The Effect of Structural Parameters on Response Characteristics of Aeroelastic System in the Presence of Dynamic Stall

The effect of structural paramters on the response and aerodynamic stiffness characteristics of the free aeroelastic system under the influence of dynamic stall is investigated adopting CFD (Computational Fluid Dynamics) method. The equilibrium angle of the spring and the structural stiffness are taken as parameters of interest. Systems with small equilibrium angles enter the symmetric limit-cycle state more quickly after a Hopf bifurcation and experience dynamic stall in both directions, rather than slowly decreasing in minimum angle of attack and remaining in the asymmetric limit-cycle state before dynamic stall in the opposite direction, as is the case with systems with large spring equilibrium angles. Thus, aerodynamic stiffness of system with large equilibrium angles can be more significantly influenced by the change in aerodynamic moment characteristics at the minimum angle of attack. Furthermore, by increasing the initial angular velocity, we find that the system response all becomes symmetric limit cycle and therefore the aerodynamic stiffness appears to have a monotonically increasing characteristic. As to the effect of structural stiffness, it is found that the limit cycle amplitude first increases with structural stiffness after bifurcation, then the amplitude is unchanged with varying structural stiffness at higher Mach number. Energy maps show that the parametric distribution of the energy transfer contributes to this phenomenon. Moreover, when entering the symmetric limit cycle state, the structural stiffness no longer has a significant effect on the aerodynamic stiffness of the system, as the increase in the aerodynamic stiffness is determined solely by the increase in dynamic pressure without the effect of changes in moment characteristics.

Comparison of two end-to-end continuous sutures for intestinal anastomoses in dogs.

Background: Single-layer appositional closures are preferred to inverting or everting patterns, as submucosal apposition has been shown to promote primary healing of the intestinal wall, whereas inverted or everted closures require second-intention healing and can increase the risk of luminal stenosis or anastomosis site leakage. There are different suture patterns available, but relatively few studies comparing these aspects have been published.The aim of this study was to compare two suture techniques for end-to-end anastomosis of the canine intestine (jejunum and colon): handsewn intestinal anastomosis by appositional simple continuous suture and inverting Cushing suture. The objectives of this study were to investigate 1.) whether the type of suture influences the specific effort to which the anastomosis site is submitted to, 2.) whether the anastomosis technique influences the diameter of the intestinal lumen and 3.) survival and complication rates in canine clinical cases undergoing end-to-end anastomoses. Results: The equilibrium angle for implanting the sutures in an anastomosis is 35°, aspect completely fulfilled by the simple continuous suture. The efforts to which sutures are submitted to in anastomoses are minimal for the Cushing suture. The difference in size of the anastomoses’ lumen between simple continuous suture and the Cushing suture are minimal, without being statistically relevant. The differences between the lumen of the anastomoses performed using PDS and those performed using PGA are not statistically relevant. The retrospective analysis of the outcome for 676 dogs (clinical cases) that underwent intestinal resection and anastomosis reveals that the dehiscence rate was 1.48%, out of which 1.18% following simple continuous anastomoses, and 0.3% following Cushing anastomoses. Narrowing of the intestinal lumen due to anastomotic healing was not registered.Conclusions: Use of the Cushing suture should be considered for performing an end-to-end intestinal anastomosis, although more studies are required to determine if there are any clinically significant differences between the sutures investigated in this study.

Development of a vibrationless sorting system

Aim of study: Size classification is essential in many industrial processes. Most classical sorting systems use vibrations as a means of classification function. In this study, a vibration-free sorting system called helical cylindrical screen has been developed against the disadvantages of vibrating systems and proposed to be used in the sorting of crop seeds.Area of study: Adana City, Turkey.Material and methods: The movement of the seed mass on the screen surface was formulated and the mass movement along the circular-helical paths was analytically expressed, leading to some operational parameters for evaluation in the screen design. By combining the mass movement parameters with effective separation conditions, an algorithm was obtained against the desired mass flow rate to determine the appropriate values of the design parameters. Experiments were performed on the machine, which was manufactured to sort peanut seeds into two different sizes, small and large.Main results: The results obtained in the experiments (separation efficiency, mass flow rate, effect of grain size on separation efficiency and equilibrium angle) were compared with the theoretical ones. The separation efficiency of the machine (99% and above) was quite good and is not affected at all by the small size ratio contained in the mixtures. The limitations of the theoretical velocities (axis and tangent) of a seed moving on the cylindrical sieve were found to be consistent with those obtained experimentally.Research highlights: The helical cylindrical sieve can be used for other particulate agricultural products with smooth surfaces such as soybeans, kidney beans, peas, etc.

Study on Mechanical Model of Balance and Stiffness Characteristics of Fiber Reinforced Bellows Type Rubber Hose

The mechanical model related to the balance and stiffness characteristics of the bellows type rubber hose under internal pressure was studied. Based on the thin shell theory without considering bending moments and shear force, the equilibrium equation of the bellows type hose was established to obtain the mechanical equilibrium angle under different mechanical environments. Considering the deformation characteristics of the rope structure and the mechanical equilibrium angle of the hose, the deformation of the bellows type rubber hose was divided into two stages, including winding angle deflection and tensile deformation of fiber. Then the constitutive model of anisotropic material was introduced, and the physical equation of the bellows type hose was established to obtain the mechanical model of the balance and stiffness characteristics. According to the mechanical model, the influence of initial fiber winding angle, fiber layer thickness, the radius at the two ends of the hose, the length of hose, the curvature radius and internal pressure of hose on the balance and stiffness characteristics of hose was studied. Eventually, the structure of the hose was designed based on the mechanical model, to optimize the balance and stiffness characteristics of hose. The balance and stiffness characteristics of the optimized hose were verified by experiments. The theoretical and experimental results indicated that, the mechanical model of the balance and stiffness characteristics of the hose can be the theoretical basis for the optimization of structural parameters.

Establishment and verification of theoretical model for forming design of balanced curved rubber hose

This article focuses on the establishment of theoretical model for the formation of balanced curved rubber hose under pressure. According to the rotation angle of the cord along the axial direction in the curved rubber hose is the same as that in the straight hose before forming, the theoretical model of the straight hose length was established. Then based on the thin shell theory without considering bending moments and shear force, and considering the deformation characteristics of the rope structure and the mechanical equilibrium angle of the hose, the theoretical model of the balance performance was established. According to the theoretical model, the influence of structural parameters of curved hose on the length of the straight hose and the balance performance of hose was studied. Eventually, the finite element model was established to simulate the deformation process of the curved hose. Based on the calculation results of the theoretical and simulation model, the experiment of forming and balance performance of the curved hose was carried out. The experimental results are in good agreement with the theoretical and simulation model.

Flow physics and dynamics of flow-induced pitch oscillations of an airfoil

We conduct a computational study of flow-induced pitch oscillations of a rigid airfoil at a chord-based Reynolds number of 1000. A sharp-interface immersed boundary method is used to simulate two-dimensional incompressible flow, and this is coupled with the equations for a rigid foil supported at the elastic axis with a linear torsional spring. We explore the effect of spring stiffness, equilibrium angle-of-attack and elastic-axis location on the onset of flutter, and the analysis of the simulation data provides insights into the time scales and mechanisms that drive the onset and dynamics of flutter. The dynamics of this configuration includes complex phenomena such as bifurcations, non-monotonic saturation amplitudes, hysteresis and non-stationary limit-cycle oscillations. We show the utility of ‘maps’ of energy exchange between the flow and the airfoil system, as a way to understand, and even predict, this complex behaviour.

Establishing the torsional rigidity of a rotation module responsible for the flexion-extension motions of the elbow

The paper presents and discusses a system devised for the mobilisation of the elbow including a pair of agonist-antagonist pneumatic muscles aimed mainly at ensuring the accuracy of the rotation angle. This system is of SISO type (single input - single output) with the variable Δp (the pressure by that one of the muscles is charged symmetrically in the detriment of the other) as its input value. Further discussed are the dependency of the equilibrium angle on Δp and the possibility of controlling the torsional rigidity by adjusting the sum of the feed pressures.

Effects of non-equilibrium angle fluctuation on F1-ATPase kinetics induced by temperature increase

Non-equilibrium angle fluctuation in molecular motor F1-ATPase induces non-Arrhenius kinetics and negative correlation between Pi release and hydrolysis dwell time.

Computational study of infrared spectra of silica polymorphs via classical mechanics

A potential energy model that correctly reflects zeolite framework interactions is the premise for computational studies of the physical and chemical processes occurring inside zeolites, such as catalytic chemical reactions and adsorption. Infrared spectroscopy is a widely-used technique that is sensitive to the accuracy of the potential energy model. This work aims to develop such a potential that reproduces the infrared spectra of zeolites. In the first part of this thesis, the performance of two published potentials is tested in terms of predicting structural and dynamical properties for five silica polymorphs (three siliceous zeolites: siliceous faujasite, sodalite and silicalite; quartz; and cristobalite). Comparison between the silica polymorphs' model-predicted equilibrium angle distributions and infrared spectra shows that the core-shell model [Schroeder and Sauer, J. Phys. Chem. 1996, 100, 11043] predicts a broader Si-O-Si angle distribution and shifts angle-bending infrared modes to lower wavenumbers. The MZHB potential [Sahoo and Nair, J. Comput. Chem. 2015, 36, 1562], on the other hand, predicts angle-bending infrared modes that are consistently shifted to higher wavenumbers. The second part of this thesis presents a new potential via reparameterizing and extending the MZHB potential based on a sensitivity analysis, which investigates the relationships between model parameters and the structural properties of silica polymorphs. Better infrared predictions are achieved by the new potential. The results of the sensitivity analysis indicate that the lattice parameter might be a possible target for the parameterization of atomic partial charges for crystalline materials.

Evaluating the Effects of Ankle-Foot Orthosis Mechanical Property Assumptions on Gait Simulation Muscle Force Results

Musculoskeletal modeling and simulation techniques have been used to gain insights into movement disabilities for many populations, such as ambulatory children with cerebral palsy (CP). The individuals who can benefit from these techniques are often limited to those who can walk without assistive devices, due to challenges in accurately modeling these devices. Specifically, many children with CP require the use of ankle-foot orthoses (AFOs) to improve their walking ability, and modeling these devices is important to understand their role in walking mechanics. The purpose of this study was to quantify the effects of AFO mechanical property assumptions, including rotational stiffness, damping, and equilibrium angle of the ankle and subtalar joints, on the estimation of lower-limb muscle forces during stance for children with CP. We analyzed two walking gait cycles for two children with CP while they were wearing their own prescribed AFOs. We generated 1000-trial Monte Carlo simulations for each of the walking gait cycles, resulting in a total of 4000 walking simulations. We found that AFO mechanical property assumptions influenced the force estimates for all the muscles in the model, with the ankle muscles having the largest resulting variability. Muscle forces were most sensitive to assumptions of AFO ankle and subtalar stiffness, which should therefore be measured when possible. Muscle force estimates were less sensitive to estimates of damping and equilibrium angle. When stiffness measurements are not available, limitations on the accuracy of muscle force estimates for all the muscles in the model, especially the ankle muscles, should be acknowledged.