An investigation into computational modelling of cavitation in a propeller's slipstream

This paper reports on the ongoing developments of cavitation modelling so far which include preliminary validation studies for simulating the performances of two benchmark model propellers: i.e. PPTC propeller with inclined shaft; and E779A propeller, in non-cavitating and cavitating conditions. The main purpose of this study is to estimate the propeller’s performance in cavitating conditions particularly developing tip vortex cavitation. The simulations in open water and cavitating conditions were carried out in uniform flow using a commercial CFD package. Firstly, the validation studies were conducted for non-cavitating condition. The comparison with the benchmark experimental data showed good agreement for the thrust and torque coefficients as well as for the open water efficiency. Next, the cavitation developed on the propeller was simulated using a numerical model based on the Rayleigh-Plesset equation. Propulsion coefficients (KT, KQ) and the cavity patterns on the benchmark propellers’ blades showed very good agreement with the experimental data. However, the tip vortices off the blades could only be traced for E779A propeller by using a new mesh refinement approach

An improved tip vortex cavitation model for propeller-rudder interaction

The paper starts with the computational modelling of the tip vortex cavitation in uniform flow conditions with an isolated propeller in detail and provides experimental validation. It then moves onto further modelling to include the effect of non-uniform flow and the presence of a rudder placed in the propeller slipstream. The propeller-rudder arrangement of the Newcastle University research vessel, The Princess Royal, and associated experimental data were used for Experimental Fluid Dynamics (EFD) analysis to validate the modelling. The cavitation simulations were conducted using commercial CFD software, Star CCM+. A new meshing technique, which utilizes a Mesh Adaptive Refinement approach for Cavitation Simulations (MARCS), recently developed by the authors, has been applied successfully to simulate the tip vortex cavitation, particularly to trace its extension up to the rudder in the propeller slipstream. The comparison of the CFD and EFD methods for the isolated propeller in cavitation tunnel conditions showed very good agreement in terms of the thrust and torque coefficients of the propeller as well as the sheet and tip vortex cavitation patterns observed. The cavitation simulations have been extended for the same propeller by using the new mesh refinement approach to include the effect of the hull wake and the presence of the rudder. Although the latter simulations fall short of the EFD results and hence they are still under development, the paper presents the developments and results so far to achieve the ultimate aim of this study, i.e. computational modelling of cavitating tip vortices of a propeller interacting with a rudder

Computational fluid dynamic investigations of propeller cavitation in the presence of a rudder

This paper presents the preliminary results of a computational study for cavitation modelling of marine propellers particularly developing tip vortex cavitation in the presence of a rudder. The main purpose of the study is to estimate the propeller’s performance in cavitating conditions and to investigate the propeller-rudder interaction especially due to the tip-vortex cavitation. The cavitation simulations were conducted using commercial Computational Fluid Dynamics (CFD) software, Star CCM+. In the study, the INSEAN E779A model propeller was used as a benchmark. Firstly, validation studies were conducted in cavitating conditions using only the propeller in isolation. The cavitation on the propeller was simulated by using a numerical model, which is known as Schnerr–Sauer cavitation model, based on the Rayleigh-Plesset equation. Then, the rudder with an airfoil section was introduced behind the propeller and the simulations were repeated to investigate the effect of the rudder on the propeller performance as well as to study the propeller-rudder interaction from the cavitation point of view. Two cases with different advance coefficients (J) and cavitation numbers (σ) were simulated to compare the computational results with experiments which were obtained from open literature. For the tip vortex cavitation modelling, recently developed volumetric control method using spiral geometry was applied to generate finer mesh around the propeller tip region where the tip vortex cavitation may occur. The comparison with the benchmark experimental data showed good agreement in terms of thrust and torque coefficients as well as sheet and tip vortex cavitation patterns for the propeller in the absence of the rudder. The comparisons also showed good agreement in terms of the velocity and pressure distributions and hence enabled accurate extension of the tip vortex cavitation until the rudder to focus on the interaction of the tip vortex cavitation with the rudder

An improved mesh adaption and refinement approach to cavitation simulation (MARCS) of propellers

This paper presents the improvements of cavitation modelling for marine propellers particularly developing tip vortex cavitation. The main purpose of the study is to devise a new approach for modelling tip vortex cavitation using Computational Fluid Dynamics (CFD) methods with commercial software, STAR-CCM+. The INSEAN E779A model propeller was used for this study as a benchmark propeller. Utilizing this propeller, firstly, validation studies were conducted in non-cavitating conditions together with grid and time step uncertainty studies. Then, the cavitation was simulated on the propeller using a numerical cavitation model, which is known as the Schnerr–Sauer model, based on the Rayleigh-Plesset equation. While a Reynolds Averaged Navier Stokes (RANS) model was used for open water simulations, Detached Eddy Simulations (DES) and Large Eddy Simulations (LES) models were preferred for cavitation simulations to capture the cavitation and evaluate its effect on propeller performance accurately. Although the comparison with the benchmark experimental data showed good agreement for the thrust and torque coefficients as well as sheet cavitation pattern, tip vortex cavitation could not be adequately simulated using the existing method. After an evaluation of the interaction between cavitation modelling and generated meshes, two techniques, which involved volumetric control and adaptive mesh refinement, were used in combination on the region where the tip vortex cavitation is likely to occur. The first technique, which is called a ‘volumetric control method’, was developed using spiral geometry around the propeller tip region to generate a finer mesh for capturing tip vortex cavitation. Although this method gave better tip vortex cavitation extension than the method without any mesh refinement or with tube refinement, it still required to be improved to extend the tip vortices further into the propeller slipstream. The second method, which is called ‘adaptive mesh refinement’, was introduced using the pressure distribution data from the results of the ‘volumetric control method’. This improved approach, which is called “Mesh Adaption and Refinement for Cavitation Simulation (MARCS)”, has been successfully applied to simulate the tip vortices trailing from the blades of the INSEAN E779A propeller as demonstrated in the paper. The results of the simulations showed an excellent agreement with the experiments in the open literature by tracking the tip vortex cavitation along this propeller’s slipstream

Suppression of tip vortex cavitation noise of propellers using PressurePoresTM technology

This study aims to demonstrate the merits of pressure-relieving holes at the tip region of propellers, which is introduced as “PressurePoresTM” technology as a retrofit on marine propellers to mitigate tip vortex cavitation noise for a quieter propeller. Shipping noise originates from various sources on board a vessel, amongst which the propeller cavitation is considered to dominate the overall radiated noise spectrum above the inception threshold. Thus, by strategically introducing pressure-relieving holes to modify the presence of cavitation, a reduction in the overall cavitation volume can be achieved. This mitigation technique could consequently result in a reduction of the radiated noise levels while maintaining the design efficiency as much as possible or with the least compromise. The strategic implementation of the holes was mainly aimed to reduce the tip vortex cavitation as this is one of the major contributors to the underwater noise emissions of a ship. In this paper, the details and results of a complementary numerical and experimental investigation is presented to further develop this mitigation concept for underwater radiated noise (URN) and to validate its effectiveness at model scale using a research vessel propeller. An overall finding from this study indicated that a significant reduction in cavitation noise could be achieved (up to 17 dB) at design speed with a favourable strategic arrangement of the pressure pores. Such a reduction was particularly evident in the frequency regions of utmost importance for marine fauna while the propeller lost only 2% of its efficiency

Yol Verme Davranışı: Sürücülerin Yol Verme Davranışını Anlamak Üzerine Karma Yöntemli Bir Çalışma

Sürücülerin yayalara yol verme davranışını incelemek üzere saha gözlemleri ve yarı-yapılandırılmış mülakatlar yapılmıştır. 1140 araç-yaya gözlemi sonucunda yapılan Cramer’in V katsayısı ve lojistik regresyon analizleri, sürücü cinsiyeti ve yaya yaşı ile yol verme davranışı arasında anlamlı bir ilişki olduğunu göstermiştir. Yaş ve cinsiyetin yanı sıra, sürücü-yaya ilişkisinin doğasını anlamak adına yol özelliklerinin bu ilişkiye etkisi de incelenmiştir. Mülakatlar ise tematik analiz yöntemi ile incelenmiş ve katılımcıların yol verme davranışı ile ilgili düşünceleri 4 tema altında toplanmıştır. Bunlar; "Karşılaşma yerleri", "Kurallara olan güven", "Yol verme davranışını etkileyen faktörler" ve "Geleceğe yönelik çözümler" olarak belirlenmiştir. Hem saha gözlemleri hem de mülakatlar sürücü-yaya ilişkisinin trafik güvenliği ile ilgili önemli bir faktör olduğunu göstermiştir

TARİHİ SİLLE SUBAŞI HAMAMI TAŞIYICI SİSTEM ANALİZİ

TARİHİ SİLLE SUBAŞI HAMAMI TAŞIYICI SİSTEM ANALİZİÖzetBu çalışmada, 19. yüzyıl Osmanlı Dönemi’nde inşa edilen ve Konya İli Selçuklu İlçesi’ne bağlı Sille Ak Mahallesi’nde bulunan tarihi Subaşı Hamamı’nın mevcut durum değerlendirmesi yapılıp, yapının statik ve dinamik yükler altındaki durumu incelenmiştir. Yapının üç boyutlu modeli oluşturulmuş, sonlu elemanlar yöntemine göre lineer analizi yapılmış ve taşıyıcı elemanları üzerinde oluşan gerilmeler ile yerdeğiştirmeler incelenmiştir. Subaşı Hamamı mimari açıdan kesit ve iç tasvir olarak iki sıcaklık, iki ılıklık ve bir su deposundan oluşmaktadır. İki sıcaklık ve iki ılıklık mekanının üzeri tuğladan yapılmış kubbeden, su deposunun üzeri ise beşik tonoz ile örtülmüştür. 19.5x18 metre boyutuna sahip olan hamamın yapılan araştırma, inceleme ve analiz sonucunda, yapının mevcut kesitlerinin büyük olmasından dolayı basınç ve kesme gerilmelerine karşı yeterli dayanımının olduğu; kubbe, beşik tonoz ve kapı köşelerinde bazı çatlakların oluştuğu; modal analiz sonunda mod şekilleri incelendiğinde en fazla zorlanan kısmın beşik tonoz olduğu tespit edilmiştir.Anahtar Kelimeler: Tarihi Yapı, Yığma Yapı, Taşıyıcı Sistem Analizi, Statik Lineer AnalizSTRUCTURAL ANALYSIS OF HISTORICAL SILLE SUBASI BATH AbstractIn this study, the present situation of the historical Subasi Bath, which was built in the 19th century Ottoman Period and located in the Sille Ak District of the Selcuklu District of Konya Province, was evaluated and the status of the building under static and dynamic loads was examined. A three-dimensional model of the structure was created using a computer program, a linear analysis was made according to the finite element method, and the stresses and displacements on the carrier elements were examined. Subasi Bath consists of two the hottest rooms, two the tepidity rooms and one water reservoir in terms of architectural cross-section and internal depiction. The hottest and the tepidity rooms spaces are covered with a dome made of brick, while the water tank is covered with a cradle vault. As a result of the research, examination and analysis of the bath, which has a size of 19.5x18 meters, it has sufficient resistance against pressure and shear stresses due to the big cross sections of the building; there are some cracks in the dome, cradle vault and door corners; When the modal analysis was examined, the most critical part was found to be the cradle vault.Keywords: Historical Structure, Masonry Structure, Structural Analysis, Static Analysi

Tip vortex cavitation simulation of a propeller in a Gate Rudder® system

The GATE RUDDER® system is a novel propulsion arrangement or Energy Saving Device (ESD) inspired by the new concept of elementary propulsive efficiency and its optimization in a ship’s wake to recover more energy. The performance of a GATE RUDDER® system in the hull wake, therefore, is important not only for the efficiency but also from the cavitation, noise and vibration point of view. The World’s first gate rudder was installed on a 2,400 GT container ship in 2017 in Japan. By using the data associated with this vessel and other model test data with different ships, this paper explores the differences on the efficiency and cavitation performance of a conventional rudder and propeller system with the GATE RUDDER® system using Experimental and Computational Fluid Dynamics (EFD and CFD) approaches. There is specific emphasis on the accurate simulation of the tip vortex cavitation of the propeller in both rudder systems which has been modelled by using Yilmaz’s recently developed advanced adaptive mesh refinement approach. The results of the CFD simulations are compared with the results of the model tests conducted in the Emerson Cavitation Tunnel and the full-scale experiences with the above-mentioned container vessel as discussed in the paper

The changes in Alkaline, Neutral and Acid Protease Activities of ArtemiaEnriched with Commercial Emulsion and Different Additive Combinations

Thebiochemicalcompositionsandthechangesobservedinalkaline,neutralandacidproteaseactivities of Artemia enriched with commercial emulsion and different additive combinations were determined. Artemia nauplii (ArtN), GroBiotic-A (GA), Red Algamac (RA), Red Algamac:GroBiot-ic-A(50:50)(RA:GA(50:50)),Spirulina(SP),Spirulina:RedAlgamac(50:50)(SP:RA(50:50)),Spiruli-na:GroBiotic-A (50:50) (SP:GA (50:50)) and Spirulina:Red Algamac:GroBiotic-A (33:33:33) (SP:RA:GA (33:33:33)) were tested in the study. The lowest and highest protein contents after the enrichment of Artemia were 40.74±1.02% (RA) and 55.03±1.26% (SP:RA:GA (33:33:33)), respectively. The lowest lipidcontentsoftestedgroupswerefoundin5.63±0.47%(GA)and5.63±0.84%(RA:GA(50:50)).The highest lipid value after the enrichment were observed in 16.98±1.15 % (RA). The lowest and highest ash values observed after the enrichment were 4.51±0.27% (SP:GA (50:50)) and 6.07±0.35% (RA) (p lt;0.05). The lowest and highest protease activities of the pH=3, pH=4, pH=5, pH=6, pH=7 and pH=8.5 values were 18.18±0.37 U/mg protein (GA), 31.04±0.38 U/mg protein (RA), 9.1±0.32 U/mgprotein(SP),9.66±0.19U/mgprotein(SP),16.94±0.61U/mgprotein(SP),63.09±0.75U/mgprotein(SP)and33.77±0.59U/mgprotein(RA:GA(50:50)),57,54±0.34U/mgprotein(RA:GA(50:50)), 23.75±0.28 U/mg protein (GA), 40.82±0.49 U/mg protein (GA), 69.94±0.65 U/mg protein (GA), and 286.14±8.2 U/mg protein (GA) (p lt;0.05). In conclusion, GA and SP:RA:GA (33:33:33) en-richment combinations are recommended as an alternative to enrichment products. On the other hand,SPandRAshouldnotbeusedaloneduetothedisadvantagessuchasthebiochemicalcomposition and proteolytic enzyme activities of Artemia observed in the present study

Numerical cavitation noise prediction of a benchmark research vessel propeller

This paper presents the preliminary results of a numerical study for noise prediction of a benchmark propeller in open water/uniform flow conditions. The experimental benchmark test data for the research vessel, “The Princess Royal”, were used for validation purposes. The numerical analyses were implemented by using a viscous solver based on the finite volume method while the experimental data were obtained from model tests conducted at the Genova University Cavitation Tunnel. The main aim of the study is to predict propeller hydro-acoustic performance under cavitating conditions. The hydrodynamic flow field was solved using a RANS (Reynolds-averaged Navier-Stokes) solver. The Schnerr-Sauer cavitation model based on a reduced Rayleigh-Plesset equation together with a VOF approach was used to model sheet cavitation on the propeller blades. The computed hydrodynamic characteristics and sheet cavity patterns were shown to be in good agreement with the Genoa experimental data, thus providing a firm basis for cavitating noise predictions. The hydro-acoustic performance of the model propeller was predicted by using a hybrid method. In the noise simulations, RANS equations were equipped with a porous FW-H (Ffowcs Williams-Hawkings) formulation. The different propeller operational conditions were simulated using this hybrid method. The numerical results were also validated with the experimental data for the propeller hydro-acoustic performance. Whereas such validations showed promising results by means of overall noise spectrum with the benchmark test cases in the low-frequency range, the numerical prediction overestimated the 1st BPF values (around 20 dB) in five loading conditions. Besides, in some loading conditions, especially between 200 and 800 Hz, the difference between numerical predictions and the experiment was found around 5–10 dB