Air Load Research Articles

Unification of hydrogen-enhanced damage understanding through strain-life experiments for modeling

Strain-life testing of a 4130 pressure vessel steel was conducted in hydrogen gas through the careful adaptation of an existing hydrogen-gas mechanical-testing apparatus. The strain-life mechanical results reveal that hydrogen has a significant effect on the strain-life, and impacts both the elastic and plastic responses of the material. Microscopy analysis shows a distinct difference in the microstructural development of the material after cyclic loading in air compared to after loading in hydrogen gas. These experimental results will inform coupled damage and deformation modeling.

Assessment of the impact of hydrogen on the stress developed ahead of a fatigue crack

The microstructure generated in a low carbon steel under cyclic loading in air and a 40 MPa gaseous hydrogen environment has been compared as a function of distance from the crack tip. The presence of hydrogen resulted in the formation of a smaller and more equiaxed dislocation cell structure that extended further from the crack tip than the one generated in air. This enhancement and extension of the dislocation structure by hydrogen is consistent with it modifying the generation rate and mobility of dislocations as well as dislocation interactions. Qualitative assessment of the dislocation structure ahead of the crack tip found the stress ahead of the crack tip to vary linearly as ln(1/x), where x is the distance from the crack tip irrespective of the test environment. Hydrogen caused a shift to higher stresses, implying the critical damage level for crack propagation will be achieved more rapidly with a concomitant increase in the crack propagation rate.

Incidence of Alarming Microbial Pathogens over Refuse Dump Sites and Its ‘Harmful Distance’ in Port Harcourt, Southern Nigeria

Aim: Microbial air quality over illegal refuse dump sites in Port Harcourt, Nigeria, was conducted to assess the aero-microbial contaminant of dumpsite to the closest neighbourhood and the harmful distance.
 Place and Duration of Study: The dump sites were located at oil mill market (Latitude 4.8578 N4°51'28.06344'' Longitude 7.06653 E7°3'59.50152'') and Iloabuchi Timber market (longitude N4.790191, latitude E6.988416) all in Port Harcourt, South South Nigeria. The samplings were carried out between June (dry season) and July (wet season) 2018.
 Methodology: The microbial concentration of air around the dump sites were measured using the “sedimentation method” that involved exposing different sterile Petri dishes containing nutrient agar, Mac Conkey agar, and sabauroud dextrose agar to the air for ten minutes. The exposures were carried out at different locations within and around the dump site viz; Top of the dumpsite at different altitude (3ft, 6ft and 9ft above dump surface), 0m, 10m away from the dumpsite, and at the nearest neighbourhood which is about 100m away from the dumpsite. These samplings were carried out to the left and right sides of the dump sites. The samplings were carried out between June and July 2018, so as to compare the microbial load between the dry and wet seasons.
 Result: The microbes at the dump sites were in most cases higher than the microbes at the neighbourhood (100m away to the left and right). Seasonal occurrence revealed that microbial load in air during the dry season (6.037±0.92 cfu/min-m2) is higher than during the wet season (1.814±0.19 CFU/min-m2). Percentage variation amongst heterotrophic bacterial isolates revealed, Staphylococcus massiliensis (47.90%) > Erwinia psidii (18.24%) > Shigella dysenteriae (18.17%) > Bacillus simplex (6.08%) > Saminicoccus kunminingensis (3.23%) > Corynebacteriun afermentans (3.00%) > Paenibacillus celluositrophycus (2.25%) > Streptococcus parasuis (5.26%); percentage variation amongst enteric bacterial isolates revealed, Staphylococcus aureus (28.57%) > Geobacillus stearothermophilus (20.82%) > Escherichia coli (8.16%) and Bacillus carboniphilus (8.16) > Salmonella enterica (6.94%) > Bacillus smithii (6.12%) > Macrococcus brunensis (4.49%) > Lactobacillus kitasatonis (3.67%) > Klebsiella pneumonia (2.86%) > Staphylococcus saccharolyticus (2.45%) > Bacillus badius (2.04%) = Paenibacillus lautus (2.04%) > Brevibacillus laterosporus (1.63%). The fungal distribution revealed, Aspergillus fumigatus (16.62%) > Microsporium canis (15.40%) > Aspergillus flavus (14.75%) > Aspergillus niger (10.99%) > Conidiobolus coronatus (10.19%) > Pheaocremonium parasiticum (6.97%) > Fusarium chlamydosporium (6.70%) > Trychophyton etriotrephon (5.63%) > Trychophyton quinckeanum (4.02%) > Lichtheeimia corymbifera (3.57%) > Cladosporium cladosporioides (2.95%) > Saccharomyces spp (2.68]%). 
 Conclusion: The presence of microbial pathogens such as Escherichia coli, Staphylococcus aureus, Bacillus spp, Klebsiella pneumonia, Salmonella enterica and Aspergillus species, is alarming and of great health concern. The harmful distance exceeds 100m away from the dump site which encroached 30 meters into residential areas. This research work revealed the relevance of Environmental air monitoring in any Governmental Waste Management System and the potential hazard of open dump system of waste disposal around residential area.

Fluid-structure interactions for the air blast loading of elastomer-coated concrete

The fluid-structure interaction (FSI) effect experienced by an elastomer-coated concrete slab subjected to blast loading in air is studied numerically. The aim is to establish whether a flexible coating alters blast-structure interactions and whether this can explain the apparent blast mitigating capability of this retrofit solution as reported in published experimental investigations. Numerical models for a typical concrete and spray-on elastomer coating are established and a Coupled Eulerian–Lagrangian (CEL) model is employed to predict the air blast response. A 1D FSI analysis suggests that the elastomer coating increases the peak compressive stress in the concrete during short timescale pressure wave interactions. But the effect on the total imparted momentum is small, across a range of target mass and blast intensity. However, due to momentum sharing, the impulse imparted to the concrete plate is reduced in the coated configuration. By extending the analysis into 2D, it is found that the displacement of a concrete slab is marginally reduced when coated on either the blast-receiving or non-blast-receiving face. Thus, it is postulated that the elastomer contributes a small, beneficial mechanical effect. Finally, the need for a fully coupled (CEL) approach to model the blast-structure interaction is interrogated. For a wide range of cases, the results suggest that using a purely Lagrangian approach, in which a pressure-time history is directly applied to the structure (thereby neglecting full representation of FSI effects), is sufficient to capture the deflection behaviour of coated concrete plates. However, it is shown that the significance of the error associated with this simplification depends on the blast intensity and slab geometry under consideration.

Analysis of a DOAS operation in different Spanish climates using an experimentally validated TRNSYS model

Current ventilation airflow rates imposed by building regulations eventually force HVAC systems to remove high latent loads. Dedicated outdoor air systems (DOASs) equipped with a desiccant wheel, are an alternative to conventional refrigeration equipment for humidity control in buildings. This paper studies the operation of a DOAS intended to remove the ventilation air and space latent load in different Spanish climates during the summer season. The model developed in TRNSYS was validated with experimental data using the root mean standard error (RMSE). Maximum RMSE of 0.94 °C and 0.472 g/kg were obtained for the temperatures and humidity ratios of the process and regeneration airflows. The RMSE for the compressor power input was of 52.2 W. The results obtained with the developed model showed that the DOAS exhibited better performance in humid climates with moderate temperatures (Bilbao and Barcelona). It was also found that its application in dry climates (Madrid) was not appropriate, and that a high outdoor temperature lowered the DOAS efficiency when comparing cities with similar latent loads (Bilbao and Sevilla) or when comparing residential and commercial schedules.

LPV Modeling and Tracking Control of Dissimilar Redundant Actuation System for Civil Aircraft

Dissimilar redundant actuation systems (DRAS) are in practice in advanced aircraft in order to increase reliability and to resolve the actuator failure issue due to common cause. This paper addresses the problem of force fighting that occurs due to dynamics mismatch of two dissimilar actuators in DRAS and provides a method to achieve precise tracking of aircraft control surface. The nonlinear system dynamics are first transformed into linear parameter varying (LPV) form using recursive least square (RLS) method. The LPV observer based controller is then designed to synchronize the positions of dissimilar actuators in DRAS and to drive the control surface smoothly. By applying linear matrix inequalities (LMIs), parameter dependent Lyapunov function (PDLF) is obtained to achieve global stability and to compute the controller and observer gains. To test controller according to real flight condition, an external disturbance signal that acts as air load is applied at the control surface input. Several simulations on the nonlinear system validate the dominant performance of proposed controller as compared to the existing methods in literature.

Effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing

This paper studies the effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing with four degrees of freedom (4-DOF). A clearance function is used to describe the film thickness of air journal bearings with angular misalignment along two perpendicular directions. The finite different method (FDM) and an iterative procedure are applied to solve the Reynolds equation and obtain the air film pressure distribution. Various eccentricity ratios and rotating speeds are taken into considerations for the comparisons of static performances of the air journal bearing under different tilt angles. The results show that the air film thickness, load capacity, stiffness, load moment, attitude angle and volume flow rate are affected greatly by the angular misalignment.

Structural Transformations Influence on Mechanical-and-Physical and Chemical Properties of Fe-Cr-Co Alloys in Heating

Four model alloys of the Fe-Cr-Co system have been tested under elongation at a standart rate and under pure bending with a constant load in air and in a corrosive medium after different treatment. Fractographic studies were performed depending on the cobalt content and duration of thermal aging at 450 °C. The experiment results are that the Fe-Cr-Co-based alloys with 5–10 % of cobalt are an acceptable composition for maraging steels since they have high strength and ductility, as well as corrosion resistance and low sensitivity to stress corrosion cracking.

An analytical model for cross-flow indirect evaporative cooling considering condensation under various fresh air conditions

The indirect evaporative cooling (IEC) regarded as an energy efficient technology has been widely applied to reduce thermal load from the fresh airflow in air conditioning system. When the climate is hot and humid, the condensation would take place in fresh air channels. With the aim of evaluating the performance of IEC with condensation, this paper presents a 2-D analytical model for cross-flow IEC considering condensation. The performance under various fresh air conditions has been investigated. The results show that the condensation would reduce the thermal load of fresh air significantly. Although the occurrence of condensation would weaken sensible heat transfer, the latent heat transfer even reaches up to 4.6 kW and around 40% moisture content of fresh air would be removed under full condensation state.

A NILM method for cooling load disaggregation based on artificial neural network

The demand of building energy management has increased due to high energy saving potentials. Load monitor and disaggregation can provide useful information for building energy management systems with detailed and individual loads of the building, so corresponding energy efficient measures can be taken to reduce the energy consumption of buildings. The technique is investigated widely in residential buildings known as Non-Intrusive Load Monitoring (NILM). However, relevant studies are not sufficient for non-residential buildings, especially for the cooling loads. This paper proposes a NILM method for cooling load disaggregation using artificial neural network. The cooling load is disaggregated into four categories: building envelope load, occupant load, equipment load and fresh air load. Two approaches are used to realize the load disaggregation: one is based on the Fourier transfer of the cooling loads, the other takes the cooling load, dry-bulb temperature and humidity of outdoor air, and time as inputs. By implementing the methods in a metro station, the performance of the proposed method can be obtained. Results show that both approaches can realize the load disaggregation accurately, with a RMSE less than 11.2. The second approach is recommended with a higher accuracy.

Fatigue properties of B1914 superalloy at high temperatures

B1914 is a nickel-based superalloy with an increased amount of B (boron) and C (carbon) to reach an adequate amount of borides and carbides in the cast structure ensuring improved creep properties. However, the influence of the structure on the material high-cycle fatigue properties is not sufficiently described. The present study brings the experimental results on the high-cycle fatigue properties of a cast polycrystalline nickel-based boron-rich B1914 superalloy, obtained at temperatures of 800, 900 and 950 °C. The cast superalloy was processed by hot isostatic pressing (HIP) to diminish the casting defects. The fatigue tests were performed in symmetrical loading in laboratory air. The fracture surfaces of the specimens were studied by scanning electron microscopy in order to describe the influence of temperature on the fatigue crack initiation and propagation. Change of the primary fatigue crack propagation mechanism from the crystallographic to the non-crystallographic mechanism was observed with increasing temperature. Decrease of a material lifetime and decrease of the fatigue endurance limit due to the increasing testing temperature was observed.

ОБЕСПЫЛИВАНИЕ ВОЗДУХА ПРИ ПОГРУЗКЕ И ТРАНСПОРТИРОВКЕ ТВЕРДЫХ ПОЛЕЗНЫХ ИСКОПАЕМЫХ

ОБЕСПЫЛИВАНИЕ ВОЗДУХА ПРИ ПОГРУЗКЕ И ТРАНСПОРТИРОВКЕ ТВЕРДЫХ ПОЛЕЗНЫХ ИСКОПАЕМЫХ

Gimbaled Tiltrotor Conversion Flight Loads Prediction Using Three-Dimensional Structural Analysis

This paper presents a method for modeling gimbaled rotor aeromechanics in Experimental 3D structural dynamics solver, which is a next-generation three-dimensional finite-element-based rotor structural dynamics solver. The rotor is modeled using a single blade with a free flap hinge at the hub, the motion of which is suppressed at integer multiples of the blade passage frequency by introducing harmonics of the joint rotation angle as additional trim variables, efficiently simulating gimbal kinematics. Rotor frequencies are examined for a three-bladed gimbaled rotor model and are found to combine the modes of both free flap hinge and fixed flap hinge (cantilevered) one-bladed models, similar to a teetering rotor, justifying the gimbal modeling methodology. Gimbal flapping is examined for a proprotor in edgewise flight: successful suppression of steady and 3/rev flapping indicates the gimbal model accurately represents the rotor kinematics. Air loads and blade loads are examined with and without with the gimbal model, revealing an increase in 3/rev sectional normal aerodynamic force on the blade but a decrease in the 3/rev flap and lag bending moment when the gimbal is added. Three-dimensional axial stress distribution at the blade root is examined, revealing only minor differences with and without the gimbal model, primarily in the flex beam.

Comparison of EnergyPlus and IES to model a complex university building using three scenarios: Free-floating, ideal air load system, and detailed

The energy performance gap is one of the most discussed issues in the design community since energy modeling became an integral part of the building design process. Different limitations apply to almost every building performance simulation (BPS) software available today and to have confidence in the predictions of whole-building energy models it is necessary to have a thorough understanding of various features, specific capabilities, and disadvantages of BPS tools. The main contribution of this work is the use of three methods of evaluation with different levels of complexity, free-floating, ideal air load system, and detailed method to analyze and compare the capabilities of EnergyPlus and IES to model complex LEED silver multi-purpose university building. Consequently, this study provides new information regarding capabilities of two extensively used BPS tools to model advanced and innovative buildings, and in particular HVAC systems that are increasingly becoming used in high-performance commercial and institutional buildings worldwide. The difference between the total energy consumptions of the EnergyPlus and IES models developed according to the final construction drawings was approximately 2.1%, whereas differences between the heating and cooling loads of the EnergyPlus and IES models with ideal air load systems were 6 MWh (1.7%) and 0.86 MWh (7.8%), respectively. The high consistency between the models’ aggregated predictions are particularly pertinent and encouraging for certification programs such as LEED, which take into account aggregated energy consumption data in their assessments. The findings also emphasize the importance of the modeler's assumptions regarding the modeling of HVAC systems and their impact on the model's predictions.

Microbial air contamination with air borne bacteria in the outdoor environment at Janakpurdham, Nepal

Background and Objectives: Bacteria can cause allergic asthma and seasonal allergies, diseases which are increasingly prevalent in developing nations. Allergic asthma is currently affecting millions of people in Nepal. Therefore, the objective of this study was designed to measure the bacterial load in outdoor air.
 Materials and Methods: Airborne outdoor bacteria were assessed during the spring season using conventional methods to investigate the enumeration of airborne microorganisms. This was determined by sampling air using the ‘settle plate technique’. The air samples were collected during the spring season (February-March) from 10 different areas of Janakpur. Counts of airborne bacteria were measured as CFUs collected by gravity onto Nutrients Agar plates. Samples were taken periodically over a period of 2 months of February and March 2017.
 Results: A total of 7,404 bacterial colonies were counted on 30 Petri plates that were exposed for 1 hour. The maximum number of colonies of bacteria was 412. Similarly, the least number of bacterial colonies was 32. Higher numbers of CFUs were found in the petri plates which were exposed for 1 hour in comparison to the petri plates which were exposed for 30 minutes. According to the measurement, 36.6% of total CFUs of bacteria were collected during morning hours, 28.4% during day time and 35% during evening hours. Also, the highest numbers of colonies of bacteria were found in the petri plates that were exposed in ward number 7 and the least number of bacterial colonies were obtained in ward number 9.
 Conclusion: The bacteriological quality of air in janakpur was very poor. Very high microbial load was found in the outdoor air in Janakpur. The microbial count was found higher in morning than the noon and evening.

High Speed Pneumatic Stepper Motor for MRI Applications.

Presented in this paper is an exploration into the efficacy of a plastic, four-cylinder piston pneumatic motor designed for driving medical instruments inside magnetic resonance imaging (MRI) systems. Because of the increasing use of MRI for diagnostic and interventional purposes and the benefits that could be realized by operating with real-time MR image guidance, there exists a significant need for MRI compliant surgical devices. Some type of actuation mechanism is necessary to drive such devices. The motor can be controlled to operate in a "step" type motion by using pneumatic valves to sequentially apply air pressure to push the piston surfaces, meaning the motor is metal-free and does not use electricity. The stepwise nature of this piston stepper motor is ideal for the accurate, controlled movements required for MRI-guided interventions. The motor was geared down by a gearbox to increase torque. Performance indices determined include output torque and achievable rotational velocity with respect to factors such as air pressure and load conditions. The stepper motor achieved speeds of approximately 2000rpm, and maximum output torques of approximately 19Nmm. The motor represents a high speed pneumatic stepper motor design capable of actuating devices in MR environments without affecting image quality.

A New Spin on Small-Scale Combustor Geometry

The ultra-compact combustor (UCC) is an innovative combustor system alternative to traditional turbine engine combustors with the potential for engine efficiency improvements with a reduced volume. Historically, the UCC cavity had been configured such that highly centrifugally loaded combustion took place in a recessed circumferential cavity positioned around the outside diameter (OD) of the engine. One of the obstacles with this design was that the combustion products had to migrate radially across the span of a vane while being pushed downstream by a central core flow. This configuration proved difficult to produce a uniform temperature distribution at the first turbine rotor. The present study has taken a different spin on the implementation of circumferential combustion. Namely, it aims to combine the combustion and space saving benefits of the highly centrifugally loaded combustion of the UCC in a new combustor orientation that places the combustor axially upstream of the turbine versus radially outboard. An iterative design approach was used to computationally analyze this new geometry configuration with the goal of fitting within the casing of a JetCat P90RXi. This investigation revealed techniques for implementation of this concept including small-scale combustor centrifugal air loading development, maintaining combustor circumferential swirl, combustion stability, and fuel distribution are reported. The final combustor configuration was manufactured and experimentally tested, validating the computational results. Furthermore, dramatic improvements in the uniformity of the turbine inlet temperature profiles are revealed over historical UCC concepts.

The High-Temperature Creep Behavior of In-Situ TiB2 Particulate Reinforced Al12Si4Cu2NiMg Composite

In the present work, the in-situ TiB2/Al12Si4Cu2NiMg (denoted as ‘Al-12Si’) composites were successful synthesized through the salt-metal reaction route. The influences of weight fraction (0, 4, and 9 wt.%) and heat treatment (T5 and T7) on the tensile creep deformation were studied at ≥623 K under constant load in air. At the investigated temperature and stress condition, TiB2 particles increased creep deformation resistance, as compared to the unreinforced alloy, while the composites presented similar strength when the weight fraction of reinforcement increased from 4% to 9%. It was found that the steady-state creep rate was lower in the 4 wt.% TiB2/Al-12Si composite (T5), as compared with that in the 4 wt.% TiB2/Al-12Si composite (T7). The result has been rationalized by using the load-partitioning model and relative to the evolution of the rigid phase. The creep deformation of the 4 wt.% TiB2/Al-12Si composite was controlled by the climb of dislocations in the aluminum alloy matrix.

Characterization of an Aircraft Auxiliary Power Unit Test Rig for Cycle Optimization Studies

Detailed information of the thermodynamic parameters, system performance, and operating behavior of aircraft auxiliary power units (APU) cycles is rarely available in literature. In order to set up numeric models and study cycle modifications, validation data with well-defined boundary conditions is needed. Thus, the paper introduces an APU test rig based on a Garrett GTCP36-28 with detailed instrumentation, which will be used in a further step as a demonstration platform for cycle modifications. The system is characterized in the complete feasible operating range by alternating bleed air load and electric power output. Furthermore, simulations of a validated numerical cycle model are utilized to predict the load points in the operating region which were unstable during measurements. The paper reports and discusses turbine shaft speed, compressor air mass flow, fuel mass flow, efficiencies, compressor outlet pressure and temperature, turbine inlet and outlet temperature as well as exhaust gas emissions. Furthermore, the results are discussed with respect to the difference compared to a Hamilton Sundstrand APS3200. Though the efficiencies of the GTCP36-28 are lower compared to the APS3200, the general behavior is in good agreement. In particular, the effects of separate compressors for load and power section are discussed in contrast to the GTCP36-28 system design comprising a single compressor. In general, it was shown that the GTCP36-28 is still appropriate for the utilization as a demonstration platform for cycle modification studies.

Residual stress gradient and relaxation upon fatigue deformation of diamond-like carbon coated aluminum alloy in air and methanol environments

Amorphous diamond-like carbon coating (DLC) of 2 μm in thickness was deposited over the aluminum alloy substrate using magnetron sputtering deposition technique. In order to understand the efficacy of coating deposition, coated specimens were subjected to rotating bending fatigue in air and methanol environments respectively. Raman spectroscopy was used in conjunction with grazing incidence X-diffraction technique to obtain depth-resolved residual stress gradients of coated-aluminum substrate. The residual stress generated due to coating deposition was calculated using Raman spectroscopy and it was −1.13 ± 0.16 GPa (compressive in nature). Furthermore, Raman spectroscopy was utilized for the quantification of stress relaxation upon fatigue loading in air and methanol environments. It was observed that the irrespective of the testing environment, good correlation exists between the stress relaxation magnitude and number of cycles endured before failure.