scholarly journals Phase manipulation and the harmonic components of ringing forces on a surface-piercing column

2014 ◽  
Vol 470 (2168) ◽  
pp. 20130847 ◽  
Author(s):  
C. J. Fitzgerald ◽  
P. H. Taylor ◽  
R. Eatock Taylor ◽  
J. Grice ◽  
J. Zang
Keyword(s):  
Water Waves ◽  
Fourier Transforms ◽  
Time History ◽  
Wave Force ◽  
Separation Method ◽  
Coastal Protection ◽  
Time Histories ◽  
Local Wave ◽  
Harmonic Components ◽  
Force Time

A general phase-based harmonic separation method for the hydrodynamic loading on a fixed structure in water waves of moderate steepness is proposed. An existing method demonstrated in the experimental study described by Zang et al. (Zang et al. 2010 In Proc. Third Int. Conf. on Appl. of Phys. Modelling to Port and Coastal Protection. pp. 1–7.) achieves the separation of a total diffraction force into odd and even harmonics by controlling the phase of incident focused waves. Underlying this method is the assumption that the hydrodynamic force in focused waves possesses a Stokes-like structure. Under the same assumption, it is shown here how the harmonic separation method can be generalized, so that the first four sum harmonics can be separated by phase control and linear combinations of the resultant time-histories. The effectiveness of the method is demonstrated by comparisons of the Fourier transforms of the combined time-histories containing the harmonics of interest. The local wave elevations around the focus time are also visualized for the first three harmonics in order to reveal the local dynamics driving components within the wave force time-history.

Damage Detection in Rods Using Wave Propagation and Regression Analysis

1999 ◽  
Author(s):  
K. T. Feroz ◽  
S. O. Oyadiji
Keyword(s):  
Wave Propagation ◽  
Regression Analysis ◽  
Damage Detection ◽  
Numerical Study ◽  
Time History ◽  
Ball Impact ◽  
Spherical Ball ◽  
Time Histories ◽  
Measured Strain ◽  
Force Time

Abstract The phenomena of wave propagation in rods was studied both numerically and experimentally. The finite element (FE) code ABAQUS was used for the numerical study while PZT (lead zirconium titanate) sensors and a 50 MHz transient recorder were used experimentally to monitor and to capture the propagation of stress pulses. For the study of damage detection in the rods the analyses and the experiments were repeated by introducing slots in a fixed axial location of the rod. A longitudinal wave was induced in the rod via collinear impact which was modelled in the FE analyses using the force-time history computed from the classical Hertz contact theory. In the experimental measurements this was achieved by a spherical ball impact at one plane end of the rods. It is shown that the predicted and measured strain-time histories for the defect-free rod and for the rods with defect correlate quite well. These results also show that defects can be located using the wave propagation phenomena. A regression analysis technique of the predicted and measured strain histories of the defect free rod and of the rod with defect was also performed. The results show that this technique is more efficient for smaller defects. In particular, it is shown that the area enclosed by the regression curve increases as the defect size increases.

scholarly journals Numerical simulation of pounding damage to caisson under storm surge

2018 ◽  
Vol 38 ◽  
pp. 03046
Author(s):  
Chen Yu
Keyword(s):  
Numerical Simulation ◽  
Storm Surge ◽  
Failure Mode ◽  
Structural Model ◽  
Time History ◽  
Element Model ◽  
Wave Force ◽  
New Method ◽  
Wave Direction ◽  
Force Time

In this paper, a new method for the numerical simulation of structural model is proposed，which is employed to analyze the pounding response of caissons subjected to storm surge loads．According to the new method，the simulation process is divided into two steps. Firstly, the wave propagation caused by storm surge is simulated by the wave-generating tool of Flow-3D, and recording the wave force time history on the caisson. Secondly，a refined 3D finite element model of caisson is established，and the wave force load is applied on the caisson according to the measured data in the first step for further analysis of structural pounding response using the explicit solver of LSDYNA. The whole simulation of pounding response of a caisson caused by “Sha Lijia” typhoon is carried out. The results show that the different wave direction results in the different angle caisson collisions, which will lead to different failure mode of caisson, and when the angle of 60 between wave direction and front/back wall is simulated, the numerical pounding failure mode is consistent with the situation.

EFFECT OF THE FLUID ON THE IMPACT FORCE OF THE WET MISSILE

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Duc-Kien Thai ◽  
Seung-Eock Kim
Keyword(s):  
Impact Force ◽  
Force Plate ◽  
Time History ◽  
Research Centre ◽  
Element Analysis ◽  
Time Histories ◽  
Target Wall ◽  
Force Time ◽  
Missile Test ◽  
The Impact

In this paper, the force-time histories of soft missiles, with and without filled water, impacting the target wall were investigated using finite element analysis. The force plate tests, with a dry missile (test FP8) and a wet missile (test FP16) carried out by Technical Research Centre of Finland (VTT), were used. The numerical analysis results were verified by comparing with those of experiments. A parametric analysis with different missile velocities was also performed to investigate the force-time history and impulse of the missile impact on target plate. Based on a comparison with the Riera approach, the coefficients were proposed to modify the Riera function. The analysis results show that, the Riera function accurately predicted the impact force time history in the case of the dry missile. However, in the case of the wet missile, the coefficients α from 1.24 to 1.45 are recommended to be added to the second term of the Riera function in the case in which the impact velocity is in the range of 70 m/s to 200 m/s.

scholarly journals Dynamic effects induced by the impact of debris flows on protection barriers

2018 ◽  
Vol 10 (1) ◽  
pp. 116-131 ◽  
Author(s):  
Maddalena Marchelli ◽  
Valerio De Biagi
Keyword(s):  
Impact Force ◽  
Time History ◽  
Element Model ◽  
Interaction Force ◽  
Accurate Analysis ◽  
Vibration Period ◽  
Time Histories ◽  
Mode Vibration ◽  
Force Time ◽  
The Impact

Debris flow is a transient phenomenon that causes large disasters. Retaining systems, whose design is still nowadays a crucial issue, can mitigate this risk. Multiple surges can arise during this phenomenon; thus, an accurate analysis might consider the impact force time histories rather than only its maxima. The aim of this work is to analyze the effects of the interaction between the debris and the barrier during one surging phenomenon. A discrete element model models the granular motion and the interaction between the debris and a rigid open barrier set at the end of the channel. The estimated interaction force time history is then used as input impact force for the dynamic structural analyses of the piles. A total of 12 different structural sections are adopted and the internal forces at the base are critically compared. It results that the first mode vibration period is the parameter that largely affects the behavior of the piles.

Impact factor method for design of bridge foundations under ship collisions

2016 ◽  
Vol 20 (4) ◽  
pp. 534-548 ◽  
Author(s):  
Junjie Wang ◽  
Yanchen Song ◽  
Zhiran Yu
Keyword(s):  
Impact Factor ◽  
Impact Force ◽  
Time History ◽  
Rigid Wall ◽  
Static Method ◽  
Factor Method ◽  
Empirical Function ◽  
Time Histories ◽  
Dynamic Amplification ◽  
Force Time

Due to the complexity involved and limited study on the topic, the equivalent static method, adopted in the current codes for structural design of bridges under ship collisions, does not take into account the dynamic amplification effect correctly. In this article, impact factor method is proposed to estimate the response of bridge’s piers and foundations, as a better alternative of the equivalent static method. Through refined numerical simulations of ship-rigid wall collisions for nine typical ships under various impact velocities, 81 impact force time-histories are obtained. The period-dependent impact factor is defined, and empirical function of it is proposed and parameters in the empirical function are determined by the 81 sample impact force time-histories. Finally, both impact factor method and dynamic time-history method are used to estimate the responses of piers and foundations of two example bridges, and the precision of impact factor method is discussed.

URANS Prediction of Ship Hydrodynamics in Head Sea Waves at Zero Forward Speed With Model Testing Validation

2016 ◽  
Author(s):  
Yuting Jin ◽  
Shuhong Chai ◽  
Jonathan Duffy ◽  
Christopher Chin ◽  
Neil Bose ◽  
...  
Keyword(s):  
Water Depth ◽  
Potential Flow ◽  
Water Waves ◽  
Transfer Functions ◽  
Experimental Studies ◽  
Time History ◽  
Wave Force ◽  
Ship Motion ◽  
Sea Waves ◽  
Ship Hydrodynamics

The paper presents computations on predicting the hydrodynamics of a generic floating liquefied natural gas (FLNG) hull form in regular head sea waves using unsteady Reynolds-Averaged Navier-Stokes (URANS) solver StarCCM+. Initially, model scale simulations were conducted at model test basin water depth (d = 0.8m), with detailed verification and validation study performed to estimate numerical uncertainties. The simulation results were compared with potential flow solutions and validated against experimental studies. Using the verified numerical setup, ship hydrodynamics including wave induced loads, moments as well as ship motion responses in deep water waves (d = 8.0m) have been studied. The computed time history results were decomposed by Fourier series to obtain force/moment and motion transfer functions on the frequency domain. From the obtained results, the presented URANS approach demonstrates slightly better accuracy compared with potential flow (PF) solutions. It is also found that water depth has great influences on the computed wave force and ship motion transfer functions for certain range of wave frequencies.

Signal Processing Methods for Determining the Properties of Bolted Joints

2015 ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Signal Processing ◽  
Fourier Transforms ◽  
Time History ◽  
Bolted Joints ◽  
Vibration Signals ◽  
Time Histories ◽  
Subsequent Motion ◽  
The One ◽  
Signal Processing Methods ◽  
General Scope

If a structure containing bolted joints is set into vibration and the subsequent motion measured it may be possible to determine some properties of the structure and the joints. However, it is not generally straightforward to interpret the decaying vibration signals and considerable signal processing may be necessary. Typically the vibration is nonlinear and this must be taken into account. Three methods for data analysis are investigated here: filtering time histories, working with short Fourier transforms and the use of empirical mode decompositions. Some progress is made with the first two but the third is disappointing but full of promise. The general scope of the objectives is to obtain properties such as frequency and damping that are changing in time. One of the key difficulties is that several nonlinear resonances are superimposed in a general decaying time history. Extracting the one required from the others is the main signal processing task.

Soft Computing Based Force Recovery Technique for Hypersonic Shock Tunnel Tests

2018 ◽  
Vol 18 (05) ◽  
pp. 1871004 ◽  
Author(s):  
Ramesh Babu Pallekonda ◽  
Soumya Ranjan Nanda ◽  
Santosha K. Dwivedy ◽  
Vinayak Kulkarni ◽  
Viren Menezes
Keyword(s):  
Fuzzy Inference ◽  
Time History ◽  
Shock Tunnel ◽  
Force Balance ◽  
Inference System ◽  
Time Histories ◽  
Recovery Technique ◽  
Hypersonic Shock ◽  
Force Recovery ◽  
Force Time

A hemispherical model equipped with a three component accelerometer force balance has been tested in a shock tunnel at Mach 8.0 freestream conditions. A novel technique has been devised using the Artificial Neuro-Fuzzy Inference System (ANFIS) for recovering the forces experienced by the model during the experiments. Implementation of this methodology in calibration of the force balance showed encouraging agreement with the impulse forces recovered from the calibration tests. The same recovery procedure is then adopted to obtain the time history of the forces for 0[Formula: see text] and 15[Formula: see text] angle of attack experiments. The drag recovered in steady state is found to agree well with the conventional methods with minor discrimination for the lift and pitching moment. In light of the limitation of the accelerometer force balance theory due to the unaccountability of model dynamics, the force recovery technique proposed herein is found simple to implement and can be opted as a tool for prediction of the aerodynamic coefficients and force time histories.

Physical Modelling of Hydrodynamic Loads on Piggyback Pipelines in Combined Wave and Current Conditions

2010 ◽  
Author(s):  
Masˇa Brankovic´ ◽  
Hammam Zeitoun ◽  
James Sutherland ◽  
Andrew Pearce ◽  
Vagner Jacobsen ◽  
...  
Keyword(s):  
Time History ◽  
Physical Modelling ◽  
Model Tests ◽  
Test Method ◽  
Hydrodynamic Loads ◽  
Time Histories ◽  
Flow Mechanisms ◽  
Force Time ◽  
The Stability ◽  
Pipeline Design

One of the aspects of pipeline design is ensuring pipeline stability on the seabed under the action of environmental loads. During the 1980s, significant efforts were made to improve the understanding of hydrodynamic loads on single pipeline configurations on the seabed (Reference 1). The stability of piggyback (bundled) pipeline configurations is less well understood, with little quantitative data readily available to the design engineer for practical application in engineering problems (References 2–6). This paper describes an extensive set of physical model tests performed for piggyback on-seabed and piggyback-raised-from seabed (spanning or lifting pipeline) configurations to determine hydrodynamic forces in combined wave and current conditions. The piggyback is nominally in the 12 o’clock position. The well-established carriage technique was used, in order to obtain data for use in full-scale stability modelling. The model tests are benchmarked against existing test data, to confirm the validity of the test method. Key findings are presented in terms of non-dimensional coefficients, and force time histories for the vertical and horizontal forces. A brief interpretation of the hydrodynamic load behaviour of the Piggyback System is provided by considering the physical flow mechanisms causing the force time history variation; furthermore the influence of the seabed separation on the piggyback loads is also discussed.

CO and H2O Time-Histories in Shock-Heated Blends of Methane and Ethane for Assessment of a Chemical Kinetics Model

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
O. Mathieu ◽  
C. R. Mulvihill ◽  
E. L. Petersen ◽  
Y. Zhang ◽  
H. J. Curran
Keyword(s):  
Chemical Kinetics ◽  
Laminar Flame ◽  
Combustion Process ◽  
Time History ◽  
Good Marker ◽  
Ignition Delay Times ◽  
Depletion Rate ◽  
Time Histories ◽  
Main Components ◽  
Detailed Kinetics

Methane and ethane are the two main components of natural gas and typically constitute more than 95% of it. In this study, a mixture of 90% CH4/10% C2H6 diluted in 99% Ar was studied at fuel lean (equiv. ratio = 0.5) conditions, for pressures around 1, 4, and 10 atm. Using laser absorption diagnostics, the time histories of CO and H2O were recorded between 1400 and 1800 K. Water is a final product from combustion, and its formation is a good marker of the completion of the combustion process. Carbon monoxide is an intermediate combustion species, a good marker of incomplete/inefficient combustion, as well as a regulated pollutant for the gas turbine industry. Measurements such as these species time histories are important for validating and assessing chemical kinetics models beyond just ignition delay times and laminar flame speeds. Time-history profiles for these two molecules were compared to a state-of-the-art detailed kinetics mechanism as well as to the well-established GRI 3.0 mechanism. Results show that the H2O profile is accurately reproduced by both models. However, discrepancies are observed for the CO profiles. Under the conditions of this study, the CO profiles typically increase rapidly after an induction time, reach a maximum, and then decrease. This maximum CO mole fraction is often largely over-predicted by the models, whereas the depletion rate of CO past this peak is often over-estimated for pressures above 1 atm.

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