ME6105 HW2: Planning your Simulation. Design of a Competitive Self Contained Trash Compactor

Transcription

1 ME6105 HW2: Planning your Simulation Simulation-Based Based Design Study Design of a Competitive Self Contained Trash Compactor (Ref: ctor2.jpg) Group Members: Patrick Chang Benjamin Lee Aditya Shah Ryan Stewart

2 Table of Contents Task 1: Identify the Decision Situation... 1 Task 2: Determine an Objectives Hierarchy... 3 Task 3: Identify the design alternatives... 6 Task 4: Identify the Structure of the Design Problem... 8 Task 5: Identify the Simulation Scenario for an Energy-Based System Model Task 6: Assess your plan Task 7: Articulate your Learning Objectives i

3 Task 1: Identify the Decision Situation Based on our similar interests, we have chosen our application domain to be the modeling and simulation of industrial hydraulic systems. The system under consideration here is a trash compactor specifically a self-contained trash compactor. Trash compactors are used in the area of waste processing to reduce the volume of trash through compaction and, to a lesser extent, reduce the problems of rodents and smell associated with trash storage. Trash compactors come in many sizes from electric powered residential trash compactors to hydraulically operated industrial trash compactors. The various types of industrial compactors are shown in the diagram below. Our system of interest will be the Self-Contained Compactor. Indoor Trash Compactors Compactor Cart Combo All in One Trash Compactors Portable (Casters) Compactor Bins Portable PortaPack Compactors (Container Ready) High-Rise Compactors Automatic Compacting Receptacles Outdoor Trash Compactors Compacting Dumpsters Vertical Outdoor Compactors Pre-Crushers Compactors Stationary Comapctors Self-Contained Compactors Miniature Self-Contained Compactors Specialty Compactors and Crushers Portable Bin Compactors Table 1. Types of Industrial Compactors ( Services/Compactors/Trash_Compactors/Trash_Compactor_Application_Guide.htm) Self-contained Compactors are useful for storing wet waste because the compacting and storage units are contained on the same structure, i.e. they are not separable. This allows for better sealing between the two areas. The compactors are transported to the dumpsite where they are tipped to remove the trash. There are substantial cost benefits derived from compacting since the number of times it would have to be tipped (i.e. removal of garbage) would be drastically reduced. Figure 1 shows a side view of the trash compactor. The system of interest for this project will be the hydraulic system for trash compaction along with the electric motor input. As shown in the figure, hydraulic cylinders drive the compactor blade forward. It moves by a stroke equal to the length of the inlet area and the amount of ram penetration (usually around 6 ). An electric motor supplies power to a fixed or variable displacement pump that operates the hydraulic cylinders. Though information is not yet available, there may be some kind of mechanism that provides a mechanical advantage to increase the force output. Design of a Competitive Self Contained Trash Compactor 1

4 Trash inlet Storage area Inlet area length Ram penetration Pump and Electric Motor To electric mains To pump To cylinder Figure 1. Side view of compactor Therefore, the design decision will be to determine the characteristics of the hydraulic components (the pump, cylinders and electric motor). Along with the hydraulic components, cost is a factor that will be considered and the objective will be to minimize the cost of the hydraulic system (both component cost and the cost associated with the power consumption). The model is confined to the hydraulic system and how it affects performance and cost. Aesthetics, retail cost, size of container, safety features, and other factors that contribute to the overall product are not considered. Therefore, the decision scenario can be scoped within the authority of the decision maker who is considered to be a hydraulics engineer. Design of a Competitive Self Contained Trash Compactor 2

5 Task 2: Determine an Objectives Hierarchy In order to discover and express the design objectives in the creation of a competitive compactor, a fundamental objective hierarchy diagram was created. The hierarchy diagram is attached as Figure 2 below. As is shown, the overall goal of creating a competitive compactor is defined by the objectives of minimizing cost to the end user, maximizing safety, and maximizing performance. The objective of minimizing cost to the end user can be further decomposed into the minimization of purchase and operating costs. Additionally, the maximization of performance can be defined by the maximization of system efficiency and trash capacity, and the minimization of cycle time. Create Competitive Compactor Cost to End User Safety Performance Purchase Cost Operating Cost System Efficiency Trash Capacity Cycle Time Figure 2. Fundamental Objective Hierarchy Diagram A means objective network diagram was generated in order to assist with the implementation of the fundamental objectives and is supplied as Figure 3. As is shown, the overall objective of creating a competitive compactor can be achieved by performing the means objectives listed. Of the objectives noted in the diagrams, a select few seem to be more important in the accomplishment of the overall objective. These include the maximization of trash capacity, the minimization of operating and purchase costs, and the minimization of cycle time. Each of these objectives has attributes that with certain assumptions are comprehensive and measureable. If the volume of the storage container is assumed to be fixed to set value, the trash capacity can be comprehensively measured by the compaction ratio, which is defined as the ratio of the compressed volume divided by the uncompressed volume. The cycle time is an explicit measure of performance, and as a result its value must be comprehensive and measurable. The operating cost can be approximated by the electrical power necessary to operate the compactor if the cost of labor and unloading of the compactor can be neglected. Finally, the purchase cost of the compactor can be approximated by the sum of the part costs if a fixed manufacturer's margin is assumed. Design of a Competitive Self Contained Trash Compactor 3

6 Create a Competitive Compactor Cost Safety Performance Purchase Cost Operating Cost use of Safety Features System Efficiency Trash Capacity Production Cost Cycle Time Input Power Line Losses Component Leakages Pump Efficiency Compaction Ratio Storage Volume Pump Displacement Cylinder Speed Inlet Length Travel Length Ram Penetration Frictional losses the Maximum Ram Force System Pressure Figure 3. Means Objective Network Diagram Design of a Competitive Self Contained Trash Compactor 4

7 All of these objectives are capable of being modeled in some way. However, even though all of these objectives can be modeled, the purchase cost would not be suitable for an energy based systems model, and would require an alternate format. Additionally, the solution to the optimization of the current selection of objectives should not yield a trivial solution, as they tend to compete directly. For example, in order to increase trash capacity, force supplied by and distance traveled by the hydraulic cylinder should increase. As a result, increases in the values of the attributes measuring operating cost and also cycle time should increase undesirably as well. Table 2 lists the attributes associated with the various objectives being considered in the model. The objectives that are expected to be modeled in this project are marked with an *. Objectives Attribute (units) Can it be Modeled in Modelica? * Trash Capacity Compaction Ratio Yes * Cycle Time Cycle Time (s) Yes * Operating Cost Input Power/Cycle (kw-hr) Yes * Purchase Cost Total Component Cost ($) No System Efficiency η= Yes Table 2. Objective and Attribute Relations Design of a Competitive Self Contained Trash Compactor 5

8 Task 3: Identify the Design Alternatives The design alternatives being considered in this project will need to be limited in order to fit within the scope of the class. Since the model has been confined to the representation of the hydraulic system, clearly only parameters defined in hydraulic domain should be suitable for use. The chosen parameters should both have a measurable effect on the chosen design objectives, as well as be suitable for modeling within an energy based system model. The design variables which have been selected to be considered include the pump displacement, the motor speed and the bore diameter of the hydraulic cylinders. A remaining design variable is to be chosen to fully characterize the hydraulic cylinder, and its selection is to be made based upon a high level decision in the hydraulic cylinder architecture. There are two hydraulic cylinder architectures that are currently being considered for application in the compactor. The first architecture is a double acting cylinder, a diagram of which is shown in Figure 4. The double acting cylinder is capable of powered extension and retraction, as shown in Figure 4. If the double acting cylinder is selected, then the rod diameter plays a key role in the transfer of hydraulic force. As a result the remaining design variable would be the rod diameter. Extension Retraction Figure 4. Extension and Retraction of a Double Acting Cylinder The second architecture being considered is a single acting cylinder, which is shown in Figure 5. A single acting cylinder is only capable of powered extension, and relies upon a spring with stiffness k to retract, as shown in Figure 5. If the single acting cylinder is selected, then the stiffness of the spring plays a larger role in the transfer of hydraulic force, resulting in its selection as the final design variable. Extension Retraction Figure 5. Extension and Retraction of a Single Acting Cylinder Design of a Competitive Self Contained Trash Compactor 6

9 A second design alternative which is currently being considered is the application of a mechanical device which would create mechanical advantages in some manner. However, if the device were to be included in the model, its application domain would fall not into the hydraulic system, but rather the mechanical system. As a result, the parameters defining its geometry will not be considered as design variables. Design of a Competitive Self Contained Trash Compactor 7

10 Task 4: Identify the Structure of the Design Problem A chance event is a decision element that engineers cannot predict or control. For the hydraulic trash compactor, three main chance events will affect the design problem structure: trash density input, friction due to trash, and economic climate. The first two chance events are associated with the content and characteristics of the trash. The third chance event deals with the economic conditions affecting the product cost. These three chance events are explained in detail: - Because of the non-uniform density of the trash, the compacter will either have to exert more or less force to compact the trash. For instance, a cardboard will provide less resistance than a steel rod. This discrepancy in the composition of the trash material will have an indirect effect on the power consumed by the compactor. - The content of the trash in the compactor can cause changes in the friction exerted on the compactor. For example, wet trash, such as unfinished drink containers or cleaning supplies, can cause generate a higher coefficient of friction than dry trash. The extra friction generated by this trash will require the compacter to generate forces of different magnitudes to crush the garbage. - The economic climate of the market will directly influence the product price of the hydraulic compactor. Depending on the cost of materials, fluids, and power, the overall cost of the compactor can change dramatically. Several calculation outcomes exist for the hydraulic actuator. The four main calculation outcomes affecting the overall performance utility of the compactor are the product cost, cycle time, compaction ratio of the trash, and power consumed. These four calculations will be the criteria used to calculate the overall utility of the compactor. Additionally, other calculations will influence these four major calculations. The pump and cylinder cost compose the overall product cost calculation. Also, the calculated force at the hydraulic cylinder will affect the overall power consumed by the compactor. Figure 6 outlines the influence diagram for the modeling and simulation of the hydraulic trash compactor. All of the initial decision factors have been compacted into two primary decisions: sizing the pump and sizing the cylinder. The pump has two main sub-decisions: the pump diameter and the pump speed. The sizing of the cylinder also has two sub-decisions: the bore diameter and the rod diameter (for a double acting cylinder) or spring constant, k, (for a single acting cylinder). The pump sizing and the cylinder sizing are related sequentially in that the pump parameters will likely be known before the cylinder parameters are determined. The decisions and chance outcomes directly affect calculation outcomes which in return will affect the overall performance utility. It can be seen from the diagram that most of the modeling difficulty will arise from the nature of the trash in the compactor. Design of a Competitive Self Contained Trash Compactor 8

11 Figure 6. Influence Diagram for the Hydraulic Trash Compactor Design of a Competitive Self Contained Trash Compactor 9

12 Task 5: Identify the Simulation Scenario for an Energy- Based System Model In order to relate the design objectives to decision alternatives, three out of the four objectives require an energy-model. For example, to minimize the cycle time of the trash compactor will need an energy-based model to analyze the forces involved in the system in order to predict cycle times under different system conditions or different system parameters. Similarly, the minimize power consumed and maximize compaction ratio objectives require energy-based models. On the other hand, the minimize cost objective does not require an energy-based model because costs are not directly depended on physical properties and can be modeled using different tools. For HW3, we plan to address all three objectives that require an energy-based model. We believe it is possible to capture all three of these design objectives within a single model. In this model, we will consider several different energy domains. We will need the electrical domain because the minimize power consumed objective talks about minimizing the electrical energy that will be the input into the system. Next, the system will need to make use of the hydraulic domain because the trash compactor design incorporates hydraulic pistons directly. These hydraulics will additionally call upon the translation and rotational energy domains in the pumps and pistons of the hydraulic system. In this regard, the two key physical phenomena that will be relevant to our model are friction and pressure. The friction will arise as internal losses in the components of the design, but will be most prominent in modeling the trash inside the compactor. Additionally, pressure is intrinsic to the function of hydraulics and will need to be considered continually. In order to create the physical model for HW3, several underlying assumptions will need to be made. The most important of these assumptions will be based upon modeling the trash in the compactor. It will be extremely difficult to create a model that will be able to handle not only the different orientations in which trash can be placed inside the container, but also the type of content of the trash itself. Similarly, it will be difficult to model how these different orientations and concentrations will affect the forces on the compactor. For these reasons, there will be a series of assumptions needed to simplify the trash model to reasonable modeling parameters. For example, some assumptions that we expect to make in the model is that all the trash is of equal density and evenly distributed throughout the container. Design of a Competitive Self Contained Trash Compactor 10

13 Task 6: Assess Your Plan The two biggest sources of uncertainty in this plan lie in the cost minimization objective and the trash model. For minimizing cost, there is a lot of uncertainty of the prices of many of the components that may be used in our design. In addition, the price of power is uncertain and can vary with time. Even if the prices are known, since cost is the only objective not in system model, we are as yet unsure on how we can relate this information to the results of the model and compare it to the other three objectives. If we are unable to resolve these issues, we will simply not include this objective in the overall assignment because it is subordinate to the modeling of the system itself. Aside from cost, there is a lot of uncertainty in how the trash in the compactor will be modeled. It is certain that the trash needs to be modeled in some form, in order to analyze the forces in the compactor system; however, since the type of trash and orientation of the trash can be seemingly random, we are unsure of how we can model it appropriately. Unlike the uncertainty in the cost, if problems do arise in this model, we cannot simply remove it from consideration. Instead, we will have to simplify the model by creating more accurate assumptions of the trash. Design of a Competitive Self Contained Trash Compactor 11

14 Task 7: Articulate Your Learning Objectives Aditya Shah: Before this course, I never really did much analysis at the system level. It was more related to detailed design of specific sub-systems and there would be a lot of rework and redesign at later stages because the effects at the system level were not studied beforehand. I have had personal experiences with the problems related to uncertainty in designing of products, both in my undergraduate project as well as at my family business, when we set out to design new products. This course along with the course in SysML will improve my ability to represent the system level design in a more concrete way using the different tools available. There are several objectives that I would like to take from this project and the course in general: I want to better learn how to develop analysis models at the system level when the design is not yet finalized and is also unknown in many ways and how to search the different options available for that specific alternative. I want to gain a better understanding of hydraulic systems. I want to improve my ability to break up complex systems in to its logical sub-parts in such a way as to facilitate object oriented modeling and the reuse of models in other systems. I want to learn how to use Dymola and other tools that allow for the modeling and simulation of complex systems and their interactions across various disciplines (mechanical, hydraulics, electrical, and others). Patrick Chang: As a design engineer in a world where computers are becoming more and more critical in design practice, I believe that modeling and simulation will be absolutely necessary in order for me to be a competitive designer. Consequently, I will need to develop a modeling mindset, or, in other words, the ability to know when modeling is feasible and how to model and simulate a system accurately. These objectives can be attained by accomplishing several important goals: Learn how to model a system in an object-oriented fashion by splitting functions into discrete, cohesive sub-functions. Distinguish what phenomena are suitable or practical to be modeled in a system in order to accurately simulate real-world situations. Determine the overall utility of modeling certain systems, as well as variants of a system. Determine when the value of modeling outweighs the cost. Essentially, I want to know when applying the modeling and simulation process is important in the design process. Learn how to use a modeling program, such as Dymola, correctly and efficiently. In addition to these primary goals, I seek to accomplish some auxiliary goals, including learning about and utilizing hydraulic components and using modeling and simulation in a team setting. Design of a Competitive Self Contained Trash Compactor 12

15 Ryan Stewart: In the long term, I wish to work as an engineering director or development manager at a product oriented company. In this mindset, understanding the capabilities of modeling and simulation will be extremely important to me. In the future world, products will have to be made within shorter and shorter life cycles. With this in mind, I need to be well versed in the different tools that will expedite the product realization process. In particular, I will need to understand the capabilities and limitations of different modeling techniques as they relate to product realization. My specific learning objectives are listed below: Recognize the strengths and weaknesses of object oriented models and simulations Learn where in the product realization process that modeling and simulation can be used to expedite design Learn how to relate client preferences and company goals to system models for the purpose of optimization Learn how to formulate design problems into discrete sub-tasks that can be worked on in tandem Ben Lee: When a choice between design alternatives is to be decided, it is generally not clear which of the alternatives may yield a more desirable result. A proper decision will consider the impact of the choice not only at the part or subsystem level, but to the entire system. The process of system engineering can therefore become complex very quickly, and overwhelming if the engineer is not familiar with the methods he or she utilizes. My goals in the class and project stem from this idea, and are listed below. Become familiar with Model Based System Engineering by implementing it correctly in the scope of the project. Gain experience with software such as Dymola and ModelCenter that allow a designer to capture information and use it efficiently. Test my knowledge base in hydraulic systems through its application to an unfamiliar domain of compacting. Additionally, I would like to be able to refine my research interests in the area such that it may help me begin to focus in on a master's thesis. Design of a Competitive Self Contained Trash Compactor 13