The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
D C Helm - One of the best experts on this subject based on the ideXlab platform.
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inverse procedure for calibrating parameters that control land subsidence caused by subsurface Fluid Withdrawal 1 methods
Water Resources Research, 2008Co-Authors: D C HelmAbstract:[1] Land subsidence prediction depends on a selected theoretical model and the calibration of its parameter values. An inverse model is developed that calibrates five parameters of a compacting confined aquifer system: K′v (vertical hydraulic conductivity of the aquitards), S′skv (aquitard nonrecoverable skeletal specific storage), S′ske (aquitard recoverable skeletal specific storage), Ssk (skeletal specific storage of the aquifer), and p′max 0 (initial preconsolidation stress within the aquitards). This inverse model combines a procedure for finding an initial set of parameter values and an inverse adjustment procedure. Initial values are estimated by using a new graphic method for the analysis of field data. The follow-up inverse procedure is a computer algorithm that combines the Newton-Raphson method with Helm's one-dimensional finite difference subsidence model (COMPAC). COMPAC offers two options: a constant-parameter simulation and a stress-dependent parameter simulation. The classical least squares criterion is employed as the objective function of this inverse procedure. Three characteristics of the objective function are considered. This inverse model is applied to calculations of an idealized compacting confined aquifer system using Helm's model. This investigation shows that the final values for the five parameters lead to simulated compaction error of less than 1%. This contrasts to the initial error of more than 60%. These results indicate that the proposed inverse procedure (model) can be applied to actual field data.
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inverse procedure for calibrating parameters that control land subsidence caused by subsurface Fluid Withdrawal 2 field application
Water Resources Research, 2008Co-Authors: D C HelmAbstract:[1] The inverse procedure (InvCOMPAC) that was developed in part 1 of this two-part paper is applied to two aquifer systems at two sites in Shanghai. The present part 2 illustrates how to calibrate transient land subsidence parameter values on the basis of in situ data. The new graphic-analytic method yields initial parameter values for use in the inverse procedure. For the upper and lower confined aquifer systems at multiple-extensometer sites F09 and F16 in Shanghai, their final parameter values are calibrated further by InvCOMPAC, a computer-based inverse model. The simulation error of transient subsidence over a period of 13 and 20 years, respectively, at sites F09 and F16 is decreased to 11.8 and 13.9%, respectively, from an initial graphic-analytic result of 72.1 and 415.3%. This demonstrates that InvCOMPAC is applicable to complex field conditions. The new graphic-analytic method is necessary in order to find a realistic set of initial parameter values. Calibrated parameter values are used to predict future subsidence in the field. Predictions indicate that a large amount of ongoing residual nonrecoverable compaction will occur and will not equilibrate with the anticipated decline of groundwater levels at these sites. The reason is that the vertical nonrecoverable skeletal specific storage of the aquitards is 2−3 orders of magnitude larger than the vertical recoverable skeletal specific storage of both the aquitards and the aquifer. The vertical hydraulic conductivity is too small for the aquitards to drain sufficiently quickly for them to reach a new equilibrium in response to water level declines. It is recommended that groundwater levels be kept above the past maximum preconsolidation pressure levels within the aquitards. This will prevent continued nonrecoverable compaction from occurring.
Martin E. Blohm - One of the best experts on this subject based on the ideXlab platform.
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Effect of hemodialysis on impedance cardiography (electrical velocimetry) parameters in children
Pediatric Nephrology, 2019Co-Authors: Meike Wilken, Jun Oh, Dominique Singer, Hans O Pinnschmidt, Martin E. BlohmAbstract:Background Pediatric hemodialysis (HD) patients have a high incidence of cardiovascular morbidity and mortality. The study aim was to investigate whether impedance cardiography (electrical velocimetry, EV) is suitable as a hemodynamic trend monitoring tool in pediatric patients during HD. Methods Measurements by EV were obtained before, during, and after HD in a prospective single-center pediatric observational study. In total, 54 dialysis cycles in four different pediatric patients with end-stage kidney disease on chronic HD were included. EV parameters analyzed were heart rate (HR), stroke volume (SV), stroke volume index (SI), cardiac output (CO), cardiac index (CI), thoracic Fluid content (TFC), index of contractility (ICON), stroke volume variation (SVV), variation of ICON (VIC), R-R interval (TRR), pre-ejection period (PEP), left ventricular ejection time (LVET), and systolic time ration (STR). Systemic vascular resistance index (SVRI) was calculated. Results EV did measure significant changes in cardiovascular parameters associated with HD. The following parameters increased after HD: HR (9%), SVV (19%), VIC (33%), PEP (8%), and STR (18%). A decrease after HD was measured in SV (18%), SI (18%), CO (10%), CI (10%), TFC (10%), ICON (7%), TRR (7%), LVET (8%), and LVET (8%). SVRI was not affected by HD. The changes were correlated to ultrafiltration. HD cycles without Fluid Withdrawal also altered cardiovascular parameters. Conclusions Pediatric HD with and without Fluid Withdrawal changes hemodynamic EV monitoring parameters. Possibly EV may be useful to optimize HD management in pediatric patients.
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Effect of hemodialysis on impedance cardiography (electrical velocimetry) parameters in children.
Pediatric Nephrology, 2019Co-Authors: Meike Wilken, Jun Oh, Dominique Singer, Hans O Pinnschmidt, Martin E. BlohmAbstract:BACKGROUND: Pediatric hemodialysis (HD) patients have a high incidence of cardiovascular morbidity and mortality. The study aim was to investigate whether impedance cardiography (electrical velocimetry, EV) is suitable as a hemodynamic trend monitoring tool in pediatric patients during HD. METHODS: Measurements by EV were obtained before, during, and after HD in a prospective single-center pediatric observational study. In total, 54 dialysis cycles in four different pediatric patients with end-stage kidney disease on chronic HD were included. EV parameters analyzed were heart rate (HR), stroke volume (SV), stroke volume index (SI), cardiac output (CO), cardiac index (CI), thoracic Fluid content (TFC), index of contractility (ICON), stroke volume variation (SVV), variation of ICON (VIC), R-R interval (TRR), pre-ejection period (PEP), left ventricular ejection time (LVET), and systolic time ration (STR). Systemic vascular resistance index (SVRI) was calculated. RESULTS: EV did measure significant changes in cardiovascular parameters associated with HD. The following parameters increased after HD: HR (9%), SVV (19%), VIC (33%), PEP (8%), and STR (18%). A decrease after HD was measured in SV (18%), SI (18%), CO (10%), CI (10%), TFC (10%), ICON (7%), TRR (7%), LVET (8%), and LVET (8%). SVRI was not affected by HD. The changes were correlated to ultrafiltration. HD cycles without Fluid Withdrawal also altered cardiovascular parameters. CONCLUSIONS: Pediatric HD with and without Fluid Withdrawal changes hemodynamic EV monitoring parameters. Possibly EV may be useful to optimize HD management in pediatric patients.
Pietro Teatini - One of the best experts on this subject based on the ideXlab platform.
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Reservoir compaction and land subsidence
Revue Européenne de Génie Civil, 2006Co-Authors: Giuseppe Gambolati, Massimiliano Ferronato, Pietro TeatiniAbstract:ABSTRACT Subsurface hydrocarbon removal induces a reservoir compaction that migrates to the ground surface and causes the land to subside. While compaction depends primarily on the Fluid pore pressure drawdown, the thickness and the mechanical compressibility of the depleted formation, the amount of compaction reaching the surface depends on the depth and size of the producing field and the stiffness of the overburden. This paper presents a list of the most famed sites worldwide that have experienced anthropogenic land subsidence because of underground Fluid Withdrawal and reviews the basic mechanisms controlling the reservoir compaction and the related ground settlement. Finally, some mathematical models, that can be effectively used to simulate and predict the occurrence, and the most recent techniques for accurately and timely measuring and monitoring the deep compaction and the land surface displacements are described.
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Encyclopedia of Hydrological Sciences - Anthropogenic Land Subsidence
Encyclopedia of Hydrological Sciences, 2005Co-Authors: Giuseppe Gambolati, Pietro Teatini, Massimiliano FerronatoAbstract:Fluid removal from subsurface reservoirs, in the form of gas, oil, groundwater, geothermal water, and brine, produces a compaction of the depleted formations which migrates totally or partially to the ground surface thus inducing anthropogenic land subsidence. The paper presents: (i) a list of the major subsiding areas worldwide, (ii) a review of the mechanism which causes a measurable settlement above aquifer systems and gas/oil fields, (iii) a description of the currently available techniques to measure land subsidence and in situ rock compaction, (iv) a brief description of some mathematical models to predict the magnitude of subsidence, and (v) a description of a few remedial options that are available to control the event and mitigate the related environmental impact. Keywords: Fluid Withdrawal/injection; land subsidence; mathematical modelling; monitoring technique
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surface flow boundary conditions in modeling land subsidence due to Fluid Withdrawal
Ground Water, 2004Co-Authors: Massimiliano Ferronato, Giuseppe Gambolati, Pietro TeatiniAbstract:Land subsidence due to subsurface Fluid (water, gas, oil) Withdrawal is often predicted by either finite element or finite difference numerical models based on coupled poroelastic theory, where the soil is represented as a semi-infinite medium bounded by the traction-free (ground) surface. One of the variables playing a most important role on the final outcome is the flow condition used on the traction-free boundary, which may be assumed as either permeable or impermeable. Although occasionally justified, the assumption of no-flow surface seems to be in general rather unrealistic. A permeable boundary where the Fluid pressure is fixed to the external atmospheric pressure appears to be more appropriate. This paper addresses the response, in terms of land subsidence, obtained with a coupled poroelastic finite element model that simulates a distributed pumping from a horizontal aquifer confined between two relatively impervious layers, and takes either a permeable boundary surface, i.e., constant hydraulic potential, or an impermeable boundary, i.e., a zero Neumann flow condition. The analysis reveals that land subsidence is rather sensitive to the flow condition implemented on the traction-free boundary. In general, the no-flow condition leads to an overestimate of the predicted ground surface settlement, which could even be 1 order of magnitude larger than that obtained with the permeable boundary.
Meike Wilken - One of the best experts on this subject based on the ideXlab platform.
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Effect of hemodialysis on impedance cardiography (electrical velocimetry) parameters in children
Pediatric Nephrology, 2019Co-Authors: Meike Wilken, Jun Oh, Dominique Singer, Hans O Pinnschmidt, Martin E. BlohmAbstract:Background Pediatric hemodialysis (HD) patients have a high incidence of cardiovascular morbidity and mortality. The study aim was to investigate whether impedance cardiography (electrical velocimetry, EV) is suitable as a hemodynamic trend monitoring tool in pediatric patients during HD. Methods Measurements by EV were obtained before, during, and after HD in a prospective single-center pediatric observational study. In total, 54 dialysis cycles in four different pediatric patients with end-stage kidney disease on chronic HD were included. EV parameters analyzed were heart rate (HR), stroke volume (SV), stroke volume index (SI), cardiac output (CO), cardiac index (CI), thoracic Fluid content (TFC), index of contractility (ICON), stroke volume variation (SVV), variation of ICON (VIC), R-R interval (TRR), pre-ejection period (PEP), left ventricular ejection time (LVET), and systolic time ration (STR). Systemic vascular resistance index (SVRI) was calculated. Results EV did measure significant changes in cardiovascular parameters associated with HD. The following parameters increased after HD: HR (9%), SVV (19%), VIC (33%), PEP (8%), and STR (18%). A decrease after HD was measured in SV (18%), SI (18%), CO (10%), CI (10%), TFC (10%), ICON (7%), TRR (7%), LVET (8%), and LVET (8%). SVRI was not affected by HD. The changes were correlated to ultrafiltration. HD cycles without Fluid Withdrawal also altered cardiovascular parameters. Conclusions Pediatric HD with and without Fluid Withdrawal changes hemodynamic EV monitoring parameters. Possibly EV may be useful to optimize HD management in pediatric patients.
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Effect of hemodialysis on impedance cardiography (electrical velocimetry) parameters in children.
Pediatric Nephrology, 2019Co-Authors: Meike Wilken, Jun Oh, Dominique Singer, Hans O Pinnschmidt, Martin E. BlohmAbstract:BACKGROUND: Pediatric hemodialysis (HD) patients have a high incidence of cardiovascular morbidity and mortality. The study aim was to investigate whether impedance cardiography (electrical velocimetry, EV) is suitable as a hemodynamic trend monitoring tool in pediatric patients during HD. METHODS: Measurements by EV were obtained before, during, and after HD in a prospective single-center pediatric observational study. In total, 54 dialysis cycles in four different pediatric patients with end-stage kidney disease on chronic HD were included. EV parameters analyzed were heart rate (HR), stroke volume (SV), stroke volume index (SI), cardiac output (CO), cardiac index (CI), thoracic Fluid content (TFC), index of contractility (ICON), stroke volume variation (SVV), variation of ICON (VIC), R-R interval (TRR), pre-ejection period (PEP), left ventricular ejection time (LVET), and systolic time ration (STR). Systemic vascular resistance index (SVRI) was calculated. RESULTS: EV did measure significant changes in cardiovascular parameters associated with HD. The following parameters increased after HD: HR (9%), SVV (19%), VIC (33%), PEP (8%), and STR (18%). A decrease after HD was measured in SV (18%), SI (18%), CO (10%), CI (10%), TFC (10%), ICON (7%), TRR (7%), LVET (8%), and LVET (8%). SVRI was not affected by HD. The changes were correlated to ultrafiltration. HD cycles without Fluid Withdrawal also altered cardiovascular parameters. CONCLUSIONS: Pediatric HD with and without Fluid Withdrawal changes hemodynamic EV monitoring parameters. Possibly EV may be useful to optimize HD management in pediatric patients.
Massimiliano Ferronato - One of the best experts on this subject based on the ideXlab platform.
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Reservoir compaction and land subsidence
Revue Européenne de Génie Civil, 2006Co-Authors: Giuseppe Gambolati, Massimiliano Ferronato, Pietro TeatiniAbstract:ABSTRACT Subsurface hydrocarbon removal induces a reservoir compaction that migrates to the ground surface and causes the land to subside. While compaction depends primarily on the Fluid pore pressure drawdown, the thickness and the mechanical compressibility of the depleted formation, the amount of compaction reaching the surface depends on the depth and size of the producing field and the stiffness of the overburden. This paper presents a list of the most famed sites worldwide that have experienced anthropogenic land subsidence because of underground Fluid Withdrawal and reviews the basic mechanisms controlling the reservoir compaction and the related ground settlement. Finally, some mathematical models, that can be effectively used to simulate and predict the occurrence, and the most recent techniques for accurately and timely measuring and monitoring the deep compaction and the land surface displacements are described.
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Encyclopedia of Hydrological Sciences - Anthropogenic Land Subsidence
Encyclopedia of Hydrological Sciences, 2005Co-Authors: Giuseppe Gambolati, Pietro Teatini, Massimiliano FerronatoAbstract:Fluid removal from subsurface reservoirs, in the form of gas, oil, groundwater, geothermal water, and brine, produces a compaction of the depleted formations which migrates totally or partially to the ground surface thus inducing anthropogenic land subsidence. The paper presents: (i) a list of the major subsiding areas worldwide, (ii) a review of the mechanism which causes a measurable settlement above aquifer systems and gas/oil fields, (iii) a description of the currently available techniques to measure land subsidence and in situ rock compaction, (iv) a brief description of some mathematical models to predict the magnitude of subsidence, and (v) a description of a few remedial options that are available to control the event and mitigate the related environmental impact. Keywords: Fluid Withdrawal/injection; land subsidence; mathematical modelling; monitoring technique
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surface flow boundary conditions in modeling land subsidence due to Fluid Withdrawal
Ground Water, 2004Co-Authors: Massimiliano Ferronato, Giuseppe Gambolati, Pietro TeatiniAbstract:Land subsidence due to subsurface Fluid (water, gas, oil) Withdrawal is often predicted by either finite element or finite difference numerical models based on coupled poroelastic theory, where the soil is represented as a semi-infinite medium bounded by the traction-free (ground) surface. One of the variables playing a most important role on the final outcome is the flow condition used on the traction-free boundary, which may be assumed as either permeable or impermeable. Although occasionally justified, the assumption of no-flow surface seems to be in general rather unrealistic. A permeable boundary where the Fluid pressure is fixed to the external atmospheric pressure appears to be more appropriate. This paper addresses the response, in terms of land subsidence, obtained with a coupled poroelastic finite element model that simulates a distributed pumping from a horizontal aquifer confined between two relatively impervious layers, and takes either a permeable boundary surface, i.e., constant hydraulic potential, or an impermeable boundary, i.e., a zero Neumann flow condition. The analysis reveals that land subsidence is rather sensitive to the flow condition implemented on the traction-free boundary. In general, the no-flow condition leads to an overestimate of the predicted ground surface settlement, which could even be 1 order of magnitude larger than that obtained with the permeable boundary.