From DDL Wiki

Client Comments on Report 1

We received your report, and we have some comments and questions. It looks like there are quite a few possible directions for improvement, and you should have a great starting point for brainstorming solution concepts in phase 2. Please respond point by point to the items below. We are looking forward to seeing your ideas in Report 2.

• Executive Summary: Very thorough and clear. Would be even better if somewhat shorter (~50%) keeping major findings and compacting filler/transition/intro text.

The reasoning behind the somewhat lengthy executive summary is as follows. We wanted to include as much relevant information as possible since this is the often the only part of a report that an executive, the person with the authority to make major engineering decisions ever reads. That being said we felt it was better to provide an executive with enough information to fully justify his or her decision and not have to second guess themselves. Compared to the length of the report, the executive summary at approximately 620 words is not that lengthy. We feel that removing the filler, transition, and intro text would detract from the over all clarity of the summary. Also, if the executive summary is lacking or poorly written an executive or someone responsible for reading the rest of the report will likely pay little attention to it. We can assume that at least most people will read the executive summary. We cannot assume that they'll read the entire report.

• Stakeholder Needs: Good start, but aren't there other important potential stakeholders (e.g.: repair/maintenance, rental owner, etc.)? Please include major needs in a bullet list. There appear to be many important needs missing, such as low cost, safety, quiet operation, intuitive use, flexibility to dish shape and size, operation time, low energy consumption, ease of installation, ease of storage, etc. Please be more comprehensive.

Please see the updated Report 1 wiki page for a more precise list of user needs. These were generated as a result of research conducted for Report 2. Please see Report for even further details and reasoning.

• Use: Good documentation of basic use. Is there any chance of the user hooking up hoses backward? Is there any chance of a hose falling out of the sink due to fluid dynamic forces? Flexibility in attachment to faucets was mentioned in the presentation but not the report. We are surprised that you did not bring up issues such as cups flipping over in the dishwasher and filling with water. Hopefully you will address more of these in the phase 2 user study.

Issues such as cups flipping over and other common user complaints have been addressed in Report II that was transmitted on October 6, 2009. We are currently in the process of loading its contents to the wiki.

A few additional pieces of information are provided after a request for more information. There is no possibility of the user hooking the inlet hose or outlet hose backwards. Both hoses are anchored to the unit, thus leaving only one end to be attached to a faucet or drain. The inlet hose comes with a special adapter capable of screwing on to a faucet with threads. The outlet hose has no threads and cannon be "attached" to anything. The outlet hose in this case was simply placed in a sink to drain. The chance of the drainage hose falling out of the sink due to dynamic fluid forces is very close to zero. The water drains with such a a slow velocity that even the small jerk associated with the pump's transient is negligible. We would say that it is safe to conclude that the hose would only fall from a very shallow or small sink or drain.

• Assembly: An assembly image with labeled components appears to be missing.

Pictures with major external components are given for the assembly as a whole before dissection. The bill of materials has been updated to include labeled parts for assemblies.

• Mechanical Function: Good general explanation, but what prevents the faucet from continuing to feed water into the unit even while the pump is not running? What is the valve mechanism that switches the inlet from the faucet to recycled water? An assembly image with components labeled would be a big help to understanding details.

There is no valve that explicitly switches the inlet from the faucet to recycled water. For the dishwasher, the fresh water from the inlet is controlled by the main solenoid inlet valve. As we understand it, this feed water is fed into the device using the natural pressure of the water line. Once water has entered the device, the main pump is used to recycle and move the water until it is time to be drained via the wast pump. Assembly images below have been labeled.

• Mechanical Analysis: Please include a complete free body diagram of each problem you are solving, and clearly define your notation, including subscripts, before or immediately after you use them. Please state the equations you are using and write them out before plugging in numbers.
  • For the numbers you have assumed (P2=65 psi, c =0.01 N-s) please explain why you chose those values and cite references where appropriate.

Citations have been made for data that was found elsewhere. The data for the damping ratio and the system inertia was based off estimations of observable properties.

• • Point 2 is zero velocity and a desired pressure? The pressure build up is at the point of stagnation - why a pressure target instead of a velocity target?

We are seeking a pressure target because pressure is what is relevant to how effectively material is removed from the plate. Additionally there will always be a stagnation point at the top of the dishwasher so the velocity is necessarily zero.

• • Why is Aout 8 times the orifice?

There are 8 orifices through which the water flows, only one is relevant to the torque produced. This is elucidated in the revised report.

• • What is beta and inv?

Beta is a correction factor that accounts for non uniform velocity profiles in pipes. It is a part of the basic equation, but as the flow is external the velocity is uniform. This is elucidated in the report. There is no variable inv.

• • Are you assuming the 45degree orifice is the only orifice?

It is the only orifice that contributed to producing a moment. This is mentioned in the revised report.

• • Why do you think approach 2 with 90 cycles is more reasonable than 200?

We feel 90 cycles is more reasonable because it means a lower power consumption for the pump and that there is still a very high recycle rate for the water in the pump. Elaborated on in the revised report

• • To determine the flow rate in the pump, can you tell how much of the running time is spent pulling in clean water from the sink at the beginning of the cycle, and how much water that is? Is there any other way to find the flow rate other than guessing what the scale is compared to the other dishwasher you found numbers for?

This is not possible as we are unable to measure the flow rate or the state of the inlet value at any given time. Additionally the inlet flow rate is not relevant as the water is recycled and there is no way to measure the rate in the washer either.

• • What design implications does your analysis have?

It allows us to spec out a main pump, one of the most critical components. This is elaborated on in the revised report.

Please see the main Wiki page for an updated and better explained analysis.

• Bill of Materials: Good list. Is the sprayer arm injection molded as a single piece? You should be clear in your text that there are significantly more than 64 unique parts, since you have many subassemblies listed with single part numbers. Given the complexity of the product, this is okay, but please be clear.

The bill of materials has been edited. Please see the main wiki article. We believe the sprayer arm to be made via injection molding.

• DFMA: Good observations.
• FMEA: What happens if faucet not turned on? Is the wobbling of the spray arm intentional in order to add variability to the spray pattern?

FMEA Comments: If the faucet is not turned on, the solenoid valve will open, attempt to allow water in, and be unable to do so. The pump will run for a full cycle since there is no water to raise the float to trip the shutoff circuit. The dishes will not get cleaned and the user should be able to quickly diagnose the problem. No damage is done to the unit.
The spray arm wobbling may be intentional. However, it is most likely not necessary as the jets cover the entire area and the nature of fluid flows mean that even small variations cause large changes in fluid direction. The possible additional variability is not worth the possible failure of one of the most critical components.

• DFE: Since use phase seems to dominate, it looks like energy efficiency is the most critical factor - and possibly a good selling point. Please describe the assumptions made in this section and explain your conclusions.

The assumptions and conclusions have been more clearly defined. The frequency of use was every 3 days and the amount of detergent used was 2 ounces per use. Also the conclusions that were covered in the executive summary have been explained in the DFE analysis section.

• If any of your images, figures, or text were taken from another source, please be certain to provide proper attribution.