Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in ...Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in this paper.The five-point central difference method is used for spatial discretization,and the fourth-order Adams predictor-corrector scheme is employed for marching in time.The domain-decomposition method is applied for the wave-current generation and absorption.The effects of currents on the wave profile and velocity field are examined under two conditions:the same velocity of currents at the still-water level and the constant flow volume of currents.Wave profiles and velocity fields demonstrate substantial differences in three types of currents owing to the diverse vertical distribution of current velocity and vorticity.Then,loads on small-scale vertical cylinders subjected to regular waves and three types of background currents with the same flow volume are investigated.The maximum load intensity and load fluctuation amplitude in uniform,linear shear,and quadratic shear currents increase sequentially.The stretched superposition method overestimates the maximum load intensity and load fluctuation amplitude in opposing currents and underestimates these values in following currents.The stretched superposition method obtains a poor approximation for strong nonlinear waves,particularly in the case of the opposing quadratic shear current.展开更多
The non-linear dynamic behaviors of thermoelastic circular plate with varying thickness subjected to radially uniformly distributed follower forces are considered. Two coupled non-linear differential equations of moti...The non-linear dynamic behaviors of thermoelastic circular plate with varying thickness subjected to radially uniformly distributed follower forces are considered. Two coupled non-linear differential equations of motion for this problem are derived in terms of the transverse deflection and radial displacement component of the mid-plane of the plate. Using the Kantorovich averaging method, the differential equation of mode shape of the plate is derived, and the eigenvalue problem is solved by using shooting method. The eigencurves for frequencies and critical loads of the circular plate with unmovable simply supported edge and clamped edge are obtained. The effects of the variation of thickness and temperature on the frequencies and critical loads of the thermoelastic circular plate subjected to radially uniformly distributed follower forces are then discussed.展开更多
Medium-term forecasting is an important category of electric load forecasting that covers a time span of up to one year ahead. It suits outage and maintenance planning, as well as load switching operation. We propose ...Medium-term forecasting is an important category of electric load forecasting that covers a time span of up to one year ahead. It suits outage and maintenance planning, as well as load switching operation. We propose a new methodol-ogy that uses hourly daily loads to predict the next year hourly loads, and hence predict the peak loads expected to be reached in the next coming year. The technique is based on implementing multivariable regression on previous year's hourly loads. Three regression models are investigated in this research: the linear, the polynomial, and the exponential power. The proposed models are applied to real loads of the Jordanian power system. Results obtained using the pro-posed methods showed that their performance is close and they outperform results obtained using the widely used ex-ponential regression technique. Moreover, peak load prediction has about 90% accuracy using the proposed method-ology. The methods are generic and simple and can be implemented to hourly loads of any power system. No extra in-formation other than the hourly loads is required.展开更多
<span style="font-family:Verdana;">This study presents an intelligent approach for load frequency control (LFC) of small hydropower plants (SHPs). The approach which is based on fuzzy logic (FL), takes...<span style="font-family:Verdana;">This study presents an intelligent approach for load frequency control (LFC) of small hydropower plants (SHPs). The approach which is based on fuzzy logic (FL), takes into account the non-linearity of SHPs—something which is not possible using traditional controllers. Most intelligent methods use two-</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">input fuzzy controllers, but because such controllers are expensive, there is </span><span style="font-family:Verdana;">economic interest in the relatively cheaper single-input controllers. A n</span><span style="font-family:Verdana;">on-</span></span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">linear control model based on one-input fuzzy logic PI (FLPI) controller was developed and applied to control the non-linear SHP. Using MATLAB/Si</span><span style="font-family:Verdana;">- </span><span style="font-family:Verdana;">mulink SimScape, the SHP was simulated with linear and non-linear plant models. The performance of the FLPI controller was investigated and compared with that of the conventional PI/PID controller. Results show that the settling time for the FLPI controller is about 8 times shorter;while the overshoot is about 15 times smaller compared to the conventional PI/PID controller. Therefore, the FLPI controller performs better than the conventional PI/PID controller not only in meeting the LFC control objective but also in ensuring increased dynamic stability of SHPs.</span>展开更多
The first decision we need to make in a structural load assessment is what approach should be applied, a linear approach or a non-linear one. The correct decision comes from understanding of the technology used in the...The first decision we need to make in a structural load assessment is what approach should be applied, a linear approach or a non-linear one. The correct decision comes from understanding of the technology used in the linear and non-linear approaches and also comes from the understanding of the problem to he analyzed. From engineering practice, it has been found that many non-linear effects can be taken into account in a linear model with appropriate approach. A study of hydrodynamic structural load on a stinger of a pipe-laying vessel is presented in this paper. The results of a non-linear analysis are compared to those of linear models with different approaches, and how the nonlinear effect can be involved in a linear model is discussed. The recommendations on how to estimate the non-linear effects in a linear structural load model is discussed.展开更多
This paper presents a non-linear simulation of the impact on a structure with different energy absorption systems using finite element models. Literature review on bistable structure, aluminum foam and expandable poly...This paper presents a non-linear simulation of the impact on a structure with different energy absorption systems using finite element models. Literature review on bistable structure, aluminum foam and expandable polystyrene is presented and taken as basis to propose energy absorption systems. Using a base structure, these systems are implemented by means of finite element modeling. A comparison of the damage caused to the structure in case of impact without implementing energy absorption system, and implementing energy absorption systems based on bistable structures, polystyrene foam and aluminum foam are shown here in. The results demonstrate the advantages of using energy absorption systems on structures under impact loads.展开更多
This paper presents development of 3D non-linear finite element model to simulate the response and predict the behavior of un-bonded mild steel bars under axial and bending loading. The models were successfully analyz...This paper presents development of 3D non-linear finite element model to simulate the response and predict the behavior of un-bonded mild steel bars under axial and bending loading. The models were successfully analyzed with the finite element software ANSYS, taking into account the nonlinear material properties of the reinforced mild steel bars. A bending strain relationship is derived based on a parametric study involving multiple nonlinear finite element models. A mild steel fracture criterion based on low-cycle fatigue models is proposed to control the total (elastic and plastic) strains in the mild steel bar below a maximum permissible limit. In addition, FE predictions of bar elongation due to strain penetration reasonably agreed with a proposed empirical equation by Raynor and Lehman. It was concluded that the equation proposed by Raynor and Lehman is considered valid for estimating the additional unbounded length and can be used in both analysis and design.展开更多
<p align="left"> <span style="font-family:Verdana;">The present study evaluates the effects of occlusal loading on an implant-supported dental implant with external hexagon dental impla...<p align="left"> <span style="font-family:Verdana;">The present study evaluates the effects of occlusal loading on an implant-supported dental implant with external hexagon dental implant-abutment systems, using the finite element method analysis. Tensile analyses were performed to simulate different axial and obliquous masticatory loads. The influence of the variations in the contouring conditions of the interfaces was analyzed to weigh the osseointegration with linear and non-linear cases, by means of a parametric design. The geometry selected to place the prostheses was a jaw section, considering the properties of the set of cortical and trabecular bones. The results show that for non-linear contour conditions, the stress presents smaller value distributions and signals a different place in the screw-implant interface as the factor of the greater weight in this study. The location indicated that von Mises stress concentrations are not exclusive to the contact regions studied, moving to an area that is not in direct contact with the non-linear contact interfaces. In addition, the direction of load with an angle of 15 degrees presented the highest values of von Mises stress.</span> </p>展开更多
Ice-breaking methods have become increasingly significant with the ongoing development of the polar regions.Among many ice-breaking methods,ice-breaking that utilizes a moving load is unique compared with the common c...Ice-breaking methods have become increasingly significant with the ongoing development of the polar regions.Among many ice-breaking methods,ice-breaking that utilizes a moving load is unique compared with the common collision or impact methods.A moving load can generate flexural-gravity waves(FGWs),under the influence of which the ice sheet undergoes deformation and may even experience structural damage.Moving loads can be divided into above-ice loads and underwater loads.For the above-ice loads,we discuss the characteristics of the FGWs generated by a moving load acting on a complete ice sheet,an ice sheet with a crack,and an ice sheet with a lead of open water.For underwater loads,we discuss the influence on the ice-breaking characteristics of FGWs of the mode of motion,the geometrical features,and the trajectory of motion of the load.In addition to discussing the status of current research and the technical challenges of ice-breaking by moving loads,this paper also looks ahead to future research prospects and presents some preliminary ideas for consideration.展开更多
More than 200 years after Parkinson's disease was first described by the English surgeon whose name would eventually be given to the condition,available treatments remain purely symptomatic,leaving a critical unme...More than 200 years after Parkinson's disease was first described by the English surgeon whose name would eventually be given to the condition,available treatments remain purely symptomatic,leaving a critical unmet clinical need for a diseasemodifying therapy.展开更多
Gas explosion in confined space often leads to significant pressure oscillation.It is widely recognized that structural damage can be severe when the oscillation frequency of the load resonates with the natural vibrat...Gas explosion in confined space often leads to significant pressure oscillation.It is widely recognized that structural damage can be severe when the oscillation frequency of the load resonates with the natural vibration frequency of the structure.To reveal the oscillation mechanism of gas explosion load,the experiment of gas explosion was conducted in a large-scale confined tube with the length of 30 m,and the explosion process was numerically analyzed using FLACS.The results show that the essential cause of oscillation effect is the reflection of the pressure wave.In addition,due to the difference in the propagation path of the pressure wave,the load oscillation frequency at the middle position of the tunnel is twice that at the end position.The average sound velocity can be used to calculate the oscillation frequency of overpressure accurately,and the error is less than 15%.The instability of the flame surface and the increase of flame turbulence caused by the interaction between the pressure wave and the flame surface are the main contributors to the increase in overpressure and amplitude.The overpressure peaks calculated by the existing flame instability model and turbulence disturbance model are 31.7%and 34.7%lower than the numerical results,respectively.The turbulence factor model established in this work can describe the turbulence enhancement effect caused by flame instability and oscillatory load,and the difference between the theoretical and numerical results is only 4.6%.In the theoretical derivation of the overpressure model,an improved model of dynamic turbulence factor is established,which can describe the enhancement effect of turbulence factor caused by flame instability and self-turbulence.Based on the one-dimensional propagation theory of pressure wave,the oscillatory effect of the load is derived to calculate the frequency and amplitude of pressure oscillation.The average error of amplitude and frequency is less than 20%.展开更多
In rock drilling and blasting,the misfire of electronic detonators will not only affect the rock fragmentation result but also bring serious potential safety hazards to engineering construction.An accurate and compreh...In rock drilling and blasting,the misfire of electronic detonators will not only affect the rock fragmentation result but also bring serious potential safety hazards to engineering construction.An accurate and comprehensive understanding of the failure mechanisms of electronic detonators subjected to impact loading is of great significance to the reliability design and field safety use of electronic detonators.The spatial distribution characteristics and failure modes of misfired electronic detonators under different application scenarios are statistically analysed.The results show that under high impact loads,electronic detonators will experience failure phenomena such as rupture of the fuse head,fracture of the bridge wire,falling off of the solder joint,chip module damage and insufficient initiation energy after deformation.The lack of impact resistance is the primary cause of misfire of electronic detonators.Combined with the underwater impact resistance test and the impact load test in the adjacent blasthole on site,the formulas of the impact failure probability of the electronic detonator under different stress‒strength distribution curves are deduced.The test and evaluation method of the impact resistance of electronic detonators based on stress‒strength interference theory is proposed.Furthermore,the impact failure model of electronic detonators considering the strength degradation effect under repeated random loads is established.On this basis,the failure mechanism of electronic detonators under different application environments,such as open-pit blasting and underground blasting,is revealed,which provides scientific theory and methods for the reliability analysis,design and type selection of electronic detonators in rock drilling and blasting.展开更多
With increasing water depth,marine drilling conductors exhibit higher slenderness ratios,significantly reducing their resistance to environmental loads in Arctic waters.These conductors,when subjected to combined wind...With increasing water depth,marine drilling conductors exhibit higher slenderness ratios,significantly reducing their resistance to environmental loads in Arctic waters.These conductors,when subjected to combined wind,current,and ice loads,may experience substantial horizontal displacements and bending moments,potentially compromising off-shore operational safety and wellhead stability.Additionally,soil disturbance near the mudline diminishes the conductor’s bearing capacity,potentially rendering it inadequate for wellhead support and increasing operational risks.This study introduces a static analysis model based on plastic hinge theory to evaluate conductor survivability.The conductor analysis divides the structure into three segments:above waterline,submerged,and embedded below mudline.An idealized elastic-plastic p-y curve model characterizes soil behavior beneath the mudline,while the finite difference method(FDM)analyzes the conductor’s mechanical response under complex pile-head boundary conditions.Numerical simulations using ABAQUS validate the plastic hinge approach against conventional methods,confirming its accuracy in predicting structural performance.These results provide valuable insights for optimizing installation depths and bearing capacity designs of marine drilling conductors in ice-prone regions.展开更多
A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that th...A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that the loading parameters(initial normal stress,normal stiffness,and shear velocity)determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle,creating different morphologies of macroscopic step-path rupture surfaces and asperities on them.The differences in stress state and rupture surface induce different cyclic shear responses.It shows that high initial normal stress accelerates asperity degradation,raises shear resistance,and promotes compression of intermittent joints.In addition,high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints.High shear velocity results in a higher shear resistance,greater dilation,and greater compression.Finally,shear strength is most sensitive to initial normal stress,followed by shear velocity and normal stiffness.Moreover,average dilation angle is most sensitive to initial normal stress,followed by normal stiffness and shear velocity.During the shear cycles,frictional coefficient is affected by asperity degradation,backfilling of rock debris,and frictional area,exhibiting a non-monotonic behavior.展开更多
Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the informa...Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the information on the seismic behavior of joints of space frames(3D joints)is insufficient.The 3D joints are subjected to bi-directional excitation,which results in an interaction between the shear strength obtained for the joint in the two orthogonal directions separately.The bi-directional seismic behavior of corner reinforced concrete(RC)joints is the focus of this study.First,a detailed finite element(FE)model using the FE software Abaqus,is developed and validated using the test results from the literature.The validated modeling procedure is used to conduct a parametric study to investigate the influence of different parameters such as concrete strength,dimensions of main and transverse beams framing into the joint,presence or absence of a slab,axial load ratio and loading direction on the seismic behavior of joints.By subjecting the models to different combinations of loads on the beams along perpendicular directions,the interaction of the joint shear strength in two orthogonal directions is studied.The comparison of the interaction curves of the joints obtained from the numerical study with a quadratic(circular)interaction curve indicates that in a majority of cases,the quadratic interaction model can represent the strength interaction diagrams of RC beam to column connections with governing joint shear failure reasonably well.展开更多
Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force,especially for deep-buried pipes.To better reflect the soil arching effect resulting from the excavation...Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force,especially for deep-buried pipes.To better reflect the soil arching effect resulting from the excavation of rectangular jacked pipes and the distribution of the earth pressure on jacked pipes,we present an analytical solution for predicting the vertical earth pressure on deep-buried rectangular pipe jacking tunnels,incorporating the tunnelling-induced ground loss distribution.Our proposed analytical model consists of the upper multi-layer parabolic soil arch and the lower friction arch.The key parameters(i.e.,width and height of friction arch B and height of parabolic soil arch H 1)are determined according to the existing research,and an analytical solution for K l is derived based on the distribution characteristics of the principal stress rotation angle.With consideration for the transition effect of the mechanical characteristics of the parabolic arch zone,an analytical solution for soil load transfer is derived.The prediction results of our analytical solution are compared with tests and simulation results to validate the effectiveness of the proposed analytical solution.Finally,the effects of different parameters on the soil pressure are discussed.展开更多
To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specificall...To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specifically designed for methane in-situ deflagration fracturing.This experimental system,which is capable of withstanding pressures up to 150 MPa and meanwhile applying axial and confining pressures of up to 50 MPa to rock cores,enables the coupled simulation on methane deflagration and rock core fracturing processes.With the aid of this experimental system,physical simulation experiments on in-situ methane deflagration fracturing were conducted,and the following findings were obtained.Methane deflagration loads in enclosed wellbores exhibit characteristics of multi-level pulsed oscillation.With the rise of initial gas pressure,the peak deflagration load increases approximately linearly,with the pressure amplification factor spanning from 23.14 to 31.10,and its peak loading rate grows exponentially.Accordingly,the fracture volume and fracture porosity augment.To be specific,when the initial gas pressure rises from 0.6 to 2.4 MPa,the fracture volume and fracture porosity augment by factors of 14.0 and 8.73,respectively.The fractal dimension of spatial distribution of fractures also increases with the rise of deflagration load,indicating that a higher deflagration load conduces to the development of a larger and more complex fracture network.Methane deflagration fracturing is characterized as a composite fracture mode that involves the impact of strong stress waves and the driving force of high-pressure fluids.The primary factors influencing damage to coal-rock include the high-stress impact in the initial stage of deflagration,the fluid pressure driving effect in the middle stage,and the thermal shock resulting from high temperatures in the later stage.展开更多
The current single-atom catalysts(SACs)for medicine still suffer from the limited active site density.Here,we develop a synthetic method capable of increasing both the metal loading and mass-specific activity of SACs ...The current single-atom catalysts(SACs)for medicine still suffer from the limited active site density.Here,we develop a synthetic method capable of increasing both the metal loading and mass-specific activity of SACs by exchanging zinc with iron.The constructed iron SACs(h^(3)-FNC)with a high metal loading of 6.27 wt%and an optimized adjacent Fe distance of~4 A exhibit excellent oxidase-like catalytic performance without significant activity decay after being stored for six months and promising antibacterial effects.Attractively,a“density effect”has been found at a high-enough metal doping amount,at which individual active sites become close enough to interact with each other and alter the electronic structure,resulting in significantly boosted intrinsic activity of single-atomic iron sites in h^(3)-FNCs by 2.3 times compared to low-and medium-loading SACs.Consequently,the overall catalytic activity of h^(3)-FNC is highly improved,with mass activity and metal mass-specific activity that are,respectively,66 and 315 times higher than those of commercial Pt/C.In addition,h^(3)-FNCs demonstrate efficiently enhanced capability in catalyzing oxygen reduction into superoxide anion(O_(2)·^(−))and glutathione(GSH)depletion.Both in vitro and in vivo assays demonstrate the superior antibacterial efficacy of h^(3)-FNCs in promoting wound healing.This work presents an intriguing activity-enhancement effect in catalysts and exhibits impressive therapeutic efficacy in combating bacterial infections.展开更多
Nonlinear variations in the coordinate time series of global navigation satellite system(GNSS) reference stations are strongly correlated with surface displacements caused by environmental loading effects,including at...Nonlinear variations in the coordinate time series of global navigation satellite system(GNSS) reference stations are strongly correlated with surface displacements caused by environmental loading effects,including atmospheric, hydrological, and nontidal ocean loading. Continuous improvements in the accuracy of surface mass loading products, performance of Earth models, and precise data-processing technologies have significantly advanced research on the effects of environmental loading on nonlinear variations in GNSS coordinate time series. However, owing to theoretical limitations, the lack of high spatiotemporal resolution surface mass observations, and the coupling of GNSS technology-related systematic errors, environmental loading and nonlinear GNSS reference station displacements remain inconsistent. The applicability and capability of these loading products across different regions also require further evaluation. This paper outlines methods for modeling environmental loading, surface mass loading products, and service organizations. In addition, it summarizes recent advances in applying environmental loading to address nonlinear variations in global and regional GNSS coordinate time series. Moreover, the scientific questions of existing studies are summarized, and insights into future research directions are provided. The complex nonlinear motion of reference stations is a major factor limiting the accuracy of the current terrestrial reference frame. Further refining the environmental load modeling method, establishing a surface mass distribution model with high spatiotemporal resolution and reliability, exploring other environmental load factors such as ice sheet and artificial mass-change effects, and developing an optimal data-processing model and strategy for reprocessing global reference station data consistently could contribute to the development of a millimeter-level nonlinear motion model for GNSS reference stations with actual physical significance and provide theoretical support for establishing a terrestrial reference frame with 1 mm accuracy by 2050.展开更多
Ice load on underwater vehicles breaking through ice covers from underneath is a significant concern for researchers in polar exploration,and the research on this problem is still in its early stages.Both mechanical e...Ice load on underwater vehicles breaking through ice covers from underneath is a significant concern for researchers in polar exploration,and the research on this problem is still in its early stages.Both mechanical experimental measurement and numerical simulation pose research challenges.This study focuses on the ice load of a cylinder structure breaking upward through the ice sheet form underneath in the Small Ice Model Basin of China Ship Scientific Research Center(CSSRC SIMB).A high-speed camera system was employed to observe the ice sheet failure during the tests,in which,with the loading position as center,local radial cracks and circumferential cracks were generated.A load sensor was used to measure the overall ice load during this process.Meanwhile,a numerical model was developed using LS-DYNA for validation and comparison.With this model,numerical simulation was conducted under various ice thicknesses and upgoing speeds to analyze the instantaneous curves of ice load.The calculation results were statistically analyzed under different working conditions to determine the influence of the factors on the ice load of the cylinder.The study explores the measurement method about ice load of objects vertically breaking through model ice sheet and is expected to provide some fundamental insights into the safety design of underwater structures operating in ice waters.展开更多
基金Supported by the Development and Application Project of Ship CAE Software.
文摘Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in this paper.The five-point central difference method is used for spatial discretization,and the fourth-order Adams predictor-corrector scheme is employed for marching in time.The domain-decomposition method is applied for the wave-current generation and absorption.The effects of currents on the wave profile and velocity field are examined under two conditions:the same velocity of currents at the still-water level and the constant flow volume of currents.Wave profiles and velocity fields demonstrate substantial differences in three types of currents owing to the diverse vertical distribution of current velocity and vorticity.Then,loads on small-scale vertical cylinders subjected to regular waves and three types of background currents with the same flow volume are investigated.The maximum load intensity and load fluctuation amplitude in uniform,linear shear,and quadratic shear currents increase sequentially.The stretched superposition method overestimates the maximum load intensity and load fluctuation amplitude in opposing currents and underestimates these values in following currents.The stretched superposition method obtains a poor approximation for strong nonlinear waves,particularly in the case of the opposing quadratic shear current.
基金Natural Science Research Project of Education Department of Shaanxi Province,China(No.08JK394).
文摘The non-linear dynamic behaviors of thermoelastic circular plate with varying thickness subjected to radially uniformly distributed follower forces are considered. Two coupled non-linear differential equations of motion for this problem are derived in terms of the transverse deflection and radial displacement component of the mid-plane of the plate. Using the Kantorovich averaging method, the differential equation of mode shape of the plate is derived, and the eigenvalue problem is solved by using shooting method. The eigencurves for frequencies and critical loads of the circular plate with unmovable simply supported edge and clamped edge are obtained. The effects of the variation of thickness and temperature on the frequencies and critical loads of the thermoelastic circular plate subjected to radially uniformly distributed follower forces are then discussed.
文摘Medium-term forecasting is an important category of electric load forecasting that covers a time span of up to one year ahead. It suits outage and maintenance planning, as well as load switching operation. We propose a new methodol-ogy that uses hourly daily loads to predict the next year hourly loads, and hence predict the peak loads expected to be reached in the next coming year. The technique is based on implementing multivariable regression on previous year's hourly loads. Three regression models are investigated in this research: the linear, the polynomial, and the exponential power. The proposed models are applied to real loads of the Jordanian power system. Results obtained using the pro-posed methods showed that their performance is close and they outperform results obtained using the widely used ex-ponential regression technique. Moreover, peak load prediction has about 90% accuracy using the proposed method-ology. The methods are generic and simple and can be implemented to hourly loads of any power system. No extra in-formation other than the hourly loads is required.
文摘<span style="font-family:Verdana;">This study presents an intelligent approach for load frequency control (LFC) of small hydropower plants (SHPs). The approach which is based on fuzzy logic (FL), takes into account the non-linearity of SHPs—something which is not possible using traditional controllers. Most intelligent methods use two-</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">input fuzzy controllers, but because such controllers are expensive, there is </span><span style="font-family:Verdana;">economic interest in the relatively cheaper single-input controllers. A n</span><span style="font-family:Verdana;">on-</span></span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">linear control model based on one-input fuzzy logic PI (FLPI) controller was developed and applied to control the non-linear SHP. Using MATLAB/Si</span><span style="font-family:Verdana;">- </span><span style="font-family:Verdana;">mulink SimScape, the SHP was simulated with linear and non-linear plant models. The performance of the FLPI controller was investigated and compared with that of the conventional PI/PID controller. Results show that the settling time for the FLPI controller is about 8 times shorter;while the overshoot is about 15 times smaller compared to the conventional PI/PID controller. Therefore, the FLPI controller performs better than the conventional PI/PID controller not only in meeting the LFC control objective but also in ensuring increased dynamic stability of SHPs.</span>
文摘The first decision we need to make in a structural load assessment is what approach should be applied, a linear approach or a non-linear one. The correct decision comes from understanding of the technology used in the linear and non-linear approaches and also comes from the understanding of the problem to he analyzed. From engineering practice, it has been found that many non-linear effects can be taken into account in a linear model with appropriate approach. A study of hydrodynamic structural load on a stinger of a pipe-laying vessel is presented in this paper. The results of a non-linear analysis are compared to those of linear models with different approaches, and how the nonlinear effect can be involved in a linear model is discussed. The recommendations on how to estimate the non-linear effects in a linear structural load model is discussed.
文摘This paper presents a non-linear simulation of the impact on a structure with different energy absorption systems using finite element models. Literature review on bistable structure, aluminum foam and expandable polystyrene is presented and taken as basis to propose energy absorption systems. Using a base structure, these systems are implemented by means of finite element modeling. A comparison of the damage caused to the structure in case of impact without implementing energy absorption system, and implementing energy absorption systems based on bistable structures, polystyrene foam and aluminum foam are shown here in. The results demonstrate the advantages of using energy absorption systems on structures under impact loads.
文摘This paper presents development of 3D non-linear finite element model to simulate the response and predict the behavior of un-bonded mild steel bars under axial and bending loading. The models were successfully analyzed with the finite element software ANSYS, taking into account the nonlinear material properties of the reinforced mild steel bars. A bending strain relationship is derived based on a parametric study involving multiple nonlinear finite element models. A mild steel fracture criterion based on low-cycle fatigue models is proposed to control the total (elastic and plastic) strains in the mild steel bar below a maximum permissible limit. In addition, FE predictions of bar elongation due to strain penetration reasonably agreed with a proposed empirical equation by Raynor and Lehman. It was concluded that the equation proposed by Raynor and Lehman is considered valid for estimating the additional unbounded length and can be used in both analysis and design.
文摘<p align="left"> <span style="font-family:Verdana;">The present study evaluates the effects of occlusal loading on an implant-supported dental implant with external hexagon dental implant-abutment systems, using the finite element method analysis. Tensile analyses were performed to simulate different axial and obliquous masticatory loads. The influence of the variations in the contouring conditions of the interfaces was analyzed to weigh the osseointegration with linear and non-linear cases, by means of a parametric design. The geometry selected to place the prostheses was a jaw section, considering the properties of the set of cortical and trabecular bones. The results show that for non-linear contour conditions, the stress presents smaller value distributions and signals a different place in the screw-implant interface as the factor of the greater weight in this study. The location indicated that von Mises stress concentrations are not exclusive to the contact regions studied, moving to an area that is not in direct contact with the non-linear contact interfaces. In addition, the direction of load with an angle of 15 degrees presented the highest values of von Mises stress.</span> </p>
基金Supported by the National Natural Science Foundation of China(Nos.52192693,52192690,52371270,U20A20327)the National Key Research and Development Program of China(Nos.2021YFC2803400).
文摘Ice-breaking methods have become increasingly significant with the ongoing development of the polar regions.Among many ice-breaking methods,ice-breaking that utilizes a moving load is unique compared with the common collision or impact methods.A moving load can generate flexural-gravity waves(FGWs),under the influence of which the ice sheet undergoes deformation and may even experience structural damage.Moving loads can be divided into above-ice loads and underwater loads.For the above-ice loads,we discuss the characteristics of the FGWs generated by a moving load acting on a complete ice sheet,an ice sheet with a crack,and an ice sheet with a lead of open water.For underwater loads,we discuss the influence on the ice-breaking characteristics of FGWs of the mode of motion,the geometrical features,and the trajectory of motion of the load.In addition to discussing the status of current research and the technical challenges of ice-breaking by moving loads,this paper also looks ahead to future research prospects and presents some preliminary ideas for consideration.
基金funded by The Michael J.Fox Foundation for Parkinson’s Research(grant numbers:17244 and 023410)Science Foundation Ireland(grant number:19/FFP/6554)(to ED)。
文摘More than 200 years after Parkinson's disease was first described by the English surgeon whose name would eventually be given to the condition,available treatments remain purely symptomatic,leaving a critical unmet clinical need for a diseasemodifying therapy.
基金financial support from National Natural Science Foundation of China(Grant No.52378488)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX22_0222).
文摘Gas explosion in confined space often leads to significant pressure oscillation.It is widely recognized that structural damage can be severe when the oscillation frequency of the load resonates with the natural vibration frequency of the structure.To reveal the oscillation mechanism of gas explosion load,the experiment of gas explosion was conducted in a large-scale confined tube with the length of 30 m,and the explosion process was numerically analyzed using FLACS.The results show that the essential cause of oscillation effect is the reflection of the pressure wave.In addition,due to the difference in the propagation path of the pressure wave,the load oscillation frequency at the middle position of the tunnel is twice that at the end position.The average sound velocity can be used to calculate the oscillation frequency of overpressure accurately,and the error is less than 15%.The instability of the flame surface and the increase of flame turbulence caused by the interaction between the pressure wave and the flame surface are the main contributors to the increase in overpressure and amplitude.The overpressure peaks calculated by the existing flame instability model and turbulence disturbance model are 31.7%and 34.7%lower than the numerical results,respectively.The turbulence factor model established in this work can describe the turbulence enhancement effect caused by flame instability and oscillatory load,and the difference between the theoretical and numerical results is only 4.6%.In the theoretical derivation of the overpressure model,an improved model of dynamic turbulence factor is established,which can describe the enhancement effect of turbulence factor caused by flame instability and self-turbulence.Based on the one-dimensional propagation theory of pressure wave,the oscillatory effect of the load is derived to calculate the frequency and amplitude of pressure oscillation.The average error of amplitude and frequency is less than 20%.
基金supported by the Chongqing Youth Talent Support Program(Cstc2022ycjh-bgzxm0079)the Chinese National Natural Science Foundation(52379128,51979152)+2 种基金Science Fund for Distinguished Young Scholars of Hubei Proivnce(2023AFA048)Educational Commission of Hubei Province of China(T2020005)the Young Top-notch Talent Cultivation Program of Hubei Province.
文摘In rock drilling and blasting,the misfire of electronic detonators will not only affect the rock fragmentation result but also bring serious potential safety hazards to engineering construction.An accurate and comprehensive understanding of the failure mechanisms of electronic detonators subjected to impact loading is of great significance to the reliability design and field safety use of electronic detonators.The spatial distribution characteristics and failure modes of misfired electronic detonators under different application scenarios are statistically analysed.The results show that under high impact loads,electronic detonators will experience failure phenomena such as rupture of the fuse head,fracture of the bridge wire,falling off of the solder joint,chip module damage and insufficient initiation energy after deformation.The lack of impact resistance is the primary cause of misfire of electronic detonators.Combined with the underwater impact resistance test and the impact load test in the adjacent blasthole on site,the formulas of the impact failure probability of the electronic detonator under different stress‒strength distribution curves are deduced.The test and evaluation method of the impact resistance of electronic detonators based on stress‒strength interference theory is proposed.Furthermore,the impact failure model of electronic detonators considering the strength degradation effect under repeated random loads is established.On this basis,the failure mechanism of electronic detonators under different application environments,such as open-pit blasting and underground blasting,is revealed,which provides scientific theory and methods for the reliability analysis,design and type selection of electronic detonators in rock drilling and blasting.
基金financially supported by the National Natural Science Foundation of China(Grant No.U22B20126)the National Key Research and Development Program of China(Grant No.2022YFC2806100).
文摘With increasing water depth,marine drilling conductors exhibit higher slenderness ratios,significantly reducing their resistance to environmental loads in Arctic waters.These conductors,when subjected to combined wind,current,and ice loads,may experience substantial horizontal displacements and bending moments,potentially compromising off-shore operational safety and wellhead stability.Additionally,soil disturbance near the mudline diminishes the conductor’s bearing capacity,potentially rendering it inadequate for wellhead support and increasing operational risks.This study introduces a static analysis model based on plastic hinge theory to evaluate conductor survivability.The conductor analysis divides the structure into three segments:above waterline,submerged,and embedded below mudline.An idealized elastic-plastic p-y curve model characterizes soil behavior beneath the mudline,while the finite difference method(FDM)analyzes the conductor’s mechanical response under complex pile-head boundary conditions.Numerical simulations using ABAQUS validate the plastic hinge approach against conventional methods,confirming its accuracy in predicting structural performance.These results provide valuable insights for optimizing installation depths and bearing capacity designs of marine drilling conductors in ice-prone regions.
基金financially supported by the National Natural Science Foundation of China(Grant No.42172292)Taishan Scholars Project Special Funding,and Shandong Energy Group(Grant No.SNKJ 2022A01-R26).
文摘A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that the loading parameters(initial normal stress,normal stiffness,and shear velocity)determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle,creating different morphologies of macroscopic step-path rupture surfaces and asperities on them.The differences in stress state and rupture surface induce different cyclic shear responses.It shows that high initial normal stress accelerates asperity degradation,raises shear resistance,and promotes compression of intermittent joints.In addition,high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints.High shear velocity results in a higher shear resistance,greater dilation,and greater compression.Finally,shear strength is most sensitive to initial normal stress,followed by shear velocity and normal stiffness.Moreover,average dilation angle is most sensitive to initial normal stress,followed by normal stiffness and shear velocity.During the shear cycles,frictional coefficient is affected by asperity degradation,backfilling of rock debris,and frictional area,exhibiting a non-monotonic behavior.
文摘Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the information on the seismic behavior of joints of space frames(3D joints)is insufficient.The 3D joints are subjected to bi-directional excitation,which results in an interaction between the shear strength obtained for the joint in the two orthogonal directions separately.The bi-directional seismic behavior of corner reinforced concrete(RC)joints is the focus of this study.First,a detailed finite element(FE)model using the FE software Abaqus,is developed and validated using the test results from the literature.The validated modeling procedure is used to conduct a parametric study to investigate the influence of different parameters such as concrete strength,dimensions of main and transverse beams framing into the joint,presence or absence of a slab,axial load ratio and loading direction on the seismic behavior of joints.By subjecting the models to different combinations of loads on the beams along perpendicular directions,the interaction of the joint shear strength in two orthogonal directions is studied.The comparison of the interaction curves of the joints obtained from the numerical study with a quadratic(circular)interaction curve indicates that in a majority of cases,the quadratic interaction model can represent the strength interaction diagrams of RC beam to column connections with governing joint shear failure reasonably well.
基金Project(2022YJS073)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2024YFE0198500)supported by the National Key Research and Development Program of China:Intergovernmental International Science and Technology Innovation CooperationProject(U2469207)supported by the National Natural Science Foundation Railway Innovation and Development Joint Fund Project,China。
文摘Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force,especially for deep-buried pipes.To better reflect the soil arching effect resulting from the excavation of rectangular jacked pipes and the distribution of the earth pressure on jacked pipes,we present an analytical solution for predicting the vertical earth pressure on deep-buried rectangular pipe jacking tunnels,incorporating the tunnelling-induced ground loss distribution.Our proposed analytical model consists of the upper multi-layer parabolic soil arch and the lower friction arch.The key parameters(i.e.,width and height of friction arch B and height of parabolic soil arch H 1)are determined according to the existing research,and an analytical solution for K l is derived based on the distribution characteristics of the principal stress rotation angle.With consideration for the transition effect of the mechanical characteristics of the parabolic arch zone,an analytical solution for soil load transfer is derived.The prediction results of our analytical solution are compared with tests and simulation results to validate the effectiveness of the proposed analytical solution.Finally,the effects of different parameters on the soil pressure are discussed.
基金National Key Research and Development Program of China,2020YFA0711800,Ting LiuNational Natural Science Foundation of China,52274241,Ting Liu,52474261,Ting Liu+2 种基金Basic Research Program of Jiangsu,BK20240207,Ting Liuthe Fundamental Research Funds for the Central Universities(2023KYJD1007)China Postdoctoral Science Foundation(2022M722672).
文摘To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specifically designed for methane in-situ deflagration fracturing.This experimental system,which is capable of withstanding pressures up to 150 MPa and meanwhile applying axial and confining pressures of up to 50 MPa to rock cores,enables the coupled simulation on methane deflagration and rock core fracturing processes.With the aid of this experimental system,physical simulation experiments on in-situ methane deflagration fracturing were conducted,and the following findings were obtained.Methane deflagration loads in enclosed wellbores exhibit characteristics of multi-level pulsed oscillation.With the rise of initial gas pressure,the peak deflagration load increases approximately linearly,with the pressure amplification factor spanning from 23.14 to 31.10,and its peak loading rate grows exponentially.Accordingly,the fracture volume and fracture porosity augment.To be specific,when the initial gas pressure rises from 0.6 to 2.4 MPa,the fracture volume and fracture porosity augment by factors of 14.0 and 8.73,respectively.The fractal dimension of spatial distribution of fractures also increases with the rise of deflagration load,indicating that a higher deflagration load conduces to the development of a larger and more complex fracture network.Methane deflagration fracturing is characterized as a composite fracture mode that involves the impact of strong stress waves and the driving force of high-pressure fluids.The primary factors influencing damage to coal-rock include the high-stress impact in the initial stage of deflagration,the fluid pressure driving effect in the middle stage,and the thermal shock resulting from high temperatures in the later stage.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFB3804500)the National Natural Science Foundation of China(Grant No.52202352,22335006)+4 种基金the Shanghai Municipal Health Commission(Grant No.20224Y0010)the CAMS Innovation Fund for Medical Sciences(Grant No.2021-I2M-5-012)the Basic Research Program of Shanghai Municipal Government(Grant No.21JC1406000)the Fundamental Research Funds for the Central Universities(Grant No.22120230237,2023-3-YB-11,22120220618)the Basic Research Program of Shanghai Municipal Government(23DX1900200).
文摘The current single-atom catalysts(SACs)for medicine still suffer from the limited active site density.Here,we develop a synthetic method capable of increasing both the metal loading and mass-specific activity of SACs by exchanging zinc with iron.The constructed iron SACs(h^(3)-FNC)with a high metal loading of 6.27 wt%and an optimized adjacent Fe distance of~4 A exhibit excellent oxidase-like catalytic performance without significant activity decay after being stored for six months and promising antibacterial effects.Attractively,a“density effect”has been found at a high-enough metal doping amount,at which individual active sites become close enough to interact with each other and alter the electronic structure,resulting in significantly boosted intrinsic activity of single-atomic iron sites in h^(3)-FNCs by 2.3 times compared to low-and medium-loading SACs.Consequently,the overall catalytic activity of h^(3)-FNC is highly improved,with mass activity and metal mass-specific activity that are,respectively,66 and 315 times higher than those of commercial Pt/C.In addition,h^(3)-FNCs demonstrate efficiently enhanced capability in catalyzing oxygen reduction into superoxide anion(O_(2)·^(−))and glutathione(GSH)depletion.Both in vitro and in vivo assays demonstrate the superior antibacterial efficacy of h^(3)-FNCs in promoting wound healing.This work presents an intriguing activity-enhancement effect in catalysts and exhibits impressive therapeutic efficacy in combating bacterial infections.
基金supported by the Basic Science Center Project of the National Natural Science Foundation of China(42388102)the National Natural Science Foundation of China(42174030)+2 种基金the Special Fund of Hubei Luojia Laboratory(220100020)the Major Science and Technology Program for Hubei Province(2022AAA002)the Fundamental Research Funds for the Central Universities of China(2042022dx0001 and 2042023kfyq01)。
文摘Nonlinear variations in the coordinate time series of global navigation satellite system(GNSS) reference stations are strongly correlated with surface displacements caused by environmental loading effects,including atmospheric, hydrological, and nontidal ocean loading. Continuous improvements in the accuracy of surface mass loading products, performance of Earth models, and precise data-processing technologies have significantly advanced research on the effects of environmental loading on nonlinear variations in GNSS coordinate time series. However, owing to theoretical limitations, the lack of high spatiotemporal resolution surface mass observations, and the coupling of GNSS technology-related systematic errors, environmental loading and nonlinear GNSS reference station displacements remain inconsistent. The applicability and capability of these loading products across different regions also require further evaluation. This paper outlines methods for modeling environmental loading, surface mass loading products, and service organizations. In addition, it summarizes recent advances in applying environmental loading to address nonlinear variations in global and regional GNSS coordinate time series. Moreover, the scientific questions of existing studies are summarized, and insights into future research directions are provided. The complex nonlinear motion of reference stations is a major factor limiting the accuracy of the current terrestrial reference frame. Further refining the environmental load modeling method, establishing a surface mass distribution model with high spatiotemporal resolution and reliability, exploring other environmental load factors such as ice sheet and artificial mass-change effects, and developing an optimal data-processing model and strategy for reprocessing global reference station data consistently could contribute to the development of a millimeter-level nonlinear motion model for GNSS reference stations with actual physical significance and provide theoretical support for establishing a terrestrial reference frame with 1 mm accuracy by 2050.
文摘Ice load on underwater vehicles breaking through ice covers from underneath is a significant concern for researchers in polar exploration,and the research on this problem is still in its early stages.Both mechanical experimental measurement and numerical simulation pose research challenges.This study focuses on the ice load of a cylinder structure breaking upward through the ice sheet form underneath in the Small Ice Model Basin of China Ship Scientific Research Center(CSSRC SIMB).A high-speed camera system was employed to observe the ice sheet failure during the tests,in which,with the loading position as center,local radial cracks and circumferential cracks were generated.A load sensor was used to measure the overall ice load during this process.Meanwhile,a numerical model was developed using LS-DYNA for validation and comparison.With this model,numerical simulation was conducted under various ice thicknesses and upgoing speeds to analyze the instantaneous curves of ice load.The calculation results were statistically analyzed under different working conditions to determine the influence of the factors on the ice load of the cylinder.The study explores the measurement method about ice load of objects vertically breaking through model ice sheet and is expected to provide some fundamental insights into the safety design of underwater structures operating in ice waters.
