Performance improvement of thermally stratified storage tank via applying radial perforated inlet structure and dynamic flow control

The authors study the performance of different dynamic window flow control mechanisms in an ISDN (integrated services digital network) environment. The network model assumed is simple but general enough to account for different network environments. Virtual circuits belonging to several throughput classes are considered, and delay-throughput and grade of service performance are evaluated for different flow control mechanisms. The effectiveness of the throttled window control in a multi-throughput-class environment is demonstrated. The use of priority in dynamic flow control is suggested and proved to be effective in increasing the overall network performance. >

Efficient temperature estimation for thermally stratified storage tanks with buoyancy and mixing effects

In a recent paper we presented an analysis of flow control in store-and-forward computer communication networks using a token mechanism. The analysis assumed equilibrium conditions for a selected set of system parameters which were not dynamically adjusted to stochastic fluctuations in the system load; this mechanism was referred to as "static flow control." In this paper we study a "dynamic flow control" in which parameters of the system are dynamically adjusted to match the availability of resources in the network. Based on Markov decision theory, an optimal policy to dynamically select the number of tokens is formulated. Because an exact solution to the problem is extremely difficult, an effective heuristic solution to the problem is presented. Numerical results are given and it is shown that the throughput-delay performance of a network is better with dynamic control than with static control.

Flow control mechanisms have been a topic of academic research for several years. With the growth of business-wide information systems such as enterprise resource planning and supply chain, better planning, scheduling and control of the business transformation process is required in order to achieve increased throughput, reduced inventories, shorter lead times and reduced tardiness. This research compares two new approaches to flow control, output flow control and bottleneck flow control to a real-time flow control system, dynamic flow control. Both output and bottleneck flow control mechanisms are much simpler to implement and manage than dynamic flow control in that they do not require continual feedback and rescheduling. Line characteristics, such as location of breakdowns with respect to the bottleneck, the location of the bottleneck when breakdowns occur, and the impact of variability of processing times on the performance measures (output, WIP level, lateness, and number of tardy jobs) for these three flow control mechanisms are compared. Both output and bottleneck flow control mechanisms perform favourably (particularly bottleneck) under different scenarios and warrant further study across a wider range of scenarios (mixed models, job shops, etc.).

Experimental investigation of a stratified chilled-water thermal storage system

High penetration of intermittent renewable energy imposes new challenges to the operation and control of power systems. Power system security needs to be ensured dynamically as the system operating condition continuously changes. The dynamic stochastic optimal power flow (DSOPF) control algorithm using the Adaptive Critic Designs (ACDs) has shown promising dynamic power flow control capability and has been demonstrated in a small system. To further investigate the potential of the DSOPF control algorithm for large power systems, a 70-bus test power system with different generation resources, including large wind plants, is developed. A two-level DSOPF control scheme is proposed in this paper to scale up the DSOPF algorithm for this 70-bus system. The lower-level area DSOPF controllers control their own area power network. The top-level global DSOPF controller coordinates the area controllers by adjusting the inter-area tie-line flows. This two-level architecture distributes the control and computation burden to multiple area DSOPF controllers, and reduces the training difficulty for implementing the DSOPF control for a large power network. Simulation studies on the 70-bus power system with large wind variation are shown to demonstrate the effectiveness of the proposed two-level DSOPF control scheme.

: We consider flow control algorithms consisting of two parts: quasi- static flow control and dynamic flow control. The quasi-static part uses short term average information on network utilization to allocate maximum data rates and to determine routes for each user. The rates are allocated to achieve an optimal trade-off between assigned priority cost functions for each user and the cost of congestion in the network. This optimization can be done by a distributed algorithm and is essentially no more complicated than optimizing routing alone. The dynamic flow control has the function of admitting or rejecting individual units of traffic into the network so as to enforce the maximum allocated rates and to prevent congestion by smoothing out the fluctuations in buffer occupancy. (Author)

Dynamic window flow control is an extension to sliding window flow control. An improved increase policy for dynamic window flow control is developed and evaluated. The improved increase policy is named the jump policy for its ability to jump to a possibly optimum window size. The jump policy has a varying increase rate that is a function of the last window size at which a frame loss occurred. Over a variety of configurations, the jump policy yields a higher effective throughout when compared to existing linear and parabolic increase policies. A simulation study to validate the improvement of the jump policy is described. >

Electromagnetic transient model and field-circuit coupling numerical calculation of Sen transformer based on finite-element method

When the network has burst high concurrent access traffic, the traffic allocated to each node in the cluster will exceed the maximum processing capacity of the machine, which needs to be solved by applying flow control technology. For this reason, this paper studies the flow control technology under the microservice architecture, and proposes an adaptive dynamic service flow control strategy based on the srTCM algorithm, which can dynamically regulate and differentiate the tasks entering the service node according to the request type and the running state of the machine. Experiments show that the research results of this paper are better than the common current limiting schemes.

Focusing on massive demand and high-frequency trains in urban rail transit, this paper proposes a novel joint optimization approach for train scheduling and dynamic passenger flow control strategy under oversaturated conditions to minimize the total number of waiting passengers. In view of the relationship between the number of boarding/alighting passengers and the dwell time of trains, the problem is formulated as a mixed-integer linear programming (MILP) model. This model can achieve the trade-off between the utilization of trains and passengers. The ILOG CPLEX is adopted to solve the proposed model. And a real-world case study of the Beijing Metro Line 5 is given to demonstrate the feasibility and effectiveness. Through jointly optimizing train schedule and flow control, the average boarding rate of passengers increases from 36.34% to 87.55%. The results show that the proposed flow control is effective in alleviating the oversaturated situations at platforms and trains.

The available bit rate (ABR) service category has been approved by the ATM Forum to make use of bandwidth available after satisfying the requirements of real-time services. Thus, many flow control algorithms have been proposed within the context of the ABR service. We have proposed a dynamic rate-based flow control (DRFC) scheme with the primary goal of supporting the ABR service effectively and with the additional advantage of simplicity. This paper investigates the behaviour of the DRFC scheme in conjunction with virtual source/virtual destination (VS/VD) technique. The performance is evaluated in terms of allowed cell rates, number of transmitted cells, buffer occupancy, and link utilization. It has been observed that the implementation of VS/VD technique improves the performance with minimum buffer requirements.

The mechanisms which contribute to a loss of capacity in stratified storage tanks are usually grouped into heat transfer through the tank walls, conduction across the thermocline, and the flow dynamics of the charge and discharge process. In this paper, we use analytical solutions of the unsteady one-dimensional energy equation to show that the flow dynamics are generally orders of magnitude more important than the other factors. Heat transfer through the tank walls constitutes a loss which is less than a couple percent of the tank capacity for reasonably sized, underground or above-ground, insulated tanks. The importance of convective fluid motion relative to one-dimensional conduction across the thermocline is quantified with a single parameter. Values for this parameter can be estimated from measurements of in-tank temperature profiles or outlet temperature profiles. The model solutions are also used to calculate an estimate of the maximum first law efficiency for stratified storage. Published data shows current storage tanks generally operate at efficiencies of 50 to 80%. The efficiency of a storage-based cooling system is shown to be the product of storage efficiency and chiller efficiency. Storage tank losses must therefore be offset by improvements in chiller efficiency if these systems are to compare favorably with conventional cooling systems on the basis of energy efficiency.

System-on-Chip (SoC) designs become more complex nowadays. The communication between each processing element often suffers challenges due to the wiring problem. Networks-on-Chip (NoC) provides a practical solution to solve the problem. The major components in NoC are routers, which are dominated by the buffer size. Previous mechanisms need large buffer size to achieve high performance. In this paper, a dynamic channel flow control mechanism is proposed to realize the channel resource sharing globally, which can increase the throughput and the channel utilization rate. An 8 × 8 mesh on-chip network is implemented on a cycle accurate simulator. By the experimental result, the proposed mechanism can reduce the buffer size by 30% as compared with virtual channel flow control at the same throughput. Moreover, the throughput can be improved by 20% as compared with wormhole flow control.

Restructuring of the power industry that have arisen from the unbundling of the electrical industry have led to complex and still unsolved problems related to transmission system expansion owing to the singular characteristics of their investments. These difficulties are currently issues of considerable interest for researchers and policy-makers since the lack of adaptation of the transmission infrastructure may damage operations and free competition in the emerging electrical sector. In this context, some degree of dynamic control within the transmission investments is deemed to be necessary in order to face the increasing uncertainties of the new market scenarios through contingent claims, which allow the planner to adapt the investment under scenarios where the uncertain variables unfold unfavorably. Under this conjuncture, this paper presents an approach for valuing the dynamic power flow control of FACTS devices under uncertain variables of liberalized power markets as well as the evaluation of the flexibility of power transmission investments through a Real Option Valuation approach based on the Least Square Monte Carlo method. In order to illustrate the proposed valuation approach, a study case is presented, where it shows that the flexibility of the dynamic controllers under uncertainties could plenty justify the higher cost of these devices.