Pressure Curves Research Articles

IORSim: A Mathematical Workflow for Field-Scale Geochemistry Simulations in Porous Media

Reservoir modeling consists of two key components: the reproduction of the historical performance and the prediction of the future reservoir performance. Industry-standard reservoir simulators must run fast on enormous and possibly unstructured grids while yet guaranteeing a reasonable representation of physical and chemical processes. However, computational demands limit simulators in capturing involved physical and geochemical mechanisms, especially when chemical reactions interfere with reservoir flow. This paper presents a mathematical workflow, implemented in IORSim, that makes it possible to add geochemical calculations to porous media flow simulators without access to the source code of the original host simulator. An industry-standard reservoir simulator calculates velocity fields of the fluid phases (e.g., water, oil, and gas), while IORSim calculates the transport and reaction of geochemical components. Depending on the simulation mode, the geochemical solver estimates updated relative and/or capillary pressure curves to modify the global fluid flow. As one of the key innovations of the coupling mechanism, IORSim uses a sorting algorithm to permute the grid cells along flow directions. Instead of solving an over-dimensionalized global matrix calling a Newton–Raphson solver, the geochemical software tool treats the species balance as a set of local nonlinear problems. Moreover, IORSim applies basis swapping and splay tree techniques to accelerate geochemical computations in complex full-field reservoir models. The presented work introduces the mathematical IORSim concept, verifies the chemical species advection, and demonstrates the IORSim computation efficiency. After validating the geochemical solver against reference software, IORSim is used to investigate the impact of seawater injection on the NCS Ekofisk reservoir chemistry.Article HighlightsThe IORSim sorting algorithm decouples the nonlinear geochemical reaction calculations into recurring one-dimensional problems to assure numerical stability and computation efficiency. To the best of our knowledge, this work presents the mathematical concept, implementation, and application of topological sorting for the first time on (industry) field-scale problems.IORSim combines topological sorting with basis swapping and splay trees to significantly reduce computation times. Moreover, a high-speed forward simulation mode was developed to allow the post-advection of chemical components to visualize species distribution, water chemistry, and mineral interactions. If the geochemical reactions interfere with the fluid flow, the IORSim backward mode uses relative permeability curves to update the global fluid flow at each time step.We validate the implemented topological scheme on a reservoir grid, show the computation efficiency, and compare the impact of explicit, implicit, and grid refinement on numerical dispersion.The decoupled flow simulator and geochemical reaction calculations allow seamless integration of full-field reservoir models that contain complex geological structures, a large number of wells, and long production histories.The computation capabilities of IORSim are demonstrated by simulating and reproducing the impact of seawater injection in the southern segment of the giant Ekofisk field (more than 50 years of injection and production history). IORSim shows that seawater injection changed the Ekofisk mineralogy and impacted the produced water chemistry. In the investigated Ekofisk case, seawater promoted calcite dissolution and led to the precipitation of magnesite and anhydrite. Moreover, surface complexation modeling revealed that sulfate is adsorbed on the calcite surface.

In‐mold rheology and automated process control for injection molding of recycled polypropylene

AbstractManufacturing plastic parts with secondary feedstocks has risen to the forefront of importance in recent years. However, the variation in molecular weight and rheology of secondary feedstock can lead to inconsistent part quality. This work evaluates the effectiveness of a novel closed‐loop adaptive process control system that adjusts nozzle pressure in response to in‐mold pressure data. Five different recycled polypropylene blends, with a broad distribution of flow properties, were evaluated to determine the effectiveness of the control system at reducing processing variation. The experimental results show that the process control strategy reduced the variation within the mold, as seen by in‐mold pressure curves and calculated in‐mold viscosity values. Additionally, the parameters that control the automated process adjustments were investigated, showing the importance of optimization. The analysis of the correlation between in‐mold rheology and mechanical properties showed a slight variation in the mechanical properties and parts weight with a coefficient of variation of under 5%. Overall, the results demonstrate the ability of pressure‐controlled molding and automated viscosity adjustment to reduce the variability when molding a secondary feedstock.Highlights Pressure‐controlled injection molding of recycled polypropylene. Automated closed‐loop adaptive process control methodology. Methodology resulted in a reduction in pressure variation during molding. Changes in mechanical properties and in‐mold viscosity were investigated. Results show the potential of pressure‐controlled molding at reducing variation.

Low salinity water flooding: estimating relative permeability and capillary pressure using coupling of particle swarm optimization and machine learning technique

The reservoir’s properties are required for proper reservoir simulation, which also involves uncertainties. Experimental methods to estimate the relative permeability and capillary pressure data are expensive and time-consuming. This study aims to determine the relative permeability and capillary pressure functions of a sandstone core in the presence and absence of clay during low-salinity water floods. The data were provided by automatic history matching the results from previously lab-reported studies through coupling a simulator with the particle swarm optimization algorithm. Correlations were proposed using multiple-linear regression for relative permeability and capillary pressure parameters at low-salinity conditions. They were validated against experimental results of no clay and clayey formation with regression of 95% and 97%. To assign one curve of relative permeability and capillary pressure to the grid cells of the simulator, averaging techniques were implemented. The effect of salinity and clay content on the obtained curves was investigated. Changing salinity from 42000 to 4000 ppm, the reduction in water relative permeability appeared to be higher than the oil relative permeability increment. Moreover, a noticeable shift in the relative permeability curves toward the highest saturations related to the clay content was observed. The proposed hybrid method could be a suitable tool to estimate the relative permeability and capillary pressure functions of the water-based EOR methods.

Examining Invasion‐Percolation Across the Cathode Layered Assembly in Polymer Electrolyte Membrane Fuel Cells: Oxygen Resistance, Wettability and Cracks

AbstractEfficient evacuation of water generated by oxygen reduction reaction is necessary to increase catalyst utilization in polymer electrolyte membrane Fuel Cells. However, analysis of two‐phase transport is challenged by the wide range of pore sizes present in the membrane electrode assembly (MEA), varying from 10–100 nm in the catalyst layer (CL), 10–1000 nm in the microporous layer (MPL) and 10 μm in the gas diffusion layer (GDL). In this work, a novel multiscale invasion‐percolation model accounting for the cathode CL, MPL and GDL is presented. Saturation in the macroporous GDL is modeled through an all‐or‐nothing invasion law (empty/filled), while a macroscopic description in terms of the capillary pressure curve is adopted for the MPL and the CL. The oxygen transport resistance across the cathode MEA is quantified using the computed saturation distributions. Among other conclusions, the results show that MPL addition is crucial to avoid local flooding at the CL/GDL interface, providing localized access points to the GDL rather than massively invading interfacial macropores. However, excessive MPL hydrophobicity can cause CL flooding. Water removal from the CL can be enhanced by using a more hydrophilic MPL, a hydrophobic CL or the addition of a moderate volume fraction of cracks. Oxygen transport can be further improved by modulating the arrangement of water in the GDL with patterned wettability, provided that the number of MPL cracks is low.

Impact of Pressure-Dependent Interfacial Tension and Contact Angle on Capillary Heterogeneity Trapping of CO2 in Storage Aquifers

Summary Carbon dioxide (CO2) capillary trapping increases the total amount of CO2 that can be effectively immobilized in storage aquifers. This trapping, manifesting itself as accumulated CO2 columns at a continuum scale, is because of capillary threshold effects that occur below low-permeability barriers. Considering that capillary pressure is dictated by heterogeneous pore throat size, the trapped CO2 column height and associated CO2 saturation will vary spatially within a storage aquifer. This variation will be influenced by two pressure-dependent interfacial parameters—CO2/brine interfacial tension (IFT) and CO2/brine/rock contact angle. Our objective is to understand how the pressure dependence of these two parameters affects the heterogeneity of capillary trapped CO2 at a continuum scale. Our conceptual model is a 1D two-zone system with the upper zone being a flow barrier (low permeability) and the lower zone being a flow path (high permeability). The inputs to this model include microfacies-dependent capillary pressure vs. saturation curves and permeability values. The input capillary pressure curves were collected in the literature that represents carbonate microfacies (e.g., dolograinstone) in a prevalent formation in the Permian Basin. We then used the Leverett j-function to scale the capillary pressure curve for the two zones that are assigned with the same or different microfacies. During scaling, we considered the influence of pressure on both the IFT and contact angle of CO2/brine/dolomite systems. We varied the zone permeability contrast ratio from 2 to 50. We then assumed capillary gravity equilibriums and calculated the CO2 saturation buildup corresponding to various trapped CO2 column heights. The CO2 saturation buildup is defined as the CO2 saturation in the lower layer minus that in the upper one. We found that the saturation buildup can be doubled when varying pressure in a storage aquifer, after considering pressure-dependent IFT and contact angles. Thus, assuming these two parameters to be constant across such aquifers would cause large errors in the quantification of capillary trapping of CO2. The whole study demonstrates the importance of considering pressure-dependent interfacial properties in predicting the vertical distribution of capillary trapped CO2. It has important implications in developing a better understanding of leakage risks and consequent storage safety.

Analysis of flow characteristics of a pump turbine under the transient condition of 75% load rejection

Abstract In this study, the flow calculations for a pump turbine under the transient condition of 75% load rejection was conducted. The model incorporated a boundary layer on the surface of the guide vane, with the node coordinates of each element in the boundary layer region being updated. This approach ensured the stability of the boundary layer mesh. Experimental measurements provided parameter curves for inlet pressure, outlet pressure, runner speed, and guide vane opening over time. The pressure fluctuation at each monitoring point was compared with the experimental data, and a good agreement was found. Additionally, the variation curve of the axial hydraulic thrust of the head cover and the pressure distribution nephogram of the head cover at typical moments were analysed. The results of this study could be used as a reference for the safe and stable operation of pumped-storage power stations.

Analysis and Modeling Study on the Effect of Working Parameters of Portable Neutron Tubes on Target Current

Abstract As an important parameter index of sealed neutron tubes, their high-pressure side target current directly affects neutron yield. The working parameters of a neutron tube affect the target current. Using self-developed neutron tubes, the influence of operating parameters of neutron tubes on target current was studied. The effect curves of gas pressure, anode high pressure, and target high pressure on neutron yield were obtained, and the secondary electron suppression characteristics of the target current were obtained. Further, we analyze and fit a multi-parameter coupling model for the target current, to provide a theoretical basis for establishing the working state and improving the performance of sealed neutron tubes.

Optimization method of fracturing fluid volume intensity for SRV fracturing technique in shale oil reservoir based on forced imbibition: A case study of well X-1 in Biyang Sag of Nanxiang Basin, China

An optimization method of fracturing fluid volume strength was introduced taking well X-1 in Biyang Sag of Nanxiang Basin as an example. The characteristic curves of capillary pressure and relative permeability were obtained from history matching between forced imbibition experimental data and core-scale reservoir simulation results and taken into a large scale reservoir model to mimic the forced imbibition behavior during the well shut-in period after fracturing. The optimization of the stimulated reservoir volume (SRV) fracturing fluid volume strength should meet the requirements of estimated ultimate recovery (EUR), increased oil recovery by forced imbibition and enhancement of formation pressure and the fluid volume strength of fracturing fluid should be controlled around a critical value to avoid either insufficiency of imbibition displacement caused by insufficient fluid amount or increase of costs and potential formation damage caused by excessive fluid amount. Reservoir simulation results showed that SRV fracturing fluid volume strength positively correlated with single-well EUR and an optimal fluid volume strength existed, above which the single-well EUR increase rate kept decreasing. An optimized increase of SRV fracturing fluid volume and shut-in time would effectively increase the formation pressure and enhance well production. Field test results of well X-1 proved the practicality of established optimization method of SRV fracturing fluid volume strength on significant enhancement of shale oil well production.

Computing Relative Permeability and Capillary Pressure of Heterogeneous Rocks Using Realistic Boundary Conditions

Relative permeability and capillary pressure are key parameters in multiphase flow modelling. In heterogeneous porous media, flow direction- and flow-rate dependence result from non-uniform saturation distributions that vary with the balance between viscous, gravitational, and capillary forces. Typically, relative permeability is measured using constant inlet fractional-flow—constant outlet fluid pressure conditions on samples mounted between permeable porous plates to avoid capillary end-effects. This setup is replicated in numeric experiments but ignores the extended geologic context beyond the sample size, impacting the saturation distribution and, consequently, the upscaled parameters. Here, we introduce a new workflow for measuring effective relative permeability and capillary pressure at the bedform scale while considering heterogeneities at the lamina scale. We harness the flexibility of numeric modelling to simulate continuum-REV-scale saturation distributions in heterogeneous rocks eliminating boundary artefacts. Periodic fluid flux boundary conditions are applied in combination with arbitrarily oriented, variable-strength pressure gradient fields. The approach is illustrated on a periodic model of cross-bedded sandstone. Stepping saturation while applying variable-strength pressure-gradient fields with different orientations, we cover the capillary-viscous force balance spectrum of interest. The obtained relative permeability and capillary pressure curves differ from ones obtained with traditional approaches highlighting that the definition of force balances needs consideration of flow direction as an additional degree of freedom. In addition, we discuss when the common viscous and the capillary limits are applicable and how they vary with flow direction in the presence of capillary interfaces.

Laboratory experimental study of the forming and failure mechanisms of soil arching during EPBS tunnelling in sand

The effect of soil arching often leads to delayed ground collapse disasters when the tunnelling instability of earth pressure balance shields (EPBS) in sand. To reveal the formation and evolution of soil arching in sand, a laboratory-scale EPBS tunnelling model test was conducted. This EPBS tunnelling system simulated the entire process of shield tunnelling, which includes stable tunnelling, tunnel face instability, and ground collapse. The application of multi-field monitoring and three-dimensional scanning has revealed the influence of soil arching on sand layer collapse. The results indicate that: (1) Controlling the actual sand discharge rate to approach the theoretical rate can achieve stability of the tunnel face during the excavation process; (2) Maintaining higher soil pressure on the cutterhead can alleviate the loosening of the sand layer ahead; (3) The loosening zone in the vertical direction of the excavation section is significantly larger than that in the horizontal direction; (4) After the loose zone develops to the surface, each failure of the soil arching will cause significant surface subsidence, which can serve as a precursor to sudden ground collapse. The study provides a reference for the safe construction of tunnel engineering in sand.

The Effectiveness of Pattern Scanning Laser Trabeculoplasty as an Additional Treatment for the Patients of Open-Angle Glaucoma Receiving Full Ocular Hypotensive Medications.

Objectives: Our purpose was to examine the effectiveness of pattern scanning laser trabeculoplasty (PSLT) as an additional treatment for patients of open-angle glaucoma (OAG) receiving maximized ocular hypotensive medications (OHM). Methods: A total of 40 eyes of 33 patients (average age 72.7 ± 10.7 years) who had not previously undergone open glaucoma surgery or laser trabeculoplasty and were treated with maximized OHM between June 2018 and March 2022 were included. A 360-degree PSLT was conducted, and postoperative intraocular pressure (IOP) and survival curves at 1, 3, 6, 9, and 12 months were evaluated. Results: According to the Kaplan-Meier survival analysis, the average survival time was 8.1 months and the survival rate at 12 months was 0.55, with death defined as postoperative IOP reduction of less than 10% or requiring additional treatment. The average survival time was 4.9 months and the survival rate at 12 months was 0.28, with death defined as postoperative IOP reduction of less than 20% or requiring additional treatment. Nine eyes showed increased IOP (three eyes) or worsened visual field (six eyes) during the course and underwent additional open glaucoma surgery. In the 31 eyes which received no additional treatment after PSLT, the mean preoperative IOP was 18.5 ± 3.9 mmHg, which reduced to 15.3 ± 4.1 mmHg (p = 1.62 × 10-6), 15.5 ± 3.4 mmHg (p = 1.51 × 10-5), 15.7 ± 4.0 mmHg (p = 1.75 × 10-5), 14.7 ± 4.38 (p = 2.89 × 10-6), and 15.0 ± 4.0 mmHg (p = 5.74 × 10-9) at 1, 3, 6, 9, and 12 months after PSLT, respectively. The IOP reduction rate one year after PSLT was 18.7%. Of the 31 eyes, 13 (42%) achieved a 20% reduction in IOP compared to the baseline. Conclusions: Adjunctive treatment with PSLT in OAG patients receiving maximized OHM may be effective over 12 months of follow-up.

Strange Quark Stars: The Role of Excluded Volume Effects

We study cold strange quark stars employing an enhanced version of the quark-mass density-dependent model, which incorporates excluded volume effects to address non-perturbative QCD repulsive interactions. We provide a comparative analysis of our mass formula parametrization with previous models from the literature. We identify the regions within the parameter space where three-flavor quark matter is more stable than the most tightly bound atomic nucleus (stability window). Specifically, we show that excluded volume effects do not change the Gibbs free energy per baryon at zero pressure, rendering the stability window unaffected. The curves of pressure versus energy density exhibit various shapes—convex upward, concave downward, or nearly linear—depending on the mass parametrization. This behavior results in different patterns of increase, decrease, or constancy in the speed of sound as a function of baryon number density. We analyze the mass–radius relationship of strange quark stars, revealing a significant increase in maximum gravitational mass and a shift in the curves toward larger radii as the excluded volume effect intensifies. Excluded volume effects render our models compatible with all modern astrophysical constraints, including the properties of the recently observed low-mass compact object HESSJ1731.

Pressure-guided evaluation of pulmonary vein occlusion during cryoballoon pulmonary vein isolation for atrial fibrillation compared to contrast-guided approach

Abstract Introduction Single-shot ablation devices (e.g. cryoballoon [CB] technique) have simplified pulmonary vein isolation (PVI) for interventional treatment of atrial fibrillation (AF). Vein occlusion is mainly assessed utilizing contrast media (CM) during CB ablation. However, this approach entails possible risks, including renal impairment and adverse contrast-related allergic reactions. Furthermore, the assessment of pulmonary venography is often challenging and necessitates fluoroscopy exposure. Purpose The primary objective of this study is to compare procedural data and outcome of pressure-guided (PG) vs. conventional (CM) assessment of vein occlusion. Methods and results From 07/2018 to 12/2022, 915 patients with AF (59% paroxysmal) undergoing CB-PVI at our hospital were prospectively enrolled (single-center experience). 369 (40,3%) patients (age 64,5 ± 10 years; 154 females 41,7%) underwent PVI with the use of CM (CM group), while in 546 (59,7%) cases (age 65,3 ± 10 years; 222 females 40,6%) pressure curve assessment (PG group) was exclusively used to guide the procedure (and no contrast was given). Compared with the CM approach, pressure-guided procedures had lower X-ray time (9,5±5min vs 6,4±3,5min, P<0,0001) and X-ray dose (586±546cGy/cm2 vs 96,7±93 cGy/cm2, P<0,0001). Procedure time (PG: 90,3±20,1min, CM: 92,7±22,7 min, p:0,1 ) and ablation time (PG: 1352 ± 365 min, CM: 1393 ± 651 min, p: 0,2) were not different between groups. There was no significant difference observed in the BMI between the two groups, with a mean value of ca. 28.2 ± 4 kg/m2. In 79 redo-procedures, persistent isolation of all pulmonary veins was observed in 11/45 (25%) patients in the CM group and 21/34 (61%) patients in the PG group (p: 0.001). Conclusion Compared to current (CM) assessment of vein occlusion, pressure monitoring is associated with less X-ray exposure during the index procedure and more frequent durable isolation of all PVs during repeat study for recurrence.

Experimental Study of Plugging Agent Particle Size and Concentration on Temporary Plugging Fracturing in Shale Formation

During the temporary plugging fracturing (TPF) process, the pressure response and pumping behavior significantly differ from those observed during conventional fracturing fluid pumping. Once the temporary plugging agent (TPA) forms a plug, subsequent fracture initiation and propagation become more intricate due to the influence of the TPA and early fractures. Factors such as concentration, particle size, and ratio of the TPA notably affect the effectiveness of TPF. This study employs a true triaxial hydraulic fracturing simulation system to conduct TPF experiments with varying particle size combinations and concentrations at both in-fracture and in-stage locations. The impact of different TPA parameters on the plugging effectiveness is assessed by analyzing the morphology of the induced fractures and the characteristics of pressure curves post experiment. Results indicate that combining dfferent particle sizes enhances plugging effectiveness, with a combination of smaller and larger particles exhibiting superior plugging effectiveness, resulting in a pressure increase of over 25.9%. As the concentration of the TPA increases, the plugging fracture pressure rises, accompanied by rapid pressure response and significant plugging effects, leading to more complex fracture morphology. For shale reservoirs, the density of bedding planes (BPs) influences the morphology and width of conventional hydraulic fractures, thereby affecting the effectiveness of subsequent refracturing. Rock samples with a relatively low BP density demonstrate effective plugging initiation both in-fracture and in-stage, facilitating the formation of complex fracture networks. Conversely, specimens with a relatively high BP density exhibit superior plugging effectiveness in-stage compared to in-fracture plugging.

Mathematical Physics Analysis of Nozzle Shaping at the Gas Outlet from the Aperture to the Differentially Pumped Chamber in Environmental Scanning Electron Microscopy (ESEM).

A combination of experimental measurement preparations using pressure and temperature sensors in conjunction with the theory of one-dimensional isentropic flow and mathematical physics analyses is presented as a tool for analysis in this paper. Furthermore, the subsequent development of a nozzle for use in environmental electron microscopy between the specimen chamber and the differentially pumped chamber is described. Based on experimental measurements, an analysis of the impact of the nozzle shaping located behind the aperture on the character of the supersonic flow and the resulting dispersion of the electron beam passing through the differential pumped chamber is carried out on the determined pressure ratio using a combination of theory and mathematical physics analyses. The results show that nozzle shapes causing under-expanded gas outflow from the aperture to the nozzle have a worse impact on the dispersion of the primary electron beam. This is due to the flow velocity control. The controlled reduction in the static pressure curve on the primary electron beam path thus causes a significantly higher course of electron dispersion values than variants with shapes causing over-expanded gas outflow.

The effect of open-end ignition at different positions on the explosion behaviors of H2/CO/Air in variable cross-section pipe

This work is focused on the explosion performance of syngas/air premixed gas in a self-designed variable cross-section pipe under varying ignition positions (IP1, IP2) and hydrogen volume fraction (α(H2)). Results show that α(H2) has a great influence on the propagation of the flame as well as the maximum flame front velocity (FFVmax) and the maximum overpressure (Pmax). As α(H2) in the syngas increases, the time the flame stays in the pipe is gradually reduced, the FFVmax as well as the Pmax increase regardless of the ignition position. Differently, when α(H2) < 50%, the tclosed at IP1 is shorter than that at IP2. The opposite is true when α(H2) ≥ 50%. This is attributed to the difference in flame velocity and the effect of film breakage. Both α(H2) and variable cross-section chamber structure all affect the evolution of the flame morphology. When ignition at IP2, a “M” flame is observed for the first time at α(H2) = 20%, and a flame resembling a “T” shape appears at α(H2) = 70%. Ignition positions have a great influence on overpressure oscillation. In the case of α(H2) = 15%, the Fourier transform is performed for the pressure curve. When ignited at IP1, secondary unstable oscillations occur during the later stage of flame propagation. However, when ignition at IP2, primary instability oscillations occur in both the early and late stages of flame propagation. The variable cross-section chamber structure plays a role in the flame front velocity (FFV) and overpressure. After the flame front enters the variable section chamber, the FFV reduces, and when the flame front leaves the variable section chamber, due to the sudden decrease of the cross-sectional area, the FFV increases significantly, and FFVmax and Pmax are obtained at this moment.

Characteristic Changes of the Stance-Phase Plantar Pressure Curve When Walking Uphill and Downhill: Cross-Sectional Study.

Monitoring of gait patterns by insoles is popular to study behavior and activity in the daily life of people and throughout the rehabilitation process of patients. Live data analyses may improve personalized prevention and treatment regimens, as well as rehabilitation. The M-shaped plantar pressure curve during the stance phase is mainly defined by the loading and unloading slope, 2 maxima, 1 minimum, as well as the force during defined periods. When monitoring gait continuously, walking uphill or downhill could affect this curve in characteristic ways. For walking on a slope, typical changes in the stance phase curve measured by insoles were hypothesized. In total, 40 healthy participants of both sexes were fitted with individually calibrated insoles with 16 pressure sensors each and a recording frequency of 100 Hz. Participants walked on a treadmill at 4 km/h for 1 minute in each of the following slopes: -20%, -15%, -10%, -5%, 0%, 5%, 10%, 15%, and 20%. Raw data were exported for analyses. A custom-developed data platform was used for data processing and parameter calculation, including step detection, data transformation, and normalization for time by natural cubic spline interpolation and force (proportion of body weight). To identify the time-axis positions of the desired maxima and minimum among the available extremum candidates in each step, a Gaussian filter was applied (σ=3, kernel size 7). Inconclusive extremum candidates were further processed by screening for time plausibility, maximum or minimum pool filtering, and monotony. Several parameters that describe the curve trajectory were computed for each step. The normal distribution of data was tested by the Kolmogorov-Smirnov and Shapiro-Wilk tests. Data were normally distributed. An analysis of variance with the gait parameters as dependent and slope as independent variables revealed significant changes related to the slope for the following parameters of the stance phase curve: the mean force during loading and unloading, the 2 maxima and the minimum, as well as the loading and unloading slope (all P<.001). A simultaneous increase in the loading slope, the first maximum and the mean loading force combined with a decrease in the mean unloading force, the second maximum, and the unloading slope is characteristic for downhill walking. The opposite represents uphill walking. The minimum had its peak at horizontal walking and values dropped when walking uphill and downhill alike. It is therefore not a suitable parameter to distinguish between uphill and downhill walking. While patient-related factors, such as anthropometrics, injury, or disease shape the stance phase curve on a longer-term scale, walking on slopes leads to temporary and characteristic short-term changes in the curve trajectory.

Validation of pneumatic crack detection in hole expansion test

According to the standard ISO 16630, the hole expansion test (HET) has to be stopped at the instant when the first through-thickness crack appears at the edge of the hole. The detection of the crack is challenging, since the maximum opening width should not exceed 0.1 mm at the inner diameter according to the newest version of the standard from 2017. A pneumatic crack detection has been introduced in which a pressure drop is used to identify the through-thickness crack. In the present paper, this method for stopping the hole expansion test is validated. It was tested for steels with different edge crack sensitivities and compared to stopping with force drop method. Therefore, the curves of pressure and force have been analysed. The influence of hole insertion method (shear cutting or abrasive water jet cutting) as well as specific hole expansion parameters (punch speed, air pressure) have been investigated. Besides the expanded diameters to evaluate the edge crack sensitivity, the opening width of the edge cracks were analysed to determine the suitability of the crack detection methods for different hole expansion ratios (HER).

Method Development for the Prediction of Melt Quality in the Extrusion Process.

Simulation models are used to design extruders in the polymer processing industry. This eliminates the need for prototypes and reduces development time for extruders and, in particular, extrusion screws. These programs simulate, among other process parameters, the temperature and pressure curves in the extruder. At present, it is not possible to predict the resulting melt quality from these results. This paper presents a simulation model for predicting the melt quality in the extrusion process. Previous work has shown correlations between material and thermal homogeneity and the screw performance index. As a result, the screw performance index can be used as a target value for the model to be developed. The results of the simulations were used as input variables, and with the help of artificial intelligence-more precisely, machine learning-a linear regression model was built. Finally, the correlation between the process parameters and the melt quality was determined, and the quality of the model was evaluated.

Slamming Characteristics Due to the Special Shape of New Sandglass-Type Model in Waves by Comparing with Cylindrical Model

For the new sandglass-type FPSO, the unique shape of its floating body with oblique side and external expansion can significantly improve the motion performance, but meanwhile may result in specific slamming characteristics in waves. On this basis, this paper establishes a CFD method including numerical wave-tank technique based on the Open FOAM platform. Therein, the velocity-inlet boundary method and the active absorption method are applied for numerical wave-making and wave-absorption. Compared with experimental results, the numerical method can be validated to be accurate enough to simulate wave slamming on floating ocean platforms. Then, the specific slamming phenomena on the sandglass-type floating body under a classic long wave can be investigated by comparing with the cylindrical model, including nonlinear wave rollover and breaking, water cushion, rooster-tail wave, side wave, water tongue, and so on. The mechanism of these phenomena and their effects on slamming pressure are studied. The essences of typical peaks in the time-history curve of the slamming pressure are mainly discussed. More interestingly, the main peak can be found to be related to the small peak due the amount of the broken water and the thickness of the water cushion. Finally, the slamming characteristics of the sandglass-type model in a classic short-wave condition are comparatively discussed.