Narrower System Reliability Bounds With Incomplete Component Information and Stochastic Process Loading

2017 ◽  
Vol 17 (4) ◽  
Author(s):  
Yao Cheng ◽  
Daniel C. Conrad ◽  
Xiaoping Du
Keyword(s):  
System Reliability ◽  
Operating Conditions ◽  
Reliability Estimation ◽  
Design Stage ◽  
Shared Environment ◽  
Limited Information ◽  
Reliability Bounds ◽  
Component Design ◽  
Wide Range ◽  
Stochastic Load

Incomplete component information may lead to wide bounds for system reliability prediction, making decisions difficult in the system design stage. The missing information is often the component dependence, which is a crucial source for the exact system reliability estimation. Component dependence exists due to the shared environment and operating conditions. But it is difficult for system designers to model component dependence because they may have limited information about component design details if outside suppliers designed and manufactured the components. This research intends to produce narrow system reliability bounds with a new way for system designers to consider the component dependence implicitly and automatically without knowing component design details. The proposed method is applicable for a wide range of applications where the time-dependent system stochastic load is shared by components of the system. Simulation is used to obtain the extreme value of the system load for a given period of time, and optimization is employed to estimate the system reliability bounds, which are narrower than those from the traditional method with independent component assumption and completely dependent component assumption. Examples are provided to demonstrate the proposed method.

Reduction of System Reliability Model Uncertainty by Considering Dependent Components With Stochastic Process Loading

2016 ◽  
Author(s):  
Yao Cheng ◽  
Xiaoping Du
Keyword(s):  
Model Uncertainty ◽  
System Reliability ◽  
Epistemic Uncertainty ◽  
Shared Environment ◽  
Reliability Model ◽  
Design Component ◽  
Operation Conditions ◽  
Component Design ◽  
Wide Range ◽  
Stochastic Load

When component dependence is ignored, a system reliability model may have large model (epistemic) uncertainty with wide reliability bounds. This makes decision making difficult during the system design. Component dependence exists due to the shared environment and operation conditions. It is difficult for system designers to model component dependence because they may not have access to component design details if the components are designed and manufactured by outside suppliers. This research intends to reduce the system reliability model uncertainty with a new way for system designers to consider the component dependence implicitly and automatically without knowing component design details. The proposed method is applicable for a wide range of applications where the time-dependent system stochastic load is shared by components of the system. Simulation is used to obtain the extreme value of the system load for a given period of time, and optimization is employed to estimate the system reliability interval. As a result, the epistemic uncertainty in system reliability can be reduced.

System reliability prediction with shared load and unknown component design details

2017 ◽  
Vol 31 (3) ◽  
pp. 223-234 ◽  
Author(s):  
Zhengwei Hu ◽  
Xiaoping Du
Keyword(s):  
System Reliability ◽  
Limit State ◽  
Common Factor ◽  
Design Stage ◽  
Limited Information ◽  
System Load ◽  
Component Design ◽  
Reliability Method ◽  
Other Information ◽  
State Functions

AbstractIn many system designs, it is a challenging task for system designers to predict the system reliability due to limited information about component designs, which is often proprietary to component suppliers. This research addresses this issue by considering the following situation: all the components share the same system load, and system designers know component reliabilities with respect to the component load, but do not know other information, such as component limit-state functions. The strategy is to reconstruct the equivalent component limit-state functions during the system design stage such that they can accurately reproduce component reliabilities. Because the system load is a common factor shared by all the reconstructed component limit-state functions, the component dependence can be captured implicitly. As a result, more accurate system reliability can be produced compared with traditional methods. An engineering example demonstrates the feasibility of the new system reliability method.

scholarly journals Modeling in marine ice engineering

2021 ◽  
Vol 11 (4) ◽  
pp. 557-567
Author(s):  
A.A. Dobrodeev ◽  
◽  
K.E. Sazonov ◽  
Keyword(s):  
Modeling And Simulation ◽  
Operating Conditions ◽  
Design Stage ◽  
Modern World ◽  
Marine Structures ◽  
Modeling Methods ◽  
Wide Range ◽  
Comparative Advantages ◽  
Quantitative Results

In the modern world, it is already difficult to imagine the creation of a significant engineering structure without modeling its external and internal appearance, the operation modeling of the main mechanisms, operating conditions and many other design features and emerging phenomena at the design stage. The paper interprets modeling and simulation as one of the computational methods that allow us to obtain quantitative results when studying ice impact on marine structures, for e.g. icebreakers and transport vessels, platform substructures, hydro-technical installations. In connection with the above, from the existing classification of modeling methods, the authors consider the physical and mathematical ones in the work. They present comparative advantages of both methods in their application in the problems of marine ice engineering, as well as the prospects for their development for solving a wide range of scientific problems aimed at the development of Arctic shipbuilding.

Analysis of hydraulic components using computational fluid dynamics models

1998 ◽  
Vol 212 (7) ◽  
pp. 619-629 ◽  
Author(s):  
M Borghi ◽  
G Cantore ◽  
M Milani ◽  
R Paoluzzi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Close Correlation ◽  
Operating Conditions ◽  
Complete Analysis ◽  
Dimensional Solution ◽  
Scaling Technique ◽  
Component Design ◽  
Wide Range ◽  
Key Factor

This paper presents some results obtained during the computational fluid dynamics (CFD) analysis of internal flows inside a hydraulic component, using a scaling technique applied to numerical pre- and post-processing. The main aim of the work is to demonstrate the reduction of computational work needed for a complete analysis of component behaviour over a wide range of operating conditions. This result is achieved through the adoption of a methodology aimed at giving the highest level of generality to a non-dimensional solution, thereby overcoming the two major limitations encountered in the use of CFD in fluid power design: computer resources and time. In the case study, the technique was applied to a hydraulic distributor and computations were performed with a commercial computational fluid dynamics code. The key factor of this technique is the evaluation, for a given distributor opening, of the Reynolds number of the flow in the metering region. Provided that this number is high enough to ensure that the discharge coefficient has reached its asymptotic value, the characterization of the flow by a single non-dimensional numerical run can be shown. The theoretical contents of the analysis of the re-scaling technique, which focuses on the engineering information necessary in component design, are described in detail. The bases for its subsequent application to actual cases are then outlined. Finally, a fairly close correlation between numerical results and experimental data is presented.

Experimental Study of Thermal Performance and Pressure Drop in Compact Heat Exchanger Installed in Automotive

2006 ◽  
Author(s):  
M. H. Saidi ◽  
A. A. Mozafari ◽  
A. R. Esmaeili Sany ◽  
J. Neyestani
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Operating Conditions ◽  
Design Stage ◽  
Practical Usefulness ◽  
Experimental Prediction ◽  
Wide Range

In this Study, radiator performance for passenger car has been studied experimentally in wide range of operating conditions. Experimental prediction of Nusselt number and heat transfer coefficient for coolant in radiator tubes are also performed with ε–NTU method. The total effectiveness coefficient of radiator and heat transfer coefficient in air side is calculated via try and error method considering experimental data. The Colburn factor and pressure drop are also estimated for this heat exchanger. Examples of application demonstrate the practical usefulness of this method to provide empirical data which can be used during the design stage.

System Reliability Analysis With Dependent Component Failures During Early Design Stage—A Feasibility Study

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Yao Cheng ◽  
Xiaoping Du
Keyword(s):  
System Reliability ◽  
Reliability Prediction ◽  
Design Stage ◽  
Early Design ◽  
Early Design Stage ◽  
Design Concepts ◽  
Reliability Bounds ◽  
Lack Of Information ◽  
Dependent Component ◽  
Component Failures

It is desirable to predict product reliability accurately in the early design stage, but the lack of information usually leads to the use of independent component failure assumption. This assumption makes the system reliability prediction much easier, but may produce large errors since component failures are usually dependent after the components are put into use within a mechanical system. The bounds of the system reliability can be estimated, but are usually wide. The wide reliability bounds make it difficult to make decisions in evaluating and selecting design concepts, during the early design stage. This work demonstrates the feasibility of considering dependent component failures during the early design stage with a new methodology that makes the system reliability bounds much narrower. The following situation is addressed: the reliability of each component and the distribution of its load are known, but the dependence between component failures is unknown. With a physics-based approach, an optimization model is established so that narrow bounds of the system reliability can be generated. Three examples demonstrate that it is possible to produce narrower system reliability bounds than the traditional reliability bounds, thereby better assisting decision making during the early design stage.

A Study of the Performance of Inertia Air Filters

1969 ◽  
Vol 184 (3) ◽  
pp. 166-174
Author(s):  
D. E. Gee ◽  
B. N. Cole
Keyword(s):  
Performance Testing ◽  
Operating Conditions ◽  
Design Stage ◽  
Small Scale ◽  
Operating Characteristics ◽  
Test Rig ◽  
Fundamental Study ◽  
Air Filters ◽  
Test Programme ◽  
Wide Range

This paper presents an experimental and theoretical study of the design and performance of inertia air filters, with particular reference to rail traction duty. Using a specially constructed test rig, performance testing of commercially available filters was carried out over a wide range of operating conditions. Subsequently, a more fundamental study of some design variables was carried out in a small-scale test rig. The testing was supported by a theoretical approach using a digital computer model of the inertia filtration process. The results of the work indicate that the inertia filter is suited to high-volume, low pressure drop applications. However, operational difficulties, owing to dust build-up occurring within the filter and variations of bleed ratio, may be encountered. The theoretical model was shown to reproduce all the major operating characteristics of the filters measured in the test programme, and to respond to design changes in a similar way to that indicated by earlier published work. A hypothesis of the mechanism of separation is proposed, and it is suggested that the performance of new filter layouts can be examined at the design stage. Supporting work describes the selection, measurement, and production of a suitable range of polydisperse solids for the test programme.

ESP Mechanical Shaft Seals: Trials and Tribulations of Lab Testing

2021 ◽  
Author(s):  
John W. Sheldon ◽  
Francisco Alhanati ◽  
Jared Schoepp
Keyword(s):  
System Reliability ◽  
Influential Factors ◽  
Operating Conditions ◽  
Test Apparatus ◽  
Interesting Phenomenon ◽  
Factors Affecting ◽  
Operational Conditions ◽  
Wide Range ◽  
Design Selection ◽  
Shaft Seals

Abstract Mechanical Shaft Seals (MSSs) are critical sub-components in Electric Submersible Pump (ESP) Seal Chamber Sections (SCSs), as they are the primary barriers used to isolate wellbore fluids from the motor oil. However, several ESP operators have observed relatively high MSS failure rates in certain applications, resulting in significant impacts on overall ESP system reliability and operational costs. In some cases, during teardowns, wellbore fluids were found in the lower chambers of the SCS, without any signs of damage to the MSSs or the bags/bellows in the SCS. Thus, to improve the run-life of ESP systems in their applications, operators identified the need to better understand the main influential factors affecting leakage rates through the MSS, including factors associated with the MSS characteristics and its operational conditions. To accomplish this, a test apparatus was built to allow the testing of MSSs in a wide range of operational conditions. This paper summarizes the technical challenges and key learnings that arose from building and commissioning such a test apparatus, as well as conducting several tests on multiple MSSs of a single design. Through commissioning of the test apparatus and subsequent testing, several limitations of the apparatus were identified and corrected through upgrades. Many of these upgrades were related to ensuring reasonably accurate measurement of the leakage rate through the MSSs, in both directions. Unexpected behaviours of the MSS were also observed during some tests. One example is the interesting phenomenon of reverse-pumping where, under certain conditions, leakage occurs in the opposite direction of the applied differential pressure. Finally, questions arose about the importance of certain aspects of quality control for MSSs and/or SCS assembly procedures. The above effort to build and commission a MSS testing apparatus has resulted in unique insight into shaft seal behaviour and continues to shine light on gaps in the industry understanding of factors affecting leakage through MSSs. It certainly provides evidence that there are many ‘unknown unknowns’ about MSS performance under challenging downhole operating conditions, and that the effort is worth continuing to support better MSS design/selection, and SCS assembly, as part of improving ESP system reliability.

Engine Variables Affecting the SI Engine Knock

2001 ◽  
Author(s):  
Mansoor Karimifar
Keyword(s):  
Pressure Fluctuations ◽  
Careful Analysis ◽  
Operating Conditions ◽  
Design Stage ◽  
Control Loops ◽  
Numerical Result ◽  
Crank Angle ◽  
Wide Range ◽  
General Aspects ◽  
Experimental Findings

Abstract To program the automatic performance control loops of the modern cars at the design stage, numerical result of engine variables effecting knock intensity is the most important tool. Although general aspects of the effect of engine operating conditions on knock have been studied in previous investigations, precise numerical results of that, are not available. The procedures proposed in the past to provide the requirements of the models either predicting or measuring knock are complicated and the details are not presented. In the current work, on the basis of the ‘sampling frequency theorem’ and in regard to the measured frequency of the knocking-pressure fluctuations, a fast on-line data acquisition system was designed and developed. The system was used on a variable compression ratio research engine using two different fuels. Large number of the engine pressure crank angle data were recorded at different operating conditions. Knock, intensity measurement was carried out using a developed criteria obtained by a careful analysis of pressure oscillations at 0.25 degree crank angle intervals. This lead to identification of cycles having specified knock intensity over a wide range of operating conditions. Effect of engine variables on knock intensity was therefore measured numerically for both fuels. Using the simple criteria to study the effect of engine operating conditions on the intensity of knock produced the results which agreed with the earlier experimental findings.

scholarly journals DEVELOPMENT OF THE NUMERICAL METHODOLOGY FOR THE ESTIMATION OF RESONANT PROCESSES AT GASTURBINE ENGINE FLOW DUCT

2020 ◽  
pp. 12-19
Author(s):  
Nikolay Shuvaev ◽  
◽  
Aleksandr Siner ◽  
Ruslan Kolegov ◽  
◽  
...  
Keyword(s):  
High Pressure ◽  
Unsteady Flow ◽  
Aircraft Engine ◽  
Operating Conditions ◽  
Design Stage ◽  
High Pressure Compressor ◽  
Wide Range ◽  
Resonant Processes ◽  
Flow Duct ◽  
Pressure Compressor

Ensuring safety of flights is the most important task that is being solved in the process of designing an aircraft engine and aircraft. The most complex are the physical processes occurring inside the aircraft engine, especially in its gas generator: combustion chamber, high-pressure compressor and high-pressure turbine. The unsteady flow of gas in the flow duct of the aircraft engine is very complex, it is difficult to model, because the flow is characterized by a wide range of time and space scales. Unsteady flow in a high-pressure compressor can cause surge and breakdown of the compressor and the entire engine as a whole. Along with the detachment flows causing the surge, in the flow duct there can be resonant phenomena associated with the propagation of powerful sound waves along the flow duct of the engine, which, when a direct and reflected wave is imposed, create a very powerful standing wave that affects the structure. With a certain combination of conditions, the coincidence of the natural frequencies of the oscillations of the air volume and the solid body, such resonant processes in the flow duct of the gas turbine engine can lead to serious breakdowns, such as breakage of rotor blades and guide vanes, destruction of the aeroengine framework and other. The main difficulty is that it is problematic to identify such processes at the design and debugging stage, since there are no suitable mathematical models, and for experimental verification it is required to withstand the specific operating conditions of the node that are not known in advance. This work is devoted to the creation of a calculation technique that will allow in the future to diagnose resonance phenomena at the design stage and thereby significantly reduce the costs for the design, testing and manufacture of an aircraft engine. The proposed technique is based on the nonstationary Navier-Stokes equations for a compressible gas.

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