Engineering Approach for Quay-Side Mooring Subject to Waves

2015 ◽  
Author(s):  
Blanca Peña ◽  
Erik P. ter Brake ◽  
James O. Russell
Keyword(s):  
Time Domain ◽  
Vertical Wall ◽  
Real Life ◽  
Added Mass ◽  
Wave Radiation ◽  
Wave Loading ◽  
Numerical Instability ◽  
Literature Study ◽  
Working Solution ◽  
Negative Damping

Wave motions from vessels moored in ports open to the sea impact the operability of loading operations, and should be assessed as part of any port (re)development plan. When analyzing vessels moored by a quay-side, time domain simulations may show numeric instabilities resulting in unreliable outcomes. The origin of the numerical instability might lie in the hydrodynamic added mass and wave radiation damping typically calculated using potential flow methods. For certain frequencies, these tend to give negative values. This negative added mass is a known phenomenon in the industry. Combined with negative damping, it is believed to cause instability in non-linear (coupled) time domain simulations. In these cases, the vessel seems to generate energy rather than dissipate it. As such, the simulations are unlikely to realistically represent real-life scenarios. This paper describes an engineering method to mitigate numerical instability and derive a working solution to address the operability of loading a vessel subject to wave loading at a quay-side. The work covers a literature study into negative added mass and damping caused by shallow water and vicinity of objects such as a vertical wall. This is followed by an engineering study using 3D diffraction and time domain software.

An Investigation Into the Limitations of the Panel Method and the Gap Effect for a Fixed and a Floating Structure Subject to Waves

2016 ◽  
Author(s):  
Blanca Peña ◽  
Aaron McDougall
Keyword(s):  
Time Domain ◽  
Real Life ◽  
Added Mass ◽  
Panel Method ◽  
Gap Effect ◽  
Wave Radiation ◽  
Literature Study ◽  
Floating Structure ◽  
Cfd Analyses ◽  
Wave Induced

The wave-induced motions of vessels moored next to a fixed object and open to the sea impact the operability of many offshore operations, and should be assessed in order to avoid accidents and catastrophes. When analysing vessels moored by a fixed object (e.g. quay-side or platform), time domain simulations have shown numeric instabilities resulting in unreliable outcomes. The origin of the numerical instability might lie in the hydrodynamic added mass and wave radiation damping. This is typically calculated using potential flow methods and influenced by the existence of standing waves in the gap between the two bodies. For certain frequencies, these give negative values, potentially causing instabilities in non-linear (coupled) time domain simulations. In these cases, the vessel can behave unexpectedly, generating energy rather than dissipating it. As such, certain simulations have been disregarded as they are unlikely to accurately represent real-life scenarios. This paper investigates and compares added mass and damping using two different tools and studies the gap effect when conducting diffraction analysis using 3D panel methods. The work covers a literature study into potential theory, multibody analysis, Computational Fluid Dynamics (CFD) and lid techniques. This is followed by a study conducted using both panel method and CFD analyses. The results from both approaches have been compared, showing interesting information and the necessity of researching more into the problem addressed in this paper.

Time-Domain Nonlinear SSI Analysis of Foundation Sliding Using Frequency-Dependent Foundation Impedance Derived From SASSI

2008 ◽  
Author(s):  
Mansour Tabatabaie ◽  
Thomas Ballard
Keyword(s):  
Frequency Domain ◽  
Linear Systems ◽  
Time Domain ◽  
Soil Structure ◽  
Wave Radiation ◽  
Far Field ◽  
Frequency Dependent ◽  
Nonlinear Springs ◽  
Mat Foundation ◽  
The Time Domain

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using the de-convolution method and/or spatially variable ground motions. For structures that exhibit nonlinearities such as potential base sliding and/or uplift, the frequency-domain procedure is not applicable as it is limited to linear systems. For such problems, it is necessary to solve the problem in the time domain using the direct integration method in programs such as ADINA [2]. The authors recently introduced a sub-structuring technique called distributed parameter foundation impedance (DPFI) model that allows the structure to be partitioned from the total SSI system and analyzed in the time domain while the foundation soil is modeled using the frequency-domain procedure [3]. This procedure has been validated for linear systems. In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used to validate two linear time-domain ADINA models: Model 1 consisting of the mat foundation+DPFI derived from the linear SASSI model and Model 2 consisting of the total SSI system (mat foundation plus a soil block). After linear alignment, the nonlinear springs were added to both ADINA models and re-analyzed in time domain. Model 2 provided the target nonlinear solution while Model 1 provided the results using the DPFI+nonlinear springs. By increasing the amplitude of the vibration load, different levels of foundation sliding were simulated. Good agreement between the results of two models in terms of the displacement response of the mat and cyclic force-displacement behavior of the springs validates the accuracy of the procedure presented herein.

scholarly journals Wave Impact Loads on Vertical Seawalls: Effects of the Geometrical Properties of Recurve Retrofitting

Water ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 2849
Author(s):  
Shudi Dong ◽  
Md Salauddin ◽  
Soroush Abolfathi ◽  
Jonathan Pearson
Keyword(s):  
Impact Force ◽  
Vertical Wall ◽  
Impact Loads ◽  
Geometrical Shape ◽  
Wave Loading ◽  
Wave Impact ◽  
Static Loads ◽  
Geometrical Properties ◽  
Overhang Length ◽  
Overturning Moment

This study investigates the variation of wave impact loads with the geometrical configurations of recurve retrofits mounted on the crest of a vertical seawall. Physical model tests were undertaken in a wave flume at the University of Warwick to investigate the effects of the geometrical properties of recurve on the pressure distribution, overall force, and overturning moment at the seawall, subject to both impulsive and non-impulsive waves. Additionally, the wave impact and quasi-static loads on the recurve portion of the retrofitted seawalls are investigated to understand the role of retrofitting on the structural integrity of the vertical seawall. Detailed analysis of laboratory measurements is conducted to understand the effects of overhang length and height of the recurve wall on the wave loading. It is found that the increase in both recurve height and overhang length lead to the increase of horizontal impact force at an average ratio of 1.15 and 1.1 times larger the reference case of a plain vertical wall for the tested configurations. The results also show that the geometrical shape changes in recurve retrofits, increasing the overturning moment enacted by the wave impact force. A relatively significant increase in wave loading (both impact and quasi-static loads) are observed for the higher recurve retrofits, while changes in the overturning moment are limited for the retrofits with longer overhang length. The data generated from the physical modelling measurements presented in this study will be particularly helpful for a range of relevant stakeholders, including coastal engineers, infrastructure designers, and the local authorities in coastal regions. The results of this study can also enable scientists to design and develop robust decision support tools to evaluate the performance of vertical seawalls with recurve retrofitting.

On the Radiation and Diffraction of Surface Waves by Submerged Spheroids

1989 ◽  
Vol 33 (02) ◽  
pp. 84-92
Author(s):  
G. X. Wu ◽  
R. Eatock Taylor
Keyword(s):  
Degrees Of Freedom ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Added Mass ◽  
Wave Radiation ◽  
Legendre Functions ◽  
Incoming Wave ◽  
Six Degrees Of Freedom ◽  
Damping Coefficients ◽  
Exciting Forces

The problem of wave radiation and diffraction by submerged spheroids is analyzed using linearized three-dimensional potential-flow theory. The solution is obtained by expanding the velocity potential into a series of Legendre functions in a spheroidal coordinate system. Tabulated and graphical results are provided for added mass and damping coefficients of various spheroids undergoing motions in six degrees of freedom. Graphs are also provided for exciting forces and moments corresponding to a range of incoming wave angles.

Dynamic Parameter Identification Using Ambient Response Analysis and Ibrahim Time Domain Approach: A Case Study on a Steel Plate Structure

2011 ◽  
Vol 110-116 ◽  
pp. 2395-2399
Author(s):  
M.A. Anuar ◽  
Liyana Roslan ◽  
A.A. Mat Isa
Keyword(s):  
Time Domain ◽  
Natural Frequencies ◽  
Steel Plate ◽  
Real Life ◽  
Dynamic Parameter ◽  
Modal Parameters ◽  
Response Analysis ◽  
Control Failure ◽  
Dynamic Parameter Identification ◽  
Testing Condition

Since the level of vibration always depends on the natural frequencies of the system, it is important to know the modal parameters of such system to control failure and provide prevention actions. However, for many mechanical engineering machines or structures, there is a demand and necessity to determine real-life modal parameters using actual operating condition. This type of testing condition cannot be done in lab environment because most of the mechanical structure is big in size and heavy. Thus, the purpose of this paper is to study the natural frequencies of a steel plate by using Operational Modal Analysis (OMA) and Ibrahim Time Domain (ITD). Comparison of results between both approaches will be shown.

Time-domain solution for second-order wave radiation

1993 ◽  
Vol 6 (2-3) ◽  
pp. 241-258 ◽  
Author(s):  
Kwok Fai Cheung ◽  
Michael Isaacson ◽  
Joseph Y.T. Ng
Keyword(s):  
Time Domain ◽  
Second Order ◽  
Wave Radiation

Experimental and Numerical Study of Coupled Dynamic Response of a Mini Tension Leg Platform

2004 ◽  
Vol 126 (4) ◽  
pp. 318-330 ◽  
Author(s):  
Anitha Joseph ◽  
V. G. Idichandy ◽  
S. K. Bhattacharyya
Keyword(s):  
Finite Element Method ◽  
Time Domain ◽  
Natural Frequencies ◽  
Numerical Study ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Scaled Model ◽  
Wave Flume ◽  
Exploration And Production

Role of mini tension leg platforms (TLP) in oil exploration and production in marginal deepwater fields is becoming increasingly important. Mini TLP combines the simplicity of a spar and favorable response features of a TLP. In this paper, the results of a detailed experimental and numerical investigation of the coupled dynamic behavior of a mini TLP are reported with special attention to hull-tether coupling. The experimental study has been carried out using a scaled model in wave flume with specially designed tethers whose first two “string” natural frequencies are excited by waves, thus achieving strong hull-tether coupling. The numerical study has been carried out using a nonlinear time domain finite element method specifically addressed to compliant offshore platforms using a combination of potential theory based wave loading and Morison-type wave loading. Extensive comparisons between numerical and experimental results have been made both for platform motions and deflected shapes of the tethers and conclusions drawn.

scholarly journals Time-domain determination of earthquake fault parameters from short-period P-waves

1976 ◽  
Vol 66 (5) ◽  
pp. 1459-1484
Author(s):  
Paul G. Somerville ◽  
Ralph A. Wiggins ◽  
Robert M. Ellis
Keyword(s):  
Time Domain ◽  
Time Function ◽  
Wave Radiation ◽  
Model Parameters ◽  
Half Cycle ◽  
Rupture Velocity ◽  
Fault Surface ◽  
Fault Parameters ◽  
Short Period

abstract Source parameters of two shallow earthquakes have been determined by the time-domain analysis of short-period teleseismic recordings. For each event, the effect of the receiver crust was deconvolved from a set of globally distributed recordings using the homomorphic method. The resulting seismograms were compared with the form of the elastic-wave radiation computed from Savage's model of radially spreading rupture on a plane elliptical fault surface. This time-domain approach has permitted the determination of several kinematic parameters pertaining to the dynamics of rupture that are not ordinarily evaluated from spectral analysis. These parameters are rupture velocity, the direction of farthest rupture propagation, and the duration of a ramp dislocation time function which was prescribed to be the same everywhere on the fault surface. The application of a general linear inverse scheme has shown that the model parameters (notably rupture velocity and dimension) are only weakly coupled. Inversion is also used to determine the range of acceptable parameter values and indicates the importance of array recordings in constraining the models. A consistent discrepancy between the observed and model seismograms during the first half-cycle of motion is attributed to the incorrect prescription of the dislocation time function. It is suggested that a space-dependent function determined theoretically by Kostrov in 1964 would tend to remove this discrepancy.

scholarly journals Total Radiated Power Measurement in an Uncalibrated Reverberation Chamber

2019 ◽  
Vol 69 (5) ◽  
pp. 427-430
Author(s):  
Deepshikha Gururani ◽  
Harish S. Rawat ◽  
Satya K. Dubey ◽  
V.N. Ojha
Keyword(s):  
Quality Factor ◽  
Time Domain ◽  
Indoor Environment ◽  
Real Life ◽  
Power Measurement ◽  
Shielding Effectiveness ◽  
Reverberation Chamber ◽  
Radiated Power ◽  
Reverberation Chambers ◽  
The Time Domain

With the increased use of wireless communication in recent years, the use of reverberation chamber (RC) has increased to a great extent. Reverberation chambers have been eminently used for EMC testing and shielding effectiveness. The environment it provides is very similar to the reverberant surroundings that antenna undergoes in real life use. An experiment to measure total radiated power of antenna, antenna efficiency and quality factor of chamber in indoor environment is proposed. This will make the measurement very simple and inexpensive as designing and calibration of chamber will not be needed. In this paper, we have used three different techniques to compare total radiated power, quality factor, Rician K factor and efficiency of a patch antenna measured in indoor environment with RC data. The three method used include plate stirring method and two time domain methods. The time domain methods use modulated pulse and Gaussian pulse respectively for the measurement. The antenna and chamber parameters are measured in the real time and the data matched well with the RC data for different techniques.

scholarly journals Politik Hukum Berkeadaban Perspektif Filsafat Islam

2018 ◽  
Author(s):  
Jurnal ARISTO
Keyword(s):  
Human Life ◽  
Real Life ◽  
Literature Study ◽  
Islamic Philosophy ◽  
Philosophical Approach ◽  
Philosophical Perspective ◽  
Political Concept ◽  
The World ◽  
Islamic Civilization ◽  
Islamic Values

This is the result of research that aims to explain the legal and political civilization civilized in Isla philosophical perspective. With literature study method and the philosophical approach of the data collected, verified and analyzed. The results showed that as the core of the Islamic civilization which can affect all aspects of human life and therefore civilization should become a legal political concept in accordance with Islamic values that have alignments to the virtues of the world of human life and the hereafter. Political law as a legal way to achieve legal establishment have made many disalahgunkan for maneuvering behind the legality of the law. The necessity to fix the legal politics only interest-oriented materialistic secular with Islamic philosophy, as with the values of Islam that comes from God as the highest authority over all can be transformed into a real life human being, so that the safety and happiness of the world and the hereafter can achieved.

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