Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment m...Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. Recommendations for abutment modeling are made.展开更多
The present study attempts to investigate the role of rigid claws and smooth adhesive pads in the locust Locusta migratoria manilensis,when attaching to various substrates.We measured the attachment forces on sandpape...The present study attempts to investigate the role of rigid claws and smooth adhesive pads in the locust Locusta migratoria manilensis,when attaching to various substrates.We measured the attachment forces on sandpaper and silicate glass plate of locusts with intact attachment system,and those with either the pretarsal claws or the tarsal pads having been entirely destroyed,to explore the role of pads and claws when a locust is walking on various substrates.To obtain information about morphological characteristics and material properties of the claws,we examined the intact and fractured claws by scanning electron microscopy,and tested the fractural force in a fracture experiment.We proposed a mechanical model for locust climbing on a slanting surface to analyze the conduction and final result of the attachment forces generated by the attachment organs on the fore-,mid-and hindlegs.Attachment forces generated by locusts with destroyed pads were similar to those generated by locusts with intact attachment system on both substrates,which presumably indicated that the claws have a significantly important role when attaching to various substrates.The result of the fracture experiment demonstrated that the claws are made of relatively stiff material,and their shear strength ranged between 39-45 MPa.Mechanical analysis of locust climbing on slanting surface showed that the force generated by the hindlegs suspended the whole body of locust up from the surface and pushed the body forward,while the midlegs steadily suspended the centre of gravity and the forelegs pulled the suspended body forward.The results obtained contribute to the further interpretation of the interaction mechanisms between insect attachment system and substrates,and supply information for designing and manufacturing slippery plates for trapping plague locusts.展开更多
Corrugated paperboard is a kind of inexpensive and environmental-friendly packaging material, and may be made into pads of package cushioning to protect products from shock and vibration damage by isolation during dis...Corrugated paperboard is a kind of inexpensive and environmental-friendly packaging material, and may be made into pads of package cushioning to protect products from shock and vibration damage by isolation during distribution. This article deals with the characterization of dynamic packaging properties of corru-gated paperboard pads, such as dynamic cushioning curves, vibration transmissibility and frequency curves. The main feature of article is the evaluation on the dynamic shock cushioning property and vibration trans-missibility of corrugated paperboard pads by a series of experimental studies on the drop shock tester and vibration tester, the establishment of experimental formulas of dynamic cushioning curves, and the analysis of resonance frequencies and vibration transmissibility. By using the fitting polynomial of curve and method of the least mean square, the experimental formulas with third order polynomial function of dynamic cush-ioning curves for corrugated paperboard pads are obtained. By using linear vibration theory with single de-gree of freedom, the resonance frequencies, vibration transmissibility and damping ratios of corrugated pa-perboard pads at different static loads are acquired. All results show the dynamic properties relevant to de-sign applications of corrugated paperboard pads for protective packaging.展开更多
The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scann...The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scanning techniques,and the 3D dynamic model of the rail-sleeper-ballast bed was constructed using the coupled discrete element method-multiflexible-body dynamics(DEM-MFBD)approach.We analyse the meso-mechanical dynamics of the ballast bed with USPs under dynamic load on a train and verify the correctness of the model in laboratory tests.It is shown that the deformation of the USPs increases the contact area between the sleeper and the ballast particles,and subsequently the number of contacts between them.As the depth of the granular ballast bed increases,the contact area becomes larger,and the contact force between the ballast particles gradually decreases.Under the action of the elastic USPs,the contact forces between ballast particles are reduced and the overall vibration level of the ballast bed can be reduced.The settlement of the granular ballast bed occurs mainly at the shallow position of the sleeper bottom,and the installation of the elastic USPs can be effective in reducing the stress on the ballast particles and the settlement of the ballast bed.展开更多
BACKGROUND As one of the most common aesthetic surgical procedures carried out today,blepharoplasty should be in the repertoire of every plastic surgeon.The term blepharoplasty encompasses a wide range of techniques a...BACKGROUND As one of the most common aesthetic surgical procedures carried out today,blepharoplasty should be in the repertoire of every plastic surgeon.The term blepharoplasty encompasses a wide range of techniques and options that must be tailored to the specific defect and patient one has to treat.A sound knowledge of the upper and lower eyelids’anatomy is essential for proper surgical execution.Trends have shifted towards more conservative methods(especially of the fat compartment)and sometimes in combination with augmentation techniques,helping to reach a rejuvenated appearance.AIM To present an overview of the surgical techniques considered for upper lid blepharoplasty and fat pad management,in addition to information on how a surgeon may approach the best treatment for his patient based on current publications in literature.METHODS We searched the literature published between 2013,to 2023 using Medline and Reference Citation Analysis.The database was searched using the keywords“upper blepharoplasty”AND“fat”.Papers without full text/abstracts and reviews were excluded.The search strategy followed the PRISMA.The American Society of Plastic Surgeons guidelines for Therapeutic Studies checklist was used to assess all articles.Two authors individually reviewed each article and rated them for importance and relevance to the topic.A consensus was sought and the most relevant studies.RESULTS After the application of the selection criteria used in our review,13 publications were found to address upper lid blepharoplasty specifically.Three of these studies were reviews and three were retrospective studies.Five publications were comparative studies and a further two were clinical trials.CONCLUSION The tendency of modern surgery is to be conservative,by removing adipose tissue only if strictly necessary and restoring the volume of the upper eyelid in a concept of beauty that espouses a"full"sight.There is no gold standard technique to achieve younger and enhanced eyelids.Long-term prospective comparative stu展开更多
Train braking performance is important for the safety and reliability of railway systems. The availability of a tool that allows evaluating such performance on the basis of the main train features can be useful for tr...Train braking performance is important for the safety and reliability of railway systems. The availability of a tool that allows evaluating such performance on the basis of the main train features can be useful for train system designers to choose proper dimensions for and optimize train＇s subsystems. This paper presents a modular tool for the prediction of train braking performance, with a par- ticular attention to the accurate prediction of stopping distances. The tool takes into account different loading and operating conditions, in order to verify the safety require- ments prescribed by European technical specifications for interoperability of high-speed trains and the corresponding EN regulations. The numerical results given by the tool were verified and validated by comparison with experimental data, considering as benchmark case an Ansaldo EMU V250 train--a European high-speed train--currently developed for Belgium and Netherlands high-speed lines, on which technical information and experimental data directly recorded during the preliminary tests were available. An accurate identification of the influence of the braking pad friction factor on braking performances allowed obtaining reliable results.展开更多
When a human lands from a high drop,there is a high risk of serious injury to the lower limbs.On the other hand,cats can withstand jumps and falls from heights without being fatally wounded,largely due to their impact...When a human lands from a high drop,there is a high risk of serious injury to the lower limbs.On the other hand,cats can withstand jumps and falls from heights without being fatally wounded,largely due to their impact-resistant paw pads.The aim of the present study was to investigate the biomechanism of impact resistance in cat paw pads,propose an optimal hierarchical Voronoi structure inspired by the paw pads,and apply the structure to bionic cushioning shoes to reduce the impact force of landing for humans.The microstructure of cat paw pads was observed via tissue section staining,and a simulation model was reconstructed based on CT to verify and optimize the structural cushioning capacity.The distribution pattern,wall thickness of compartments,thickness ratio of epidermis and dermis,and number of compartments in the model were changed and simulated to achieve an optimal composed structure.A bionic sole was 3D-printed,and its performance was evaluated via compression test and a jumping-landing experiment.The results show that cat paw pads are a spherical cap structure,divided from the outside to the inside into the epidermis,dermis,and compartments,each with different cushioning capacities.A finite element simulation of different cushioning structures was conducted in a cylinder with a diameter of 20 mm and a height of 10 mm,featuring a three-layer structure.The optimal configuration of the three layers should have a uniform distribution with 0.3–0.5 mm wall thickness,a 1:1–2 thickness ratio of epidermis and dermis,and 100–150 compartments.A bionic sole with an optimized structure can reduce the peak impact force and delay the peak arrival time.Its energy absorption rate is about 4 times that of standard sole.When jumping 80,100,and 120 cm,the normalized ground reaction force is also reduced by 8.7%,12.6%and 15.1%compared with standard shoes.This study provides theoretical and technical support for effective protection against human lower limb landing injuries.展开更多
The menstrual cycle is always considered as a big nightmare by many women. This research aims to make this process smooth and safe by developing natural sanitary pads which are used to absorb and retain menstrual bloo...The menstrual cycle is always considered as a big nightmare by many women. This research aims to make this process smooth and safe by developing natural sanitary pads which are used to absorb and retain menstrual blood from the body. Some existing sanitary pads contain 90% plastics made of non-woven polypropylene/polyethylene sheets, super absorbent polymers, and polyethylene back sheets that will take up to 600 - 800 years to decompose. So, biodegradable sanitary pads using natural fibers are the best alternative to eliminate the pads which contain non-biodegradable materials. In this research, nonwoven bamboo will be used as the top layer, nonwoven cotton will be used as the second layer, the absorbent core is to be made by the combination of kenaf and chitosan fibers as the third layer, cotton as the fourth layer, and cornstarch-based bioplastic sheets as the bottom layer. These biodegradable natural materials will change the menstrual process into a healthy one as well as create a robust ecological community.展开更多
In order to investigate propagation regularity of hydraulic fractures in the mode of multi-well pads, numerical modeling of simultaneous hydraulic fracturing of multiple wells was conducted. The mathematical model was...In order to investigate propagation regularity of hydraulic fractures in the mode of multi-well pads, numerical modeling of simultaneous hydraulic fracturing of multiple wells was conducted. The mathematical model was established coupling rock deformation with fluid flow in the fractures and wellbores. And then the model was solved by displacement discontinuity method coupling with implicit level set method. The implicit method was based on fracture tip asymptotical solution and used to determine fracture growth length. Simulation results showed that when multiple wells were fractured simultaneously, adjacent fractures might propagate towards each other, showing an effect of attraction other than repulsion. Fracture spacing and well spacing had significant influence on the propagation path and geometry of multiple fractures. Furthermore, when multiple wells were fractured simultaneously, stress reversal regions had a large area, and stress reversal regions were distributed not only in the area between fractures but also on the outside of them. The area of stress reversal regions was related to fracture spacing and well spacing. Results indicated that multi-well fracturing induced larger area of stress reversal regions than one-well fracturing, which was beneficial to generating complex fracture network in unconventional reservoirs.展开更多
Non-contacting finger seals represent an advanced non-contacting and compliant seal in gas turbine sealing technology.This paper proposes a new structure of noncontacting finger seals with double interlocking pads.The...Non-contacting finger seals represent an advanced non-contacting and compliant seal in gas turbine sealing technology.This paper proposes a new structure of noncontacting finger seals with double interlocking pads.The numerical analysis model based on the thermo-fluid-structure coupling method for the new type finger seal was established.The influence of working conditions on leakage of the seal was studied and compared with the single padded non-contacting finger seal.The results show that the interface between the bottom of the finger pad and rotor surface is the main leakage path that forms the gas film with obvious variations of pressure and flow velocity.Under high temperature and high pressure operating conditions,the hydrodynamic effect of the gas film is enhanced,and lifting force is significantly improved.The deformation of fingers is composed of elastic deformation and thermal deformation.At room temperature,the deformation of fingers is mainly elastic deformation and points to the center of the rotor,which reduces the gas film clearance.The deformation of fingers at high temperature and high pressure creates a circumferentially convergent gap between the bottom of the pad and the rotor,which is beneficial to improve the loading capacity and to reduce leakage of the seal.Compared with the typical single padded noncontacting finger seal,the double interlocking padded finger seal proposed in this paper reduces the leakage factor by about 37%,which provides an advanced seal concept with the potential to improve sealing performance under high temperature and high pressure working conditions.展开更多
A frequency and amplitude dependent model is used to describe the complex behavior of rail pads. It is implemented into the dynamic analysis of three dimensional coupled vehicle-slab track （3D-CVST） systems. The veh...A frequency and amplitude dependent model is used to describe the complex behavior of rail pads. It is implemented into the dynamic analysis of three dimensional coupled vehicle-slab track （3D-CVST） systems. The vehicle is treated as a 35-degree- of-freedom multi-body system, and the slab track is represented by two continuous Bernoulli-Euler beams supported by a se- ries of elastic rectangle plates on a viscoelastic foundation. The rail pad model takes into account the influences of the excita- tion frequency and of the displacement amplitude through a fractional derivative element, and a nonlinear friction element, re- spectively. The Granwald representation of the fractional derivatives is employed to numerically solve the fractional and non- linear equations of motion of the 3D-CVST system by means of an explicit integration algorithm. A dynamic analysis of the 3D-CVST system exposed to excitations of rail harmonic irregularities is primarily carried out, which reveals the dependence of stiffness and damping on excitation frequency and displacement amplitude. Subsequently, sensitive analyses of the model parameters are investigated by conducting the dynamic analysis of the 3D-CVST system subjected to excitations of welded rail joint irregularities. Following this, parameters of the rail pad model are optimized with respect to experimental values. For elu- cidation, the 3D-CVST dynamic model incorporated with the rail pads model is used to calculate the wheel/rail forces induced by excitations of measured random track irregularities. Further, the numerical results are compared with experimental data, demonstrating the reliability of the proposed model.展开更多
基金Supported by:U.S.National Science Foundation to the Pacifi c Earthquake Engineering Research Center(PEER)Under Grant No.EEC-9701568
文摘Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. Recommendations for abutment modeling are made.
基金supported by the National Natural Science Foundation of China (50775214)the Fundamental Research Funds of China Agricul-tural University for Special Post-graduate Research and Innovation Funding (kycx09099)
文摘The present study attempts to investigate the role of rigid claws and smooth adhesive pads in the locust Locusta migratoria manilensis,when attaching to various substrates.We measured the attachment forces on sandpaper and silicate glass plate of locusts with intact attachment system,and those with either the pretarsal claws or the tarsal pads having been entirely destroyed,to explore the role of pads and claws when a locust is walking on various substrates.To obtain information about morphological characteristics and material properties of the claws,we examined the intact and fractured claws by scanning electron microscopy,and tested the fractural force in a fracture experiment.We proposed a mechanical model for locust climbing on a slanting surface to analyze the conduction and final result of the attachment forces generated by the attachment organs on the fore-,mid-and hindlegs.Attachment forces generated by locusts with destroyed pads were similar to those generated by locusts with intact attachment system on both substrates,which presumably indicated that the claws have a significantly important role when attaching to various substrates.The result of the fracture experiment demonstrated that the claws are made of relatively stiff material,and their shear strength ranged between 39-45 MPa.Mechanical analysis of locust climbing on slanting surface showed that the force generated by the hindlegs suspended the whole body of locust up from the surface and pushed the body forward,while the midlegs steadily suspended the centre of gravity and the forelegs pulled the suspended body forward.The results obtained contribute to the further interpretation of the interaction mechanisms between insect attachment system and substrates,and supply information for designing and manufacturing slippery plates for trapping plague locusts.
文摘Corrugated paperboard is a kind of inexpensive and environmental-friendly packaging material, and may be made into pads of package cushioning to protect products from shock and vibration damage by isolation during distribution. This article deals with the characterization of dynamic packaging properties of corru-gated paperboard pads, such as dynamic cushioning curves, vibration transmissibility and frequency curves. The main feature of article is the evaluation on the dynamic shock cushioning property and vibration trans-missibility of corrugated paperboard pads by a series of experimental studies on the drop shock tester and vibration tester, the establishment of experimental formulas of dynamic cushioning curves, and the analysis of resonance frequencies and vibration transmissibility. By using the fitting polynomial of curve and method of the least mean square, the experimental formulas with third order polynomial function of dynamic cush-ioning curves for corrugated paperboard pads are obtained. By using linear vibration theory with single de-gree of freedom, the resonance frequencies, vibration transmissibility and damping ratios of corrugated pa-perboard pads at different static loads are acquired. All results show the dynamic properties relevant to de-sign applications of corrugated paperboard pads for protective packaging.
基金supported by the National Natural Science Foundation of China under Grants Nos.52165013 and 51565021.
文摘The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scanning techniques,and the 3D dynamic model of the rail-sleeper-ballast bed was constructed using the coupled discrete element method-multiflexible-body dynamics(DEM-MFBD)approach.We analyse the meso-mechanical dynamics of the ballast bed with USPs under dynamic load on a train and verify the correctness of the model in laboratory tests.It is shown that the deformation of the USPs increases the contact area between the sleeper and the ballast particles,and subsequently the number of contacts between them.As the depth of the granular ballast bed increases,the contact area becomes larger,and the contact force between the ballast particles gradually decreases.Under the action of the elastic USPs,the contact forces between ballast particles are reduced and the overall vibration level of the ballast bed can be reduced.The settlement of the granular ballast bed occurs mainly at the shallow position of the sleeper bottom,and the installation of the elastic USPs can be effective in reducing the stress on the ballast particles and the settlement of the ballast bed.
文摘BACKGROUND As one of the most common aesthetic surgical procedures carried out today,blepharoplasty should be in the repertoire of every plastic surgeon.The term blepharoplasty encompasses a wide range of techniques and options that must be tailored to the specific defect and patient one has to treat.A sound knowledge of the upper and lower eyelids’anatomy is essential for proper surgical execution.Trends have shifted towards more conservative methods(especially of the fat compartment)and sometimes in combination with augmentation techniques,helping to reach a rejuvenated appearance.AIM To present an overview of the surgical techniques considered for upper lid blepharoplasty and fat pad management,in addition to information on how a surgeon may approach the best treatment for his patient based on current publications in literature.METHODS We searched the literature published between 2013,to 2023 using Medline and Reference Citation Analysis.The database was searched using the keywords“upper blepharoplasty”AND“fat”.Papers without full text/abstracts and reviews were excluded.The search strategy followed the PRISMA.The American Society of Plastic Surgeons guidelines for Therapeutic Studies checklist was used to assess all articles.Two authors individually reviewed each article and rated them for importance and relevance to the topic.A consensus was sought and the most relevant studies.RESULTS After the application of the selection criteria used in our review,13 publications were found to address upper lid blepharoplasty specifically.Three of these studies were reviews and three were retrospective studies.Five publications were comparative studies and a further two were clinical trials.CONCLUSION The tendency of modern surgery is to be conservative,by removing adipose tissue only if strictly necessary and restoring the volume of the upper eyelid in a concept of beauty that espouses a"full"sight.There is no gold standard technique to achieve younger and enhanced eyelids.Long-term prospective comparative stu
文摘Train braking performance is important for the safety and reliability of railway systems. The availability of a tool that allows evaluating such performance on the basis of the main train features can be useful for train system designers to choose proper dimensions for and optimize train＇s subsystems. This paper presents a modular tool for the prediction of train braking performance, with a par- ticular attention to the accurate prediction of stopping distances. The tool takes into account different loading and operating conditions, in order to verify the safety require- ments prescribed by European technical specifications for interoperability of high-speed trains and the corresponding EN regulations. The numerical results given by the tool were verified and validated by comparison with experimental data, considering as benchmark case an Ansaldo EMU V250 train--a European high-speed train--currently developed for Belgium and Netherlands high-speed lines, on which technical information and experimental data directly recorded during the preliminary tests were available. An accurate identification of the influence of the braking pad friction factor on braking performances allowed obtaining reliable results.
基金approved by the Science and Ethics Committee of the School of Biological Science and Medical Engineering at Beihang University(protocol code:BM201900125).
文摘When a human lands from a high drop,there is a high risk of serious injury to the lower limbs.On the other hand,cats can withstand jumps and falls from heights without being fatally wounded,largely due to their impact-resistant paw pads.The aim of the present study was to investigate the biomechanism of impact resistance in cat paw pads,propose an optimal hierarchical Voronoi structure inspired by the paw pads,and apply the structure to bionic cushioning shoes to reduce the impact force of landing for humans.The microstructure of cat paw pads was observed via tissue section staining,and a simulation model was reconstructed based on CT to verify and optimize the structural cushioning capacity.The distribution pattern,wall thickness of compartments,thickness ratio of epidermis and dermis,and number of compartments in the model were changed and simulated to achieve an optimal composed structure.A bionic sole was 3D-printed,and its performance was evaluated via compression test and a jumping-landing experiment.The results show that cat paw pads are a spherical cap structure,divided from the outside to the inside into the epidermis,dermis,and compartments,each with different cushioning capacities.A finite element simulation of different cushioning structures was conducted in a cylinder with a diameter of 20 mm and a height of 10 mm,featuring a three-layer structure.The optimal configuration of the three layers should have a uniform distribution with 0.3–0.5 mm wall thickness,a 1:1–2 thickness ratio of epidermis and dermis,and 100–150 compartments.A bionic sole with an optimized structure can reduce the peak impact force and delay the peak arrival time.Its energy absorption rate is about 4 times that of standard sole.When jumping 80,100,and 120 cm,the normalized ground reaction force is also reduced by 8.7%,12.6%and 15.1%compared with standard shoes.This study provides theoretical and technical support for effective protection against human lower limb landing injuries.
文摘The menstrual cycle is always considered as a big nightmare by many women. This research aims to make this process smooth and safe by developing natural sanitary pads which are used to absorb and retain menstrual blood from the body. Some existing sanitary pads contain 90% plastics made of non-woven polypropylene/polyethylene sheets, super absorbent polymers, and polyethylene back sheets that will take up to 600 - 800 years to decompose. So, biodegradable sanitary pads using natural fibers are the best alternative to eliminate the pads which contain non-biodegradable materials. In this research, nonwoven bamboo will be used as the top layer, nonwoven cotton will be used as the second layer, the absorbent core is to be made by the combination of kenaf and chitosan fibers as the third layer, cotton as the fourth layer, and cornstarch-based bioplastic sheets as the bottom layer. These biodegradable natural materials will change the menstrual process into a healthy one as well as create a robust ecological community.
基金supported by the National Natural Science Foundation of China(Grant Nos.51234007&51490654)the National Science Foundation for Young Scientists of China(Grant No.51404291)+1 种基金Fundamental Research Funds for Central Universities(Grant Nos.14CX05024A&14CX02045A)Shandong Provincial Natural Science Foundation(Grant No.ZR2014EEQ010)
文摘In order to investigate propagation regularity of hydraulic fractures in the mode of multi-well pads, numerical modeling of simultaneous hydraulic fracturing of multiple wells was conducted. The mathematical model was established coupling rock deformation with fluid flow in the fractures and wellbores. And then the model was solved by displacement discontinuity method coupling with implicit level set method. The implicit method was based on fracture tip asymptotical solution and used to determine fracture growth length. Simulation results showed that when multiple wells were fractured simultaneously, adjacent fractures might propagate towards each other, showing an effect of attraction other than repulsion. Fracture spacing and well spacing had significant influence on the propagation path and geometry of multiple fractures. Furthermore, when multiple wells were fractured simultaneously, stress reversal regions had a large area, and stress reversal regions were distributed not only in the area between fractures but also on the outside of them. The area of stress reversal regions was related to fracture spacing and well spacing. Results indicated that multi-well fracturing induced larger area of stress reversal regions than one-well fracturing, which was beneficial to generating complex fracture network in unconventional reservoirs.
文摘Non-contacting finger seals represent an advanced non-contacting and compliant seal in gas turbine sealing technology.This paper proposes a new structure of noncontacting finger seals with double interlocking pads.The numerical analysis model based on the thermo-fluid-structure coupling method for the new type finger seal was established.The influence of working conditions on leakage of the seal was studied and compared with the single padded non-contacting finger seal.The results show that the interface between the bottom of the finger pad and rotor surface is the main leakage path that forms the gas film with obvious variations of pressure and flow velocity.Under high temperature and high pressure operating conditions,the hydrodynamic effect of the gas film is enhanced,and lifting force is significantly improved.The deformation of fingers is composed of elastic deformation and thermal deformation.At room temperature,the deformation of fingers is mainly elastic deformation and points to the center of the rotor,which reduces the gas film clearance.The deformation of fingers at high temperature and high pressure creates a circumferentially convergent gap between the bottom of the pad and the rotor,which is beneficial to improve the loading capacity and to reduce leakage of the seal.Compared with the typical single padded noncontacting finger seal,the double interlocking padded finger seal proposed in this paper reduces the leakage factor by about 37%,which provides an advanced seal concept with the potential to improve sealing performance under high temperature and high pressure working conditions.
基金supported by the National Basic Research Program of China("973"Project)(Grant Nos.2013CB036202 and 2013CB036206)the Science and Technology Development Program of China Railway Corporation(Grant No.2014G002-B)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.2682013CX029)the 2013 Cultivation Program for the Excellent Doctoral Dissertation of Southwest Jiaotong University
文摘A frequency and amplitude dependent model is used to describe the complex behavior of rail pads. It is implemented into the dynamic analysis of three dimensional coupled vehicle-slab track （3D-CVST） systems. The vehicle is treated as a 35-degree- of-freedom multi-body system, and the slab track is represented by two continuous Bernoulli-Euler beams supported by a se- ries of elastic rectangle plates on a viscoelastic foundation. The rail pad model takes into account the influences of the excita- tion frequency and of the displacement amplitude through a fractional derivative element, and a nonlinear friction element, re- spectively. The Granwald representation of the fractional derivatives is employed to numerically solve the fractional and non- linear equations of motion of the 3D-CVST system by means of an explicit integration algorithm. A dynamic analysis of the 3D-CVST system exposed to excitations of rail harmonic irregularities is primarily carried out, which reveals the dependence of stiffness and damping on excitation frequency and displacement amplitude. Subsequently, sensitive analyses of the model parameters are investigated by conducting the dynamic analysis of the 3D-CVST system subjected to excitations of welded rail joint irregularities. Following this, parameters of the rail pad model are optimized with respect to experimental values. For elu- cidation, the 3D-CVST dynamic model incorporated with the rail pads model is used to calculate the wheel/rail forces induced by excitations of measured random track irregularities. Further, the numerical results are compared with experimental data, demonstrating the reliability of the proposed model.
