Height Of Elements Research Articles

The experimental method for testing relaxation of pneumatic elements with a rubber-cord casing

The method for the experimental study of the viscoelastic properties of pneumatic elements with a rubber-cord casing is proposed. Based tests of relaxation in which the height of the pneumatic element is kept constant (a practically incompressible fluid is used as the working medium). The implementation of the method is illustrated by the example of the rubber-cord casing of the balloon type of model N-50. The value of the absorption coefficient (relative hysteresis) is established, which in order of magnitude coincides with the value of the absorption coefficient of tread rubbers given in literary sources. In the process of holding the height of the pneumatic element at a constant level, increments of the force of the pneumatic element and overpressure are proportional to each other with a proportionality coefficient depending on the value of the internal volume and height of the air element. The comparative analysis of the features of the operation of pneumatic elements in cases where the working medium is a gas or liquid is done. The results obtained are of interest in the development of vibration protection and vibration isolation systems for technical objects, the design of which includes air springs, air damping shock absorbers and rubber-hydraulic vibration mounts.

The experimental method for determining the geometric characteristics of pneumatic elements with rubber-cord casing

The method for experimentally constructing the geometric characteristics of pneumatic elements with rubber-cord casing at zero and quasi-zero pressure is proposed. The practical implementation of the method by the example of the rubber-cord shell of the balloon type of model N-50 is illustrated. The processed experimental data in an analytical form presents the empirical dependences of the internal volume on the height of the pneumatic element at zero and quasi-zero overpressure. The obtained parameters are mandatory for the model of air spring and study the damping phenomenon. The results obtained are intended for the development of vibration protection and vibration isolation systems for technical objects, the design of which includes air springs and air damping shock absorbers.

The experimental method for determining the isobaric power characteristics of pneumatic elements with rubber-cord casing

A method for the experimental construction of isobaric static (equilibrium) power characteristics of pneumatic elements with a rubber-cord casing at a constant temperature is proposed. This method also allows you to determine isobar geometric characteristics, establishing a relationship between the height of the pneumatic element and the increment of its internal volume relative to some fixed position. The practical implementation of the method is illustrated by the example of a pneumatic element with a rubber-cord casing of the balloon type of the model N-50. The agreement of the experiment with the theoretical data calculated by the traditional method, widely used in the scientific literature, is analyzed. The obtained parameters are mandatory for the model of air spring and study the damping phenomenon. The results of the study are intended to develop vibration protection and vibration isolation systems for technical objects, the design of which includes air springs and air damping shock absorbers.

Simplification bias: lessons from laboratory and field experiments on flow through aquatic vegetation

AbstractWe present a critical analysis of experimental findings on vegetation–flow–sediment interactions obtained through both laboratory and field experiments on tidal and coastal environments. It is well established that aquatic vegetation provides a wide range of ecosystem services (e.g. protecting coastal communities from extreme events, reducing riverbank and coastal erosion, housing diverse ecosystems), and the effort to better understand such services has led to multiple approaches to reproduce the relevant physical processes through detailed laboratory experiments. State‐of‐the‐art measurement techniques allow researchers to measure velocity fields and sediment transport with high spatial and temporal resolution under well‐controlled flow conditions, yielding predictions for hydrodynamic and sediment transport scenarios that depend on simplified or bulk vegetation parameters. However, recent field studies have shown that some simplifications on the experimental setup (e.g. the use of rigid elements, a single diameter, a single element height, regular or staggered layout) can bias the outcome of the study, by either hiding or amplifying some of the relevant physical processes found in natural conditions. We discuss some observed cases of bias, including general practices that can lead to compromises associated with simplified assumptions. The analysis presented will identify potential pathways to move forward with laboratory and field measurements, which could better inform predictors to produce more robust, universal and accurate predictions on flow–vegetation–sediment interactions. © 2020 John Wiley & Sons, Ltd.

Fundamental Investigation on Seismic Retrofitting Method of Aging Concrete Structural Wall Using Carbon Fiber Sheet‐Constitutive Law of Rectangular Section

Aging building structure has become a world problem. This problem is particularly serious in developing and underdeveloped countries. The multihazard resilience and sustainability (e.g., seismic performance) decrease at the aging building. A construction method for strengthening aging‐reinforced concrete buildings by wrapping structural members with carbon fiber sheets has been proposed and implemented in recent years. Authors aim to develop a seismic retrofitting method of aging concrete structural wall with a rectangular cross section using carbon fiber sheets. In this paper, authors examined the stress‐strain relationship of concrete elements with rectangular cross sections reinforced by wrapping with carbon fiber sheets. Monotonic uniaxial compression tests were performed on 21 specimens using the ratio of the long side to the short side and the ratio of the element height to the short side of the concrete cross section, the weight of the carbon fiber sheet, and the chamfer radius of section corners as variables. The tests revealed that (1) the compressive strength decreases and ultimate strain increases as the ratio of the long to short side (longitudinal ratio) of the cross section increases even in a range the ratio exceeds 2 and (2) the ratio of the element height to the short side does not significantly affect the stress‐strain relationship. Furthermore, authors proposed evaluation formulas for the constitutive law of concrete elements with rectangular cross sections including the longitudinal ratio which exceeds 2 reinforced by carbon fiber sheets and confirmed that the formulas can reproduce the test results with good accuracy.

Başlangıç y plus Değerinin Etkileri: γ-Reθ SST Türbülans Modeli Kullanılarak 3D NACA 4412 Kanadının Sayısal Analizi

In this numerical study, the effects of the initial y plus , which is a dimensionless wall distance, on the results of aerodynamic coefficients of designed a wing using NACA 4412 airfoil are investigated. For this purpose, the wing is designed and external flow analysis is carried out according to constant altitude. ANSYS Fluent, which is a Computational Fluid Dynamics (i.e. CFD) program and solves the problems according to the Finite Volume Method (i.e. FVM), is used for external flow analysis. Pressure-based method is used for numerical studies. Thus, the differences of coefficients on the wall, which are the results of the change in the initial y plus , are calculated ideally. Because of one of the best methods to solve the problems on transition zone, γ-Re θ SST turbulence model is used for this study. Using this model for each analysis, first element heights (i.e. the distance to the nearest wall) are calculated according to 9 different y plus (i.e. 1, 5, 10, 30, 45, 60, 75, 90, 105). According to the first element heights, the inflation layers are created on the wing and the 3D control volumes are formed along the boundary region. To be more comprehensible, orthogonal quality-skewness values, expressing the quality of control volumes, are presented for each boundary. The changes in lift coefficients and drag coefficients on the same wing according to these 9 different y plus are presented numerically. In addition, obtained results are evaluated and as described in the literature, it is observed that to calculate the aerodynamic forces with the γ-Re θ SST turbulence model is directly proportional to the initial y plus . As a consequence, this paper demonstrates that there are obvious differences detection of separation and determination of reattach region of flow occurring on the wing according to the initial y plus.

Characteristics of the pressure fluctuations generated in turbulent boundary layers over rough surfaces

Experiments were carried out in high Reynolds number turbulent boundary layers over rough surfaces of diverse geometries. Roughness configurations varied in element height, distribution (random versus ordered), shape and spacing. Rough surfaces comprising of two superposed element geometries were also tested. All flows were free of transitional effects with upwards of 40 000 and ratios above 73. The wall-pressure spectrum and turbulent velocity profiles revealed that the roughness element spacing has the greatest impact on the turbulent structures in the boundary layer. The high-frequency scaling on shear friction velocity, , (Meyers et al.J. Fluid Mech., vol. 768, 2015, pp. 261–293) was validated and was shown to be the viscous contribution to the overall surface drag. An empirical formula for the pressure drag on roughness elements was developed to reflect the finding that the pressure drag is a function of only two variables: sparseness ratio and roughness Reynolds number . Results also suggest that the viscous contribution to drag approaches a constant non-zero value at high Reynolds numbers, and ‘fully rough-wall flow’ may occur at higher than previously thought.

Design of axisymmetric double-surface refractive optical elements generating required illuminance distributions

We propose a novel technique for designing double-surface axisymmetric refractive optical elements with minimized Fresnel losses and maximized lighting efficiency. The design of the optical element is reduced to the integration of three explicit ordinary differential equations. Minimization of the Fresnel losses is provided by ensuring equal refraction angles on both “working” surfaces of the optical element. To demonstrate high performance of the method, we designed axisymmetric double-surface optical elements generating uniform illuminance distributions both in the far (angular size of 50°) and in the near (angular size of 90°) field. The lighting efficiency exceeds 87.8% for both point and extended light sources. Besides, we demonstrated that optical surfaces designed using the proposed method can serve as an excellent initial approximation in the case of a large extended light source. In the considered example with the ratio of the element height to the source diameter of only 2.2, the lighting efficiency of the optimized element exceeds 89.5%, whereas the uniformity of the resulting illuminance distribution exceeds 96%.

Turbulization of a wake behind the double roughness elements in a hypersonic boundary layer

The study of the effect of close placing of two individual elements of roughness with the cylindrical shape on the nature of laminar-turbulent transition were performed. Experiments were performed for a blunt conical model with the radius 9 mm at Mach number M = 5. These double elements of roughness with different heights and divergence angles between elements were allocated at the blunted nose of the tested model. Measurements with a hot-wire anemometer provided information about the averaged and unsteady parameters of the boundary layer in the wake behind the roughness elements. For all types of roughness, we confirmed existence of an effective height of roughness; for the heights above the effective one, we observe deformation of the boundary layer margin and the growth of non-equilibrium in the wake. Process of turbulization behind a double roughness element (similar to the case of single roughness) is accompanied by the generation of longitudinal vortices and by the deformation of the velocity profile. Depending on this deformation, pulsations in the wake either enhance or decline. In contrast to the single roughness configuration, the double element roughness decreases the mass flowrate for a narrow range of angles (and fullness of the boundary layer profile is more significant). Meanwhile, flow turbulization occurs right behind the single element of turbulization, for the case of double element turbulization, the main gain in the mass flowrate occurs with the wake (developing from the boundary between twin elements). Roughness has significant influence on unsteady characteristics of the boundary layer (when the height of roughness element is lower than the effective height). The wake downstream the double elements roughness exhibits the interaction between vortices, and this reduces the effective Reynolds number (compared to the case of single roughness).

Bow-Tie-Shaped Radiating Element for Single and Dual Circular Polarization

A fully metallic radiating element is presented in this article for single and dual circular polarization applications. The shape of the radiating element corresponds to a bow-tie-shaped field rotator designed to generate two orthogonal modes in quadrature as a basis for circular polarization. The bow-tie-shaped basic element is able to provide low axial ratio with a compact, easy-to-manufacture profile. In addition, it allows diverse ways of operation: feeding through a rectangular waveguide provides single circular polarization, while square waveguide is used for dual circular polarization. The radiating element has been designed at the Ku band and validated by the competitive experimental results. In the case of single circular polarization, over 21% bandwidth has been obtained under 15 dB return loss and 3 dB axial ratio criteria, with a radiating element height of $0.75 {\lambda }_{0}$ (free-space wavelength) at 18 GHz. The dual circularly polarized version achieves 18.3% bandwidth when 15 dB return loss and 3 dB axial ratio are established. In this case, the required antenna height is slightly higher than ${\lambda }_{0}$ at 18 GHz.

Hydraulic Jump below Abrupt Asymmetric Expanding Stilling Basin on Rough Bed

The present research describes a laboratory study of hydraulic jump in the abrupt asymmetric expansion stilling basin as an energy dissipator by changing the geometry of walls and bed roughness elements. The experiments were carried out in a horizontal flume with 10 m length, 0.5 m width, and 0.5 m depth for a range of the upstream Froude numbers ( F r 1 ) from 5 to 11. Four physical models with expansion ratio of α = 0.33, 0.5, 0.67, and 1 and asymmetry ratio of Δ = 0.16 were installed in the flume and two different heights of roughness elements ( h = 1.4 and 2.8 cm) were also considered. The results indicated that the sequent depth and the jump length as well as the roller length below abrupt asymmetric expansion on the rough bed were decreased in comparison to the same parameters of the jump in a prismatic channel with smooth bed. It was revealed that the roughness elements have the effective role on stabilization of the hydraulic jump location. The analysis of energy dissipation efficiency confirmed that the spatial jump in the abruptly expanded basin with roughened bed was more efficient than classical jump. In order to estimate the hydraulic jump characteristics, empirical relationships associated with expansion ratio of basin walls, relative height of roughness elements and upstream Froude number were proposed based on the experimental data that resulted in preliminary design of an abrupt asymmetric enlarged basin.

Assessment of inner–outer interactions in the urban boundary layer using a predictive model

Urban-type rough-wall boundary layers developing over staggered cube arrays with plan area packing density, $\unicode[STIX]{x1D706}_{p}$, of 6.25 %, 25 % or 44.4 % have been studied at two Reynolds numbers within a wind tunnel using hot-wire anemometry (HWA). A fixed HWA probe is used to capture the outer-layer flow while a second moving probe is used to capture the inner-layer flow at 13 wall-normal positions between $1.25h$ and $4h$ where $h$ is the height of the roughness elements. The synchronized two-point HWA measurements are used to extract the near-canopy large-scale signal using spectral linear stochastic estimation and a predictive model is calibrated in each of the six measurement configurations. Analysis of the predictive model coefficients demonstrates that the canopy geometry has a significant influence on both the superposition and amplitude modulation. The universal signal, the signal that exists in the absence of any large-scale influence, is also modified as a result of local canopy geometry suggesting that although the nonlinear interactions within urban-type rough-wall boundary layers can be modelled using the predictive model as proposed by Mathis et al. (J. Fluid Mech., vol. 681, 2011, pp. 537–566), the model must be however calibrated for each type of canopy flow regime. The Reynolds number does not significantly affect any of the model coefficients, at least over the limited range of Reynolds numbers studied here. Finally, the predictive model is validated using a prediction of the near-canopy signal at a higher Reynolds number and a prediction using reference signals measured in different canopy geometries to run the model. Statistics up to the fourth order and spectra are accurately reproduced demonstrating the capability of the predictive model in an urban-type rough-wall boundary layer.

Implications of modeling approaches on seismic performance of low- and mid-rise office and hospital shear wall buildings

This paper investigates implications of using three conceptually different modeling approaches for reinforced concrete (RC) shear walls on seismic performance of several building designs including low-rise and mid-rise office and hospital buildings. Selected archetype buildings are designed to meet current code provisions for a site in downtown Los Angeles and are analyzed considering hazard levels characterized with 50%, 10%, and 2% probabilities of exceedance in 50 years. The study considers different models for structural walls, with either coupled or uncoupled shear and flexural behavior, and either linear or constant curvature distribution along the element height. FEMA P-58 methodology is used to assess damage and associated building repair cost. Performance assessment study illuminates the importance of utilizing high-fidelity models that consider coupled shear and flexural responses when conducting performance assessments for low- and mid-rise RC shear wall buildings; variations in median loss estimates obtained using uncoupled models range from 70% to 130% of the coupled model. In addition, the study reveals that the repair cost for hospitals are approximately 2 to 4 times larger than for office buildings due to significant damage to hospital equipment, warranting the use of RC structural walls for hospital builidngs in the regions of high seismicity. Finally, the study shows that the curtain walls generate significant loss in the case of low-rise RC wall buildings, reaching up to 50% of the total loss and highlighting the need for improved provisions for curtain walls for this type of construction.

Study of Aerodynamic Surface Roughness for Baghdad City Using Signal-Level Measurements

Roughness length is one of the key variables in micrometeorological studies and environmental studies in regards to describing development of cities and urban environments. By utilizing the three dimensions ultrasonic anemometer installed at Mustansiriyah university, we determined the rate of the height of the rough elements (trees, buildings and bridges) to the surrounding area of the university for a radius of 1 km. After this, we calculated the zero-plane displacement length of eight sections and calculated the length of surface roughness. The results proved that the ranges of the variables above are ZH (9.2-13.8) m, Zd (4.3-8.1) m and Zo (0.24-0.48) m.

Study of Aerodynamic Surface Roughness for Baghdad City Using Signal-Level Measurements

Roughness length is one of the key variables in micrometeorological studies and environmental studies in regards to describing development of cities and urban environments. By utilizing the three dimensions ultrasonic anemometer installed at Mustansiriyah university, we determined the rate of the height of the rough elements (trees, buildings and bridges) to the surrounding area of the university for a radius of 1 km. After this, we calculated the zero-plane displacement length of eight sections and calculated the length of surface roughness. The results proved that the ranges of the variables above are ZH (9.2-13.8) m, Zd (4.3-8.1) m and Zo (0.24-0.48) m.

Sensitivity analysis of factors influencing a heat pipe-based thermal management system for a battery module with cylindrical cells

Structural parameters have a significant effect on the thermal performance of a battery thermal management system (BTMS). In the present study, a thermal management system based on heat pipes is proposed for a battery module with cylindrical cells. A computational fluid dynamics model is built for the BTMS and validated with experimental results. An orthogonal numerical test is conducted to obtain the sensitivity of various parameters, including the battery spacing, the thickness of conduction element, the circumference angle between battery and conduction element, and the height of conduction element on the thermal performance for the proposed BTMS. Results show that the height of conduction element has the most sensitive effect on the maximum temperature and temperature difference of battery module; the circumference angle between battery and conduction element is the second; the battery spacing and the thickness of conduction element has the minimal effect. The best thermal performance is obtained under the condition of 19 mm battery spacing, 4 mm conduction element thickness, 120° circumference angle and 60 mm conduction element height. Based on the optimal parameters, the maximum temperature and the temperature difference of battery module are 27.62 °C and 1.08 °C, respectively.

Tracking of Crack Formation in Concrete Using Acoustic Emission Method and Digital Image Correlation

The paper presents analysis of crack formation in a reinforced concrete beam using an acoustic emission method (AE) and a digital image correlation (DIC). The examined element was loaded monotonically until reaching 50 kN force during the three-point bending test. Six acoustic emission sensors (two on the left and right surfaces of the sample and the other two on the bottom surface) combined with three-dimensional location method were used to find the destructive processes. The optical measuring system ARAMIS (DIC) was used to verify the obtained results. This device help to specify the location of crack and track its development on the basis of the strain map. The crack width was measured in 6 sections, which were located in different positions of the element height with the use of ARAMIS software. First section was applied at the centre of gravity of the longitudinal reinforcement. The following cross-sections were set every 2 cm towards the top edge of the element. In the first part of the analysis, a graphical comparison of the strain map (obtained with ARAMIS system) and the location of events (obtained with AEWin software) was made. In the second part of the analysis, the obtained crack width results were compared with number of AE events counted in zones, which were defined around the previously mentioned sections. The statistical analysis (Pearson’s linear correlation) shows that the number of recorded events depends on the maximum crack width, the average crack width as well as the crack width increase registered between successive load levels. The results of the study conclude that simultaneous use of DIC and AE methods provided complete information on local strain and damage location in concrete.

Optimization of sequential grinding process in a fuzzy environment using genetic algorithms

The paper presents the methodology of optimization of the sequential grinding process with the application of fuzzy logic for the definition of objectives and constraints imposed on the machining process. The presented method includes the succession of several subsequent operations and the dimensional and shape inaccuracies between them. The use of the fuzzy sets theory enabled the definition of not only the space of expectable solutions, but also the space of acceptable solutions for which the goals and limits imposed on the grinding process are partially met. The presented methodology was used to optimize the process of sequential grinding of small ceramic elements (corundum ceramics with Al2O3 content of 92–99%.) The definition of fuzzy objective and constraints in the process of sequential grinding of small ceramics elements was proposed. The influence of the speed of the rotary grinding table and the machining allowance on the deviation of the flatness and height of the grinding elements and the value of the component of the normal grinding force were determined. Using the developed relationships, the definition of fuzzy objectives and constraints defined in the process output parameter space was transferred to the process parameter set space. In such a defined space, the optimization process was carried out using the genetic algorithm. The analysis of the impact of the applied t-norm functions used for aggregation of the fuzzy objective and constraints on the obtained results was performed. It was shown that in the case of sequential grinding of small ceramic elements, the use of minimum t-norm for an aggregation of grinding objective and constraints allows to achieve the highest process efficiency.

Multiple Harmonic Suppression Method for Induction Motor Based on Hybrid Morphological Filters

In order to solve the problem of torque ripple caused by current harmonic of induction motors (IMs) in electric vehicles (EVs) drive system, this paper presents a novel control method in the feedback channel based on morphological filters (MFs) to suppress the current harmonics. First, an analytical model of current harmonics is established, and the current harmonic composition to be filtered in the feedback channel of motor control systems is provided. Second, on the basis of filtering requirements on the feedback channel and the basic idea of mathematical morphology, a hybrid digital MF is designed. The MF is subsequently added on the current loop to suppress the current harmonic components. The shape, width and height of the structural elements of the filter are optimized by parameters comparison methods to improve the performance of the filter in harmonic suppression. Finally, compared with the method based on Butterworth Filter and without filters, simulation and experimental results verify the feasibility and effectiveness of the proposed method for suppressing harmonics.

On “Cavitation on Chip” in Microfluidic Devices With Surface and Sidewall Roughness Elements

In this paper, cavitating flows are characterized in 29 microfluidic devices in order to achieve a comprehensive perspective regarding flow patterns in microscale, which is crucial in the applications, such as energy harvesting and biomedical treatment. While the assessment of size effects is vital for the design and development of microfluidic devices involving phase change, surface/sidewall roughness and pressure pulses as a result of nanomechanical oscillations increase the performance with respect to cavitation by providing more cavitation bubbles. A typical device generates cavitating flows under different conditions (from inception to choked flow). In this device, a restrictive element and a big channel downstream of the restrictive element—where the cavitation is formed and developed—are included. The cavitating flows are obtained inside 24 sidewall roughened and 5 surface roughened/plain microfluidic devices at different pressure drops. The length and height of the sidewall roughness elements are varied to achieve the most optimum performance in terms of cavitation generation. Moreover, different surface roughened and plain devices are considered to provide a comprehensive overview of cavitation generation in microscale. The results show that sidewall roughness elements have a remarkable effect on the cavitation inception and flow patterns. [2019-0025]