We were discussing the basic concept ofÂ dimensional homogeneityÂ and Buckingham pi theorem in the subject of fluid mechanics, in our recent posts.

Now we will go ahead to understand the basic differentiate between model and prototype with the help of this post.

### Model, prototype and dimensional analysis

In order to secure the information about the performance of any hydraulic structure such as dam or any hydraulic machine such as turbine, before going for construction and manufacturing of actual of structure or machine, models are prepared of the actual structure or machine and experiments are carried out on the models to secure the desired result.

If result obtained from the experiment carried out on the models of actual structure or machine is not achieved as desired, respective modification will be carried out to secure the desired result.

Let us consider one example of an aircraft. If we want to design and manufacture one aircraft, first we must have the fundamental information about the aircraft like drag forces etc.Â

Various experiments will be carried out on the aircraft in order to secure all the desired result. If we want to conduct the experiments on actual aircraft, it will not feasible as it will be very expensive and not safe also.

#### So what we will do?

We will prepare one model of the actual aircraft. Model of the actual aircraft will be in smaller size. We will conduct the experiments over this model of actual aircraft and we will analyse the result obtained from the experiment.

If result obtained from the experiment is not as per requirement, we will do some modification in the design and other parameters of the model of the actual aircraft.

Once we will secure the desired result from experiments, we will send this model to production cell and construction and manufacturing of the actual aircraft will be commenced on the basis of the prepared model of the actual aircraft.

Therefore we can define the model as the small scale replica of the actual structure or machine. Actual structure or machine will be termed as prototype.

We have considered above the case of designing and manufacturing of an aircraft. We have discussed above that the model of actual aircraft will be in smaller size as compared to the actual aircraft. But, it is not always necessary that model will be in smaller size as compared to the actual structure or machine.

In some cases, model of the machine might be in larger size as compared to the actual machine.

Let us think the case of designing and manufacturing of watch. As we know very well that parts used in manufacturing of watch will be of very small size and it will be very difficult to conduct the experiments and analyse the results to predict the performance of the watch.

Therefore in this case, model will be prepared of larger size as compared to the actual size of the watch. After preparing the correct model, manufacturing of the respective set of watches will be commenced on the basis of the model.

Therefore, model could be of smaller size or larger size as compared to the actual machine.
We can define the model analysis as the study of the models of actual machines.

### Advantage of the dimensional and model analysis

Let us see here few advantages of the dimensional and model analysis

With the help of dimensional and model analysis, we can easily secure the information about the performance of actual machine or structure before going for manufacturing of actual machine or structure.

With the help of dimensional and model analysis, we can also consider the alternative design of actual machine or structure and we can select most economical and safe design.

With the help of dimensional and model analysis, we will secure the relationship between variables influencing a flow problem in terms of dimensionless parameters and this relationship will help in conducting the experiments on the model.

We will see another important topic in the field of fluid mechanics i.e. similitude and similarityÂ with the help of our next post.

Do you have any suggestions? Please write in comment box.

### Reference:

Fluid mechanics, By R. K. Bansal