Rishad A. Irani

Ice Nucleation Studies of Mineral Dust Particles with a New Continuous Flow Diffusion Chamber

A new continuous flow diffusion chamber (CFDC) has been designed and constructed to study the ice nucleation efficiency of natural and anthropogenic aerosol particles over a range of temperatures and supersaturations. The CFDC system at Dalhousie University, Canada is based on the design of (Rogers et al. 1988, 1994) at Colorado State University, USA. A steady airflow (2.83 lpm) composed of sheath flows and an aerosol flow passes through the annular gap of the diffusion chamber. The walls of the chamber are ice-covered and are held at different temperatures. Aerosol particles are injected into the center of the gap near the location of maximum supersaturation. Particles greater than 5 μm in aerodynamic diameter are removed with impactors before entry to the chamber. Ice crystals are identified with an optical particle counter at the outlet of the chamber. In this article we report on the ice nucleation results of two mineral dust particles of potential atmospheric relevance, kaolinite and montmorillonite. Our results indicate that kaolinite and montmorillonite act as efficient ice nuclei in deposition/condensation nucleation mode. The onset relative humidity of both kaolinite and montmorillonite mineral dust particles were determined. The percentage of active ice nuclei is higher in montmorillonite compared to kaolinite at each temperature within the experimental conditions. The fraction of active ice nuclei increases with decreasing temperature and also with increasing relative humidity.

Modelling a Single-Wheel Testbed for Planetary Rover Applications

This paper presents a dynamic model for a smooth wheel travelling through loose sandy soil. Many models that are used for such wheel-soil interactions are typically static or quasi-static models. The new model builds upon these widely-used models by adding the dynamic effect of the soil deformation. The new model is validated using experiments that were carried on a new single wheel testbed which was constructed at Dalhousie University. During experiments with a smooth wheel it was noticed that the track of the wheel had repeatable ridges. Moreover, it was noticed that the corresponding torque and force data also had oscillations in it with the periods of the harmonic coinciding with the ridges in the sand left by the track of the wheel.Copyright

Dynamic Wheel-Soil Model for Lightweight Mobile Robots with Smooth Wheels

This paper extends traditional wheel–soil modeling for lightweight mobile robots operating with smooth wheels on dry sandy soil to capture the transient oscillations that have been observed in drawbar pull measurements. To model these drawbar pull fluctuations, a new dynamic pressure–sinkage relationship was extrapolated from the literature and experimental observations of smooth rigid wheels operating in sandy soil. The resulting two-dimensional high-fidelity analytical model was validated with a unique single-wheel testbed designed from a Blohm Planomat 408 computer-numerically-controlled creep-feed grinding machine. For the experimental conditions used in this research, the resulting model is able to predict the fluctuating values of the drawbar pull for a variety of slip ratios and normal loads tested with a smooth rigid wheel in sandy soil. The new model was tuned at a single normal load over a variety of slip ratios and was then able to predict the amplitude and frequency of the oscillations about the mean drawbar pull at different normal loads and slip ratios.

Development of a new cutting fluid delivery system for creepfeed grinding

This paper develops and validates a new cutting fluid application technique for creepfeed grinding with aluminium oxide grinding wheels. The new fluid delivery system incorporates several concepts found in the literature including high-speed fluid application, coherent jets, air scrapers and concentration effects associated with synthetic cutting fluids. Experiments were carried out on a Blohm Planomat 408 creepfeed grinding machine in Dalhousie Universitys Grinding Laboratory. These experiments show that the new coolant delivery system can achieve an 83% increase in material removal rate over a state-of-the-art coherent jet and provide the capability of keeping the liquid cutting streams separate during creepfeed grinding. As a result, this new system has the potential to significantly increase production rates.

Controller design and motion compensation for marine towed bodies

At sea, a vessel is subjected to waves. If the ship is towing a submerged body containing sensory equipment, then any ship motion at the surface can impart unwanted disturbances on the towed body via the tow line. To help compensate for these disturbances, a winch on-board the host vessel can be operated in response to the surface ships motion by reeling in or reeling out the tow line. A corresponding method, however, is needed to determine how much cable the winch controller should pay in or out to effectively attenuate unwanted towed-body motion. This paper, therefore, proposes and explores four different approaches that, using various combinations of sensor measurements such as ship inertial measurement unit data and measured tow-line angle, can be used to try to establish appropriate winch control actions for motion compensation of marine towed bodies. Small-scale towed-body experiments using a spherical tow body as well as computer simulations are carried out to test the control approaches and, by analyzing the corresponding motion reduction achieved by each of these winch control strategies, the most effective method is identified.

Vortex-Induced Vibrations of a Low-tension Cable-Sheave System Modeled using Nonlinear Finite Elements

This work presents a finite element model of a cablesheave system constructed to model cable vibrations due to vortex shedding in low-tension cases. The study assesses the potential for vortex shedding to lead to detachment of the cable from the sheave. The absolute nodal coordinate formulation is utilized to define the cable structural dynamics. Vortex shedding forces are incorporated by coupling the cable’s equations of motion to a Van der Pol equation, also known as a wakeoscillator and the cable-sheave interaction is described using a contact penalty method. The study examines the contribution of vortex shedding occurring at the cable’s natural frequency to the cable motion. For the cases studied the model demonstrates that vortex shedding alone results in very small vibration amplitudes and thus is unlikely to result in cable detachment. Keywords—finite element method; absolute nodal coordinate formulation; cable-sheave interaction; vortex-induced vibration

Application of a dynamic pressure-sinkage relationship for lightweight mobile robots

This paper investigates a dynamic pressure-sinkage relationship which can be used in a wheel-soil model to better capture periodic variations observed in sinkage, drawbar pull and normal force as a rigid wheel interacts with loose sandy soil. The dynamic wheel-soil model can be used for wheels with or without grousers. Several case studies are presented to demonstrate the usefulness and applicability of this dynamic pressure-sinkage relationship. Hill climbing experiments were carried out using a smooth-wheel micro rover with a fixed suspension to confirm operational regions of the dynamic pressure-sinkage relationship. Single wheel testbed experiments were carried out to determine how well the model can predict changes in the number and length of the grousers on the wheel. It was concluded that dynamic pressure-sinkage relationship can predict the observed oscillations in the sinkage, drawbar pull and normal force with a single tuning case as the slip ratio and the configuration of the wheel changes.