Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally,but the lack of studies of real environmental conditions on these absorbers is felt...Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally,but the lack of studies of real environmental conditions on these absorbers is felt.The present work investigates the effect of viscoelasticity on the stability and bifurcations of a system attached to a nonlinear energy sink(NES).In this paper,the Burgers model is assumed for the viscoelasticity in an NES,and a linear oscillator system is considered for investigating the instabilities and bifurcations.The equations of motion of the coupled system are solved by using the harmonic balance and pseudo-arc-length continuation methods.The results show that the viscoelasticity affects the frequency intervals of the Hopf and saddle-node branches,and by increasing the stiffness parameters of the viscoelasticity,the conditions of these branches occur in larger ranges of the external force amplitudes,and also reduce the frequency range of the branches.In addition,increasing the viscoelastic damping parameter has the potential to completely eliminate the instability of the system and gradually reduce the amplitude of the jump phenomenon.展开更多
Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between and shear rat...Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between and shear rate (), and topologically constrained dimension number and a were derived. Linear viscoelastic parameters and and topologically constrained dimension number and as a function of the primary molecular weight, molecular weight between entanglements and the entanglement sites sequence distribution in polymer chain were determined. A new method for determination of viscoelastic parameters G and topologically constrained dimension number a and and molecular weight and from the shear flow measurements was proposed. It was used to determine those parameters and structures of HDPE, making a good agreement between these values and those obtained by other methods. The agreement affords a quantitative verification for the molecular theory of nonlinear viscoelasticity with constrained entanglement in polymer melts.展开更多
Based on Womersley’s theory, the frequency equation satisfied by a complex wave velocity of a pulse wave in arteries was generalized to viscoelastic blood, a general formula of the complex wave velocity with regard t...Based on Womersley’s theory, the frequency equation satisfied by a complex wave velocity of a pulse wave in arteries was generalized to viscoelastic blood, a general formula of the complex wave velocity with regard to both linearly viscoelastic arteries and linearly viscolelastic blood was obtained, and the effects of the viscoelastic property of blood on the phase velocity and the wave attenuation of the pulse wave using the formula systematically was discussed. It is concluded that the influence of the blood elasticity on the wave propagation of a pulse wave in arteries is weaker than that of the arterial viscosity and may be neglected in larger arteries.展开更多
Frequency-dependent amplitude versus offset(FAVO)inversion is a popular method to estimate the frequency-dependent elastic parameters by using amplitude and frequency information of pre-stack seismic data to guide flu...Frequency-dependent amplitude versus offset(FAVO)inversion is a popular method to estimate the frequency-dependent elastic parameters by using amplitude and frequency information of pre-stack seismic data to guide fluid identification.Current frequency-dependent AVO inversion methods are mainly based on elastic theory without the consideration of the viscoelasticity of oil/gas.A fluid discrimination approach is proposed in this study by incorporating the viscoelasticity and relevant FAVO inversion.Based on viscoelastic and rock physics theories,a frequency-dependent viscoelastic solid-liquid decoupling fluid factor is initially constructed,and its sensitivity in fluid discrimination is compared with other conventional fluid factors.Furthermore,a novel reflectivity equation is derived in terms of the viscoelastic solid-liquid decoupling fluid factor.Due to the introduction of viscoelastic theory,the proposed reflectivity is related to frequency,which is more widely applicable than the traditional elastic reflectivity equation directly derived from the elastic reflectivity equation on frequency.Finally,a pragmatic frequency-dependent inversion method is introduced to verify the feasibility of the equation for frequency-dependent viscoelastic solid-liquid decoupling fluid factor prediction.Synthetic and field data examples demonstrate the feasibility and stability of the proposed approach in fluid discrimination.展开更多
Aim:The oxidized low-density lipoprotein(OxLDL) plays an important role in atherosclerosis yet it remains unclear if it damages circulating erythrocytes. Method: In this study。
There are complex and perfect coagulation, anticoagulation and fibrinolysis systems in the human body and their fine regulatory mechanisms. Once the coagulation system and its regulatory mechanisms are destroyed, blee...There are complex and perfect coagulation, anticoagulation and fibrinolysis systems in the human body and their fine regulatory mechanisms. Once the coagulation system and its regulatory mechanisms are destroyed, bleeding or thrombosis will occur very soon. In the blood coagulation, the blood viscoelasticity changes. Therefore, the thrombus elasticity measurement technology can be used to continuously monitor the changing blood viscoelasticity in order to study the process of coagulation. The results of the interaction among the various components of the blood can be obtained from coagulation to fibrinolysis by bedside detection. The traditional electromagnetic induction sensors, based on conventional coil inductance, are manufactured complexly, high cost and non-linear. Therefore, this paper proposes a non-Newtonian fluid viscoelasticity measurement method based on the piezoelectric effect. We use the piezoelectric bimorphs with the diameter of 21 mm and the total thickness of 0.38 mm and DSM coupling probes with the length of 3 mm, 5 mm and 7 mm to design the piezoelectric bimorphs driver. The viscoelasticity of different non-Newtonian fluids is tested. The vibration amplitudes of the piezoelectric bimorphs and liquid surfaces range from 0.43 μm to 3.52 μm. Consequently, the feasibility of in vitro detection of thrombus is confirmed in principle and the above scheme is validated theoretically and experimentally, which provides the basis for the measurement of blood viscoelasticity, the in vitro detection of thrombus and the manufacture of blood coagulation instrument.展开更多
Elastic modulus is an important physical parameter of molding sand; it is closely connected with molding sand’s properties. Based on theories of rheology and molding sand microdeformation, elastic modulus of molding ...Elastic modulus is an important physical parameter of molding sand; it is closely connected with molding sand’s properties. Based on theories of rheology and molding sand microdeformation, elastic modulus of molding sand was measured and investigated using the intelligent molding sand multi-property tester developed by ourselves. The measuring principle was introduced. Effects of bentonite percentage and compactibility of the molding sand were experimentally studied. Furthermore, the essential viscoelastic nature of green sand was analyzed. It is considered that viscoelastic deformation of molding sand consists mainly of that of Kelvin Body of clay membrane, and elastic modulus of molding sand depends mainly on that of Kelvin Body which is the elastic component of clay membrane between sands. Elastic modulus can be adopted as one of the property parameters, and can be employed to evaluate the viscoelastic properties of molding sand.展开更多
Polymeric solid electrolyte system composed of triglycidyl ether of glycerol （TGEG）, diglycidyl ether of polyethylene glycol （DGEPEG）and LiClO<sub>4</sub> salt were synthesized. In this" system th...Polymeric solid electrolyte system composed of triglycidyl ether of glycerol （TGEG）, diglycidyl ether of polyethylene glycol （DGEPEG）and LiClO<sub>4</sub> salt were synthesized. In this" system the electrolyte has a pecularity that not merely can the LiClO<sub>4</sub> provide ionic carriers, but also catalyze the crosslinking reaction without adding an usual curing agent. The effect of salt content and degree of crosslinking on the viscoelasticity and ionic conductivity were studied. Both WLF and VTF equations were used to treat the experimental data in order to elucidate the mechanism of ionic conduction. It was found that the ionic conductivity of the system is carded out through the segmental motion mechanism. However, the data must be treated with care. For example, in evaluating WLF parameters, the contribution concerned with ionic carrier generation with temperature to the conductivity must be differentiated from that concerned with segmental motion. Besides, the temperature range suitable to WLF equation must also be considered. For VTF equation, it might be inapplicable ff the temperature is too low and close to the glass transition temperature of the specimen. Further study is needed in order to have a quantitative information on the limitation of these equations.展开更多
This paper deals with blood fiow caused by microvascular vasomotion with the focus on the effects of blood viscoelasticity on the pressure rise and wall resistance. It is shown that rnicrovascular vasomotion plays a r...This paper deals with blood fiow caused by microvascular vasomotion with the focus on the effects of blood viscoelasticity on the pressure rise and wall resistance. It is shown that rnicrovascular vasomotion plays a role of the 'second heart' of the body which is of importance in conveying blood, and that the effects of blood viscoelasticity greatly depend on the Weissenberg number and mean flow rate.展开更多
An explicit relation between constitutive porameters and quasi-static displacementof viscoelasticity is derived under a kind of boundary condition,and an iterative form of optimixed idenification is presented .Viscoel...An explicit relation between constitutive porameters and quasi-static displacementof viscoelasticity is derived under a kind of boundary condition,and an iterative form of optimixed idenification is presented .Viscoelastic constitutive models are identifiedfrom a two order differential model ,and effects of information errors on results of inverse analysis are discussed.展开更多
Despite the wide usage of isotropic fibrous composites with a viscoelastic polymer matrix,no analytic model for their mechanical behaviour is known.This paper develops such a model for time-dependent Young's modul...Despite the wide usage of isotropic fibrous composites with a viscoelastic polymer matrix,no analytic model for their mechanical behaviour is known.This paper develops such a model for time-dependent Young's modulus,showing that for typical constituents the time constants of composites are up to about 6% greater than the matrix shear time constant.Viscoelasticity is strongly suppressed for stiff fibres even at modest fibre volume fractions.Comparison with known results for particle and oriented fibre composites confirms isotropic fibrous composites as between the two in terms of viscoelastic behaviour,but more similar to the latter.展开更多
A double-network model is established, which consists of the segments, E and A-constituent chains, the polymeric chains entangled with other ones by multi-entanglement and polymeric chains connected to a great number ...A double-network model is established, which consists of the segments, E and A-constituent chains, the polymeric chains entangled with other ones by multi-entanglement and polymeric chains connected to a great number of destructible particles by multi-adsorption, based on which the E and A-constituent chains can be recreated and released dynamically. The distribution function of the end-to-end vector, the statistical distribution function of conformation for two kinds of chains in the multi-entanglement and multi-adsorption states and their number of polymeric chains are calculated by the combination of statistical mechanics and kinetics. Then the viscoelastic free energies of deformation for two kinds of the networks and suspensions are calculated by Boltzmann’s statistical theory. Also. elastic modulus and memory function for two kinds of the network and suspensions are derived. Consequently, a new molecular theory of the non-linear viscoelasticity for polymeric suspensions is proposed, and the constitutive equation and material function with yielding and thinning for the polymeric suspensions in different flow fields are derived from this theory.展开更多
It has been reported that overweight Japanese males have poorly organised dermis and their skin may be fragile to external forces because of decreased dermal echogenicity. However, it is unknown whether the changes in...It has been reported that overweight Japanese males have poorly organised dermis and their skin may be fragile to external forces because of decreased dermal echogenicity. However, it is unknown whether the changes in the dermal structure actually affect the dermal function. The objective of this study was to clarify the relationship between dermal structural parameters and dermal functional parameters in overweight and obese Japanese males. A cross-sectional, observational study was conducted on Japanese male volunteers. Two ultrasound scanners, a 20-MHz Dermascan C<sup>®</sup> and an 18-MHz Mylab<sup>TM</sup> five<sup>®</sup> were used to evaluate dermal structure. Echogenicity of the lower dermis and dermal thickness of the participants’ abdomens and thighs were measured. A Cutometer<sup>®</sup> MPA580 was used to evaluate skin viscoelasticity, skin deformation (R0) and elasticity (R2, R7). The correlation between dermal structural parameters and skin viscoelasticity were validated using Pearson’s correlation coefficient or Spearman’s correlation coefficient by rank test. A total of 79 male volunteers were recruited of which 43 were control subjects with BMI <25 (age, 22 - 63 years), 25 were overweight subjects with BMI ≥ 25 to <30 (age, 23 - 64 years) and the 11 obese subjects had a BMI ≥ 30 (age, 26 - 47 years). There was no correlation between dermal structural parameters and skin viscoelasticity in the abdomens or thighs of all 79 participants. On the other hand, in the 36 overweight and obese participants, thigh dermal echogenicity was significantly and negatively correlated with R0 (r = -0.456, p < 0.01) and dermal thickness in the abdomen was significantly and positively correlated with R0 (r = 0.464, p < 0.01). The dermal functional parameter was significantly correlated with dermal structural parameters in overweight and obese males;in other words, a decrease in dermal function may be caused by structural changes in the dermis during obesity.展开更多
By the measurement and analysis on the viscoelasticity of cooked cocoons,theconclusion has been obtained that under the condition of random sampling,the loga-rithm attenuation factor of amplitude obeys normal distribu...By the measurement and analysis on the viscoelasticity of cooked cocoons,theconclusion has been obtained that under the condition of random sampling,the loga-rithm attenuation factor of amplitude obeys normal distribution. The measuring sam-ple size of cooked cocoons is explored.The mathimatic formula between cook periodand the logarithm attenuation factor of amplitude of cooked cocoon is known.Thisperfected the theory of measuring the degree of cocoon cooking by instruments.展开更多
This article presents the mass and heat transport aspects in viscoelastic nanofluid flows under the presence of velocity slip conditions. To explore the nonNewtonian behavior, a Maxwell viscoelasticity-based micropola...This article presents the mass and heat transport aspects in viscoelastic nanofluid flows under the presence of velocity slip conditions. To explore the nonNewtonian behavior, a Maxwell viscoelasticity-based micropolar is considered. Moreover, a porous medium saturates the stretching sheet. A set of similarity variables is introduced to derive the dimensionless ordinary differential equations of velocity, concentration, and temperature profiles. The numerical solution is computed by using the MATLAB bvp4c package. The salient flow features of velocity, concentration, and temperature profiles are described and discussed through various graphs. It is observed that with an increase in the slip parameter, the micro-rotation velocity also increases. The temperature of nanoparticles gets maximum values by varying the viscoelastic parameter and the porosity parameter while an opposite trend is noted for the micro-rotation parameter. The local Nusselt number and the local Sherwood number increase by increasing the viscoelastic parameter, the porosity parameter, and the slip velocity parameter. The graphical computation is performed for a specified range of parameters, such as 0 ≤ M ≤ 2.5, 0 ≤σm ≤ 2.5, 0 ≤ K1 ≤ 1.5, 0.5 ≤ Pr ≤ 3.0, 0 ≤σ≤ 1.5, 0.5 ≤ Sc ≤ 2.0, 0.2 ≤ Nb ≤ 0.8, and 0.2 ≤ Nt ≤ 0.8.展开更多
Concrete structures may suffer considerable restraint stresses during their hardening period. This is caused by several deformation impacts, especially temperature field changings due to hydration heat and volume chan...Concrete structures may suffer considerable restraint stresses during their hardening period. This is caused by several deformation impacts, especially temperature field changings due to hydration heat and volume changes due to autogenous shrinkage. Mainly affected are massive concrete members, but also the application of new concrete types or the erection of outstanding constructions requires further investigations in this context. 3D-FEM analyses of hydration heat induced temperature development in combination with the well known shrinkage give sufficient results for the deformation impact. The according elastic restraint stresses can be determined with consideration of the concrete’s rising elastic modulus and the restraint degree of the system. But due to duration of the heat flow process, the height of restraint stresses is strongly dependent from the viscoelasticity of the concrete. The viscoelastic effects consist of many components constituted by changing material properties influencing themselves. In practice, different simplified approaches are available for considering this in calculations. Their implementation in time step analyses is not generally admitted and requires expertise. In contrast, present research develops material models needing specific input parameters for every use case. This contribution focuses on a practicable approach considering the superposition of the viscoelastic behaviour of every stress increment in time step FEM analysis. The differentiation between the pure viscoelastic material behaviour (as it is given in the codes for idealistic conditions like creep or relaxation) and the according viscoelastic system response (addicted to the systems variable restraint degree) allows the transfer of this model into practice. As one application example of this approach, the compatibility check and the FEM-based recalculation of the monitoring program of a massive power plant slab will be presented.展开更多
The viscoelastic behavior of melts for two systems composed of intercalated nanocomposites based on low density polyethylene and 3 wt% loading of cetyltrimethyl- ammonium bromide modified montmorillonite was studied. ...The viscoelastic behavior of melts for two systems composed of intercalated nanocomposites based on low density polyethylene and 3 wt% loading of cetyltrimethyl- ammonium bromide modified montmorillonite was studied. The results obtained through examining the dynamic storage module G’ and dynamic loss module G" values of the composite revealed that the dynamic viscoelastic properties of composite strongly depended on intercalation of polymer, and exhibited dramatically change with altering intercalation conditions. Only when modified montmorillonite content was about 3 wt%, the composite showed a trend of pseudo-solidlike at lower frequencies.展开更多
The main aim of this paper is to study the approximation to viscoelasticity type equations with a Crouzeix-Raviart type nonconforming finite element on the anisotropic meshes. The superclose property of the exact solu...The main aim of this paper is to study the approximation to viscoelasticity type equations with a Crouzeix-Raviart type nonconforming finite element on the anisotropic meshes. The superclose property of the exact solution and the optimal error estimate of its derivative with respect to time are derived by using some novel techniques. Moreover, employing a postprocessing technique, the global superconvergence property for the discretization error of the postprocessed discrete solution to the solution itself is studied.展开更多
基金financial support from K.N.Toosi University of Technology,Tehran,Iran。
文摘Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally,but the lack of studies of real environmental conditions on these absorbers is felt.The present work investigates the effect of viscoelasticity on the stability and bifurcations of a system attached to a nonlinear energy sink(NES).In this paper,the Burgers model is assumed for the viscoelasticity in an NES,and a linear oscillator system is considered for investigating the instabilities and bifurcations.The equations of motion of the coupled system are solved by using the harmonic balance and pseudo-arc-length continuation methods.The results show that the viscoelasticity affects the frequency intervals of the Hopf and saddle-node branches,and by increasing the stiffness parameters of the viscoelasticity,the conditions of these branches occur in larger ranges of the external force amplitudes,and also reduce the frequency range of the branches.In addition,increasing the viscoelastic damping parameter has the potential to completely eliminate the instability of the system and gradually reduce the amplitude of the jump phenomenon.
基金The authors gratefully a.cknowledge financial supportfrom th6 Natiol-al Natural Science Foundatiol- of CI-h-a. The number of
文摘Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between and shear rate (), and topologically constrained dimension number and a were derived. Linear viscoelastic parameters and and topologically constrained dimension number and as a function of the primary molecular weight, molecular weight between entanglements and the entanglement sites sequence distribution in polymer chain were determined. A new method for determination of viscoelastic parameters G and topologically constrained dimension number a and and molecular weight and from the shear flow measurements was proposed. It was used to determine those parameters and structures of HDPE, making a good agreement between these values and those obtained by other methods. The agreement affords a quantitative verification for the molecular theory of nonlinear viscoelasticity with constrained entanglement in polymer melts.
文摘Based on Womersley’s theory, the frequency equation satisfied by a complex wave velocity of a pulse wave in arteries was generalized to viscoelastic blood, a general formula of the complex wave velocity with regard to both linearly viscoelastic arteries and linearly viscolelastic blood was obtained, and the effects of the viscoelastic property of blood on the phase velocity and the wave attenuation of the pulse wave using the formula systematically was discussed. It is concluded that the influence of the blood elasticity on the wave propagation of a pulse wave in arteries is weaker than that of the arterial viscosity and may be neglected in larger arteries.
基金the sponsorship of National Natural Science Foundation of China(41974119,U1762103)Science Foundation from Innovation and Technology Support Program for Young Scientists in Colleges of Shandong province and Ministry of Science and Technology of China(2020RA2C620131)。
文摘Frequency-dependent amplitude versus offset(FAVO)inversion is a popular method to estimate the frequency-dependent elastic parameters by using amplitude and frequency information of pre-stack seismic data to guide fluid identification.Current frequency-dependent AVO inversion methods are mainly based on elastic theory without the consideration of the viscoelasticity of oil/gas.A fluid discrimination approach is proposed in this study by incorporating the viscoelasticity and relevant FAVO inversion.Based on viscoelastic and rock physics theories,a frequency-dependent viscoelastic solid-liquid decoupling fluid factor is initially constructed,and its sensitivity in fluid discrimination is compared with other conventional fluid factors.Furthermore,a novel reflectivity equation is derived in terms of the viscoelastic solid-liquid decoupling fluid factor.Due to the introduction of viscoelastic theory,the proposed reflectivity is related to frequency,which is more widely applicable than the traditional elastic reflectivity equation directly derived from the elastic reflectivity equation on frequency.Finally,a pragmatic frequency-dependent inversion method is introduced to verify the feasibility of the equation for frequency-dependent viscoelastic solid-liquid decoupling fluid factor prediction.Synthetic and field data examples demonstrate the feasibility and stability of the proposed approach in fluid discrimination.
基金supported by National Natural Science Foundation of China(NSFC10572159)supported by "111 Project" entitled "Biomechanics&Tissue Repair Engineering"(No.:B06023)Chongqing Science&Technology Council(CSTC 2006ba5010)
文摘Aim:The oxidized low-density lipoprotein(OxLDL) plays an important role in atherosclerosis yet it remains unclear if it damages circulating erythrocytes. Method: In this study。
文摘There are complex and perfect coagulation, anticoagulation and fibrinolysis systems in the human body and their fine regulatory mechanisms. Once the coagulation system and its regulatory mechanisms are destroyed, bleeding or thrombosis will occur very soon. In the blood coagulation, the blood viscoelasticity changes. Therefore, the thrombus elasticity measurement technology can be used to continuously monitor the changing blood viscoelasticity in order to study the process of coagulation. The results of the interaction among the various components of the blood can be obtained from coagulation to fibrinolysis by bedside detection. The traditional electromagnetic induction sensors, based on conventional coil inductance, are manufactured complexly, high cost and non-linear. Therefore, this paper proposes a non-Newtonian fluid viscoelasticity measurement method based on the piezoelectric effect. We use the piezoelectric bimorphs with the diameter of 21 mm and the total thickness of 0.38 mm and DSM coupling probes with the length of 3 mm, 5 mm and 7 mm to design the piezoelectric bimorphs driver. The viscoelasticity of different non-Newtonian fluids is tested. The vibration amplitudes of the piezoelectric bimorphs and liquid surfaces range from 0.43 μm to 3.52 μm. Consequently, the feasibility of in vitro detection of thrombus is confirmed in principle and the above scheme is validated theoretically and experimentally, which provides the basis for the measurement of blood viscoelasticity, the in vitro detection of thrombus and the manufacture of blood coagulation instrument.
文摘Elastic modulus is an important physical parameter of molding sand; it is closely connected with molding sand’s properties. Based on theories of rheology and molding sand microdeformation, elastic modulus of molding sand was measured and investigated using the intelligent molding sand multi-property tester developed by ourselves. The measuring principle was introduced. Effects of bentonite percentage and compactibility of the molding sand were experimentally studied. Furthermore, the essential viscoelastic nature of green sand was analyzed. It is considered that viscoelastic deformation of molding sand consists mainly of that of Kelvin Body of clay membrane, and elastic modulus of molding sand depends mainly on that of Kelvin Body which is the elastic component of clay membrane between sands. Elastic modulus can be adopted as one of the property parameters, and can be employed to evaluate the viscoelastic properties of molding sand.
基金The project supported by National Natural Science Foundation of China.
文摘Polymeric solid electrolyte system composed of triglycidyl ether of glycerol （TGEG）, diglycidyl ether of polyethylene glycol （DGEPEG）and LiClO<sub>4</sub> salt were synthesized. In this" system the electrolyte has a pecularity that not merely can the LiClO<sub>4</sub> provide ionic carriers, but also catalyze the crosslinking reaction without adding an usual curing agent. The effect of salt content and degree of crosslinking on the viscoelasticity and ionic conductivity were studied. Both WLF and VTF equations were used to treat the experimental data in order to elucidate the mechanism of ionic conduction. It was found that the ionic conductivity of the system is carded out through the segmental motion mechanism. However, the data must be treated with care. For example, in evaluating WLF parameters, the contribution concerned with ionic carrier generation with temperature to the conductivity must be differentiated from that concerned with segmental motion. Besides, the temperature range suitable to WLF equation must also be considered. For VTF equation, it might be inapplicable ff the temperature is too low and close to the glass transition temperature of the specimen. Further study is needed in order to have a quantitative information on the limitation of these equations.
文摘This paper deals with blood fiow caused by microvascular vasomotion with the focus on the effects of blood viscoelasticity on the pressure rise and wall resistance. It is shown that rnicrovascular vasomotion plays a role of the 'second heart' of the body which is of importance in conveying blood, and that the effects of blood viscoelasticity greatly depend on the Weissenberg number and mean flow rate.
文摘An explicit relation between constitutive porameters and quasi-static displacementof viscoelasticity is derived under a kind of boundary condition,and an iterative form of optimixed idenification is presented .Viscoelastic constitutive models are identifiedfrom a two order differential model ,and effects of information errors on results of inverse analysis are discussed.
文摘Despite the wide usage of isotropic fibrous composites with a viscoelastic polymer matrix,no analytic model for their mechanical behaviour is known.This paper develops such a model for time-dependent Young's modulus,showing that for typical constituents the time constants of composites are up to about 6% greater than the matrix shear time constant.Viscoelasticity is strongly suppressed for stiff fibres even at modest fibre volume fractions.Comparison with known results for particle and oriented fibre composites confirms isotropic fibrous composites as between the two in terms of viscoelastic behaviour,but more similar to the latter.
文摘A double-network model is established, which consists of the segments, E and A-constituent chains, the polymeric chains entangled with other ones by multi-entanglement and polymeric chains connected to a great number of destructible particles by multi-adsorption, based on which the E and A-constituent chains can be recreated and released dynamically. The distribution function of the end-to-end vector, the statistical distribution function of conformation for two kinds of chains in the multi-entanglement and multi-adsorption states and their number of polymeric chains are calculated by the combination of statistical mechanics and kinetics. Then the viscoelastic free energies of deformation for two kinds of the networks and suspensions are calculated by Boltzmann’s statistical theory. Also. elastic modulus and memory function for two kinds of the network and suspensions are derived. Consequently, a new molecular theory of the non-linear viscoelasticity for polymeric suspensions is proposed, and the constitutive equation and material function with yielding and thinning for the polymeric suspensions in different flow fields are derived from this theory.
文摘It has been reported that overweight Japanese males have poorly organised dermis and their skin may be fragile to external forces because of decreased dermal echogenicity. However, it is unknown whether the changes in the dermal structure actually affect the dermal function. The objective of this study was to clarify the relationship between dermal structural parameters and dermal functional parameters in overweight and obese Japanese males. A cross-sectional, observational study was conducted on Japanese male volunteers. Two ultrasound scanners, a 20-MHz Dermascan C<sup>®</sup> and an 18-MHz Mylab<sup>TM</sup> five<sup>®</sup> were used to evaluate dermal structure. Echogenicity of the lower dermis and dermal thickness of the participants’ abdomens and thighs were measured. A Cutometer<sup>®</sup> MPA580 was used to evaluate skin viscoelasticity, skin deformation (R0) and elasticity (R2, R7). The correlation between dermal structural parameters and skin viscoelasticity were validated using Pearson’s correlation coefficient or Spearman’s correlation coefficient by rank test. A total of 79 male volunteers were recruited of which 43 were control subjects with BMI <25 (age, 22 - 63 years), 25 were overweight subjects with BMI ≥ 25 to <30 (age, 23 - 64 years) and the 11 obese subjects had a BMI ≥ 30 (age, 26 - 47 years). There was no correlation between dermal structural parameters and skin viscoelasticity in the abdomens or thighs of all 79 participants. On the other hand, in the 36 overweight and obese participants, thigh dermal echogenicity was significantly and negatively correlated with R0 (r = -0.456, p < 0.01) and dermal thickness in the abdomen was significantly and positively correlated with R0 (r = 0.464, p < 0.01). The dermal functional parameter was significantly correlated with dermal structural parameters in overweight and obese males;in other words, a decrease in dermal function may be caused by structural changes in the dermis during obesity.
文摘By the measurement and analysis on the viscoelasticity of cooked cocoons,theconclusion has been obtained that under the condition of random sampling,the loga-rithm attenuation factor of amplitude obeys normal distribution. The measuring sam-ple size of cooked cocoons is explored.The mathimatic formula between cook periodand the logarithm attenuation factor of amplitude of cooked cocoon is known.Thisperfected the theory of measuring the degree of cocoon cooking by instruments.
文摘This article presents the mass and heat transport aspects in viscoelastic nanofluid flows under the presence of velocity slip conditions. To explore the nonNewtonian behavior, a Maxwell viscoelasticity-based micropolar is considered. Moreover, a porous medium saturates the stretching sheet. A set of similarity variables is introduced to derive the dimensionless ordinary differential equations of velocity, concentration, and temperature profiles. The numerical solution is computed by using the MATLAB bvp4c package. The salient flow features of velocity, concentration, and temperature profiles are described and discussed through various graphs. It is observed that with an increase in the slip parameter, the micro-rotation velocity also increases. The temperature of nanoparticles gets maximum values by varying the viscoelastic parameter and the porosity parameter while an opposite trend is noted for the micro-rotation parameter. The local Nusselt number and the local Sherwood number increase by increasing the viscoelastic parameter, the porosity parameter, and the slip velocity parameter. The graphical computation is performed for a specified range of parameters, such as 0 ≤ M ≤ 2.5, 0 ≤σm ≤ 2.5, 0 ≤ K1 ≤ 1.5, 0.5 ≤ Pr ≤ 3.0, 0 ≤σ≤ 1.5, 0.5 ≤ Sc ≤ 2.0, 0.2 ≤ Nb ≤ 0.8, and 0.2 ≤ Nt ≤ 0.8.
文摘Concrete structures may suffer considerable restraint stresses during their hardening period. This is caused by several deformation impacts, especially temperature field changings due to hydration heat and volume changes due to autogenous shrinkage. Mainly affected are massive concrete members, but also the application of new concrete types or the erection of outstanding constructions requires further investigations in this context. 3D-FEM analyses of hydration heat induced temperature development in combination with the well known shrinkage give sufficient results for the deformation impact. The according elastic restraint stresses can be determined with consideration of the concrete’s rising elastic modulus and the restraint degree of the system. But due to duration of the heat flow process, the height of restraint stresses is strongly dependent from the viscoelasticity of the concrete. The viscoelastic effects consist of many components constituted by changing material properties influencing themselves. In practice, different simplified approaches are available for considering this in calculations. Their implementation in time step analyses is not generally admitted and requires expertise. In contrast, present research develops material models needing specific input parameters for every use case. This contribution focuses on a practicable approach considering the superposition of the viscoelastic behaviour of every stress increment in time step FEM analysis. The differentiation between the pure viscoelastic material behaviour (as it is given in the codes for idealistic conditions like creep or relaxation) and the according viscoelastic system response (addicted to the systems variable restraint degree) allows the transfer of this model into practice. As one application example of this approach, the compatibility check and the FEM-based recalculation of the monitoring program of a massive power plant slab will be presented.
文摘The viscoelastic behavior of melts for two systems composed of intercalated nanocomposites based on low density polyethylene and 3 wt% loading of cetyltrimethyl- ammonium bromide modified montmorillonite was studied. The results obtained through examining the dynamic storage module G’ and dynamic loss module G" values of the composite revealed that the dynamic viscoelastic properties of composite strongly depended on intercalation of polymer, and exhibited dramatically change with altering intercalation conditions. Only when modified montmorillonite content was about 3 wt%, the composite showed a trend of pseudo-solidlike at lower frequencies.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10274032 and 320200265）, National Natural Science Foundation of Jiangsu Province, China （Grant No BK2004081）.
基金This research is supported by the NSF of China (10371113 10471133),SF of Henan ProvinceSF of Education Committee of Henan Province (2006110011)
文摘The main aim of this paper is to study the approximation to viscoelasticity type equations with a Crouzeix-Raviart type nonconforming finite element on the anisotropic meshes. The superclose property of the exact solution and the optimal error estimate of its derivative with respect to time are derived by using some novel techniques. Moreover, employing a postprocessing technique, the global superconvergence property for the discretization error of the postprocessed discrete solution to the solution itself is studied.
