Ko-Choong Woo

Modelling of Ground Moling Dynamics by an Impact Oscillator with a Frictional Slider

This paper describes current research into the mathematical modelling of a vibro-impact ground moling system. Due to the structural complexity of such systems, in the first instance the dynamic response of an idealised impact oscillator is investigated. The model is comprised of an harmonically excited mass simulating the penetrating part of the mole and a visco-elastic slider, which represents the soil resistance. The model has been mathematically formulated and the equations of motion have been developed. A typical nonlinear dynamic analysis reveals a complex behaviour ranging from periodic to chaotic motion. It was found out that the maximum progression coincides with the end of the periodic regime.

Application of the harmonic balance method to ground moling machines operating in periodic regimes

Abstract A new system for ground moling has been patented by the University of Aberdeen and licensed world-wide. This new system is based on vibro-impact dynamics and offers significant advantages over existing systems in terms of penetrative capability and reduced soil disturbance. This paper describes current research into the mathematical modelling of the system. Periodic response is required to achieve the optimal penetrating conditions for the ground moling process, as this results in reduced soil penetration resistance. Therefore, there is a practical need for a robust and efficient methodology to calculate periodic responses for a wide range of operational parameters. Due to the structural complexity of a real vibro-impact moling system, the dynamic response of an idealised impact oscillator has been investigated in the first instance. This paper presents a detailed study of periodic responses of the impact oscillator under harmonic forcing using the alternating frequency-time harmonic balance method. Recommendations of how to effectively adapt the alternating frequency-time harmonic balance method for a stiff impacting system are given.

New electro-vibroimpact system

In this paper, a new vibro-impact mechanism based on a solenoid-actuated vibrator and its optimization are presented. The vibratory unit deploying electro-mechanical interactions of a conductor with oscillating magnetic field has been realized. The combination of resonance in an RLC circuit and a solenoid is found to create an oscillatory motion to the metal bar within the solenoid. This results in impacts of the metal bar on an obstacle block. Unanimously, the electromagnetic force generated within the solenoid acts as a non-linear electromagnetic spring. Hence, a vibro-impact mechanism gets created. This system is improved by adding a solid-state relay in series to the RLC circuit, which switches the power supply on and off periodically in accordance to a train of square waves produced by a function generator. This new control over the supplied harmonic voltage allows a small scale in the geometry of the vibratory unit but significantly increases the magnitude of impact forces and the progression rates obtained. This implies a very promising deployment of the mechanism in actual soil conditions.

Mechanical Oscillator in a Magnetic Field

An analytical solution for a system exhibiting oscillations of a conductor in magnetic field which is controlled by a discrete waveform is developed by means of multiple scales. The solution provides a guideline to design an effective control strategy so as to guide the system to a desirable attractor. Initial tests were also conducted to investigate the effect of hydrodynamic forces on an inertia excited by this mechanism.

Experimental investigation of a multi-stage impedance pumping system

Impedance pumping is defined as a valveless pumping mechanism, where an elastic tube is joined with a tube of different impedance, a periodic asymmetrical compression on part of the elastic tube will produce a unidirectional flow. Numerical and experimental studies had been conducted in the past in the field of impedance pumping, but no work was found to exploit the principle of impedance pumping for the transportation of large amounts of fluids in industries. This piece of work describes the investigation of open-loop multi-stage valveless pumping experimentally. Computational Fluid Dynamics (CFD) simulations were done and proven the validity of impedance pumping in a large scale apparatus [12]. In this paper, demonstration of experimental setup will be discussed and results are presented. This investigation concentrates on the synchronization of pumping location as two actuators are implemented in the experiment and aims to generate a larger pressure head and net flow rate. Results showed that only at c...