A Global-Analysis Approach to Robust Control

2006 ◽  
Author(s):  
Anders Lindquist
Keyword(s):  
Robust Control ◽  
Global Analysis ◽  
Analysis Approach

Comparative Study of Drilling Riser Running/Retrieving Analysis Methodologies

2021 ◽  
Author(s):  
Leandro Vale ◽  
Conor Gallagher ◽  
Marcelo Souza ◽  
Daniel Carneiro
Keyword(s):  
Complex Geometry ◽  
Global Analysis ◽  
Fe Analysis ◽  
Analysis Approach ◽  
Harsh Environment ◽  
Local Response ◽  
Offshore Drilling ◽  
Global Response ◽  
Offshore Oil ◽  
Water Depths

Abstract Drilling risers are key components in offshore oil exploration and are present in most of the well construction phases (drilling, casing, cementing and completion). Mobile offshore drilling units can operate in different sites exposed to a range of environmental loadings and water depths. Global riser analyses based on the FE (finite element) method are performed to assess the system feasibility and operating envelopes. In harsh environment and ultradeep water scenarios, the riser running/retrieving operation is one of the most critical due to top-angle limits and riser stress as a result of either contact with the inside of the diverter housing/substructures or loading at the gimbal-spider (API-RP-16Q [1], ISO 13624-1 [2]). The use of beam-column elements is satisfactory for modelling the riser global response, however it may lead to result uncertainty in terms of local response associated with complex geometry, over-stress, stress concentration and contact modelling (DNV-ST-F201 [3], DNVGL-RP-F203 [4], ISO 13628-7 [5]). The objective of this paper is to compare riser analysis results from a global and a local FE analysis. This comparison is used to identify any limitations associated with the use of a global riser analysis approach for determining structural limits for the riser during deployment/retrieving operations. Several recommendations are also provided regarding the use of the global analysis approach.

Analysis Approach for Estimating Wellhead Fatigue

2018 ◽  
Author(s):  
Kristoffer H. Aronsen ◽  
Sergey Kuzmichev ◽  
Guttorm Grytøyr ◽  
Kathrine Gregersen ◽  
Finn Kirkemo ◽  
...  
Keyword(s):  
Global Analysis ◽  
Lower Boundary ◽  
Coupled Model ◽  
Element Model ◽  
Fatigue Analysis ◽  
Sensitivity Analyses ◽  
Analysis Approach ◽  
Multiple Wave ◽  
Lower Boundary Condition ◽  
Engineering Approach

A structured technology development process targeting to combine industry and Statoil’s experience has produced an engineering approach for wellhead fatigue analysis that is verified against measurements of load and load effects in actual subsea wells. This paper outlines Statoil’s wellhead fatigue analysis approach, which is based on the new industry standard for wellhead fatigue analyses, DNVGL-RP-E104, ref. [1]. Parts of the methodology has been presented in previous papers. The present paper provides a birds eye view, putting all the pieces together into one coherent methodology. The development and validation of an engineering approach for estimating the bending moment in the surface casing, between the wellhead housing and top of cement, will be presented in detail; this has previously been referred to as load sharing between wellhead and conductor. The wellhead fatigue analysis approach is based on a “coupled model”, which in this case means that the conductor with PY-soil springs are included in the model, compatible with industry recommendations [1], with the following main characteristics: • The lower boundary condition is modelled as a conductor in soil with a bending stiffness equivalent of the well system. • Soil and template interaction is modelled by discrete springs. • The global riser load analysis is run with long crested waves and head sea. Directionality of the waves are handled by reduction factors applied to the damage rate. Alternatively, directionality effects may be included by running multiple wave directions with short crested waves. • Fatigue capacity of the hotspots in the well system is represented by ΔM-N curves generated from detailed FE models. Typically, ΔM-N curves are established for connectors, welds between housings and casings, and for the wellhead housings. The paper includes validation against full scale measurements for a wellhead of preloaded type. In addition, it is demonstrated how the approach can be used for wellheads where the high-pressure housing may rotate inside the low-pressure housing. For this case, the validation is performed against a full 3D solid element model. The analysis approach presented is computationally effective and it will hence enable increased focus on sensitivity analyses. Analysis work is moved from time consuming local- and global analysis, to effective post-processing of data. Uncertainty in the input parameters has been found to significantly influence the fatigue estimate. Understanding these effects is considered vital for making conscious decisions on the fatigue life of a well. See e.g. [8], [10] and [20]. As pointed out already in 1985 by Valka et.al., ref. [5], and also by Milberger et. al., ref. [6], the cement level, and the relative motion of the two housings, represent large uncertainties. Macke et. al, ref. [10], showed that the additional uncertainty due to cement level and friction between housings exceeds the levels covered by the traditional fatigue safety factor of DFF = 10. A method is proposed to handle this in a consistent manner.

Activation Volumes for the Hydration Reactions of Carbon Dioxide

2016 ◽  
Vol 69 (3) ◽  
pp. 262
Author(s):  
William Conway ◽  
Debra Fernandes ◽  
Carlos Rodríguez ◽  
Robert Burns ◽  
Manuel Martínez ◽  
...  
Keyword(s):  
Rate Constants ◽  
Global Analysis ◽  
Measurement Data ◽  
Current Data ◽  
Analysis Approach ◽  
Joint Analysis ◽  
Hydration Reaction ◽  
Kinetic Measurements ◽  
Decomposition Reactions ◽  
Reaction With Water

The hydration of CO2(aq) via reaction with H2O and OH– has been investigated using a high-pressure stopped flow apparatus, and the relevant rate constants for the reactions have been determined using a global analysis approach. The joint analysis of a series of kinetic measurements, for the formation and decomposition reactions, at a range of pressures from 400 to 1000 atm has been performed, and from the pressure dependence of the rate constants, the corresponding activation volume profiles determined for the two kinetic pathways. While a previous report exists for the hydration reaction with water, to our knowledge the activation volumes for the reaction of CO2 with hydroxide in this paper are the first to be reported in the literature. The extensive measurement data and robustness of the analysis approach, which additionally incorporates into, and corrects for, the effect of ionic strength on the kinetic data, positions the current data as the most reliable to date.

scholarly journals A global analysis approach for investigating structural resilience in urban drainage systems

2015 ◽  
Vol 81 ◽  
pp. 15-26 ◽  
Author(s):  
Seith N. Mugume ◽  
Diego E. Gomez ◽  
Guangtao Fu ◽  
Raziyeh Farmani ◽  
David Butler
Keyword(s):  
Global Analysis ◽  
Analysis Approach ◽  
Urban Drainage ◽  
Drainage Systems ◽  
Urban Drainage Systems
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