A Time Domain Prediction Method for Vortex-Induced Vibrations of a Flexible Pipe With Time-Varying Tension

2018 ◽  
Author(s):  
Mengmeng Zhang ◽  
Shixiao Fu ◽  
Haojie Ren ◽  
Runpei Li ◽  
Leijian Song
Keyword(s):  
Time Domain ◽  
Method Comparison ◽  
Prediction Method ◽  
Hydrodynamic Forces ◽  
Experimental Results ◽  
Force Model ◽  
Time Varying ◽  
Flexible Pipe ◽  
Time Step ◽  
Axial Tension

Prediction of vortex induced vibration (VIV) for a long-flexible pipe has always been an important concern for the design of risers. Currently, VIV prediction methods are mainly based on the linear beam theory, where the axial tension is treated as time-independent, and the couples between VIV and axial tension are totally ignored. However, experimental results have illustrated strong couples between the axial tension and VIV [1–2]. The purpose of this paper is to develop a time domain VIV prediction model. This model consists of pipe’s structural non-linearity, couplings between axial force, cross-flow/in-line (CF/IL) VIV responses, and the hydrodynamic forces. The hydrodynamic forces are further divided into vortex-induced force in CF and IL directions, and drag force in IL direction. The former one is determined via empirical force model based on forced oscillation test of rigid cylinders. The IL drag coefficients model considering the effects of VIV developed by Song [3] is adopted. VIV responses under these hydrodynamic forces at each time step are solved by Newton-Raphson method. Comparison between present method and the experimental results under uniform flows and shear flows are conducted, which verified the feasibility and reliability of the proposed method. In addition, by comparing the results under constant tension and time-varying tension, it is proved that the time-varying tension has a significant effect on VIV responses, especially under the case of high flow velocity and high vibration mode.

A high order finite-difference scheme for time-domain modelling of time-varying seismoelectric waves

Geophysics ◽  
2021 ◽  
pp. 1-49
Author(s):  
Yanju Ji ◽  
Li Han ◽  
Xingguo Huang ◽  
Xuejiao Zhao ◽  
Kristian Jensen ◽  
...  
Keyword(s):  
Porous Media ◽  
Finite Difference ◽  
Time Domain ◽  
Calculation Method ◽  
High Order ◽  
Difference Approximation ◽  
Time Varying ◽  
Time Step ◽  
Static Approximation ◽  
High Order Finite Difference

Simulation of the seismoelectric effect serves as a useful tool to capture the observed seismoelectric conversion phenomenon in porous media, thus offering promising potential in underground exploration activities to detect pore fluids such as water, oil and gas. The static electromagnetic (EM) approximation is among the most widely used methods for numerical simulation of the seismoelectric responses. However, the static approximation ignores the accompanying electric field generated by the shear wave, resulting in considerable errors when compared to analytical results, particularly under high salinity conditions. To mitigate this problem, we propose a spatial high-order finite-difference time-domain (FDTD) method based on Maxwell's full equations of time-varying EM fields to simulate the seismoelectric response in 2D mode. To improve the computational efficiency influenced by the velocity differences between seismic and electromagnetic waves, different time steps are set according to the stability conditions, and the seismic feedback values of EM time nodes are obtained by linear approximation within the seismic unit time step. To improve the simulation accuracy of the seismoelectric response with the time-varying EM calculation method, finite-difference coefficients are obtained by solving the spatial high-order difference approximation based on Taylor expansion. The proposed method yields consistent simulation results compared to those obtained from the analytical method under different salinity conditions, thus indicating its validity for simulating seismoelectric responses in porous media. We further apply our method to both layered and anomalous body models and extend our algorithm to 3D. Results show that the time-varying EM calculation method could effectively capture the reflection and transmission phenomena of the seismic and EM wavefields at the interfaces of contrasting media. This may allow for the identification of abnormal locations, thus highlighting the capability of seismoelectric response simulation to detect subsurface properties.

scholarly journals Time-Domain Hydro-Elastic Analysis of a SFT (Submerged Floating Tunnel) with Mooring Lines under Extreme Wave and Seismic Excitations

2018 ◽  
Vol 8 (12) ◽  
pp. 2386 ◽  
Author(s):  
Chungkuk Jin ◽  
Moo-Hyun Kim
Keyword(s):  
Time Domain ◽  
Hydrodynamic Forces ◽  
Random Wave ◽  
Element Formulation ◽  
Elastic Analysis ◽  
Seismic Excitations ◽  
Time Step ◽  
Mooring Lines ◽  
Submerged Floating Tunnel ◽  
Elastic Responses

Global dynamic analysis of a 700-m-long SFT section considered in the South Sea of Korea is carried out for survival random wave and seismic excitations. To solve the tunnel-mooring coupled hydro-elastic responses, in-house time-domain-simulation computer program is developed. The hydro-elastic equation of motion for the tunnel and mooring is based on rod-theory-based finite element formulation with Galerkin method with fully coupled full matrix. The dummy-connection-mass method is devised to conveniently connect objects and mooring lines with linear and rotational springs. Hydrodynamic forces on a submerged floating tunnel (SFT) are evaluated by the modified Morison equation for a moving object so that the hydrodynamic forces by wave or seismic excitations can be computed at its instantaneous positions at every time step. In the case of seabed earthquake, both the dynamic effect transferred through mooring lines and the seawater-fluctuation-induced seaquake effect are considered. For validation purposes, the hydro-elastic analysis results by the developed numerical simulation code is compared with those by a commercial program, OrcaFlex, which shows excellent agreement between them. For the given design condition, extreme storm waves cause higher hydro-elastic responses and mooring tensions than those of the severe seismic case.

In-Line Vibrations of Flexible Pipes

2017 ◽  
Author(s):  
Jan V. Ulveseter ◽  
Svein Sævik
Keyword(s):  
Frequency Domain ◽  
Vortex Shedding ◽  
Time Domain ◽  
Linear Time ◽  
Domain Model ◽  
Integration Scheme ◽  
Force Model ◽  
Prediction Tool ◽  
Flexible Pipe ◽  
Non Linear

A semi-empirical prediction tool for pure in-line vortex-induced vibrations is under development. The long-term goal is to be able to realistically model the dynamic behavior of free spanning pipelines exposed to arbitrary time dependent external flows at low velocities. Most VIV programs operate in frequency domain, where only steady currents and linear structural models can be simulated. In contrast, the proposed model predicts hydrodynamic forces as function of time, enabling a time integration scheme to solve the equation of motion. Non-linear time domain simulations allow for modelling of excitation from non-steady currents. In addition, non-linear effects such as soil-pipe interaction, varying tension, and response dependent material, stiffness and damping properties may be included in the analysis, when combining the hydrodynamic force model with a structural non-linear finite element model. Hydrodynamically, the proposed prediction tool consists of the general Morison equation plus two vortex shedding forcing terms. The latter two are able to synchronize with the structural motion for a given frequency band, to induce vibrations in lock-in regimes. In this paper, the proposed pure in-line VIV model is compared to the frequency domain model VIVANA and DNV Recommended Practice, simulating experiments with a model-scale flexible pipe exposed to current velocities at which cross-flow vibrations have not yet developed. A few experimental data points are included in verifying the performance of the newly developed time domain model. The effect of changing empirical coefficients in the vortex shedding forcing terms, and allowing only one of the terms to excite structural vibrations during a simulation, is numerically investigated. A goal is to obtain increased understanding of how the proposed time domain model performs when simulating VIV of a flexible pipe, which is more complex than that of an elastically mounted rigid cylinder since several natural frequencies and corresponding modes might be excited.

VIV Response and Fatigue Damage of Flexible Cylinders With Time-Varying Axial Tension

2018 ◽  
Author(s):  
Yuan Yuchao ◽  
Xue Hongxiang ◽  
Tang Wenyong ◽  
Liu Jun
Keyword(s):  
Fatigue Damage ◽  
Structural Response ◽  
Design Stage ◽  
Small Scale ◽  
Time Varying ◽  
Flexible Cylinder ◽  
Time Step ◽  
Response Characteristics ◽  
Axial Tension ◽  
Tension Time

The time-varying effect of axial tension has recently attracted increasing focus when investigating vortex-induced vibration (VIV) for flexible cylinders. This paper applies an alternative time domain force–decomposition model to predict VIV response, in which the structural stiffness will be updated at each time step to take the tension variation into account. Firstly, the adopted numerical model is compared against the latest published experimental results of a small-scale cylinder with constant and time-varying tensions. Then, extensive cases of a long flexible cylinder are designed to investigate the tension time-varying effect on structural response and fatigue damage respectively. Several new response characteristics different from the constant tension case are analyzed from the VIV mechanism level. Fatigue analysis also reveals the influence laws of the amplitude and frequency of varying tension. Mathieu-type resonance between VIV and time-varying tension excitation is captured, under which structural response as well as fatigue damage will enlarge significantly. Some conclusions drawn by this research can provide reference at the engineering design stage of marine slender structures.

Advanced Fault Isolation Technique Using Electro-Optical Terahertz Pulse Reflectometry (EOTPR) for 2D and 2.5D Flip-Chip Package

2012 ◽  
Author(s):  
Lihong Cao ◽  
Manasa Venkata ◽  
Meng Yeow Tay ◽  
Wen Qiu ◽  
J. Alton ◽  
...  
Keyword(s):  
Time Domain ◽  
Flip Chip ◽  
Time Domain Reflectometry ◽  
Fault Isolation ◽  
Experimental Results ◽  
Terahertz Pulse ◽  
Isolation And Identification ◽  
Isolation Technique ◽  
Non Destructive

Abstract Electro-optical terahertz pulse reflectometry (EOTPR) was introduced last year to isolate faults in advanced IC packages. The EOTPR system provides 10μm accuracy that can be used to non-destructively localize a package-level failure. In this paper, an EOTPR system is used for non-destructive fault isolation and identification for both 2D and 2.5D with TSV structure of flip-chip packages. The experimental results demonstrate higher accuracy of the EOTPR system in determining the distance to defect compared to the traditional time-domain reflectometry (TDR) systems.

scholarly journals An Advance-Tracing Boundary Element Method in the Time Domain for Solving the Radiating Problem of an Arbitrary Obstacle Accelerating Randomly

2017 ◽  
Vol 2017 ◽  
pp. 1-12
Author(s):  
Jui-Hsiang Kao
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Time Domain ◽  
Boundary Integral ◽  
Normal Velocity ◽  
Time Step ◽  
Random Acceleration ◽  
The Time Domain ◽  
First Time ◽  
Element Method

This research develops an Advance-Tracing Boundary Element Method in the time domain to calculate the waves that radiate from an immersed obstacle moving with random acceleration. The moving velocity of the immersed obstacle is multifrequency and is projected along the normal direction of every element on the obstacle. The projected normal velocity of every element is presented by the Fourier series and includes the advance-tracing time, which is equal to a quarter period of the moving velocity. The moving velocity is treated as a known boundary condition. The computing scheme is based on the boundary integral equation in the time domain, and the approach process is carried forward in a loop from the first time step to the last. At each time step, the radiated pressure on each element is updated until obtaining a convergent result. The Advance-Tracing Boundary Element Method is suitable for calculating the radiating problem from an arbitrary obstacle moving with random acceleration in the time domain and can be widely applied to the shape design of an immersed obstacle in order to attain security and confidentiality.

Optimization Design of Drawbead in Drawing Tools of Autobody Cover Panel

2002 ◽  
Vol 124 (2) ◽  
pp. 278-285 ◽  
Author(s):  
Gang Liu ◽  
Zhongqin Lin ◽  
Youxia Bao
Keyword(s):  
Optimization Algorithm ◽  
Optimization Design ◽  
Design Method ◽  
Experimental Results ◽  
Hybrid Optimization ◽  
Force Model ◽  
Hybrid Optimization Algorithm ◽  
Design Plan ◽  
Formed Part ◽  
Restraining Force

In the tooling design of autobody cover panels, design of drawbead will affect the distribution of drawing restraining force along mouth of dies and the relative flowing velocity of the blank, and consequently, will affect the distributions of strain and thickness in a formed part. Therefore, reasonable design of drawbead is the key point of cover panels’ forming quality. An optimization design method of drawbead, using one improved hybrid optimization algorithm combined with FEM software, is proposed in this paper. First, we used this method to design the distribution of drawbead restraining force along the mouth of a die, then the actual type and geometrical parameters of drawbead could be obtained according to an improved drawbead restraining force model and the improved hybrid optimization algorithm. This optimization method of drawbead was used in designing drawing tools of an actual autobody cover panel, and an optimized drawbead design plan has been obtained, by which deformation redundancy was increased from 0% under uniform drawbead control to 10%. Plastic strain of all area of formed part was larger than 2% and the minimum flange width was larger than 10 mm. Therefore, not only better formability and high dent resistance were obtained, but also fine cutting contour line and high assembly quality could be obtained. An actual drawing part has been formed using the optimized drawbead, and the experimental results were compared with the simulating results in order to verify the validity of the optimized design plan. Good agreement of thickness on critical areas between experimental results and simulation results proves that the optimization design method of drawbead could be successfully applied in designing actual tools of autobody cover panels.

The Study on the Influence of Pipe-Soil Interaction on VIV for Different Free Span Types

2017 ◽  
Author(s):  
Chongyao Zhou ◽  
Gang Xu ◽  
Zhiming Huang ◽  
Dagang Zhang ◽  
Naiquan Ye ◽  
...  
Keyword(s):  
Time Domain ◽  
Cross Flow ◽  
Sensitivity Study ◽  
Structural Damping ◽  
Flexible Pipe ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
Different Types ◽  
Main Factors ◽  
Parameter Influence

Subsea pipeline laid on the seabed will experience free span when the lay path is long and seabed is rugged. Hydrodynamic loads caused by the currents around the pipeline can induce oscillations in both cross-flow and in-line directions. This phenomenon is called vortex-induced vibration (VIV) which is the most common case that could induce serious fatigue problems. The pipe-soil interaction is one of the main factors that influence the vibration. In this paper, a study focusing on the effect of pipe-soil interaction on VIV for different types of free span is presented. The Milan wake oscillator is applied to calculate the dynamic response induced by VIV in Orcaflex, and the results are compared with experimental data to identify its validity. A sensitivity study is also performed to study the parameter influence of the Milan wake oscillator model. Four types of free span (including the multiple free spans) are modeled in Orcaflex and time domain VIV analysis is carried out to study the influence of pipe-soil interaction. Comparison among different types of free span is discussed. The influence of structural damping is studied for flexible pipe only because its influence on steel pipe is negligible. The influence of structural damping on flexible pipe is studied by means of a predefined moment-curvature curve. In addition, several cases are studied to investigate the influence of tension on VIV by Milan wake oscillator.

A time domain prediction method for the vortex-induced vibrations of a flexible riser

2018 ◽  
Vol 59 ◽  
pp. 458-481 ◽  
Author(s):  
Mengmeng Zhang ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Xiaoying Tang ◽  
Yue He
Keyword(s):  
Time Domain ◽  
Prediction Method ◽  
Flexible Riser ◽  
Vortex Induced Vibrations ◽  
Domain Prediction
Sign in / Sign up

Export Citation Format

Share Document