Rack Storage Research Articles

Optimization of cold-formed steel beam cross-sections for pallet rack storage systems

This paper aims to obtain optimized cold-formed beam cross-sections for industrial pallet rack storage systems. The optimal sections were obtained by applying fitness functions aimed at reducing cross-sectional area and/or displacement and solving them using the Genetic Algorithm. These functions imposed a behavioral constraint so that all optimized solutions had the same resistant bending moment. The calculation of the characteristic resistant bending moment was carried out according to the direct strength method, with load factors defined by the elastic stability analysis with CUFSM, in an analysis routine implemented on the MATLAB platform. Four parameterized sections were studied, verifying the optimum set of height, width and stiffening elements that met the objectives defined by functions, assuming reference values of a rectangular hollow section. Manufacturing constraints were also taken into account. The results show that it is possible to manufacture cold-formed beams that consume less material and/or have a better moment of inertia in relation to the reference section, without compromising the strength of the structural element.

Velocity-based rack storage location assignment for the unidirectional robotic mobile fulfillment system

Nowadays, the robotic mobile fulfillment system (RMFS) has been increasingly used by online retailers. Compared with traditional picker-to-parts warehouses, the racks of RMFS do not have to return to the same location after picking, thus we can dynamically change their locations, which brings great potential to efficiently fulfill orders. Aiming at minimizing the sum of rack travel distances, the key question is how to reassign a rack to an unoccupied storage location after picking items from the rack. However, the issue involves two challenges for unidirectional RMFS, one is that huge differences may exist between the classical Manhattan distance estimation and the actual distance for the unidirectional aisles in RMFS, and the other one is that we need to account for the frequency of rack moving for multi-item orders. We thus first propose closed-form formulas to optimally estimate the cycle travel distance for each rack. Then, by overcoming the repeated counting issue for multi-item orders, we propose a novel SKU (Stock Keeping Units)-correlation-based algorithm to choose high-velocity racks, which can better fulfill multi-item orders. Finally, embedding the cycle travel distance and SKU-correlation-based velocity, we propose a Velocity-based Rack Storage Location Assignment method (VRSLA) to solve the rack storage location assignment problem by assigning high-velocity racks to the nearest storage locations. Collaborating with a large online retailer in China, we demonstrate the performance of VRSLA by using both small-scale and large-scale datasets. The computational results show that VRSLA not only can achieve near-best solutions compared with an integer programming model solved by Gurobi, but also outperforms four state-of-the-art assignment methods in literature (random, velocity-based class, shortest path, and sale-based) by reducing the rack travel distance up to 43.32%. We also found that the stronger the correlation between SKUs on the racks or the larger the size of the RMFS, the shorter the rack travel distance by the proposed VRSLA method.

УДОСКОНАЛЕННЯ ІСНУЮЧИХ МЕТОДІВ ОЦІНЮВАННЯ ФУНКЦІОНУВАННЯ АЕРОПОРТІВ ПРИ МІЖНАРОДНІЙ ІНТЕГРАЦІЇ

The article is devoted to the study of methods for assessing the operation of airports under international integration and their improvement. The recent scientific studies on assessing the operation of international airports were analyzed and it was found that the most actively used methods are the initial data envelopment analysis (DEA) and various variants of quantile regression, Tobit regression, assurance region methods, SBI and DMU, Malmquist index, classification and regression tree, bootstrapping tool and other tools. It was confirmed that the existing methods for assessing the airports’ operation have a significant number of indicators for calculations based on the evaluation of economic, technical or overall efficiency. The parametric methods for assessing the operation of airports, their advantages and disadvantages were characterized. The methodology of stochastic frontier analysis (SFA), the use of a non-parametric approach to evaluate airport performance, and the evaluation of the overall efficiency of two-stage DMUs with shared resources were described. The methodical approaches based on the use of the spatial regression model, the AAG model and the stochastic frontier model were characterized. The methodology for determining the target function Effi to assess the efficiency of each airport DMUi was described. The scheme for assessing the airports’ operation by input and output indicators was proposed, which includes a three-module assessment system for the passenger, cargo and joint modules. The cargo module is the authors’ own development and its creation is justified by the fact that a significant number of air cargo flows are served by passenger aircraft. The group of input indicators of the cargo module includes the length of the loading and unloading work front, the number of cargo receiving points, the working area of rack and stack storage, the number of electric forklifts and lift trucks, as well as the number of cargo warehouses, and the number of general and special categories of cargo are defined as output indicators.

A bi-level optimization approach for joint rack sequencing and storage assignment in robotic mobile fulfillment systems

A bi-level optimization approach for joint rack sequencing and storage assignment in robotic mobile fulfillment systems

Storage systems’ impact on order picking time: An empirical economic analysis of flow-rack storage systems

Manual order picking (OP) is still the predominant warehousing system in brick-and-mortar grocery retailing, making human workers an integral part of operations. Besides human capabilities, the storage system design was found to impact performance, quality, and worker well-being as the major outcomes of OP systems. In warehousing practice, full-pallet storage systems and high-density flow-rack storage systems are often used in parallel within the same warehouse. However, empirical performance comparisons simultaneously considering picking and replenishment processes are largely missing for such systems. We aspire to close this research gap by empirically examining the economic impact of a high-density flow-rack storage system in which 28 different items are stored in a storage location with the ground floor size of three full pallets. The flow-rack storage system is designed with a slight slope, such that items automatically roll to the front to ensure a first-in-first-out product flow. We apply a parametric log-logistic accelerated failure time model where log-transformed picking time is the dependent variable. Using real-world data containing 2,357,976 picks performed by 192 order pickers in a German grocery warehouse, we find that the high-density flow-rack storage system accelerates the OP process by up to 4.60%, reducing the important performance indicator of picking time. In terms of replenishments, our findings indicate that replenishment processes are decelerated by 38,65% compared to normal pallet-sized rack storage places. Assuming identical labor costs for all warehouse tasks, we finally derive an optimal economic replenishment quantity per storage location in high-density flow-rack storage.

Pallet Recognition for Forklift: A Literature Review

Abstract: Forklift trucks are essential tools for manual pallet handling. Storage heights at high rack storage areas often reach up to 12 meters in which bulky Cargo can hide the view of forklift operator. Pallet recognition is afundamental issue for Industries & warehouses, Particularly, a pallet recognition approach is presented to recognize pallets in the warehouses, based on calculating the degree of similarity at each location of the palette. Once a pallet has been recognized, it is matched that data with stored data. Transporting and handling pallets in a storage area is the essential function of a forklift truck. The view of the forklift truck driver is limited during his work by the lift pole, the fork, and the roof of the forklift truck. If a pallet is loaded the view is additionally hindered by its load. When the storage rack is not at a ground level or near to it the pallet handling becomes more difficult because of the distance between the forklift truck driver and the storage rack. To support the forklift truck driver during his work, there is need to advance theforklifts with different technologies and systems which provide diversity in Working and safety, security for forklift operator and other workers. This paper shows various results from research on different pallet recognition and forklift operation systems.

Industry Expertise Heuristics for Dimensioning Shelf Space of Rack Storage Location in a Distribution Centre with Zone Picking

Industry Expertise Heuristics for Dimensioning Shelf Space of Rack Storage Location in a Distribution Centre with Zone Picking

Design of a Wms with Opc Ua-Based Control of An Automated Rack Storage as Study Project in Computer Science and Proof-Of-Concept for Skill-Based Engineering

Design of a Wms with Opc Ua-Based Control of An Automated Rack Storage as Study Project in Computer Science and Proof-Of-Concept for Skill-Based Engineering

Rack retrieval and repositioning optimization problem in robotic mobile fulfillment systems

Robotic mobile fulfillment systems provide a new solution for e-commerce retailers to fulfill customers’ orders, wherein racks are moved by mobile robots to workstations so pickers can retrieve the purchased products. While such automated parts-to-picker systems can save on labor costs, they raise new operational challenges. In this paper, we investigate the rack storage and robot assignment to racks problem during order processing. We formulate this problem with the goal of minimizing the makespan of the system. Based on a rolling horizon framework and the simulated annealing method, we develop a matheuristic decomposition approach, which involves the solution of a special axial 3-index assignment problem in each stage to solve the problem. We test the performance of the proposed method for both large-scale cases based on a real-world dataset and small-scale instances generated synthetically. Computational results demonstrate the good performance of the proposed approach.

Collaborative Optimization of Storage Location Assignment and Path Planning in Robotic Mobile Fulfillment Systems

The robotic mobile fulfillment system (RMFS) is a new automatic warehousing system, a type of green technology, and an emerging trend in the logistics industry. In this study, we take an RMFS as the research object and combine the connected issues of storage location assignment and path planning into one optimization problem from the perspective of collaborative optimization. A sustainable mathematical model for the collaborative optimization of storage location assignment and path planning (COSLAPP) is established, which considers the relationship between the location assignment of goods and rack storage and path planning in an RMFS. On this basis, we propose a location assignment strategy for goods clustering and rack turnover, which utilizes reservation tables, sets AGV operation rules to resolve AGV running conflicts, and improves the A-star(A*) algorithm based on the node load to find the shortest path by which the AGV handling the racks can complete the order picking. Ultimately, simulation studies were performed to ascertain the effectiveness of COSLAPP in the RMFS; the results show that the new approach can significantly improve order picking efficiency, reduce energy consumption, and lessen the operating costs of the warehouse of a distribution center.

Evaluation of a zone-based model for commodity classification using a representative fuel

This study presents the development of a zone-based model for commodity classification. The model divides the rack storage into multiple zones with each representing one tier of commodity. The fire spread within each zone is modeled using energy conservation for burning surface area. The water transport between zones is modeled using mass conservation. Effective properties are used to simplify the commodity behavior for fire spread and suppression. Model parameters are estimated or optimized based on experimental data. The model performance is evaluated against a representative commodity with well-established flammability properties. The chemical heat release rate matches generally well with experimental data under different storage heights and water application conditions. The model is able to predict the values of Critical Delivered Flux (CDF) for higher-tier storage based on two lower-tier experiments. The predicted CDF values reasonably agree with the experimental results. This work demonstrates a means to generalize results from tests under controlled water application conditions, which is critical to improve the cost-effectiveness of commodity classification.

Design of Integrated Smart Fire Protection System for Rack Storage

It is very difficult to suppress fire by rapid flame spread through flue space between flammable commodities on the rack when a fire occurs in the rack storage. At present, the fire protection system for rack storage in Korea has many issues, and the new fire protection system was designed and developed by it. A smart system using the sensor network and artificial intelligence was designed to detect fire very rapidly and track the location of a fire. In the very early stages, the system was constructed using vertical open sprinkler pipes, wet pipes, and solenoid valves to allow water to spray near fire locations. Based on the design results, the system was installed and tested, and the full-scale test was successfully completed.

AI Based Digital Transformation for Rack Storage Management in Smart Factory

AI Based Digital Transformation for Rack Storage Management in Smart Factory

Application of the thermal pyrolysis model to predict flame spread over continuous and discrete fire load

Classical thermal theory of piloted ignition is applied in CFD predictions of flame spread over the combustible surface and fire growth in a rack-storage facility. In the thermal model, flaming ignition and burning of a solid combustible is described in terms of the ignition temperature and the prescribed burning rate, thereby avoiding consideration of the finite-rate pyrolysis, reducing the number of the model parameters, and enabling development of the simplified analytical theory. The analytical theory formulated in this work is shown to replicate the experimental dynamics of either pyrolysis zone propagation or total heat release rate; simultaneous replication of both is not possible because of unrealistic assumption of the planar pyrolysis front. Thorough investigation of the thermal model performance in CFD simulations of upward propagation of the turbulent flame over the vertical combustible surface (in comparison with the predictions by the finite-rate pyrolysis model) reveals the drawbacks inherent in the thermal model. In contrast with the finite-rate model and the experimental data available, the thermal model predicts an abrupt increase of the burning rate in the infinitely thin front and assumes spatially independent burning rate in the pyrolysis zone. To overcome these drawbacks, a simple modification to the thermal model is introduced allowing for the steady burning rate to increase with the vertical distance.The abovementioned limitations of the thermal model are not expected to be crucial for an array of combustible items with the vertical size of about 1 m and below. As such, the thermal model offers a simple and robust approach to predict fire growth in rack storage facilities. FDS simulations have shown a good representation of the experimental growth of the heat release rate in a rack storage fire. The model parameters (ignition temperature, mass burning rate, burn-out time, and heat of gasification) must be properly selected for a given type of fuel load. Dynamics of fire growth predicted in this work with the thermal pyrolysis model is in agreement with that observed in the full-scale test and in the earlier published simulations with a comprehensive pyrolysis model.

An Efficacy Evaluation of Water Mist Protection Against Solid Combustible Fires in Open Environment

CEN and NFPA standards have accepted water mist for protecting solid combustible fires more challenging than light hazard fires in open environment, but with little data in the public domain to support such applications. Therefore, a series of exploratory experiments was conducted to evaluate the efficacy of fire suppression in open environment by water mist sprays for a rack storage of corrugated cardboard cartons on wood pallets (Fire A), and for a palletized storage of cartoned plastics stacked on wood pallets (Fire B). Both are in the accepted hazard categories by both standards. Representative water mist sprays were employed to provide water application densities of 4.1 mm/min and 6.1 mm/min for Fire A, and 8.1 mm/min for Fire B. These sprays had downward thrust forces ranging from 18 N to 73 N per spray, and volume median droplet diameters from 75 µm to 345 µm. A standard ½-in. pendent sprinkler was also employed to provide the suppression performance references for these two fire hazards. In each experiment, four open sprinklers or nozzles were centered 1.7 m above the fuel array with nozzle spacing ranging from 2.6 × 2.6 m to 3 × 3 m. All experiments were conducted under a 20-MW calorimeter with no ceiling presence. Water discharge in each experiment was started at a designated fire convective heat release rate of 1000 kW. The experiments indicated that, for the same application density, not all water mist sprays having different characteristics would lead to a comparable fire suppression result. Therefore, each water mist system should be tested individually for the same intended protection. Furthermore, the results showed that when water mist protection was effective, it required application densities comparable to those of sprinkler protection to provide comparable fire suppression results in open environment under the present experimental conditions.

Application of a simplified pyrolysis model to predict fire development in rack storage facilities

The simplified (thermal) pyrolysis model is applied to simulate flame spread and fire growth in the rack storage facility using the FDS software. Pyrolysis in the combustible material is not explicitly considered, and the ignition temperature and the burning rate are used as the input parameters. Once the fuel surface temperature reaches the ignition temperature, the material ignites and burns at a prescribed burning rate. This approach is found to reasonably replicate both the transient development of the heat release rate and flame dynamics observed in the full-scale rack storage fire with 2x4x3 cardboard boxes in the rack, provided the model parameters (thermal properties of the fuel, ignition temperature, average heat release rate per unit area, burn-out time, and heat of gasification) are properly selected.Distinct flame propagation regimes including buoyancy-driven upward flame spread, horizontal flame spread, and buoyancy-opposed downward flame propagation are observed in the simulations of the rack-storage fire development. Both measured and predicted HRR growth rates appear to be faster than that in a t-squared fire, mainly because of the developed combustible surface densely packed within the compact volume and due to availability of vertical gaps creating chimney-like effect and horizontal gaps providing permanent supply of fresh air.It is shown how the full-scale test data enable selection of the model parameters. In particular, average value of the heat release rate per unit area is evaluated by joint consideration of the measured dynamics of the growing heat release rate and the surface area engulfed in fire. The burn-out time and the effective thickness of the fuel layer is estimated as the period from ignition to the time instant after which the measured heat release rate starts to decay. The heat of gasification is selected by fitting the predicted transient dependence of the heat release rate to that measured in the full-scale tests. Optimum values of the model parameters are consistent with the literature data for cardboard, and this indicates possibility of the simplified thermal pyrolysis model to predict rack storage fire dynamics with an alternative fire load, for which the full-scale test data may not be available. Further work is required to validate this approach for a wider range of full-scale fire tests.

Evaluation of Oxygen Reduction System (ORS) in Large-scale Fire Tests

An oxygen reduction system (ORS) is a fire prevention system that uses a low-oxygen environment to reduce, if not eliminate, the potential for ignition and fire propagation in a protected space. The key parameter for ORS design is the limiting oxygen concentration (LOC), defined as the lowest O2 concentration that can support combustion for a given fuel. The present work examines LOCs of solid fuels at large scale in a configuration representative of a rack-storage and discusses the results in relation to the design concentration for ORS.To simulate ORS applications in engineering practice, a two-tier fuel array of standard commodities in rack storage configuration was set up in an enclosure. A constant N2/Air mixture flow was supplied to the enclosure at a desired oxygen concentration. The oxygen concentration was varied from 9% up to 17%. A premixed flame with a constant heat release rate was used as the ignition source to maintain repeatable test conditions. This premixed flame ignitor represents potential heat sources such as electric arc and hot work that are not sensitive to oxygen level. The tested materials included five standard commodities: Class 3, Cartoned Unexpanded Plastic (CUP), Cartoned Expanded Plastic (CEP), Uncartoned Unexpanded Plastic (UUP) and Uncartoned Expanded Plastic (UEP). This paper reports detailed test results at different oxygen levels only for Class 3. The impact of the test conditions on fire propagation was examined and the results showed that the oxygen concentration was the major parameter to control fire propagation. When successful flame spread is initiated by the igniter, the fire size tends to be larger as the igniter is sustained for a longer time. The results of fire propagation success were obtained for the five standard commodities under different oxygen concentrations with a sustained igniter (hard limits) and without a sustained igniter (soft limits). The LOC was defined as an oxygen concentration at 0.05 probability of flame spread by using statistical analysis. The resulting LOC values measured for different commodities in a two-tier rack storage are:• Cartoned (Class 3, CUP and CEP) – hard limit 11.1%,• Uncartoned (UUP and UEP) – hard limit 13.0%,• Cartoned (Class 3, CUP and CEP) – soft limit 13.8%,• Uncartoned (UUP and UEP) – soft limit 14.7%.These LOCs are generally lower than the oxygen design concentrations recommended by existing standards including VdS 3527 and EN 16750 due to different test conditions. The hard limits resemble fundamental LOC for gases and vapors and do not depend significantly on the ignition duration and array size, while the soft limits vary significantly with the size and configuration of the fuel array and ignition duration. It is concluded that the hard limits are more suitable for ORS design purposes.

Ensuring Competitiveness of Logistics Service by Selecting the Type of Storing Single-Piece Cargoes

Efficient transportation of cargoes from the point of the cargo traffic start to the final consumers can significantly influence competitiveness of logistics service that leads to the necessity of analysing the known approaches to substantiating the selection of the storing type (pile storage or rack storage) when warehousing single-piece cargoes. To formalize the problem of selection based on the analysis, the authors develop the model, which is suggested to use the quantity of the stored pallets with single item cargoes. The calculations according to the suggested mathematical model envisage intensive computations with repeated calculations; therefore the corresponding recursive algorithms are developed for this mathematical model. The corresponding recursive algorithms for the model are easily realized in the software product. The developed algorithms can be easily realized in the software product with graphic interface on the enterprises delivering logistics services to enhance their competitiveness.

Investigation of pallet stacking pattern on unit load bridging

Considering the effect of packages during pallet design will reduce costs and improve the sustainability of supply chains. Currently, many mechanical interactions between the pallet and the package product are not being considered during the pallet design process. This study investigates the effect of the magnitude and type of interlocking between layers of packaged products.The bending of the pallet supporting a unit load of corrugated boxes was measured under four common support conditions, warehouse rack storage spanning the pallet width and length, fork tine support across the pallet width, and floor stacking. Five different pallet stacking patterns were analyzed from column stacking to fully interlocked stacking.It was determined that interlocking packages reduces pallet deflection up to 53%. This is more significant for lower stiffness pallets and when the payload carried by the pallet is greater than the rated load capacity of the pallet. Increasing the magnitude of the interlocking reduces the deflection of the pallet by 11.6%.These results provide a guideline on improving pallet design and help further the understanding of the interaction between pallets and the orientation of packaged products placed on the pallet.

Design of Concentrated Sprinkler for Rack Storage

Design of Concentrated Sprinkler for Rack Storage