Bump Height Research Articles

Numerical investigation of aerospike semi-cone angle and a small bump on the spike stem in reducing the aerodynamic drag and heating of spiked blunt-body: New correlations for drag and surface temperature

Aerodynamic drag and heat reduction effectivity of the aerospike attached to the blunt-body at various aerospike semi-cone angles (θS), lateral injection from the aerospike stem, and a small bump on the aerospike stem, at different Mach number is numerically investigated. An open-source computational fluid dynamics code, i.e., rhoCentralFoam, a density-based solver in OpenFOAM is employed to solve the governing equations of supersonic turbulent flow. Menter's two-equation turbulence model, i.e., k−ω shear stress transport model is employed for turbulence modeling. A significant reduction in the total drag force (TDf) on the blunt-body is observed with the increase in aerospike θS at a fixed spike length (L)/blunt-body diameter (D) ratio for Mach 2 and 5. With the increase in θS>15° for L/D = 1 and θS>10° for L/D = 2, a significant decrease in the magnitude of coefficient of pressure is observed for Mach 5. Results show a maximum percentage reduction of 23.611% and 61.414% in TDf at L/D = 2 and θS=45° for Mach 2 and 5, respectively. Correlations are developed for the estimation of total drag force on the blunt-body and average surface temperature of the nose at Mach 2 and 5. Lateral injection substantially improves the aerodynamic heat reduction capability of the aerospike owing to the rapid expansion of the injectant in the main flow. An alternate passive technique (a small bump on the spike stem) capable of producing higher aerodynamic drag reduction compared to the active technique (i.e., lateral injection) is proposed. The small bump on the spike facilitates an early initiation of boundary layer separation and leads to the formation of a large recirculation zone ahead of the nose. Results indicate a higher reduction in aerodynamic drag with the increase in bump height (HB) compared to lateral and no injection at Mach 2 and 5. Present results have been validated with the experimental results available in the literature.

Study on the surface structure effect of anode flow channel in proton exchange membrane fuel cell

The paper mainly discusses the transport behavior of hydrogen gas in the anode flow channel of the Proton Exchange Membrane Fuel Cell. The flow pattern of hydrogen gas at the anode is affected by the surface structure of flow channel. In order to accurately simulate the transport characteristics of the hydrogen gas in the anode flow channel, a structured 3-D multi-block, staggered grid system is used for spatial discretization in numerical methods, and the finite volume method is used to sequentially iteratively solve the continuous and momentum conservation equations. The coupling between velocity and pressure in the flow field is calculated by the PISO algorithm. Two shapes design of three-dimensional smooth straight flow channel and three-dimensional bump straight flow channel are adopted in this paper. The hydrogen gas with Reynolds number 200 enters the smooth straight flow channel. The flow field inside the flow channel has been developed about 0.3 ms. At the same inlet Reynolds number and straight flow channels of three kind of bump height ratio (h/H=0.25, h/H=0.5, h/H=0.75), these calculation results are discovered that the height ratio of the bump increases and the backflow effect becomes more obvious. The current density of the Proton Exchange Membrane Fuel Cell is further analyzed by the flow field variation in the bump flow channel.

Direct numerical simulation of a turbulent boundary layer over a bump with strong pressure gradients

Abstract

Inconsistencies in Reporting Risk Factors for Medial Patellofemoral Ligament Reconstruction Failure: A Systematic Review

Background: Medial patellofemoral ligament (MPFL) reconstruction is a common surgical treatment for patients with recurrent patellar instability. A variety of risk factors, such as age, trochlear dysplasia, patella alta, and increased tibial tubercle–trochlear groove (TT-TG) distance, have been identified and may lead to postoperative failure or poor outcomes. Purpose: While a large number of risk factors have been identified, significant heterogeneity exists in evaluating and reporting these risk factors in the literature. The goal of this study was to perform a systematic review to determine risk factors associated with worse outcomes after MPFL reconstruction and their consistency of being controlled for or analyzed among studies. Study Design: Systematic review; Level of evidence, 4. Methods: A systematic review of the literature was performed using the MEDLINE database to identify relevant clinical outcome studies after MPFL reconstruction for recurrent patellar instability. Eligible studies were evaluated for risk factors that were associated with MPFL failure, defined as recurrent instability or lack of improvement on patient-reported outcome (PRO) scores. Each study was then evaluated for inclusion of these risk factors. Results: Ten studies were included in the final analysis, comprising 1287 knees from 1275 patients who underwent isolated MPFL reconstruction. Of these 10 studies, 8 defined outcomes based on PROs and 3 defined outcomes based on postoperative recurrent instability (1 study included both outcomes). In the PRO failure group, 12 risk factors were found across all studies: trochlear dysplasia, trochlear bump height, elevated TT-TG, patellar tilt, hyperlaxity, age at first dislocation, age at surgery, body mass index, bilateral symptoms, WARPS/STAID score (weak atraumatic, risky anatomy, pain, and subluxation/strong, traumatic, anatomy normal, instability, and dislocation), femoral tunnel malposition, and femoral tunnel widening. In the recurrent instability failure group, 7 risk factors were found across all studies: trochlear dysplasia, bump height, patella alta, higher sulcus angle, higher congruence angle, preoperative J sign, and femoral tunnel malposition. Trochlear dysplasia and femoral tunnel malposition were consistently cited in several studies as risk factors for worse PROs and higher rates of recurrent instability. Patella alta was indicated as a significant risk factor for recurrent instability in 1 of 2 studies analyzing postoperative instability failures and was not associated with worse PROs in any of the studies analyzed. Similarly, elevated TT-TG distance was not a significant risk factor in any of the studies that analyzed recurrent instability as the failure endpoint. Conclusion: While various risk factors are postulated to affect outcomes after MPFL reconstruction, there remains inconsistency within the literature regarding the inclusion of all risk factors in a given analysis. Furthermore, the significance of these risk factors varies among studies in terms of whether they affect postoperative outcomes. We found that more severe trochlear dysplasia (types C and D) and femoral tunnel malposition (>10 mm from Schöttle’s point) appear to have the most consistent effect on producing higher rates of recurrent dislocation as well as worse PROs. Despite this, the role of concomitant bony procedures to adjust certain pathoanatomic risk factors in addition to MPFL reconstruction remains unknown. Future high-level studies must be conducted that respect the multifactorial nature of patellar instability and should analyze all risk factors (demographic, anatomic, and radiographic) reported to affect outcomes.

Dynamic response of horizontally curved composite steel I-girder bridges

The dynamics behavior of horizontally curved composite steel I-girder bridges is investigated by using three-dimensional finite element models. The analyzed bridge is modeled by using ANSYS 15.0 program with SOILD185 and SHELL181 elements to represent concrete and steel members, respectively. AASHTO HL-93 truck is simulated as 3D mass-spring-damper model consisting of five lumped-masses which connected by rigid beams and supported by spring-damper elements which are used to represent the suspension of vehicle body and tires. Gap and actuator elements are used to represent the separation between the tires and road surface and surface roughness condition, respectively. Four different roughness profiles are generated based on power spectral density (PSD) for very good, good, average, and poor roads. The dynamic analysis is carried out under different cases of vehicular loading positions for bridges with radius of curvature ranged from (35 to 200 m). Seven vehicle speeds are chosen to investigate the effect of this factor on the bridge dynamic response, also the effect of bump height at approach span is studied. The results are presented in terms of Impact Factors (IM). The results show that the IM-radius of curvature relationship is significantly influenced by the position of vehicle on transverse sections of the bridge. For the out-lane loading, the IM values for all girders tend to increase as the radius of curvature decreases. A 45 km/hr vehicle speed provides higher IM value for the good roughness bridge to be at 120 km/hr under poor road surface. The bump heights has a significant effect on IMs at lower speed limit, where the IM value increases with the increasing of bump height.

Friction and Wear Performance of Double-bump Design of Piston Skirt Main Thrust Side

As a key component of the engine, piston have to work in harsh environment for a very long time, its friction performance and operational reliability have been the research focus. In this paper, a four-cylinder diesel engine was used as the research object. The dynamic model considering multi-factors such as inertial parameters, surface roughness, thermal deformation and elastic deformation was established in Ricardo-Pisdyn software. The research mainly focused on the double-bump design of the main thrust side of the piston (exploring the parameters of the upper bump height, cavity depth etc.) on the friction and wear performance. The research showed that appropriately increasing the depth of the cavity can improve the wear within a certain range. However, if the cavity depth increase too much, the abrasion of the main thrust surface will be aggravated. After optimizing of the clearance and adopting the double-bump profile on the main thrust side, the accumulated wear load of the piston can be significantly reduced and its friction and wear performance will be improved. In this paper, the optimized accumulated wear load decreases from 31.65 MW/m2 to 14.64 MW/m2, drops by 53.7 %.

Thermal-mechanical reliability analysis of WLP with fine-pitch copper post bumps

PurposeThis study aims to investigate the several parameters in wafer-level packaging (WLP) to find the most critical factor impacting the thermal fatigue life, such as the height of copper post, the height of solder bump, the thickness of chip. The FEA results indicate the height of solder bumps is the most important factor in the whole structure.Design/methodology/approachThe copper post bumps with 65 µm pitch are proposed to investigate the thermal-mechanical performance of WLP. The thermal cycle simulation is used to evaluate the reliability of WLP by using finite element analysis (FEA). Taguchi method is adopted to obtain the sensitivity of parameters of three-dimension finite element model, for an optimized configuration.FindingsIt can be found that the optimal design has increased thermal fatigue life by 147% compared with the original one.Originality/valueIt is concluded that the finite element simulation results show outstanding thermal-mechanical performances of the proposed 65 µm pitch copper post bumps of WLP, including low plastic strain, high thermal fatigue life, which are desired for mobile device.

DYNAMIC ANALYSIS OF COMPOSITE MULTI I-GIRDERS BRIDGE USING FINITE ELEMENT METHOD

Three dimensional finite element models are developed to deal with the bridge-vehicle interaction problem of simply supported composite multi I-girders bridge. The bridge is modeled by using ANSYS 15.0 program with solid and shell elements to represent concrete and steel members, respectively. AASHTO HL-93 truck is idealized as 3D non-linear model consisting of five lumped masses connected by rigid beams and supported by spring-dampers. The separation between the tires and road surface and surface roughness condition are simulated by Gap and actuator elements, respectively. The road surface roughness profiles are generated from power spectral density (PSD) and cross spectral functions. The models used are capable to take all bridge and vehicle responses into consideration with no limitations on the complexity of the models. The dynamic responses of the multi I-girder bridge are investigated under conditions of various loading positions, roughness classes, vehicle speeds, and bump height. The dynamic behaviors are presented in terms of Dynamic Amplification Factors (DAF). The results show the girder that itself supporting the moving vehicle has lower value of DAF because of higher static responses. A 45 km/hr vehicle speed provides higher DAF value. The bump heights have significant effect on DAFs for bridge with short span.

Bump detection in the presence of dependency: Does it ease or does it load?

We provide the asymptotic minimax detection boundary for a bump, i.e. an abrupt change, in the mean function of a stationary Gaussian process. This will be characterized in terms of the asymptotic behavior of the bump length and height as well as the dependency structure of the process. A major finding is that the asymptotic minimax detection boundary is generically determined by the value of its spectral density at zero. Finally, our asymptotic analysis is complemented by non-asymptotic results for AR($p$) processes and confirmed to serve as a good proxy for finite sample scenarios in a simulation study. Our proofs are based on laws of large numbers for non-independent and non-identically distributed arrays of random variables and the asymptotically sharp analysis of the precision matrix of the process.

Systematic Analysis of the Impact of Bump Height Manufacturing Errors on the Unbalance Response of a Foil Journal Bearing

Abstract The present work exhibits the numerical investigation of the bump height-manufacturing errors on the unbalance response of an aerodynamic foil journal bearing. This is the first study on the impact of manufacturing errors based on an important number of samples. A statistical analysis predicts the mean values of the characteristics and the standard errors of the mean. The paper presents the most important aspects of the numerical model that was used and the way it was implemented for the unbalance analysis of a four degrees-of-freedom rotor. It was considered that the bump height-manufacturing errors had a normal distribution (i.e., each bump had a different random height) around the design (mean) height value. The standard deviation of the bump heights (the same for all bumps) is a measure of the magnitude of the manufacturing errors. The results give a qualitative but above all quantitative overview of the impact of machining errors on some characteristics of aerodynamic foil bearings.

Mechanical scribing test analysis of lateral ridges law on aluminum

In order to study the rule of lateral uplift of pure aluminum (purity is 99.999%) during mechanical scribing, based on the mechanical scribing test device, the tool tip angles are 80 °, 85 °, 90 °, 95 °, 100 ° The diamond cone cutter is used to perform mechanical scoring test on pure aluminum with a depth range of 5μm-25μm. Through the bump height detection analysis, lateral ridge height and groove depth - mathematical statistical relationship knife sharp corners, through the known parameters such as groove depth, groove on the bump height is pre-sentence, thereby pre-Groove play an important role in the control.

Limiting stiffness coefficients analysis of texture foil journal bearing

The purpose of this study is to explore the limiting stiffness coefficients of a foil journal bearing with the texture bump profile of top foil. The limiting stiffness coefficients are evaluated based on simplified compressible Reynolds equation for large bearing numbers with high speeds of foil journal bearing. A limiting pressure gradient solution for a texture bump of top foil bearing is analyzed. The analytical model accounts for the top foil texture bump profile and bottom foil bump compliance. Results of linearized nondimensional stiffness coefficients obtained using infinitesimal perturbation method are compared for various top foil texture bump profiles. The influence of top foil texture bump extent and height on the limiting stiffness coefficients of a foil journal bearing are investigated.

Haptic Surface Display based on Miniature Dielectric Fluid Transducers

We present a lightweight, low power, and compliant miniature dielectric fluid transducer intended for haptic surface display. The actuator has a large strain and fast response without an external compressor. It consists of a thin oil-filled pouch with a 1.5 mm diameter opening covered with a silicone membrane. The application of voltage causes the pouch to squeeze the oil and form a bump by stretching the silicone membrane. The actuator produces 1.45 mm bump height at 3 kV and 13 mN at 3.5 kV using ≈10 μl of oil. The power consumption is <; 3 mW. Though the largest bump height has a bandwidth near 5 Hz, the device achieves perceivable vibration at 200 Hz with a bump height of 200 μm. The actuators can be packed closely and controlled individually to create dynamic texture displays, suitable for active surface exploration with the fingertips. The simulation results show the width of the actuator can be reduced without affecting the performance. Tests with human subjects show that users differentiated simple bump patterns with a 98.8% success rate.

Thin Film Characterization on Cu/SnAg Solder Interface for 3D Packaging Technologies

Copper is a commonly used interconnect metal in microelectronic interconnects due to its exceptional electrical and thermal properties. Particularly in applications of the 2.5 and 3D integration, Cu is utilized in through-silicon-vias (TSVs) and flip chip interconnects between microelectronic chips for providing miniaturization, lower power and higher performance than current 2D packaging approaches. SnAg capped Cu pillars are a common high-density interconnect technology for flip chip bonding. For these interconnects, specific properties of the Cu surface, such as roughness and cleanliness, are an important factor in the process to ensure quality solder bumps. During electroplating, tight processing parameters must be met so that defects are avoided, and high bump uniformity is achieved. An understanding of the interactions at the solder and Cu pillar interface is needed, based on the electroplating parameters, to determine the best method for populating solder on the wafer surface. In this study, surface treatment techniques such as oxygen plasma cleaning were performed on the Cu surfaces and the SnAg plating chemistry for depositing the solder were evaluated through hull cell testing to qualitatively determine the range of current densities to investigate. It was observed that current density while plating played a large role in solder bump deposition morphology. At the higher current densities greater than 60 mA/cm2, bump height non-uniformity and dendritic growth are observed and at lower current densities, less than or equal to 60 mA/cm2, uniform, continuous bump height occurred.

Airport pavement roughness evaluation based on cockpit and center of gravity vertical accelerations

Pavimentos irregulares são geralmente responsáveis por acelerações verticais (VA) que afetam as aeronaves, aumentam a distância de parada e dificultam a leitura dos instrumentos de navegação na cabine dos pilotos. O International Roughness Index (IRI) e o Boeing Bump Index (BBI) são utilizados atualmente para quantificar a irregularidade longitudinal dos pavimentos aeroportuários e identificar seções que demandam atividades de manutenção e reabilitação (M&amp;R). Contudo, tais índices baseiam-se apenas nas respostas dinâmicas de um automóvel a 80 km/h às irregularidades longitudinais dos pavimentos rodoviários, bem como nas características físicas das irregularidades (comprimento e altura), respectivamente, ignorando o efeito das VA nas aeronaves. Ainda, limites críticos atuais, sugeridos por Sayers &amp; Karamihas e ANAC para IRI (2,0 e 2,5 m/km, respectivamente) e pela FAA para BBI (1,0) podem subestimar a condição real do pavimento. Este artigo avalia o efeito da irregularidade longitudinal nas acelerações na cabine dos pilotos (VACP) e no centro de gravidade (VACG). O software ProFAA permitiu calcular os índices e simular as VA em 4 aeronaves representativas atravessando 20 pistas de pouso e decolagem em 10 velocidades de taxiamento variando de 37 a 370 km/h. Comparações estatísticas e análises de regressão foram realizadas. Principais resultados mostram que VACP é 50% maior do que VACG e que ultrapassa o limite critico de 0,40 g quando o IRI e BBI estão acima de 3,7 m/km e 0,20, respectivamente. Um estudo de caso é também apresentado para comparar esses limites e sugere que a tomada de decisão baseada em IRI e VA pode trazer diferenças significativas na quantidade de atividades de M&amp;R.

Mechanical Properties and Microstructure of Cu Core Solder Ball (CCSB) Compared with SAC305 Solder for 2.5D and 3D Structure Package (PKG)

Package structures are continually becoming more complicated to achieve high-performance devices. Thus, the 2D structure of package needs to be modified to a 2.5D or 3D structure. Therefore, standoff properties at the solder joint are required to prevent Si chip damage and electrical shorts when the solder joint is located between the substrate and interposer. Cu-core solder balls (CCSB) are the most popular interconnection choice for a 2.5D package because they have better standoff properties than the general SAC solder. The mechanical properties of CCSBs were evaluated by ball shear tests and measuring bump height as compared with Sn–3.0 wt.%Ag–0.5 wt.% Cu solder. The bump heights of CCSBs and Sn–3.0 wt.%Ag–0.5 wt.% Cu were measured under several compressive pressure conditions at room temperature, 175 °C and 235 °C. The stand-off height of the CCSBs dramatically better than that of Sn–3.0 wt.%Ag–0.5 wt.% Cu solder under high pressure and temperature. The shear strength of the CCSBs was stronger than that of SAC solder at all multiple reflows due to the finer microstructure and higher stacking of dislocations at the interface of the Cu core ball surface.

Stability Control Investigation of a Self-Balancing Platform on the Robot Smart Car Using Navigation Parameters

A self-balancing platform is constructed on a robot smart car, and its navigation parameters are investigated by running the car outdoors on a straight surface with structured bumps of 3and 5 mm in height. A ball-and-socket joint are supported at the centre of the platform, which is to be freely rotated with the lateral and longitudinal movement of the platform and in each axis, is controlled by three servomotors. Which move according to the recorded data movements from a gyro-accelerometer sensor which controlled by an Arduino UNO. The SimMechanics Matlab simulation helps to give the initial values of all parameters and the additional unexpected signals due to the influence of bumps on the vibration signals, with the proportional-integral-derivative (PID) controller, used to control the relationship of the rapid simulation of the robot smart car and mathematical model between platform and car shock absorber system with respect to the servomotor’s rotation angle. These bump is more effective on the pitch and roll angle values when compared to other parameters, with more than 815 degrees and error up to 35 degrees due to vibration signals, and the time required for stabilization increases due to the bump height and the navigation parameters, roll angle from 2 to 6 in mean change value 2, yaw angle from 43 to 59 in mean change value 8 and pitch angle from 1 to 2 in mean change value 0.5, which indicates that yaw, roll and pitch angle have variation changing in Mission Planner software

PAVEMENT CONDITION ANALYSIS VIA VEHICLE MOUNTED ACCELEROMETER DATA

Road anomalies and irregularities such as potholes and uneven surfaces are a common hazard in South East Asia and developing countries. Such hazards pose a threat to the safety and well-being of both civilians going about their daily routine and tourists who are exploring the city. Since bicycles and rickshaws are still a common mode of transport used by both civilians and tourists in many South East Asian countries, it is essential to improve the overall quality and smoothness of pavements which are traversed by these vehicles. Management of international sporting and recreational events also require satisfactory road and pavement conditions. Before pavement conditions can be improved, it is an essential prerequisite to obtain comprehensive information about road irregularities such as the location and also severity of the road irregularity (depth of the potholes and height of bumps). In this paper, we propose a method for obtaining mathematical models that represent the overall condition of the pavements that are part of a commonly traversed cycling route. Such mathematical models and coefficients can be stored in the cloud of an Internet of Things (IOT) data analytics systems subsequently leading to identification of regions with severe road irregularities.&#x0D; ABSTRAK: Kerosakan pada permukaan jalan raya merupakan salah satu faktor risiko kemalangan yang berlaku secara meluas di negara Asia Tenggara dan negara membangun yang lain. Memandangkan kenderaan seperti beca dan basikal masih diguna pakai secara meluas di negara membangun, adalah mustahak untuk membaik pulih kerosakan jalan raya. Pengurusan sukan antarabangsa dan rekreasi juga memerlukan keadaan jalan dan laluan pejalan kaki yang baik. Sebelum kerja membaik pulih dapat dilakukan, maklumat lengkap mengenai tahap kerosakan jalan raya dan lokasi kerosakan diperlukan. Dalam kajian ini satu kaedah telah diperkenalkan untuk mendapatkan persamaan matematik yang menggambarkan keadaan sebenar permukaan jalan raya, di mana sebahagiannya merupakan laluan berbasikal yang selalu digunakan. Model matematik dan pekali ini boleh di simpan dalam sistem analisis data awan Internet Benda (IOT) kemudiannya dapat mengenal pasti kawasan jalan yang rosak dan tidak rata.

Study on the performance of gas foil thrust bearings with stacked bump foils

Purpose This paper aims to improve the load capacity of gas foil thrust bearing (GFTB) and to introduce and study a novel bearing with stacked bump foils. Design/methodology/approach For the proposed novel GFTB supported by stacked foils, some bump-type gaskets with several partial arches are inserted below the regular bump foil, and the height of each arch can be made differently. These features make the bump foil thickness and height gradually increase, which can bring enhanced support stiffness and convergent film at the trailing edge. Based on a new nonlinear bump stiffness model considering bump rounding and friction force, the finite element and finite difference method were used to solve the coupling Reynolds equation, energy equation and foil deformation equation. Finally, the structural stiffness and static characteristics of the novel GFTB were gained and compared with the traditional bearing. Findings The novel GFTB has an additional convergence effect in the parallel section, which improves the static performance of bearing. The bearing capacity, friction moment, power loss and temperature rise of the novel GFTB are all higher than those of the traditional bearing, and the static characteristics are related to the parameters of stacked bump foils. Originality/value The stacked bump foils bring a fundamental enhancement on the load capacity of GFTB. The results are expected to be helpful to bearing designers, researchers and academicians concerned. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0449/

Asymptotic regimes in elastohydrodynamic and stochastic leveling on a viscous film

An elastic sheet that deforms near a solid substrate in a viscous fluid is a situation relevant to various dynamical processes in biology, geophysics and engineering. Here, we study the relaxation dynamics of an elastic plate resting on a thin viscous film that is supported by a solid substrate. By combining scaling analysis, numerical simulations and experiments, we identify asymptotic regimes for the elastohydrodynamic leveling of a surface perturbation of the form of a bump, when the flow is driven by either the elastic bending of the plate or thermal fluctuations. In both cases, two distinct regimes are identified when the bump height is either much larger or much smaller than the thickness of the pre-wetted viscous film. Our analysis reveals a distinct crossover between the similarity exponents with the ratio of the perturbation height to the film height.