Determination of the Wave Spectrum From Observed Motions of a Vehicle in a Seaway

1967 ◽  
Vol 11 (03) ◽  
pp. 199-208
Author(s):  
Wilbur Marks
Keyword(s):  
Wave Spectrum ◽  
Full Scale ◽  
The State ◽  
Vertical Acceleration ◽  
Time Histories

If, during full-scale trials, it is not possible to measure the state of the sea with a reliable wavemeter, then certain motion records may be combined to achieve the same end. The derivation of the wave spectrum from the time histories of pitch, heave (vertical acceleration), and bow immersion is presented. The problem of the conversion of acceleration to displacement is discussed. The method is applied to the particular case of the hydrofoil boat Sea Legs.

Relation Between Full-Scale and Model Data

2020 ◽  
Author(s):  
Horia Hangan ◽  
Maryam Refan ◽  
Djordje Romanic
Keyword(s):  
Numerical Simulations ◽  
State Of The Art ◽  
Full Scale ◽  
The State ◽  
Reduced Model ◽  
Model Data ◽  
Model Simulations ◽  
Velocity Scale ◽  
Scale Data

This chapter introduces recent results aiming to compare full-scale data and simulations of tornadoes and to establish a framework through which simulations of tornado-like vortices (both physical and numerical) can be compared to full-scale data. Physical and sometimes numerical simulations of non-synoptic winds such as tornadoes and downbursts are performed at a reduced (model) scale (Λl) compared to reality (prototype). That approach implies that there is also a timescale (Λt) and a velocity scale (Λv) involved, and the three of them are interlinked. The proper determination of these scales is critical in the process of translating results from model simulations to reality. This chapter discusses the state of the art of determining these scales for two types of non-synoptic winds—tornadoes and downbursts.

scholarly journals SPLASHNIK-THE TAYLOR MODEL BASIN DISPOSABLE WAVE BUOY

2011 ◽  
Vol 1 (7) ◽  
pp. 6
Author(s):  
Wilbur Marks ◽  
Robert G. Tuckerman
Keyword(s):  
Fixed Point ◽  
Energy Spectrum ◽  
Wave Spectrum ◽  
The State ◽  
Measuring System ◽  
Vertical Acceleration ◽  
Height Distribution ◽  
Taylor Model ◽  
Wave Measurement ◽  
The Waves

In connection with full scale ship trials, it is often necessary to have a description of the state of the sea which may be used as a scale against which to measure ship performance. Visual observations of waves have proven to be unreliable in the past and are, in any event, not sufficiently detailed to be adequately descriptive, for many problems. Hindcasting** the state of the sea depends on wind information (speed, duration, area of sea covered, and rate of growth and/or decay) obtained from six hourly weather maps. The wind data is used in conjunction with certain empirical^theoretical formulations to produce an energy spectrum of waves at the place and time of interest. The energy spectrum is a good descriptive tool, because it gives information on the energy content of the wave frequencies present and provides an estimate of the height distribution of the waves as well as certain other statistical quantities. However, hindcasting the wave spectrum is unsatisfactory for two reasons: 1) estimation of the wind field from sparse observations spaced six hours apart is highly subjective, and 2), no specific energy spectrum formulation has as yet been verified. There is still another method for description of the seaway. If the waves at a fixed point can be measured for a sufficient length of time, then this sample record can be converted into a wave (energy) spectrum that will adequately characterize the state of the sea. There are many systems that will measure waves, but the requirement that wave measurements complement simultaneous ship motions measurements, in all states of sea, eliminates most of the known instruments. In particular, it is required that the waves be observed at a fixed point for a period of hours, while the ship conducts certain maneuvers which may remove it several miles from the point of observation. This means that the wave measurement system must be physically divorced from the ship. Furthermore, many tests will be made in heavy seas so that it will not be practical to seek out the instrument and recover it. As a consequence of the conditions imposed by the particular problem stated here, the wave measuring system must be able to: 1. Telemeter information to the ship for at least 7 hours at a distance of at least 8 nautical miles, 2. Be launched from the deck of a ship in waves perhaps 25 feet high, and 3. Be inexpensively constructed ($125.00 - $150.00) so as to be expendable. Since investigation revealed that no known instrument had embodied in it all three of these features, it was decided to design and build an appropriate system, at the David Taylor Model Basin. After some consideration of the imposed conditions, it was decided that a small floating buoy (SPLASHNIK) which measures apparent vertical acceleration and telemeters the information back to the ship could be designed to fulfill the requirements. The intent of this paper is to describe the SPLASHNIK system, the data reduction method, some experimental verification of the method, and some proposed improvements. It should be noted that this technique of wave measurement (recording of vertical acceleration) is not new. In fact, one instrument described by Dorrestein (1957) is somewhat similar to the SPLASHNIK and has been in operation for several years. Other institutions are also known to be experimenting with accelerometer wave buoys. However, several basic design differences make the SPLASHNIK especially useful as a tool in the study of ship behavior. A drawing of the SPLASHNIK appears in Figure 1.

Respirometry for determination of the influents SS-concentration

1996 ◽  
Vol 33 (1) ◽  
pp. 311-323 ◽  
Author(s):  
A. Witteborg ◽  
A. van der Last ◽  
R. Hamming ◽  
I. Hemmers
Keyword(s):  
Experimental Design ◽  
Activated Sludge ◽  
Substrate Concentration ◽  
Full Scale ◽  
Activated Sludge Process ◽  
Respiration Rates ◽  
On Line ◽  
Large Measurement ◽  
Set Up

A method is presented for determining influent readily biodegradable substrate concentration (SS). The method is based on three different respiration rates, which can be measured with a continuous respiration meter which is operated in a cyclic way. Within the respiration meter nitrification is inhibited through the addition of ATU. Simulations were used to develop the respirometry set-up and decide upon the experimental design. The method was tested as part of a large measurement programme executed at a full-scale plant. The proposed respirometry set-up has been shown to be suitable for a semi-on-line determination of an influent SS which is fully based on the IAWQ #1 vision of the activated sludge process. The YH and the KS play a major role in the principle, and should be measured directly from the process.

scholarly journals Steady State Response of Linear Time Invariant Systems Modeledby Multibond Graphs

2021 ◽  
Vol 11 (4) ◽  
pp. 1717
Author(s):  
Gilberto Gonzalez Avalos ◽  
Noe Barrera Gallegos ◽  
Gerardo Ayala-Jaimes ◽  
Aaron Padilla Garcia
Keyword(s):  
Steady State ◽  
Linear Time ◽  
Direct Determination ◽  
The State ◽  
Steady State Response ◽  
State Variables ◽  
Linear Time Invariant ◽  
State Response ◽  
Time Invariant

The direct determination of the steady state response for linear time invariant (LTI) systems modeled by multibond graphs is presented. Firstly, a multiport junction structure of a multibond graph in an integral causality assignment (MBGI) to get the state space of the system is introduced. By assigning a derivative causality to the multiport storage elements, the multibond graph in a derivative causality (MBGD) is proposed. Based on this MBGD, a theorem to obtain the steady state response is presented. Two case studies to get the steady state of the state variables are applied. Both cases are modeled by multibond graphs, and the symbolic determination of the steady state is obtained. The simulation results using the 20-SIM software are numerically verified.

A State-Space Approach to the Synthesis of Random Vertical and Crosslevel Rail Irregularities

1990 ◽  
Vol 112 (1) ◽  
pp. 83-87 ◽  
Author(s):  
R. H. Fries ◽  
B. M. Coffey
Keyword(s):  
Numerical Simulation ◽  
White Noise ◽  
State Space ◽  
Spectral Characteristics ◽  
The State ◽  
Second Derivatives ◽  
Time Histories ◽  
Sample Interval ◽  
Rail Irregularities ◽  
Derivatives Of

Solution of rail vehicle dynamics models by means of numerical simulation has become more prevalent and more sophisticated in recent years. At the same time, analysts and designers are increasingly interested in the response of vehicles to random rail irregularities. The work described in this paper provides a convenient method to generate random vertical and crosslevel irregularities when their time histories are required as inputs to a numerical simulation. The solution begins with mathematical models of vertical and crosslevel power spectral densities (PSDs) representing PSDs of track classes 4, 5, and 6. The method implements state-space models of shape filters whose frequency response magnitude squared matches the desired PSDs. The shape filters give time histories possessing the proper spectral content when driven by white noise inputs. The state equations are solved directly under the assumption that the white noise inputs are constant between time steps. Thus, the state transition matrix and the forcing matrix are obtained in closed form. Some simulations require not only vertical and crosslevel alignments, but also the first and occasionally the second derivatives of these signals. To accommodate these requirements, the first and second derivatives of the signals are also generated. The responses of the random vertical and crosslevel generators depend upon vehicle speed, sample interval, and track class. They possess the desired PSDs over wide ranges of speed and sample interval. The paper includes a comparison between synthetic and measured spectral characteristics of class 4 track. The agreement is very good.

Use of DNVGL-RP-C203 for Determining the Fatigue Capacity of Connectors

2021 ◽  
Author(s):  
Anthony Muff ◽  
Anders Wormsen ◽  
Torfinn Hørte ◽  
Arne Fjeldstad ◽  
Per Osen ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Testing ◽  
Experimental Testing ◽  
High Strength ◽  
Element Model ◽  
Fatigue Analysis ◽  
Full Scale ◽  
The Finite Element Model

Abstract Guidance for determining a S-N based fatigue capacity (safe life design) for preloaded connectors is included in Section 5.4 of the 2019 edition of DNVGL-RP-C203 (C203-2019). This section includes guidance on the finite element model representation, finite element based fatigue analysis and determination of the connector design fatigue capacity by use of one of the following methods: Method 1 by FEA based fatigue analysis, Method 2 by FEA based fatigue analysis and experimental testing and Method 3 by full-scale connector fatigue testing. The FEA based fatigue analysis makes use of Appendix D.2 in C203-2019 (“S-N curves for high strength steel applications for subsea”). Practical use of Section 5.4 is illustrated with a case study of a fatigue tested wellhead profile connector segment test. Further developments of Section 5.4 of C203-2019 are proposed. This included acceptance criteria for use of a segment test to validate the FEA based fatigue analysis of a full-scale preloaded connector.

Research of the Wood’s Alloy Crystallization Process Using the Acoustic Method

2021 ◽  
Vol 410 ◽  
pp. 855-861
Author(s):  
Aleksandr Yu. Yaroslavkin ◽  
Eugene A. Tyurin ◽  
Darya A. Melnikova
Keyword(s):  
Speed Of Sound ◽  
Crystallization Process ◽  
Ultrasonic Method ◽  
Single Pulse ◽  
Acoustic Method ◽  
The State ◽  
Sound Signal ◽  
Frequency Range ◽  
Wood’S Alloy

The article examines the process of crystallization of Wood alloy using the ultrasonic method. The dependence of the determination of the speed of sound in three aggregate states of the alloy (liquid, solid, transition (liquid-solid)) was derived. The relation-ship with the amplitude values of the sound signal, a single pulse in determining the speed of sound, as well as in determining the state of the alloy is carried out. The data obtained allow us to analyze the state of the alloy and the measurement time and the specified frequency range directly in the process of crystallization.

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