Modelling of dimensional stability of fiber reinforced composite materials

Various methods of predicting the expansion and diffusion properties of composite laminates are reviewed. The prediction equations for continuous fiber composites can be applied to SMC composites as the effective fiber aspect ratio in the latter is large enough. The effect of hygrothermal expansion on the dimensional stability of composite laminates was demonstrated through the warping of unsymmetric graphite/epoxy laminates. The warping is very sensitive to the size of the panel, and to the moisture content which is in turn sensitive to the relative humidity in the environment. Thus, any long term creep test must be carried out in a humidity-controlled environment. Environmental effects in SMC composites and bulk polyester were studied under seven different environments. The SMC composites chosen are SMC-R25, SMC-R40, and SMC-R65

A Generalized Compressible Cavitation Model

A new multi-phase model for low speed gas/liquid mixtures is presented; it does not require ad-hoc closure models for the variation of mixture density with pressure and yields thermodynamically correct acoustic propagation for multi-phase mixtures. The solution procedure has an interface-capturing scheme that incorporates an additional scalar transport equation for the gas void fraction. Cavitation is modeled via a finite rate source term that initiates phase change when liquid pressure drops below its saturation value. The numerical procedure has been implemented within a multi-element unstructured framework CRUNCH that permits the grid to be locally refined in the interface region. The solution technique incorporates a parallel, domain decomposition strategy for efficient 3D computations. Detailed results are presented for sheet cavitation over a cylindrical headform and a NACA 66 hydrofoil

Lower extremity soft tissue surgery in spastic cerebral palsy: experience from a government rehabilitation unit

Background: Spastic cerebral palsy (CP) remains the most common type of CP and may be managed surgically or non-surgically depending upon its severity. Recent advances have replaced single-level surgery by the concept of multilevel surgery where multiple levels of musculoskeletal pathology, in one/both lower limbs, are addressed during one operative procedure, requiring only one hospital admission and one period of rehabilitation. This study assessed the outcome of lower limb soft tissue surgery in children with spastic CP in a government rehabilitation unit and measured its feasibility with limited infrastructure facilities and patient compliance.Methods: The study comprised of 26 patients aged between 2-12 years. Physical examination and GMFCS scores were recorded and evaluation of sitting balance, standing balance and gait were done. Musculotendinous soft tissue lower limb surgery was performed at one or more levels unilaterally or bilaterally and the results were interpreted.Results: Complete or near complete correction of deformities were attained by all children postoperatively. Significant improvements were noted in the gross motor functional classification system (GMFCS) scores. All parents and children were satisfied with the surgical outcome and reported improvement in functional abilities and locomotion in the follow-up along with better quality of life and mobility. Conclusions: Lower limb soft tissue surgery is a valuable aid in improving functional abilities and locomotion in children with spastic CP. Surgery should be undertaken depending upon clinical indications and can be successfully carried out in government hospitals with ordinary infrastructure in developing countries as well

Simulations of a Liquid Hydrogen Inducer at Low-Flow Off-Design Flow Conditions

The ability to accurately model details of inlet back flow for inducers operating a t low-flow, off-design conditions is evaluated. A sub-scale version of a three-bladed liquid hydrogen inducer tested in water with detailed velocity and pressure measurements is used as a numerical test bed. Under low-flow, off-design conditions the length of the separation zone as well as the swirl velocity magnitude was under predicted with a standard k-E model. When the turbulent viscosity coefficient was reduced good comparison was obtained a t all the flow conditions examined with both the magnitude and shape of the profile matching well with the experimental data taken half a diameter upstream of the leading edge. The velocity profiles and incidence angles a t the leading edge itself were less sensitive to the back flow length predictions indicating that single-phase performance predictions may be well predicted even if the details of flow separation modeled are incorrect. However, for cavitating flow situations the prediction of the correct swirl in the back flow and the pressure depression in the core becomes critical since it leads to vapor formation. The simulations have been performed using the CRUNCH CFD(Registered Trademark) code that has a generalized multi-element unstructured framework and a n advanced multi-phase formulation for cryogenic fluids. The framework has been validated rigorously for predictions of temperature and pressure depression in cryogenic fluid cavities and has also been shown to predict the cavitation breakdown point for inducers a t design conditions

Unsteady Analyses of Valve Systems in Rocket Engine Testing Environments

This paper discusses simulation technology used to support the testing of rocket propulsion systems by performing high fidelity analyses of feed system components. A generalized multi-element framework has been used to perform simulations of control valve systems. This framework provides the flexibility to resolve the structural and functional complexities typically associated with valve-based high pressure feed systems that are difficult to deal with using traditional Computational Fluid Dynamics (CFD) methods. In order to validate this framework for control valve systems, results are presented for simulations of a cryogenic control valve at various plug settings and compared to both experimental data and simulation results obtained at NASA Stennis Space Center. A detailed unsteady analysis has also been performed for a pressure regulator type control valve used to support rocket engine and component testing at Stennis Space Center. The transient simulation captures the onset of a modal instability that has been observed in the operation of the valve. A discussion of the flow physics responsible for the instability and a prediction of the dominant modes associated with the fluctuations is presented

Simulation of Cavitation Instabilities in Inducers

The cavitating performance of a sub-scale configuration of the SSME low pressure fuel pump (LPFP) has been simulated at off-design flow conditions where a back-flow vortex is generated at the leading edge. The numerical simulations have been compared with measured experimental data both for velocity profiles upstream of the inducer as well dynamic pressure traces on the shroud at the leading edge. Velocity profiles in the back-flow vortex for flow rates down to 70 percent of design were quantified; the swirl velocity comparisons were good while the axial velocity profile were reasonable but slightly over predicted the core velocity. Dynamic cavitating performance was modeled at a moderate Nss number of 20000 for 90 percent of design flow coefficient where rotational cavitation modes are present The source of this instability resulted from the interaction of the cavity with the neighboring blade leading to the detachment of the cavity that rotates relative to the blade and generates an asymmetric cavity pattern. The asymmetrical cavities generate a large radial load on the shaft which rotates at the fundamental mode of the rotational cavitation. For the sub-scale configuration the radial force amplitude was 186 lb-f which gives a non-dimensional force factor of 0.0116. Spectral analyses of the dynamic pressure traces on the shroud, at the leading edge plane, were compared with experimental measurements. The fundamental rotational cavitation mode was observed to be 125 Hz which is approximately 1.29 N (rotational frequency is 96. Hz); both the frequency and relative amplitude compared well with the unsteady measurements. In addition to the fundamental rotation cavitation mode the data shows substantial energy with multiple peaks in the 5 -7.5 N range. This range was reasonably represented in the numerical results although the spectrum was not as rich. A helical pressure wave at the fundamental mode is found to propagate upstream and a potential for interaction with structural elements was identified.http://deepblue.lib.umich.edu/bitstream/2027.42/84299/1/CAV2009-final122.pd

Computing Thermal Effects of Cavitation in Cryogenic Liquids

A computer program implements a numerical model of thermal effects of cavitation in cryogenic fluids. The model and program were developed for use in designing and predicting the performances of turbopumps for cryogenic fluids. Prior numerical models used for this purpose do not account for either the variability of properties of cryogenic fluids or the thermal effects (especially, evaporative cooling) involved in cavitation. It is important to account for both because in a cryogenic fluid, the thermal effects of cavitation are substantial, and the cavitation characteristics are altered by coupling between the variable fluid properties and the phase changes involved in cavitation. The present model accounts for both thermal effects and variability of properties by incorporating a generalized representation of the properties of cryogenic fluids into a generalized compressible-fluid formulation for a cavitating pump. The model has been extensively validated for liquid nitrogen and liquid hydrogen. Using the available data on the properties of these fluids, the model has been shown to predict accurate temperature-depression values