Study on the integrity detection and evaluation method of damaged pipeline
To detect the integrity of damaged pipeline and accurately evaluate its damaged condition, a CCD image data guided digital automatic ultrasonic testing system was designed to realize the dynamic measurement of a pipeline damaged surface, and extract the characteristic parameter of damaged pipeline. Based on the three-dimensional discrete point set which gathered to describe the integrity of damaged pipeline, we establish a damaged pipeline entity model which is closer to the actual condition, analyze and simulate mechanical properties under the actual load by using the numerical simulation software (ABAQUS), to get the most dangerous region and the trend of stress and displacement. This method provides more reliable reference for integral safety analysis and evaluation of damaged pipeline.
Stability of Vertically Bent Pipelines Buried in Sand
This paper discusses the stability of underground pipelines with preformed vertical bends buried in sandy soil. More specifically, the minimum cover height required to prevent the pipe from bowing under the action of forces due to temperature change and internal pressure is estimated. The variables considered include the pipe and soil materials, diameter, thickness, overburden height, bend radius, bend angle, internal pressure, fluid specific weight, and temperature variation. A comprehensive three-dimensional finite element analysis is carried out. The results are extracted from the output obtained. These results are put in a database which is used to develop general regression models to determine the relationships among the different variables. Different buckling modes are also considered. All of these results and models are entered into a computer software program for ready access.
The analysis of nonlinear systems in the frequency domain using Nonlinear Output Frequency Response Functions
Abstract The Nonlinear Output Frequency Response Functions (NOFRFs) are a concept which provides a new extension of the well-known concept of the Frequency Response Function (FRF) of linear systems to the nonlinear case. The present study introduces a NOFRFs based approach for the analysis of nonlinear systems in the frequency domain. It is well known that a nonlinear system can, under rather general conditions, be represented by a polynomial type Nonlinear Auto Regressive with eXogenous input (NARX) model. From the NARX model of a nonlinear system under study, the NOFRFs based approach for the frequency analysis of nonlinear systems involves solving a set of linear difference equations known as the Associated Linear Equations (ALEs) to determine the system nonlinear output responses and then the NOFRFs of the system up to an arbitrary order of nonlinearity of interests. The results enable a representation of the frequency domain characteristics of nonlinear systems by means of a series of Bode diagram like plots that can be used for nonlinear system frequency analyses for various purposes including, for example, condition monitoring, fault diagnosis, and nonlinear modal analysis.