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2 2017

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Minimal Energy Dissipation Rate and Director Orientation Relative to External Dissipative Fields such as Temperature and Velocity Gradients in Nematic and Cholestric Liquid Crystals

Sarman S., Wang Y-L., Laaksonen A.

Computational Methods in Science and Technology

2017

Vol. 23, No. 3

239--250

The purpose of this review article is to summarize observations accumulated over the years on director alignment phenomena in nematic and cholesteric liquid crystals by molecular dynamics simulation of molecular model systems and by experiment on real systems. The main focus is on the alignment angle between the director and external dissipative fields such as velocity gradients in various flow geometries and temperature gradients doing irreversible work on the system. A general observation is that the director attains an orientation relative to the field where the energy dissipation rate is minimal in the steady state. In the case of planar elongational flow, it can be proven by using symmetry arguments that the energy dissipation rate must be either maximal or minimal and simulations have shown that is minimal. In planar Couette flow both simulations and experiments imply that the energy dissipation rate is minimal in the steady state. Finally, in the case of heat conduction, symmetry arguments imply that the energy dissipation rate must be either minimal or maximal and simulations and experiments indicate that it is minimal. All these observations can be explained by applying a recently proven theorem according to which the energy dissipation rate is minimal in the steady state in the linear regime at low fields.

Instrumentation and monitoring of Large-Span Culvert Built under a Railway in Finland

Asp O., Laaksonen A.

Archiwum Instytutu Inżynierii Lądowej

2017

Nr 23

53--60

Large span soil-steel culverts are rarely used in Finland as vehicular underpasses. The large span and low soil cover height together with high traffic loads place high demands on the construction of culvert backfills. Traffic-induced stress changes and the fatigue resistance of the plates play a major role in the endurance of a culvert. According to design calculations, the most critical section of the culvert is the crown. For this reason, the focus of this project is on the assessment of the structural behaviour and performance of the crown area under the influence of traffic load. The structural performance of the culvert was verified by monitoring stress changes and deformations under live railway traffic, which proved the suitability of the multi-plated culvert built under a railway.