Resistance of a Ship Undergoing Oscillatory Motion

2010 ◽  
Vol 54 (02) ◽  
pp. 120-132
Author(s):  
Lawrence J. Doctors ◽  
Alexander H. Day ◽  
David Clelland
Keyword(s):  
Finite Depth ◽  
Mean Value ◽  
Wave Resistance ◽  
General Effect ◽  
Towing Tank ◽  
Ship Model ◽  
Average Value ◽  
Unsteady Effects ◽  
Oscillatory Cycle ◽  
Resistance Tests

In this paper, we describe extensions to the research of Doctors et al. (Doctors, L. J., Day, A. H., and Clelland, D., 2008, Unsteady effects during resistance tests on a ship model in a towing tank, Journal of Ship Research, 52, 4, 263–273) and Day et al. (Day, A. H., Clelland, D., and Doctors, L. J., 2009, Unsteady finite-depth effects during resistance tests in a towing tank, Journal of Marine Science and Technology, 14, 3, 387–397) in which the oscillations in the wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model were measured and predicted, in the cases of relatively deep and relatively shallow water. In the current study, the ship model was towed with a harmonic velocity component superimposed on the usual constant forward velocity. This work constitutes a first step in the understanding of the unsteady hydrodynamics of a racing shell (rowing boat). We show here that the unsteady wave resistance varies considerably from the traditional (steady) average value. Indeed, the wave resistance is frequently negative during part of the oscillatory cycle. However, the general effect is an increase in the temporal mean value of the wave resistance; this suggests that every effort should be made to reduce the unsteadiness of the motion. We also demonstrate that the unsteady wave-resistance theory provides an excellent prediction of the measured effects summarized here. These predictions are often within a few percent of the measured values of the resistance.

scholarly journals Unsteady Effects During Resistance Tests on a Ship Model in a Towing Tank

2008 ◽  
Vol 52 (04) ◽  
pp. 263-273
Author(s):  
Lawrence J. Doctors ◽  
Alexander H. Day ◽  
David Clelland
Keyword(s):  
Wave Resistance ◽  
Excellent Correlation ◽  
Experiment Data ◽  
Towing Tank ◽  
Ship Model ◽  
History Of ◽  
Rate Of Decay ◽  
Unsteady Effects ◽  
Velocity History ◽  
Resistance Tests

It is known that there are oscillations in the wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model. In this work, the unsteady thin-ship resistance theory has been applied to this case. The results have been compared with experiment data obtained using a towing carriage the velocity history of which can be programmed. It is demonstrated here that generally excellent correlation exists between the theory and the experiments. In particular, one can predict the influence of Froude number, rate of acceleration, and type of smoothing of the acceleration on the characteristics of the oscillations. These characteristics include the amplitude, rate of decay, frequency, and phasing of the oscillations in the curve of wave resistance versus time.

Unsteady finite-depth effects during resistance tests on a ship model in a towing tank

2009 ◽  
Vol 14 (3) ◽  
pp. 387-397 ◽  
Author(s):  
Alexander H. Day ◽  
David Clelland ◽  
Lawrence J. Doctors
Keyword(s):  
Finite Depth ◽  
Towing Tank ◽  
Ship Model ◽  
Resistance Tests ◽  
Depth Effects

Unsteady Wave-Making Resistance of an Accelerating Ship

2020 ◽  
Author(s):  
Mingxin Li ◽  
Zhi-Ming Yuan ◽  
Ronald W. Yeung
Keyword(s):  
Surface Condition ◽  
Oscillation Amplitude ◽  
Solution Procedure ◽  
Wave Resistance ◽  
Boundary Integral ◽  
Ship Model ◽  
Implicit Finite Difference ◽  
Force Components ◽  
Unsteady Effects ◽  
Nonlinear Free Surface

Abstract To measure the resistance of a ship in a towing tank, the target speed of the ship model is achieved by towing the model from the rest at a given acceleration imposed by the carriage. The fluctuations in resistance are generated because of the impulse effects during rapid acceleration. Such acceleration effects in deep water have been studied by previous works [1–3]. In shallow water, the unsteady effects are expected to be stronger, making the fluctuating resistance persisting longer. In order to predict the unsteady waves and to estimate the unsteady oscillating components in the wave resistance, a numerical method based on 3D unsteady potential-flow theory was developed. An implicit finite-difference algorithm coupled with an iterative boundary integral-equation solution procedure was used to deal with the unsteady linear and nonlinear free-surface condition. The results showed that both the acceleration intensity and water depth have a significant effect on the oscillation amplitude of the unsteady wave resistance as well as other force components. Findings of these computations and comparative evaluation of experimental observation are made where relevant. The findings in the present work can be applied to provide guidance for using the appropriate settings, e.g., magnitude and duration of carriage acceleration, when conducting ship-model resistance tests.

Optimal Ship Forms for Minimum Wave Resistance

1981 ◽  
Vol 25 (02) ◽  
pp. 95-116
Author(s):  
Chi-Chao Hsiung
Keyword(s):  
Linear Inequality ◽  
Inequality Constraints ◽  
Wave Resistance ◽  
Ship Hull ◽  
Towing Tank ◽  
Ship Model ◽  
Linear Inequality Constraints ◽  
Merchant Ship ◽  
Programming Techniques ◽  
Hull Forms

By introducing a set of "tent" functions to approximate the ship hull function, the Michell integral for wave resistance is reduced to a standard quadratic form in terms of ship offsets. With linear-inequality constraints of the type 0 ≤ H(x, z) ≤ B;C ≤ Hx(x,z) ≤ D(where H(x,z) is the hull function and B, C, D are constants), we are able to find various optimal ship forms of minimum wave resistance by applying quadratic programming techniques to the problem. Three optimal forms have been chosen among a number of computed results for tests in the ship-model towing tank. All three models have afterbodies identical with that of Series 60, Block 60, a standard merchant ship hull of good quality. Although the experimentally determined residuary resistance is in no better agreement with the theoretically predicted results than is usual in such comparisons, the order of "goodness" of the hull-forms as predicted and as measured was the same for Fn ≥ 0.36 and also for 0.20 ≤ Fn ≤ 0.26.

scholarly journals Thinner Sea Ice Contribution to the Remarkable Polynya Formation North of Greenland in August 2018

2021 ◽  
Author(s):  
Xiaoyi Shen ◽  
Chang-Qing Ke ◽  
Bin Cheng ◽  
Wentao Xia ◽  
Mengmeng Li ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
Reanalysis Data ◽  
Mean Value ◽  
Ocean Model ◽  
North Coast ◽  
Average Value ◽  
The North ◽  
Wind Sea ◽  
The One

AbstractIn August 2018, a remarkable polynya was observed off the north coast of Greenland, a perennial ice zone where thick sea ice cover persists. In order to investigate the formation process of this polynya, satellite observations, a coupled ice-ocean model, ocean profiling data, and atmosphere reanalysis data were applied. We found that the thinnest sea ice cover in August since 1978 (mean value of 1.1 m, compared to the average value of 2.8 m during 1978–2017) and the modest southerly wind caused by a positive North Atlantic Oscillation (mean value of 0.82, compared to the climatological value of −0.02) were responsible for the formation and maintenance of this polynya. The opening mechanism of this polynya differs from the one formed in February 2018 in the same area caused by persistent anomalously high wind. Sea ice drift patterns have become more responsive to the atmospheric forcing due to thinning of sea ice cover in this region.

Experimental Study of a Tanker Ship Squat in Shallow Water

2014 ◽  
Vol 66 (2) ◽  
Author(s):  
Mohammadreza Fathi Kazerooni ◽  
Mohammad Saeed Seif
Keyword(s):  
Experimental Study ◽  
Shallow Water ◽  
Experimental Approach ◽  
Model Tests ◽  
Ship Hull ◽  
Experimental Results ◽  
Shallow Waters ◽  
Towing Tank ◽  
Ship Model

One of the phenomena restricting the tanker navigation in shallow waters is reduction of under keel clearance in the terms of sinkage and dynamic trim that is called squatting. According to the complexity of flow around ship hull, one of the best methods to predict the ship squat is experimental approach based on model tests in the towing tank. In this study model tests for tanker ship model had been held in the towing tank and squat of the model are measured and analyzed. Based on experimental results suitable formulae for prediction of these types of ship squat in fairways are obtained.

scholarly journals Resistance reduction on trimaran ship model by biopolymer of eel slime

2015 ◽  
Vol 12 (2) ◽  
pp. 95-102
Author(s):  
Y. Yanuar ◽  
G. Gunawan ◽  
M. A. Talahatu ◽  
R. T. Indrawati ◽  
A. Jamaluddin
Keyword(s):  
Drag Reduction ◽  
Frictional Resistance ◽  
Skin Surface ◽  
Fish Skin ◽  
Total Drag ◽  
Towing Tank ◽  
Ship Model ◽  
Resistance Reduction ◽  
Towing Tank Test ◽  
Tank Test

Resistance reduction in ship becomes an important issue to be investigated. Energy consumption and its efficiency are related toward drag reduction. Drag reduction in fluid flow can be obtained by providing polymer additives, coating, surfactants, fiber and special roughness on the surface hull. Fish skin surface coated with biopolymers viscous fluid (slime) is one method in frictional resistance reduction. The aim of this is to understanding the effect of drag reduction using eel slime biopolymer in unsymmetrical trimaran ship model. The Investigation was conducted using towing tank test with variation of velocity. The dimension of trimaran model are L = 2 m, B = 0.20 m and T = 0.065 m. The ship model resistance was precisely measured by a load cell transducer. The comparison of resistance on trimaran ship model coated and uncoated by eel slime are shown on the graph as a function of the total drag coefficient and Froude number. It is discovered the trimaran ship model by eel slime has higher drag reduction compared to trimaran with no eel slime at similar displacement. The result shows the drag reduction about 11 % at Fr 0.35.

scholarly journals Mandibular Morphology Differences Between Edentulous And Dentate Assessed By Panoramic Radiographs

2017 ◽  
Vol 16 (2) ◽  
Author(s):  
Lidya Irani Nainggolan ◽  
Aude Layakni Girsang
Keyword(s):  
Panoramic Radiography ◽  
Mechanical Stimulus ◽  
Mean Value ◽  
Notch Depth ◽  
Cross Sectional ◽  
Gonial Angle ◽  
Average Value ◽  
Mandibular Morphology ◽  
Edentulous Patients ◽  
Ramus Height

Introduction: Facial profile can be influenced by edentulous condition that can change mandibular morphology that can affect mastication, digestion and psychosocial life. Edentulism causes absence of occlusal mechanical stimulus, decrease the activity of mastication muscles and increase mandibular bone resorption. These changes can be assessed using panoramic radiography by looking at the vertical dimension of the head of the condyle and its shape, ramus, and the angle of the mandible. The aim of the study was to assess the mean value and differences of mandibular morphology in edentulous and dentate patients using panoramic radiography. Materials and Methods: This was an analytical study with cross-sectional approach using purposive sampling methods. 50 dentate and edentulous patients who came to Dentistry Hospital of University of Sumatera Utara were used as sample. Data analysis was done using Independent T test and MannWhitney test. Results: Results showed that the average value of gonial angle, ramus height, condylar height, antegonial notch depth and ramus notch depth in edentulous patients were 125,38 ± 9,51; 35.98mm ± 4.26; 5.58mm ± 0.90; 2.11mm ± 1.04; and 2.73mm ± 0, 88, and the results showed that the average value of mandibular morphology in dentate patients were 123.34 ± 7.07; 38.15mm ± 3.23; 6.95mm ± 1.25; 1.41mm ± 0.77; and 2.15mm ± 0.59. Conclusion(s): There were significant differences in the values of ramus height, condylar height, antegonial notch depth, and ramus notch depth. Difference was also found in gonial angle value, but was not statistically significant.

scholarly journals Pengembangan LKPD Tema Tanah Airku Sub Tema Kota Palembang untuk Anak Kelompok B

2019 ◽  
Vol 1 (2) ◽  
pp. 129-141
Author(s):  
Gustiana Yuantini ◽  
Hasmalena Hasmalena ◽  
Syafdaningsih Syafdaningsih
Keyword(s):  
Small Group ◽  
Mean Value ◽  
Average Score ◽  
Self Evaluation ◽  
Average Value ◽  
Expert Review ◽  
Group Evaluation ◽  
Observation Methods ◽  
Evaluation Stage ◽  
Group B

This research aims to develop valid and practical student worksheet. Subjects in this research were B2 and B3 groups in state kindergarten of Pembina 2 Palembang. The model developed in this development was Rowntree consisting of One to one evaluation and small group evaluation. It was aimed to see the practicality and it used the Tessmer evaluation stage which consisted of self evaluation, expert review. Data collection techniques used in this research were interview, walkthrough and observation methods. According to the results of the research, it showed that the validity of the material and design obtained an average value of 3.77 in very valid categories. Student worksheet practicality test in terms of observations with a mean value of 95% in very practical category. The small group evaluation stage obtained an average score of 92% in the very practical category. Questionnaire result was 97% in valid category. From the result, it can be concluded that student worksheet theme of my homeland and sub-theme of Palembang city for group B children is valid and practical. It is also worth to use as learning student worksheet with Theme of my homeland

scholarly journals Pengaruh Model Pembelajaran Problem Based Learning pada Materi Hukum-Hukum Dasar Kimia terhadap Hasil Belajar Siswa Kelas X MAN 2 Model Palu

2018 ◽  
Vol 7 (3) ◽  
pp. 102
Author(s):  
Tri Sulistiyawati Lamalat ◽  
Supriadi Supriadi ◽  
Siti Nuryanti
Keyword(s):  
Statistical Analysis ◽  
Learning Outcomes ◽  
Problem Based Learning ◽  
Sampling Technique ◽  
Learning Model ◽  
Mean Value ◽  
Control Group ◽  
Control Group Design ◽  
Average Value ◽  
Quasi Experimental

Research on the effect of the problem-based learning model in the basic laws of chemistry on student’s learning outcomes in class X MAN 2 Model Palu has been done. This study aimed to determine the effect of the application of the problem-based learning model in the basic laws of chemistry on student’s learning outcomes in class X MAN 2 Model Palu. The type of research was a quasi-experimental study non-randomized design with pretest-posttest control group design. The sample was conducted with a purposive sampling technique. The study sample was students in class X MIA 6 as an experimental group (n = 22) and students in class X MIA 3 as a control group (n = 22). The data testing of students' learning outcomes used a non-parametric statistical analysis, the analysis of Mann-Whitney U-Test. The research results indicated that the mean value of the experiment class was high compared to the control class, 22.61 >18.39. The statistical analysis obtained that sig. 2-tailed (0,032) ˂ 0.05 and Zcalculation (-2.149) ˂ Ztable (-1.96). The average value of the experiment class was 82.95 while the average value of the control class was 73.64. So it can be concluded that there is the effect of applying the problem-based learning model in the basic laws of chemistry on student’s learning outcomes. 

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