Clearance Heights Research Articles

Evaluation of highway debris flow hazard based on geomorphic evolution theory coupled with material response rate

Assessments of highway feasibility frequently lack the detailed data and geological information necessary to conduct hazard evaluations of debris flows. This study discusses the processes of debris flow development when regional rainfall meets the critical level required for debris flow initiation. It utilizes geomorphic evolution theory and establishes a regional risk assessment matrix for debris flow by combining information about gullies and source sensitivity. Considering the location relationship between the highway and debris flow gullies, a rapid evaluation method for debris flow risk assessment along the G318 highway in Sichuan Province is proposed by modifying the judgment matrix. The four debris flow gullies constructed during the upgrading project in Yajiang County, stretching from the west of the city to the Shearer Bay section, were analyzed via examples. The results show that, among the four selected debris flow gullies, two had medium hazard levels, and two had high hazard levels. The validation results are consistent with the actual results, implying that the evaluation method used in this study is accurate and feasible. This method is suitable for the rapid evaluation of debris flow disaster hazards in the feasibility assessment stage of a highway because it relies on readily available data sources, and the evaluation results are fast and convenient. The highway passes through four debris flow gullies, which directly impact the alignment of this particular section of the geological route and the engineering layout. Based on current specifications, the maximum impact range of a one-time debris flow under the given frequency conditions was calculated using the "rainfall method." The results showed that the maximum impact ranges of a debris flow, occurring once in 100 years, for four gullies would be 9.08 m, 9.09 m, 10.86 m, and 10.08 m. The safe clearance heights of bridges over the four gullies should be 14.58 m, 14.59 m, 16.36 m, and 16.3 m. Additionally, the safety clearance width for all gullies should be 5.0 m.

Large-Scale Agrivoltaics Visualisations for Assessing Landscape Impacts and Social Acceptance

Visual landscape impacts are of great importance when it comes to social acceptance measures of renewable energy. Although agrivoltaics seems to have higher acceptance values than other renewable energy infrastructures due to the dual land use approach, it is expected that they have a bigger visual impact on the landscape scenery than ground-mounted installations due to the increased land requirements and clearance heights. This article presents the development of a game-based visualisation approach using open-source software and open data (open government data) for visualising energy landscapes by creating large-scale interactive and immersive 3D visualisations. The results show that the use of open geodata and available open-source gaming technologies can be used to create comprehensive digital VR landscapes for assessing the visual impacts of agrivoltaics. Furthermore, the data-driven approach can provide additional indicators for evaluating planning scenarios and investigating the social acceptability due to renewable energy expansion.

Aseptic loosening of the option stemmed tibial tray in the Zimmer NexGen LPS total knee arthroplasty system

BackgroundWe investigated the relationship between the backside deformation of polyethylene (PE) tibial inserts and aseptic loosening of the Option stemmed tibial tray used with Zimmer NexGen posterior-stabilised (PS) devices. We hypothesized that explanted inserts used in PS designs would exhibit greater extents of PE backside deformation than those used in equivalent cruciate retaining (CR) designs and that PE inserts retrieved from total knee arthroplasties (TKAs) revised for aseptic tibial tray loosening would exhibit greater extents of backside deformation than TKAs revised for other reasons. MethodsA total of 73 explanted fixed-bearing TKAs (42 CR and 31 PS) were examined. PE components underwent geometric examination with a coordinate measuring machine using validated techniques. Multiple regression modelling was used to identify variables associated with revision secondary to aseptic loosing and to determine factors associated with increased PE backside deformation. ResultsPE inserts retrieved from TKAs with aseptic loosening had significantly greater backside deformation than those retrieved from TKAs revised for other reasons (p < 0.001). Greater PE backside deformation was significantly associated with larger tray/insert clearance heights (p < 0.001), thinner inserts (p < 0.001) and PS TKAs (p = 0.001). ConclusionPE backside deformation was significantly greater in the PS TKAs. This may provide one explanation for the increased rate of aseptic loosening reported with the Option tibial tray used with the Legacy Posterior Stabilised (LPS) system.

Effect of moving end wall on tip leakage flow in a compressor cascade with different clearance heights

Numerical simulations have been carried out to investigate the effect of the moving end wall on the tip leakage flow structure in a compressor cascade with four different tip clearance heights. A detailed comparison of the leakage flow’s loss; mass flow rate; and the tip leakage vortex and its roll-up, trajectory, size, and interaction with the passage flow was made. The results show that the performance of the cascade changes more severely as the tip clearance height increases with the moving end wall than with the stationary end wall. The roll-up of the tip leakage vortex has been studied by analyzing the pathline structure and vorticity distribution. An alternative explanation is proposed for the initial roll-up mechanism of the tip leakage vortex. The vorticity transport is responsible for the initial roll-up of the vortex, whereas the leakage jet/passage flow shearing is responsible for the vortex development. The smaller the clearance height is, the easier it is for the moving end wall to alter the vorticity transport from the gap to the tip leakage vortex.

The UNSW tip clearance flow noise test rig

A new test rig to measure the far-field sound, surface pressure fluctuations and flow-field in tip clearance flows has been designed at UNSW. The test rig is a part of the UNSW anechoic wind tunnel (UAT) and has been designed to allow studies of the tip clearance flow and sound radiation across a vast parameter space—tip clearance height, Reynolds number, angle of attack, and the tip geometry. This paper will present and discuss the design, characterization, and capabilities of this new test rig, along with some far-field sound results for a tip clearance flow formed by placing a stationary cambered airfoil adjacent to a wall. The measurements were performed for 51 different clearance heights at free-stream velocity of 30 m/s. The geometric angle of attack in the measurements was 5.6 and the clearance height Reynolds number ranged between 2000 and 102,000. The far-field sound was measured using a 64-microphone spiral phased array and the array output was beamformed to reveal the tip clearance noise sources. It is expected that the test rig will aid in a better understanding of the sound radiated by tip clearance flows which may be used to devise noise control strategies in the future.

Utilizing of 500 MHz Ground Penetrating Radar Antenna Coupling at Different Interval Heights Clearance

Understanding the characteristics of the GPR antenna for underground utility detection purposes is critical to ensuring that buried pipes and cables can be accurately located. Considering the ground coupling antenna is the most effective way to carry out the GPR scan, most of the operators applied this setup to ensure the maximum amount of the electromagnetic wave could be penetrated into the ground. However, the contact between the GPR and the ground surface causes the bottom of the antenna enclosure to become scratched and worn out. Due to the cost and time involved in transportation to replace the antenna protector, a few GPR operators changed the protector to the cheapest one, which affects the characteristics of the antenna and could alter the depth of the underground utilities. A 500 MHz GPR antenna are tested to identify the optimum antenna coupling based on the accuracy assessment at various interval clearance heights in order to reduce damage and preserve the antenna. An experiment was carried out at Department of Survey and Mapping Malaysia (JUPEM) Kuala Lumpur’s Underground Utility Test Base. Based on the result of the signal strength, the higher the antenna is lifted, the higher the rate of the signal becomes weak or lost. For the depth accuracy test, the high differences in depth when the antenna is lifted up at 4cm to 6cm based on the result of comparison with the standard values provided by the JUPEM. On the other hand, the accuracy of each antenna height is compared and validated based on the Residual Mean Square Error (RMSE). Overall, this study could lead to the conclusion that the result of the assessment is within the acceptable RMSE tolerance, which is below 0.1m. The objective of the research is successfully achieved when the antenna at a 3cm to 6cm interval height setup provides the best clearance based on the criteria of signal strength, depth comparison, and accuracy assessment. Finally, the issue of contact between the antenna and the ground surface, which causes the antenna to become scratched and worn out, could be reduced and preserved as a result of the findings.

Geomorphic effects of natural flood management woody dams in upland streams

AbstractOne popular Natural Flood Management (NFM) technique involves the construction of channel‐spanning woody dams in low‐order streams that maintain a clearance height above base flows. While extensive research has examined the geomorphic effects of natural wood accumulations, little has been documented of NFM woody dams, which are structurally distinct from natural accumulations and may produce different patterns of erosion and deposition. This consideration is crucial because changes in physical habitat characteristics have implications for flood management objectives as well as ecosystem structure and functioning. This study adopted a Before‐After Control‐Impact (BACI) design to assess the geomorphic effects of NFM woody dams in the upper River Cover catchment, United Kingdom. One baseline survey prior to and three monitoring surveys up to 2 years following dam construction were conducted. Structure‐from‐Motion (SfM) photogrammetry was employed to capture topographic change, supplemented by bathymetric surveys. Results highlight that where the dams remained secure in place, they promoted in‐stream habitat diversity by creating underflow pools. Sediment storage was observed only where the dams had clearance heights &lt;0.3 m from the stream bed. Additionally, the dams commonly led to bank erosion, likely enhanced by inherent bank instability in the study catchment as observed along the control reaches. However, volumes of sediments eroded and deposited were not statistically different between the control and woody dam reaches. Longer monitoring is required to determine whether these effects on channel morphology and habitat diversity will persist, amplify, or diminish over time, and to better understand the longevity of NFM woody dams.

Effects of fusion height of tip winglet on the clearance flow in a compressor cascade

The leakage flow generated by rotor clearance seriously affects efficiency and stability of a compressor. In order to reduce the effect of leakage flow, the tip winglet has been applied at the tip of a transonic compressor cascade. Numerical simulation has been used to investigate the influence of tip winglets with different fusion heights on the flow field structure. Furthermore, the effect of winglets was analyzed under different clearance heights and incidence angles. Results reveal that the winglet can weaken the kinetic energy of the leakage flow. The development of the leakage vortex along the pitchwise is suppressed, and the total pressure loss is decreased near the tip. The increase in the tip separation vortex scale leads to a remarkable decrease in the leakage flow rate. With the increase in fusion height, the scale of tip separation vortex decreases gradually, and the suppression effect on the leakage flow rate is weakened. The optimal scheme can reduce the loss by 3.3% and leakage flow rate by 13.4%. The suppression effect of the winglet on flow loss increases gradually with the increase in incidence angle. Moreover, the suppression effect of the winglet on leakage flow and flow loss increases first and then decreases with the increase in tip clearance.

Effect of vorticity transport on flow structure in the tip region of axial compressors

Numerical simulations are carried out to investigate the flow structure in the blade tip region of axial compressors. Various tip clearance heights and end wall motion conditions in a linear compressor cascade are studied to assess the effect of vorticity transport on the tip leakage flow (TLF). Moreover, the effect of vorticity transport on the TLF in a compressor rotor at different operating conditions is studied using delayed detached eddy simulation. The results show that the vorticity transport at both the blade tip and the end wall plays an important role in the roll-up and evolution of the tip leakage vortex (TLV), resulting in great impacts on the loss and stability of the TLV. It is found that the TLV is composed of a two-layer structure. The inner vortex core region formed by the vorticity transport from the blade tip shear layer to the TLV has a great effect on the strength and loss of the vortex, and the structure of the outer shear layer is altered by the secondary vortex formed by the vorticity transport from the end wall shear layer and thus affects the stability of the TLV. By the mechanism of the vorticity transport, the effects of the clearance height, the end wall motion, and the non-uniform clearance as a control method can be explained uniformly. The new understanding of the TLF structure and the vorticity transport mechanism helps to improve the performance of axial compressors by controlling the vorticity transport of the TLF.

Study on Heat Transfer at Steel-Concrete Interface of Shield Tunnel Composite Segment under Fire

During the actual construction process and operation period of the tunnel project, due to improper construction operation techniques, long-term load effects, concrete shrinkage and creep, etc., it is difficult for the steel plate and concrete to be in close contact, and there is a void between the two. This results in discontinuous heat transfer. In order to seek the real heat transfer state between steel plate and concrete under high temperature of fire, this paper mainly adopts the methods of model test, theoretical analysis and numerical simulation to study the heat transfer of composite segment steel plate and concrete contact interface under high temperature of fire. The heat transfer process between steel plates and concrete with different thicknesses at different void heights is studied, the temperature time history curve is obtained, and the temperature at the interface and the transition heat transfer coefficient are calculated. The results show that within 5 minutes of the fire, the heat is basically absorbed by the steel plate, the temperature of the concrete is basically unchanged, and the transition heat transfer coefficient rapidly decreases from 1.0 to about 0.2–0.3. When the fire continues to develop, the concrete temperature increases rapidly and the transition heat transfer coefficient increases. With the increase of the void height, the temperature difference between the concrete interface and the steel plate interface gradually increases. According to the data fitting, the relationship between the concrete interface temperature T and the time x and the void height t is obtained. It can be used to calculate the temperature of the concrete interface at a certain moment when the composite segments with different clearance heights are on fire, which has important engineering application value for reducing the adverse consequences of shield tunnel fire.

Kinematics of the Final Approach and Take-Off Phases in World-Class Men and Women Pole Vaulters

The pole vault is a highly technical event where the athletes must successfully convert horizontal velocity during the run-up to vertical velocity at take-off. The aim of this study was to compare the kinematics of men's and women's world-class pole vaulting. Video data were collected of the best clearances by 14 men and 11 women at the 2018 IAAF World Indoor Championships using three high-speed cameras (200 Hz). Running velocity, step lengths, step times, and pole angles were measured during the run-up; during take-off, distance from the plant box, angle and velocity of take-off, and relative positions of the foot and hands were measured. Men achieved greater clearance heights with faster run-ups, faster take-off velocities and higher hand grip positions (all p < 0.001), with each of the last three steps longer for men when expressed as absolute values (all p < 0.001), but not when expressed relative to stature. There were no differences in run-up pole angles, step times, take-off angle, take-off contact time or time from pole plant to take-off. Women differed in their approach and take-off for characteristics affected by stature and strength, such as fewer run-up steps, shorter take-off distances, and lower grip heights. These lower grips result from a shorter, lighter pole, and this disadvantage was greater than slower run-up velocities. Coaches should therefore note that sex-based differences occur in the pole vault that result from anthropometric differences, but which do not negate the adoption of similar technical models of vaulting.

New ideas for steel‐concrete composite bridges overpassing highways – VFT‐RS technology

AbstractRoads overpassing highways or speedways are rather a common case, as such bridges occur in average every 2 km of highways in densely populated areas. Due to the high number and similar boundary conditions, the design and realization tends to be standardized and repetitive. The total length ranges mostly between 40 and 55 m, whereas the construction height is a limiting factor since minimum clearance heights must be guaranteed both for safety as well as for driving comfort. Due to these reasons, highway overpasses have been a field of application where steel‐framed composite decks have proven their efficiency for this task.Starting from Germany, the VFT technology (prefabricated composite beam) has spread in several European countries in the last decades as further development of the standard steel‐concrete composite solution. Its configuration fits perfectly to integral frame bridges built over existing infrastructure with the scope to minimize the traffic disturbance.In this paper a further step is proposed: the VFT‐RS technology. The change consists in using standard rolled sections by adapting them into the integral frame bridge configuration, further enhancing the structural efficiency with the benefits of high‐steel strength. The possibility of weathering steel or hot‐dip galvanization create the unique offer of a maintenance‐free solution.

Experimental study on vaporous cavitation of R134a in micron clearance

Cavitation is likely to occur in micron clearance, which affects the efficiency and reliability of the fluid machinery. Due to the confinement effect and high-speed shearing, evolution process of cavitation bubbles takes on new characteristics in the confined clearance. In this paper, a visualized experimental apparatus was developed based on the structural characteristics of micron clearance. The cavitation characteristics and bubble dynamics of R134a in divergent and convergent flow path are captured in the high-speed visualization experiment. For the single cavitation bubble, the growth, deformation and fragmentation processes are investigated under different subcooling degrees and clearance heights. The shape and growth process of single-bubble is captured during experiment. The fitting curves are obtained based on the flow and the single-bubble morphology in the micron clearance. The occurrence probability of single-bubble and bubble cluster varies with subcooling degree, clearance height and pressure difference.

Experimental and Numerical Analysis of the Gas Flow in the Axisymmetric Radial Clearance

This paper focuses on the analysis of the gas flow in the axisymmetric mini gap bounded by the surface of the top of the labyrinth seal tooth and the surface of the body. It includes the results of experimental research and numerical calculations. Experimental research focused on the analysis of gas flow for six clearance heights in a wide range of pressure drops. Based on this research, we determined the mass flow in the clearance. Using the Saint-Venant equation, we determined the flow coefficient versus the pressure ratio upstream and downstream from the seal. Flow coefficients for various clearance heights obtained from the experiment can be divided into two data groups, the values of which differ significantly. To explain changes in the value of the gas flow coefficient for selected clearance heights, numerical analysis of the said gas flow was performed using the Fluent software. This analysis allowed us to explain the reason for the variability of the flow coefficient. This research can be the basis for determining the change of seal integrity during operation for staggered and stepped seals.

Influence of tip clearance and cavity depth on heat transfer in a cutback squealer tip

Numerical simulations are conducted to present the aerothermal performance of a turbine blade tip with cutback squealer rim. Two different tip clearance heights (0.5%, 1.0% of the blade span) and three different cavity depths (2.0%, 3.0%, and 6.0% of the blade span) are investigated. The results show that a high heat transfer coefficient (HTC) strip on the cavity floor appears near the suction side. It extends with the increase of tip clearance height and moves towards the suction side with the increase of cavity depth. The cutback region near the trailing edge has a high HTC value due to the flush of over-tip leakage flow. High HTC region shrinks to the trailing edge with the increase of cavity depth since there is more accumulated flow in the cavity for larger cavity depth. For small tip clearance cases, high HTC distribution appears on the pressure side rim. However, high HTC distribution is observed on suction side rim for large tip clearance height. This is mainly caused by the flow separation and reattachment on the squealer rims.

A numerical investigation to analyze effect of turbulence and ground clearance on the performance of a roof top vertical–axis wind turbine

Recent attempts to discover energy–efficient and cost–effective power generation systems unleash tremendous capabilities of urban rooftops vertical–axis wind turbines (VAWT). Their advantages of Omni–directionality, low noise and less maintenance cost allow direct integration to urban neighborhood having unstable wind conditions. Despite continuous effort to investigate performance under a range of operating conditions, aspects such as Turbulent Intensity (TI) and ground clearance remain relatively less explored. Such effects originate either due to sharp topographical variations or placement of the turbine blades in proximity to the ground. In the present work, we perform a parametric study to quantify the performance of VAWT under various levels of TI and ground clearance. We conduct high fidelity Computational Fluid Dynamics (CFD) simulations using ANSYS Fluent and k−ε turbulence model. The H-type VAWT is employed having rated power of 1.5kW, diameter (D)of 2.5mchord length (c) of 0.2m and operates at prescribed wind speed (U0)of 12.0m/sand Tip Speed Ratio (TSR) of 1.5–4.5. We determine the performance of turbine under four levels of TI i.e., 0%, 5%, 15%25%at five ground clearance levels of 1.0c,2.5c,4.0c,7.5cand 10.0c. The results show a performance loss of 30.10%, 20.65%, 10.65% at turbine clearance heights of 1.0c,2.5c, 4.0c respectively. The height of 7.5c yield higher and more consistent performance under given operating conditions. The results for induced turbulence identify a decrease in the performance up to 45.42% corresponding to 25%TI level.

Investigation on tip clearance control for the high-pressure rotor of an uncooled vaneless counter-rotating turbine

In order to develop a tip clearance control system for an uncooled vaneless counter-rotating turbine, tip clearance variation of its high pressure rotor blade at off-design conditions is analyzed. Aero-thermal interaction simulation is performed to predict the temperature and deformation of the solid blade. At operating conditions with rotating speeds greater than 60% design value and expansion ratios greater than 85% design value, the blade tip clearance height at leading edge remains unchanged when the expansion ratio decreases, meanwhile that at trailing edge decreased obviously. However, the tip clearance height variations at the leading edge and trailing edge are almost the same in a conventional subsonic turbine at such conditions. The cause is that the flow in the high-pressure rotor is choked at these conditions. The choked flow results in that the fluid and solid blade temperatures upstream of the throat are not affected by the back pressure and only those downstream of the throat increases with the back pressure. Consequently, the blade height at leading edge keeps constant, and that at trailing edge varies because of thermal expansion. To avoid the rubbing of the blade and case, the blade height at trailing edge is diminished by 30%. As a result, the blade tip clearance height at low speed operating conditions increases in axial direction. Such a design leads to a stronger tip leakage flow. More flow losses might be generated. Therefore, a casing cooling method is proposed to control the blade tip clearance height at leading edge and trailing edge respectively. The deformations of the casing with different mass flow rate of cooling air at design and off-design conditions are calculated. It shows that the blade tip clearance heights at leading edge and at trailing edge of the rotor can be well controlled with appropriate amount of cooling air.

One-dimensional simulation of Couette–Poiseuille flow with variable cross section for the full range of gas rarefaction

Clearance mass flows are a major loss mechanism in dry running rotatory positive displacement vacuum pumps. Therefore, a detailed knowledge of the clearance mass flow is crucial to calculate the operation of those pumps. The small clearance heights and the large pressure range of such pumps require a wide range of gas rarefaction parameters to be taken into account. The flow in the clearance can be described as a combined Couette–Poiseuille flow with variable cross section. This is typically done by solving the Stokes equation, but especially at high gas rarefaction parameters, the inertia cannot be neglected any more, which can lead to choking of the flow. A one-dimensional approach for the compressible fluid flow was provided by Shapiro. It is shown that this approach can be carried over for the rarefied gas flow. The problem is solved in bounds for the constant total temperature and compared to experimental investigations by varying the pressure ratio and the circumferential speed of the clearance boundary in a wide range of gas rarefaction parameters.

The effect of ground clearance on the aerodynamics of a generic high-speed train

The influence of ground clearance on the flow around a simplified high-speed train is investigated in this paper. Four clearance heights are studied using IDDES. After a grid independence study, the results of the simulations are validated against experimental data present in the literature. It is found that the drag decreases when reducing the clearance gap from the baseline height to a possibly critical height, while drag remains constant when the clearance is lower than this critical height. The negative lift (downforce) increases with the decreasing of the clearance gap. The flow is particularly influenced by the gap height at the underbody and wake regions, where a lower underbody velocity and a higher wake velocity are observed with lower clearance down to case h2. Therefore, the different topologies of the wake are presented and described. Particular attention is paid to the description of the wake flow and to the position and the formation of the flow mixing region. Specifically, with decreasing clearance, the mix of the tail downwash and underbody flows happen earlier, and the core of the counter-rotating vortices in the wake tends to develop with an increasing height trend. Overall, aerodynamic performance and flow structure descriptions show positive and negative effects when decreasing gap clearances, which should be taken into account for new design strategies.

Performance Improvement of Single Screw Compressor by Meshing Clearance Adjustment Used in Refrigeration System

The single screw compressor (SSC) is widely used in air compression and refrigeration systems due to its many advantages. The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance. In this paper, mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights. The refrigerating capacity, volume efficiency and adiabatic efficiency of the SSC are calculated and discussed. Three prototypes, with different meshing clearance heights, were manufactured to study the internal influence mechanisms. The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results. Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%–7.98% and 5.92%–9.4%, respectively. Based on the models, analysis under varying meshing clearance heights and working conditions was performed. Taking into account working performance, actual manufacturing conditions and manufacturing cost limitations, a meshing clearance height range from 0.01 mm to 0.08 mm is suggested. This study can provide important theoretical data and experimental support for the design, manufacturing and optimization of single screw compressors.