Hybridization of Theory and Experiment in Optimizing Di-Hull Configuration With Respect to Wave Resistance

2017 ◽  
Author(s):  
Dongchi Yu ◽  
Ronald W. Yeung
Keyword(s):  
Wave Spectrum ◽  
Wave Resistance ◽  
Fast Method ◽  
Interference Effects ◽  
Hybridization Procedure ◽  
Cut Method ◽  
Interference Wave ◽  
Analytical Expressions ◽  
Theory And Experiments ◽  
Theory And Experiment

A fast method for optimizing the configuration of a di-hull system is to take advantage of the wave-cut signatures of each hull and evaluate the combined resistance of the hull system using analytical expressions that portray the interference effects of the hull-generated waves. This interference formula is available in Yeung et al. [1] and can be used in conjunction with the wave-cut signatures. The Longitudinal Wave-cut Method (LCM) is utilized to acquire the wave-making spectrum for each monohull. Then the di-hull interference wave resistance is deduced by substituting these experimentally-acquired information into analytical expressions for resistance computation. The pre-acquired wave-spectrum information can be stored and used for a combination of any component hulls, identical or not. This hybridization procedure of theory and experiments is tested and evaluated. Its merits and deficiencies are discussed.

Response-Based Estimation of Sea State Parameters

2007 ◽  
Author(s):  
Ulrik D. Nielsen
Keyword(s):  
Closed Form ◽  
Energy Content ◽  
Wave Spectrum ◽  
Final Outcome ◽  
Bayesian Modelling ◽  
Sea State ◽  
Safe Navigation ◽  
Wave Radar ◽  
Frequency Components ◽  
Analytical Expressions

Reliable estimation of the on-site sea state parameters is essential to decision support systems for safe navigation of ships. The sea state parameters can be estimated by Bayesian Modelling which uses complex-valued frequency response functions (FRF) to estimate the wave spectrum on the basis of measured ship responses. It is therefore interesting to investigate how the filtering aspect, introduced by FRF, affects the final outcome of the estimation procedures. The paper contains a study based on numerical generated time series, and the study shows that filtering has an influence on the estimations, since high frequency components of the wave excitations are not estimated as accurately as lower frequency components. Moreover, the paper investigates how the final outcome of the Bayesian Modelling is influenced by the accuracy of the FRF. Thus, full-scale data is analysed by use of FRF calculated by a 3-D time domain code and by closed-form (analytical) expressions, respectively. Based on comparisons with wave radar measurements and satellite measurements it is seen that the wave estimations based on closed-form expressions exhibit a reasonable energy content, but the distribution of energy appears to be incorrect.

scholarly journals CASIMIR EFFECT: THEORY AND EXPERIMENTS

2012 ◽  
Vol 14 ◽  
pp. 171-180
Author(s):  
ASTRID LAMBRECHT ◽  
SERGE REYNAUD
Keyword(s):  
Casimir Effect ◽  
Thermal Fluctuations ◽  
Current Status ◽  
Quantum Field ◽  
Fundamental Physics ◽  
Open Questions ◽  
Effect Theory ◽  
Theory And Experiments ◽  
Theory And Experiment ◽  
The Ideal

The Casimir effect is a crucial prediction of Quantum Field Theory which has fascinating connections with open questions in fundamental physics. The ideal formula written by Casimir does not describe real experiments and it has to be generalized by taking into account the effects of imperfect reflection, thermal fluctuations, geometry as well as the corrections coming from surface physics. We discuss these developments in Casimir physics and give the current status in the comparison between theory and experiment after years of improvements in measurements as well as theory.

Calculations of Spin-Wave Energy Gap in Transition Metals

1991 ◽  
Vol 253 ◽  
Author(s):  
V.P. Antropov ◽  
A.I. Liechtenstein
Keyword(s):  
Spin Wave ◽  
Scattering Theory ◽  
Density Functional ◽  
Energy Gap ◽  
Theoretical Calculations ◽  
Wave Spectrum ◽  
Functional Approach ◽  
Stiffness Constant ◽  
Analytical Expressions ◽  
Spin Wave Spectrum

ABSTRACTAnalytical expressions for the total energy derivative with respect to the magnetic moment rotations have been derived in the relativistic local-spin density functional approach and multiple scattering theory. The spin-wave stiffness constant as well as the gap in the spin-wave spectrum due to relativistic anisotropy effects is calculated in KKR-ASA approximation for bcc Fe. This is compared with other theoretical calculations and available experimental data.

Theory and Experiment Study on Laser Self-Mixing Interference with Multiway Feedback External Cavity

2017 ◽  
Vol 870 ◽  
pp. 47-52
Author(s):  
Yu Zhang ◽  
Hai Huan ◽  
Dong Dong Xu ◽  
Ling Xiao Huang ◽  
Song Lu
Keyword(s):  
Phase Modulation ◽  
External Cavity ◽  
Low Frequency ◽  
The Self ◽  
Interference Signal ◽  
Experiment Study ◽  
Experiment System ◽  
Cavity Structure ◽  
Interference Wave ◽  
Theory And Experiment

The self-mixing interference (SMI) effect with multiway feedback is analyzed in this paper. The basic theory of SMI with multiway feedback external cavity (MFEC) can be derived from the theory of interference as well as the theory of laser self-mixing interference (LSMI). Based on the external cavity structure with MFEC, a SMI model with two feedback external cavity structure is proposed. The expressions of the phase and output power in the MFEC are deduced and some simulation analyses are made. It is found that the output signal of the SMI system with two external cavity is sinusoidal or sawtooth waves, which is similar to the signal of SMI with a low frequency sinusoidal phase modulation. The density of interference signal fringes is uneven in one period and the shape of the interference wave is determined by the intensity of the external feedback. Furthermore, a SMI with two feedback external cavity experiment system is considered, and the experiment verifies the simulations.

scholarly journals Wave resistance: the effect of varying draught

1925 ◽  
Vol 108 (748) ◽  
pp. 582-591 ◽  
Keyword(s):  
Wave Resistance ◽  
Plane Section ◽  
Experimental Results ◽  
Interference Effects ◽  
Different Types ◽  
Order Of Magnitude ◽  
The Right ◽  
Right Order ◽  
Considerable Range ◽  
Simplified Form

1, In previous studies in the theory of wave resistance, while the water-plane section of the model was of a reasonably ship-like form, the draught was assumed to be infinite. In the following paper the model has the same simple lines and has vertical sides, but the draught is finite. The investigation shows how the resistance at different speeds depends on the draught, but it was undertaken specially for other reasons. In view of certain applications, it was important to find how the interference effects due to bow and stern waves are affected by varying draught. It is shown now that these become less prominent with diminishing draught, but the maxima and minima occur at practically the same positions. Further, when the ratio of draught to length is of the order of the values in actual ship models, one is in a position to attempt a comparison between the absolute values of theoretical and experimental results. Curves are shown in fig. 2 (p. 590) for the variation of resistance with velocity in three cases—when the draught is infinite, and when it is one-tenth and one-twentieth of the length of the model. The latter values cover approximately the usual ratios in practice. On the same diagram are reproduced experimental curves for three models of different types, the data being reduced to the same non-dimensional co-ordinates. Making allowance for the differences of form between these models and for the simplified form for which the calculations have been made, the results show that the calculated values are of the right order of magnitude over a considerable range of velocity. Differences in the two sets of curves, such as the greater prominence of interference effects in the theoretical curves, are discussed.

Plowing Friction in Dry and Lubricated Metal Sliding

1986 ◽  
Vol 108 (3) ◽  
pp. 301-312 ◽  
Author(s):  
K. Komvopoulos ◽  
N. Saka ◽  
N. P. Suh
Keyword(s):  
Plastic Deformation ◽  
Friction Coefficient ◽  
Coefficient Of Friction ◽  
Interfacial Friction ◽  
Dry Sliding ◽  
The Coefficient Of Friction ◽  
Analytical Expressions ◽  
Cutting Experiments ◽  
Theory And Experiment ◽  
Lubricated Sliding

Experimental evidence for plowing under dry and lubricated sliding conditions is presented and analytical expressions for the coefficient of friction due to plowing are obtained. The theoretical friction coefficient was found to be a function of the sharpness of the hard asperities, the interfacial “friction” conditions and the shape of the plastic zone. The agreement between theoretical and experimental friction coefficients from lubricated sliding and cutting experiments was remarkably good. The discrepancy between theory and experiment in the case of dry sliding between like metals was shown to be due to plastic deformation of the asperities. Consequently, a different model for plowing was proposed for the case of dry sliding between like metals which produced estimates for the coefficient of friction in fair agreement with the experimental results.

scholarly journals Analytical expressions for electrodynamic parameters of the shielded microstrip line

2021 ◽  
Vol 9 (4) ◽  
pp. 68-76
Author(s):  
A. N. Kovalenko ◽  
A. D. Yarlykov
Keyword(s):  
Mathematical Model ◽  
Power Series ◽  
Projection Method ◽  
Microstrip Line ◽  
Wave Resistance ◽  
Strip Conductor ◽  
Static Approximation ◽  
Quasi Static Approximation ◽  
Wide Range ◽  
Analytical Expressions

On the basis of an electrodynamic model of a screened microstrip line, built on the basis of the projection method using the Chebyshev basis, which explicitly takes into account the edge features of the field, a mathematical model of a microstrip line with a strip conductor was developed. The line width does not exceed the height of the substrate. In this case, the current density on the strip conductor is approximated by only one basis function. Analytical expressions are presented in the form of a sum of slowly and rapidly converging series to determine the main electrodynamic parameters of the line – wave resistance and deceleration coefficient. Due to logarithmic features, slowly converging series are summed up and transformed into rapidly converging power series. In addition, limit expressions in the form of improper integrals are given for the main electrodynamic parameters of an open microstrip line in the quasi-static approximation. Due to the logarithmic features, these integrals are also converted to rapidly converging power series. As a result, simple approximate formulas were obtained. They allow calculating the deceleration coefficient and wave impedance of the line with an error not exceeding 1%, when the width of the strip conductor is less than twice the thickness of the substrate. The results of calculating the electrodynamic parameters obtained on the basis of the developed mathematical model and on the basis of the projection method with an accuracy of up to 5 significant digits are presented. These results make it possible to establish the limits of applicability of the quasi-static approximation and to determine the error in calculating the deceleration coefficient and wave resistance using the obtained analytical expressions. The error does not exceed 0.1%, if the width of the strip conductor is less than twice the thickness of the substrate in a wide range of changes in the substrate dielectric constant and frequency.

Wave Pattern Measurements Using a Half-Ship Model

1977 ◽  
Vol 21 (03) ◽  
pp. 148-156
Author(s):  
Gerald E. Bellows
Keyword(s):  
High Speed ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Ship Model ◽  
Cut Method ◽  
Hull Forms

This report describes an investigation of the wave pattern of a half-ship model. Using a 5-ft (1.6 m) ship model that has been cut in half along the vertical centerline plane and by towing this half model very close to one wall of the model tank, a wave pattern corresponding to that produced on one side of a symmetric ship model is obtained. The longitudinal-cut method is used to measure the wave pattern. Comparisons of the wave resistance of the half model and whole model are given. It is apparent from these that the results are in agreement for distances from the wall of less than 3 in. (76 mm). These results show that the length of a longitudinal cut before reflection occurs can be doubled by using this procedure rather than towing a conventional ship model in the center of the tank. This is especially useful for tests of high-speed hull forms.

Michell Investigation of the Significant Influence on the Hydrodynamic of a Warp-Chine Pentamaran

2020 ◽  
Vol 36 (03) ◽  
pp. 202-212
Author(s):  
W. Sulistyawati ◽  
_ Yanuar ◽  
A. S. Pamitran
Keyword(s):  
Wave Pattern ◽  
Wave Resistance ◽  
Numerical Calculations ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Towing Tank ◽  
Wave Interference ◽  
Interference Wave ◽  
Cfd Analyses ◽  
Field Wave

This study attempted to investigate the hydrodynamic performance of various pentamaran configurations with a focus on the interference flow around the component hulls. A computer simulation was conducted based on Michell’s thin ship theory alongside a commercial CFD computation as a comparison. Experiments in the towing tank were performed to validate the numerical calculations, resulting in some hydrodynamic characteristics on the far-field wave pattern, wave interference, wave resistance, and total resistance. Analyses on both transversal and divergent waves were performed to assess the magnitude of wave resistance occurring due to the placement of the side hull to the main hull. Analyses on both waves were also conducted to assess the magnitude of wave resistance due to the placement of outriggers. Looking at the results, numerical calculations based on Michell’s theory were in parallel with experimental data, particularly at Fn greater than .4. Michell’s theory was observed as doing a little preferable agreement with the results of experiments than CFD. Besides, flow patterns obtained numerically from Michell’s and CFD analyses appeared as identical to photographs observed in a towing tank. This investigation identified that a configuration with aligning placement of the main to side hull on the formation of arrow tri-hull, near the Kelvin angle, would cancel the wave formed by the leading hull and can be used as a practical setting to reduce the total wave resistance.

On the Effect of Non-Linear Boundary Conditions on the Wave Disturbance and Hydrodynamic Forces of Underwater Vehicles Travelling Near the Free-Surface

2020 ◽  
Author(s):  
William Lambert ◽  
Stefano Brizzolara
Keyword(s):  
Free Surface ◽  
Analytical Solution ◽  
Boundary Conditions ◽  
Energy Content ◽  
Wave Spectrum ◽  
Hydrodynamic Forces ◽  
Wave Resistance ◽  
Wave Disturbance ◽  
Surface Boundary ◽  
Non Linear

Abstract This study compares the effect of non-linear free-surface boundary conditions for a high-order non-linear free-surface Rankine-source boundary element method on wave disturbance and hydrodynamic forces acting on an underwater vehicle travelling near a calm free-surface. In particular, simulations for a steady nonaxisymmetric prolate spheroid using different basis flows and linearization techniques were compared to an analytical method achieved by Chatjigeorgiou using a multipole expansion of Green’s functions. It appears that at low Froude numbers, the basis flow used in the formulation contributes significantly to differences in the steady solutions for wave resistance and pitch, whereas for higher Froude numbers the linearization technique becomes a more defining feature. Upon observation of the analytical solution for wave resistance, one can see that it was formed under a Neumann-Kelvin formulation and this is supported by the Neumann-Kelvin simulations converging well to the analytical solution. Further comparisons were made using a wave directional energy spectrum gathered from transverse wave cuts of the free wave pattern. The spectral analysis allows for a higher level of comparison between all of the different cases, establishing a direct relation between the change in wave resistance and the energy content variation of the particular wave spectrum components.

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