INSTALACION ELECTRICA

Simulation is not a tool to be applied indiscriminately with little or no fore-thought. The decision to use simulation itself requires some consideration. Is the application appropriate for simulation? Are other approaches equally as effective yet less expensive? These and other questions should be raised when exploring the potential use of simulation. Once it has been determined that simulation is the right approach, other preparations should be made to ensure that the necessary personnel and resources are in place to conduct the study. Personnel must be iden- tified and trained. The right software should also be carefully selected. The nature of the study and the policies of the organization will largely dictate how to prepare for a simulation project.

5.2.1 Selecting an Application

The decision to use simulation usually begins with a systemic problem for which a solution is being sought. The problem might be as simple as getting better utilization from a key resource or as complex as how to increase throughput while at the same time reducing cycle time in a large factory. Such problems become opportunities for system improvement through the use of simulation.

While many opportunities may exist for using simulation, beginners in simu- lation should select an application that is not too complicated yet can have an im- pact on an organization’s bottom line. On the one hand, you want to focus on problems of significance, but you don’t want to get in over your head. The first simulation project should be one that is well defined and can be completed within a few weeks. This pilot project might consist of a small process such as a manu- facturing cell or a service operation with only a few process steps. The goal at this point should be focused more on gaining experience in simulation than making dramatic, enterprisewide improvements.

Conducting a pilot project is much like a warm-up exercise. It should be treated as a learning experience as well as a confi- dence and momentum builder.

As one gains experience in the use of simulation, more challenging projects can be undertaken. As each project is considered, it should be evaluated first for its suitability for simulation. The following questions can help you determine whether a process is a good candidate for simulation:

• Is the process well defined?

• Is process information readily available?

• Does the process have interdependencies?

• Does the process exhibit variability?

• Are the potential cost savings greater than the cost of doing the study?

• If it is a new process, is there time to perform a simulation analysis?

• If it is an existing process, would it be less costly to experiment on the actual system?

• Is management willing to support the project?

The wisdom of asking these questions should be clear. You don’t want to waste time on efforts or problems that are too unstructured or for which simulation is not well suited. The last question, which relates to management support, is a reminder that no simulation project should be undertaken if management is un- willing to support the study or take the recommendations of the study seriously. Obviously, multiple projects may fit the criteria just listed, in which case the list of candidates for simulation should be prioritized using a cost–benefit analysis (a.k.a. biggest-bang-for-the-buck analysis). Management preferences and timing may also come into play in prioritization.

5.2.2 Personnel Identification

One of the first preparations for a simulation project is to have management assign a project leader who works alone or with a project team. When assessing personnel requirements for the simulation, consideration should be given to factors such as level of expertise, length of the assignment, and organizational structure. Large companies, for example, often have a central simulation group that provides sim- ulation services to entities within the organization. In some organizations, simulation is used no more than once or twice a year, such as when a major change in opera- tion is being considered. In such situations, it may be more cost-effective to hire a simulation consultant than to do the simulation in-house. While the decision to use a consultant is usually based on the level and availability of in-house simulation expertise as well as the difficulty of the project, the opportunity to train additional people or acquire increased simulation expertise to apply to future projects should not be overlooked.

Assuming the simulation will be done internally, either a simulation special-ist should be assigned to lead the project or an engineer or manager who works closely with the specialist should be assigned. The person or group doing the modeling should be well trained and proficient in the use of one or more simula-tion packages. If no such experienced individual exists, management must be willing to invest in employee training in simulation.

The process owner should take an active role in the project and, if possible, even lead the effort. If the process owner refuses or doesn’t have time to get involved in the simulation project, the effort will be largely wasted. It is impera-tive to have someone involved who not only understands the process and what possible design options are feasible, but who also has responsibility for the system’s performance.

5.2.3 Software Selection

Once the responsibility for doing simulation has been assigned, software tools, if not already in possession, need to be acquired to develop the simulation model.

Having the right tool for the job can mean the difference between success and fail- ure in a simulation project. Modeling efforts sometimes go on for months without much progress because of limited capabilities in the software.

Simulation soft- ware can’t make a simulation succeed, but it can make it fail.

Selecting the right simulation software requires that an assessment first be made of the simulation requirements. Then alternative products should be evalu-ated against those requirements. If simulation is to be used in multiple applica-tions that are quite diverse, it may be desirable to have more than one simulation product so that the right tool is used for the right job.

In selecting simulation software, attention should be given to the following criteria:

• Quality—Reliable algorithms, absence of bugs, and graceful handling of user input errors.

• Features and capability—Ability to model systems of any size and complexity and meet simulation needs in terms of external interfacing, animation, reporting, and so forth.

• Ease of use—Intuitive editing and built-in constructs that minimize the time and effort to learn and use the product.

• Services—Quality and level of training and technical support, including the long-term sustainability of this service.

• Cost—The total cost of ownership (TCO), which includes cost of procurement, training, support, and labor to use the software.

Although fewer than a dozen major products are on the market, there are over a hundred products from which to choose. It is best to conduct an initial screening to develop a short list. Then a more in-depth evaluation can be conducted on the three or four finalists. In conducting the initial screening, different products should be screened in terms of their ability to meet minimum requirements in the areas just identified. Often vendor literature or buying guides are helpful at this stage of the evaluation. Magazines such as IIE Solutions and OR/MS Today run regular reviews of simulation products.

In the final evaluation phase, the products should be examined with greater scrutiny in each of the areas just listed. Since all major software products have bugs, it is best to look for a product that is mature and has a large user base. This will help ensure that even rare bugs have been identified and fixed. Simulation features are pretty easy to assess because most vendors have feature lists avail-able. One of the most difficult criteria to assess in a simulation product is ease of use. Most vendors will likely claim that their product is the easiest to use, so it is always a good idea to have the vendor being considered build a simple model in your presence that is representative of the target application. This is the best way to test the suitability and ease of use of the software. At a minimum, it is good to experiment building simple models with the software to see how user friendly it is.

Many vendors offer guarantees on their products so they may be returned after some trial period. This allows you to try out the software to see how well it fits your needs.

The services provided by the software provider can be a lifesaver. If working late on a project, it may be urgent to get immediate help with a modeling or soft- ware problem. Basic and advanced training classes, good documentation, and lots of example models can provide invaluable resources for becoming proficient in the use of the software.

When selecting simulation software, it is important to assess the total cost of ownership. There often tends to be an overemphasis on the purchase price of the software with little regard for the cost associated with learning and using the software. It has been recommended that simulation software be purchased on the basis of productivity rather than price (Banks and Gibson 1997). The purchase price of the software can sometimes be only a small fraction of the cost in time and labor that results from having a tool that is difficult to use or inadequate for the application.

Other considerations that may come into play when selecting a product in-clude quality of the documentation, hardware requirements (for example, is a graphics accelerator card required?), and available consulting services.