Saturday, August 27, 2011

Kenmore Washing Machine Lid Switch Failure Analysis

More than a month ago we had another malfunction of our washing machine, instead of dryer, this time it was washer. That morning, after washing one load of laundry, the washer stopped working on the second load - it let water in but won't agitate the laundry!

What failed?

Based on her experience with centrifuge, Lily quickly realized it was most likely due to the malfunction of the safety device on the lid, which we later found out to be a lid switch (see a picture of the stand alone lid switch assembly below) . It was validated: when she used a screw driver to push on the switch assembly, the washing machine started running! I unscrewed the assembly main body from the washer's frame and squeezed it everywhere, and put it back in - the washer could work normally.

However the washer stopped working again the following week. I turned off the washing machine (for Safety!!) and removed the lid switch from the frame again. Upon investigation, it turned out that the plastic case of the working unit fractured. I searched (note - I used this website to identify the failed part in my dryer previously) and eventually found out the part is officially called lid switch Assembly. We decided to replace the part.

After I identified the part, I went back to look at it again. When I squeezed the fractured part back together, and turned on the washer, it ran again. So I used steel wire to tie the fractured part together and then wrap the bundled part with duct tapes. The washing machine worked fine that week.

Why did it fail?

Typically this part should not fail. I thought about the cause of the failure, and quickly determined that it was due to the fact that we let the lid close on its free fall after loading laundry; in applied mechanics terminology, it is the impact of pin (on the lid) to the lid switch which caused the fracture and shortened the life of the part. The impact force is much larger than static force. If we close the lid all the way by hand, the max force on the lid switch would be just half its weight, the lid switch should last very long time.

With this understanding, we started a new rule right away - close the washing machine washer's and dryer's lids/covers gently by hand. With this practice, the washer has been working for a month without any problem. I expect that my temporary fix should be a permanent fix with gentle closing of the lid. We will not replace the lid switch after all!

Quantitative Failure Analysis

I was wondering how much higher the force would be due to free fall impact than statically closing it. So I did a hand calculation from Newtonian mechanics and preformed a simulation to show the dynamic process.

The lid (cover) is modeled as flat plate which can freely rotate at one side (the triangle symbol in the following figure).

Based on conservation of energy, we have the following relations - basically it is that the potential energy of the vertical lid equals to the (rotational)kinetic energy when the lid is horizontal (close position) When the lid (D=18 inch) free falls to horizontal position right before it hit the lid, its angular velocity is 8.01radians/second or 459 deg/second! It takes a lot of force to stop the lid with high angular velocity in a very short time. If I assume that the lid would be stopped in 0.001 second (both plate and lid switch are assumed to be rigid), then the impact force would be 250 times of the static force.

A simulation that model the lid as steel, and the lid switch as a rigid block, showed the impact force is 165times the static force (half weight of the cover). Since both lid and lid switch are deformable objects, and the solid spring on the lid switch actually deforms a lot when pressed, or in other words, not all of the potential energy is converted into kinetic energy, some of it is conveted into strain(deformation) energy. The force amplification is estimated to be more close to 100.

Note: This is the first time I performed a quantitative failure analysis outside my professional work. Hindsight, I think tha it would be helpful to show that high school physics (newtonian mechanis) can be used to solve real world daily life problems.

Saturday, August 20, 2011

Itinerary for Trip to Banff and Jasper

Travel to expansive national parks requires good planing to get most out of the trip. Here is our Banff/Jasper Itinerary (and adjustment due to weather)

Day 0:  – Fly out of DFW in the Thursday evening to Calgary Canada, Stay at Best Western near Airport (note: save airfare when flying Thursday)

Day 1:  – Drive to Banff in the morning

Johnston Canyon (Half day): 2.7 km one way, elevation gain 120 m, 2 hours round trip
view: waterfalls and glacier rivers

visit info centre.

Hike to Stanley Glacier (cancelled due to rain)
4.2 km one way, elevation gain 395 m, 4 hours round trip

Hiked Sulphur Mountains and Take Sulphur Mtn gondola down (added)
5.5km one way, 655m elevation gain

view: summit renowned for its breathtaking mountain views

Day 2:  - Moriane Lake area and Lake Louise

Walk along the lake shore
Canoe in the lake (canceled due to weather related closing of the canoe rental)
Hiking to Larch Valley; 2.8km one way, elevation gain 465m, 3 hour round trip

view: unique larch forest high above Moraine Lake; breathtaking Ten Peaks.

Canoed on Lake Louise in the afternoon (added)

Day 3:  - Lake Louise area

Lake Louise Lake shore and Plain of Six Glaciers
7.3 km one way, elevation gain 365 m, 5 hours round trip

View: glaciers, lake Louise from above

Tea house at the trail end

Side trip to Abbot Pass Viewpoint: 1.5 km one way; 50 m elevation gain; 1 hour round trip Look down into crevasses on the Lower Victoria Glacier, and look up to Abbot Hut, one of the highest buildings in Canada.

Lake Louise Ski area and 93A byway (added)

Day 4:  - Drive to Jasper - Icefield Parkway and Columbia Icefield

Icefield Parkway - several glaciers/glacier lakes/canyons along the way

Columbia Icefield - tour icefield via Icefield explorer

Day 5: Mt Edith Cavell, Maligne Canyon/Lake

Hike Mt Edith Cavell: 7km one way, 500m elevation gain, 5 hour round trip

view: angles glacier, cavell glacier, alpine meadows

Maligne Canyon

Maligne Lake (saw bull Elk on the way to and from it)

Day 6: Drive from Jasper to Banff

Hike Bow Glacier Fall trail: 4.6 km one way, elevation gain 155 m, 3 hours round trip

view: bow glacier, bow glacier fall (can reach the bottom of the fall), glacier river and bow lake

Drive Lake Minnewanka Loop - consider boat trip if weather is good (was late for the lake cruise)

Day 7: Drive to Calgary and fly home in the afternoon

visited Olympic Park on the way to airport


Banff and Jasper's glaciers are not as magnificent as Alaska; their wildlife - especially big animals are not as abundant as Yellowstone. The unique feature of Banff and Jasper is that everything is close to each other - glaciers, waterfalls, canyons, mountain peaks, glacier lakes, all packed along trans Canada highway 1 and highway 93. They are more beautiful and elegant than Alaska and Yellowstone.

The other feature of the parks is easy access to trails to mountain peaks - according to Lily's tabulation, we hiked a total of more than 55 km in the mountains, and had total of ~ 2500m elevation gain ! We did not climb mountains at Alaska or Yellowstone.

Saturday, August 13, 2011

A Peek at Amsterdam and Netherlands

A short business visit to Rijswijk, Netherlands in mid July gave me a one afternoon’s time to stroll the streets of Amsterdam.

Amsterdam is a city by canals, It has relatively narrow streets, wide canals. Canal cruises are a favorite mean to see the city. There were many tourists walking in the street, like busy street in Shanghai, China. There were police cars but I saw more police on bike patrolling the busy street of Amsterdam.

There are several big churches for the several street I walked on. It seems that there are churches in every direction. Another distinct feature of the city is that there are Muslims everywhere (by way of look and cloths), I saw them in the streets and on the trains – many Muslim women taking their kids to/from Amsterdam.

Netherlands has the most impressive public transportation: Trains, buses, trams. There are two catagory of train carts - 1st and 2nd class. The train runs regularly, reaches most locations. The trains are handicap and bike friendly - there is bike section on every cart. The following picture shows Amsterdam central train station. It seems that the trains are run on honor system for train tickets – no body check the tickets for getting on or off the train. It turned out that there are inspectors checking tickets at peak hours.

The Dutches I met were friendly and everyone can speak English! I got many helps from them when purchasing train tickets from kiosk.

Netherlands is a flat and green land,. It is as level as water surface. It has many sheep and horses on its green land. I did not see stand alone houses there. Most residential housing I saw was cluster homes, town houses and apartment buildings

Saturday, August 6, 2011

Birds and Flowers at Banff and Jasper

There are over 250 types of birds in the mountains. The forest is so vast it is not easy to spot them. The common birds we saw are gray jays - which were noisy, and flocked at parking lot or restaurants waiting for free food from tourists.

The other common bird is Black-billed Magpie - there are a lot of them in the town of Banff.

We saw this pheasant like bird on the trail to plains of six glaciers - which is sooty grouse

The most pleasing and good looking bird we saw on the trails was white crowned sparrow. When we were near the plains of six glaciers, flocks of these sparrows scurrying through brushy borders and overgrown fields - just as "All About Birds" described, a few of them kind of followed us, jumping from tree top to tree top just slightly ahead of us, making short chirping sound. I thought that it was due to the fact that a big dog was on the trail just tens of yards ahead of us with a hiker. The next time we saw the sparrows was on Mt Edith Cavell. I heard this beautiful bird sound, and eventually located the bird on the top of very tall pine tree. The sound is best described by the website All about Birds - "The song of the White-crowned Sparrow is one of the most-studied sounds in all of animal behavior. Different subspecies across the country sing clearly different songs, but they’re all recognizable by the sweet, whistling introduction, a succession of jumbled whistles, and a buzz or trill near the end. Songs last 2-3 seconds. " - Despite back light, Lily recorded this beautiful sound on camcorder. It was really a pleasure to hike in the beautiful mountain, with spectacular scenery and now beautiful music!!

Typically the flowers in the parks, are small and close to ground due to high altitude and cool weather. There are too many type of flowers to name for me. Here are some of the flowers I captured on my camera. There are flowers then there are bees and butterflies - but butterflies barely rest on flowers by the trails.