This article deals with solutions of transient vibration of a rectangular viscoelastic orthotropic thin 2D plate for particular deformation models according to Flu¨gge and Timoshenko-Mindlin.The linear model,a ge...This article deals with solutions of transient vibration of a rectangular viscoelastic orthotropic thin 2D plate for particular deformation models according to Flu¨gge and Timoshenko-Mindlin.The linear model,a general standard viscoelastic body,of the rheologic properties of a viscoelastic material was applied.The time and coordinate curves of the basic quantities displacement,rotation,velocity,stress and deformation are compared.The results obtained by an approximate analytic method are compared with numerical results for 3D plate generated by FEM application and with experimental investigation.展开更多
A multi-degree-of-freedom device is proposed,which can achieve efficient vibration reduction as the main objective and energy harvesting as the secondary purpose.The device comprises a multiscale nonlinear vibration a...A multi-degree-of-freedom device is proposed,which can achieve efficient vibration reduction as the main objective and energy harvesting as the secondary purpose.The device comprises a multiscale nonlinear vibration absorber(NVA)and piezoelectric components.Energy conversion and energy measurement methods are used to evaluate the device performance from multiple perspectives.Research has shown that this device can efficiently transfer transient energy from the main structure and convert a portion of transient energy into electrical energy.Main resonance and higher-order resonance are the main reasons for efficient energy transfer.The device can maintain high vibration reduction performance even when the excitation amplitude changes over a large range.Compared with the single structures with and without precompression,the multiscale NVA-piezoelectric device offers significant vibration reduction advantages.In addition,there are significant differences in the parameter settings of the two substructures for vibration reduction and energy harvesting.展开更多
Exact solutions are obtained for transient torsio- nal responses of a finitely long, functionally graded hollow cylinder under three different end conditions, i.e. free-free, free-fixed and fixed-fixed. The cylinder w...Exact solutions are obtained for transient torsio- nal responses of a finitely long, functionally graded hollow cylinder under three different end conditions, i.e. free-free, free-fixed and fixed-fixed. The cylinder with its external surface fixed is subjected to a dynamic shearing stress at the internal surface. The material properties are assumed to vary in the radial direction in a power law form, while keep invariant in the axial direction. With expansion in the axial direction in terms of trigonometric series, the governing equations for the unknown functions about the radial coordinate r and time t are deduced. By applying the variable substitution technique, the superposition method and the separation of variables consecutively, series-form solutions of the equations are obtained. Natural frequencies and the transient torsional responses are finally discussed for a functionally graded finite hollow cylinder.展开更多
BACKGROUND Vibration-controlled transient elastography(VCTE)is proposed as a second step of examination to assess liver fibrosis in patients with nonalcoholic fatty liver disease(NAFLD)after triaging by the fibrosis-4...BACKGROUND Vibration-controlled transient elastography(VCTE)is proposed as a second step of examination to assess liver fibrosis in patients with nonalcoholic fatty liver disease(NAFLD)after triaging by the fibrosis-4(FIB-4)index.Recently,VCTEbased scoring systems,including FibroScan-AST(FAST),Agile 3+,and Agile 4,emerged to determine the status of NAFLD.However,the significance of these scoring systems remains unknown in narrowing the high-risk group of NAFLD patients with comorbidities,including hepatocellular carcinoma(HCC)and esophagogastric varices(EGV).AIM To clarify the significance of VCTE-based scoring systems to narrow the high-risk group of NAFLD patients with comorbidities.METHODS We performed a cross-sectional study to investigate the usefulness of VCTE-based scoring systems and other fibrosis markers to narrow the high-risk group of patients with NAFLD.FIB-4 index was used for the first triage.Risk groups of FAST,Agile 3+,and Agile 4 were stratified according to the published data.Among the 191 patients with NAFLD,there were 26(14%)and 25 patients(13%)with HCC and EGV,respectively.RESULTS When 1.3 was used as a cutoff value,the FIB-4 index narrowed the risk group to 120 patients,in which all patients with HCC and/or EGV were included.High risk group of Agile 3+could subsequently narrow the risk group.The prevalence of HCC and EGV at this step were 33%(26/80)and 31%(25/80),respectively.In further narrowing of EGV,Agile 4 aggregated the patients with EGV into 43 patients,of whom 23(53%)had EGV.FAST failed to narrow the risk group of patients with comorbidities.When 2.6 was used as a cutoff value of the FIB-4 index,three patients with HCC and two patients with EGV were missed at the first triage.CONCLUSION Agile 3+and Agile 4 are useful to narrow the NAFLD patient group,in which patients may have HCC and/or EGV.展开更多
基金supported by the grant project GA CR 101/07/0946
文摘This article deals with solutions of transient vibration of a rectangular viscoelastic orthotropic thin 2D plate for particular deformation models according to Flu¨gge and Timoshenko-Mindlin.The linear model,a general standard viscoelastic body,of the rheologic properties of a viscoelastic material was applied.The time and coordinate curves of the basic quantities displacement,rotation,velocity,stress and deformation are compared.The results obtained by an approximate analytic method are compared with numerical results for 3D plate generated by FEM application and with experimental investigation.
基金Project supported by the National Natural Science Foundation of China(Nos.11972050 and 12332001)。
文摘A multi-degree-of-freedom device is proposed,which can achieve efficient vibration reduction as the main objective and energy harvesting as the secondary purpose.The device comprises a multiscale nonlinear vibration absorber(NVA)and piezoelectric components.Energy conversion and energy measurement methods are used to evaluate the device performance from multiple perspectives.Research has shown that this device can efficiently transfer transient energy from the main structure and convert a portion of transient energy into electrical energy.Main resonance and higher-order resonance are the main reasons for efficient energy transfer.The device can maintain high vibration reduction performance even when the excitation amplitude changes over a large range.Compared with the single structures with and without precompression,the multiscale NVA-piezoelectric device offers significant vibration reduction advantages.In addition,there are significant differences in the parameter settings of the two substructures for vibration reduction and energy harvesting.
基金supported by the National Natural Science Foundation of China ( 10872179 and 10725210)the Zhejiang Provincial Natural Science Foundation of China (Y7080298) Zijin Plan of Zhejiang University
文摘Exact solutions are obtained for transient torsio- nal responses of a finitely long, functionally graded hollow cylinder under three different end conditions, i.e. free-free, free-fixed and fixed-fixed. The cylinder with its external surface fixed is subjected to a dynamic shearing stress at the internal surface. The material properties are assumed to vary in the radial direction in a power law form, while keep invariant in the axial direction. With expansion in the axial direction in terms of trigonometric series, the governing equations for the unknown functions about the radial coordinate r and time t are deduced. By applying the variable substitution technique, the superposition method and the separation of variables consecutively, series-form solutions of the equations are obtained. Natural frequencies and the transient torsional responses are finally discussed for a functionally graded finite hollow cylinder.
文摘BACKGROUND Vibration-controlled transient elastography(VCTE)is proposed as a second step of examination to assess liver fibrosis in patients with nonalcoholic fatty liver disease(NAFLD)after triaging by the fibrosis-4(FIB-4)index.Recently,VCTEbased scoring systems,including FibroScan-AST(FAST),Agile 3+,and Agile 4,emerged to determine the status of NAFLD.However,the significance of these scoring systems remains unknown in narrowing the high-risk group of NAFLD patients with comorbidities,including hepatocellular carcinoma(HCC)and esophagogastric varices(EGV).AIM To clarify the significance of VCTE-based scoring systems to narrow the high-risk group of NAFLD patients with comorbidities.METHODS We performed a cross-sectional study to investigate the usefulness of VCTE-based scoring systems and other fibrosis markers to narrow the high-risk group of patients with NAFLD.FIB-4 index was used for the first triage.Risk groups of FAST,Agile 3+,and Agile 4 were stratified according to the published data.Among the 191 patients with NAFLD,there were 26(14%)and 25 patients(13%)with HCC and EGV,respectively.RESULTS When 1.3 was used as a cutoff value,the FIB-4 index narrowed the risk group to 120 patients,in which all patients with HCC and/or EGV were included.High risk group of Agile 3+could subsequently narrow the risk group.The prevalence of HCC and EGV at this step were 33%(26/80)and 31%(25/80),respectively.In further narrowing of EGV,Agile 4 aggregated the patients with EGV into 43 patients,of whom 23(53%)had EGV.FAST failed to narrow the risk group of patients with comorbidities.When 2.6 was used as a cutoff value of the FIB-4 index,three patients with HCC and two patients with EGV were missed at the first triage.CONCLUSION Agile 3+and Agile 4 are useful to narrow the NAFLD patient group,in which patients may have HCC and/or EGV.
