Experimental and Numerical Studies on the Shear Stability of Ship’s Thin Plates

The stability of thin plate plays an important role in the design and strength check of ship structure. In order to study the shear stability of ship’s thin plates, in-plane shear buckling tests were carried out using a picture frame fixture and a 3D full-field strain measurement system. The critical buckling load, full-field displacement/strain information, and load-displacement curve were obtained. The finite element model with the frame fixture was established based on ABAQUS, with the eigenvalue buckling analysis and nonlinear buckling analysis being carried out to obtain the mechanical response information of the buckling and post-buckling of the ship’s thin plate. The effectiveness and accuracy of the numerical simulation method are verified by comparing the numerical simulation with the experimental results. On this basis, the critical buckling load obtained by shear test, numerical simulation, and theoretical calculation is analyzed, and the function of the frame shear fixture and its influence on the critical buckling load are defined. The research in this paper provides a useful reference for the testing and simulation of in-plane shear stability of ship’s thin plates.

Shear, Stability and Mixing within the Ice-Shelf-Ocean Boundary Current

When the inclined base of an ice shelf melts into the ocean, it induces both a statically-stable stratification and a buoyancy-forced, sheared flow along the interface. Understanding how those competing effects influence the dynamical stability of the boundary current is the key to quantifying the turbulent transfer of heat from far-field ocean to ice. The implications of the close coupling between shear, stability and mixing are explored with the aid of a one-dimensional numerical model that simulates density and current profiles perpendicular to the ice. Diffusivity and viscosity are determined using a mixing length model within the turbulent boundary layer and empirical functions of the gradient Richardson number in the stratified layer below. Starting from rest, the boundary current is initially strongly stratified and dynamically stable, slowly thickening as meltwater diffuses away from the interface. Eventually, the current enters a second phase where dynamical instability generates a relatively well-mixed, turbulent layer adjacent to the ice, while beneath the current maximum, strong stratification suppresses mixing in the region of reverse shear. Under weak buoyancy forcing the timescale for development of the initial dynamical instability can be months or longer, but background flows, which are always present in reality, provide additional current shear that greatly accelerates the process. A third phase can be reached when the ice shelf base is sufficiently steep, with dynamical instability extending beyond the boundary layer into regions of geostrophic flow, generating a marginally-stable pycnocline through which the heat flux is a simple function of ice-ocean interfacial slope.

Comparison of the Chemical and Technological Characteristics of Wholemeal Flours Obtained from Amaranth (Amaranthus sp.), Quinoa (Chenopodium quinoa) and Buckwheat (Fagopyrum sp.) Seeds

A sound fundamental knowledge of the seed and flour characteristics of pseudocereals is crucial to be able to promote their industrial use. As a first step towards a more efficient and successful application, this study focuses on the seed characteristics, chemical composition and technological properties of commercially available pseudocereals (amaranth, quinoa, buckwheat). The levels of starch, fat, dietary fiber and minerals were comparable for amaranth and quinoa seeds but the protein content is higher in amaranth. Due to the high amount of starch, buckwheat seeds are characterised by the lowest amounts of fat, dietary fibre and minerals. Its protein content ranged between that of amaranth and quinoa. Buckwheat seeds were larger but easily reduced in size. The lipid fraction of the pseudocereals mostly contained unsaturated fatty acids, with the highest prevalence of linoleic and oleic acid. Palmitic acid is the most abundant unsaturated fatty acid. Moreover, high levels of P, K and Mg were found in these pseudocereals. The highest phenolic content was found in buckwheat. Amaranth WMF (wholemeal flour) had a high swelling power but low shear stability. The pasting profile strongly varied among the different quinoa WMFs. Buckwheat WMFs showed high shear stability and rate of retrogradation.