Seongho Cho

A Fire Detection and Rescue Support Framework with Wireless Sensor Networks

Recently, wireless sensor network (WSN) technology has been widely used in various fields such as public safety applications since it provides a wide range of surveillance and monitoring applications with an inexpensive price. In this paper, we investigate the use of wireless sensor network technology for fire detection and rescue system. We propose a framework, which can detect fires promptly and support rescue activities, using wireless sensor devices. Our framework consists of fire detection sensor network, information gathering layer, middleware, and escape support system. We have implemented a test-bed and evaluated the performance of fire detection via experiments.

Comparative Study of Spray Characteristics of Gas-Centered and Liquid-Centered Swirl Coaxial Injectors

This study investigated the spray and Sauter mean diameter characteristics of gas-liquid swirl coaxial injectors by measuring and analyzing spray angles and mean drop sizes. Two different types of gas-liquid swirl coaxial injectors were designed and tested for this experiment: 1) a gas-centered swirl coaxial injector and 2) a liquid-centered swirl coaxial injector. The spray patterns were obtained for both types of injectors. The spray angles of these liquidcentered swirl coaxial injectors showed a decreasing trend as a function of the momentum flux ratio over the conditions studied. Good agreement was generally achieved between the predicted and measured spray angles. On the other hand, with increasing momentum flux ratio, the spray angle of the gas-centered swirl coaxial injector initially decreased when the momentum flux ratios were relatively low, but the trend reversed over the high momentum flux ratio range studied. The Sauter mean diameter data of these two types of injectors were also obtained using an image-processing method. Results showed that the Sauter mean diameter distribution of the liquid-centered swirl coaxial injector had a solid cone shape, whereas the gas-centered swirl coaxial injector exhibited two distinct Sauter mean diameter distribution regimes. The gas-centered swirl coaxial injector had a solid cone shape along the centerline, and it had a hollow cone shape at the periphery.

A dynamic load sharing mechanism in multihomed mobile networks

An entire network can be managed as a single mobility entity when it moves as a unit. To support network mobility (NEMO), a mobile router has been introduced to manage the mobility of whole nodes inside the network. In this mobile network, multiple mobile router (MR)s and home agent (HA)s scenarios are considered to provide reliability and load sharing. In this paper, we present a neighbor MR authentication and registration mechanism in multihomed mobile networks. Also, using registered MRs, we propose a HA-based dynamic load sharing mechanism. Using measured latency from periodic binding update (BU) messages, the HA shares traffic load with an alternative tunnel. Our proposed mechanism requires no additional signaling messages except some options in the BU message.

A Unified Route Optimization Scheme for Network Mobility

Recently Network Mobility(NEMO) is being concerned as new mobility issue. Lots of NEMO issues are already being touched in IETF NEMO WG but the solution is still premature especially to the Route Optimization (RO). NEMO has several problem spaces that need RO such as nested tunnels problem. Unfortunately, there is no solution that can be universally applied as one for all that results in supporting the coherent network mobility. In this paper, we propose a unified route optimization scheme that can solve several types of RO problem by using Path Control Header (PCH). In our scheme, Home Agent (HA) does piggyback the PCH on the packet which is reversely forwarded from Mobile Router (MR). That enables any PCH-aware routing facility on the route to make a RO tunnel with MR using the Care-of address of MR contained in the PCH. By applying to some already known NEMO RO problems, we show that our scheme can incrementally optimize the routes via default HA-MR tunnel through the simple PCH interpretation.

ATFRC: Adaptive TCP Friendly Rate Control Protocol

TFRC (TCP Friendly Rate Control) is a \(\it rate\it-\it based\it\) congestion control protocol for non-TCP flows. TFRC controls the sending rate by using the TCP throughput equation considering the triple duplicate ACKs and the timeouts. However, this equation provides the conservative throughput bound of TCP. This conservativeness causes lower throughput and slower response time for TFRC than those for TCP. In this paper, we propose the Adaptive TCP Friendly Rate Control (ATFRC) protocol. Reflecting the transient behavior of TCP, we divide the throughput calculation periods into two. For each period, we adapt the sending rate based on different TCP throughput bounds. Simulation results show that the proposed algorithm gets closer to the long-term fair share of TCP than that of TFRC. In addition, ATFRC has faster convergence time than TFRC when bandwidth is available.

Interference-Aware Multi-Channel Assignment in Multi-Radio Wireless Mesh Networks

Wireless Mesh Network (WMN) is a promising model with benefits in coverage extension and throughput improvement. In WMN, multiple channels are available for improving system performance through concurrent transmission. For maximum utilization, per-node channel quality and inter-channel interference should be considered in multi-channel assignment. We propose a new multi-channel assignment method. First, we model the mesh network connectivity after a multi-graph which has multiple edges between two nodes. From this connectivity graph, we generate a multi-channel conflict graph, then we allocate multiple channels so that they do not overlap, using list coloring algorithm. We also propose a new sub-graph list coloring algorithm to enhance channel allocation performance. From computer simulations, we verify the performance of the algorithm.

Quantification of the transient mass flow rate in a simplex swirl injector

When a heat release and acoustic pressure fluctuations are generated in a combustor by irregular and local combustions, these fluctuations affect the mass flow rate of the propellants injected through the injectors. In addition, variations of the mass flow rate caused by these fluctuations bring about irregular combustion, which is associated with combustion instability, so it is very important to identify a mass variation through the pressure fluctuation on the injector and to investigate its transfer function. Therefore, quantification of the variation of the mass flow rate generated in a simplex swirl injector via the injection pressure fluctuation was the subject of an initial study. To acquire the transient mass flow rate in the orifice with time, the axial velocity of flows and the liquid film thickness in the orifice were measured. The axial velocity was acquired through a theoretical approach after measuring the pressure in the orifice. In an effort to understand the flow area in the orifice, the liquid film thickness was measured by an electric conductance method. In the results, the mass flow rate calculated from the axial velocity and the liquid film thickness measured by the electric conductance method in the orifice was in good agreement with the mass flow rate acquired by the direct measuring method in a small error range within 1% in the steady state and within 4% for the average mass flow rate in a pulsated state. Also, the amplitude (gain) of the mass flow rate acquired by the proposed direct measuring method was confirmed using the PLLIF technique in the low pressure fluctuation frequency ranges with an error under 6%. This study shows that our proposed method can be used to measure the mass flow rate not only in the steady state but also in the unsteady state (or the pulsated state). Moreover, this method shows very high accuracy based on the experimental results.

Surface Instability on Cryogenic Swirl Flow at Sub- to Supercritical Conditions

An experimental investigation was conducted to discover the characteristics of a cryogenic swirl flow at subcritical to supercritical conditions. In the experiment, liquid nitrogen was injected into a high-pressure chamber through an open-type simplex swirl injector. The flow was imaged by high-speed photography, and the instability frequency was measured by the laser beam diagnostics of the flow. Comparing the flow images of the cryogenic and conventional swirl flows, different behaviors were noted, and it was hypothesized that the instability of the cryogenic swirl flow was dominated by the precessing vortex core in the central toroidal recirculation zone. When the ambient condition of the flow was changed from subcritical to supercritical, the phase change and subsequent density change of the injectant differed, and flow actions, such as the behavior of the downstream flow, the spray angle, the wavelength, and the propagation velocity, changed drastically. When measuring the frequency of the flow insta...

Quantifying the Variation of the Mass Flow Rate generated in a Simplex Swirl Injector by Pressure Fluctuation

When a heat release and acoustic pressure fluctuations are generated in a combustor by irregular and local combustions, these fluctuations affect the mass flow rate of the propellants injected through the injectors. In addition, variations of the mass flow rate by these fluctuations bring about irregular combustion, which is associated with combustion instability. Therefore, it is very important to identify a mass variation through the pressure fluctuation on the injector and to investigate its transfer function. Therefore, quantification of the variation of the mass flow rate generated in a simplex swirl injector via the injection pressure fluctuation was the subject of an initial study. To acquire the transient mass flow rate in the orifice with time, the flow axial velocity and the liquid film thickness in the orifice were measured. The axial velocity was acquired through a theoretical approach after measuring the pressure in the orifice. In an effort to understand the flow area in the orifice, the liquid film thickness was measured by an electric conductance method. In the results, the mass flow rate calculated by the axial velocity and the liquid film thickness measured by the electric conductance method in the orifice were in good agreement with the mass flow rate acquired by the direct measuring method in a small error range within 1 percent in the steady state and within 4 percent for the average mass flow rate in a pulsated state. In addition, the amplitude(gain) of the mass flow rate acquired using the proposed direct measuring method was confirmed using the PLLIF technique for low pressure fluctuation frequency ranges. This study shows that the proposed method can be used to measure the mass flow rate not only in the steady state but also in the unsteady state(or the pulsated state), as the mass flow rate in the orifice can be acquired with time. Moreover, this method shows very high accuracy based on the experimental results.

TCP performance improvement with ACK pacing in wireless data networks

Wireless data services are fundamental in ubiquitous networks. In wireless data networks, the TCP congestion mechanism can mistake a wireless channel error or blackout for congestion on the route. Several wireless TCP protocols have been proposed considering TCP performance degradation in wireless systems. However, these protocols are too complex to deploy in wireless systems. In this paper, we propose the ACK Pacing algorithm for long lasting loss periods like a hand-off or a blackout. By pacing ACK packets sending, we prevent bursty data delivery to the old path and a spurious timeout occurrence. Also, paced ACK packets trigger the route update to the new path faster. The proposed algorithm can be implemented in the wireless-node-side which is easily applicable to wireless systems. From simulation results, ACK Pacing improves TCP performance compared with many TCP variations. The ACK Pacing algorithm shows good performance during a long lasting loss period.