| 1. |
- Bohman, Hannes, 1965-, et al.
(author)
-
Thicker carotid intima layer, thinner media layer and higher intima/media ratio in women with recurrent depressive disorders : a pilot study using non-invasive high frequency ultrasound
- 2010
-
In: World Journal of Biological Psychiatry. - : Informa Healthcare. - 1562-2975 .- 1814-1412. ; 11:1, s. 71-75
-
Journal article (peer-reviewed)abstract
- Background. Growing evidence indicates that depression is an important risk factor for coronary heart disease. Thus, the aim of the present study has been to investigate if young women with adolescent onset and recurrent depressive disorders have signs of carotid intima and media changes already at the age of 30. Methods. Fifteen subjects with adolescent onset recurrent depressive disorders, mean age 31.5 years, were compared to 20 healthy women with a mean age of 39.6 years. The thickness of carotid artery intima and media was assessed, using non-invasive high-frequency ultrasound (25MHz). Results. The subjects with recurrent depressive disorders had significantly thicker carotid intima, significantly thinner carotid media and significantly higher intima/media ratio despite the fact that they were about 10 years younger than the healthy women. Hypertension, obesity or smoking could not explain the results. Conclusion. Already at the age of 30, subjects with recurrent depressive disorders with adolescent onset do have early signs of carotid intima and media changes, indicating a less healthy artery wall, despite otherwise no clinical signs of cardiovascular disease.
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| 2. |
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| 3. |
- Larsson, Bengt, et al.
(author)
-
Molecular oxygen in the rho Ophiuchi cloud
- 2007
-
In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 466:3, s. 5-
-
Journal article (peer-reviewed)abstract
- Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission.Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs.Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz.Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org
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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Allroth, Jens, 1984, et al.
(author)
-
Sailing Yacht Transom Sterns-a Systematic CFD Investigation
- 2015
-
In: Proceedings, 5th High Performance Yacht Design Conference, Auckland, 8-11 March 2015. - 9781909024373 ; , s. 257-266
-
Conference paper (peer-reviewed)abstract
- The question adressed in this project is whether modern hull lines with wide, box-shaped transoms, that seem to originate from extreme racing machines, are also beneficial for modern performance cruisers from a hydrodynamic performance point of view. A new 41 ft (12.3 m) hull was designed as an average of contemporary performance hulls in the 40 ft segment. The aft part of the hull was stretched stepwise and cut at constant length overall in order to systematically increase the transom size. Six hull variations with box shaped transoms were created in this way. To investigate the influence of the transom shape, the six hull variants were redesigned with a more rounded transom. The resistance was calculated for all twelve hulls in the upright and heeled conditions at Froude numbers 0.35 and 0.60. The computations were carried out using a Reynolds-Averaged Navier-Stokes (RANS) solver with a Volume of Fluid (VOF) representation of the free surface. The solver was validated against several hulls in the Delft Systematic Yacht Hull Series (DSYHS). Very different optima are found for the low and high speed cases. In an upwind-downwind race the round transoms performed best for the three fastest transom sizes. The fastest hull around the course has an immersed transom area to midship area ratio of 0.16 and it has a rounded shape. It is 1.9 % faster than a more box like transom. Overall the round transoms are faster around the race course.
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| 8. |
- Andersson, Anton, et al.
(author)
-
Design of a Foiling Optimist
- 2018
-
In: Journal of Sailboat Technology. ; 2018, s. 1-24
-
Journal article (peer-reviewed)abstract
- Because of the successful application of hydrofoils on the America's Cup catamarans in the past two campaigns the interest in foiling sailing craft has boosted. Foils have been fitted to a large number of yachts with great success, ranging from dinghies to ocean racers. An interesting question is whether one of the slowest racing boats in the world, the Optimist dinghy, can foil, and if so, at what minimum wind speed. The present paper presents a comprehensive design campaign to answer the two questions. The campaign includes a newly developed Velocity Prediction Program (VPP) for foiling/non-foiling conditions, a wind tunnel test of sail aerodynamics, a towing tank test of hull hydrodynamics and a large number of numerical predictions of foil characteristics. An optimum foil configuration is developed and towing tank tested with satisfactory results. The final proof of the concept is a successful on the water test with stable foiling at a speed of 12 knots.
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| 9. |
- Andersson, A, et al.
(author)
-
The Foiling Optimist
- 2017
-
In: The Proceedings of the 4th International Conference on Innovation in High Performance Sailing Yachts, Lorient, France, 28-30 June 2017.. ; , s. 19-30
-
Conference paper (peer-reviewed)
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| 10. |
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| 11. |
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| 12. |
- Bonitz, Sabine, 1985, et al.
(author)
-
Experimental Investigation of the Near Wall Flow Downstream of a Passenger Car Wheel Arch
- 2018
-
In: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 11:1, s. 22-34
-
Journal article (peer-reviewed)abstract
- The flow around and downstream of the front wheels of passenger cars is highly complex and characterized by flow structure interactions between the external flow, fluid exiting through the wheelhouse, flow from the engine bay and the underbody. In the present paper the near wall flow downstream of the front wheel house is analyzed, combining two traditional methods. A tuft visualization method is used to obtain the limiting streamline pattern and information about the near wall flow direction. Additionally, time resolved surface pressure measurements are used to study the pressure distribution and the standard deviation. The propagation of the occurring flow structures is investigated by cross correlations of the pressure signal and a spectral analysis provides the characteristic frequencies of the investigated flow. It is found that two main flow phenomena can be observed: one originates from flow exiting the upper wheelhouse and a second one resulting from a separation on the lower wheel house edge. The frequency spectrum reveals a dominant Strouhal number of 0.2. As the observed flow structures are attributed to the wheel-wheelhouse interaction, a closed wheelhouse configuration is also investigated and the results confirm that the fluctuations and observed flow structures are created by the flow interaction between the wheel, wheelhouse and the rotation of the wheel.
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| 13. |
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| 14. |
- Bonitz, Sabine, 1985, et al.
(author)
-
Investigation of three-dimensional flow separation patterns and surface pressure gradients on a notchback vehicle
- 2014
-
In: Imeche (Hg.) 2014 – International vehicle aerodynamics conference. - 9780081001998 ; , s. 55-65
-
Conference paper (peer-reviewed)abstract
- One main goal in the aerodynamic development of passenger vehicles is reducedfuel consumption. As vehicles are bluff bodies, drag is dominated by pressure drag,which is mainly caused by detached flow. To enable further reductions of the drag,it is of great importance to understand the physical phenomena behind separation.In this paper the influence of surface pressure gradients on the flow pattern of afull-scale passenger vehicle is investigated. The objective is threefold: i) Presentthe flow pattern on upper parts of the vehicle, ii) discuss the pressure gradientsaround selected areas and iii) link separation with the pressure field.
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| 15. |
- Bonitz, Sabine, 1985, et al.
(author)
-
Numerical investigation of crossflow separation on the a-pillar of a passenger car
- 2018
-
In: Journal of Fluids Engineering, Transactions of the ASME. - : ASME International. - 1528-901X .- 0098-2202. ; 140:11
-
Journal article (peer-reviewed)abstract
- The flow around passenger cars is characterized by many different separation structures, typically leading to vortices and areas of reversed flow. The flow phenomena in these patches show a strong interaction and the evolution of flow structures is difficult to understand from a physical point of view. Analyzing surface properties, such as pressure, vorticity, or shear stress, helps to identify different phenomena, but still it is not well understood how these are created. This paper investigates the crossflow separation (CFS) on the A-pillar of a passenger car using numerical simulations. It is discussed how the CFS and the resulting A-pillar vortex can be identified as well as how it is created. Additionally, the vortex strength is determined by its circulation to understand and discuss how the vortex preserves until it merges with the rear wake of the vehicle.
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| 16. |
- Bonitz, Sabine, 1985, et al.
(author)
-
Structures of Flow Separation on a Passenger Car
- 2015
-
In: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 8:1, s. 177-185
-
Journal article (peer-reviewed)abstract
- The phenomenon of three-dimensional flow separation is and has been in the focus of many researchers. An improved understanding of the physics and the driving forces is desired to be able to improve numerical simulations and to minimize aerodynamic drag over bluff bodies. To investigate the sources of separation one wants to understand what happens at the surface when the flow starts to detach and the upwelling of the streamlines becomes strong. This observation of a flow leaving the surface could be captured by investigating the limiting streamlines and surface parameters as pressure, vorticity or the shear stress. In this paper, numerical methods are used to investigate the surface pressure and flow patterns on a sedan passenger vehicle. Observed limiting streamlines are compared to the pressure distribution and their correlation is shown. For this investigation the region behind the antenna and behind the wheel arch, are pointed out and studied in detail. Besides the discussion of the correlation between limiting streamlines and the surface pressure distribution, it is discussed how the surface pressure and limiting streamline development is formed. It is shown how vortices emanating from the antenna influence the surface pressure and therefore the limiting streamline pattern. Behind the front wheel arch it is explained how the separation bubble upstream influences the development of the limiting streamlines further downstream.
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| 17. |
- Bonitz, Sabine, 1985, et al.
(author)
-
Unsteady pressure analysis of the near wall flow downstream of the front wheel of a passenger car under yaw conditions
- 2018
-
In: International Journal of Heat and Fluid Flow. - : Elsevier BV. - 0142-727X. ; 73, s. 188-198
-
Journal article (peer-reviewed)abstract
- The flow around passenger cars is complex and is characterized by many different structures and interactions. The occurring flow phenomena around a car determine crucial vehicle properties such as the driving stability, the noise level, the aerodynamic performance and the vehicle contamination. Therefore, it is of high importance to increase the understanding of the developing flow phenomena. Generic models are widely used to investigate flow structures and their interactions, but cannot serve to derive a general flow field for detailed full-scale vehicle models. A particularly complex area is the flow around the wheels and its interaction with the vehicle geometry. Studies on wheel-wheelhouse flow focus mainly on the geometrical influence of the wheel size, rim and tyre on the aerodynamic drag and the flow field close to the wheel. The present work investigates the flow behind the front wheel arch of a full-scale passenger car. Time resolved surface pressure measurements were taken to study the near wall flow under different yaw conditions. Based on the data obtained, flow structures are identified and their propagation speed is calculated. Further, characteristic frequencies observed are discussed. It is found that coherent structures are present behind the front wheel arch, one above the wheel centre height and one below it. These remain even under large yaw angles, no matter if the vehicle is yawed to lee- or windward. The investigation further shows that two characteristic frequencies can be found, St=0.03 and St=0.2, whereby the latter is caused by the wheel rotation. The same frequencies also occur under yaw conditions, but yawing the measurement area to leeward results in less pronounced frequency peaks.
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| 18. |
- Broberg, Leif, 1955, et al.
(author)
-
A Calculation Method for Ship Stern Flows Using an Analytical Body Fitted Coordinate System
- 1984
-
In: 15th Symposium on Naval Hydrodynamics, Hamburg 1984. ; , s. Code 7423-
-
Conference paper (peer-reviewed)abstract
- A new method for calculating ship stern flows is described. The method is based on the thin boundary layer equations cast in an analytic, body-fitted coordinate system. The major part of the paper deals with the definition and generation of this system and the computation of the related metrics and Christoffel symbols. Derivations of the governing flow equations are also made, using tensor algebra, and a short account is given of the numerical solution method. Finally, results from some test calculations are presented.
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| 19. |
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| 20. |
- Ekström, David, et al.
(author)
-
Optimization of the Internal Structure and Shape of a 470 Dinghy Centerboard
- 2020
-
In: Proceedings (MDPI). - Basel Switzerland : MDPI. - 2504-3900. ; 49:1
-
Conference paper (peer-reviewed)abstract
- The purpose of this paper is to design an improved centerboard for the Olympic 470 sailing dinghy sailing upwind. The design is improved by introducing a composite design that makes the centerboard twist to windward when sailing upwind, thereby reducing the angle of attack of the hull. The results show that a beneficial twist up to 1.5° is possible to achieve without compromising the centerboard strength. According to our estimates, by utilizing the improved design it is possible to obtain a gain of up to 9 s per race in a world cup race.
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| 21. |
- Engström, Carl-Peter, 1945, et al.
(author)
-
Functional status and well being in chronic obstructive pulmonary disease with regard to clinical parameters and smoking: a descriptive and comparative study.
- 1996
-
In: Thorax. - 0040-6376. ; 51:8, s. 825-30
-
Journal article (peer-reviewed)abstract
- BACKGROUND: Self-assessment questionnaires which measure the functional and affective consequences of chronic obstructive pulmonary disease (COPD) give valuable information about the effects of the disease and may serve as important tools with which to evaluate treatment. METHODS: A cross sectional comparative study was performed between patients with COPD (n = 68), stratified according to pulmonary function, and a healthy control group (n = 89). A battery of well established clinical and quality of life measures (the Sickness Impact Profile (SIP), Mood Adjective Check List (MACL), and Hospital Anxiety and Depression scale (HAD)) was used to examine in which functional and affective aspects the patient group differed from the control group and how these measures related to pulmonary function and smoking habits. RESULTS: Compared with the controls, COPD affected functional status in most areas, not just those requiring physical activity. Forty six patients with forced expiratory volume in one second (FEV1) below 50% predicted showed particularly high levels of dysfunction in ambulation, eating, home management, and recreation/ pastimes (SIP). Despite this, their level of psychosocial functioning and mood status was little different from that of the healthy controls. Among the patients, a subgroup reported substantial psychological distress, but mood status was only weakly, or not at all, related to pulmonary function. Smoking habits did not affect functional status or well being. CONCLUSIONS: Quality of life is not significantly affected in patients with mild to moderate loss of pulmonary function, possibly due to coping and/or pulmonary reserve capacity. This suggests that generic self-assessment questionnaires are of limited value for detecting the early consequences of COPD. However, in later stages of the disease they are sensitive enough to discriminate between patients with different levels of pulmonary dysfunction. The low correlations between the indices of pulmonary function and the indices of affective status suggest that well being depends, to a large extent, on factors outside the clinical domain.
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| 22. |
- Engström, Carl-Peter, 1945, et al.
(author)
-
Health-related quality of life in COPD: why both disease-specific and generic measures should be used.
- 2001
-
In: The European respiratory journal : official journal of the European Society for Clinical Respiratory Physiology. - 0903-1936. ; 18:1, s. 69-76
-
Journal article (peer-reviewed)abstract
- Although research has consistently demonstrated that chronic obstructive pulmonary disease (COPD) impairs health-related quality of life (HRQL), little agreement has been evidenced regarding the factors identified as contributing to impaired HRQL. The aim was to study such factors using well established generic and specific HRQL instruments. The patients (n=68) were stratified by forced expiratory volume in one second (FEV1) to represent a wide range of disease severity. Pulmonary function, blood gases and 6-min walking distance test (6MWD) were assessed. HRQL instruments included: St George's Respiratory Questionnaire (SGRQ), Sickness Impact Profile (SIP), Hospital Anxiety and Depression Scale and Mood Adjective Check List. The strength of the impact of COPD on HRQL was represented along a continuum ranging from lung function, functional status (physical and psychosocial) to wellbeing. Although correlations between FEV1 versus SGRQ total and SIP overall scores (r=-0.42 and -0.32) were stronger than previously reported, multiple regression analyses showed that lung function contributed little to the variance when dyspnoea-related limitation, depression scores and 6MWD were included in the models. These three factors were important to varying degrees along the whole range of HRQL. Physiological, functional and psychosocial consequences of chronic obstructive pulmonary disease are only poorly to moderately related to each other. The present study concludes that a comprehensive assessment of the effects of chronic obstructive pulmonary disease requires a battery of instruments that not only tap the disease-specific effects, but also the overall burden of the disease on everyday functioning and emotional wellbeing.
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| 23. |
- Engström, Carl-Peter, 1945, et al.
(author)
-
Long-term effects of a pulmonary rehabilitation programme in outpatients with chronic obstructive pulmonary disease: a randomized controlled study.
- 1999
-
In: Scandinavian journal of rehabilitation medicine. - 0036-5505. ; 31:4, s. 207-13
-
Journal article (peer-reviewed)abstract
- Fifty patients with severe chronic obstructive pulmonary disease (FEV1 < 50% pred.) were randomized to a rehabilitation group and a control group. The rehabilitation group took part in an individualized multidisciplinary, outpatient 12-month rehabilitation programme. Exercise training was intensive during the first 6 weeks and was then gradually replaced by an individual home-training programme and booster sessions. Controls received the usual outpatient care. Positive effects were found in terms of maximum symptom-limited exercise tolerance and walking distance (13.5 and 12.1% increase, respectively) in the rehabilitation group compared with the controls. Quality of life measurements showed minor beneficial effects on the Sickness Impact Profile, indicating a higher level of activity. No effect was seen on the St George's Respiratory Questionnaire or the Mood Adjective Check List. Patients expressed their enthusiasm for the rehabilitation programme in a study-specific questionnaire.
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| 24. |
- Engström, Carl-Peter, 1945, et al.
(author)
-
Reliability and validity of a Swedish version of the St George's Respiratory Questionnaire.
- 1998
-
In: The European respiratory journal : official journal of the European Society for Clinical Respiratory Physiology. - 0903-1936. ; 11:1, s. 61-6
-
Journal article (peer-reviewed)abstract
- The St George's Respiratory Questionnaire (SGRQ) was designed to measure quality of life (QoL) in obstructive pulmonary disease. Its reliability, validity and sensitivity have been demonstrated. The aim was to develop a Swedish version of the SGRQ and to confirm its scaling and clinical properties. The SGRQ was adapted for Swedish conditions following a translation-backtranslation procedure. The psychometric and clinical evaluation included 68 patients with chronic obstructive pulmonary disease (COPD). Supplementary QoL, clinical and physiological data were collected. A follow-up study was performed 1 yr later. Correlation analysis used a multitrait-multimethod model. Internal consistency reliability and discriminant validity were documented by performing a multitrait analysis. The results confirmed expected levels of associations. Correlation coefficients between the SGRQ total score and the Sickness Impact Profile Total score (a generic health measure), forced expiratory volume in one second (FEV1) and 6 min walking distance were 0.69, -0.42 and -0.61 respectively. The pattern of correlations in the Swedish data set was very similar to that of the original. The stability of the SGRQ scores was confirmed at follow-up after 1 yr. The reliability was satisfactory, with Cronbach's alpha coefficients >0.80 for the SGRQ and its subdimensions. In conclusion, the Swedish version of the St George's Respiratory Questionnaire is reliable, valid and compares well with the corresponding tests of the original version.
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| 25. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
A device for reducing the resistance of transom stern hulls
- 2021
-
In: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 235
-
Journal article (peer-reviewed)abstract
- A novel idea to reduce the resistance of a transom stern hull in displacement and semi-planing modes is investigated. By placing a spoon-shaped device in the recirculating zone behind the transom, the momentum of the forward-moving water will be absorbed, and a pushing force generated on the device. Numerical and experimental techniques are applied on a transom stern hull to optimize the shape and position of the device and to explore in detail the physics behind the gain. For the towed hull at a Froude number of 0.4, the maximum measured resistance reduction is 11%, while the computed maximum reduction is 17%. In self-propulsion with one propeller, the measured power reduction is 15%. The power cannot be computed with the applied propeller model, which is an axial body-force distribution in the propeller disk, but the reduction in thrust using the device is 11%. More significant gains are possible at smaller Froude numbers, while the effect is reduced at higher Froude numbers. Larger gains are achieved by splitting the thrust on two propellers. © 2021 The Authors
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| 26. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
A device for reducing the resistance of water surface vessels
- 2020
-
Patent (other academic/artistic)abstract
- An object of the invention is to decrease the hull resistance of a water surface vessel. This object is reached with a water surface vessel extending in a longitudinal direction parallel to an intended direction of straight travel, the vessel presenting a transom, wherein the vessel is arranged to travel in a recirculating zone speed interval in which water is moving towards the transom in a recirculating zone behind the transom, wherein the vessel comprises a pushing device presenting a pushing surface located in relation to the intended direction of straight travel of the vessel behind the transom, at least a portion of the pushing surface facing at least partly backwards in relation to the intended direction of straight travel of the vessel, which pushing surface is arranged to be at least partly submerged into the recirculating zone when the vessel is travelling in the recirculation zone speed interval.
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| 27. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
A pressure jump method for modeling waterjet/hull interaction
- 2014
-
In: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 88, s. 120-130
-
Journal article (peer-reviewed)abstract
- A fast and robust method for the simulation of waterjet hull interaction is presented. Balancing the thrust force of the waterjet unit with the hull resistance, a method is developed for the prediction of the flow rate through the unit. The method is called the Pressure Jump Method and may be used in combination with both potential flow/boundary layer methods and more advanced viscous flow methods, for instance of the RANS type. In the present work the potential flow/boundary layer approach has been used. Validation of the method is accomplished through comparison of predicted results with measured data. The inlet velocity ratio, nozzle velocity ratio, gross thrust and thrust deduction are all within the experimental scatter. For the case studied the force and moment created by the waterjet unit cause the hull to sink deeper and attain a bow down trim compared to the bare hull case. The thrust deduction fraction is positive both in the computations and the measurements.
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| 28. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
Analysis of the thrust deduction in waterjet propulsion – The Froude number dependence
- 2018
-
In: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 152, s. 100-112
-
Journal article (peer-reviewed)abstract
- The definition of thrust deduction in waterjet propulsion is different from that of a propeller driven hull and cannot be interpreted in the same way. A particularly interesting feature of the waterjet thrust deduction is the large variation with Froude number. This is well known from experience, but has never been fully explained. The objective of this paper is to use CFD to address the reasons for these large variations. To this end, the thrust deduction fraction is split into resistance increment fraction and jet thrust deduction fraction. The former is due to the self-propelled hull resistance change in comparison with the bare hull resistance and the latter is due to the difference between gross and net thrust. This split reveals that the main reason for the thrust deduction variation is the hull resistance change. Analysis of the resistance increment in different speed ranges is performed by studying the hydrostatic and hydrodynamic pressure changes on the hull as well as the friction change due to the waterjet system. Despite the negative thrust deduction fraction in the intermediate speed range there is no indication of a resistance reduction compared to that of the bare hull at these speeds.
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| 29. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
Contribution of different parameters to the thrust deduction of a waterjet propelled hull
- 2013
-
In: 12th International Conference on Fast Sea Transportation, FAST 2013; Amsterdam; Netherlands; 2 December 2013 through 5 December 2013.
-
Conference paper (peer-reviewed)abstract
- In order to model the waterjet-hull interaction a method, which is based on the potential flow assumption with non-linear free surface boundary conditions, is developed and validated. By means of this method the effect of the sinkage, trim and local flow variation on the resistance increment of a waterjet driven craft has been estimated. Besides, assuming that each of the aforementioned parameters independently influences the resistance change, the resistance increment of the hull is estimated through a linear expansion in a Taylor series, which is a function of the hull sinkage, trim and the flow rate through the waterjet unit. Knowing the magnitude of each single parameter separately helps to understand the physics behind the thrust deduction and may aid in the optimization of the hull/propulsor configuration. Also it sheds some light on the reason for the negative thrust deduction fractions sometimes found on waterjet driven hulls.
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| 30. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
Net and Gross Thrust in Waterjet Propulsion
- 2016
-
In: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 60:2, s. 78-91
-
Journal article (peer-reviewed)abstract
- The measurement of the net thrust of a waterjet unit is a cumbersome task and thus as an alternative, the thrust of the waterjet system is expressed based on the momen- tum flux change through the waterjet unit, called gross thrust. The relation between net thrust and gross thrust is not fully understood, and in the current paper this relation is investigated by employing numerical simulations of the flow around a planing waterjet- propelled hull. The validation of the bare hull and self-propelled hull simulations is carried out through comparison of the computed results with experimental data.
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| 31. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
On transom clearance
- 2015
-
In: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 99, s. 55-62
-
Journal article (peer-reviewed)abstract
- This paper deals with transom stern flow phenomena around the Froude number where the transom clears the water. Experimental and numerical results for a high-speed hull exhibit a pronounced peak in the resistance coefficient at the clearance speed. This is associated with a maximum in the non- dimensional transom submergence, a minimum in the pressure coefficient at the transom edge and a maximum in the curvature of the flow leaving the edge. Just before clearance, the sum of the hydrodynamic and hydrostatic pressures on the transom yields a force pointing forwards, thereby reducing resistance. This pushing force diminishes abruptly as the transom becomes dry. The total pressure resistance of the rest of the hull increases rapidly just before clearance, mostly due to the increase in hydrostatic pressure resistance, caused by the sudden increase in aft draft. It is the rapid loss of the transom pushing force, together with the rapid increase in pressure resistance of the rest of the hull just before clearance that creates the peak in the total resistance coefficient.
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| 32. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
Pressure Jump Approach for Modeling Waterjet/Hull Interaction
- 2011
-
In: 14th Numerical Towing Tank Symposium (NuTTS'11).
-
Conference paper (other academic/artistic)abstract
- The aim of the current paper is to introduce a method, which is not dependent on the pressure distribution on the waterjet intake streamtube. First the conventional momentum flux method is going to be discussed and then another approach, which is independent of the intake streamtube properties, is going to be introduced. This method, which here in this paper is called pressure jump approach, is adapted to a potential flow solver in SHIPFLOW commercial code. The code comes with a linear/none-linear free surface model and is capable of obtaining equilibrium sinkage and trim angle of the hull iteratively. A sink disk along with a body force at its center is applied for modelling the pump system effect.
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| 33. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
WATERJET HULL INTERACTION
- 2010
-
In: 13th Numerical Towing Tank Symposium.
-
Conference paper (other academic/artistic)abstract
- The main objective of this work is to render the parameters involved in the watejet-hull interaction and finally define the weight of each of these parameters on the thrust deduction fraction. This would help to know how to control the thrust deduction fraction and try to keep this factor below zero to gain more efficiency for the hull and waterjet assembly. Aiming this goal, current paper is going to discuss some strategies for modeling waterjet-hull interaction starting with very simplified assumptions. The applied solver in this work is a potential code including a linear/none-linear free surface model which is capable of handling 6DoF simulation for calculating sinkage of a hull and its’ trim angle.
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| 34. |
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| 35. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
Waterjet Propulsion and Negative Thrust Deduction
- 2015
-
In: Fourth International Symposium on Marine Propulsors, SMP’15.
-
Conference paper (peer-reviewed)abstract
- The thrust deduction fraction of waterjet-propelled hulls is often reported to be negative in the speed range close to the operating speeds. In this paper, employing a numerical method, the bare hull and the self-propelled hull flows are studied. The changes between the bare hull and self- propelled hull resistances are investigated for understanding whether it is the waterjet hull resistance decrease which contributes to the negative thrust deduction fraction or there are some other effects rather than the resistance increment.
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| 36. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
Waterjet Propulsion and Thrust Deduction
- 2014
-
In: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 58:4, s. 201-215
-
Journal article (peer-reviewed)abstract
- The goal of this article is to describe and investigate the parameters that play a role in the waterjet–hull interaction. In general, these parameters can be split into sinkage, trim, and local flow variation from the bare hull to the self-propelled hull. Each of these parameters has in turn been split into components, which are estimated in relative size. For this purpose, a newly developed method for modeling waterjet-driven ves- sels is used. Knowing the magnitude of each single parameter separately helps to understand the physics behind the thrust deduction and may aid in the optimization of the hull/propulsor configuration.
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| 37. |
- Finnsgård, Christian, 1974, et al.
(author)
-
High Performance Sailing in Olympic Classes - a Research Outlook and Proposed Directions
- 2015
-
In: Proceedings, 5th High Performance Yacht Design Conference, Auckland, 8-11 March 2015. - : Royal Institution of Naval Architects. - 9781909024373 ; , s. 141-149
-
Conference paper (peer-reviewed)abstract
- The purpose of this paper is to explore research opportunities in Olympic sailing classes. Olympic classes provide high-performance sailing using a diversity of equipment, with the understanding that the equipment, individual athletes, and the knowledge relating to those two factors impacts performance. Thus, the Olympic motto, “Citius, Altius, Fortius” (Latin for “Faster, Higher, Stronger”), governs everyday life for many engineers. During the last few years, Chalmers has supported a project that focuses on the possibilities and challenges for research combined with engineering knowledge in the area of sports. The initiative has generated external funding and gained great acclaim within Chalmers, among staff and students, in the Swedish sports movement, and in large companies, as well as within small and medium sized enterprises. The project focuses on five sports: swimming, equestrian events, floorball, athletics, and sailing. The contribution from this paper describes an outlook identifying eight areas containing research opportunities: sailing dynamics, how to sail in Olympic classes, fluid structure interaction, surface structures, turbulence induction on the rig, equipment in Olympic classes, and applying game theory to sailing.
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| 38. |
- Han, Kaijia, 1974, et al.
(author)
-
A numerical study of hull/propeller/rudder interaction
- 2008
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In: Proceedings, 27th Symposium on Naval Hydrodynamics, 5-10 October 2008, Seoul.
-
Conference paper (peer-reviewed)abstract
- A numerical study of the interaction between the hull, propeller and rudder is presented in this paper. The flow around a ship hull at full scale is first calculated using a RANS solver with a series of systematically generated grids. This grid dependence study is made for the total resistance of the hull and a grid density is chosen. The total resistance of the same ship at four Froude numbers at model scale are computed and compared with experiments. Then self-propulsion tests of the hull and propeller with and without rudder are simulated and compared with measured data. Good agreement is found. By moving the rudder backwards, the effect of the distance between propeller and rudder behind the hull is captured and shows the same tendency as the experiment. Flow fields, such as axial velocity contours at the propeller plane, slipstream deformation, due to the rudder, and limiting streamlines on the surface of rudder and hull are illustrated. Comparisons between two configurations with rudder at different positions are made. It is demonstrated that the present method is promising for evaluating self-propulsion characteristics of hull/propeller/rudder configurations.
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| 39. |
- Han, Kaijia, 1974, et al.
(author)
-
A procedure for optimizing cavitating blades in a given wake
- 2006
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In: Ship Technology Research. - 0937-7255. ; 53:1, s. 39-52
-
Journal article (peer-reviewed)abstract
- The blade geometry of a cavitating propeller in a given wake is optimized to maximize propeller efficiency and minimize propeller induced pressure fluctuations. The Keller criterion, the cavity volume and other constraints are considered in the optimization process. Such constraints are cavity area, cavity length and face side pressure and they are switched on separately or simultaneously to investigate their influence on cavitation and efficiency. Optimization is made starting from a near optimum propeller as well as from an off-design propeller. Results indicate that the present optimization technique can yield higher efficiency and lower pressure amplitude with tolerable cavitation for a cavitating propeller in a given wake.
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| 40. |
- Han, Kaijia, 1974, et al.
(author)
-
A procedure for optimizing cavitating propeller blades in agiven wake
- 2005
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In: 8th Numerical Towing Tank Symposium.
-
Conference paper (peer-reviewed)abstract
- The blade geometry of a cavitating propeller in a given wake is optimized to maximize propeller efficiency and minimize propeller induced pressure fluctuations. The Keller criterion, the cavity volume and other constraints are considered in the optimization process. Such constraints are cavity area, cavity length and face side pressure and they are switched on separately or simultaneously to investigate their influence on cavitation and efficiency. Optimization is made starting from a near optimum propeller as well as from an off-design propeller. Results indicate that the present optimization technique can yield higher efficiency and lower pressure amplitude with tolerable cavitation for a cavitating propeller in a given wake.
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| 41. |
- Han, Kaijia, 1974, et al.
(author)
-
A RANS study on the interaction between a propeller and a rudder in open water
- 2007
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In: 10th Numerical Towing Tank Symposium (NuTTS 2007).
-
Conference paper (other academic/artistic)abstract
- When designing a ship, it is important to estimate accurately the effects of propeller-rudder interaction, as the rudder behind a propeller and a ship has a great effect both on the propulsive and maneuvering performance. In order to both understand the physical phenomenon and validate the RANS solver SHIPFLOW, the interaction between a propeller and a rudder in open water is qualitatively and quantitatively predicted and validated against experimental data. Furthermore, the propeller slipstream deformation is illustrated and the regain of rotational losses by the rudder is estimated.
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| 42. |
- Han, Kaijia, 1974, et al.
(author)
-
Numerical optimization of a propeller behind a ship hull at full scale
- 2006
-
In: 26th Symposium on Naval Hydrodynamics. ; VOL II, s. P87-98
-
Conference paper (other academic/artistic)abstract
- A propeller behind a ship hull (the Hamburg test case) at full scale is optimized to minimize the delivered power at a given ship speed by adjusting the geometry and the revolution speed. An uncertainty analysis and a wake validation are made for the CFD (Computational Fluid Dynamics) code SHIPFLOW. The minimum iteration number and grid density were carefully selected to decrease the computation time needed. The optimization is done with a parallel Adaptive Range Genetic Algorithm in the coarse grid and a local optimization starting from the optimized design is performed to check whether it is a local optimal, at least. Then the verification of the optimal propeller for both objective function and constraint in three finer grids is made. To satisfy the constraints in the finer grids, we make a manual correction by adjusting one design variable. At the same time, an automatic optimization starting from the optimum we obtained in the coarse grid is made in the finest grid with a local optimization method, DHC (Dynamic Hill Climbing). The designs by manual correction and automatic optimization are compared. Furthermore, an off-design propeller behind the same ship is also optimized with the same design variables, constraint and objective function. An optimum close to the one obtained in the near-optimum propeller optimization is found. Results indicate that the present optimization procedure can yield lower delivered power for both a near-optimum and an off-design propeller.
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| 43. |
- Hino, Takanori, et al.
(author)
-
Introduction, conclusions and recommendations
- 2021
-
In: Lecture Notes in Applied and Computational Mechanics. - Cham : Springer International Publishing. - 1860-0816 .- 1613-7736. ; 94, s. 1-21
-
Book chapter (other academic/artistic)abstract
- The Tokyo 2015 Workshop on CFD in Hydrodynamics was the seventh in a series started in 1980. The purpose of the Workshops is to regularly assess the state of the art in Numerical Hydrodynamics and to provide guidelines for further developments in the area. The 2015 Workshop offered 16 test cases for three ship hulls. A total of 36 participating groups of CFD specialists submitted their computed results during the fall of 2015. The results were compiled by the organizers and discussed at a meeting in Tokyo in December 2015. In this chapter the background and development of the Workshops since the start are presented. The three hulls used in the 2015 Workshop are introduced and the computations requested from the participants are specified. Based on a questionnaire sent to all participants the details of their CFD methods are listed, and finally the general conclusions from each chapter and recommendations for future Workshops are presented. The detailed results of the computations are discussed in subsequent Chapters.
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| 44. |
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| 45. |
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| 46. |
- Janson, Carl-Erik, 1957, et al.
(author)
-
Calculation of deep-water wash waves using a combined Rankine/Kelvin source method
- 2003
-
In: Journal of Ship Research. - 0022-4502 .- 1542-0604. ; 47:4, s. 313-326
-
Journal article (peer-reviewed)abstract
- This paper presents a method for computation of far-field wash waves in deep water. The method combines a nonlinear Rankine source method in an inner domain with a Kelvin source method for the far-field waves in an outer domain. Kelvin sources are distributed on a vertical matching wall, positioned at the outer edge of the inner domain. These sources are used to specify a boundary condition for the disturbance velocity potential on the matching wall. The boundary condition is used in the Rankine source solution of the inner domain. The size of the inner domain can be reduced in the transverse direction compared to a method using Rankine sources only, as the wave reflections at the edge of the inner domain are eliminated. Further, the far-field waves can be computed using the solution on the matching wall together with the Kelvin source distribution. The verification of the present method includes a comparison for a single Kelvin point source and a comparison to a Rankine source method at intermediate distances for the Wigley hull and for a catamaran. A grid dependence study for the position, size, and panel density on the matching wall is included for the Wigley hull. Computed and measured longitudinal wave cuts are compared for a catamaran both in the inner and the outer domain. Good agreement is obtained.
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| 47. |
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| 48. |
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| 49. |
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| 50. |
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