scholarly journals Wave Loads and Motions of Long Structures in Directional Seas

1987 ◽  
Vol 109 (2) ◽  
pp. 126-132 ◽  
Author(s):  
M. Isaacson ◽  
O. U. Nwogu
Keyword(s):  
Wave Train ◽  
Wave Spectrum ◽  
Numerical Procedure ◽  
Reduction Factor ◽  
The Body ◽  
Response Ratio ◽  
Wave Loads ◽  
Force Reduction Factor ◽  
Spreading Function ◽  
Wave Directionality

The present paper deals with the effects of wave directionality on the loads and motions of long structures. A numerical procedure based on Green’s theorem is developed to compute the exciting forces and hydrodynamic coefficients due to the interaction of a regular oblique wave train with an infinitely long, semi-immersed floating cylinder of arbitrary shape. The linear transfer function approach is used to determine the wave loads and motions of a structure of finite length in short-crested seas. The effect of wave directionality is expressed as a frequency-dependent, directionally averaged reduction factor for the wave loads and a response ratio for the body motions. Numerical results are presented for the force reduction factor and response ratio of a long floating box subject to a directional wave spectrum with a cosine-power-type energy spreading function.

Contact force analysis on two-fingered robot grasping

2020 ◽  
pp. 146441932096402
Author(s):  
Jiun-Ru Chen ◽  
Wei-En Chen ◽  
CH Liu ◽  
Yin-Tien Wang ◽  
CB Lin ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Contact Force ◽  
Numerical Procedure ◽  
Spherical Body ◽  
Solution Procedure ◽  
The Body ◽  
Contact Forces ◽  
Grasping Forces ◽  
Robot Grasping ◽  
Force Displacement

A procedure for inverse kinetic analysis on two hard fingers grasping a hard sphere is proposed in this study. Contact forces may be found for given linear and angular accelerations of a spherical body. Elastic force-displacement relations predicted by Hertz contact theory are used to remove the indeterminancy produced by rigid body modelling. Two types of inverse kinetic analysis may be dealt with. Firstly, as the fingers impose a given tightening displacement on the body, and carry it to move with known accelerations, corresponding grasping forces may be determined by a numerical procedure. In this procedure one contact force may be chosen as the principal unknown, and all other contact forces are expressed in terms of this force. The numerical procedure is hence very efficient since it deals with a problem with only one unknown. The solution procedure eliminates slipping thus only nonslip solutions, if they exist, are found. Secondly, when the body is moving with known accelerations, if the grasping direction of the two fingers is also known, then the minimum tightening displacement required for non-sliding grasping may be obtained in closed form. In short, the proposed technique deals with a grasping system that has accelerations, and in this study the authors show that indeterminancy may be used to reduce the complexity of the problem.

Numerical Prediction of Impact-Related Wave Loads on Ships

2006 ◽  
Vol 129 (1) ◽  
pp. 39-47 ◽  
Author(s):  
Thomas E. Schellin ◽  
Ould el Moctar
Keyword(s):  
Stokes Equations ◽  
Numerical Procedure ◽  
Navier Stokes ◽  
Ship Motions ◽  
Normal Velocity ◽  
Wave Loads ◽  
Navier Stokes Equations ◽  
Critical Areas ◽  
Strip Theory ◽  
A Chain

We present a numerical procedure to predict impact-related wave-induced (slamming) loads on ships. The procedure was applied to predict slamming loads on two ships that feature a flared bow with a pronounced bulb, hull shapes typical of modern offshore supply vessels. The procedure used a chain of seakeeping codes. First, a linear Green function panel code computed ship responses in unit amplitude regular waves. Ship speed, wave frequency, and wave heading were systematically varied to cover all possible combinations likely to cause slamming. Regular design waves were selected on the basis of maximum magnitudes of relative normal velocity between ship critical areas and wave, averaged over the critical areas. Second, a nonlinear strip theory seakeeping code determined ship motions under design wave conditions, thereby accounting for the nonlinear pressure distribution up to the wave contour and the frequency dependence of the radiation forces (memory effect). Third, these nonlinearly computed ship motions constituted part of the input for a Reynolds-averaged Navier–Stokes equations code that was used to obtain slamming loads. Favorable comparison with available model test data validated the procedure and demonstrated its capability to predict slamming loads suitable for design of ship structures.

Numerical Prediction of Impact-Related Wave Loads on Ships

2006 ◽  
Author(s):  
Thomas E. Schellin ◽  
Ould El Moctar
Keyword(s):  
Stokes Equations ◽  
Numerical Procedure ◽  
Finite Amplitude ◽  
Navier Stokes ◽  
Ship Motions ◽  
Normal Velocity ◽  
Wave Loads ◽  
Critical Areas ◽  
Strip Theory ◽  
A Chain

We present a numerical procedure to predict impact-related wave-induced (slamming) loads on ships. The procedure was applied to predict slamming loads on two ships that feature a flared bow with a pronounced bulb, hull shapes typical of modern offshore supply vessels. The procedure used a chain of seakeeping codes. First, a linear Green function panel code computed ship responses in unit amplitude regular waves. Wave frequency and wave heading were systematically varied to cover all possible combinations likely to cause slamming. Regular design waves were selected on the basis of maximum magnitudes of relative normal velocity between ship critical areas and wave, averaged over the critical areas. Second, a nonlinear strip theory seakeeping code determined ship motions under design wave conditions, thereby accounting for the ship’s forward speed, the swell-up of water in finite amplitude waves, as well as the ship’s wake that influences the wave elevation around the ship. Third, these nonlinearly computed ship motions constituted part of the input for a Reynolds-averaged Navier-Stokes equations (RANSE) code that was used to obtain slamming loads. Favourable comparison with available model test data validated the procedure and demonstrated its capability to predict slamming loads suitable for design of ship structures.

The Research of Statistic Prediction for Wave Loads Based on Three Dimensional Method

2013 ◽  
Author(s):  
Yihan Zhang ◽  
Huilong Ren ◽  
Hui Li ◽  
Xiaoyu Li
Keyword(s):  
Structural Strength ◽  
Wave Spectrum ◽  
Three Dimensional ◽  
Frequency Interval ◽  
Wave Loads ◽  
Short Term ◽  
Empirical Formulas ◽  
Strength Assessment ◽  
Term Prediction

The exact prediction of wave loads for ship or other marine structure is the key to its design and the assessment of structural strength, reliability and security. The short-term and long-term prediction of wave loads are always used in direct calculation for structural strength, fatigue strength assessment and so on based on spectral analysis method. In this paper, the numerical calculation method for statistic prediction is discussed firstly, including the Weibull distribution fitted method and the stack method. Further more, it is necessary to find a quick solution in order to improve the efficiency to compute the nonlinear equation in the second method. Then, some main factors that may influence the long-term or short-term prediction are discussed, such as wave spectrum, wave scatter diagram, incident wave angle interval and frequency interval. Finally, the wave loads prediction for a series of typical bulk carriers and oil tankers are calculated by the uniform predict method discussed above base on three dimensional wave loads calculation theory. The results showed that the method used in this paper can predict the statistic value of wave loads induced by irregular incident waves conveniently and efficiently. A rule to choose a series of uniform factors is confirmed for statistic prediction and some empirical formulas for long-term value of wave bending moment are concluded which are very useful in marine engineering.

An Evaluation of Two-Level Seismic Design Procedure

1993 ◽  
Vol 9 (1) ◽  
pp. 121-135 ◽  
Author(s):  
Chia-Ming Uang
Keyword(s):  
Structural Damage ◽  
Limit State ◽  
Design Procedure ◽  
Reduction Factor ◽  
Performance Criteria ◽  
Ultimate Limit State ◽  
Seismic Codes ◽  
Seismic Force ◽  
Force Reduction Factor ◽  
Force Reduction

The two-level design philosophy is recognized by modern seismic codes. When this philosophy is implemented in the code, the intensities of the two design earthquakes, the structural performance criteria, explicit versus implicit design approach, and the effectiveness to achieve the performance criteria vary considerably from one code to the other. For the ultimate limit state, the UBC was compared with seismic codes of Canada, Japan, and Eurocode. It was found that a trend to deviate from the UBC approach of using a single seismic force reduction factor (i.e., Rw) is apparent. Instead, an approach using a compound force reduction factor which considers the contribution of structural ductility and structural overstrength is preferred. For the serviceability limit state, a comparison of the level of design earthquakes and performance criteria of the UBC, Tri-Services Manual, and the Japanese code indicates that the UBC produces the most flexible structure, and that UBC does not control structural damage. It is suggested that the UBC adopts an explicit serviceability design procedure.

Development of Seismic Force Reduction and Displacement Amplification Factors for Autoclaved Aerated Concrete Structures

2006 ◽  
Vol 22 (1) ◽  
pp. 267-286 ◽  
Author(s):  
Jorge L. Varela ◽  
Jennifer E. Tanner ◽  
Richard E. Klingner
Keyword(s):  
Reduction Factor ◽  
Test Results ◽  
Lateral Loads ◽  
Autoclaved Aerated Concrete ◽  
Laboratory Test Results ◽  
Seismic Force ◽  
Force Reduction Factor ◽  
Aerated Concrete ◽  
Hysteretic Characteristics ◽  
Force Reduction

This paper addresses the development and application of a rational procedure to select the seismic force reduction factor ( R) and the displacement amplification factor ( Cd) for the design of autoclaved aerated concrete (AAC) structures. The values of R and Cd are proposed based on a combination of laboratory test results and numerical simulation. The test results are obtained from 14 AAC shear-wall specimens tested under simulated gravity and quasi-static reversed cyclic lateral loads. Analytical responses are predicted using nonlinear analysis models whose hysteretic characteristics are based on the experimentally observed responses. Using an iterative procedure, typical AAC structures are designed using successively larger trial values of the factor, R, until the structure's response (either ductility or drift) exceeds the experimentally determined capacity. A lower fractile of those critical values, modified for probable structural overstrength, is taken as a reasonable value of 3 for R. Using an analogous procedure, a reasonable value of Cd is determined as 3. These values will undoubtedly be refined based on field experience, just as they have been for other structural systems.

Frequency and Time Domain Analyses of Vessel Motions During Tropical Cyclones

2009 ◽  
Author(s):  
J. R. Whelan ◽  
Y. Drobyshevski ◽  
J. D. McConochie
Keyword(s):  
Wind Speed ◽  
Frequency Domain ◽  
Data Base ◽  
Tropical Cyclones ◽  
Time Domain ◽  
Wave Train ◽  
Wave Spectrum ◽  
North West ◽  
Motion Responses ◽  
Time Histories

A permanently turret moored floating facility located off the North West coast of Australia is likely to be exposed to tropical cyclones, which exhibit extreme wave height, wind and surface currents. Furthermore the cyclonic eye and fringes are characterised by rapidly varying metocean conditions, particularly wind speed and direction. It is necessary to understand the weather vaning and motion responses of the vessel during these transient conditions for successful facility development. This paper presents weather vaning and motion analyses of a Floating Storage and Offloading (FSO) vessel during the passage of tropical cyclones. A synthetic tropical data base developed by Woodside Energy Limited was used to generate the cyclonic conditions. The data base contains storms with return periods ranging from 10 to 100,000 years. Time histories of wave spectrum, wind and current at half-hourly intervals for several cyclones were examined. The weather vaning and motions responses of the FSO were computed using two methods: (1) a frequency domain quasi-stationary approach, and (2) a time domain approach. In the frequency domain analyses the metocean conditions were treated as stationary for each half-hour interval and the mean vessel heading and most probable amplitudes of motions were calculated. In the time domain analyses, the time histories of metocean conditions were closely matched to the synthesised cyclonic conditions, and time histories of vessel heading and motion responses were generated. Multiple realisations were simulated for each cyclone to assess variability of results associated with wave train random seed. A key finding of the study is that the worst roll response tends to occur after the eye of the cyclone has passed, at which time the wind and waves were highly non-collinear. At this time the vessel weather vanes so as to experience waves which are substantially beam-on. When the cyclonic eye is directly over the site, there is a reduction in wind speed and as a consequence the vessel weather vanes into the sea. This causes a corresponding reduction in the roll response. Results from both analysis methods have been compared and good agreement is observed. The applicability and limitations of the two analyses methods are also considered.

scholarly journals Wire antenna theory applied to the assessment of the radiation hazard in the vicinity of the GSM base stations

2003 ◽  
Vol 1 (1) ◽  
pp. 15-26 ◽  
Author(s):  
Vesna Roje
Keyword(s):  
Numerical Modeling ◽  
Numerical Procedure ◽  
Base Station ◽  
Incident Field ◽  
The Body ◽  
Base Stations ◽  
Simplified Model ◽  
Radiation Hazard ◽  
Wire Antenna ◽  
Antenna Theory

Safety aspects of the GSM base station radiation concerning human health have been analyzed. The numerical modeling of the human body was performed by utilizing the antenna theory and BEM numerical procedure. The simplified model of the body represented by thick cylindrical scatterer placed vertically on the perfect conducting ground was used. Measurements of the radiated fields have been done at a few sites, and the results were incorporated in the numerical calculations as an incident field.

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