to explain the underlying physics using the pre-existing theoretical formulations. When the bulk dimension of a system is comparable to or smaller than the mean free path (MFP) of the thermal carriers, classical theories, such as Fourier’s Law of heat conduction, are unable to accurately explain the system energy dynamics. The phenomena of energy transit and conversion at the micro to nanoscale is an interesting topic of research due to the substantial changes in behavior that are documented when compared to those at the macro size. This review article is broadly divided into two parts. Initially, the recent development in the field of molecular dynamic (MD) simulations is emphasized. Classical MD simulation is such a powerful tool that provides insight into the length scale... [more]
Polyphenols as Antioxidant/Pro-Oxidant Compounds and Donors of Reducing Species: Relationship with Human Antioxidant Metabolism
Celia María Curieses Andrés, José Manuel Pérez de la Lastra, Celia Andrés Juan, Francisco J. Plou, Eduardo Pérez-Lebeña
February 10, 2024 (v1)
Keywords: antioxidant metabolism, antioxidant/pro-oxidant features, NRF2/ARE axis, polyphenols
In this review, we have focused mainly on the study of their antioxidant and pro-oxidant capacity, and the analysis of the oxidation of the catechol group to o-quinone. The redox balance established between the different oxidase and reductase enzymes generates reducing species, H+ and e−, and allows the oxidation of polyphenolic groups to quinones to be reversible. This continuous balance between these nucleophilic and electrophilic substances allows the activation of the NRF2/ARE axis, which regulates cellular antioxidant responses against oxidative stress, as well as cell proliferation. Understanding the ambivalent character of polyphenols, which can act simultaneously as antioxidants and pro-oxidants, will allow the design of specific therapies that can serve science and medicine in their tasks.
Novel Control Technology for Reducing Output Power Harmonics of Standalone Solar Power Generation Systems
Hwa-Dong Liu, Jhen-Ting Lin, Xin-Wen Lin, Chang-Hua Lin, Shoeb-Azam Farooqui
February 10, 2024 (v1)
Keywords: adjustable frequency and duty cycle, cake sweetness maximum power point tracking, standalone solar power system, total voltage harmonic distortion
This study presents a standalone solar power system that incorporates a photovoltaic (PV) module, a boost converter, an H-bridge inverter, a low-pass filter (LPF), and a microcontroller unit (MCU). A novel cake sweetness maximum power point tracking (CS MPPT) algorithm and adjustable frequency and duty cycle (AFDC) control strategy has been proposed and efficiently applied to the solar power system for optimizing the system efficiency and output power quality. The experimental results show that the proposed CS MPPT algorithm achieves an efficiency of 99% under both the uniform irradiance conditions (UIC) and partial shading conditions (PSC). Subsequently, the AFDC control strategy is applied to the H-bridge inverter which improves the output AC voltage and AC current and thereby improving the power quality. The system ensures a stable 110 Vrms/60 Hz AC output voltage with only 2% total voltage harmonic distortion of voltage (THDv), and produces a high-quality output voltage with reduce... [more]
Antibacterial Activities of Oral Care Products Containing Natural Plant Extracts from the Thai Highlands against Staphylococcus aureus: Evaluation and Satisfaction Studies
Saranya Chaiwaree, Kannika Srilai, Kantaporn Kheawfu, Patcharin Thammasit
February 10, 2024 (v1)
Subject: Biosystems
Keywords: antibacterial, highland areas, mouth spray, natural plant extracts, oral ulcer gel, satisfaction
In this research, we aimed to assess antibacterial activity and develop oral care products from three natural plant extracts from the Thai highlands. The plants, including Camellia sinensis var. assamica, Zanthozylum limonella Alston, and Acorus calamus L., were extracted using two traditional extraction techniques: maceration and hydrodistillation methods. The extracts were characterized by percentage yield, total phenolic, and total flavonoid contents. Antibacterial activity against Staphylococcus aureus, which play a role in oral health and disease, was investigated. C. sinensis var. assamica extract had the highest content of phenolic acid (38.15 ± 4.12 mg GAE/g extract) and flavonoids (44.91 ± 2.76 mg QE/g extract). Interestingly, a combination of C. sinensis with Z. limonella and A. calamus provides a greater inhibitory effect against S. aureus. Furthermore, oral care products were prepared as a natural product mixture in two preparations: (i) oral ulcers gel and (ii) oral spray.... [more]
Prediction of Lost Circulation in Southwest Chinese Oil Fields Applying Improved WOA-BiLSTM
Xianming Liu, Wen Jia, Zhilin Li, Chao Wang, Feng Guan, Kexu Chen, Lichun Jia
February 10, 2024 (v1)
Subject: Optimization
Keywords: Bidirectional Long Short Term Memory, correlation analysis, improved whale optimization algorithm, lost circulation prior to drilling, prediction model
Drilling hazards can be significantly decreased by anticipating potential mud loss and then putting the right well control measures in place. Therefore, it is critical to provide early estimates of mud loss. To solve this problem, an enhanced WOA (Whale Optimization Algorithm) and a BiLSTM (Bidirectional Long Short Term Memory) optimization based prediction model of lost circulation prior to drilling has been created. In order to minimize the noise in the historical comprehensive logging data, a wavelet filtering technique was first used. Then, according to the nonlinear Spearman rank correlation coefficient between mud loss and logging parameter values from large to small, seven characteristic parameters were preferred, and the sliding window was used to extract the relevant data. Secondly, the number of neurons in the first and second hidden layers, the maximum training time, and the initial learning rate of the BiLSTM model were optimized using the enhanced WOA method. The BiLSTM ne... [more]
Study on Variable Stress Corrosion Susceptibility of Four Typical High-Strength Sucker Rods in High-Salinity Well Fluids
Fenna Zhang, Jia Li, Hongying Zhu, Chuankai Jing, Bin Wang, Yaoguang Qi
February 10, 2024 (v1)
Subject: Materials
Keywords: high-salinity conditions, high-strength sucker rod, single-factor test, SSRT, stress corrosion cracking susceptibility
To study the corrosion characteristics of high-strength sucker rods in high-salinity well fluids under alternating stresses, a single-factor stress corrosion test was designed. The slow strain rate tensile test (SSRT) was carried out for four kinds of high-strength sucker rods under different Cl− and HCO3− concentrations and with different service strengths, and the variable stress corrosion cracking susceptibility was analyzed. The results show that the elongation loss and absorbed work loss of the H-grade ultra-high-strength 4330 sucker rod after stress corrosion are greater than those of both the high-strength 4142 sucker rod and the high-strength 20CrMoA sucker rod. The elongation and absorbed work loss of the 30CrMoA and 20CrMoA sucker rods are less affected by the changes in Cl− and HCO3−. With the increase in use strength, the elongation and absorbed work loss of the high-strength sucker rod increase. The change in the surface of the sucker rod during the corrosion process is in... [more]
Dynamic Modeling and Parameter Identification of Double Casing Joints for Aircraft Fuel Pipelines
Lingxiao Quan, Chen Fu, Renyi Yao, Changhong Guo
February 10, 2024 (v1)
Keywords: double casing joint, flow–solid coupling, free modal, parameters identification
Double casing joints are flexible pipe joints used for connecting aircraft fuel pipelines, which can compensate for the displacement and corner of the connected pipes and have complex mechanical characteristics. However, it is difficult to use sensors to directly measure the mechanical connection parameters of flexible joints. In this paper, we construct a coupling dynamics model and parameter identification of a double casing joint. Firstly, we analyze the structure and working principle of double-layer casing joints and establish the dynamics model of a single-layer flexible joint based on the transfer matrix method. Then, we deduce the coupling matrix of the inner and outer pipeline according to the deformation coordination conditions combined with matrix dimension extension. We establish the coupling dynamics model of flow−solid coupling of double casing joints. Furthermore, parameters such as equivalent stiffness and damping of each motion of the double casing joint in the casing... [more]
A Review of Macroscopic Modeling for Shale Gas Production: Gas Flow Mechanisms, Multiscale Transport, and Solution Techniques
Yuyang Liu, Xiaowei Zhang, Wei Zhang, Wei Guo, Lixia Kang, Dan Liu, Jinliang Gao, Rongze Yu, Yuping Sun
February 10, 2024 (v1)
Keywords: hydraulic fractures, macroscopic modeling, shale gas reservoir
The boost of shale gas production in the last decade has reformed worldwide energy structure. The macroscale modeling of shale gas production becomes particularly important as the economic development of such resources relies on the deployment of expensive hydraulic fracturing and the reasonable planning of well schedules. A flood of literature was therefore published focused on accurately and efficiently simulating the production performance of shale gas and better accounting for the various geological features or flow mechanisms that control shale gas transport. In this regard, this paper presents a holistic review of the macroscopic modeling of gas transport in shale. The review is carried out from three important points of view, which are the modeling of the gas flow mechanisms, the representation of multiscale transport, and solution techniques for the mathematical models. Firstly, the importance of gas storage and flow mechanisms in shale is discussed, and the various theoretical... [more]
Study on Mechanism and Regularity of Rock Breaking by Pulsed Water Injection with Particles
Tian Zhao, Qingxiang Wu, Haifeng Lv, Heng Song, Xinke Yang, Tiancheng Fang
February 10, 2024 (v1)
Subject: Environment
Keywords: hard formation, particles, pulse, rock breaking, rock drilling, water injection
In recent years, the drilling technology applied to deep and ultra-deep formations has developed rapidly, but the drilling speed for hard formations is low. Therefore, it is very important to study the drilling methods for deep and hard strata. Particle pulsed jet drilling is a new drilling method based on particle jet impact drilling technology and high-pressure pulsed water jet impact drilling technology. In this paper, the mathematical models of the shear layer amplification coefficient and wave velocity are established based on a similar network theory, and the motion equations of a single particle and particle swarm are established according to the motion of particles in a pulsed jet environment. Then, based on the self-designed particle jet impact rock-breaking experimental platform, the numerical simulation results are compared, analyzed, and verified. The results show that the rock-breaking efficiency increases with the increase in the average velocity of the particle pulsed je... [more]
Exploration of Pyrolysis Behaviors of Waste Plastics (Polypropylene Plastic/Polyethylene Plastic/Polystyrene Plastic): Macro-Thermal Kinetics and Micro-Pyrolysis Mechanism
Weiwei Xuan, Shiying Yan, Yanwu Dong
February 10, 2024 (v1)
Subject: Materials
Keywords: DFT, pyrolysis kinetics, ReaxFF-MD, TG–MS, waste plastics
Pyrolysis is a promising technology used to recycle both the energy and chemicals in plastics. Three types of plastics, polyethylene plastic (PE), polypropylene plastic (PP) and polystyrene plastic (PS) were investigated using thermogravimetry−mass spectrometry (TG−MS) and reactive force field molecular dynamics (ReaxFF-MD) simulation. The thermogravimetric analysis showed that all three plastics lost weight during the pyrolysis in one step. The thermal decomposition stability is PS < PP < PE. The activation energies and reaction mechanism function of the three plastics were determined by the Kissinger and CR methods. Meanwhile, the ReaxFF-MD combined with density functional theory (DFT) was used to calculate the kinetics, as well as explore the pyrolysis mechanism. The calculated kinetic results agree well with the experimental methods. The common pyrolysis reaction process follows the dissociation sequence of the polymer to polymeric monomer and, then, to the gas molecules. Bas... [more]
Pyrolysis Behavior and Kinetics of Typical Crop Straw in Henan Province at Different Heating Rates
Po Hu, Chenghao Hou, Xinyu Lan, Honghao Sheng
February 10, 2024 (v1)
Subject: Materials
Keywords: pyrolysis, straw, temperature rise rate
Straw, which is characterized by its low cost, large quantity, and rich supply of biomass energy, is often converted into energy that can be utilized in industrial production through pyrolysis technology. This paper examines the pyrolysis experiments of four kinds of straw (rice, wheat, peanut, and corn) from the Henan Province of China, conducted in an air environment with varying temperature-rise rates. Based on the experimental results, an analysis was conducted on the effect of the rate of temperature rise on the degree of straw pyrolysis and the pyrolysis characteristics of each type of straw. The activation energies of the pyrolysis reactions were calculated utilizing the Kissinger−Akahira−Sunose (KAS), Flynn−Wall−Ozawa (FWO), and Starink methods. It was concluded that the pyrolysis process of all four types of straw could roughly be classified into three stages: dehydration and drying stage, volatile release stage, and carbonization stage. Among the four types of straw evaluated... [more]
Showing records 26 to 50 of 263. [First] Page: 1 2 3 4 5 6 Last