Historical Perspective on Wind-Induced Vibration of Above-Ground Pipeline Configurations on the Alaskan North Slope

Abstract Steady arctic winds blowing across the flat topography of Alaska’s North Slope oil fields often induce vertical oscillations in above-ground pipelines, as a result of cyclic lift forces associated with the vortex shedding phenomenon. Extensive studies have been undertaken to better understand and control this complicated aerodynamic phenomenon. This paper provides a 30 plus year historical perspective on wind-induced vibration (WIV) of above-ground, cross-county pipeline configurations on the North Slope of Alaska. The paper includes an overview of the dynamic characteristics (e.g., mode shapes and frequencies) of typical “generic” multi-span cross-county pipeline configurations, the WIV phenomenon and the results of field instrumentation programs including free-vibration testing and long-term WIV monitoring. The paper illustrates a relatively simple framework for screening pipelines for WIV exposure as a function of azimuth orientation that utilizes publicly available, historical North Slope wind speed and direction observations. The paper also describes how systems of auxiliary mass damper (AMD) devices tuned to the WIV susceptible pipeline vibration frequencies are used to provide highly effective WIV mitigation over a broad frequency range. Relative motion across the dissipative elements of the tuned AMD devices which are attached to the pipeline at anti-node locations results in hysteretic energy dissipation which can dramatically increase the effective modal damping ratios of the lightly damped pipeline system and proportionately decrease the corresponding modal WIV response amplitudes. The effectiveness of AMDs is supported by data from laboratory tests over a wide range of temperatures and frequencies, field free-vibration tests and WIV monitoring programs. The paper concludes with a summary of how pipeline WIV has been successfully and widely mitigated across a large inventory of WIV-susceptible North Slope pipeline configurations using a triple-tuned and spatially distributed family of AMD devices spanning a broad-band of vibration frequencies for mitigation of primary (and if necessary, secondary) mode WIV.