• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.114-121
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• 2004

Frictional heating in brakes causes thermoelastic distortion of the contacting bodies and hence affects the contact pressure distribution. The resulting thermo-mechanical coupling can cause thermoelastic instability (TEI) if the sliding speed is sufficiently high, leading to non-uniform heating called hot spots and low frequency vibration known as hot judder. The vibration of brakes to the known phenomenon of frictionally-excited thermoelastic instability is estimated studying the interface temperature and pressure evolution with time. A simple model has been considered where a layer with half-thickness$\alpha$slides with speed V between two half-planes which are rigid and non-conducting. The advantage of this properlysimple model permits us to deduce analytically the critical conditions for the onset of instability, which is the relation between the critical speed and the growth rate of the interface temperature and pressure. Symmetrical component of pressure and temperature distribution at the layer interfaces can be more unstable than antisymmetrical component. As the thickness $\alpha$ reduces, the system becomes more apt to thermoelastic instability. For perturbations with wave number smaller than the critical$m_{cr}$ the temperature increases with m vice versa for perturbations with wave number larges than $m_{cr}$ , the temperature decreases with m.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.18-25
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• 2005

In this study, the main focus is the simulation of acoustic wave scattering in trailing edge and the analysis of the generation mechanism of instability wave by the interaction of trailing edge, shear flow and initial disturbance. The numerical algorithm is based on CFD/CAA hybrid method with high-order computational aeroacoustic method. It is found that steady mean flow gradient terms play a crucial role on the generation of instability wave through the comparison of simulations of Simple Linearized Euler Equation and Full Linearized Euler Equation. Through the comparison with the results of Full Navier-Stokes Equation, it is reasonable and efficient to use the Full Linearized Euler Equation in the initial generation mechanism of the instability wave near the trailing edge.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.3
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• pp.320-329
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• 2017

In this research, we have calculated characteristics of wave-piercing high-speed planing hull, by using a RANS solver and overset grid method, for comparing with experimental measurements of that and simulating with several appendages, since the computed results of commercial CFD code look reasonable for the prediction of the performances of planing hulls on calm water in planing conditions. As a result, it is confirmed that the dynamic instability phenomena in pitch and heave motions (porpoising) occurred after a certain $Fn_V$, and effectively suppressed using some of appendages, especially the 0.5L spray rail is suppressed to 24-55 % in the pitch motion and 33-55 % in the heave motion. In spray phenomenon, 1L hard chine suppress spray effectively and it is effective to set the angle of appendages to be less than $0^{\circ}$ in order to suppress wave.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.294-299
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• 2012

An investigation into the influence of ultrasonic standing wave on the structural behavior of propane/air premixed flame has been made to get a clue to the combustion reaction acceleration and combustion instability, as well. Visualization technique utilizing the Schlieren method was employed for the observation of structural variation of the premixed flame. The flame shape and propagation velocity were measured according to the variation of equivalence ratio. It was found that the standing wave distorted the flame front and expedited a transition to the flame with turbulent nature.

• Journal of applied mathematics & informatics
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• v.42 no.1
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• pp.105-121
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• 2024

We consider incompressible, inviscid, stratified shear flows in β plane. First, we obtained an unbounded instability region intersect with semi-ellipse region. Second, we obtained a bounded instability regions depending on Coriolis, stratification parameters and basic velocity profile. Third, we obtained a criterion for wave stability. This has been illustrated with standard examples. Also, we obtained upper bound for growth rate.

• International Journal of Aerospace System Engineering
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• v.2 no.2
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• pp.58-61
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• 2015

Combustion instability in solid rocket motors is a long-term open problem since the first rockets were used. Based on the numerous previous studies, it is known that the limit cycle amplitude is one of the key characteristics of the nonlinear combustion instability in solid rocket motors. Flandro's extended energy balance corollary, aims to predict the limit cycle amplitude of complex, nonlinear pressure oscillations for rockets or air-breathing engines, and leads to a precise assessment of nonlinear combustion instability in solid rocket motors. However, based on the comparison with experimental data, it is revealed that the Flandro's method cannot accurately describe such a complex oscillatory pressure. Thus in this work we make modifications of the nonlinear term in the nonlinear wave equations which represents the interaction of different modes. Through this modified method, a numerical simulation of the cylindrical solid rocket has been carried out, and the simulated result consists well with the experimental data. It means that the added coefficient makes the nonlinear wave growth equations describe the experimental data better.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.232-235
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• 2007

A comprehensive numerical study was carried out to identify the on-set condition of the cell structures of oblique detonation waves (ODWs). Mach 7 incoming flow was considered with all other flow variables were fixed except the flow turning angles varying from 35 to 38. For a given flow conditions theoretical maximum turning angle is $38.2^{\circ}$ where the oblique detonation wave may be stabilized. The effects of grid resolution were tested using grids from $255{\times}100$ to $4,005{\times}1,600$. The numerical smoked foil records exhibits the detonation cell structures with dual triple points running opposite directions for the 36 to 38 turning angles. As the turning angle get closer to the maximum angle the cell structures gets finer and the oscillatory behavior of the primary triple point was observed. The thermal occlusion behind the oblique detonation wave was observed for the $38^{\circ}$ turning angle.

• Journal of Korean Society of Steel Construction
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• v.29 no.6
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• pp.401-410
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• 2017

This study deals with dynamic instability of a tendon moored submerged floating tunnel (SFT) due to tendon slack. In general, environmental loadings such as wave and current govern SFT design. Especially, the wave force, whose amplitude and direction continuously change, directly induces the dynamic behavior of the SFT. The motion of the floating tube, induced by the wave force, leads dynamic response of the attached tendons and the dynamic change of internal forces of the tendons significantly affects to the fatigue design as well as the structural strength design. When the severe motion of the SFT occurs due to significant waves, tendons might lose their tension and slack so that the floating tube can be transiently instable. In this study, the characteristics of dynamic instability of the SFT due to tendon slack are investigated performing hydrodynamic analysis. In addition, the effects of draft, buoyancy-weight ratio, and tendon inclination on tendon slack and dynamic instability behavior are analytically investigated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.161-169
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• 1989

A stability problem on wave instability of natural convection flow along isothermal vertical cylindrical surfaces has been formulated, accounting for the non-parallelism of the basic flow and thermal fields. Then the problem is solved numerically under the simplifying assumption of the parallelism of the basic flow quantities. It is shown that the flow corresponding to the same characteristic boundary layer thickness becomes more stable as the value of the curvature parameter increases. The stability characteristics for Pr=0.7 appear to be more sensitive to the curvature parameter than those for Pr=7.

• Structural Engineering and Mechanics
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• v.14 no.4
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• pp.455-472
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• 2002

The paper involves the study on the elastic and elasto-plastic stress wave propagation in the 1-D and 2-D solid media. The Smooth Particle Hydrodynamics equations governing the elastic and elasto-plastic large deformation dynamic response of solid structures are presented. The proposed additional stress points are introduced in the formulation to mitigate the tensile instability inherent in the SPH approach. Both incremental rate approach and leap-frog algorithm for time integration are introduced and the new solution algorithm is developed and implemented. Two examples on stress wave propagation in aluminium bar and 2-D elasto-plastic steel plate are included. Results from the proposed SPH approach are compared with available analytical values and finite element solutions. The comparison illustrates that the stress wave propagation problems can be effectively solved by the proposed SPH method. The study shows that the SPH simulation is a reliable and robust tool and can be used with confidence to treat transient dynamics such as linear and non-linear transient stress wave propagation problems.