Yatay silindirik depolama tanklarında ızgara perdelerin sıvı çalkantısını ve basıncını azaltmaya olan etkisinin SPH ile modellenmesi
Modeling of the effect of baffles on liquid sloshing and pressure reduction in horizontal cylindrical storage tanks with SPH
Yazar: EMİNE KÖSE
Danışman: DOÇ. DR. NECATİ ERDEM ÜNAL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Hidrolik ve Su Kaynakları Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Sıvıların hareketinin ve hareket etkilerinin simülasyonu son yıllarda büyük önem kazanmıştır. Tasarlanma şekilleri kullanılan alana göre değişiklik gösterip, bu amaçlar doğrultusunda birçok simülasyon modeli ortaya çıkmış ve mühendislik alanlarındaki çalışmalara dahil edilmiştir. Sıvı çalkantısı belirli bir miktar sıvı ile doldurulmuş bir 
kabın hareketini ifade eder. Bu çalkantıların incelenmesi ve bulundukları kaba olan etkilerinin simülasyonu son zamanlarda önem kazanan çalışmalardandır. İlk çalkantı çalışmaları uçakların yakıt deposundaki çalkantıların ortaya çıkarabileceği sorunların incelenip ortadan kaldırılması için yapılmıştır. Günümüzde su, akaryakıt, sıvılaştırılmış gaz (LNG veya LPG) ve kimyasal maddeler gibi birçok sıvı belirli depolama yöntemleriyle depolandığı ve çeşitli araçlar ile taşındığı için, bu çalışmalara verilen önem artmıştır. Araç yakıt depolarında oluşacak şiddetli çalkantılar aracın 
dengesini bozacak kadar etkili olabilir. Yapılan çalışmalar bu çalkantıların en çok sıvı yüzeyinde meydana geldiğini, ve bunları azaltmak için de tankın içine çeşitli perdeler yerleştirilmesi gerektiğini göstermiştir. Bu çalışmada, silindirik tanklardaki çalkantılardan dolayı meydana gelecek basınç değişimleri belirlenerek, bu basınçların ızgara perdeler kullanarak azaltımının Smoothed Particle Hydrodynamics (SPH) modeline dayalı olan DualSPHysics ile modellenmesi amaçlanmıştır. Modelleme için iki başlıktan ve bir ana tanktan oluşan yatay silindirik bir depolama tankı kullanılmıştır. Tankın üzerinde basınç ölçümü yapabilmek için 8 adet basınç ölçme noktası konulmuştur. İlk olarak model parametreleri olan sıvı tipi, sıvı yüksekliği, zaman adımı, ızgara perde tipi, ızgara perde kalınlığı, yüksekliği, yerleşim yeri ve açısı seçilmiştir. Kararlaştırılan parametreler ile 29 adet ızgara perdeli, 1 adet perdesiz model kurulup çalıştırılmıştır. SPH modelinde ızgara perde çizim kodu bulunmadığı için, ızgara perdeli modeller AutoCAD programında 3D olarak çizilip STL dosyası olarak kaydedilmiş ve SPH programına aktarılmıştır. Amaç ızgarsız modelde oluşan basınçların azaltılması olduğu için ızgara perdeli modellerden elde edilen basınç değerleri perdesiz model 
basınç değerleriyle karşılaştırılmıştır. Ölçüm noktalarının bulunduğu tank başlığına etki eden x yönündeki kuvvetlerden yararlanılarak çalkantı sönümleme oranı hesaplanmıştır. 0 ile 1 arasında olan bu değerlerden 1'e en yakın olanlar en etkili model olarak seçilmiştir. Sonuç olarak kurulan 29 modelden 12 modelin tank içindeki çalkantıyı ve basıncı azalttığı, kullanılan SPH modelinin basınç hesaplarını yapmada ve model simülasyonunu oluşturmada çok iyi sonuçlar verdiği görülmüştür. Kullanılan ızgara perde parametrelerinden basıncı azaltmada en çok açı, yerleşim yeri ve ızgara 
perde boyu etkili olmuştur. Izgara perde kalınlığı ise herhangi bir etkiye sahip olmamıştır. Tank çalkantı simülasyonlarını izlemek için ParaView programı kullanılmıştır. ParaView programına aktarılan SPH modelinin 'surface' çıktıları sayesinde simülasyonlar izlenmiştir. SPH modelinde bazı iyileştirmelere gidilmesi gerektiği gözlemlenmiştir. Kullanılan parametreler değiştikçe modelin çalışma sürecinde de ciddi şekilde değişiklik olduğu için programın çalışma süresi iyileştirilmelidir. Program katı yüzeyde düzgün ölçüm yapamadığı için ölçüm noktaları tank başlığı üzerinde olmayacak ve tank içinde kalacak şekilde yerleştirilmiştir. Programın ölçüm noktası hassasiyeti giderilmelidir. 
Model parçacık prensibine dayandığı için parçacık boyutu değiştikçe hem programın çalışma süresinin arttığı, hem de ölçüm hataları çıktığı gözlemlenmiştir. Bu sebepleparçacık boyutunun modelin çalıştırılmasına olan etkisi azaltılmalıdır.

Abstract:
Simulation of the motion and motion effects of liquids has gained great importance in recent years. The way they are designed varies according to the area used, and many simulation models have emerged in line with these purposes and have been included in the studies in the fields of engineering. Sloshing of liquid refers to the movement of a container filled with a certain amount of liquid. Examining these sloshings and simulating their effects on the tank they are in are studies that have gained importance recently. The first sloshing studies were carried out to examine and eliminate the problems that may arise from sloshing in the fuel tank of the aircraft, and the results still constitute the aircraft design principles. Today, since many liquids such as water, fuel oil, liquefied gas (LNG or LPG) and chemicals are stored with certain storage methods and transported by various vehicles, the importance given to these studies has 
increased. Earthquake effects, vehicle maneuvers or structural vibrations cause sloshing in the transported liquids. Violent sloshing in vehicle fuel tanks can be so effective that it disturb balance of vehicle. Studies have shown that these sloshings occur mostly on the liquid surface, and to reduce them, various baffle walls must be placed inside the tank. It has been concluded that the most effective method to reduce the effects of sloshing is to use baffles placed in the tank. In this study, it is aimed to determine the pressure changes that will occur due to sloshing in cylindrical tanks and to model the reduction of these pressures using baffles with DualSPHysics, which is based on the Smoothed Particle Hydrodynamics (SPH) model. A horizontal cylindrical LNG type storage tank with a length of 1910 millimeters and an inner diameter of 380 millimeters, consisting of two heads and a main tank, was used for modelling. As the tank model used, the 1000 𝑚3 LNG independent C tank designed to be used on the LNG fuel ship was modeled and used in 1/17.8 scale. In order to be able to measure pressure on surface of the tank, a total of 8 pressure measuring points were placed, 7 on the right head of the tank and 1 on the top of the tank. The tank was moved by a sloshing force applied to a line running horizontally along the z-axis passing through the midpoint of the tank. By taking the beginning of the tank clockwise around this axis, the pitching motion was applied and turbulence was created in the tank. The water in the tank was first started to move by hitting the right head on which the measurement points were located. In order to reduce the turbulence in the tank and the pressure that this turbulence will create on the tank walls, baffles with different height (H), thickness (t), distance to the tank head (P) and placement angle (𝜃) are placed inside the tank. The baffles used were placed in the tank symmetrically with respect to the center, with equal inclination angles and 
positions. The main working principle of the program consists of a total of 4 files: XML, BAT and output files (out, vtk). The first two of these files were created by the model creator, and the remaining two were created by the program as result files after the program was run. Tank dimensions, fullness parameters of the liquid, periodic motion 
definitions were created in the XML file of the model, and the definition of calculation points was created in the BAT file. After defining the model parameters in the XML file, the model was run with the BAT file. In the main models, first, the model parameters such as liquid type, liquid height, time step, baffle type, baffle thickness, height, location and angle were selected. Water was used as a liquid in the models, and 60% Di was chosen as the appropriate filling level since it is considered a dangerous operating condition and can bring large impact pressure at the monitoring point near the free surface. Three different baffles were used as fine, baseline and coarse baffle type. As a result of the error rate and parameter selection, baseline type baffle was used in the main models. With the agreed 
parameters, a total of 29 models with baffle and 1 model without baffle, which were created in 17 initial stages and 12 in final stages, were set up and run. The model simulation was created for 15 seconds, and the pressure values of the model were read and recorded at every 0.04 second time step. The pressure values formed as a result of the turbulence of the 29 baffled models installed were compared with the pressure values formed in the non-baffled model, and the most suitable type model was selected. Since there is no baffle drawing code in the SPH model, the baffle drawing models
were drawn in 3D in AutoCAD, saved as STL file and transferred to the SPH program. Since the aim is to reduce the pressures formed in the non-baffled model, the pressure values obtained from the baffled models were compared with the pressure values of the non-baffled model. The anti-sloshing ratio was calculated by using the forces in the x direction acting on the tank head where the measurement points are located. Of these values between 0 and 1, the ones closest to 1 were chosen as the most effective model. It has been observed that the 17 models created in the first stage do not give 
good results in reduce the sloshing, on the contrary, in some cases, they increase the impact pressure due to sloshing (models with negative anti-sloshing rate). When the model simulation was followed, it was seen that the pressure increase was caused by the inadequacy of the baffle sizes. In the model turbulence simulation, it is seen that the water hitting the grates jumps over the grate and reaches the tank head before it can completely break its energy. Considering that this effect is due to the inadequacy of the baffle lengths, 12 new baffled models were installed with longer lengths. It has been observed that the created models reduce the impact pressure caused by the sloshing very well. As a result, it has been seen that 12 models out of 29 installed models reduce the sloshing and pressure in the tank, and the SPH model used gives very good results in making pressure calculations and creating model simulation. From the baffle parameters used, the baffle angle, location and baffle length were the most effective in reducing the pressure. Baffle thickness did not have any effect. If the model that reduces the turbulence best is considered as a parameter comparison; As an angle (θ) 23º, as baffle height (H) full length 380 mm, the distance to the tank head (P) in the middle of the tank was found to be the most suitable parameter. ParaView program was used to monitor the tank sloshing simulations. Thanks to the 'surface' outputs of the SPH model transferred to the ParaView program, tank sloshing simulations were monitored, the cause of the errors and the effects of the sloshing were better observed. It was observed that the SPH program performed very well in all models created, and its usability was observed in all future turbulence studies. When the model simulation images and pressure values created by the program are compared with a previous study, it has been seen that very close results are obtained. Minor differences between SPH models and comparison models are due to the particle size of the SPH model infrastructure. In addition, particle size sensitivity was noticed in the SPH model used. For this, non-baffled models with different particle sizes were created and pressure 
values at certain points were measured and evaluated. It has been observed that as the particle size is enlarged, the value in the pressure values deviates considerably from the true value. The reason for this is thought to be due to the increasing inter-particle distance as the particle size increases. In addition, it was determined that there was a 
significant change in the working time of the model. For these reasons, it was observed that some improvements should be made in the SPH model. As the parameters used change, the running time of the program should be improved, as the working process of the model changes drastically. Since the program cannot measure roughness on solid surfaces, the measurement points are placed not on the tank head and remain in the tank. The measurement point precision of the program must be eliminated. Since the model is based on the particle principle, it has been observed that as the particle size changes, both the running time of the program increases and measurement errors occur. For this reason, the effect of particle size on the operation of the model should be reduced.