Search

As a relatively complex part of aero-engine turbine blades, the integral impeller is characterized by complex space, high steepness, and distortion. An actual five-axis computerized numerical control (CNC) machining process unaffected by the machining quality and accuracy of a large curvature range. Consequently, knowing how to reasonably adjust the feed speed of a path in view of further improving the efficiency has always been difficult. This research adopts the method of combining computer-aided manufacturing (CAM) and CNC and proposes a direct interpolation algorithm for the double non-uniform rational B-spline curves based on the typical characteristics of the integral impeller. First, in the CNC, the integral impeller is divided into high-speed regions and three-dimensional characteristic parameters of the integral impeller in CAM. Second, in the low-speed area, the feature-divided high- and low-speed areas are discretized on the basis of the interpolation period and equal arc length. Then, the low-speed area speed is adjusted to meet the kinematic constraints according to the dichotomous configuration. Finally, the discrete speed is smoothly filtered by the Finite Impulse Response (FIR) filter to be able to meet the dynamic response characteristics of the machine tool. Simulations and experiments show that the algorithm can effectively improve the speed and smoothness of the inlet and exhaust edges of the overall impeller, effectively reduce the calculation amount of the numerical control system, and improve the overall machining efficiency of the impeller under the requirements of machining accuracy.

The high frequency (HF) square-wave injection sensorless algorithm uses saliency to estimate the motor position affected by the inductance. The structure of the permanent magnets will affect the inductance of the motor, then affect the position estimation performance of the sensorless algorithm. This paper studies the relationship between the inductance and the position estimation accuracy of the HF square-wave injection sensorless algorithm for tubular permanent magnet synchronous linear motor (TPMSLM). Through the finite element simulation, the distribution law of the TPMSLM inductance with the change of the PM structure is quantitatively analyzed, and the influence of the PM structure parameters on the differential amplitude of the HF current is given. The HF square-wave voltage is injected into the stationary reference frame, and the frequency is half of the PWM switching frequency. The HF current differential equation is obtained without any filter, and the estimated position of the mover is extracted by a phase-locked loop. Finally, the experiment of sensorless position estimation is carried out by two prototypes with different PM structure parameters at different speeds, verifying the effectiveness of the analysis.

Fractional circuit elements become increasingly popular due to their versatility in various applications. However, the bottleneck in deploying these tools in practice is related to an open problem, i.e, infinite energy problem. On this topic, many valuable achievements have been made. Some scholars don’t dare to use fractional circuit elements because of the infinite energy problem while some scholars believe that there is no paradox compared with classical finite energy or even some scholars think that this problem has been successfully solved. However, there is still no consensus on this topic and confusion remains widespread. Consequently, a comprehensive review on infinite energy problem is needed imperatively. At this point, this paper reviews the consequences, root causes, and potential mitigation approaches through the modeling analysis and literature survey. This review starts with the fractional capacitors. Subsequently, other fractional circuit elements and fractional order operators/systems are considered. Finally, the main technical challenges as well as future researches on this topic are highlighted carefully.

Most engineering components are subjected to cyclic loading in service and design against fatigue failure is often a key consideration in design. For fracture mechanics fatigue analysis, fatigue crack growth (FCG) tests are often required to determine the relevant Paris power law parameters for the material under the environment concerned. Standards allow use of different specimen geometries for FCG tests such as compact tension (CT), centre crack tension (CCT), single edge notch bend (SENB) and single edge notch tension (SENT). However, when selecting specimen geometry for fatigue crack growth rate (FCGR) testing, there is often doubt about which specimen geometry is more appropriate and whether they give similar FCGR. There is limited work to compare the FCGR between different specimen geometries. This paper first briefly introduces the guidance on FCG test specimen geometries in standards and compares the advantages and disadvantages of these specimen geometries. A comprehensive literature review is carried out to compare the FCGR data between different specimen geometries. FCGR tests are conducted on SENB, SENT and CCT specimens of C-Mn steel to investigate any effects of specimen symmetry/asymmetry and crack constraint on FCGR. Based on the literature review and test data, it is concluded that FCGR is independent of the specimen geometries examined.

This study investigated the biomechanical effects of thenar muscles (abductor pollicis brevis (APB), superficial head of flexor pollicis brevis (sFPB), opponens pollicis (OPP)) on the transverse carpal ligament formed carpal arch under force application by individual or combined muscles (APB, sFPB, OPP, APB-sFPB, sFPB-OPP, APB-OPP, and APB-sFPB-OPP). In ten cadaveric hands, thenar muscles were loaded under 15% of their respective maximal force capacity, and ultrasound images of the cross section of the distal carpal tunnel were collected for morphometric analyses of the carpal arch. The carpal arch height and area were significantly dependent on the loading condition (p

Anti-typhoon drilling riser, a solution to overcome high time cost of offshore drilling riser emergency retrieval under the situation of imminent arrival of a typhoon, is to modify the existing drilling riser to make it disconnectable closer to the surface and leave the long riser string below (and subsea blowout preventer (BOP)) in a safe and freestanding mode to survive the typhoon. The freestanding riser is held up by a buoyancy can system. And during the normal drilling operation, the buoyancy can maintain neutral thus it has limited effect on the riser overall global performance. However, locally the buoyancy can system will have some effect on the riser system nearby. To study these effects, numerical analytical methodology and results of anti-typhoon drilling rise under connected mode and freestanding mode are proposed, and a model test of 1:21 scale factor is designed. Three configuration modes: freestanding mode, connected mode and disconnecting mode are simulated in the tank test. A series of load cases under various current and wave, buoyancy upthrust are conducted in the experimental test to evaluate the hydrodynamic and strength performance of the riser near buoyancy can. The numerical solution and model test design can be a significant basis of water tank test for anti-typhoon drilling riser and a valuable reference for deepwater drilling engineering.

Fatigue design recommendations provided by API RP 2SK, ISO 19901-7 and DNVGL-OS-E301 for studless chain links are based on data of steel grades R3 and R4 and mainly of link diameter of 76mm. Mooring systems utilising larger diameter links and higher strength steels (e.g. grade R5) are now in operation. Consequently, industry expressed a need for fatigue test data in seawater of higher steel grade and larger diameter chain to confirm whether the existing fatigue design guidance is applicable. A joint industry project (JIP) was launched by TWI to investigate fatigue performance of high strength and large diameter mooring chain in free corrosion seawater. A test rig was designed and manufactured which was capable of testing studless mooring chain links up to 127mm link diameter under tension-tension loading. Twenty-three full-scale fatigue tests were conducted on high strength steel grades (R4 and R5) and larger diameter chains (76mm and 127mm) generating 72 link failures. Magnetic particle inspections (MPI) were carried out to characterise the location of cracking, crack size and crack growth rate. This paper describes the results obtained in the JIP.

Offshore pipelines are generally subjected to variable amplitude (VA) loading in service due to waves or ocean currents. Welded joints often represent the most critical locations for fatigue cracking. Use of the current fatigue design guidance, for example, BS 7608, to assess fatigue performance of the welded joints in such structure may lead to inaccurate estimates depending on the nature of the VA loading spectrum. Further studies on the effect of VA loading spectra on fatigue performance of welded joints are needed. In this research, both uniaxial and 3-point bending fatigue tests were performed on non-load carrying fillet welded plates under VA loading spectra to investigate the effects of mean stress and the type of VA loading spectra. The influence of plate thickness was also investigated. Test results suggest that the spectrum with a high constant maximum tensile stress (cycling-down) could significantly degrade fatigue performance of welded joints, with the damage parameter D only at around 0.5. The severity of this type of loading spectrum depends on the mean stress level and the plate thickness. An analytical model has been developed to predict fatigue crack propagation (FCP) by considering the interaction of stresses in the loading spectrum. The model considers the impact of the mean stress generated by the preceding load on FCP in the subsequent cycles. FCP predicted by the model shows a good agreement with the experimental data.

The well-designed feedrate optimization algorithm can obtain higher machining efficiency with various machining related constraints, thus, it is widely considered in the high-speed and high-precision machining. However, the low computational efficiency still limits the application of the optimization method. For the non-linear optimization problem of spline toolpath with feedrate-, actuator velocity-, acceleration- and jerk-limited, a linear approximation is adopted by a pseudo-jerk method and the efficient linear programming method can be applied to solve the optimization problem. To improve computational efficiency further, curvature-base window technique is presented and the whole spline toolpath is split at the curvature extreme points, which are also named critical points in traditional planning method. Thereafter, a novel feedback interpolation is presented based on Steffensen iterative accelerator method to eliminate the feedrate fluctuation caused by nonanalytic relationship of spline parameter and arc-length. Finally, simulations and experiments validations show that the proposed method is able to reduce computational burden and traversal time notably with multi-constraints.

Engineering critical assessment (ECA) is increasingly being used in the offshore industry to determine the maximum tolerable initial flaw size in girth welds for pipelines and risers. To account for the effect of the stress concentration factor (SCF) at the weld toe on the stress intensity factor range, ΔK, a magnification factor, Mk, is used. The existing Mk solutions given in BS 7910 were developed for fatigue assessment of flaws at the toes of fillet and butt welds and may not be suitable for assessing flaws at girth weld root toes, where the weld width is relatively small. On the other hand, for single-sided girth welds, fatigue cracking often initiates from weld toes on the root side, rather than on the weld cap side. Finite element (FE) modelling was performed to determine a 2D Mk solution for ECA of a flaw at the weld root bead toe. The weld root bead profile was uniquely characterised by five variables including weld root bead width, weld root bead height, hi-lo, weld root bead angle and weld root bead radius. Following a parametric sensitivity study, defect size, weld root bead height and hi-lo were identified as the governing parameters. A total of 6,000 FE simulations was performed and three types of defect models, which covered different combinations of weld root bead height and hi-lo, were generated and analysed. A series of automation scripts were developed in the Python programming language and the Mk solution for each type of defect model was developed and provided in a parametric equation. The accuracy of the 2D Mk solutions was confirmed by the experimental data, in terms of both fatigue crack growth and S-N curves. It was found that the methods and Mk solutions currently recommended in BS 7910 and DNV OS-F101 are inappropriate for assessing a flaw at a girth weld root toe.

Fatigue crack growth rates (FCGR) in corrosive environment depends on loading frequency. Frequency scanning testing is often used to determine this effect. However, it is well known that the effect of loading frequency also depends on the magnitude of stress intensity factor range, ΔK. It is generally found that, with decreasing loading frequency, FCGR decreases in the low ΔK regime, increases and then decreases after reaching the saturating loading frequency in the intermediate ΔK regime, and keeps increasing in the high ΔK regime. To accurately characterise the effect of loading frequency on FCGR, several frequency scanning tests are required for a particular application (corrosive environment, material, welding procedure etc), each at a different ΔK level. These are time consuming and expensive tests. A novel screening frequency scanning test method has thus been developed. The method is similar to the step load fracture toughness test method often used to make a quicker estimate of fracture toughness of material in corrosive environment. In the screening frequency scanning test, both loading frequency and ΔK are changed in steps. At a relatively low and constant ΔK level, loading frequency is reduced in steps, after a certain amount of crack growth. Once the FCGR exhibits decreasing or has achieved a saturating loading frequency with decreasing loading frequency, ΔK is then increased to another higher level and the above process is repeated; the above procedures are repeated until the target maximum ΔK and the lowest loading frequency have been achieved. This method allows an estimate of the effect of loading frequency on FCGR in a large ΔK range using a single specimen. The results of the screening frequency scanning tests demonstrated that this method was feasible and provided a good and quick estimate of the effect of loading frequency on FCGR.

During the storage and transportation of aviation kerosene, spill fire and explosion caused by the corrosion of pipeline or faulty operation when released and ignited, will pose a huge threat to tanks or facilities nearby. It is critical to investigate the interaction mechanism between spreading and burning of aviation kerosene spill fires to effectively plan for civil aviation safety. In order to gain a better understanding of aviation kerosene spill fire on sloping surface, a large-scale experimental platform with varying slope of oil groove or substrate surface for aviation kerosene spill fire has been designed and built. Aviation kerosene was selected as the fuel in the continuous spill fire for different leaking rates based on the rotation of the peristaltic pump. Spill fires with the substrate slope of 0° (as the baseline case), 0.5°, 1° and 3° were conducted. The typical burning characteristic parameters of spill fire measured are included burning area, burning rate, flame front et al. It is obtained that 1) the characteristic parameters except the averaged steady burning rate for continuous aviation kerosene spill fire increases apparently with the increasing leaking rate. 2) The effect of substrate slope on the burning of continuous spill fire is significant even though there is only 0.5° variation of the slope. 3) There is a diametrically opposite findings for the averaged steady burning rates and the initial spreading rates of continuous aviation kerosene spill fire decrease with the increasing substrate slope.

This paper presents a trajectory planning method for high-speed CNC machine tools. Generally, the kinematic parameters of a machine are limited to an agreed range in the trajectory planning process. However, a new single-step strategy trajectory planning method is proposed under a driving force limit condition. This method minimizes the acceleration and deceleration time when the speed changes. This kind of force limit method guarantees the tracking performance of a servo system. This paper proposes a method for time domain automatic feed rate adjustment to meet the requirements of the planning trajectory. In this method, two trajectory planning processes are provided. These processes are the two-axis straight line segment and the two-axis corner transfer segment planning process. An adapter for asymmetric contour error calculation method is then proposed, and the continuous G-code trajectory planning method is realized under this error calculation method. Finally, we compare our proposed algorithm with other algorithms through simulations and experiments, and then we prove the superiority of our proposed algorithm.

Cargo compartment fire has become the major security threat for cruising aircraft, the depressurization measurement could effectively suppress the cargo compartment fire through the reduction of the air pressure and oxygen concentration. The objective of this work is to study fire behavior characteristics in half confined chamber and high altitude laboratory at identical low atmospheric pressure, and explore the controlling effects of air exhaust condition, oxygen concentration. N-heptane pool fire experiments were conducted separately in Langfang low pressure chamber (altitude 50m) and Kangding airport laboratory (altitude 4290m) at 60 kPa air pressure, both assembled ISO-9705, but their gas supplying condition is different. Mass burning rate, gas composition, flame temperature, and radiant heat flux had been measured as the principal characteristic parameters for analysis. This paper reveals the variation characteristics of the fire behavior under different oxygen concentration but identical low atmospheric pressure. The gas composition of the chamber is controlled by the liquid fire and air intake quantity, the oxygen concentration of the chamber decreases with decreasing gas intake quantity. The mass burning rate increases and the mass burning time decreases with the increase of the oxygen concentration. The higher air intake quantity or the higher oxygen concentration could increase cargo compartment fire radiation intensity, and exacerbate the fire further propagation. However, under the low oxygen concentration condition, the liquid fire still have a higher flame temperature above a certain height. The depressurization measurement could increase the flame height and flame temperature may be caused the cabin fire-resistant liners layer is easier to burn through. The more reasonable adjustment of the cargo compartment air exhaust quantity and air pressure is very meaningful for the comprehensive fire suppression of cruising commercial airplanes.

Integrating an array of buoys type converters with a flexible runway can be a viable option for cost-sharing between wave energy capturing devices and ocean space utilization structures, and thus enhance the cost-effectiveness of wave energy utilization. In this study, a configuration of multiple buoys supporting a runway is proposed. Hydrodynamic interactions among the buoys are analyzed using an exact algebraic method based on linear wave theory in the frequency domain. A parametric governing equation of compound wave energy converter referred to as a wave farm is formulated by using Hamilton’s principle which can be discretized by using Galerkin method. The effects of wave condition and the parameters of PTO on the wave energy absorption and dynamic characteristics of a runway are analyzed. This research work is aimed to provide a theoretical guideline for wave energy converters design.Copyright © 2017 by ASME

Elevator evacuation has been considered in high-rise building evacuation in the world, especially in China. Elevator safety has been widely studied for this purpose and technical standards are also available in different countries. However, it is critical to understand human behaviors in elevator evacuation before elevators can be used in building evacuation. It is expected that social relation (family, friend, classmate, etc.) will play an important role on evacuation behaviors. However, researches are largely missing on social relation and its impacts on movement and behaviors of the evacuees. This paper aims to investigate the crowd evacuation considering social relation. An evacuation experiment is conducted in a 11-storey office building. Participants who take part in the experiment include individuals, families and lovers. Evacuation behaviors especially decision-making as well as important factors affecting evacuees’ choices are discussed. Movement characteristics of evacuees in the stair are also analyzed. It is concluded that family members will take actions, such as take elevators or stairs, together. Females and evacuees in poor condition prefer to take the elevator during evacuation. Many pairs or small groups may be formed owing to social relations. The groups take more time to make decision. The members in small groups may block the traffic and slow down the speed of the crowd. Evacuation efficiency changes greatly considering small group behaviors and social relations. Experimental results are helpful for determining the effective rules and regulations in elevator evacuation in high-rise buildings.Copyright © 2016 by ASME

This research aims to investigate the effect of ambient pressure on the burning rate and heat release rate (HRR) of n-heptane pool fire. The experiments were performed in a large-scale altitude chamber of size 2 m×3 m×4.65 m under series of pressure, 24kpa, 38 kPa, 64 kPa and 75 kPa to 90 kPa. A round steel fuel pans of 34 cm in diameter and 15 cm in height was chosen for the pool fire tests. The fuel pan was filled with 99% pure liquid n-Heptane. Experimental results show that the burning rate increases rapidly after ignition until it reaches to the peak, and then maintains at a relatively stable stage. It decreases gradually until the flame extinguishes. The burning time is longer at lower pressure. The mean mass burning rate at the steady burning stage increases exponentially with pressure as ṁ ∼ Pα, with α = 0.68. HRR curve has a similar trend with the burning rate. The maximum HRR increases from 27kW to 62kW as the pressure rises from 24kPa to 90kPa. It is concluded that the ambient pressure has a significant effect on the fire heat release rate, and will further influent on other fire parameters.

In this paper, social network analysis method is applied to verify that daily life social relation is an important factor affecting individual and group behaviors and evacuation efficiency. Evacuation experiments are conducted by carrying out 15 multi-mode collaborative evacuation drills including 6 in 2014 and 9 in 2015.The same group of 30 evacuees from a undergraduate class has been tracked for two years. Social network method is used to study following behavior, leading behavior and decision-making behavior in evacuation experiments. Through the questionnaires before and after all the evacuation drills, by defining the mutual trust degree (MTD) and being followed degree (BFD), the MTD relation matrix on daily life and the BFD relation matrix in evacuation can be constructed. Then normal social relation network graph and following relation network graph in emergency are drawn. Results show that small groups and leaders will be formed automatically during group evacuation, and the leaders in emergency demonstrate some certain stability, which has some relevance with gender and relations in normal situation. When two emergency exits are available during evacuation including stair and elevator, evacuation efficiency is best when the elevator and stair are located at the same side.

Fire safety is critical for safety of airplane operation. During an emergency landing, airplane goes through dramatic external pressure change from cruise altitude to sea level, considering the impact caused by low pressure atmosphere. The objective of this work is to examine the effect of dynamic pressure on the behavior of a horizontally burning diffusion flame over a pool fuel surface based on experimental approach. The experiments were conducted in a large-scale altitude chamber of size 2 m × 3 m × 4.65 m. The pressure rise process was examined under different dynamic pressures from respectively 38 kPa, 64 kPa and 75 kPa to 90 kPa with various pressure rise rates of 100 Pa/s, 150 Pa/s, 200 Pa/s, 250 Pa/s and 300 Pa/s, which is to simulate the airplane landing process from different altitudes. The whole system of the altitude chamber is of unique capability that the pressure in the chamber can be exactly controlled by a powerful pressure controlling system, and the oxygen concentration can maintain at the level about 20%, which are achieved through controlling inlet air flow for oxygen level and outlet gas flow for pressure (static or dynamic) level. A round steel fuel pans of 34 cm in diameter and 15 cm in height were chosen for the pool fire tests. The fuel pan was filled with 99% pure liquid n-Heptane. Cold water is added beneath the fuel layer to cool the pan and minimize the temperature rise in the fuel. Parameters such as mass, mass burning rate, chamber pressure were measured. The results of those tests demonstrated the significant impact to fire behaviors caused by high altitude or low pressure atmosphere.

Fires recently at low ambient pressure such as cruising airplane and high altitude airport have attracted great attention. Understanding fire behavior under low pressure is one of important fundamental problems for fire safety engineering design in forementioned environment. Observation of cardboard fires under dynamic pressure is of significant meaning to study continuous variation of fire behaviors of solid fuel during depressurization. An altitude chamber of 2×3×4.65 m3 with a powerful pressure controlling system was designed to observe fire behavior of cardboard fires under dynamic pressure. In the chamber, two configurations of cardboard boxes filled with shredded office paper were tested under dynamic pressures at descent rates: 5.46kPa/min, 10.92kPa/min, and 19.68kPa/min for both configurations. Measured parameters in this study include flame temperature, radiative heat flux, and mass burning rate. The measurement data were analyzed to reveal depressurization effect on fire behavior.

Friction Sir Welding (FSW) process is a solid state welding technology which is widely used in manufacturing field for joints of many types of same or dissimilar materials such as aluminum alloys, magnesium alloys and steels and so on. In addition, FSW process is also a complex process associated with heat transfer, plastic deformation, grain recrystallization and material property changing phenomenon. It is commonly known that the thermal condition or the temperature distribution of space and time is important to the final welding condition. However, due to the limitation of experiment measurement and the unfinished work of numerical heat transfer model, the relationship between thermal condition and control parameters still remains a question. In this work, a new numerical model based on energy analysis and finite element method is built to calculate the thermal field of FSW process. The energy generation due to plunge depth and the converting coefficient of friction energy to heat are considered in the model. The effects of energy distribution of both sides, energy efficiency of friction, plunge depth, normal force, traverse speed and rotation speed on the temperature distribution of FSW process are investigated.Copyright © 2015 by ASME

To comprehensively reveal the difference of solid fuel fire characteristics at different altitudes, fire experiments of cardboard boxes at multiple static pressures with two configurations filled with shredded office paper were conducted in a low-pressure chamber. The measured parameters are mass burning rate, radiative heat flux, oxygen concentration and heat release rate (HRR) etc. The mass burning rate divided by fire base dimension m/D is correlated against the production of pressure-squared times length-cubed (P2L3) to the power of 0.29 based on current cardboard boxes fire test data. HRR of two boxes fire tests are higher than that of one box fire tests under fixed pressures. However, there are a higher peak of HRR under a fixed higher pressure for one-box fire tests while a lower peak of HRR under a higher pressure for two-box fire tests. The HRR would decrease sharply after reaching the peak.Copyright © 2015 by ASME

Ultrasonic welding is a complex process combining the processes of interface friction, heat transfer, plastic deformation heating, and atom diffusion and so on. Even though much work has been performed to understand ultrasonic welding process, the key characteristic process parameters of ultrasonic welding process and the key control parameters for the bond quality are still questions. Based on the interactions of bond factors and previous research of ultrasonic welding process, we believe that plastic deformation and temperature which represent the energy and strain condition at bonding interface are the key process parameters related to bond. A 3-D thermal-mechanical finite element model is built to analyze the thermal and mechanical files of ultrasonic welding process of two types of aluminum alloys under different control parameters. A possible mechanism between bond quality and control parameters based on max temperature and max plastic deformation of temperature-strain map of simulation is presented.Copyright © 2015 by ASME

Edge-defined Film-fed Growth (EFG) is a promising technology for production of silicon wafers with minimum loss of silicon material for photovoltaic applications. The growth of the hollow tubes by the EFG method is a very high temperature gradient along the direction of tube growth at the melt-solid interface. As this high temperature gradient is necessary to sustain the high speed of silicon growth through dissipating latent heat at the melt-solid interface, it generates substantial amount of thermal stresses that are associated with defect generation and deformation of the structure. With increase of the tube diameter and reduction of wall thickness, the large thermal stresses lead to significant buckling of the tube. In this study, the buckling behavior of the growing silicon tube is studied experimentally by monitoring deflection of two pairs of opposite faces of an octagonal tube during the growth. Four capacitance sensors were placed on a fixed plane normal to the translation of the tube to measure the varying thickness of the air between the sensor and the tube surface throughout the tube growth. The recorded data reveal the buckling behavior of tubes for several growth runs. Despite the different growth conditions in the EFG systems, similar patterns of buckling behavior have been observed in octagonal silicon tubes with face width of 12.5 cm. A typical buckling pattern observed can be divided into three distinctively different stages, namely seed holder-influenced stage, tube growth stage, and a random fluctuation stage. Each stage has different amplitude of deflection and covers different length of the tube. More interestingly, the recorded surface deflection reveals the displacement of the center of the tube, suggesting off-centered growth and possible instability of the meniscus. It is considered that these mechanisms may contribute to the special buckling pattern observed during growth.

Fires at high altitude airports have attracted a lot of attention. Such fires show some special characteristics because of the coupling impact of low pressure and low oxygen levels. Some experiments, which were conducted recently at high altitude locations, such as Lhasa and in some low pressure chambers, were usually extinguished due to the limited supply of oxygen. In order to reveal the dependence of fire behavior on pressure comprehensively, a low-pressure chamber with ventilation control of 2×3×4.65m3 in volume has been developed and built, which can allow larger scale fire tests to be conducted and simulate more realistic high-altitude environment. In this study, pool fire tests using 20-cm and 30-cm-diameter pans are configured under five different static pressures, e.g. 101kPa, 75kPa, 64kPa, 38kPa and 24kPa. Each test has been repeated three times. The parameters measured include flame temperature, radiative heat flux, and mass loss etc. It is concluded that under lower pressure, mass burning rate is lower, temperature is higher, and height of the flame is higher, which demonstrated that low pressure fire is more dangerous to the buildings at high altitude airports.

Gas entrainment occurs in atmospheric plasma spray (APS) after plasma jet flows into the cold surroundings, resulting in rapid decaying of speed and unwanted oxidation. Installing a solid shield or inserting a gas shroud at the end of the nozzle may be helpful to reduce air entrainment. Effects of solid shield and inert gas shroud on plasma jet are investigated numerically. It is found that solid shield and gas shroud will expand high temperature field of plasma jet in both axial and radial direction, consequently, enabling a thorough reaction of oxygen content for virtually oxygen free plasma jet. The mass fraction of the O2 gas in the plasma flow outside the shield decreases with the increase of the inert gas velocity, which maintains nearly zero in the solid shield. Inert gas velocity and its injection angle turn out to be important factors to offset the negative effects of solid shield on the main flow. It is demonstrated that the flow field is less affected when the inert gas is axially injected with the inlet velocity of 150m/s. Ar is more appropriate than N2 as an inert gas, which is mainly attributed to its physical properties.Copyright © 2014 by ASME

In this paper a cellular automata-finite elements (CAFE) model is developed by combining traditional finite elements (FE) model and cellular automata (CA) model. The microstructure under different process conditions of ultrasonic consolidation (UC) process for Al 7075 is studied. It is found that higher energy input process conditions (higher applied load and sonotrode oscillation amplitude, lower sonotrode travel speed) will lead to a higher value of dynamic recrystallization (DRX) fraction for UC deposited foils. The mean dislocation density of the UC deposited material will increase with the applied load while it decreases with the increase of sonotrode travel speed and oscillation amplitude.Copyright © 2014 by ASME

This paper presents the sensitivity analyses on vehicle motions with regard to faults of in-wheel motors and steering motor for an electric ground vehicle (EGV) with independently actuated in-wheel rear motors. Based on the vehicle model, direct method is applied to determine, to what extent, that different actuator faults affect vehicle motions such as the longitudinal velocity, lateral velocity, and yaw rate. For motion indices like vehicle sideslip angle and longitudinal acceleration, linearizations around equilibrium points are conducted and their sensitivities to actuator faults are analyzed. Results show that all mentioned vehicle motions are more sensitive to the fault of steering motor than that of in-wheel motors. In addition, the effects on vehicle motions due to four types of faults, i.e. additive, loss-of-effectiveness, time-varying-gain and stuck-at-fixed-level faults, are examined through CarSim® simulations and vehicle experiments under a representative maneuver.Copyright © 2014 by ASME

Corrosion fatigue in the tensile armor layer is a design consideration for both flexible risers and flowlines offshore. Recently, the industry has experienced a handful of in-service flexible pipe replacements due to corrosion fatigue of armor wires. That experience motivated the work effort summarized herein. This paper presents the preliminary results from an experimental program undertaken by ExxonMobil to evaluate and suggest improvements to the currently established fatigue testing methodology for armor wires in corrosive environments. In particular, the results from a frequency scanning test program for armor wires and a methodology for artificially generating pitted armor wire specimens for fatigue endurance tests are presented.Copyright © 2014 by ASME

With the emergence of large scale buildings, how to improve the efficiency of the fire prediction model has urgently been a problem in the field of fire emergency. Based on an existing fire zone model, CFAST, and some other assumptions, this paper puts forward a distributed fire model capable to make a fast and acceptable prediction. The whole building structure is divided into some small basic zones in which a group of control equations run independently relying on the local information. With a small scale of the local structure, the computational complexity will not increase significantly as the building scale enlarges. In this paper, a typical building structure with multiple rooms and a long corridor is discussed. Two kinds of models, namely fire zone model and corridor zone model are set up and run locally. At a prescribed time, based on the limited communication between those two kinds of models, the properties of the corridor can be updated. By repeating these steps, the global state can be predicted. One typical floor of a real building is used to test this distributed fire model with a 3 MW steady fire and the comparison against the conventional CFAST model is carried out. The results show that the proposed distributed fire model can perform well in a short term prediction (about 150s after fire breaks out), but for the long term prediction, the simulations are affected by the “far away” wall and HVAC condition, which resulting in a diverging solution from the conventional CFAST model.Copyright © 2013 by ASME

Airplane as one of the important transport vehicles in our life, its safety problem related to in-flight fire has attracted a wide-spread attention. The combustion behavior of the cabin fire in flight shows some special characteristics because of the high-altitude environment with low-pressure and low oxygen concentration. A low-pressure chamber of size 2 m×3 m×2 m has been built to simulate high-altitude environments, where multiple static pressures for pool fire tests can be configured in the range between standard atmospheric pressure 101.3KPa and 30KPa. Two different sizes of pool fires were tested. Then corresponding modeling were conducted by a LES code FDS V5.5 to examine the mechanism of pressure effect on the n-Heptane pool fire behavior. The burning of liquid fuel was modeled by a Clausius-Clapeyron relation based liquid pyrolysis model. The modeling data was validated against the experimental measurements. The mass burning rate of free-burning pool fire decreases with the decreasing of pressure, which was observed from the modeling to be due to the reduction of flame heat feedback to the fuel surface. Under low pressure, the fire plume temperature increases for the same burning rate. The mechanism of pressure effect on fire behavior was analyzed based on the modeling data.Copyright © 2013 by ASME

In this paper we study the lateral motion control and torque allocation for four-wheel-independent-drive electric vehicles (4WID-EVs) with combined active front steering (AFS) and direct yaw moment control (DYC) through in-vehicle networks. It is well known that the in-vehicle networks and x-by-wire technologies have considerable advantages over the traditional point-to-point communications, and bring great strengths to 4WID-EVs. However, there are also bandwidth limitations which would lead to message time delays in network communication. We propose a method on effectively utilizing the limited bandwidth resources and attenuating the adverse influence of in-vehicle network-induced time delays, based on the idea of dynamic message priority assignment according to the vehicle states and control signals. Simulation results from a high-fidelity vehicle model in CarSim® show that the proposed vehicle lateral control and torque allocation algorithm can improve the 4WID-EV lateral motion control performance, and the proposed message priority dynamic assignment algorithm can significantly reduce the adverse influence of the in-vehicle network-induced time delays.

Computational heat transfer became one of the major tools for engineering system design in 1970’s. It has been introduced into Chinese society since 1980’s, especially after Brian Spalding’s first lecture in 1984 in China. As one of Brian’s a few early visiting scholars from China, Professor W. C. Fan has begun his endeavor to expand computational heat transfer to fire research. This paper will first briefly introduce the history of the development of computational modeling with particular applications in fire research — a state funded large project, and then present some representative research work in fire research including recent works on high altitude fire and performance based design.Copyright © 2013 by ASME

Optical glass has been widely used in optical device manufacturing due to its high degree of physical and chemical homogeneity, which is considered as one of most important indicators of optical performance. Thermal stress during production has a significant impact on the optical homogeneity of the glass and it is primarily generated from temperature difference at different parts of the glass during annealing process which includes coarse and fine phases. Accumulation of thermal residual stress at early cooling stage will not only cause the cracking of the glass during process, but also affect the following fine annealing, especially, for the symmetric pattern of stress distribution. This paper focuses on mitigating of radiation influence and controlling cooling rate during coarse annealing in order to reduce thermal residual stress in the process. Numerical models are established to simulate the coarse process and investigate the homogeneity of temperature distribution at different conditions. Simulation results show that the coarse annealing process can be optimized through changing glass configuration and cooling rate.Copyright © 2013 by ASME

Large size optical glass has attracted much attention due to its applications in large optical devices. Due to stringent requirement in applications, extra thermal treatment should be investigated to increase the quality of product. During fine annealing, glass temperature is crucial for final quality of optical glass as a result of its influence on thermal stress and optical homogeneity. To ensure a high performance, temperature distribution in the glass should be homogeneous and symmetric, and maximum temperature difference is expected to be small. This paper proposed two approaches to improve the glass temperature uniformity during fine annealing. Firstly, the glass blocks are packaged with heat exchange blocks on the top and bottom surfaces and insulation layer on the side. Thickness of layers and materials usage are investigated. Simulation results show that the homogeneity and symmetry of glass temperature distribution can be improved. Temperature difference in the horizontal direction can be further reduced in the case of 10mm copper heat exchange block together with 50mm insulation layer. Secondly, a muffle apparatus is utilized and symmetry of temperature distribution can be improved. Furthermore, above two approaches can be combined. Knowledge learned in this work can be used to guide industrial fine annealing process to reduce the stress level and improve the symmetric of residual stress.Copyright © 2013 by ASME

This paper studied the stress generation in the deposition process of multilayer polycrystalline films by physical vapor deposition. A stress prediction model was proposed which is capable of describing the generation of both the intrinsic stress and thermal stress by analyzing heat/mass transfer and growth process during the deposition process. An alternative deposition of Cu and Ag layers on Si (100) was simulated. The thermal stress in the multilayer system was discussed in detail by analyzing the influence of different parameters on thermal stress, such as deposition temperature and film thickness. It is found that the thermal residual stress strongly depends on the deposition temperature and film thickness ratio and thus the thermal stress can be modified by adjusting the related parameters.Copyright © 2013 by ASME

Residual stresses (RS) are unavoidably generated in components after welding. Tensile residual stresses in engineering structures generally have an adverse effect on structural integrity, with detrimental effects on brittle fracture, corrosion properties and fatigue performance. Residual stress measurements for offshore welded joints are generally very limited. In this study, experimental measurements and numerical modelling of residual stresses were carried out and the through-thickness residual stress distributions in circumferential butt welds are presented. Pipes of two different dimensions and steels were investigated: a seamless X70 steel pipe with an outside diameter of 406mm and a seam-welded X65 steel with an outside diameter of 508mm. The measurement methods used included the centrehole air abrasion drilling, the deep-hole drilling (DHD) and the block removal, splitting and layering (BRSL). The numerical modelling was undertaken to determine whether modelling could provide a satisfactory prediction of the final residual stresses. Finally, the new experimental data were combined with the BS 7910 database to derive revised upper bound through-thickness residual stress distributions for girth welds and to provide an assessment of the impact of residual stresses on the structural integrity of circumferential welds in offshore structures.

This paper investigates thermal transport on SiC formation and engulfment in directional solidification of crystalline Si. A comprehensive computational model is developed which is capable of describing fluid and thermal transport, SiC particle formation/transport, and its pushing-engulfment near the solidification interface. It is found that the impurity of carbon concentration in the melt is affected by melt convection; the concave interface leads to the carbon accumulation in the central region near the interface; the size of the SiC particle when engulfed into solid Si is mainly determined by the solidification rate. The distributions of carbon concentration and SiC particles are determined by both melt convection, interface shape and solidification rate. The low solidification rate is not desirable for high quality Si crystal growth when the solid/liquid interface is concave.Copyright © 2012 by ASME

The prediction of response frequency of Truss Spars is important in the estimation of fatigue damage rates. Response frequency depends on the natural frequency of the structure which is influenced by the added mass. The 1:60 scale Truss Spar model tests have been conducted in towing tank at Zhejiang Ocean University (ZOU). The Truss Spar model consists of a hard tank with removable helical strakes, a truss section and a square soft tank. Model tests were carried out with simplified mooring system. In this study, results from the experiment subjected to uniform current were reported. The Reynolds numbers varied from 8E04 to 2E05. The mean added mass coefficient and the time-variable added mass coefficient were calculated. The results shown that the predicted natural frequency based on the measured added mass coefficient was approximately equal to the measured mean oscillation frequency. The added mass coefficient calculated from one oscillation cycle to the next varied considerably. The oscillation frequency from one oscillation to the next corresponded to the natural frequency including the added mass coefficient for the same cycle.

This article discusses the kinematic and dynamic modeling of a new cylindrical parallel manipulator with two translational degrees of freedom and one rotational degree of freedom. The model of dynamics is based on the Lagrange approach. Six generalized coordinates and three Lagrange multipliers are introduced in the modeling process, and they are released by the corresponding constraint functions. A case is presented to illustrate the advantages of this mechanism. The simulation results indicate that the actuator torques of this parallel manipulator possess of good properties. This model will be useful to improve the design of the mechanical components and the control algorithm of this manipulator.Copyright © 2002 by ASME