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Maintaining the integrity and longevity of structures is essential in many industries, such as aerospace, nuclear, and petroleum. To achieve the cost-effectiveness of large-scale systems in petroleum drilling, a strong emphasis on structural durability and monitoring is required. This study focuses on the mechanical vibrations that occur in rotary drilling systems, which have a substantial impact on the structural integrity of drilling equipment. The study specifically investigates axial, torsional, and lateral vibrations, which might lead to negative consequences such as bit-bounce, chaotic whirling, and high-frequency stick-slip. These events not only hinder the efficiency of drilling but also lead to exhaustion and harm to the system's components since they are difficult to be detected and controlled in real time. The study investigates the dynamic interactions of these vibrations, specifically in their high-frequency modes, using field data obtained from measurement while drilling. The findings have demonstrated the effect of strong coupling between the high-frequency modes of these vibrations on drilling system performance. The obtained results highlight the importance of considering the interconnected impacts of these vibrations when designing and implementing robust control systems. Therefore, integrating these components can increase the durability of drill bits and drill strings, as well as improve the ability to monitor and detect damage. Moreover, by exploiting these findings, the assessment of structural resilience in rotary drilling systems can be enhanced. Furthermore, the study demonstrates the capacity of structural health monitoring to improve the quality, dependability, and efficiency of rotary drilling systems in the petroleum industry. [ABSTRACT FROM AUTHOR]

Cover crops have recently been generating a lot of interest in agriculture for their agronomic benefits, including erosion control, nutrient restoration, and increased cash crop yield. However, the value of these benefits is not well established and likely highly variable. The factors that influence a farmer’s decision to adopt or not adopt cover crops are also a point of interest to conservationists and policy makers. As part of a long-term study estimating the benefits and costs of cover crops, this study analyzed five years of historic information collected from Indiana farmers, who either grew or did not grow cover crops. No significant impact was found from cover crops on cash crop yields, but several interesting correlations in cover crop use were found. Cover crop use was higher on steeper fields. There was also a high correlation between the use of cover crops and no-till. [ABSTRACT FROM AUTHOR]

Left censoring or left truncation occurs when specific failure information on machines is not available before a certain age. If only the number of failures but not the actual failure times before a certain age is known, we have left censoring. If neither the number of failures nor the times of failure are known, we have left truncation. A datacenter will typically include servers and storage equipment installed on different dates. However, data collection on failures and repairs may not begin on the installation date. Often, the capture of reliability data starts only after the initiation of a service contract on a particular date. Thus, such data may exhibit severe left censoring or truncation, since machines may have operated for considerable time periods without any reliability history being recorded. This situation is quite different from the notion of left censoring in non-repairable systems, which has been dealt with extensively in the literature. Parametric modeling methods are less intuitive when the data has severe left censoring. In contrast, non-parametric methods based on the Mean Cumulative Function (MCF), recurrence rate plots, and calendar time analysis are simple to use and can provide valuable insights into the reliability of repairable systems, even under severe left censoring or truncation. The techniques shown have been successfully applied at a large server manufacturer to quantify the reliability of computer servers at customer sites. In this discussion, the techniques will be illustrated with actual field examples. [ABSTRACT FROM AUTHOR]

The simplified two-zone model to describe fluid flow in steady-state horizontal holes with multistage hydraulic fracturing is proposed, and the analytical solution in order to calculate sizes of hydrofractures is presented. The new procedure to determine size of multistage hydrofractures in horizontal holes is tested using field data on China deposits. The calculation results prove the efficiency of the procedure in the determination of steady-state conditions. The procedure can be used in optimization of hydraulic fracturing. [ABSTRACT FROM AUTHOR]

Field investigation indicates the dip angle of a fracture zone in a Cenozoic folded sandstone formation is as large as 47°. When the dip angle is large, the flow field generated by slug test becomes radially asymmetrical with respect to test well. Taking into account the dip angle effects, a new double-porosity slug test model and its Laplace-domain solution are necessarily developed for both the oscillatory test response (as for a highly permeable condition) and non-oscillatory test response (as for a low permeable condition). For the oscillatory response, it is found that a larger dip angle causes larger amplitude while introduces little impact on period. The dip angle effect on the test response, oscillatory or non-oscillatory, is found to be more pronounced for a larger hydraulic conductivity of the fracture zone, a smaller specific storativity of the matrix, or a smaller λ ; and the application range of the current model is determined for the limiting dip angle. That is, the dip angle effect should be considered in data analysis when dip angle is larger than 30°. A set of test responses from a slug test data in the fracture zone of a 47° dip angle is analyzed by using the current model. It is found that neglecting the dip angle can result in a 63.4 % overestimate of the hydraulic conductivity of the fracture zone, a 95.5 % underestimate of the specific storativity of the matrix, and a 63.3 % underestimate of λ. [ABSTRACT FROM AUTHOR]

In a constant-head test (CHT), groundwater is withdrawn from a well that has a fixed drawdown. Accordingly, the CHT is particularly useful in aquifers of low transmissivity because the constant-head well would not be dewatered owing to overpumping. The problem of interest pertains to a CHT in a homogeneous and anisotropic unconfined aquifer, where water released by the water table decline is assumed to be instantaneous and the skin effect surrounding the constant-head well is represented by a skin factor. A two-dimensional transient well hydraulics model is developed, and its Laplace domain solutions of aquifer drawdown and the constant-head well discharge are determined. It is found that the three distinct segments typically noted in the time drawdown history of a constant-rate test (CRT) are also characteristic of the temporal drawdown variation of the CHT. However, the early time and late time asymptotes conform to the radial flow solution of a CHT in confined aquifers as given by Hantush [1964]. Under the late time radial flow conditions the asymptotic solution is in terms of an apparent storage coefficient equal to the sum of the storage coefficient and the specific yield, and a specific mass balance relation exists among the constant-head well discharge, the discharge due to aquifer storage, and the discharge resulted from the water table decline. While aquifer drawdown and the constant-head well discharge are under the influence of well skin, their ratios are free from it. A curve matching method using this ratio is developed to determine the horizontal and the vertical hydraulic conductivities, the storage coefficient, and the specific yield. When the prescribed constant drawdown is not negligibly small in comparison to the initial saturated thickness, aquifer drawdown in late times may be large, and thus a drawdown correction is needed for data analysis. It is found that the Jacob correction for large drawdown of a CRT can also be used for the late drawdown correction in a CHT. [ABSTRACT FROM AUTHOR]

In the last two decades it has become clear that component lifetime distributions are seldom exponential. Early failures due to flaws have been of major concern. Various models to cater for this observation have been suggested. The models have been developed from a component rather from a system point of view. Furthermore, no substitute for the heavily criticized MIL-HDBK-217-type prediction handbooks has been offered. This paper describes a recently developed methodology to arrive at realistic component reliability characteristics, which take into account the non-exponential component lifetime distributions. These characteristics are developed from a system's point of view, which makes it easier for the system manufacturer to assess the reliability of their systems in the field. The methodology is based on six years of research in field performance of electronic systems. The research has been carried out in close co-operation with industrial companies. [ABSTRACT FROM AUTHOR]

Objective: Federal regulations in the United States require vehicles to meet occupant performance requirements with unbelted test dummies. Removing the test requirements with unbelted occupants might encourage the deployment of seat belt interlocks and allow restraint optimization to focus on belted occupants. The objective of this study is to compare the performance of restraint systems optimized for belted-only occupants with those optimized for both belted and unbelted occupants using computer simulations and field crash data analyses.Methods: In this study, 2 validated finite element (FE) vehicle/occupant models (a midsize sedan and a midsize SUV) were selected. Restraint design optimizations under standardized crash conditions (U.S.-NCAP and FMVSS 208) with and without unbelted requirements were conducted using Hybrid III (HIII) small female and midsize male anthropomorphic test devices (ATDs) in both vehicles on both driver and right front passenger positions. A total of 10 to 12 design parameters were varied in each optimization using a combination of response surface method (RSM) and genetic algorithm. To evaluate the field performance of restraints optimized with and without unbelted requirements, 55 frontal crash conditions covering a greater variety of crash types than those in the standardized crashes were selected. A total of 1,760 FE simulations were conducted for the field performance evaluation. Frontal crashes in the NASS-CDS database from 2002 to 2012 were used to develop injury risk curves and to provide the baseline performance of current restraint system and estimate the injury risk change by removing the unbelted requirement.Results: Unbelted requirements do not affect the optimal seat belt and airbag design parameters in 3 out of 4 vehicle/occupant position conditions, except for the SUV passenger side. Overall, compared to the optimal designs with unbelted requirements, optimal designs without unbelted requirements generated the same or lower total injury risks for belted occupants depending on statistical methods used for the analysis, but they could also increase the total injury risks for unbelted occupants.Conclusions: This study demonstrated potential for reducing injury risks to belted occupants if the unbelted requirements are eliminated. Further investigations are necessary to confirm these findings. [ABSTRACT FROM AUTHOR]