Air Damping Research Articles

Clustering and motif identification for occupancy-centric control of an air handling unit

Commercial and institutional buildings often operate at a fraction of their full occupancy, yet ventilation is frequently provided assuming maximum occupancy during working hours. Forecasting building occupancy can improve the operation of system level equipment by reducing chronic overventilation. However, developing actionable occupancy forecasting techniques for controls applications is subject to technological, security, and financial barriers. This paper proposes an occupancy forecasting technique that can be implemented in a controller given these constraints. Seven months of Wi-Fi, plug-in equipment and lighting electricity data were collected from an academic office building. Using Wi-Fi data, the building’s mean occupancy was demonstrated to be less than 25% of the 1000-person maximum. Representative daily occupancy profiles were produced by different clustering techniques. A classification tree was developed to determine motif occupancy profiles for day-ahead forecasting. Corresponding electrical profiles were taken to see if they followed the same trend as the occupancy profiles; 84.5% of days shared the same trends. The electrical data were fed through the classification tree, with a successful occupancy classification rate of 70.4% and error of 47 ± 69 persons at 95% confidence. A controls implementation for adaptive outdoor air damper actuation based on this technique is proposed for future work.

Improved Modal Damping Characterization for Small-Scale Heliogyro Blades

The heliogyro solar sail maneuvers by actuating high-aspect-ratio blades at their root with sinusoidal pitch profiles, producing spin-averaged forces and moments. The lightweight blade material has little inherent damping, requiring active control to attenuate blade vibration caused by maneuvering. Paradoxically, some amount of inherent damping at the blade’s higher-frequency modes is needed to add damping to the larger-magnitude low-frequency modes, and so the control design’s robustness depends on the accuracy of the blade damping model. Therefore, characterization of blade damping is critical for increasing the Technology Readiness Level for the heliogyro. This paper describes damping characterization tests performed on small-scale heliogyro blades hanging in a high-vacuum chamber, the closest analog possible for centrifugally loaded blades in space. Improvements to the measurements and a new modal damping algorithm, which the authors call the incremental and reduced frequency response function method, allowed separate flap and twist damping ratios to be calculated for the first three modes of these lightly damped blades to within ±2% error. This unprecedented precision enables definitive conclusions that the residual air damping is insignificant and that an assumption of a linear viscous torsional blade damping model is insufficient for the design of a robust proximal blade twist feedback controller.

Design and modeling of a highly sensitive microelectromechanical system capacitive microphone

A single-chip microelectromechanical system (MEMS) capacitive microphone is designed and modeled. The mechanical model of the structure is extracted and the mathematical equations for a description of the microphone behavior are obtained. Then the proposed microphone characteristics are considered. In this structure, by adding Z-shape arms around the diaphragm, diaphragm hardness is decreased and diaphragm displacement becomes uniform. The sensitivity and the pull-in voltage are improved despite the decreasing size. The perforated diaphragm of this microphone is supported by Z-shape arms at its four corners. These arms around the diaphragm decrease the stiffness and air damping of the microphone. The behavior of this microphone is also analyzed by the finite element method. The structure has a diaphragm thickness of 2 μm, a diaphragm size of 0.32 × 0.32 mm2, an air gap of 2 μm, and a highly doped monocrystalline silicon wafer as a backplate. The proposed microphone is simulated with IntelliSuite software. According to the results, the new microphone has a sensitivity of 14.245 mV / Pa and a pull-in voltage of 5.83 V. The results show that the proposed MEMS capacitive microphone is one of the best structures in performance. The obtained mathematical equations for description of the microphone’s behavior have good agreement with the simulation results.

Characterization and pro-inflammatory potential of indoor mold particles.

A number of epidemiological studies find an association between indoor air dampness and respiratory health effects. This is often suggested to be linked to enhanced mold growth. However, the role of mold is obviously difficult to disentangle from other dampness-related exposure including microbes as well as non-biological particles and chemical pollutants. The association may partly be due to visible mycelial growth and a characteristic musty smell of mold. Thus, the potential role of mold exposure should be further explored by evaluating information from experimental studies elucidating possible mechanistic links. Such studies show that exposure to spores and hyphal fragments may act as allergens and pro-inflammatory mediators and that they may damage airways by the production of toxins, enzymes, and volatile organic compounds. In the present review, we hypothesize that continuous exposure to mold particles may result in chronic low-grade pro-inflammatory responses contributing to respiratory diseases. We summarize some of the main methods for detection and characterization of fungal aerosols and highlight in vitro research elucidating how molds may induce toxicity and pro-inflammatory reactions in human cell models relevant for airway exposure. Data suggest that the fraction of fungal hyphal fragments in indoor air is much higher than that of airborne spores, and the hyphal fragments often have a higher pro-inflammatory potential. Thus, hyphal fragments of prevalent mold species with strong pro-inflammatory potential may be particularly relevant candidates for respiratory diseases associated with damp/mold-contaminated indoor air. Future studies linking of indoor air dampness with health effects should assess the toxicity and pro-inflammatory potential of indoor air particulate matter and combined this information with a better characterization of biological components including hyphal fragments from both pathogenic and non-pathogenic mold species. Such studies may increase our understanding of the potential role of mold exposure.

A Switchable High-Performance RF-MEMS Resonator with Flexible Frequency Generations

Resonators with multi-frequency generations at the device-level are highly desired in the future multi-band, reconfigurable, and compact wireless communications. In this work, a switchable radio frequency micro-electro-mechanical system (RF-MEMS) resonator with multiple electrodes is presented. The resonator is designed to operate at the whispering gallery modes (WGMs). Simultaneous excitations of the second to seventh modes with high Q values are implemented within a single device using a pair of electrodes for driving and sensing. For effective multi-frequency excitations, the electrode span angle is optimized. The frequencies of the 37 μm and 18 μm-radius resonators range from 53 MHz to 176 MHz and 112 MHz to 366 MHz, respectively. The Q values in each mode are over 104. Moreover, with the multi-electrode configurations, the specific mode can be enhanced with other modes suppressed. A more than 6 dB improvement of the spectrum peak is realized and the high Q values are maintained. A comprehensive theory is built up to clarify the driving/sensing principles under different electrode configurations. Furthermore, the air damping is found to have a significant effect on Q values for resonator with high stiffness vibrating in all the WGMs. The Q values in vacuum have at least two times improvement. The high-performance switchable resonator could dramatically reduce the power consumption, simplify the processing circuits, and occupy less footprint, which has great potential applications in future advanced RF front end systems.

Control Performance of Damping and Air Spring of Heavy Truck Air Suspension System with Optimal Fuzzy Control

Control Performance of Damping and Air Spring of Heavy Truck Air Suspension System with Optimal Fuzzy Control

In-plane air damping of micro- and nano- mechanical resonators

This study investigates the effect of air damping on in-plane silicon micro/nano-resonators sandwiched between two electrodes (two ports) for sensing and actuation. Experimental measurements are presented for the quality factor (Q) as varying pressure for several case studies of clamped–clamped and clamped–free micro/nano-beam resonators of various geometrical parameters and airgap dimensions. The focus of this work is on large airgap dimensions, where typically squeeze-film damping is assumed negligible. In addition to the fundamental first mode, several results are shown when the resonators are operated near their second or third modes of vibrations. Several curves are generated to show the dependence of the quality factor on the resonator size, boundary condition, and mode order. Several analytical models are applied to investigate the dominant dissipations mechanisms and the models capability to predict Q on both low and higher pressure regimes, and the results are compared to the experimental data.

Moist and Mold Exposure is Associated With High Prevalence of Neurological Symptoms and MCS in a Finnish Hospital Workers Cohort.

BackgroundIndoor air dampness microbiota (DM) is a big health hazard. Sufficient evidence exists that exposure to DM causes new asthma or exacerbation, dyspnea, infections of upper airways and allergic alveolitis. Less convincing evidence has yet been published for extrapulmonary manifestations of dampness and mold hypersensitivity syndrome ).MethodsWe investigated the prevalence of extrapulmonary in addition to respiratory symptoms with a questionnaire in a cohort of nurses and midwives (n = 90) exposed to DM in a Helsinki Obstetric Hospital. The corresponding prevalence was compared with an unexposed cohort (n = 45). Particular interest was put on neurological symptoms and multiple chemical sensitivity.ResultsThe results show that respiratory symptoms were more common among participants of the study vs. control cohort, that is, 80 vs 29%, respectively (risk ratio [RR]: 2.56, p < 0.001). Symptoms of the central or peripheral nervous system were also more common in study vs. control cohort: 81 vs 11% (RR: 6.63, p < 0.001). Fatigue was reported in 77 vs. 24%, (RR: 3.05, p < 0.001) and multiple chemical sensitivity in 40 vs. 9%, (RR: 3.44, p = 0.01), the so-called “brain fog”, was prevalent in 62 vs 11% (RR: 4.94, p < 0.001), arrhythmias were reported in 57 vs. 2.4% (RR: 19.75, p < 0.001) and musculoskeletal pain in 51 vs 22% (RR: 2.02, p = 0.02) among participants of the study vs. control cohort, respectively.ConclusionThe results indicate that the exposure to DM is associated with a plethora of extrapulmonary symptoms. Presented data corroborate our recent reports on the health effects of moist and mold exposure in a workplace.

Prediction of dependability for soft landing system with air dampers with Monte Carlo method

Prediction of dependability for soft landing system with air dampers with Monte Carlo method

Effect of Geometric Imperfections on Anchor Loss and Characterisation of a Gyroscope Resonator with High Quality Factor

A critical functional part of a hemispherical resonator gyroscope (HRG) is the mechanical resonator, and a few million quality factor (Q-factor) is needed for the lowest resolution. This paper focuses on anchor loss of a HRG of a few millimeters in size. A detailed parametric study of dimensions and shell imperfections due to fabrication is carried out. A sensitivity study of the effect of shell mean radius, shell thickness, stem radius, stem height on the Qanchor is carried out. The effect of geometric imperfections such as shell offset, shell tilt, shell thickness variation, and unbalance is studied in detail. From the study, it is inferred that the anchor loss becomes very significant and approaches other loss mechanisms even with minor geometric imperfections in the hardware realisation. Based on the sensitivity study, the dimensional and geometric tolerances are arrived for precision fabrication. Precision resonator is fabricated as per the requirement of minimum anchor loss. The significance of other damping mechanisms such as air damping, excitationinduced damping, thermoelastic dynamic damping and surface dissipation is also discussed. Surface characterisation before and after surface treatment has been carried out using nanoindentation technique with regard to surface loss. Functional parameters of operating frequency and Q-factor are evaluated using laser Doppler vibrometry (LDV).

Research and Adjustment of Temperature Deviation on Heating Wall of Front and Rear Wall Opposed Coal-fired Boiler of 1000WM Unit

No.2 boiler is designed by Dongfang boiler group Co., LTD, and is ultra supercritical parameter boiler with variable pressure. In order to alleviate the side wall temperature deviation and to reduce the maximum wall temperature of super-heater, the total air volume alteration test, external secondary air damper alteration test, over-fire air alteration test and the shrinkage adjustment is performed. The test results show that oxygen increase and shrinkage adjustment can improve the deviation of wall temperature and steam temperature. After increasing oxygen, plate super-heater wall temperature deviation reduced by 26 °C, and its outlet steam temperature deviation reduced by 14 °C. After shrinkage adjustment, plate super-heater wall temperature deviation reduced by 34 °C, and the wall temperature difference of final super-heater reduced from 50 °C to 25 °C, the wall temperature of side B plate super-heater reduced by 25 °C.

A comprehensive study of non-linear air damping and “pull-in” effects on the electrostatic energy harvesters

In this paper, a new comprehensive model is presented to optimize the design of vibration based electrostatic energy harvester working in standard atmosphere. This model considers the non-linear air damping force induced by the movement of proof mass as well as the “pull-in” effect from the electrostatic force. Important parameters such as the height of stoppers on the bottom plate, the initial gap between the bottom plate and proof mass and the surface potential of the electret layer have been investigated. With the microelectromechanical system (MEMS) technology, a series of energy harvesters have been fabricated with various parameters. The measurements of devices show excellent agreement with the simulations. For the first time, the “pull-in” phenomenon has been observed during the harvesting test as our expectation. The model provides a promising optimization route for the electrostatic energy harvester with broad bandwidth, decent power output while avoiding the “pull-in” effect.

Modeling and Experimental Validation of the Chaotic Behavior of a Robot Whip

ABSTRACTAlthough the whip is a common tool that has been used for thousands of years, there have been very few studies on its dynamic behavior. With the advance of modern technology, designing and building soft- body robot whips has become feasible. This paper presents a study on the modeling and experimental testing of a robot whip. The robot whip is modeled using a Pseudo-Rigid-Body Model (PRBM). The PRBM consists of a number of pseudo-rigid-links and pseudo-revolute-joints just like a multi-linkage pendulum. Because of its large number of degrees of freedom (DOF) and inherited underactuation, the robot whip exhibits prominent transient chaotic behavior. In particular, depending on the initial driving force, the chaos may start sooner or later, but will die down because of the gravity and air damping. The dynamic model is validated by experiments. It is interesting to note that with the same amount of force, the robot whip can generate a velocity more than 3 times and an acceleration up to 43 times faster than that of its rigid counterpart. This gives the robot whip some potential applications, such as whipping, wrapping and grabbing. This study also helps to develop other soft-body robots that involve nonlinear dynamics.

Experimental design and numerical investigation of a photoacoustic sensor for a low-power, continuous-wave, laser-based frequency-domain photoacoustic microscopy.

.We have developed a photoacoustic (PA) sensor using a low-power, continuous- wave laser and a kHz-range microphone. The sensor is simple, flexible, cost-effective, and compatible with commercial optical microscopes. The sensor enables noncontact PA measurements through air, whereas most current existing PA techniques require an acoustic coupling liquid for detection. The PA sensor has three main components: one is the chamber that holds the sample, the second is a resonator column used to amplify the weak PA signals generated within the sample chamber, and the third is a microphone at the end of the resonator column to detect the amplified signals. The chamber size was designed to be as the thermal diffusion length and viscous-thermal damping of air at room pressure and temperature are 2 and 1 mm, respectively. We numerically and experimentally examined the effect of the resonator column size on the frequency response of the PA sensor. The quality factor decreased significantly when the sample chamber size was reduced from to due to thermos-viscous damping of the air. The quality factor decreased by 27%, demonstrating the need for optimal design for the sample chamber and resonator column size. The system exhibited noise equivalent molecular sensitivity (NEM) per unit bandwidth () of or or 33 zeptomol, which is an improvement of 2.2 times compared to the previous system design. This PA sensor has the potential for noncontact high-resolution PA imaging of materials without the need for coupling fluids.

Mechanical Behavior of Entangled Metallic Wire Materials under Quasi-Static and Impact Loading.

In this paper, the stiffness and damping property of entangled metallic wire materials (EMWM) under quasi-static and low-velocity impact loading were investigated. The results reveal that the maximum deformation of the EMWM mainly depends on the maximum load it bears, and that air damping is the main way to dissipate impact energy. The EMWM can absorb more energy (energy absorption rate is over 60%) under impact conditions. The EMWM has excellent characteristics of repetitive energy absorption.

Investigation of a compact model for squeeze-film air damping in the free molecular regime

Due to the huge computational cost, the Monte Carlo (MC) model is difficult to use to predict squeeze-film air damping in the free molecular regime. Sumali (2007) proposed an empirical compact formula relating MC model and the analytical energy transfer model (ETM) by fitting two curves. By using the efficient numerical model, this paper discusses the application of the compact formula for squeeze-film air damping of different microplate sizes in the free molecular regime. The results show that, for plates of various sizes, the quality factors predicted by the compact model match well with those predicted by the numerical model. The work of this paper has validated that the compact model for squeeze-film air damping proposed by Sumali (2007) can be used for plates of various sizes.

Liquid–Liquid Mass Transfer Enhancement Due to T-Junction Modified with an Air Damper

In a T-junction, flow pulsation in one limb and continuous flow on the other limb lead to an enhanced mass transfer in the extraction limb. We experimentally and theoretically establish that introd...

Efficient molecular model for squeeze-film damping in rarefied air**Project supported by the National Natural Science Foundation of China (Grant No. 51375091).

Based on the energy transfer model (ETM) proposed by Bao et al. and the Monte Carlo (MC) model proposed by Hutcherson and Ye, this paper proposes an efficient molecular model (MC-S) for squeeze-film damping (SQFD) in rarefied air by releasing the assumption of constant molecular velocity in the gap. Compared with the experiment data, the MC-S model is more efficient than the MC model and more accurate than ETM. Besides, by using the MC-S model, the feasibility of the empirical model proposed by Sumali for SQFD of different plate sizes is discussed. It is proved that, for various plate sizes, the accuracy of the empirical model is relatively high. At last, the SQFD of various vibration frequencies is discussed, and it shows that, for low vibration frequency, the MC-S model is reduced to ETM.

Simple Non-Destructive Method of Ultrathin Film Material Properties and Generated Internal Stress Determination Using Microcantilevers Immersed in Air

Recent progress in nanotechnology has enabled to design the advanced functional micro-/nanostructures utilizing the unique properties of ultrathin films. To ensure these structures can reach the expected functionality, it is necessary to know the density, generated internal stress and the material properties of prepared films. Since these films have thicknesses of several tens of nm, their material properties, including density, significantly deviate from the known bulk values. As such, determination of ultrathin film material properties requires usage of highly sophisticated devices that are often expensive, difficult to operate, and time consuming. Here, we demonstrate the extraordinary capability of a microcantilever commonly used in a conventional atomic force microscope to simultaneously measure multiple material properties and internal stress of ultrathin films. This procedure is based on detecting changes in the static deflection, flexural and torsional resonant frequencies, and the corresponding quality factors of the microcantilever vibrating in air before and after film deposition. In contrast to a microcantilever in vacuum, where the quality factor depends on the combination of multiple different mechanical energy losses, in air the quality factor is dominated just by known air damping, which can be precisely controlled by changing the air pressure. Easily accessible expressions required to calculate the ultrathin film density, the Poisson’s ratio, and the Young’s and shear moduli from measured changes in the microcantilever resonant frequencies, and quality factors are derived. We also show that the impact of uncertainties on determined material properties is only minor. The validity and potential of the present procedure in material testing is demonstrated by (i) extracting the Young’s modulus of atomic-layer-deposited TiO2 films coated on a SU-8 microcantilever from observed changes in frequency response and without requirement of knowing the film density, and (ii) comparing the shear modulus and density of Si3N4 films coated on the silicon microcantilever obtained numerically and by present method.

Fault detection in commercial building VAV AHU: A case study of an academic building

The building sector of the U.S. currently consumes over 40% of the U.S. primary energy supply. Estimates suggest that between 5% and 30% of any building's annual energy consumption is unknowingly wasted due to pathologically malfunctioning lighting and comfort conditioning systems. This paper presents analytical methods embodied within useful software tools to quickly identify and evaluate selected faults in air handling units (AHU) that cause large building energy inefficiencies. Algorithm for faults like stuck dampers and leaking dampers have been developed and tested in this particular case study. These damper fault detection algorithms can be applied to outdoor air and return air dampers both. The technical contributions of this work include expert rules that adapt to the Heating, Ventilation and Air-Conditioning (HVAC) equipment scale and operation and methods for sorting fault signals according to user-defined interests such as annual cost of energy inefficiencies. The combination of expert-rule based fault detection combined with first principles thermodynamic modeling is a unique contribution of this work that leads to quicker fault detection with minimal non-intrusive measurements. These contributions are particularly unique in their treatment of models and the careful consideration of user-interests in fault evaluation. As a first step to developing this general framework for fault detection, first-order faults such as stuck dampers and imbalanced airflows within several large air-handling units were targeted. The algorithms focused on detecting faults with minimal data and non-intrusive measurements. An example is presented of the potential energy savings in a large academic building that has been monitored. Real data from an academic building in Boston was collected from the building energy management system (BEMS) for the purpose of this study. Savings of around $3400/month or 18% of the monthly cost when a stuck damper fault occurred over an entire month in an air handler. Another fault that was investigated was that of leaking dampers which lead to savings of approximately $500/month or around 2.5% of the monthly energy expense. The savings would accrue if the fault were corrected; otherwise the occurrence of the fault causes a waste of money and energy predicted. The algorithms developed can be applied to large commercial office buildings, academic buildings, hospitals and other modern buildings in various climates as long as they have data collecting capabilities.