Hydraulic Tests Research Articles

Evaluation of Parent Well Depletion Effects on Fracture Geometry Based on Low-Frequency Distributed Acoustic Sensing in Hydraulic Fracture Test Site-2

Summary Low-frequency distributed acoustic sensing (LF-DAS) has recently received much attention for its ability to monitor fracture propagation at offset wells. Hydraulic Fracture Test Site-2 (HFTS-2), a Department of Energy–sponsored field-based research experiment, has acquired LF-DAS data sets during the stimulation of many horizontal wells in the Wolfcamp Formation of the Permian Basin. Over 100 stimulated stages with different completion designs in four horizontal wells were monitored by two horizontal offset wells and one vertical pilot hole with permanent fibers. The parent well depletion affected all four horizontal wells in almost half of their lateral section. Several studies have been performed on the acquired comprehensive data set. In this study, we apply our novel Green’s function-based inversion algorithm to calculate the fracture width of each stage and investigate the impact of parent well depletion on fracture geometry. The Green’s function-based inversion algorithm has been successfully applied to a few stages of field case studies. The Green’s function matrix was built based on linear elasticity theory (3D displacement discontinuity method) to relate the fracture openings with strain responses measured along the length of the fiber. This novel algorithm only relies on measured strain to solve fracture geometry at the monitoring well. Therefore, it is independent of the physics of the fracture propagation process and can be used to validate hydraulic fracture modeling results. Using our inversion algorithm, we can efficiently and quantitatively interpret LF-DAS data to provide information on fracture geometry and completion efficiency. We analyze more than 100 stages of the LF-DAS measurements obtained at the fiber wells B3H and B4H during B1H, B2H, and B4H stimulations. We apply our inversion algorithm for four data sets covering the stimulation of the abovementioned three wells. The fracture growth at stages in the parent well’s depleted zone is biased more toward upper formation and in the easterly direction. The fracture width at the stages in the parent well’s depletion zone is reduced compared to fracture widths at stages in the nondepleted zone irrespective of the monitoring well location relative to the treatment wells. This difference in fracture widths will affect the proppant distribution to a great extent, thereby affecting the effectiveness of the stimulation. We also illustrate the application of the inversion algorithm for stages that have both conventional fracture hits with “heart-shaped” signals as well as fracture reopening signals. Our inversion algorithm gives a reasonable estimate of the fracture width that aligns with the qualitative analysis of microseismic data sets and statistic summary of fracture hit numbers of HFTS-2. We believe that this quantitative study provides us with insights into the fracture geometry due to parent well depletion effects.

Hydraulic Conductivity Tests in the Triaxial Stress State: Is Peat an Aquitard or an Aquifer?

The characteristics of peat’s are crucial for understanding natural processes and their suitable shaping through the management of water relations. This study focused on the results of one of the first hydraulic conductivity (k) laboratory tests of exemplary peat samples from the Biebrza Valley (a peatland of very high environmental importance) in relation to the stress state and hydraulic gradient. Further, the research was devoted to a specific test procedure of peat permeability as a key feature for landform development in wetlands. Detailed tests of dark brown/black samples were selected as the reference for the research investigations. Four long-term test series of water permeability were performed in a modified triaxial compression apparatus. In all selected hydraulic gradient variants (i = 5,10,25,40,55,85), the k values decreased from 6 × 10−8 m/s to 1.6 × 10−10 m/s with a stepwise increase in the effective confining pressures tested (10, 15, 30, 45, and 90 kPa). These results were related to the inherent soil features—a relatively high peat decomposition and external driver—confining pressure (radial stress) magnitude. Compared to the other Polish peat tests, the determined k values were at the lower end of their hydraulic conductivity range. The analysed organic soil is not a typical aquifer. Despite very high porosities (~88%) and a high organic matter content (81.1–89.4%) which is favourable for water accumulation, the characterized peat showed relatively low hydraulic conductivity values. Thus, this specific soil may differentiate the groundwater flow as it complicates strong contact with surface water.

Fatty Alcohol Polyoxyethylene Ether Sodium Sulfate–Modified Cement to Improve the Bonding and Sealing of Cement to Oil-Wet Casing or Formation Surface in Shale Gas Wells

Summary In shale gas wells, oil-based mud (OBM) changes the casing and rock surface wettability during drilling. It negatively affects the bonding and sealing of cement sheaths with casing or formation rock. Although the spacer is widely used in primary cementing, the casing and formation rock surface are wetted by OBM or oil phase due to poor displacement. For this work, a novel oleophilic cement slurry modified by fatty alcohol polyoxyethylene ether sodium sulfate (AES) was investigated to decrease the negative effect of OBM- or oil-wetted surface. The contact angle of nonpolar solvent 1-bromonaphthalene on the cement surface decreased from 35° to 8°, showing an ideal oleophilic property. The hydraulic isolation capacity; microstructure of the cement-casing or cement-rock interface; and the pore structure, hydration, and mechanical property of AES-modified cement were investigated by interfacial hydraulic isolation test device, computed tomography (CT), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), thermogravimetric analyses (TGAs), and mechanical test. The results showed that the oleophilic cement could directly bond with an oil- or OBM-wetted surface and significantly eliminate the microchannel and connected pores caused by the oil phase or OBM on the interface. The fluid channeling on the OBM-wetted cement-rock and casing interface was prevented, and the sealing pressure of the interface was increased from approximately 3 to 7 MPa/m (fluid channeling occurred) to higher than 275 MPa/s (fluid channeling did not occur), respectively. Besides, the hydration degree, porosity, and mechanical property of the oleophilic cement remained at the same level as the conventional cement, indicating that the AES has no adverse effect on cement hydration and properties. The findings of this study can contribute to the cement slurry design in shale gas well cementing to improve the interface bonding and sealing when poor displacement happens.

Hysteretic energy damage coupled elastoplastic constitutive model and its application to low-cycle fatigue life prediction of martensitic steel

The microstructure of martensitic steel is analyzed by transmission electron microscopy and X-ray diffraction. The low-cycle fatigue (LCF) test of martensitic steel with different strain amplitudes is carried out by MTS universal hydraulic servo testing machine. The damage accumulation and cyclic elastic-plastic constitutive model of martensitic steel are studied. The influence of tempering on hysteretic loop and fatigue damage is discussed. With the tempering temperature increasing, the area of hysteresis loop increase, the hysteresis energy increases, and the fatigue life decreases. According to the fatigue damage accumulation model of the hysteresis energy method, an improved kinematic and isotropic composite hardening model is proposed in tempering temperature. This model is used to simulate the LCF behavior before fracture under LCF load and to predict the fatigue life with the variation of applied strain amplitude and tempering temperature. The verification results show that the modified model can well describe the phenomenon of acceleration of cyclic softening and great reduction of cyclic stress.

Analisis Kekuatan Mekanik Komposit Polimer Diperkuat Serbuk Kulit Kerang

In recent decades, the development of composite material technology has continued to increase rapidly and has been used for various applications as an alternative material to replace metal. In line with growing environmental issues, the utilization of natural materials which are abundant in nature and easy to find is the main priority for composite building materials. In this study, shell powder was used as a reinforcing material for epoxy polymer composites. The aims of this study were to obtain the average compressive, tensile, and flexural strength of shell powder-reinforced polymer composite materials, to calculate the distribution of test results using the PDF method, and to calculate the contribution of shell powder to the mechanical properties mentioned using the ANOVA method. The tensile, compressive, and flexural test specimens follow the test specimen standards of ASTM D638, ASTM D7264, and ASTM D695 respectively. The composition of shell powder consists of 10%, 30%, and 50%. Testing of these mechanical properties using a UTM-type hydraulic test equipment model WEW-300D with a capacity of 300 kN. The test results show an increase in the mechanical properties of the material. The increase occurred in compressive and flexural strength where the composition was given up to 30% and 50%, namely between 120 – 125 MPa. However, increasing the composition of shell powder at 30% and 50% actually resulted in a decrease in tensile strength between 12 – 9 MPa. Finally, based on the results of ANOVA analysis, it was shown that the addition of shell powder as a reinforcement for polymer composites significantly improved their mechanical properties.

Effects of low temperatures and high strain rates on the tensile properties of polyurethane polymers for adhesives

ABSTRACT The mechanical properties of polyurethane compounds were experimentally investigated by changing the composition of their components. Polyol components (polyoxypropylene glycol: PPG, polyoxytetramethylene glycol: PTMG, and polycarbonatediol: PCD) were mixed with monomeric methylene diphenyl diisocyanate to synthesize polyurethane pre-polymer, mixed with chain extenders (1,4’-butanediol: 1,4’-BD or dimethylthiotoluene diamine: DMTDA), and cured, to prepare four types of polyurethane resins. Tensile tests were conducted using a mechanical testing machine with a strain rate of approximately 0.3 s−1 and a hydraulic high-speed tensile testing machine with a strain rate of approximately 500 s−1. The temperature was controlled to be −40°C, −10°C, or 25°C. When PTMG was used as the polyol, the stress-strain relationship was less sensitive to temperatures and loading rates, and the material properties exhibited a relatively good balance between elongation and strength. Additionally, the use of 1,4’-BD as a chain extender resulted in higher elongation and lower strength than the use of DMTDA. Conversely, the stress-strain relationship was dramatically altered by the test conditions when PPG and PCD were used as the polyol and embrittlement under a combination of low temperature and high strain rate was confirmed. Furthermore, there were certain compositional combinations that exhibit necking at low temperatures.

Parameterization of a channel network model for groundwater flow in crystalline rock using geological and hydraulic test data

Groundwater flow in sparsely fractured crystalline rocks is highly channelized due to the existing complex hydrogeological heterogeneity in fracture networks. The impacts of multiscale hydraulic heterogeneity on channelized flow in a block of fractured rock under the unidirectional flow condition are investigated by three-dimensional (3D) discrete fracture network (DFN) modeling. A channel network (CN) model generated from DFN is used to model the channelized groundwater flow in fractured crystalline rock. An approach for parameterizing the channel conductance is proposed which uses information from the hydrogeological characterization data. The results show that the network scale hydrogeological heterogeneity dominates the distribution variability of flowrates. The proposed parameterization approach for the channel conductance is effective and robust. Based on the available hydrogeological characterization data, it is possible to compensate for the neglected heterogeneity in the CN model by enhancing the variability of assigned channel conductance. The findings from this work are useful for model simplification from 3D DFN to CN, and for overcoming the difficulty in the parameterization of CN models in applications.

Engineers and Execs Agree Shale Science Projects Are Worth It

_ It was a testimony to the impact science projects have had on the shale sector that kicked off the 15th Annual SPE Hydraulic Fracturing Technology Conference and Exhibition (HFTC) held in the Houston area. When the technical experts and executives gathered, they discussed how, after years of subsurface study, past beliefs have been dispelled and new learnings translated into multimillion- to billion-dollar business decisions. At the conference’s plenary session, attendees learned from Devon Energy about why the oil company has become a vocal champion of refracturing and the influence it had on a recent acquisition that doubled its position in the Eagle Ford Shale. Bakken Shale producer Hess Corp. tied more than a decade of work to its experimental wells that use fractures from other wells to produce oil, as well as its commitment to developing automated fracturing despite facing obstacles in industry collaboration. SM Energy also showcased a double minifrac test as an example of the new experiments guiding its unconventional strategy in the Eagle Ford and Austin Chalk formations found in south Texas. A closer look at what they had to say is here. Betting Big on Refracturing In SPE 212340, Devon offered fresh details on its big refracturing study in the Eagle Ford Shale—one that played into its decision to spend $1.8 billion last year on an acquisition in the south Texas play. It involved two parent wells originally stimulated in 2013 and then refractured in January 2022. As a result, Devon reports the respective estimated ultimate recovery (EUR) from each well soared by 27% and 46%. These are wells that had been producing about 20 to 25 B/D, and according to data shared in the paper, at least one of them topped 1,000 B/D in the weeks following the refracturing. Kourtney Brinkley described the recovery boost as a “significant step change” that helped the company realize a “need to incorporate recompletions into our development plans as we go forward.” The drilling and completions engineer who helped lead the project for Devon reported that the operator’s wider refrac program in the play has seen incremental EUR increases as high as 75% with the average being at around 50%. The figures translate to a rate of return between 97 to 220%, which she said makes them “very economic projects.” The project Brinkley outlined at the conference fell under the US Department of Energy’s (DOE) hydraulic fracturing test site program. With the help of federal funding, Devon was able to deploy an enviable array of diagnostic tools. An observation lateral was drilled to monitor refracturing along with new completions on the pad. About 420 ft of core was taken from the observation well to capture some of the pad’s parent well fracture system. The diagnostic kit included multiple fiber-optic installations, sealed wellbore pressure monitoring, downhole pressure gauges, ultrasonic imaging, and more. With this rare suite of technologies, Devon was able to learn exactly how poor the initial parent completions were while later seeing just how effective its refrac designs ended up being. First came the parent core-through that showed while a hydraulic fracture was present every 10 ft on average, the number of propped fractures represented just 8% of the total found. Ultrasonic imaging aligned, showing initial completion design netted a cluster efficiency rate of just 19%. Post-refrac, that number was increased to over 80%, which implies to Devon that there are a good degree more propped fractures today.

Experiments on the dynamic Poisson's ratio of PUR foams

AbstractPolyurethane (PUR) foams are used in various industrial applications, including vibration damping and noise reduction. Because the effective mechanical properties are needed for the engineering design process, this work presents a method to measure the dynamic Poisson's ratio for the typical range of sound frequencies. A hydraulic pulse testing machine is used to apply the harmonic displacement excitation of the cylindrical specimens for 1 − 100 Hz. The analysis of the time‐dependent deformation data is based on video recordings of a high‐speed camera and a specially derived image processing algorithm.For the Poisson's ratios of the measured foams no significant frequency dependence was found. For PUR foam with an open‐cell or mixed‐cell microstructure the dynamic Poisson's ratio is approximately 0.3. Poisson's ratios of about 0.4 were measured for PUR foams with a high density and a closed‐cell microstructure.

Gas-mechanical coupled crack initiation analysis for local air-leakage of compressed air energy storage (CAES) cavern with consideration of seepage effect

The gas-tightness and stability of compressed air energy storage (CAES) cavern (usually with three-layered struction of sealing layer, concrete lining and surrounding rock) plays an important role for ensuring the power-generation efficiency of CAES system. Since the action of the compressed air with high temperature and high pressure would possibly cause the local damage of the sealing layer and lead to the air-leakage from the sealing layer to the surrounding rock, it is necassary to study the gas-mechanical (GM) coupled crack initiation behavior of the surrounding rock in order to provide a scientific basis for anti-cracking design and stability evaluation of CAES cavern. Currently, the GM coupled crack initiation are studied mainly by experimental and numerical methods but little by theoretical method, in which the gas pressure is taken as a static pressure regardless of the seepage effect. In this paper, the calculation formulea of GM coupled Mode I and Mode II SIFs are derived by the superposition principle with the consideration of seepage effect firstly. And then the criterion of GM coupled crack initiation is established based on our K-ratio criterion in order to analyze its mechanism for local air-leakage of CAES cavern. Finally, a gas seepage device is designed to conduct the tri-axial GM coupled compression tests of pre-cracked sandstone specimens on MTS815 hydraulic servo testing machine combined with PCI-II AE instrument to measure the crack initiation stress σi and initiation angle θC. Research results show both σi and θC are decreased with the increasing of gas pressure PG, while increased with the increasing of crack inclination angle β. All of these pre-cracked sandstone specimens have initiation mechanisms of Mode II. The prediction results of initiation angle with consideration of seepage effect is more closer to the test results than those of initiation angle without consideration of seepage effect, which can prove the validity of both our SIFs calculation formulea and the GM coupled criterion with consideration of seepage effect.

Effect of initial pore pressure on the hydraulic fracturing of tight sandstone: an experimental study

Pore pressure is a crucial factor affecting reservoir stimulation, especially in unconventional reservoirs, because it can control crack initiation and propagation. However, studies on the effect of initial pore pressure on hydraulic fracturing in low-permeability reservoirs are lacking, and fracturing mechanism remains unclear. Therefore, we conducted hydraulic fracturing tests under initial pore pressure, and proposed an improved fracturing initiation criterion to elucidate the fracturing mechanism of tight sandstone. The results demonstrated that the breakdown pressure increased with the initial pore pressure by 8 to 24%, and its evolution was identified approximately by the improved initiation criterion, which resulted in the complicated, invisible and intense features of the macroscopic fracture morphology and microscopic crack. The finding was mainly due to the viscous stress induced by fracturing disturbance under initial pore pressure and represented the dual interaction between rock structure and work fluid viscosity. As a result, the change in microporous diameter in micropores and a high pressure to failure can be obtained. Accordingly, the initial pore pressure in tight sandstone may not only induce n effective stress on the skeleton but also be responsible for the double effect on the fracturing mechanism with high pressure and intense failure features, which should be given attention in unconventional reservoir stimulation.

Hydraulic bulge testing to compare formability of continuous and stretch broken carbon fiber reinforced polymer composites

Hydraulic bulge testing to compare formability of continuous and stretch broken carbon fiber reinforced polymer composites

Hydraulic bulge testing to compare formability of continuous and stretch broken carbon fiber reinforced polymer composites

Hydraulic bulge testing to compare formability of continuous and stretch broken carbon fiber reinforced polymer composites

Study of the Instantaneous Water Level Measurement Method on Unsteady Flow Based on Single Camera and Fixed Scale Compensation in the Tunnel Model

The shape of instantaneous water surface profiles for the unsteady flow in the tunnel model can be determined by measuring the instantaneous water levels at multiple points synchronously. However, the measurement accuracy of the ultrasonic method is affected greatly because of the complex state of the water surface when water level changes rapidly. Using an optical method, multicamera synchronous measurement is difficult to control, and the cost is high. For single camera measurement, the reading of the steel ruler in the image cannot be clearly seen when the distance between the measuring point and single camera is far. When the distance is short, all steel rulers cannot be captured at the same time. Hence, in this paper, a single camera and fixed scale compensation method for instantaneous water level observation in unsteady flow is proposed. A series of fixed scales is placed with the same height and width near the water surface to be measured. In order to capture dynamic images of all fixed scales with a clear water surface, a single camera is set at a far position to continuously record the water level change process within the model range. According to the height of the fixed scale, the image accuracy is compensated and the effect of the wide-angle image distortion is automatically avoided. The water level elevation is obtained according to the relationship between the fixed scale and the water surface. In this paper, the unsteady flow model measuring test is applied to the Southern Main Tunnel and the Water Distribution Pool of the Huangchigou Water Diversion Project. The accuracy of this method in measuring the dynamic water level is 1–2 mm, which meets the accuracy requirement and greatly reduces the observation cost of the model test. The proposed method may also be suitable for measuring the instantaneous water level of the unsteady flow in other similar hydraulic model tests.

A new attempt for the detection of potential water-bearing structures in tunnels via hydraulic tomography: The first numerical investigation

Water-bearing geological structures in front of the tunnel and underground engineering are prone to water inrush hazards, which seriously threaten construction safety. This study investigated the potential of hydraulic tomography (HT) in detecting water-bearing structures to prevent groundwater hazards in tunnels. We established two synthetic heterogeneous aquifers with two different water-bearing structures, fractures and cavern zones. A comprehensive HT inversion analysis was performed using hydraulic head records generated by forward hydraulic tests. The results show that 1) sufficient pumping and observation wells can assist in capturing water-bearing structures and hydraulic properties; 2) transient hydraulic tomography (THT) inversion has a better effect than steady-state hydraulic tomography (SSHT) inversion since the temporal variation of head records carries non-redundant characteristics and distribution information of water-bearing structures; 3) inverted hydraulic conductivity and specific storage fields are positively correlated with observed heads at the end and early stages of the pumping test, respectively; 4) taking geological information as a prior can greatly assist in mapping potential water-bearing structures. This study can provide valuable guidance for detecting water-bearing structures in tunnel and underground engineering and formulating effective control schemes for water inrush hazards.

Do Simple Analytical Models Capture Complex Fractured Bedrock Hydraulics? Oscillatory Flow Tests Suggest Not.

Fractured sedimentary bedrock aquifers represent complex flow systems that may contain fast, fracture-dominated flow paths and slower, porous media-dominated flow paths. Thus, characterizing the dynamics of flow and transport through these aquifers remains a fundamental hydrogeologic challenge. Recent studies have demonstrated the utility of a novel hydraulic testing approach, oscillatory flow testing, in field settings to characterize single bedrock fractures embedded in low-porosity sedimentary bedrock. These studies employed an idealized analytical model assuming Darcian flow through a nondeforming, constant-aperture, nonleaky fracture for data interpretation, and reported period-dependent effective fracture flow parameters. Here, we present the application of oscillatory flow testing across a range of frequencies and inter-well spacings on a fracture embedded in poorly cemented sedimentary bedrock with considerable primary porosity at the Field Site for Research in Fractured Sedimentary Rock. Consistent with previous studies, we show an apparent period-dependence in returned flow parameters, with hydraulic diffusivity decreasing and storativity increasing with increasing oscillation period, when assuming an idealized fracture conceptual model. We present simple analyses that examine non-Darcian flow and borehole storage effects as potential test design artifacts and a simple analytical model that examines fluid leakage to the surrounding host rock as a potential hydraulic mechanism that might contribute to the period-dependent flow parameters. These analyses represent a range of conceptual assumptions about fracture behavior during hydraulic testing, none of which account for the measured responses during oscillatory flow testing, leading us to argue that other hydraulic processes (e.g., aperture heterogeneity and/or fracture hydromechanics) are necessary to accurately represent pressure propagation through fractured sedimentary bedrock.

Experimental Study of Curing Temperature Effect on Mechanical Performance of Carbon Fiber Composites with Application to Filament Winding Pressure Vessel Design.

During the forming process of carbon fiber composite pressure vessels, the parameters of the curing and forming processes become one of the critical factors affecting the production cost and forming quality. The curing temperature of 4251 A4/B2 epoxy resin is measured in this research, and the effect of curing temperature on the mechanical properties of composite materials for winding is studied, which is finally verified in the test of pressure vessels. First, the actual curing temperature of the epoxy resin is tested and analyzed using differential scanning calorimetry (DSC). Second, under two different curing regimes, the tensile and flexural properties are tested by making pure epoxy resin matrix test pieces, Naval Ordnance Laboratory (NOL) rings, and carbon fiber composite unidirectional plates that affect the overall performance of composite pressure vessels. At the same time, the test results provide reliable process parameters for numerical simulation and manufacturing of pressure vessels. Finally, the filament-wound 35 MPa type III pressure vessel is cured and carried out using a hydraulic burst test. The results show the resin matrix has good fluidity and excellent interface bonding with carbon fiber when the curing temperature is 112 °C. Compared with the results in curing temperature of 100 °C, the tensile strength of the NOL ring reaches 2260.8 MPa, up by 22%. In the 90° direction, the tensile and flexural strengths of the unidirectional plates increase by 68.86% and 37.42%, respectively. In the 0° direction, the tensile and flexural strengths of the unidirectional plates increase by 5.82% and 1.16%, respectively. The pressure vessel bursting form is reasonable and meets the CGH2R standard. The bursting pressure of the vessel is up to 104.4 MPa, which verifies the rationality of the curing regime used in the curing process of the pressure vessel. Based on the results of this paper, the curing temperature affects the fluidity of the epoxy resin, which in turn affects the interfacial bonding properties of the composite, and the forming quality of the wound components and the pressure vessel, ultimately. When using 4251A4/B2 epoxy resin for wet winding pressure vessels, the choice of a 112 °C curing temperature will help improve the vessel's overall performance. This work could provide reliable experience and insight into the curing process analysis of pressure vessel manufacturing.

Persulfate activated with calcium peroxide to remediate RAFT soil contaminated with diesel in Arctic northern villages: on-site pilot scale study

ABSTRACT A pilot field study was conducted in a Canadian northern village (NV) to assess the remediation efficiency of sodium persulphate (SPS) alkali activated with calcium peroxide (CP) to degrade diesel from Arctic raft soil. A minimum temperature increase in the subsurface due to overall process reactions was required. The projected context of application was imperative to preserve the integrity of the remaining permafrost. The test was performed with two soil columns of 370 L buried in the ground. The columns were contaminated with 7500 mg diesel/kg representative raft soil that was matured for a period of 11 months. The continuous delivery by gravity and the static presence of the oxidizing solution was made over 33 days. During that period, SPS concentration, pH and temperatures, were monitored. SPS was activated prior to its distribution and activation by-products were confined in a surficial tank and under a sludge form. The maturation period resulted in the important natural attenuation of diesel (47%) that occurred in the shallower horizons of the soil profile. About 35% of the diesel remaining after the maturation period was removed by chemical oxidation during the operation period on site. The temperature increase measured during the SPS activation process was not significant while the temperature increase due to diesel degradation by oxidation in the subsurface was evaluated to be below 3°C. The soil columns were not clogged by the by-products as indicated by hydraulic testing before and after oxidizing treatment.

Multi-objective optimization of different dome reinforcement methods for composite cases

A multi-objective optimization method was proposed for different dome reinforcement methods of a filament-wound solid rocket motor composite case based on a Radial Basis Function (RBF) model. Progressive damage of the composite case was considered in a simulation based on Hashin failure criteria, and simulation results were validated by hydraulic burst tests to precisely predict the failure mode, failure position, and burst pressure. An RBF surrogate model was established and evaluated by Relative Average Absolute Error (RAAE), Relative Maximum Absolute Error (RMAE), Root Mean Squared Error (RMSE), and R2 methods to improve the optimization efficient of dome reinforcement. In addition, the Non-dominated Sorting Genetic Algorithm (NSGA-II) was employed to establish multi-objective optimization models of variable-angle and variable-polar-radius dome reinforcements to investigate the coupling effect of the reinforcement angle, reinforcement layers, and reinforcement range on the case performance. Optimal reinforcement parameters were obtained and used to establish a progressive damage model of the composite case with dome reinforcement. In accordance with progressive damage analysis, the burst pressure and performance factor were obtained. Results illustrated that variable-angle dome reinforcement was the optimal reinforcement method compared with variable-polar-radius dome reinforcement as it could not only ensure the reinforcement angle’s continuous changing but also decrease the mass of composite materials. Compared with the unreinforced case, the reinforced case exhibited an increase in the burst pressure and performance factor of 36.1% and 23.5%, respectively.

Remaining useful life prediction of lubrication oil by integrating multi-source knowledge and multi-indicator data

Insufficient data restrains the accuracy of the remaining useful life (RUL) prediction for lubricating oil. For this problem, multi-indicator modeling can be an effective solution. However, the unknown coupling effects of the indicators still impose difficulties. To address this issue, a coupling model integrating both knowledge and data is proposed. Originally, multi-source knowledge is embedded to guide both the state characterization and the threshold setting for improving the accuracy of the multi-indicator oil RUL prediction. In particular, the multi-indicator evidences and the knowledge-based rules, are adopted to handle overlapping information and inconsistent decision-making by considering interactions between indicators. A three-layer hierarchical model integrating evidence and rules is firstly established to connect the indicator, attribute, and oil state. Furthermore, the rule-base containing multi-failure modes is constructed to extract the random thresholds from the training samples. Finally, an exponential Wiener stochastic process embedding the oil degradation mechanism is used to describe data fluctuation. After the training stage, the probability density function of RUL is estimated. Finally, the proposed method is validated with four sets of test data from a real-world hydraulic pump bench test.