modal modelling of nonlinear sloshing in moving tanks
TRANSCRIPT
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Introduction toModal Modelling of Nonlinear Sloshing in
Moving Tanks
by
Alexander Timokha (JenaKievTrondheim)
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Swirling – 3D rotational wave motion
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Overview
• Motivation• Basic free boundary problem• Coupling with tank motions • Multimodal method • Simplest example of the modal systems for 2D
flows
• 3D sloshing in a square base tank• Problems and perspectives
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Motivation
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Historical Industry MotivationsHistorical Industry Motivations
• Air and Spacecraft (dynamics and control)• Petroleum Storage Tanks (safety due to earthquake)• Oil Ship Tanker (dynamics and safety)• (LNG) Liquefied Natural Gas Carriers (dynamics and safety)• (TLD) Tuned Liquid Damper (safety, active control)
Sloshing liquid as a subsystem: COUPLING
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Moss type LNG Carriers
Membrane type LNG Carriers
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GT NO96
Gas Transport Containment (aft end)
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Tuned Liquid Dampers
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Free boundary problem
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Fluid Sloshing in a Moving Tank
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Free Boundary Problem
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Coupling with tank‘s dynamics
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Coupling
• Functions vo(t) and ω(t) determine tank‘s motions• The tank motions are affected by hydrodynamic
forces and moments F(t) and M(t), which are computed by integrals over Φ(x,y,z,t) and their derivatives
• ODE (tank‘s dynamics) + PDE (fluid)• Difficulties for coupled modelling
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Multimodal method
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Multimodal method as an analyticallyoriented approach to sloshing and coupling
• Potential flow, no overturning waves (statement described)• Vertical wall and no roof impact• Free surface elevation as a Fourier series by natural modes (example
for 2D flow)
∀ βi (t) represent free surface modes
• Variational formulation to derive a discrete model, which leads to system of nonlinear ordinary differential equations in time for βi (t)
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Importance of filling level
• Finite water depth sloshing (filling height/tank length>0.24)– Resembles standing wave
• Shallow water sloshing (filling height/tank length<0.1)– Hydraulic jump / bore– Thin vertical jet – runup
• Intermediate depth
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General modal system by MilesLukovsky
May be reduced to ODE in the modal functions βi, finitedimensional when ordering modal functions
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Hydrodynamic Forces
and Moments
This makes hydrodynamic forces/moments by function of generalised coordinates and provides a efficient coupling, i.e. derives a dynamic system for the entire object)
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Examples of the modal systems for 2D flows
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Asymptotic multimodal systems
• Physically defined ordering between modal functions βi(t) relative to the forcing τ
• Finite depth – NarimanovMoiseyev ordering: β1=O(τ1/3), β2=Ο(τ2/3),β3=Ο(τ)
• Secondary resonance ordering with decreasing depth and increasing excitation ε implies: βi(t)=Ο(τ1/3), i=1,N; βi(t)=O(τ2/3), i=N+1,2N; βi(t)=O(τ), i=2N+1,3N
• Boussinesq ordering for intermediate and shallow depth
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NarimanovMoiseyev ordering
• Resonant problem as a test, i.e. the forcing frequency/period is close to the lowest natural frequency/period
• Excitation amplitudetank length ratio is τ• Generalized free surface coordinate β1=O(τ1/3);
β2=Ο(τ2/3); β3=Ο(τ)
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Differential equations for finite depth
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Steadystate (periodical) solutions.Duffinglike responce and secondary resonance
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Transient response (most popular example !!!)
Comparison of experimental data (elevation near the wall)
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Periodical solutions as a perturbed bifurcation problem (Τ(β,λ,τ)=0, λ=λ(ω))
Unperturbed bifurcations τ=0
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Periodical solutions as a perturbed bifurcation problem (Τ(β,λ,τ)=0, λ=λ(ω))Perturbed bifurcations τ>0
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Periodical solutions as a perturbed bifurcation problem (Τ(β,λ,τ)=0, λ=λ(ω))
Perturbed secondary bifurcation τ>0
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Modal system accounting for secondary resonanceComparison with experiments and CFD calculations
(Smoothed Particles, Flow3D fails) for largeamplitude forcing; fluid depth/tank length=0.35
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Shalow sloshing ordering: comparison with experiments
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3D sloshing in a square base tank
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Free surface elevation for square based tank with finite depth.
Modal system by FaltinsenTimokha (2003)
• ζ=∑∑βik(t) cos(πi(x+0.5L))cos(πk(y+0.5L)
• β10=O(τ1/3) β01=O(τ1/3)
• β20=O(τ2/3) β11=O(τ2/3) β02=O(τ2/3)
• β30=O(τ) β21=O(τ) β12=O(τ) β03=O(τ)
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Planar, Square(diagonal) and swirling wave patterns
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Wave amplitudes A as a function of excitation frequency σ
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Periodical waves in a square base tank for longitudinal excitation. Effect of fluid depth
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Flow types (classified) in square based tank with longitudinal excitation. Effect of fluid depth
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Periodical solutions (classified) in a square base tank for longitudinal excitation. Effect of fluid depth
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Periodical solutions (classified) in a square base tank for longitudinal excitation. Effect of fluid depth
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Perodical solutions (classified) in a square base tank for longitudinal excitation. Effect of fluid depth
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Periodical solutions (classified) in a square base tank for longitudinal excitation. Effect of fluid depth
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Problems and perspectives
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Problems and perspectives• Modal systems exist for different types of the tanks.
However… the problems consist of:• Rigorous bifurcation analysis of periodic solutions for
existing multidimensional systems and related numerical (pathfollowing) schemes.
• Cauchy problem for modal system (transient waves) – numerical schemes for modal systems of large dimension including stiffness.
• Modal systems for noncylindrical tanks• Etc.
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Thank you for your attentionReferences to some asymptotic modal systems
3. Gavrilyuk, I., Lukovsky, I., Timokha, A. 2000 A multimodal approach to nonlinear sloshing in a circular cylindrical tank. Hybrid Methods in Engineering. 2, # 4.
4. Faltinsen, O., Rognebakke, O., Lukovsky, I., Timokha, A. 2000 Multidimensional modal analysis of nonlinear sloshing in a rectangular tank with finite water depth. J. Fluid Mech. 407.
5. Faltinsen, O., Timokha, A. 2001 An adaptive multimodal approach to nonlinear sloshing in a rectangular tank. J. Fluid Mech. 432.
6. Lukovsky, I., Timokha, A. 2001 Sound effect on dynamics and stability of fluid sloshing in zerogravity. Int. J. of Fluid Mech. Res. 28.
7. Faltinsen, O., Timokha, A. 2002 Asymptotic modal approximation of nonlinear resonant sloshing in a rectangular tank with small fluid depth. J. Fluid Mech. 470.
8. Faltinsen, O., Rognebakke, O., Timokha, A. 2003 Resonant threedimensional nonlinear sloshing in a squarebase basin. J. Fluid Mech. 487.
available at http://www.imath.kiev.ua/~tim