scholarly journals Structural Response of Offshore Blast Walls under Accidental Explosion

2014 ◽  
Vol 1043 ◽  
pp. 278-282 ◽  
Author(s):  
Shaikh Atikur Rahman ◽  
Zubair Imam Syed ◽  
John V. Kurian ◽  
M.S. Liew
Keyword(s):  
Structural Response ◽  
Offshore Structures ◽  
Extensive Study ◽  
Design Guidelines ◽  
Critical Systems ◽  
Structural Behaviour ◽  
Single Degree Of Freedom ◽  
Structural Responses ◽  
Simplified Calculation ◽  
Explosion Load

Adequate blast resistant barriers are requisite to protect personnel and critical systems from the consequences of an accidental explosion and subsequent fire. Many of the blast walls currently installed in offshore structures were designed using simplified calculation approaches like Single Degree of Freedom models (SDOF) as recommended in many design guidelines. Over simplified and idealised explosion load used for response calculation and design of blast wall can lead to inadequate or overdesign of offshore blast walls. Due to lack of presence of a well-accepted design guidelines supported by extensive study, the protection provided by the conventional blast walls for offshore structures can be inadequate. In-depth understanding of structural response of blast walls under different blast loading can provide better design practice of blast walls for adequate protection. In this study, structural responses of conventional offshore blast walls were investigated. A computation fluid dynamics (CFD) approach was used to predict effect of different explosions on the barrier walls and non-linear finite elements analyses were performed to study the behaviour of the blast-loaded walls under different explosions. Effect of different parameters related to blast wall and accidental explosions were investigated to gain detail understanding of structural behaviour of typical steel blast wall.

Response of a Simple Tension Leg Platform Model to Wave Forces Calculated at Displaced Position

1984 ◽  
Vol 106 (4) ◽  
pp. 437-443 ◽  
Author(s):  
P. D. Spanos ◽  
V. K. Agarwal
Keyword(s):  
Structural Response ◽  
Offshore Structures ◽  
Wave Forces ◽  
Structural Members ◽  
Tension Leg Platform ◽  
Single Degree Of Freedom ◽  
Numerical Studies ◽  
Simple Tension ◽  
Stochastic Solution ◽  
Wave Induced

A simple single-degree-of-freedom model of a tension leg platform is used to assess the reliability of the common practice of calculating wave-induced forces at the undisplaced position of offshore structures. This assessment is conducted in conjunction with the Morison equation based modeling of the wave-induced forces on slender structural members. It is shown by numerically integrating the equation of motion that the calculation of wave forces on the displaced position of the structure introduces a steady offset component in the structural response. This is valid for either deterministically or stochastically described wave fields. Several parameter studies are conducted. Furthermore, reliable approximate analytical deterministic and stochastic solution techniques are developed which conform to and, in fact, predict the conclusions drawn from the results of the numerical studies.

Neural Network Optimization for Lifetime Structural Adaptation to Evolving Natural Events

2021 ◽  
Author(s):  
Xiaowei Wang ◽  
YeongAe Heo
Keyword(s):  
Neural Network ◽  
Structural Engineering ◽  
Structural Response ◽  
Offshore Structures ◽  
Regression Modeling ◽  
Sensitivity Analyses ◽  
Structural Adaptation ◽  
Structural Problems ◽  
Learning Rates ◽  
Structural Responses

Abstract Recent advances in data analytics, numerical modeling, and structural health monitoring (SHM) boost the application of machine learning methods in the field of structural engineering. Among them, the multi-layer neural network (MLNN) is one of the most popular ones. However, mathematical details of MLNN have yet to be well understood for structural problems. This study aims to identify optimal MLNN parameters for regression modeling of structural response estimates. SHM data-validated finite element models considering stochastic uncertainties in the natural events and structural properties are used to prepare a large dataset for regression modeling. The efficacy and accuracy of regression modeling are optimized by extensive sensitivity analyses for key MLNN parameters (e.g., numbers of hidden layers and neurons, activation functions and learning rates) via a k-fold cross-validation process. The optimized regression modeling is incorporated into a conceptual smart framework for lifetime structural performance assessment adapting to evolving natural events. The presented optimization process and smart framework is applicable to marine and offshore structures by characterizing the offshore hazards and structural responses.

Dynamic Characteristics of Multi-Story Reinforced Concrete Buildings

2016 ◽  
Vol 249 ◽  
pp. 235-240 ◽  
Author(s):  
Jónas Thór Snaebjornsson ◽  
Eythor Rafn Thorhallsson
Keyword(s):  
Reinforced Concrete ◽  
Natural Frequencies ◽  
Structural Parameters ◽  
Structural Response ◽  
Design Guidelines ◽  
Reinforced Concrete Buildings ◽  
Structural Behaviour ◽  
Measurement Systems ◽  
Concrete Buildings ◽  
International Data

Having a realistic estimate of structural parameters, such as natural frequency and damping is important for design purposes. In this study, available wind and earthquake induced acceleration data from four multi-story reinforced concrete buildings are utilized to examine structural behaviour and system parameters. The buildings measurement systems are described and the recorded structural response data presented. The data stems from two different sources of excitation, i.e. wind and earthquake, and are recorded for various excitation levels and environmental conditions. System identification analyses of the buildings are carried out applying previously verified parametric methods to the recorded data. The natural frequencies and critical damping ratios established from the recordings are compared to values estimated using design guidelines and international data compilations for reinforced concrete structures of similar type. Considerable variability is discovered between the different estimation formulas and the observed natural frequencies of the buildings are found to lie at the upper limit of the prediction formula.

Single-Degree-of-Freedom Based Pressure-Impulse Diagrams for Blast Damage Assessment

2014 ◽  
Vol 567 ◽  
pp. 499-504 ◽  
Author(s):  
Zubair Imam Syed ◽  
Mohd Shahir Liew ◽  
Muhammad Hasibul Hasan ◽  
Srikanth Venkatesan
Keyword(s):  
Damage Assessment ◽  
Structural Response ◽  
Blast Loading ◽  
Computational Effort ◽  
Degree Of Freedom ◽  
Negative Phase ◽  
Single Degree Of Freedom ◽  
Pressure Impulse ◽  
Single Degree ◽  
Structural Resistance

Pressure-impulse (P-I) diagrams, which relates damage with both impulse and pressure, are widely used in the design and damage assessment of structural elements under blast loading. Among many methods of deriving P-I diagrams, single degree of freedom (SDOF) models are widely used to develop P-I diagrams for damage assessment of structural members exposed to blast loading. The popularity of the SDOF method in structural response calculation in its simplicity and cost-effective approach that requires limited input data and less computational effort. The SDOF model gives reasonably good results if the response mode shape is representative of the real behaviour. Pressure-impulse diagrams based on SDOF models are derived based on idealised structural resistance functions and the effect of few of the parameters related to structural response and blast loading are ignored. Effects of idealisation of resistance function, inclusion of damping and load rise time on P-I diagrams constructed from SDOF models have been investigated in this study. In idealisation of load, the negative phase of the blast pressure pulse is ignored in SDOF analysis. The effect of this simplification has also been explored. Matrix Laboratory (MATLAB) codes were developed for response calculation of the SDOF system and for repeated analyses of the SDOF models to construct the P-I diagrams. Resistance functions were found to have significant effect on the P-I diagrams were observed. Inclusion of negative phase was found to have notable impact of the shape of P-I diagrams in the dynamic zone.

scholarly journals An approach to quantify the influence of ground motion uncertainty on elastoplastic system acceleration in incremental dynamic analysis

2017 ◽  
Vol 20 (11) ◽  
pp. 1744-1756 ◽  
Author(s):  
Peng Deng ◽  
Shiling Pei ◽  
John W. van de Lindt ◽  
Hongyan Liu ◽  
Chao Zhang
Keyword(s):  
Dynamic Analysis ◽  
Ground Motion ◽  
Earthquake Engineering ◽  
Structural Response ◽  
Incremental Dynamic Analysis ◽  
Degree Of Freedom ◽  
Maximum Acceleration ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Performance Based Earthquake Engineering

Inclusion of ground motion–induced uncertainty in structural response evaluation is an essential component for performance-based earthquake engineering. In current practice, ground motion uncertainty is often represented in performance-based earthquake engineering analysis empirically through the use of one or more ground motion suites. How to quantitatively characterize ground motion–induced structural response uncertainty propagation at different seismic hazard levels has not been thoroughly studied to date. In this study, a procedure to quantify the influence of ground motion uncertainty on elastoplastic single-degree-of-freedom acceleration responses in an incremental dynamic analysis is proposed. By modeling the shape of the incremental dynamic analysis curves, the formula to calculate uncertainty in maximum acceleration responses of linear systems and elastoplastic single-degree-of-freedom systems is constructed. This closed-form calculation provided a quantitative way to establish statistical equivalency for different ground motion suites with regard to acceleration response in these simple systems. This equivalence was validated through a numerical experiment, in which an equivalent ground motion suite for an existing ground motion suite was constructed and shown to yield statistically similar acceleration responses to that of the existing ground motion suite at all intensity levels.

Stability of offshore structures in shallow water depth

2011 ◽  
Vol 2 (2) ◽  
pp. 320-333
Author(s):  
F. Van den Abeele ◽  
J. Vande Voorde
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Fossil Fuels ◽  
Oil And Gas ◽  
Structural Response ◽  
Offshore Structures ◽  
Exploration And Production ◽  
Subsea Pipelines ◽  
Wave Induced ◽  
Shallow Water Depth

The worldwide demand for energy, and in particular fossil fuels, keeps pushing the boundaries of offshoreengineering. Oil and gas majors are conducting their exploration and production activities in remotelocations and water depths exceeding 3000 meters. Such challenging conditions call for enhancedengineering techniques to cope with the risks of collapse, fatigue and pressure containment.On the other hand, offshore structures in shallow water depth (up to 100 meter) require a different anddedicated approach. Such structures are less prone to unstable collapse, but are often subjected to higherflow velocities, induced by both tides and waves. In this paper, numerical tools and utilities to study thestability of offshore structures in shallow water depth are reviewed, and three case studies are provided.First, the Coupled Eulerian Lagrangian (CEL) approach is demonstrated to combine the effects of fluid flowon the structural response of offshore structures. This approach is used to predict fluid flow aroundsubmersible platforms and jack-up rigs.Then, a Computational Fluid Dynamics (CFD) analysis is performed to calculate the turbulent Von Karmanstreet in the wake of subsea structures. At higher Reynolds numbers, this turbulent flow can give rise tovortex shedding and hence cyclic loading. Fluid structure interaction is applied to investigate the dynamicsof submarine risers, and evaluate the susceptibility of vortex induced vibrations.As a third case study, a hydrodynamic analysis is conducted to assess the combined effects of steadycurrent and oscillatory wave-induced flow on submerged structures. At the end of this paper, such ananalysis is performed to calculate drag, lift and inertia forces on partially buried subsea pipelines.

scholarly journals Structural Assessment of the Hull Response of an FPSO Unit to Dropped Objects: A Case Study

2019 ◽  
Vol 26 (4) ◽  
pp. 39-46 ◽  
Author(s):  
Ozgur Ozguc
Keyword(s):  
Structural Damage ◽  
Local Buckling ◽  
Structural Response ◽  
Offshore Structures ◽  
Mechanical Equipment ◽  
Structural Members ◽  
Impact Area ◽  
Explicit Dynamic ◽  
The Impact

Abstract Offshore structures are exposed to the risk of damage caused by various types of extreme and accidental events, such as fire, explosion, collision, and dropped objects. These events cause structural damage in the impact area, including yielding of materials, local buckling, and in some cases local failure and penetration. The structural response of an FPSO hull subjected to events involving dropped objects is investigated in this study, and non-linear finite element analyses are carried out using an explicit dynamic code written LS-DYNA software. The scenarios involving dropped objects are based on the impact from the fall of a container and rigid mechanical equipment. Impact analyses of the dropped objects demonstrated that even though some structural members were permanently deformed by drop loads, no failure took place in accordance with the plastic strain criteria, as per NORSOK standards. The findings and insights derived from the present study may be informative in the safe design of floating offshore structures.

scholarly journals THE DYNAMIC RESPONSE OF OFFSHORE STRUCTURES TO TIME-DEPENDENT FORCES

1964 ◽  
Vol 1 (9) ◽  
pp. 29
Author(s):  
William S. Gaither ◽  
David P. Billington
Keyword(s):  
Degrees Of Freedom ◽  
Wind Waves ◽  
Offshore Structures ◽  
Time Dependent ◽  
Wave Forces ◽  
Ocean Bottom ◽  
Single Wave ◽  
Single Degree Of Freedom ◽  
The Many ◽  
Floating Objects

This paper is addressed to the problem of structural behavior in an offshore environment, and the application of a more rigorous analysis for time-dependent forces than is currently used. Design of pile supported structures subjected to wave forces has, in the past, been treated in two parts; (1) a static analysis based on the loading of a single wave, and (2) a dynamic analysis which sought to determine the resonant frequency by assuming that the structure could be approximated as a single-degree-of-freedom system. (Ref. 4 and 6) The behavior of these structures would be better understood if the dynamic nature of the loading and the many degrees of freedom of the system were included. A structure which is built in the open ocean is subjected to periodic forces due to wind, waves, floating objects, and due occasionally to machinery mounted on the structure. To resist motion, the structure relies on the stiffness of the elements from which it is built and the restraints of the ocean bottom into which the supporting legs are driven.

Three-Dimensional Numerical Prediction of the Hydrodynamic Loads and Motions of Offshore Structures

2000 ◽  
Vol 122 (4) ◽  
pp. 294-300 ◽  
Author(s):  
Karl W. Schulz ◽  
Yannis Kallinderis
Keyword(s):  
Flow Structure ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Structural Response ◽  
Offshore Structures ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Hydrodynamic Loads ◽  
Drag Coefficients ◽  
Lift And Drag

A generalized numerical method for solution of the incompressible Navier-Stokes equations in three-dimensions has been developed. This solution methodology allows for the accurate prediction of the hydrodynamic loads on offshore structures, which is then combined with a rigid body structural response to address the flow-structure coupling which is often present in offshore applications. Validation results using this method are first presented for fixed structures which compare the drag coefficients of sphere and cylinder geometries to experimental measurements over a range of subcritical Reynolds numbers. Additional fixed structure results are then presented which explore the influence of aspect ratio effects on the lift and drag coefficients of a bare circular cylinder. Finally, the spanwise flow variations between a fixed and freely vibrating cylindrical structure are compared to demonstrate the ability of the flow-structure method to correctly predict correlation length increases for a vibrating structure. [S0892-7219(00)00904-3]

An Assessment of Load and Response for Horizontal Slamming Loads From Model Scale Experiments

2018 ◽  
Author(s):  
Martin Storheim ◽  
Gunnar Lian
Keyword(s):  
Structural Response ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Load Level ◽  
Material Behavior ◽  
Wave Impact ◽  
Large Variability ◽  
Slamming Load ◽  
Reasonable Approach ◽  
Wave Slamming

Steep breaking waves can result in high impact loads on offshore structures, and several model test campaigns have been conducted to assess the effect of horizontal wave slamming. High loads have been measured, and they can be challenging to withstand without significant deformation. For wave slamming problems it is common to estimate the characteristic slamming load and assume that this will give an equivalent characteristic response. One challenge related to the slamming load is that it has a large variability in load level, the duration of the load and the shape of the overall load pulse. This variability can have a large impact on the estimated response to the characteristic load, causing a similar or larger variability in response. Due to the sensitivity to the structural response, it may be difficult to interpret large amounts of such data to arrive at a relevant design load without making overly conservative assumptions. This paper investigates the sensitivity of the structural response to assumptions made in the material modelling and how the short term variability is affected if we instead of load use response indicators such as plastic strain and max deformation to arrive at a characteristic load. For this purpose, a simplified dynamic response model is created, and the recorded wave impact events can then be evaluated based on the predicted structural response from the simplified model. It was found that the structural response is sensitive to the structural configuration. The assumed material behavior and hydro-elastoplastic effects were identified to greatly affect the structural response. A reasonable approach to arrive at the q-annual response seems to be to first estimate the q-annual extreme slamming load, and then run the structural analysis on several of the measured slamming time series with the estimated q-annual extreme pressure.

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