A piggyback pipeline is a special configuration of offshore pipelines for offshore oil and gas exploration and is characterized by the coupling of a large-diameter pipe with a small-diameter pipe. This study conducts ...A piggyback pipeline is a special configuration of offshore pipelines for offshore oil and gas exploration and is characterized by the coupling of a large-diameter pipe with a small-diameter pipe. This study conducts a numerical investigation of the transverse VIV characteristics of a piggyback pipeline at low Reynolds numbers, as the vortex shedding modes and vibration characteristics can be accurately represented under laminar flow conditions with minimal computational expense. The effects of influential factors, such as the mass ratio, position angle of the small pipe relative to the main pipe, and Reynolds number, on the VIV amplitude, frequency, vibration center, and mean lift coefficient are specifically examined. The results indicate that the mass ratio has a limited effect on the maximum VIV amplitude. However, as the mass ratio decreases, the lock-in region expands, and the vibration center of the piggyback pipeline deviates further from its original position. The VIV amplitude is minimized, and the lock-in region is the narrowest at a position angle of 45°, whereas the vibration center reaches its maximum displacement at a position angle of 135°. As the Reynolds number increases, the VIV amplitude slightly increases, accompanied by convergence of the vibration center toward its initial position. The mean lift coefficient and wake vortices are also analyzed to establish a connection with the vibration characteristics of the piggyback pipeline. The optimal configuration of the piggyback pipeline is also proposed on the basis of the present numerical results.展开更多
As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few exp...As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few experimental studies have been published on the scour around the piggyback pipeline under steady current. This study numerically and experimentally investigates the local scour of the piggyback pipe under steady current. The influence of prominent factors such as pipe diameter, inflow Reynolds number, and gap between the main and small pipes, on the maximum scour depth have been examined and discussed in detail. Furthermore, one formula to predict the maximum scour depth under the piggyback pipeline has been derived based on the theoretical analysis of scour equilibrium. The feasibility of the proposed formula has been effectively calibrated by both experimental data and numerical results. The findings drawn from this study are instructive in the future design and application of the piggyback pipeline.展开更多
AIM:To assess the refractive outcome of clear lensectomy combined with piggyback intraocular lens implantation in highly hyperopic patients.METHODS:This case review included 19 eyes of 10 patients with high hyperopia ...AIM:To assess the refractive outcome of clear lensectomy combined with piggyback intraocular lens implantation in highly hyperopic patients.METHODS:This case review included 19 eyes of 10 patients with high hyperopia and axial length less than 21mm.Intraocular lens power was calculated for emmetropia using the Holladay II formula in 17 eyes,and SRK/T formula in 2 eyes following clear lens extraction and piggyback intraocular lens implantation.Patients were examined periodically over 24 months for visual acuity and spherical equivalent(SE).RESULTS:The mean postoperative SE at 24 months was 0.20±1.39D(range,-3.00 to 2.50D),better than preoperative 9.81±2.62D(range,+6.00 to +14.50D)(P【0.001).Five eyes had SE within±0.5D of emmetropia and 11 eyes within±1.00D at postoperative 24 months.The mean postoperative uncorrected visual acuity(UCVA) at 24 months was 0.60±0.36,significantly improved compared to preoperative 1.39±0.33(P【0.001).The mean best-corrected visual acuity(BCVA) at 24 months was 0.49±0.35,not statistically different compared to preoperative 0.38±0.30(P=0.34).Twelve eyes maintained and 1 gained 1 or more Snellen line of BCVA,4 eyes lost 1 line,and 2 eyes lost 2 lines at 24 postoperative months.Twelve eyes best-corrected near visual acuity (BCNVA) achieved J1 at postoperative 24 months compared to preoperative 7 eyes and the other 7 eyes better than J3.CONCLUSION:Clearlensextractioncombinedpiggyback intraocular lens implantation appears to be an effective procedure to correct high hyperopia but mild overcorrection and intralenticular opacification may require secondary procedure.展开更多
OBJECTIVE: To summarize the experience in modified reconstruction of the hepatic outflow tract during piggyback liver transplantation at our hospital. METHODS: The clinical data on 67 patients undergoing piggyback liv...OBJECTIVE: To summarize the experience in modified reconstruction of the hepatic outflow tract during piggyback liver transplantation at our hospital. METHODS: The clinical data on 67 patients undergoing piggyback liver transplantation with modified hepatic outflow tract reconstruction from January 1999 to October 2002 were analyzed retrospectively. RESULTS: In this group, 7 patients (10. 45%) died perioperatively. Complications included: pulmonary infection (38 patients); multiple organ system failure (10), intraperitoneal bleeding (6), acute respiratory distress syndrome (14), thrombosis of the hepatie artery (1), and bile leakage (1). No hepatic outflow occluded. Two recipients survived for over 3 years, 8 over 2 years, and 19 over a year. CONCLUSION: Modified hepatic outflow reconstruction in piggyback live transplantation may increase the success rate of liver transplantation and decrease technical complications.展开更多
Strong deformed sediments investigated in the Hoh Xil basin may contain detailed records for early Tertiary crustal shortening in northern Tibet (Fig.1A). Sedimentary sequences in the basin consist of the Fenghuoshan ...Strong deformed sediments investigated in the Hoh Xil basin may contain detailed records for early Tertiary crustal shortening in northern Tibet (Fig.1A). Sedimentary sequences in the basin consist of the Fenghuoshan Group, the Yaxicuo Group, and the early Miocene Wudaoliang Group from lower to upper. Magnetostratigraphic research has indicated the Eocene to early Oligocene ages for the Fenghuoshan and Yaxicuo Groups (Liu, et al., 2000). Total 29 lithological sections with 20487 7m thick were measured spread all over the 101000km\+2 Hoh Xil basin, the largest Tertiary sedimentary basin in the hinterland of the Tibetan plateau, to reveal the prototype basin and its evolution processes. They include 17 sections with 14925 3m thick of the Fenghuoshan Group, 8 sections with 4273 5m thick of the Yaxicuo Group, and 4 sections with 1284 9m thick of the Wudaoliang Group.展开更多
Hepatic venous outflow obstruction after piggyback liver transplantation is a very rare complication. An unusual mechanism aggravating it is reported. A 33-year-old man with end-stage hepatitis B liver cirrhosis under...Hepatic venous outflow obstruction after piggyback liver transplantation is a very rare complication. An unusual mechanism aggravating it is reported. A 33-year-old man with end-stage hepatitis B liver cirrhosis underwent a piggyback orthotopic liver transplantation using a full-size cadaveric graft. Two months after transplantation, he developed gross ascites refractory to maximal diuretic therapy. Doppler ultrasound showed patent portal and hepatic veins. Serial computed tomography scans revealed a hypoperfused right posterior segment of the liver which subsequently underwent atrophy. Hepatic venography demonstrated a high-grade stenosis with an element of torsion of venous drainage at the anastomosis. The stenosis was successfully treated with repeated percutaneous balloon angioplasty. The patient remained asymptomatic six months afterwards with complete resolution of ascites and peripheral edema. We postulate that liver allograft segmental hypoperfusion and atrophy may aggravate or result in a hepatic venous outflow problem by the mechanism of torsion effect. Percutaneous balloon angioplasty is a safe and effective treatment modality for anastomotic stenosis.展开更多
Numerical simulations of flows past the piggyback circular cylinders in tandem arrangement are performed by solving the variational multiscale formulation of the incompressible Navier-Stokes equations using in-house f...Numerical simulations of flows past the piggyback circular cylinders in tandem arrangement are performed by solving the variational multiscale formulation of the incompressible Navier-Stokes equations using in-house finite element method(FEM)codes.The effects of the gap-spacing-to-diameter(G/D)and the two diameter ratio(d/D)on the flow characteristics and the reductions of the root-mean-square(RMS)drag and lift coefficients are considered for Reynolds numbers(Res)are 100 and 200.The validation shows the fluid force coefficients obtained by the in-house FEM codes are in good agreement with the results in the existing literatures.The obtained results show that,with a proper placement of the smaller cylinder(d/D=0.2)behind the larger cylinder,the RMS drag and lift coefficients largely decrease compared to those of the single circular cylinder.When d/D=0.2,the largest reductions of the RMS lift coefficient of the larger cylinder and the RMS total lift coefficient appear at G/D=1.2 as Re=100 and at G/D=1.0 as Re=200.It is observed that the proper placement of the smaller cylinder causes the surrounding vorticity to take opposite sign with the vorticity in the outer region so as to suppress and postpone the vortex shedding in the wake,and that the different positions of the vortex shedding at two Res cause that the largest reductions of the RMS lift coefficient of the larger cylinder and the RMS total lift coefficient appear at different G/D as Re is different.When d/D varies,the variation of the RMS total lift coefficient behaves differently at two Res.It decreases with J/D increasing at Re=100,while it no longer monotonously varies with J/D,but reaches a minimum in the considered range of d/D at Re=200.Moreover,the larger d/D results in stronger suppression and postponement of the vortex shedding in the wake.展开更多
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 52371289 and 51979192)。
文摘A piggyback pipeline is a special configuration of offshore pipelines for offshore oil and gas exploration and is characterized by the coupling of a large-diameter pipe with a small-diameter pipe. This study conducts a numerical investigation of the transverse VIV characteristics of a piggyback pipeline at low Reynolds numbers, as the vortex shedding modes and vibration characteristics can be accurately represented under laminar flow conditions with minimal computational expense. The effects of influential factors, such as the mass ratio, position angle of the small pipe relative to the main pipe, and Reynolds number, on the VIV amplitude, frequency, vibration center, and mean lift coefficient are specifically examined. The results indicate that the mass ratio has a limited effect on the maximum VIV amplitude. However, as the mass ratio decreases, the lock-in region expands, and the vibration center of the piggyback pipeline deviates further from its original position. The VIV amplitude is minimized, and the lock-in region is the narrowest at a position angle of 45°, whereas the vibration center reaches its maximum displacement at a position angle of 135°. As the Reynolds number increases, the VIV amplitude slightly increases, accompanied by convergence of the vibration center toward its initial position. The mean lift coefficient and wake vortices are also analyzed to establish a connection with the vibration characteristics of the piggyback pipeline. The optimal configuration of the piggyback pipeline is also proposed on the basis of the present numerical results.
基金financially supported by the National Key Research and Development Program of China (No.2017YFC1404700)the National Natural Science Foundation of China (Nos.51279189,51239001 and 51509023)the China Scholarship Council
文摘As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few experimental studies have been published on the scour around the piggyback pipeline under steady current. This study numerically and experimentally investigates the local scour of the piggyback pipe under steady current. The influence of prominent factors such as pipe diameter, inflow Reynolds number, and gap between the main and small pipes, on the maximum scour depth have been examined and discussed in detail. Furthermore, one formula to predict the maximum scour depth under the piggyback pipeline has been derived based on the theoretical analysis of scour equilibrium. The feasibility of the proposed formula has been effectively calibrated by both experimental data and numerical results. The findings drawn from this study are instructive in the future design and application of the piggyback pipeline.
文摘AIM:To assess the refractive outcome of clear lensectomy combined with piggyback intraocular lens implantation in highly hyperopic patients.METHODS:This case review included 19 eyes of 10 patients with high hyperopia and axial length less than 21mm.Intraocular lens power was calculated for emmetropia using the Holladay II formula in 17 eyes,and SRK/T formula in 2 eyes following clear lens extraction and piggyback intraocular lens implantation.Patients were examined periodically over 24 months for visual acuity and spherical equivalent(SE).RESULTS:The mean postoperative SE at 24 months was 0.20±1.39D(range,-3.00 to 2.50D),better than preoperative 9.81±2.62D(range,+6.00 to +14.50D)(P【0.001).Five eyes had SE within±0.5D of emmetropia and 11 eyes within±1.00D at postoperative 24 months.The mean postoperative uncorrected visual acuity(UCVA) at 24 months was 0.60±0.36,significantly improved compared to preoperative 1.39±0.33(P【0.001).The mean best-corrected visual acuity(BCVA) at 24 months was 0.49±0.35,not statistically different compared to preoperative 0.38±0.30(P=0.34).Twelve eyes maintained and 1 gained 1 or more Snellen line of BCVA,4 eyes lost 1 line,and 2 eyes lost 2 lines at 24 postoperative months.Twelve eyes best-corrected near visual acuity (BCNVA) achieved J1 at postoperative 24 months compared to preoperative 7 eyes and the other 7 eyes better than J3.CONCLUSION:Clearlensextractioncombinedpiggyback intraocular lens implantation appears to be an effective procedure to correct high hyperopia but mild overcorrection and intralenticular opacification may require secondary procedure.
文摘OBJECTIVE: To summarize the experience in modified reconstruction of the hepatic outflow tract during piggyback liver transplantation at our hospital. METHODS: The clinical data on 67 patients undergoing piggyback liver transplantation with modified hepatic outflow tract reconstruction from January 1999 to October 2002 were analyzed retrospectively. RESULTS: In this group, 7 patients (10. 45%) died perioperatively. Complications included: pulmonary infection (38 patients); multiple organ system failure (10), intraperitoneal bleeding (6), acute respiratory distress syndrome (14), thrombosis of the hepatie artery (1), and bile leakage (1). No hepatic outflow occluded. Two recipients survived for over 3 years, 8 over 2 years, and 19 over a year. CONCLUSION: Modified hepatic outflow reconstruction in piggyback live transplantation may increase the success rate of liver transplantation and decrease technical complications.
文摘Strong deformed sediments investigated in the Hoh Xil basin may contain detailed records for early Tertiary crustal shortening in northern Tibet (Fig.1A). Sedimentary sequences in the basin consist of the Fenghuoshan Group, the Yaxicuo Group, and the early Miocene Wudaoliang Group from lower to upper. Magnetostratigraphic research has indicated the Eocene to early Oligocene ages for the Fenghuoshan and Yaxicuo Groups (Liu, et al., 2000). Total 29 lithological sections with 20487 7m thick were measured spread all over the 101000km\+2 Hoh Xil basin, the largest Tertiary sedimentary basin in the hinterland of the Tibetan plateau, to reveal the prototype basin and its evolution processes. They include 17 sections with 14925 3m thick of the Fenghuoshan Group, 8 sections with 4273 5m thick of the Yaxicuo Group, and 4 sections with 1284 9m thick of the Wudaoliang Group.
文摘Hepatic venous outflow obstruction after piggyback liver transplantation is a very rare complication. An unusual mechanism aggravating it is reported. A 33-year-old man with end-stage hepatitis B liver cirrhosis underwent a piggyback orthotopic liver transplantation using a full-size cadaveric graft. Two months after transplantation, he developed gross ascites refractory to maximal diuretic therapy. Doppler ultrasound showed patent portal and hepatic veins. Serial computed tomography scans revealed a hypoperfused right posterior segment of the liver which subsequently underwent atrophy. Hepatic venography demonstrated a high-grade stenosis with an element of torsion of venous drainage at the anastomosis. The stenosis was successfully treated with repeated percutaneous balloon angioplasty. The patient remained asymptomatic six months afterwards with complete resolution of ascites and peripheral edema. We postulate that liver allograft segmental hypoperfusion and atrophy may aggravate or result in a hepatic venous outflow problem by the mechanism of torsion effect. Percutaneous balloon angioplasty is a safe and effective treatment modality for anastomotic stenosis.
基金The project was supported by the Natural Science Foundation of Jiangsu Province(Grant SBK2018040999)the Natural Science Research of Jiangsu Higher Education Institutions of China(Grant 18KJB570001)the National Natural Science Foundation of China(Grants 51879123 and 91852111).
文摘Numerical simulations of flows past the piggyback circular cylinders in tandem arrangement are performed by solving the variational multiscale formulation of the incompressible Navier-Stokes equations using in-house finite element method(FEM)codes.The effects of the gap-spacing-to-diameter(G/D)and the two diameter ratio(d/D)on the flow characteristics and the reductions of the root-mean-square(RMS)drag and lift coefficients are considered for Reynolds numbers(Res)are 100 and 200.The validation shows the fluid force coefficients obtained by the in-house FEM codes are in good agreement with the results in the existing literatures.The obtained results show that,with a proper placement of the smaller cylinder(d/D=0.2)behind the larger cylinder,the RMS drag and lift coefficients largely decrease compared to those of the single circular cylinder.When d/D=0.2,the largest reductions of the RMS lift coefficient of the larger cylinder and the RMS total lift coefficient appear at G/D=1.2 as Re=100 and at G/D=1.0 as Re=200.It is observed that the proper placement of the smaller cylinder causes the surrounding vorticity to take opposite sign with the vorticity in the outer region so as to suppress and postpone the vortex shedding in the wake,and that the different positions of the vortex shedding at two Res cause that the largest reductions of the RMS lift coefficient of the larger cylinder and the RMS total lift coefficient appear at different G/D as Re is different.When d/D varies,the variation of the RMS total lift coefficient behaves differently at two Res.It decreases with J/D increasing at Re=100,while it no longer monotonously varies with J/D,but reaches a minimum in the considered range of d/D at Re=200.Moreover,the larger d/D results in stronger suppression and postponement of the vortex shedding in the wake.
