Reliable cavitation testing of ship propulsors requires accurate modelling of the ship wake velocity field. This paper presents a progress report on efforts at the David Taylor Research Center (DTRC) to generate properly shaped velocity patterns in a water tunnel by means of partial length afterbody models. A survey of references is presented on the general topic of applications and techniques of wake simulation in water tunnels using a variety of means, including screens mounted normal to the tunnel stream; partial length (dummy model) hull representations; and full length geometrically scaled hull models. Three recent examples are described in some detail of successful wake-generating bodies designed for experiments conducted in the DTRC 36-inch Variable Pressure Water Tunnel. The wakes of these examples are taken in order of increasing degree of difficulty. In each case, there is a discussion of the target wake, the body design considerations, and the quality of the resultant simulated wake.
{"title":"Simulation of Ship Wakes in Water Tunnel Cavitation Testing of Models","authors":"Michael Wilson","doi":"10.5957/attc-1989-005","DOIUrl":"https://doi.org/10.5957/attc-1989-005","url":null,"abstract":"Reliable cavitation testing of ship propulsors requires accurate modelling of the ship wake velocity field. This paper presents a progress report on efforts at the David Taylor Research Center (DTRC) to generate properly shaped velocity patterns in a water tunnel by means of partial length afterbody models. A survey of references is presented on the general topic of applications and techniques of wake simulation in water tunnels using a variety of means, including screens mounted normal to the tunnel stream; partial length (dummy model) hull representations; and full length geometrically scaled hull models. Three recent examples are described in some detail of successful wake-generating bodies designed for experiments conducted in the DTRC 36-inch Variable Pressure Water Tunnel. The wakes of these examples are taken in order of increasing degree of difficulty. In each case, there is a discussion of the target wake, the body design considerations, and the quality of the resultant simulated wake.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125528105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A practical method for predicting tip vortex cavitation inception of marine propellers is described. Cavitation of tip vortex first occurs when the local pressure inside the vortex reduces to the vapor pressure of the fluid. The minimum pressure in the vortex is reached at the radius of the viscous core. An expression for tip vortex cavitation inception number is derived based on a study of Hsu (1989). with the assumption of power-law circulation distribution. The radius of the viscous core in this approximation depends on the circulation distribution and diffusive action of the fluid viscosity. Accurate determinations of circulation distributions for propellers operating behind ships by purely theoretical means can be quite difficult. In the present paper a calculation procedure for estimating tip vortex cavitation inception number is outlined with the aid of model experimental data. Cavitation experiments of various model propeller in simulated full scale wake were carried out in the David Taylor Research Center 36-inch Variable Pressure Water Tunnel. Experimental data have been extensively analyzed and used for tip vortex cavitation inception predictions. Some comparisons between the present prediction method and ship trial data are made. with results in good agreement.
{"title":"Scaling of Tip Vortex Cavitation Inception","authors":"C. Hsu, K. Remmers","doi":"10.5957/attc-1989-004","DOIUrl":"https://doi.org/10.5957/attc-1989-004","url":null,"abstract":"A practical method for predicting tip vortex cavitation inception of marine propellers is described. Cavitation of tip vortex first occurs when the local pressure inside the vortex reduces to the vapor pressure of the fluid. The minimum pressure in the vortex is reached at the radius of the viscous core. An expression for tip vortex cavitation inception number is derived based on a study of Hsu (1989). with the assumption of power-law circulation distribution.\u0000 The radius of the viscous core in this approximation depends on the circulation distribution and diffusive action of the fluid viscosity.\u0000 Accurate determinations of circulation distributions for propellers operating behind ships by purely theoretical means can be quite difficult. In the present paper a calculation procedure for estimating tip vortex cavitation inception number is outlined with the aid of model experimental data. Cavitation experiments of various model propeller in simulated full scale wake were carried out in the David Taylor Research Center 36-inch Variable Pressure Water Tunnel. Experimental data have been extensively analyzed and used for tip vortex cavitation inception predictions. Some comparisons between the present prediction method and ship trial data are made. with results in good agreement.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"195 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133094771","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A cambered two-dimensional NACA 66 (MOD) wing section was tested in a high speed water tunnel. Two types of cavitation, leading edge sheet and midchord transient streak cavitation, were investigated. Lift, drag and pressure coefficients were measured concurrently with cavitation observations. A method for measuring surface pressure in transient cavities was successfully developed and is discussed in the text. In a partial cavity flow the pressure coefficients measured in the wetted region of the foil away from outside the cavity were found to coincide with the pressure measurements in a fully wetted flow condition. A significant increase in lift with increasing cavity length was measured. However, the lift started to fall off when the cavity length reached about 83 percent of the chord. The occurrence of midchord transient cavities was accompanied by a significant drop in lift and an increase in drag. The influence of surface cavitation on the two dimensional foil force was found to exhibit a strong similarity to propeller thrust breakdown and thrust enhancement as measured by Emerson and Sinclair.
{"title":"The influence of Surface Cavitation on Hydrodynamic Forces","authors":"Young T. Shen, P. Dimotakis","doi":"10.5957/attc-1989-006","DOIUrl":"https://doi.org/10.5957/attc-1989-006","url":null,"abstract":"A cambered two-dimensional NACA 66 (MOD) wing section was tested in a high speed water tunnel. Two types of cavitation, leading edge sheet and midchord transient streak cavitation, were investigated. Lift, drag and pressure coefficients were measured concurrently with cavitation observations. A method for measuring surface pressure in transient cavities was successfully developed and is discussed in the text. In a partial cavity flow the pressure coefficients measured in the wetted region of the foil away from outside the cavity were found to coincide with the pressure measurements in a fully wetted flow condition. A significant increase in lift with increasing cavity length was measured. However, the lift started to fall off when the cavity length reached about 83 percent of the chord. The occurrence of midchord transient cavities was accompanied by a significant drop in lift and an increase in drag. The influence of surface cavitation on the two dimensional foil force was found to exhibit a strong similarity to propeller thrust breakdown and thrust enhancement as measured by Emerson and Sinclair.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133417214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to investigate the character of cavitation inception from rotating rods, a series of experiments were performed in the 5000x450x450 mm test section of the University of Tokyo Propeller Cavitation Tunnel. This paper presents a summary of the experimental design, a comparison of the cavitation patterns for stationary and rotating rods, and the measured noise spectrum. The test results showed that for the smaller Rod I the pattern and noise spectra of the cavitation are similar. In the case of the larger Rods 11 and III, there is some difference in the patterns and corresponding noise levels.
{"title":"Cavitation Inception on Rotating Rods","authors":"R. Latorre","doi":"10.5957/attc-1989-009","DOIUrl":"https://doi.org/10.5957/attc-1989-009","url":null,"abstract":"In order to investigate the character of cavitation inception from rotating rods, a series of experiments were performed in the 5000x450x450 mm test section of the University of Tokyo Propeller Cavitation Tunnel. This paper presents a summary of the experimental design, a comparison of the cavitation patterns for stationary and rotating rods, and the measured noise spectrum. The test results showed that for the smaller Rod I the pattern and noise spectra of the cavitation are similar. In the case of the larger Rods 11 and III, there is some difference in the patterns and corresponding noise levels.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128461812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Presented herein are the results of an exploratory study on the application of chaos theory to continuous-mode ice breaking by a towed model-scale icebreaker hull. The study shows that continuous-mode ice breaking by a towed hull comprises a chaotic-dynamic system of comparatively low dimension. The implications of this result are discussed.
{"title":"Chaotic Dynamics In Continuous Mode Icebreaking","authors":"R. Ettema, M. Sharifi, K. Georgakakos, F. Stern","doi":"10.5957/attc-1989-018","DOIUrl":"https://doi.org/10.5957/attc-1989-018","url":null,"abstract":"Presented herein are the results of an exploratory study on the application of chaos theory to continuous-mode ice breaking by a towed model-scale icebreaker hull. The study shows that continuous-mode ice breaking by a towed hull comprises a chaotic-dynamic system of comparatively low dimension. The implications of this result are discussed.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120945191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In most practical configurations where cavitation occurs, bubbles are not in a uniform or axisymmetric flow field and existing bubble dynamics models, either spherical or axisymmetric, are only more or less appropriate approximations. In this paper we will describe on-going studies which consider the fully three-dimensional bubble dynamics problem. The interaction between a growing, deforming and collapsing bubble near a boundary and/or in a non-uniform flow field is simulated numerically using a Boundary Integral Method. The collapse of a large bubble near a solid flat plate in a gravity field is considered as a first example. The plate orientation relative to the gravity field significantly influences the three-dimensional bubble shape and behavior. Another not previously solved case considered here is the growth and collapse of a bubble in a vortex line flow. The paper presents the method and shows on examples the influence of the various geometric or flow parameters on the bubble dynamics.
{"title":"A Numerical Model for Three-Dimensional Bubble Dynamics in Complex Flow Configurations","authors":"G. Chahine","doi":"10.5957/attc-1989-008","DOIUrl":"https://doi.org/10.5957/attc-1989-008","url":null,"abstract":"In most practical configurations where cavitation occurs, bubbles are not in a uniform or axisymmetric flow field and existing bubble dynamics models, either spherical or axisymmetric, are only more or less appropriate approximations. In this paper we will describe on-going studies which consider the fully three-dimensional bubble dynamics problem. The interaction between a growing, deforming and collapsing bubble near a boundary and/or in a non-uniform flow field is simulated numerically using a Boundary Integral Method. The collapse of a large bubble near a solid flat plate in a gravity field is considered as a first example. The plate orientation relative to the gravity field significantly influences the three-dimensional bubble shape and behavior. Another not previously solved case considered here is the growth and collapse of a bubble in a vortex line flow. The paper presents the method and shows on examples the influence of the various geometric or flow parameters on the bubble dynamics.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121263527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A brief history of the development of model ice is given. For a typical model test, in which the geometric scale factor equals 30, the mechanical properties of all of the different model ices are tabulated, For many of the ices, data have not been published. It is shown that only columnar grained ice can correctly model situations where compression is important. Some current concerns of ice modelling are discussed, but lack of good quality full-scale data makes an objective comparison between model and full-scale difficult.
{"title":"A current view on Sea Ice Modelling","authors":"S. Jones, G. Timco, R. Frederking","doi":"10.5957/attc-1989-014","DOIUrl":"https://doi.org/10.5957/attc-1989-014","url":null,"abstract":"A brief history of the development of model ice is given. For a typical model test, in which the geometric scale factor equals 30, the mechanical properties of all of the different model ices are tabulated, For many of the ices, data have not been published. It is shown that only columnar grained ice can correctly model situations where compression is important. Some current concerns of ice modelling are discussed, but lack of good quality full-scale data makes an objective comparison between model and full-scale difficult.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128501674","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The political situation in the U.S. in these first years of the 19th century was, on a smaller scale, much like subsequent situations, even today. The administration of Thomas Jefferson had trouble with Mediterranean mid-East terrorists working out of Libyia, pirating and taking American hostages. A naval squadron was sent to stabilize the matter. Otherwise, there was much pressure to cut down the defense budget and decommission all but ten active warships… which was done.
{"title":"1800 AD High Speed Marine Vehicles - 1800 AD","authors":"T. Gillmer","doi":"10.5957/attc-1989-013","DOIUrl":"https://doi.org/10.5957/attc-1989-013","url":null,"abstract":"The political situation in the U.S. in these first years of the 19th century was, on a smaller scale, much like subsequent situations, even today. The administration of Thomas Jefferson had trouble with Mediterranean mid-East terrorists working out of Libyia, pirating and taking American hostages. A naval squadron was sent to stabilize the matter. Otherwise, there was much pressure to cut down the defense budget and decommission all but ten active warships… which was done.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133316864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A description of the reasons for the unconservative lack of motion response scaling from model tests in waves of surface effect ships (and other air cushion vehicles) is given. The dominant influence of ambient atmospheric pressure is shown, with results considered in terms of both steady state and transient response characteristics. Special model test procedures that attempt to overcome this problem are discussed, together with a final recommended procedures for use in predicting full scale behavior.
{"title":"Scaling Problem of Dynamic Motions in Waves From Model Tests of Surface Effect Ships and Air Cushion Vehicles","authors":"P. Kaplan","doi":"10.5957/attc-1989-010","DOIUrl":"https://doi.org/10.5957/attc-1989-010","url":null,"abstract":"A description of the reasons for the unconservative lack of motion response scaling from model tests in waves of surface effect ships (and other air cushion vehicles) is given. The dominant influence of ambient atmospheric pressure is shown, with results considered in terms of both steady state and transient response characteristics. Special model test procedures that attempt to overcome this problem are discussed, together with a final recommended procedures for use in predicting full scale behavior.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124779576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
For some time, the experimental testing or model planing hulls in rough water has been done by towing tanks throughout the world. The common goal or all these efforts is to provide designers with information that will give them a better understanding or the effects of hull form on the response to waves -in terms of motions, accelerations, added resistance, loads, and operating conditions. It has become increasingly common to analyze the time series data from these experiments using a peak-trough identification. technique (PKT). Once peaks and troughs are identified, they are sorted and averaged over subsets to obtain averages of the 1/m-th highest statistics - which are the statistics currently used by planing boat designers. There are two problems involved with the current approach, one is conceptual and the other is operational: 1) 1 /m-th highest statistics involve the construction of averages based on the number or oscillations observed, however there are no rules for determining the number or small oscillations to be rejected, consequently, 2) the PKT Method requires subjective input from the user that can affect the statistics. This presentation is a joint effort between the Davidson Laboratory and Naval Academy Hydromechanics Laboratory to inform both designers and other experimentalists about the care that must taken in using the average or the 1/m-th highest statistics and to suggest alternative measures or motion and acceleration response that are objective and easy to understand. It is also hoped that this paper will start a discussion with designers about the specific nature of the hydrodynamic data needed to enable more mission and cost effective boat designs to be produced.
{"title":"Analysis Methods for Evaluating Motions and Accelerations of Planning Boats in Waves","authors":"J. Zseleczky, G. McKee","doi":"10.5957/attc-1989-011","DOIUrl":"https://doi.org/10.5957/attc-1989-011","url":null,"abstract":"For some time, the experimental testing or model planing hulls in rough water has been done by towing tanks throughout the world. The common goal or all these efforts is to provide designers with information that will give them a better understanding or the effects of hull form on the response to waves -in terms of motions, accelerations, added resistance, loads, and operating conditions.\u0000 It has become increasingly common to analyze the time series data from these experiments using a peak-trough identification. technique (PKT). Once peaks and troughs are identified, they are sorted and averaged over subsets to obtain averages of the 1/m-th highest statistics - which are the statistics currently used by planing boat designers.\u0000 There are two problems involved with the current approach, one is conceptual and the other is operational: 1) 1 /m-th highest statistics involve the construction of averages based on the number or oscillations observed, however there are no rules for determining the number or small oscillations to be rejected, consequently, 2) the PKT Method requires subjective input from the user that can affect the statistics.\u0000 This presentation is a joint effort between the Davidson Laboratory and Naval Academy Hydromechanics Laboratory to inform both designers and other experimentalists about the care that must taken in using the average or the 1/m-th highest statistics and to suggest alternative measures or motion and acceleration response that are objective and easy to understand.\u0000 It is also hoped that this paper will start a discussion with designers about the specific nature of the hydrodynamic data needed to enable more mission and cost effective boat designs to be produced.","PeriodicalId":400734,"journal":{"name":"Day 1 Tue, August 08, 1989","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1989-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122013679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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