Numerical visualization of nappe oscillation
Abstract The unsteady global dynamics of a gravitational liquid sheet interacting with a onesided adjacent air enclosure, typically referred to as nappe oscillation, is addressed, under the assumptions of potential flow and presence of surface tension effects. Preliminary physical insights of the sheet centerline sinuous modes show that the nappe dynamics features the propagation of two wave fronts both directed downstream or one downstream and the other one upstream depending on whether the flow Weber number is greater or less than unity, respectively; moreover, the overall system behaves as a driven damped spring-mass oscillator, where the liquid sheet acts as the mass and the air enclosure as the spring. The findings of the eigenvalues spectral analysis closely agree with direct numerical simulations of the partial differential equation governing in the space-time domain the global evolution of the disturbances, starting from an initial gaussian-like shape.
On the stability of a falling liquid curtain
The stability of a falling liquid curtain is investigated. The sheet of liquid is assumed two-dimensional, driven by gravity and influenced by a compressible cushion of air enclosed on one side of the curtain. The linear stability problem is formulated in the form of an integro-differential eigenvalue problem. Although experimental efforts have consistently reported a peak in the low-frequency range of the spectrum, the linear stability results do not show instabilities at these frequencies. However, a multi-modal approach combined with a projection onto low-frequency modes reveals a dominant and robust instability feature that is in good agreement with experimental measurements. This instability manifests itself as a wave packet, consisting of a linear superposition of linear global modes, that travels down the curtain and causes a strong pressure signal in the enclosed air cushion.
Professional tensions in client-centered practice: using institutional ethnography to generate understanding and transformation.
For almost 20 years, occupational therapists have advocated client-centered practice. Yet client-centered practice is fraught with tensions that arise outside the practice of individual occupational therapists. This paper is guided by two questions: What produces professional tensions in client-centered practice? and What understanding and change might be generated using institutional ethnography? The sociological theory and method of institutional ethnography are described using data from an ongoing investigation of mental health services as a social institution. Illustrated are the research aim, research questions, and institutional analysis that distinguish institutional ethnography from conventional ethnography. Two professional tensions are associated with attempts to fulfill client-centered practice in mental health. One is that of working at cross-purposes with the prevailing hierarchical structure; the other tension is that of being celebrated yet subordinated in the medical and management hierarchies of health services. Although client-centered practice is difficult to do, the authors recommend institutional ethnography as a research approach to generate understanding and transformation of the context and practice of occupational therapy.