In winter,rivers in cold regions often experience flood disasters resulted from ice jams or ice dams.Investigations of the variation of ice jam thickness and water level during an ice jammed period are not only a prac...In winter,rivers in cold regions often experience flood disasters resulted from ice jams or ice dams.Investigations of the variation of ice jam thickness and water level during an ice jammed period are not only a practical need for ice prevention to avoid disaster and plan water resource,but also essential for the development of any mathematical model for predicting the evolution of ice jam.So far,some equations based on the energy equation have been proposed to describe the relationship between ice jam thickness and water level.However,in the derivation of these equations,the local head loss coefficient at the ice jam head and the riverbed slope factor were neglected.Obviously,those reported equations cannot be used to preciously describe the flow energy equation with ice jams and accurately calculate the ice jam thickness and water level.In the present study,a more comprehensive theoretical model for hydraulic calculation of ice jam thickness has been derived by considering important and essential factors including riverbed slope and local head loss coefficient at the ice jam head.Furthermore,based on the data collected from laboratory experiments of ice jam accumulation,the local head loss coefficient at the ice jam head has been calculated,and the empirical equation for calculating the local head loss coefficient has been established by considering flow Froude number and the ratio of ice discharge to flow discharge.The results of this study not only provide a new reference for calculating ice jam thickness and water level,but also present a theoretical basis for accurate CFD simulation of ice jams.展开更多
To solve the common problem of flumes flowmeasurement accuracy without sacrificing water head, a new type of trapezoidal cutthroat flume to measure the discharge in terminal trapezoidal channels is presented.Using the...To solve the common problem of flumes flowmeasurement accuracy without sacrificing water head, a new type of trapezoidal cutthroat flume to measure the discharge in terminal trapezoidal channels is presented.Using the computational fluid dynamic method, threedimensional flow fields in trapezoidal cutthroat flumes were simulated using the RNG k-ε three-dimensional turbulence model along with the Tru VOF technique.Simulations were performed for 12 working conditions,with discharges up to 0.075 m3$s–1 to determine hydraulic performance. Experimental data for the trapezoidal cutthroat flume in terminal trapezoidal channel were also obtained to validate the simulation results. Velocity distribution of the flume obtained from simulation analyses were compared with observed results based on timeaveraged flow field and comparison yielded a solid agreement between results from the two methods, with relative error below 10%. The results indicated that the Froude number and the longitudinal average velocity increased along the convergence section and decreased in the divergent section. In the upper throat, the Froude number was less than 0.5, which meets the water measurement requirement, and the critical flow appeared near the throat section. The maximum water head loss of the trapezoidal cutthroat flume was less than 9% of the total head, compared to the rectangular cutthroat flume,and head loss of trapezoidal cutthroat flume was significantly less. Regression models developed for upstream depth versus discharge under different working conditions were satisfactory, with a relative error of less than 2.06%, which meets the common requirements of flow measurement in irrigation areas. It was concluded that trapezoidal cutthroat flumes can improve flow-measurement accuracy without sacrificing water head.展开更多
Introduction: Free flap success rates have remained stable in recent years ranging 93% to 98%. Historically, the causes of free flap failures were attributed to the surgeon’s inexperience and technique. However, ther...Introduction: Free flap success rates have remained stable in recent years ranging 93% to 98%. Historically, the causes of free flap failures were attributed to the surgeon’s inexperience and technique. However, there are factors beyond the surgical anastomosis that contribute to flap failure. The purpose of this study is to review each case of total flap loss in detail to develop a better understanding of complications. Methods: A retrospective study was performed over eleven years in a single surgeon’s practice, a predominantly head and neck reconstructive practice. All charts were independently reviewed. In patients who sustained total flap loss, a review was conducted of patient comorbidites, anesthesia records, perioperative and follow-up notes. Results: A total of 514 free flaps were performed. 76% (392) of these flaps were for head and neck reconstruction. There were 22 total flap losses (4%) and 26 partial flap losses (5%). Of the 22 total flap losses, four flaps were avulsed, five flaps were in patients later found to have coagulation disorders (homozygous mutations of the MTHFR gene and factor V Leiden), four patients were exposed to neosynephrine, two patients remained hypotensive perioperatively, and four delayed flap losses were attributed to pseudomonal infection. Five losses were technical or related to flap inexperience. Several representative case scenarios are illustrated. Conclusion: Careful review of free flap failures indicates that a thorough workup (particularly coagulation disorders), flap selection, surgeon to anesthesia communication, proper securing of the flap, and postoperative patient blood pressure and infection control have a greater part to play in this new era of anastomotic success.展开更多
BACKGROUND Chronic otitis media(COM)is an inflammatory disease that lasts for a long time.It is common in developing countries.Hearing loss can result from COM.The relationship between variations in middle ear anatomy...BACKGROUND Chronic otitis media(COM)is an inflammatory disease that lasts for a long time.It is common in developing countries.Hearing loss can result from COM.The relationship between variations in middle ear anatomy and COM was investigated in our study.AIM To compare the prevalence of middle ear anatomic variations between the cases with COM and healthy individuals.METHODS This retrospective study included 500 patients with COM and 500 healthy controls.The presence of those variants was determined:Koerner’s septum,facial canal dehiscence,high jugular bulb,jugular bulb dehiscence,jugular bulb diverticulum,sigmoid sinus anterior location and deep tympanic recesses.RESULTS A total of 1000 temporal bones were examined.The incidences of these variants were respectively(15.4%-18.6%),(38.6%-41.2%),(18.2%-4.6%),(2.6%-1.2%),(1.2%-0%),(8.6%-0%),(0%-0%).It was observed that only high jugular bulb(P<0.001)and anteriorly located sigmoid sinus frequencies(P=0.002)in the case group were statistically significantly higher than the control groups.CONCLUSION COM is a multifactorial disease and variants of middle ear have always been important in terms of potential risk for complication during surgery but rarely associated with COM as an etiology or as a consequence of the disease.We didn't find a positive correlation between COM and Koerner’s septum and facial canal defect.We ended up with a significant conclusion with the variants of dural venous sinuses-high jugular bulb,dehiscence of jugular bulb,diverticulum of jugular bulb and anteriorly located sigmoid sinus-that have been studied less and frequently associated with inner ear illnesses.展开更多
The relationship between the head loss and the discharge and circulation of the conduit of a pump system with low head is an important problem with an obvious influence on the improvement of its hydraulic performance....The relationship between the head loss and the discharge and circulation of the conduit of a pump system with low head is an important problem with an obvious influence on the improvement of its hydraulic performance. The velocity circulation from the pump guide vane makes the relationship more complicated, which has to be understood comprehensively. The results indicate that, under the condition of zero circulation, the head loss of the inlet and outlet conduits is in proportion to the square of discharge. Under the condition that the Reynolds number is satisfied with the resistant square area, the conduit loss is in proportion to the square of discharge for the similar working points with different speeds in a certain rotational speed range, indicating that the pump system efficiency is constant. The outlet conduit loss of design discharge for a pump system with low head depends on the velocity circulation from the guide vane exit, and the relationship between the loss and the circulation is an open curve with an upward direction, meaning that there is an optimal circulation for the loss. Under the condition of various working points for a pump system with low head, the head loss of the outlet conduit is under the cross influence of both the discharge and the circulation. As a result, the relationship between the head loss and the discharge is almost linear, and the mechanism needs to be further studied.展开更多
Samarahan has transformed from a small village into education hub for the past 2 decades. Rapid development and population growth had led to speedy growth in water demand. The situation is getting worse as the pipes a...Samarahan has transformed from a small village into education hub for the past 2 decades. Rapid development and population growth had led to speedy growth in water demand. The situation is getting worse as the pipes are deteriorating due to pipe aging. Therefore, there is a need to study the adequacy of water supply and relationships among roughness coefficient (C) values in Hazen Williams’ Equation with head loss and water pressure due to pipe aging at Uni-Central, a residential area located at Samarahan Sarawak. Investigations were carried out with Ductile Iron, Abestos Cement and Cast Iron pipes at age categories of 0 - 10 years, 10 - 30 years, 30 - 50 years, 50 - 70 years and >70 years. Six critical nodes named as A, B, C, D, E and F were identified to study the water pressure and head loss. Model was developed with InfoWorks Water Supply (WS) Pro software. The impact of pipe aging and materials to water pressure and head loss was not significant at Nodes A, B, C and F. However, max water pressure at Nodes D and F were only reaching 6.30 m and 7.30 m, respectively for all investigations. Therefore, some improvement works are required. Results also show that Asbestos Cement pipe has the least impact on the head loss and water pressure, followed by Ductile Iron pipe and lastly Cast Iron pipe. Simulation results also revealed that older pipes have higher roughness coefficients, indicated with lower “C” values, thus increase the head loss and reduce the water pressure. In contrast, as “C” values increased, head loss will be reduced and water pressure will be increased.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC3202502)the National Natural Science Foundation Joint Fund of China(Grant No.U2243239).
文摘In winter,rivers in cold regions often experience flood disasters resulted from ice jams or ice dams.Investigations of the variation of ice jam thickness and water level during an ice jammed period are not only a practical need for ice prevention to avoid disaster and plan water resource,but also essential for the development of any mathematical model for predicting the evolution of ice jam.So far,some equations based on the energy equation have been proposed to describe the relationship between ice jam thickness and water level.However,in the derivation of these equations,the local head loss coefficient at the ice jam head and the riverbed slope factor were neglected.Obviously,those reported equations cannot be used to preciously describe the flow energy equation with ice jams and accurately calculate the ice jam thickness and water level.In the present study,a more comprehensive theoretical model for hydraulic calculation of ice jam thickness has been derived by considering important and essential factors including riverbed slope and local head loss coefficient at the ice jam head.Furthermore,based on the data collected from laboratory experiments of ice jam accumulation,the local head loss coefficient at the ice jam head has been calculated,and the empirical equation for calculating the local head loss coefficient has been established by considering flow Froude number and the ratio of ice discharge to flow discharge.The results of this study not only provide a new reference for calculating ice jam thickness and water level,but also present a theoretical basis for accurate CFD simulation of ice jams.
基金the financial support given by the Special Fund for Agro-scientific Research in the Public Interest of China (201503125)the National Key Research and Development Program of China
文摘To solve the common problem of flumes flowmeasurement accuracy without sacrificing water head, a new type of trapezoidal cutthroat flume to measure the discharge in terminal trapezoidal channels is presented.Using the computational fluid dynamic method, threedimensional flow fields in trapezoidal cutthroat flumes were simulated using the RNG k-ε three-dimensional turbulence model along with the Tru VOF technique.Simulations were performed for 12 working conditions,with discharges up to 0.075 m3$s–1 to determine hydraulic performance. Experimental data for the trapezoidal cutthroat flume in terminal trapezoidal channel were also obtained to validate the simulation results. Velocity distribution of the flume obtained from simulation analyses were compared with observed results based on timeaveraged flow field and comparison yielded a solid agreement between results from the two methods, with relative error below 10%. The results indicated that the Froude number and the longitudinal average velocity increased along the convergence section and decreased in the divergent section. In the upper throat, the Froude number was less than 0.5, which meets the water measurement requirement, and the critical flow appeared near the throat section. The maximum water head loss of the trapezoidal cutthroat flume was less than 9% of the total head, compared to the rectangular cutthroat flume,and head loss of trapezoidal cutthroat flume was significantly less. Regression models developed for upstream depth versus discharge under different working conditions were satisfactory, with a relative error of less than 2.06%, which meets the common requirements of flow measurement in irrigation areas. It was concluded that trapezoidal cutthroat flumes can improve flow-measurement accuracy without sacrificing water head.
文摘Introduction: Free flap success rates have remained stable in recent years ranging 93% to 98%. Historically, the causes of free flap failures were attributed to the surgeon’s inexperience and technique. However, there are factors beyond the surgical anastomosis that contribute to flap failure. The purpose of this study is to review each case of total flap loss in detail to develop a better understanding of complications. Methods: A retrospective study was performed over eleven years in a single surgeon’s practice, a predominantly head and neck reconstructive practice. All charts were independently reviewed. In patients who sustained total flap loss, a review was conducted of patient comorbidites, anesthesia records, perioperative and follow-up notes. Results: A total of 514 free flaps were performed. 76% (392) of these flaps were for head and neck reconstruction. There were 22 total flap losses (4%) and 26 partial flap losses (5%). Of the 22 total flap losses, four flaps were avulsed, five flaps were in patients later found to have coagulation disorders (homozygous mutations of the MTHFR gene and factor V Leiden), four patients were exposed to neosynephrine, two patients remained hypotensive perioperatively, and four delayed flap losses were attributed to pseudomonal infection. Five losses were technical or related to flap inexperience. Several representative case scenarios are illustrated. Conclusion: Careful review of free flap failures indicates that a thorough workup (particularly coagulation disorders), flap selection, surgeon to anesthesia communication, proper securing of the flap, and postoperative patient blood pressure and infection control have a greater part to play in this new era of anastomotic success.
文摘BACKGROUND Chronic otitis media(COM)is an inflammatory disease that lasts for a long time.It is common in developing countries.Hearing loss can result from COM.The relationship between variations in middle ear anatomy and COM was investigated in our study.AIM To compare the prevalence of middle ear anatomic variations between the cases with COM and healthy individuals.METHODS This retrospective study included 500 patients with COM and 500 healthy controls.The presence of those variants was determined:Koerner’s septum,facial canal dehiscence,high jugular bulb,jugular bulb dehiscence,jugular bulb diverticulum,sigmoid sinus anterior location and deep tympanic recesses.RESULTS A total of 1000 temporal bones were examined.The incidences of these variants were respectively(15.4%-18.6%),(38.6%-41.2%),(18.2%-4.6%),(2.6%-1.2%),(1.2%-0%),(8.6%-0%),(0%-0%).It was observed that only high jugular bulb(P<0.001)and anteriorly located sigmoid sinus frequencies(P=0.002)in the case group were statistically significantly higher than the control groups.CONCLUSION COM is a multifactorial disease and variants of middle ear have always been important in terms of potential risk for complication during surgery but rarely associated with COM as an etiology or as a consequence of the disease.We didn't find a positive correlation between COM and Koerner’s septum and facial canal defect.We ended up with a significant conclusion with the variants of dural venous sinuses-high jugular bulb,dehiscence of jugular bulb,diverticulum of jugular bulb and anteriorly located sigmoid sinus-that have been studied less and frequently associated with inner ear illnesses.
文摘The relationship between the head loss and the discharge and circulation of the conduit of a pump system with low head is an important problem with an obvious influence on the improvement of its hydraulic performance. The velocity circulation from the pump guide vane makes the relationship more complicated, which has to be understood comprehensively. The results indicate that, under the condition of zero circulation, the head loss of the inlet and outlet conduits is in proportion to the square of discharge. Under the condition that the Reynolds number is satisfied with the resistant square area, the conduit loss is in proportion to the square of discharge for the similar working points with different speeds in a certain rotational speed range, indicating that the pump system efficiency is constant. The outlet conduit loss of design discharge for a pump system with low head depends on the velocity circulation from the guide vane exit, and the relationship between the loss and the circulation is an open curve with an upward direction, meaning that there is an optimal circulation for the loss. Under the condition of various working points for a pump system with low head, the head loss of the outlet conduit is under the cross influence of both the discharge and the circulation. As a result, the relationship between the head loss and the discharge is almost linear, and the mechanism needs to be further studied.
文摘Samarahan has transformed from a small village into education hub for the past 2 decades. Rapid development and population growth had led to speedy growth in water demand. The situation is getting worse as the pipes are deteriorating due to pipe aging. Therefore, there is a need to study the adequacy of water supply and relationships among roughness coefficient (C) values in Hazen Williams’ Equation with head loss and water pressure due to pipe aging at Uni-Central, a residential area located at Samarahan Sarawak. Investigations were carried out with Ductile Iron, Abestos Cement and Cast Iron pipes at age categories of 0 - 10 years, 10 - 30 years, 30 - 50 years, 50 - 70 years and >70 years. Six critical nodes named as A, B, C, D, E and F were identified to study the water pressure and head loss. Model was developed with InfoWorks Water Supply (WS) Pro software. The impact of pipe aging and materials to water pressure and head loss was not significant at Nodes A, B, C and F. However, max water pressure at Nodes D and F were only reaching 6.30 m and 7.30 m, respectively for all investigations. Therefore, some improvement works are required. Results also show that Asbestos Cement pipe has the least impact on the head loss and water pressure, followed by Ductile Iron pipe and lastly Cast Iron pipe. Simulation results also revealed that older pipes have higher roughness coefficients, indicated with lower “C” values, thus increase the head loss and reduce the water pressure. In contrast, as “C” values increased, head loss will be reduced and water pressure will be increased.
